Patent Publication Number: US-5527382-A

Title: Hydrometallurgical process for the treatment of copper bearing ore

Description:
This is a continuation of application Ser. No. 07/990,163, filed Dec. 14, 1993, now U.S. Pat. No. 5,356,457. 
    
    
     BACKGROUND 
     The present invention relates to a novel process for treating copper ore to recover the copper therefrom. 
     In hydrometallurgical process for extracting metal, such as copper, from ore containing the same, it is desirous to extract as much metal as possible from a broad granulometric fraction of the ore. The most frequently employed conventional process, leaching for instance, consumes too much time due to the fact that the flow of leaching solution is too slow, and thus uneconomical. Moreover, the conventional process wastes a significant amount of energy and requires expensive and sophisticated equipment. 
     Leaching techniques are well known for extracting common metals. Commonly used leaching techniques include 1) in situ leaching, 2) dump leaching, 3) pile leaching, 4) pan leaching, and 5) agitation leaching. 
     In in situ leaching, a leaching solution is injected to the ore that has been fragmented by explosives in the mine itself. The leaching solution percolates by gravity from the surface to the bottom, which is recovered for conventional treatment to extract the desired metals. Although this process appears to be economical in that does not require transferring of the material extracted from the mine or additional stages of comminution, it is extraordinarily slow and the recovery range is low due to the relatively coarse grain size of the treated material. Depending upon the nature of the ore and the type of operation used, this process can only recover in the range of 50 to 60% for an incredibly long leaching period of 5 to 25 years. 
     Dump leaching is normally applied to low-grade sources which have previously been deposited at specific places, in particular for those types of assays (stint assays) which are not suitable for normal in-plant processing. For instance, dumps formed of spalls generated in normal processing as for example in the case of ores from Chuquicamata, where low-grade sulfides and spalls from leaching are generated in the respective pans of oxidized ores, may be leached by this technique. As in the case of in situ leaching, this process is extraordinarily slow, and depending upon the grain size, the nature of the material and the type of operation, it is possible to recover the desired mineral up to 60% for a leaching period of 1 to 30 years. 
     Pile leaching is frequently used because of its low investment costs. This type of leaching is very similar to in situ and dump leaching processes. In pile leaching, however, the source material must first be crushed to a grain size that is normally less than one inch. It is also possible to recover more than 60% of the metal by this process for a leaching period of several weeks to several months, depending upon the characteristics of the ore and the procedure used. 
     Pan leaching is a very old technology which has been in use in Chuquicamata since 1915. In this process, the source material having the grain size of over 3/8 inch ranging from 20 to 30% of the material is leached for a period of 5 to 10 days to recover 60 to 80% of the metal, depending upon the nature of the ore treated. This leaching process may be carried out in a flooded bed or by spraying the leaching solution. 
     Agitation leaching is also a very old technology that requires fine grinding of the ore. The large surface area of the ore exposed to the solvent makes it possible to obtain a leaching period that ranges; from only 2 to 24 hours, with a maximum recovery of close to 90%, depending upon the characteristics of the ore. Although this technique is the most efficient in terms of rapid recovery, it consumes too much energy and requires the greatest initial investment. 
     As may be generally noted, with the exception of agitated leaching, the conventional leaching processes exhibit a very slow kinetic flow of solution and consequently require very prolonged periods for recovery of the metals, so that this is further reflected in a high inventory of copper in the process. 
     Agitated leaching, apart from requiring fine grinding, in some cases demands a very prolonged leaching period, which results in a significant consumption of energy. In addition, for the recovery of dissolved copper in particular, it requires stages of alternate countercurrent washing and decantation, normally carried out in extremely large thickeners. Lastly, the washed pulps must be deposited in tailing tanks, which involves very high investments and significant losses of the aqueous resource contained in the discarded pulp. 
     Leaching by percolation following curing is disclosed in Chilean Patent No. 30,851 granted to Codelco-Chile. This patent discloses a process of inhibiting a solution of silica in the leaching of silicated copper ores by adding water to the ore at the rate of 3 to 10% by weight and another stage of addition of pure industrial H 2  SO 4  at rates of 7 to 50 kg H 2  SO 4  /MT of ore. The product is then subjected to a holding period of up to 48 hours prior to leaching by percolation in pans. The object of this process is to render the silica insoluble. There is no disclosure in this patent of repulping, classification, filtration of the fine fraction from the pulp and secondary leaching in piles of the classified coarse fraction. 
     In the process disclosed in Chilean Patent No. 32,025, granted to Sociedad Minera Pudahuel, an ore which has been sufficiently preagglomerated in H 2  SO 4  and water is leached in thin layers. This patent emphasizes the importance of obtaining a consistent agglomerated product to avoid attrition of the weight of the leaching solution. In comparisons, the present invention does not require agglomerating the fine material, but rather obtains a homogeneous wetting of the initial ore. Also, the present invention does not require leaching of the agglomerated product in piles of thin layers, but rather includes the processes of repulping, classification, filtration of the fine fraction and secondary leaching of the coarse fraction. 
     A variety of existing published sources, in agitation leaching of tailings used in Nchanga plant in Zambia, disclose processes which include the stages of repulping of tailings, thickening, agitated acid leaching, thickening and filtration. However, unlike the present invention, they do not disclose stages of preliminary wetting of the material with H 2  SO 4  and water, nor do they disclose curing or holding periods. Moreover, they do not disclose stages of classification or secondary leaching in piles of preclassified coarse fractions. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention relates to a process for extracting copper from copper bearing ore, comprising the steps of substantially uniformly wetting a copper bearing ore with sulfuric acid and water in sufficient quantities and for a sufficient time to alter the surface characteristics of the ore by increasing its thickening and filtration properties and to sulfatize a significant portion of the copper therein and form a sulfatized ore; repulping the sulfatized ore with an aqueous solution for a sufficient-time to extract a substantial portion of the sulfatized copper therefrom in a solution; and recovering copper from the extracted sulfatized copper solution. 
     In this process, the copper bearing ore may have a typical grain size ranging between that resulting from crushing and that resulting from fine grinding. The amount of sulfuric acid to be used is between about 5 and 500 kg/MT and preferably between about 15 and 60 kg/MT, while the amount of water to be used ranges from 0 to about 250 kg/MT, and preferably between about 40 and 120 kg/MT. It is convenient to utilize a concentrated H 2  SO 4  solution as the source of sulfuric acid, with the water being plant water, refined process solution, or discarded electrolyte obtained from a electrolytic copper extracting process. 
     To assist in the sulfatizing of the copper in the ore, an oxidizing agent may be introduced into the copper bearing ore in the wetting stage in an amount sufficient to help oxidize copper sulfides. Also, the wetting step is followed by an aging step which generally takes place over a period of time between about 5 minutes and one year, while the repulping step has a residence time ranging from about 5 minutes to about 24 hours, and preferably is about 10 minutes or less. 
     After extracting the copper in solution, it may be recovered by a conventional solvent extraction-electrowinning process, and refined solvent extraction solution may be recycled for use as a supply of plant water. 
     The process may also comprise the steps of classifying the sulfatized copper ore into coarse and fine fractions and collecting the coarse fraction; pile leaching the coarse fraction with sulfuric acid and water to sulfatize a significant portion of the copper therein and form a sulfatized ore; and extracting a substantial portion of the sulfatized copper from the ore in a solution. Here, the pile leaching of the coarse fraction is carried out with a concentrated sulfuric acid solution at a flow rate of between about 2 and 500 liters/hour per square meter of ore. For efficiency, the percolated sulfuric acid solution from the pile leaching of the coarse fraction may be recycled to the pulping step. 
     In this embodiment, copper is recovered from the extracted sulfatized copper solution obtained from the pile leaching step directly, or it is combined with the extracted sulfatized copper solution obtained from the repulping step before recovering copper therefrom. The ore may be classified using a screen having apertures ranging from 200 Tyler sieve mesh to about 25 mm, and preferably ranging from about 2 to about 3 mm. 
     Also, this process may further comprise collecting the fine fraction; thickening the fine fraction; and countercurrently washing the thickened fine fraction to extract the sulfatized copper therefrom. Here, a flocculent may be added to the fine fraction prior to thickening in an amount of between about 5 and 500 grams per ton, and preferably between about 40 and 150 grams per ton. Thus, when the copper is recovered by a solvent extraction-electrowinning process, the percolated sulfuric acid solution from the pile leaching of the coarse fraction may be mixed with the solution coming from the fine fraction thickening and washing step; and the mixture can be recycled to the solvent extraction-electrowinning process. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The specific features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings, wherein: 
     FIG. 1 shows a first embodiment of a process flow diagram of the present invention. 
     FIG. 2 shows a second embodiment of a process flow diagram of the present invention. 
     FIG. 3 shows a third embodiment of a process flow diagram of the present invention. 
     FIG. 4 shows a fourth embodiment of a process flow diagram of the present invention. 
     FIG. 5 shows a fifth embodiment of a process flow diagram of the present invention, showing an example of industrial application. 
     FIG. 6 shows curves of temperature variation in cure pile versus holding or aging time. 
     FIG. 7 shows a schematic of a plant for treatment of altered ores. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is applicable to a broad spectrum of granulometric sizes of ore which may vary during various stages, from crushing stages to dry fine grinding. The present invention recovers metal, particularly copper, from an ore containing same, by a process of first wetting the ore with H 2  SO 4  and water, repulping, separating fine and coarse fractions and pile leaching of the coarse fraction. 
     In this process, copper-bearing ores are sulfatized by first wetting the copper source ore with controlled amounts of H 2  SO 4  and water. The amount of sulfuric acid applied to the ore can vary between about 5 and 500 kg/MT, and preferably between about 15 and 60 kg/MT. In addition, the amount of water which is applied in conjunction with the acid can be up to 250 kg/MT, preferably about 40 to 120 kg/MT. The acid can be concentrated sulfuric acid supplied by a suitable source, while the water may be supplied from conventional sources, a refined process solution or electrolyte from the electrolytic copper extraction stage, which electrolyte would otherwise be discarded. Aqueous solutions of sulfuric acid can also be used. 
     The ore has grain sizes between those of a product obtained by dry fine grinding and one obtained by crushing, and this stage can be conducted in any conventional reactor appropriate for such purposes. A preferred reactor is a rotating drum. As noted above, the purpose of this stage is to uniformly wet, rather than agglomerate, the ore. This treatment fundamentally alters the surface characteristics of the ore are so that its thickening and filtration properties are substantially increased. 
     The wetted ore is then held (i.e., aged or cured) for a period of time sufficient to obtain maximum sulfatization of the oxidized and sulfurized copper in the ore. Depending upon the characteristics of the initial material, the wetted material may pass directly after a short time to the repulping stage described below or, alternatively, may be held for a period of up to three months or longer, for the purpose of producing a high degree of sulfatization, which also promotes the sulfatization of copper sulfides. This wetting and holding stages will generally take between about 5 minutes and one year, depending upon the specific ore. 
     After this stage, the ore is repulped by way of an aqueous solution for a very short period of residence time of between about 5 minutes and 24 hours, and generally not longer than about 10 minutes, which is sufficient for most of the sulfatized copper to be extracted. 
     The sulfatized product is repulped in an aqueous solution in conventional reactors, such as washing drums which are suitable for the ore having the initial grain size varying between the size resulting from dry fine grinding and from secondary crushing. In cases where the ore is of a fine grain size or of the type coming from flotation tailings, the repulping may be performed directly in agitated reactors, and in some specific cases the previously discussed process used in the Nchanga plant, Zambia may be used. 
     The quantities of solution used in repulping may be those sufficient to obtain a pulp having the characteristics necessary for liquid feed thereof to the filtration stage. 
     It is also possible to treat both the fine and coarse fractions without the necessity of fine grinding of the coarse fraction. Depending upon the initial grain size of the material, the repulped product may be sorted or classified by conventional equipment appropriate for this purpose. If the grain size of the initial material includes coarse fractions, the repulped ore may be sorted and the coarse fraction separated from the fine fraction using any conventional equipment designed for sorting, such as shaking screens, vibratory screens, linear screens, etc. Alternatively, it is possible to sort the pulp while washing. The screen aperture may be equal to or less than 5 mm to separate the fine and coarse fractions. The coarse fractions may be washed directly in the sorting equipment and then subjected to a secondary pile leaching process. The strong solution generated from the secondary pile leaching stage is preferably used in repulping the fine fraction or, alternatively, mixed with the strong solution generated in the thickening, washing and/or filtration stage. 
     Since the fine fraction is separated from the coarse fractions, one among other advantages gained by the present invention is that the pile leaching process is performed at very high specific flows, which substantially reduces the leaching period as compared with that of conventional pile leaching. Moreover, the secondary leaching may be processed with the same solutions generated in the overall process itself, reducing the overall cost of operation. 
     The copper is generally concentrated in the fine fraction. The fine fraction of pulp, to which a flocculent has previously been added, may be sent to thickening stages and countercurrent washing and then to filtration or, alternatively, directly to filtration, depending upon its percentage of solids. Conventional thickening and filtration reactors of the types generally employed in the hydrometallurgy of common metals are used for the thickening and filtration stages. Flocculants administered in controlled doses can be used in either situation. 
     In addition, the present invention inhibits the dissolution of silica and sulfatizes copper-bearing ores, enabling small capacity plants to efficiently extract copper. In the present invention, it is also possible to make maximum use of the heat generated by the exothermal reactions during the process, which permits treatment of some refractory ores not satisfactorily treatable by known alternatives, as well as making it possible greatly to reduce the inventories of copper in process as compared with conventional processes, and since it exhibits very rapid kinetics of solution, it is possible to obtain high productions of copper in plants with small capacity. 
     Moreover, in certain instances the coarse fraction is often disintegrated into a fine fraction as a result of the aging or curing stage, thus eliminating the need for fine grinding. 
     The copper in solution may be recovered by any conventional processes, in particular by solvent extraction-electrowinning techniques. Accordingly, the present invention economically produces a high yield of copper, requiring very low inventories than the conventional alternatives. 
     The above-described process may be carried out alternatively as shown in the different embodiments of FIGS. 1-5. As has been stated above, depending upon the initial grain size, it is possible to carry out a great variety of configurations as will be explained below. Each embodiment depicted in the figures incorporates the following basic aspects: 
     1) Preliminary wetting of the ore to improve its specific thickening and filtration rates as effected by an acid cure of the ore; 
     2) Primary leaching of the mulfatized ore for very short periods; 
     3) Independent processing of the fine and coarse fractions. In general, the preleached and sorted coarse fractions are subjected to a secondary pile leaching, using the refined strong solution generated in the SX process as a leaching agent, while the fine fractions are subjected to a filtration stage. 
     The present invention has been described and illustrated in terms of different embodiments. The same element number has been used to designate the same or an equivalent step or means in the five embodiments which are illustrated. Also, the following tables give the particulars of the flow diagrams of these alternatives, with specific reference to the sequences shown in FIGS. 1 to 6. 
     FIG. 1 shows one embodiment of the process step discussed above. In this embodiment, the copper-bearing ore is crushed into fragments in step 1, using conventional primary, secondary and tertiary crushing methods. The crushed ore is sorted in step 2 and then separated into fine fraction 3 and coarse fraction 4. Both fine and coarse fractions are wetted using water in rotating drums in step 5 and the refining strong solution 6 obtained from the copper extraction processing and concentrated H 2  SO 4  7 are fed to both drums. The refined strong solution 6 and the concentrated H 2  SO 4  7 may be fed simultaneously, mixed and then fed or separately fed in any order. The fine fraction is pile cured in step 8 while the coarse fraction is pile leached at a high specific flow in step 9. The strong solution 10 which has percolated through the coarse fraction is recycled and fed to the repulping step 11. The pile cured fine fraction are repulped in a washing drum using the strong solution 10 under pressure in step 11. The repulped fined fraction is then filtered and washed in step 12, using water 13 and flocculent 14. The strong solution from step 12 is extracted by solvents in step 16, via conventional methods. The refined strong solution 17 from step 16 is fed to step 9 for pile leaching. The copper is finally extracted by conventional electrolytic methods in step 18. 
     EMBODIMENT OF FIG. 2 
     FIG. 2 shows another embodiment of the process step discussed above. In this embodiment, the copper-bearing ore is crushed into fragments in step 1, using conventional primary, secondary and tertiary crushing, as in the embodiment of FIG. 1. In this embodiment steps 2-4 of the embodiment of FIG. 1 are omitted. The crushed ore is then wetted using water in a rotating drum in step 5 and the refining solution 6 and concentrated H 2  SO 4  7 are fed to the drum. The refined strong solution and the concentrated H 2  SO 4  may be fed simultaneously, mixed and then fed or separately fed in any order. The crushed ore is then pile cured in step 8 and then repulped in a washing drum in step 19 using the strong solutions 26, 28 obtained during the secondary pile leaching of the coarser fraction 23 in step 25, which uses the refined strong solution 17 obtained during the copper extraction process in step 16. The wet crushed ore is sorted in step 20 and washed in step 21 for refining the coarse fraction. The fine fraction 22 (&lt;2 mm in grain size) and the coarse fraction 23 (&gt;2 mm in grain size) are separated at this point. 
     The fine fraction is processed according to the steps 12 through 18 defined in the embodiment of FIG. 1. However, in step 12, the residue 24 from the filtration and wash is separated and dumped out, and the refined strong solution 17 from step 16 is used for secondary pile leaching of the coarse fraction in step 25. The residue strong solution 26 obtained from the secondary pile leaching step 25 is divided for feeding to a neutralization pile 27 obtained during the crushing step 1 and to the repulping step 19. The strong solution 28 used for leaching the neutralization pile is fed also to step 19, which in turn fellows into the secondary pile leaching step 25, in step 29. 
     EMBODIMENT OF FIG. 3 
     FIG. 3 shows another embodiment of the process step discussed above. In this embodiment, the flotation tailings bearing copper from dumps are wetted in a rotating drum as processed in step 5 of the embodiment of FIG. 1. Concentrated H 2  SO 4  7 is introduced into the drum. The sulfatized tailings are pile cured in step 8 and then repulped in an agitated reactor and washing drums in step 30, with the strong solution 37 under pressure, obtained from conventional hydrometallurgical process 36, which uses the refined strong solution 35 obtained during the solvent extraction-electrowinning copper extraction process 33. Thereafter, the repulped ore is thickened and/or filtered and washed in step 31, while feeding flocculent 14 and wash solution 32. The residue 24 from step 31 is separated and discharged. The strong solution 15 from step 31 is fed to the conventional solvent extraction-electrowinning copper extraction method 33. The refined strong solution 34,35 from step 33 is reintroduced to step 5 and introduced to the conventional hydrometallurgical process 36. Note that a fresh copper bearing ore is also introduced into the conventional process 36, the strong solution 37 obtained therefrom being fed to step 30. 
     EMBODIMENT OF FIG. 4 
     FIG. 4 shows another embodiment of the process step discussed above. The copper bearing ore is crushed into fragments, using conventional primary, secondary and tertiary crushing and sorted in step 1. The dry fine grinding or fraction 39 is then wetted in a rotating drum in step 5 and concentrated H 2  SO 4  7 and the refined strong solution 34 from step 33 are added thereto. The sulfatized fine fraction is then pile cured in step 8 and then repulped in step 11 using the strong solution 28 obtained from leaching of the neutralization pile 27 using the refined strong solution 35 from step 33. The repulped fine fraction is further thickened and/or filtered and washed in step 31, while feeding a flocculent 14 and a wash solution 32. The residue 24 from step 31 is dumped out, while the strong solution 15 therefrom is fed to the conventional solvent extraction-electrowinning copper extraction processing 33. The refined strong solution 34,35 from step 33 is reintroduced to step 5 and to the neutralization pile 27, which is the coarse fraction 38 from step 1, for leaching. The strong solution 28 from leaching of the neutralization pile is reintroduced into the repulping step 11. 
     EMBODIMENT OF FIG. 5 
     FIG. 5 shows another embodiment of the process step discussed above, illustrating an example of the process from Mina Sur fissure 40. New ore 41 is introduced for pan leaching in step 43. Altered ore 42,44 is sorted into small fragments having the grain size less than 3/8&#34; and large fragments having the grain size greater than 3/8&#34;in power screen equipment in step 47. The spalls 45 from the pan leaching step are agglomerated in step 46. The agglomerated spalls are pile leached in step 48. The strong solution 50,54 with arsenic removed therefrom, obtained in step 48, is fed to the repulping step 55 and to the solvent extraction-electrowinning processing 62. 
     The sorted small fraction 49 is agglomerated in step 51 and then cured in step 53 and the sorted large fraction 52 are introduced into the pan leaching step 43 along with the new ore 41. The agglomerated ore in step 53 is repulped in a washing drum using the strong solution 50, and then sorted via a conventional vibratory screen in step 56. The sorted fine fraction 57 having the grain size less than 2mm is filtered and washed in step 59. The residue 61 from step 59 is discarded. The sorted coarse fraction 58 having the grain size greater than 2 mm is pile leached in step 64 using the refined strong solution 63 containing arsenic obtained during the solvent extraction-electrowinning processing. After the filtration and wash step 59, the strong solution is processed using a conventional solvent extraction-electrowinning copper extraction process 62. Thereafter, the strong solution 63 containing arsenic from step 62 is introduced into the pile leaching step 64. The strong solution 65 from step 64 is introduced into the pile leaching step 48. The strong solution 67 containing arsenic obtained from a treatment plant for powder from a flash oven is mixed with the strong solutions 54,60 and fed for the solvent extraction-electrowinning copper extracting processing 62. 
     FIG. 6 shows curves of temperature variation in a pile curing versus the curing time in hours. Curve 68 represents a 10,000 kg pile and curve 69 represents a 500 kg pile. As shown by the curves, the 10,000 kg pile 68 has a higher temperature curve and the temperature change over the aging time period is less than that of the 500 kg pile. This Fig. is discussed in further detail in Example 4 below. 
     FIG. 7 shows a system for treating altered copper ores which utilize the present invention. In this particular embodiment, a pile of altered ores 70 are transported via a hopper payloader (vehicle) into a sorting hopper 72 having rails. The sorting hopper separates large size ores and ores having the grain size larger than 6&#34; are discharges through the bottom 74 of the hopper 72 for removal. The smaller separated ores from the sorting hopper 72 are discharged to a first conveyor belt (not labeled), which directs the ores to an inclined conveyor 75 and then to another inclined conveyor 76 for feeding same to a shaking screen 77. The fraction 79 having a grain size larger than 3/8&#34; is separated. The rest of fraction having grain size smaller than 3/8 &#34; is directed to a fraction pile 80 via another inclined conveyor 78. The fraction from the pile 80, 81 is fed to a hopper 82 for feeding to an agglomerating drum 83 via a conveyor belt (not numbered). Water 84 and H 2  SO 4  85 are fed into the drum 83 and mixed with the fraction to wet and sulfatize same, and then pile cured 86. The cured fraction is fed into another hopper 88 via preferably a portable conveyor belt 87, which are further fed via a conveyor belt (not numbered) into a washing drum 89. The fraction is further sorted using a mesh 91 while washing and separating the coarse fraction 92 and pulp 93. Water 90 is fed into the washing drum during washing and sorting. The coarse fraction 92 is fed into a secondary leaching percolation pipe 95 and the solvent extraction refined solution 94 (same as 108) is fed to the secondary leaching percolation pipe 95, and the percolated strong solution 96 is processed for further use, while the residue 96A is discarded. 
     The pulp 93 and wash water 100 are fed to a pump 97 and discharged to a belt filter 99, while feeding a flocculent 98 to the belt filter. The filtered fraction 101 is discharged for dumping, while the filtered strong solution 103 containing copper is fed to another pump 102 for feeding to a feed reservoir 104, which feeds into a feed pump 105, which in turn discharges into a solvent extraction feed lung 106 for feeding to a solvent extraction processing. Specifically, the feed pump 105 discharges to a solvent extraction E1 plant 107 and refined at E2 plant. The refined strong solution 108 (same as 94) is collected from the E2 plant for reuse. Spent material 117 from a spent material reservoir 116 is fed to the S2 plant 109 and output at 0.5 G.P.M. Organic material 110 discharged from the E1 plant is fed to the EL plant, while feeding wash water 111 thereto. The wash water 112 is discarded. The solvent extraction feed 113 from the S1 plant is fed to the electrowinning pilot cells 114 via a reservoir (not numbered, a part of the spent reservoir 116). The drained solution 115 is fed to the spent reservoir 116. The copper is extracted by an electrolytic process 118. 
     The embodiments described herein and the specific examples of the present invention presented below are for purposes of illustrating the principles of the present invention. Accordingly, the present invention is not to be limited solely to the exact configuration, examples and steps as illustrated and set forth herein. 
     EXAMPLES 
     The examples provided herein have been evaluated at the laboratory and pilot levels, so that those skilled in the art of metallurgy can verify the importance of the present invention in the hydrometallurgy of copper. Consequently, persons skilled in such art will be able to configure other alternatives utilizing within the basic principles and spirit of the present invention. 
     EXAMPLE 1 
     In this example, the thickening of leached pulps have been compared with that of a conventional agitation leaching. 
     Standard sedimentation tests were made on pulps obtained with and without application of the present invention. The sample used was a surface composite from the No. 4 dump of altered ores coming from Mina Sur in the Chuquicamata Division, material which is characterized by its high content of kaolinite and montmorrillonite type clays and its great refractoriness to conventional hydrometallurgical processes. A summary showing the operating conditions employed and the metallurgical results obtained is presented in Table No. 1 below. 
     
                       TABLE 1                                                     
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Effect of Acid Cure on Sedimentation of Leached Pulps                     
Grain size of initial material                                            
                   100% -20 Tyler sieve                                   
                   mesh                                                   
Acid cure time                                                            
Without cure (W/OC)                                                       
                   0:00 hours                                             
With cure (WC)     24:00 hours                                            
Leaching time                                                             
Without cure (W/OC)                                                       
                   120 minutes                                            
With cure (WC)     5 minutes                                              
Dose of flocculent 40 g/t                                                 
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          DOSE IN     % SOLIDS   SPECIFIC                                 
          CURE STAGE  TO         RATE OF                                  
TYPE OF   (kg/MT)     THICKEN-   THICKENING                               
OPERATION H.sub.2 SO.sub.4                                                
                  H.sub.2 O                                               
                          ING      (m.sup.2 /TPD)                         
______________________________________                                    
W/OC      50      0       25       0.244                                  
WC        50      0       25       0.177                                  
WC        50      50      25       0.074                                  
WC        50      100     25       0.074                                  
W/OC      50      0       33       0.172                                  
WC        50      0       33       0.097                                  
W/OC      50      0       25       0.345                                  
WC        50      50      25       0.149                                  
W/OC      100     0       25       0.353                                  
WC        100     50      25       0.118                                  
W/OC      150     0       25       0.345                                  
WC        150     50      25       0.118                                  
______________________________________                                    
 NOTE: In tests without cure, the acid equivalent is added directly to the
 leaching solution.                                                       
 
    
     An examination of these data establishes that application of the proposed process is associated with a sizeable increase in the rates of separation of phases in sedimentation. 
     Considering the best of the cases, application of the present invention practically triples sedimentation rates when compared with that of the conventional process. 
     EXAMPLE 2 
     In this example, filtration of leached pulps has been compared with that of conventional agitation leaching. 
     Standard filtration tests were made on pulps obtained with and without application of the proposed process. The samples used were altered ores coming from ore of Mina Sur in the Chuquicamata Division, which material is characterized by its high content of kaolinite and montmorrillonite type clays and where the copper is found basically as atacamite and copper wad. 
     In addition, tests were performed with new ores of said Mina Sur, in which the contents of kaolinite and montmorrillonite type clays are very low and the copper is found basically as chrysocolla and copper pitch. A summary showing the operating conditions employed and the metallurgical results obtained is presented in Table No. 2 below. 
     
                       TABLE 2                                                     
______________________________________                                    
Effect of Acid Cure on Specific Rates of Filtration:                      
Comparison with Process of Leaching by Conventional                       
Agitation without Prior Acid Cure of Ore                                  
Initial Moisture                                                          
Without acid cure  0.00%                                                  
With acid cure     10.00%                                                 
Dose of H.sub.2 SO.sub.4                                                  
                   150 kg/mt                                              
Acid cure time                                                            
Without acid cure  0:00 hours                                             
With acid cure     24:00 hours                                            
Grain size of initial material                                            
                   100% -20 Tyler sieve                                   
                   mesh                                                   
% Solids in suspension                                                    
                   50%                                                    
Leaching time                                                             
Without acid cure  120 minutes                                            
With acid cure     5-15 minutes                                           
Dose of flocculent 40 g/t Magnafloc 351,                                  
                   0.05%                                                  
______________________________________                                    
           Specific Filtration Rates                                      
           kg/hour × m.sup.2                                        
TYPE of ORE  Without Acid Cure                                            
                            With Acid Cure                                
______________________________________                                    
Surface Composite                                                         
             80.26          488.13                                        
No. 4 dump                                                                
Slope No. 4 dump                                                          
             83.71          507.24                                        
Altered rock from                                                         
             86.31          542.68                                        
fissure                                                                   
Altered gravel from                                                       
             59.41          646.68                                        
fissure                                                                   
Average      77.42          546.24                                        
New Ores     88.54          1,089.18                                      
______________________________________                                    
 
    
     The above results indicate that the filtration rate increases notably when the process of the present invention was applied. For altered ores, on average, application of the novel process increased filtration capacity practically seven times, while for new ores increased about twelve times. This example constitutes one of the basic foundations of application of the present hydrometallurgical process for obtaining copper. 
     EXAMPLE 3 
     Standard leaching tests were performed, with and without application of the process of the present invention, on various samples of altered ores from the Mina Sur deposit. These ores are characterized by their high content of kaolinite and montmorrillonite type clays with absorbed copper, where the copper is found as atacamite and copper wad. These ores exhibit high refractoriness to conventional hydrometallurgical processes. 
     When these ores are processed in percolation pans, mixed 20% by weight with new ores, their recovery (altered ores) does not exceed 30%. Moreover, when this ore was processed in a leaching plant by agitation of 1200 TPD, the process proved not to be technically or economically feasible, clue to its low recovery rate and to critical problems of separation of phases in the thickeners. A summary showing the operating conditions employed and the metallurgical results obtained is presented in Table No. 3 below. 
     
                       TABLE 3                                                     
______________________________________                                    
COMPARISON OF COPPER EXTRACTIONS IN THE                                   
LEACHING PROCESS BY CONVENTIONAL                                          
AGITATION AND THE PROPOSED PROCESS                                        
LABORATORY TESTS                                                          
% Solids in leaching                                                      
                    50%                                                   
Leaching time       Conventional without                                  
                    cure (W/OC): 120 min                                  
                    Proposed with cure                                    
                    (WC): 5-15 min                                        
Moisture of initial ore                                                   
                    Conventional without                                  
                    cure (W/OC): 0%                                       
                    Proposed with cure                                    
                    (WC): 10%                                             
Grain size initial material                                               
                    100% -20 Tyler sieve                                  
                    mesh                                                  
______________________________________                                    
                       EXTRACTIONS OF                                     
CURE                   COPPER FOR DOSES                                   
TIME       TYPE OF     OF H.sub.2 SO.sub.4 (kg/MT) OF:                    
(DAYS)     OPERATION   50       75   100                                  
______________________________________                                    
SURFACE COMPOSITE No. 4 DUMP                                              
0          W/OC        39.53    --   43.52                                
1          WC          51.17    --   61.25                                
3          WC          57.22    --   65.86                                
5          WC          50.83    --   62.12                                
ALTERED GRAVEL FROM FISSURE                                               
0          W/OC        43.89    --   47.77                                
1          WC          54.52    --   54.94                                
3          WC          54.52    --   66.65                                
5          WC          53.26    --   68.23                                
ALTERED ROCK FROM FISSURE                                                 
0          W/OC        46.41    --   51.17                                
1          WC          56.95    --   59.92                                
3          WC          46.19    --   68.72                                
5          WC          54.22    --   73.75                                
SLOPE No. 4 DUMP                                                          
0          W/OC        --       33.52                                     
                                     39.61                                
1          WC          --       48.24                                     
                                     49.40                                
3          WC          --       47.82                                     
                                     52.70                                
5          WC          --       49.66                                     
                                     53.57                                
______________________________________                                    
 
    
     The above results indicate, in all cases of the proposed process, a notable increase occurs in the extractions of copper as compared to conventional system not utilizing the present process. 
     EXAMPLE 4 
     In this example, the temperatures reached in the proposed process is considered. Wetting tests on altered ores in stock were performed with doses of H 2  O and H 2  SO 4  of 100 kg/MT respectively in a pilot agglomerating drum 0.75 m in diameter×2.3 m in length. The grain size of the initial material was 100% (&lt;3/8&#34;). The product from the drum was used to build sulfatization piles of 500 kg and 10,000 kg, respectively, and systematic measurements of the temperatures reached were made. 
     A summary showing the results obtained is presented in FIG. 6, in which it may be seen that, as the size of the pile increases, temperatures remain higher over time, evidently due to the smaller heat losses due to the effect of the mass/surface relationship. For example, it is noted that in the 500 kg pile (69 in FIG. 6) the temperature reached at 72 hours of rest is practically the ambient temperature, whereas in the 10,000 kg pile 68 the temperature is maintained at 40 degrees Celsius. It must be pointed out that temperature is an important variable in hydrometallurgical processes. 
     EXAMPLE 5 
     In this process, application of the process to treatment of oxidized ores from &#34;El Abra&#34; is considered. The oxidized ores of El Abra represent a mineral source whose estimated reserves are 462 million tons, with an average total copper assay equivalent to 0.92%. Mine geology studies have classified this ore into three categories: 
     Type 1: Biotitic, representing between 20 and 25% of the deposit. 
     Type 2: Phyllitic, representing about 5% of the deposit. 
     Type 3: Feldspathic or potassic, representing between 70 and 75% of the deposit. 
     Laboratory Evaluation of the Embodiment of FIG. 1 
     This alternative considers the following sequential stages: 
     Primary, secondary and tertiary crushing in step 1 
     Dry classification to 4 mm in steps 2,8,11,12 
     Acid cure, pulping and filtration of &lt;4 mm fraction 
     Pile leaching of &gt;4 mm fraction 
     Recovery of copper dissolved by SX and EW techniques in step 33. 
     The operating conditions investigated were the following: 
     
         ______________________________________                                    
Grain size of initial material                                            
                     100% (&lt;3/8&#34;)                                         
Separating size for fine fraction                                         
                     4 mm                                                 
Assays of (&lt;4 mm) fraction                                                
                     El Abra #1: 1.52%                                    
                     El Abra #3: 2.11%                                    
Doses in cure stage                                                       
of (&lt;4 mm) fraction  H.sub.2 SO.sub.4 : 40-60-80-                         
                     100 kg/MT                                            
                     H.sub.2 O: 100 kg/MT                                 
Sulfatization time   1-3-5 days                                           
% Solids in leaching 50%                                                  
Leaching time        5 minutes                                            
Dose of flocculent prior                                                  
                     40 g/t Magnafloc                                     
to filtration        351, 0.05%                                           
Wash H2O in filtration                                                    
                     0.33 kg/MT of ore                                    
______________________________________                                    
 
    
     For the conditions evaluated, the best metallurgical results are obtained by applying the following operating conditions for the fine fraction, as listed below: 
     
         ______________________________________                                    
               ORE          ORE                                           
ITEM           EL ABRA #1   EL ABRA #3                                    
______________________________________                                    
Grain size of initial                                                     
               100% &lt;4 mm   100% &lt;4 mm                                    
material                                                                  
Doses in cure stage                                                       
(kg/MT) H.sub.2 O                                                         
               100          100                                           
H.sub.2 SO.sub.4                                                          
               60           60                                            
Aging time (days)                                                         
               3            3                                             
H.sub.2 O in repulping of                                                 
               1            1                                             
sulfatized product                                                        
(m.sup.3 /t of ore at &lt;4 mm)                                              
Leaching time in                                                          
               5            5                                             
repulping (min)                                                           
Dose of flocculent                                                        
               40           40                                            
prior to filtration                                                       
(g/t of ore at &lt;4 mm)                                                     
Wash H.sub.2 O in filtration                                              
               0.33         0.33                                          
(m.sup.3 /t of ore at &lt;4 mm)                                              
______________________________________                                    
 
    
     For the conditions indicated, it is possible to obtain the following metallurgical results: 
     
         ______________________________________                                    
                 ORE         ORE                                          
ITEM             EL ABRA #1  EL ABRA #3                                   
______________________________________                                    
Extraction of copper                                                      
                 82.95       84.66                                        
Consumption of H.sub.2 SO.sub.4                                           
                 52.60       47.42                                        
(kg/MT)                                                                   
Specific filtration rates                                                 
                 1,501       1,421                                        
(kg/hr × m.sup.2)                                                   
Average thickness of cake                                                 
                 7/8         9                                            
(mm)                                                                      
Moisture in residue (%)                                                   
                 20.88       21.92                                        
Solution of solids (%)                                                    
                 4           5                                            
H.sub.2 SO.sub.4 in strong solution (gpl)                                 
                 6           10.2                                         
______________________________________                                    
 
    
     For the overall process, total copper extractions equivalent to 80.47% were estimated, with H 2  SO 4  consumption of 48.72 kg/MT when pile leaching of the coarse fractions was included. 
     Laboratory Evaluation of the Embodiment of FIG. 2 
     This alternative considers the following sequential stages: 
     Primary, secondary and tertiary crushing in step 1 
     Acid cure of all ore in step 5 
     Pulping and classification at 4 mm 
     Filtration of &lt;4 mm fraction in steps 19,20 
     Secondary leaching in piles of &gt;4 mm fraction in step 25 
     Recovery of copper dissolved by SX and EW techniques in step 33 
     The operating conditions investigated were the following: 
     
         ______________________________________                                    
Grain size of initial material                                            
                     100% &lt;3/8&#34;                                           
Ore assays           El Abra #1:                                          
                     1.49%                                                
                     El Abra #3:                                          
                     1.80%                                                
Doses in cure stage  H.sub.2 SO.sub.4 : 40-50-60                          
                     H.sub.2 O: 100                                       
Sulfatization time   1-3-5 days                                           
H.sub.2 O in pulping (m.sup.3 /MT)                                        
                     El Abra #1: 0.50                                     
                     El Abra #3:                                          
                     0.55                                                 
Leaching time in pulping (min)                                            
                     5                                                    
Dose of flocculent prior to                                               
                     40 g/t Magnafloc                                     
filtration           351, 0.05%                                           
H.sub.2 O wash in filtration                                              
                     0.33 m.sup.3 /MT of ore                              
______________________________________                                    
 
    
     For the conditions evaluated, the best metallurgical results are obtained by applying the following operating conditions: 
     
         ______________________________________                                    
                ORE          ORE                                          
ITEM            EL ABRA #1   EL ABRA #3                                   
______________________________________                                    
Grain size of initial                                                     
                100% &lt;3/8 mm 100% &lt;3/8 mm                                 
material                                                                  
Doses in cure stage (kg/MT)                                               
H.sub.2 O       100          100                                          
H.sub.2 SO.sub.4                                                          
                40           50                                           
Aging time (days)                                                         
                5            3                                            
H.sub.2 O in repulping of                                                 
                0.5          0.55                                         
cured product (m.sup.3 /MT)                                               
Leaching time in                                                          
                5            5                                            
repulping (min)                                                           
Dose of flocculent                                                        
                40           40                                           
prior to filtration                                                       
(g/t of ore at -4 mm)                                                     
H.sub.2 O wash in filtration                                              
                0.33         0.33                                         
of &lt;4 mm fraction (m.sup.3 /MT)                                           
______________________________________                                    
 
    
     For the conditions indicated, it is possible to obtain the following metallurgical results: 
     
         ______________________________________                                    
                 ORE         ORE                                          
ITEM             EL ABRA #1  EL ABRA #3                                   
______________________________________                                    
Weight of sulfatized                                                      
                 1.08        1.11                                         
product (t/t of ore)                                                      
Specific rate of filtration                                               
                 2,229       2,337                                        
(kg/hr × m.sup.2)                                                   
Average thickness of cake                                                 
                 9           9                                            
(mm)                                                                      
Weight of residues                                                        
(kg/MT of ore):                                                           
&gt;4 mm fraction   154         151                                          
&lt;4 mm fraction   812         781                                          
Moisture of residues (%):                                                 
&gt;4 mm fraction   5.15        10.75                                        
4 mm fraction    16.49       20.74                                        
Extraction of copper                                                      
                 76.48       75.38                                        
average (%)                                                               
Consumption of H.sub.2 SO.sub.4                                           
                 37.95       45.01                                        
(kg/MT)                                                                   
Solution of solids (%)                                                    
                 3.4         6.81                                         
H.sub.2 SO.sub.4 in strong solution (gpl)                                 
                 3.5         7.70                                         
______________________________________                                    
 
    
     Note that in this embodiment, the ore in particular, has a high degree of disintegration because of the acid cure. The following tabular summary illustrates the phenomenon for the most relevant mesh sizes: 
     
         ______________________________________                                    
           TYLER       % PARTIAL  % PARTIAL                               
TYPE OF ORE                                                               
           SIEVE MESH  HEAD       RESIDUE                                 
______________________________________                                    
El Abra #1 6           45.09      11.55                                   
           20          12.99      22.30                                   
           -200         2.17      16.87                                   
El Abra #3 6           44.46       9.50                                   
           20          14.02      24.33                                   
           -200         1.95      19.24                                   
______________________________________                                    
 
    
     This phenomenon is of great importance in a conventional pile leaching process, since it may generate an excess quantity of fine fractions which would interfere with permeability of the bed in an industrial operation. In the present invention, on the other hand, the generation of fine fractions is favorable. For the overall process, total copper extractions equivalent to 82.5% were estimated, with H 2  SO 4  consumption of 44.46 kg/MT when the secondary pile leaching of the classified coarse fraction is included. 
     Preliminary Technical/Economic Analysis of the Processes Developed and the Conventional Pile Leaching Process 
     For the preliminary analysis, it was assumed that the ore treated in plant is a mixture of 25% of No. 1 ore and 75% of No. 3 ore. Moreover, it is considered that the material treated in plant corresponds to a tertiary crushing product, the investments in the mine area being similar for the Embodiments of FIGS. 1 and 2 and pile leaching. A summary showing the principal results of evaluation of the present embodiment of FIGS. 1 and 2, represented as A and B, respectively, in comparison to a conventional pile process, represented as CCP follows (does not consider mine area): 
     
         ______________________________________                                    
ITEM              A        B        CCP                                   
______________________________________                                    
Total copper      80.47    82.52    75                                    
extraction (%)                                                            
Consumption of H.sub.2 SO.sub.4                                           
                  48.72    44.46    50                                    
(kg/MT)                                                                   
Size of plant: MTD                                                        
                  60,000   60,000   60,000                                
Assay %           0.97     0.97     0.97                                  
Recovery dissolved                                                        
                  86       86       84                                    
copper (%)                                                                
Production fine copper first                                              
                  138,952  147,308  117,440                               
year of production (t)                                                    
Subsequent annual production                                              
                  147,095  150,745  133,955                               
(t)                                                                       
Investments (KUS$)                                                        
                  129,374  126,823  117,371                               
Cost of annual operation                                                  
after first year of                                                       
operation:                                                                
KUS$              58,890   66,400   48,550                                
cUS$/lb           18.16    19.98    16.44                                 
Annual income after first year                                            
of operation (KUS$)                                                       
@ 50 cUS$/lb      162,143  166,166  147,659                               
@ 65 cUS$/lb      210,786  216,016  191,956                               
@ 80 cUS$/lb      259,429  265,866  236,254                               
Annual profits after first year                                           
of operation (KUS$)                                                       
@ 50 cUS$/lb      103,253  99,766   99,109                                
@ 65 cUS$/lb      151,896  149,616  143,406                               
@ 80 cUS$/lb      200,539  199,466  187,704                               
______________________________________                                    
 
    
     Moreover, it should be noted that for the cycles of the process (45 days for pile leaching), A and B present as credit a great production of fine copper in the first year of operation, which furnishes the following additional profits when the same exercise as above is performed. 
     
         ______________________________________                                    
ITEM                A       B                                             
______________________________________                                    
Additional fine copper                                                    
                     9,992  15,148                                        
production (t)                                                            
Additional profits (KUS%)                                                 
@ 50 cUS$/lb         7,014  109,026                                       
@ 65 cUS$/lb        10,318  15,035                                        
@ 80 cUS$/lb        13,623  20,044                                        
______________________________________                                    
 
    
     The above results indicate that the process of the present invention exhibits profitability parameters which are more favorable than that of the conventional pile leaching process. 
     EXAMPLE 6 
     In this example, application of the process to the treatment of oxidized ores of Chuqui Norte is considered. The oxidized ores of Chuqui Norte represent a source which amounts to about 317 million tons with an average estimated assay of 0.86% total copper. An experimental program at the laboratory level, very similar to that developed for the oxidized ores of El Abra, was carried out. The relevant results obtained are described below: 
     Laboiratory Evaluation of the Embodiment of FIG. 1 
     The best operating conditions for carrying out the process on fine fractions are the following: 
     
         ______________________________________                                    
Grain size of initial material                                            
                      100% (&lt;4 mm)                                        
Assays                0.77% total                                         
                      copper                                              
                      0.69% soluble                                       
                      copper                                              
Doses in agglomeration stage                                              
H.sub.2 O             150 kg/MT                                           
H.sub.2 SO.sub.4      40 kg/MT                                            
Acid cure time        5 days                                              
Quantity of H.sub.2 O in repulping                                        
                      1 m.sup.3 /MT of fine                               
                      ore                                                 
Leaching time in repulping (min)                                          
                      5                                                   
Dose of flocculent prior to                                               
                      40 g/t                                              
filtration                                                                
H.sub.2 O in filtration                                                   
                      0.666 m.sup.3 /MT of                                
ore                                                                       
______________________________________                                    
 
    
     For the conditions indicated, it is possible to obtain the following metallurgical results: 
     
         ______________________________________                                    
Recovery of copper   84.31%                                               
Consumption of H.sub.2 SO.sub.4                                           
                     27.00 kg/MT                                          
Specific rate of filtration                                               
                     1,279 kg/h × m.sup.2                           
Moisture filtered cake                                                    
                     16.9%                                                
Average moisture cake                                                     
                     8 mm                                                 
______________________________________                                    
 
    
     For the process as a whole, extractions of total copper equivalent to 80.40% were estimated, with consumption of H 2  SO 4  of 19.42 kg/MT when pile leaching of the coarse fractions is included. 
     Laboratory Evaluation of the Embodiment of FIG. 2 
     The best operating conditions for carrying out the process are the following: 
     
         ______________________________________                                    
Grain size of initial material                                            
                      100% (&lt;3/8&#34;)                                        
Assays                0.68% total                                         
                      copper                                              
                      0.55% soluble                                       
                      copper                                              
Doses in agglomeration stage                                              
H.sub.2 O             100 kg/MT                                           
H.sub.2 SO.sub.4      30 kg/MT                                            
Acid cure time        5 days                                              
H.sub.2 O in repulping                                                    
                      0.47 m.sup.3 /MT ore                                
Dose of flocculent prior to                                               
                      40 g/t (&lt;4 mm)                                      
filtration &lt;4 mm fraction                                                 
                      fraction                                            
______________________________________                                    
 
    
     For the conditions indicated, it is possible to obtain the following metallurgical results: 
     
         ______________________________________                                    
Recovery of copper   70.61%                                               
Consumption of H.sub.2 SO.sub.4                                           
                     23.25 kg/MT                                          
Specific rates of filtration                                              
                     1,160 kg/h × m.sup.2                           
Moisture filtered cake                                                    
&lt;4 mm fraction       16.27%                                               
&gt;4 mm fraction       5.33%                                                
Average moisture cake                                                     
                     8 mm                                                 
______________________________________                                    
 
    
     For the process as a whole, total copper extractions equivalent to 84.72% were estimated, with consumption of H 2  SO 4  of 27.09 kg/MT when a secondary leaching of coarse fractions is included. 
     Preliminary Technical/Economic Analysis Comparing the Processes Developed and the Pile Leaching Process 
     For this preliminary analysis, a plant processing 49,024 MTD of ore with a head assay of 0.86% total copper is considered. It is assumed that the material treated in plant corresponds to a product of tertiary crushing, the investments in the mine area being similar for all three alternatives below. A summary showing the principal results of evaluation of the present embodiment of FIGS. 1 and 2, represented as A and B, respectively, in comparison to a conventional pile process, represented as CCP follows (does not consider mine area): 
     
         ______________________________________                                    
ITEM              A        B        CCP                                   
______________________________________                                    
Total copper      80.40    84.72    70.7                                  
extraction (%)                                                            
Consumption of H.sub.2 SO.sub.4                                           
                  19.42    27.09    25.50                                 
(kg/MT)                                                                   
Recovery dissolved                                                        
                  86       86       84                                    
copper (%)                                                                
Production fine copper first                                              
                  110,741  123,531  81,972                                
year of production (t)                                                    
Subsequent annual production                                              
                  123,724  130,374  108,799                               
(t)                                                                       
Investments (KUS$)                                                        
                  108,941  118,935  95,937                                
Cost of annual operation                                                  
after first year of                                                       
operation:                                                                
KUS$              42,669   48,943   33,123                                
cUS$/lb           18.19    19.98    16.44                                 
Annual income after                                                       
first year of operation (KUS$)                                            
@ 50 cUS$/lb      117,288  123,592  100,740                               
@ 65 cUS$/lb      152,474  160,670  130,962                               
@ 80 cUS$/lb      187,661  197,747  161,185                               
Annual profits after                                                      
first year of operation (KUS$)                                            
@ 50 cUS$/lb      74,619   74,649   67,717                                
@ 65 cUS$/lb      109,805  111,727  97,839                                
@ 80 cUS$/lb      144,992  148,804  128,062                               
______________________________________                                    
 
    
     Moreover, it should be noted that because of the cycles of the process (90 days for pile leaching), A and B present as credit, a great production of fine copper in the first year of operation, which furnishes the following additional profits when the same exercise as above is performed. 
     
         ______________________________________                                    
ITEM                A       B                                             
______________________________________                                    
Additional fine copper                                                    
                    15,071  21,761                                        
production (t)                                                            
Additional profits (KUS%)                                                 
@ 50 cUS$/lb        10,569  14,488                                        
@ 65 cUS$/lb        15,553  21,684                                        
@ 80 cUS$/lb        20,536  28,880                                        
______________________________________                                    
 
    
     EXAMPLE 7 
     In this example, application of treatment of old spalls from Mina Sur is considered. Continuous processing of the ores of Mina Sur in pans has led to the accumulation of spalls which for the most part have been stored in a specific sector of the dump. It is estimated that at present some 60 million tons, with an average copper assay of close to 0.47%, are accumulated in a single sector of the dump. The physical characteristics of these spalls render them practically impermeable and not treatable by the conventional methods. Based on the foregoing, a research program was initiated to evaluate the following alternatives: 
     A. Dry Classification of Spalls 
     Fine fraction : Acid cure, repulping and filtration 
     Coarse fraction: Incorporation in Chuqui oxide spalls 
     B. Acid Cure On Entire Mass Of Spalls, Repulping And Wet Classification 
     Fine fraction : Filtration 
     Coarse fraction: Incorporation in Chuqui oxide spalls 
     Evaluation at Laboratory Level of the Embodiment of FIG. 1 (Preliminary Dry Classification of Spalls) 
     The best operating conditions established for carrying out the process were the following: 
     
         ______________________________________                                    
Dry classification of spalls                                              
                    4 mm                                                  
&gt;4 mm fraction      Incorporation in                                      
                    Chuqui oxide spalls                                   
&lt;4 mm fraction      Acid cure, repulping                                  
                    and filtration                                        
Grain size initial fine                                                   
                    100% &lt;4 mm                                            
material                                                                  
Dose in agglomeration stage                                               
H.sub.2 O           100 kg/MT fine fraction                               
H.sub.2 SO.sub.4     50 kg/MT fine fraction                               
Aging time          5 days                                                
H.sub.2 O in repulping                                                    
                    867 kg/MT fine fraction                               
Leaching time in repulping                                                
                    5                                                     
(min)                                                                     
Dose of flocculent prior                                                  
                    40 g/t fine fraction                                  
to filtration                                                             
Wash H.sub.2 O in filtration                                              
                    333 kg/MT fine                                        
                    fraction                                              
______________________________________                                    
 
    
     For the conditions indicated, it is possible to obtain the following metallurgical results: 
     
         ______________________________________                                    
Extraction of copper 67.91%                                               
Consumption of H.sub.2 SO.sub.4                                           
                     42.70 kg/MT fine                                     
fraction                                                                  
Specific rate of filtration                                               
                     987 kg/hr × m.sup.2                            
Moisture filtered cake                                                    
                     19.17%                                               
Average thickness cake                                                    
                     6.5 mm                                               
______________________________________                                    
 
    
     If it is assumed that the &gt;4 mm fraction has a leaching efficiency of 70% and a similar acid consumption, with the following overall efficiencies: 
     
         ______________________________________                                    
Recovery of copper    68.39%                                              
Consumption of H.sub.2 SO.sub.4                                           
                      41.70 kg/MT                                         
______________________________________                                    
 
    
     Evaluation at Laboratory Level of the Embodiment of FIG. 2: Acid Cure on Entire Mass of Spalls, Pulping and Wet Classification 
     The best operating conditions established for carrying out the process were the following: 
     
         ______________________________________                                    
Doses in cure stage                                                       
H.sub.2 O           100 kg/MT                                             
H.sub.2 SO.sub.4     50 kg/MT                                             
Aging time          3 days                                                
H.sub.2 O in repulping                                                    
                    575 kg/mt                                             
Wet classification  8 Tyler sieve mesh                                    
Repulping time (min)                                                      
                    5                                                     
Dose of flocculent prior                                                  
to filtration       40 g/t of solids                                      
                    filtrate                                              
Wash H.sub.2 O in filtration                                              
                    192 kg/MT of spalls                                   
______________________________________                                    
 
    
     For the conditions indicated, it is possible to obtain the following metallurgical results: 
     
         ______________________________________                                    
Weight of sulfatized product                                              
                    1.15 t/t of spalls                                    
Extraction of copper                                                      
                    69.68%                                                
Consumption of H.sub.2 SO.sub.4                                           
                    47.79 kg/MT of spalls                                 
Specific rate of filtration                                               
                    917 kg/hr × m.sup.2                             
Moisture filtered cake                                                    
                    21.26%                                                
Average thickness cake                                                    
                    6/7 mm                                                
______________________________________                                    
 
    
     As in the case above, if it is assumed that the leaching efficiency of the &gt;8 Tyler sieve mesh fraction is 70% with a similar acid consumption, the total efficiencies of the process would be the following: 
     
         ______________________________________                                    
Recovery of copper    82.92%                                              
Consumption of H.sub.2 SO.sub.4                                           
                      47.79 kg/MT                                         
______________________________________                                    
 
    
     EXAMPLE 8 
     In this example, application of treatment of altered ores at pilot level is considered. A schematic flow diagram of all the installations making up the pilot plant is presented in FIG. 7. The central idea is to continue processing the (&gt;3/8&#34;) fractions in pans and the (&lt;3/8) fraction by the proposed process. 
     Treatment of the altered ores starts with their transfer from the stocks for sorting, where they are classified into fractions having &gt;3/8&#34; and &lt;3/8&#34;, the (&gt;6&#34;) fraction having previously been eliminated. The 3/8&#34;) fraction is transferred to the oxide pilot plant. The first stage of the process consists of agglomerating the ore in a pilot drum 0.75 m in diameter by 2.3 m in length, provided with a network feed of H 2  O and H 2  SO 4 . The design of the equipment makes it possible to vary the speed of rotation and inclination of the drum 83. A variable-speed belt regulates the feed. The agglomerated ore is transferred in small cars to rest piles for sulfatization. The sulfatized ore is then stored in the hopper 88 by means of a portable belt 87. 
     The second and final stage consists of purification and concentration of the strong leaching solutions of SX-EW techniques. For this purpose, a Denver SX plant 109 of 0.5 GPM is used, while electrolytic extraction of copper is effected in one of two pilot cells (114), each of 0.1 m 3  capacity, which operate with a current rectifier and variable voltage (11 anodes of Pb-Ca alloy and 12 initial sheets are used). 
     The refined solution from the SX process is finally used in the leaching of previously sorted coarse fraction. 
     The analyses of chemical, microscopic and instrumental characterization gave the following results: 
     
         ______________________________________                                    
Principal copper-bearing                                                  
                 Atacamite, copper wad                                    
species                                                                   
Principal types of clays                                                  
                 Chlorite, kaolinite and                                  
                 montmorillonite with copper                              
                 in their composition                                     
Species determined by                                                     
                 Copper and manganese ores                                
electronic microscopy                                                     
                 (copper wad and copper                                   
analysis         pitch), corresponding to                                 
                 amorphous oxides of Fe, Cu,                              
                 Mn, Si, K, Na, etc.;                                     
                 Cryptomelane, corresponding                              
                 to an amorphous oxide of                                 
                 manganese with barium and                                
                 copper in its composition;                               
                 Transparent minerals such                                
                 as atacamite and                                         
                 chrysocolla opaque minerals                              
                 such as magnetite,                                       
                 hematite, ilmenite, rutile,                              
                 sphene, limonite and                                     
                 occasionally native copper,                              
                 cuprite, chalcopyrite,                                   
                 pyrite and covelline;                                    
                 Inclusions of chrysocolla                                
                 in large grains of quartz;                               
Crystalline species detected                                              
                 Kaolinite, alpha quartz and                              
by means of X-ray diffraction                                             
                 plagioclase feldspar;                                    
analysis                                                                  
X-ray fluorescence                                                        
analysis: Majority elements                                               
                 Si, Al, K;                                               
Minority elements                                                         
                 Cu, Mn, Ti, Ca;                                          
Trace elements   S, Ba, Zr, Zn, P, Sr, Rb, Cr,                            
                 As;                                                      
Classic chemical analysis                                                 
                 (Ref. to Tables 4 to 6).                                 
and distribution of copper                                                
by mesh size                                                              
______________________________________                                    
 
    
     The altered ores have a high content of insoluble copper, which for different samples may vary from 33 to 58% of total copper present in the sample. For this reason, extractions of copper from this ore are generally low. It should be noted that the project of leaching by conventional agitation at PELA took into account a copper recovery of 55% from leaching, but the process failed to prosper and thus discontinued. 
     Tables 4, 5 and 6 shows the following: typical composition of altered ores of Mina Sur; granulometric characterization and distribution of copper by mesh of the (&lt;3/8&#34;) fraction fed to the pilot plant; and the content of impurities in the (&lt;3/8&#34;) fraction used in the pilot campaign, respectively. 
     
                       TABLE 4                                                     
______________________________________                                    
TYPICAL COMPOSITION OF ALTERED ORES                                       
OF MINA SUR                                                               
Composite Surface No. 4 Dump is represented by I;                         
Slope No. 4 Dump is represented by II;                                    
Altered Rock Fissure is represented by III;                               
Altered Gravel Fissure is represented by IV;                              
Polycom Product Pilot is represented by V; and                            
Polycom Product Semi-Ind is represented by VI.                            
             ORIGIN AND                                                   
             COMPOSITION (%)                                              
             I    II     III    IV   V    VI                              
______________________________________                                    
TOTAL COPPER:  1.58   1.27   0.64 1.74 1.40 1.29                          
SOLUBLE COPPER:                                                           
               0.75   0.54   0.32 0.82 0.68 0.87                          
INSOLUBLE COPPER:                                                         
               0.87   0.73   0.32 0.92 0.72 0.42                          
COPPER NOT:    52.53  57.48  50.00                                        
                                  52.87                                   
                                       51.43                              
                                            32.56                         
LEACHABLE IN                                                              
CONVENTIONAL                                                              
PROCESS (%)                                                               
IRON:          5.95   5.43   3.36 3.00 5.24 4.21                          
MANGANESE:     0.22   0.27   0.09 0.60 0.23 0.24                          
ALUMINUM:      10.40  13.80  9.35 9.26 10.26                              
                                            9.40                          
SILICA:                                50.15                              
                                            58.90                         
CHLORIDE                                    0.07                          
______________________________________                                    
 
    
     
                                           TABLE 5                                 
__________________________________________________________________________
GRANULOMETRIC CHARACTERIZATION AND DISTRIBUTION                           
OF COPPER BY MESH OF (&lt;3/8&#34;) FRACTION FEED TO PILOT PLANT                 
     APERT-                                                               
          GRANUL.               DISTRIB.                                  
TYLER                                                                     
     URE  DISTRIB.   COPPER     CuFT.                                     
MESH (mm) % PART.                                                         
                % CUM.                                                    
                     TOTAL                                                
                          SOLUBLE                                         
                                % PART.                                   
                                      % CUM.                              
__________________________________________________________________________
3    6.680                                                                
          2.74  2.74 1.51 1.06  3.28  3.28                                
4    4.699                                                                
          4.72  7.46 1.43 1.02  5.34  8.62                                
6    3.327                                                                
          6.46  13.92                                                     
                     1.28 0.89  6.55  15.17                               
8    2.362                                                                
          7.33  21.25                                                     
                     1.24 0.86  7.19  22.36                               
10   1.651                                                                
          7.65  28.90                                                     
                     1.22 0.83  7.39  29.75                               
14   1.168                                                                
          7.76  36.66                                                     
                     1.21 0.82  7.43  37.18                               
20   0.833                                                                
          9.05  45.71                                                     
                     1.18 0.76  8.45  45.63                               
28   0.589                                                                
          7.80  53.51                                                     
                     1.12 0.70  6.92  52.55                               
35   0.417                                                                
          8.31  61.82                                                     
                     1.08 0.65  7.10  59.65                               
48   0.295                                                                
          9.05  70.87                                                     
                     1.12 0.72  80.2  67.67                               
65   0.208                                                                
          7.88  78.75                                                     
                     1.16 0.74  7.20  74.87                               
100  0.147                                                                
          6.80  85.55                                                     
                     1.23 0.76  6.62  81.49                               
150  0.104                                                                
          5.33  90.88                                                     
                     1.37 0.81  5.78  87.27                               
200  0.074                                                                
          4.64  95.52                                                     
                     1.63 0.99  5.99  93.26                               
-200      4.48  100  1.89 1.11  6.74  100                                 
TOTAL SAMPLE         1.263                                                
                          0.816                                           
 COPPER NOT LEACHABLE IN CONVENTIONAL PROCESS (%) 35.39                   
__________________________________________________________________________
 
    
     
                       TABLE 6                                                     
______________________________________                                    
CONTENT OF IMPURITIES IN (&lt;3/8&#34;) FRACTION                                 
USED IN PILOT CAMPAIGN                                                    
SPECIES         COMPOSITION %                                             
______________________________________                                    
SILICA          56.91                                                     
ALUMINUM        8.99                                                      
IRON            4.94                                                      
TOTAL COPPER    1.26                                                      
SOLUBLE COPPER  0.82                                                      
POTASSIUM       1.28                                                      
SODIUM          1.08                                                      
MANGANESE       0.18                                                      
CHLORIDE        0.08                                                      
COBALT          0.003                                                     
ARSENIC         0.005                                                     
MOLYBDENUM      0.004                                                     
URANIUM         10 ppm                                                    
______________________________________                                    
 
    
     Pilot Tests: Wetting in Agglomerating Drum 83 (FIG. 7) 
     The agglomeration stage is technically feasible in a broad range of operating conditions: 
     
         ______________________________________                                    
Dose  H.sub.2 O       100 kg/MT                                           
Dose  H.sub.2 SO.sub.4                                                    
                      100-130 kg/MT                                       
Revolutions of drum   7-10 rpm                                            
Inclination of drum   6-10 degrees                                        
Residence time in drum                                                    
                      30-67 seconds                                       
Volume occupied by charge                                                 
                      4.22-8.21 o/v                                       
______________________________________                                    
 
    
     It is estimated that to produce 80 TPD of fine copper from the &lt;3/8&#34; fraction, a drum 3 m in diameter by 9 m in length is required. 
     Rest Times of Agglomerated Product 86 (FIG. 7) 
     It was determined that a rest time (curing) of 24 hours is adequate. Temperatures during this period vary between 80° and 50° C. 
     Repulping State in Washing Drum 89 
     The repulping stage in washing drums is technically feasible and best results are obtained with the mesh 91 having a size of 2 mm. It is alternatively feasible to consider other sorting methods, such as vibratory screens, which may produce a finer grain size possible with less number of filters. 
     Filtration Stage 99 (FIG. 7) 
     Best results are obtained under the following operating conditions: 
     
         ______________________________________                                    
Grain size of material                                                    
                     100% &lt;2 mm.                                          
at filtration                                                             
% Solids feed to filtration                                               
                     45-53%                                               
(includes addition of                                                     
flocculent)                                                               
Type of flocculent, dose                                                  
                     Guarfloc, 0.05%                                      
and concentration    80-130 g/ton                                         
                     filtered residue                                     
Type of filter cloth Multifilament                                        
Average vacuum       43 KPA                                               
Doses of H.sub.2 O in wash stage                                          
                     217-360 lg/ton                                       
                     filtered reidue                                      
______________________________________                                    
 
    
     For the conditions indicated, it is possible to obtain the following metallurgical results: 
     
         ______________________________________                                    
Preliminary solution of                                                   
                      7%                                                  
solid in washing drum                                                     
Extraction of copper up to                                                
                      58.22%                                              
filtration stage (primary                                                 
leaching)                                                                 
Consumption of fresh H.sub.2 SO.sub.4                                     
                      98 kg/MT                                            
Dry weight coarse reject (&gt;2 mm)                                          
                      277 kg/MT of feed                                   
in preliminary classification                                             
stage                                                                     
Moisture coarse reject (&gt;2 mm)                                            
                      10.43%                                              
Weight dry filtered cake                                                  
                      653 kg/MT of feed                                   
Moisture filtered cake                                                    
                      21.77%                                              
Average cake thickness                                                    
                      10.67 mm                                            
Dry cake filtration capacity                                              
                      878 kg/hr × m.sup.2                           
Content of solids in suspension                                           
                      20 ppm                                              
filtered solution                                                         
______________________________________                                    
 
    
     The composition of the filtered solution shows the following results (gpl): 
     
         ______________________________________                                    
       Cu    6.5-7.9                                                      
       H.sub.2 SO.sub.4                                                   
             1.0-3.6                                                      
       Ph    2.06-2.2                                                     
       Eh    471-480                                                      
       FeT   4.7-7.1                                                      
       Fe (II)                                                            
             0.16-0.43                                                    
       Cl    0.63-0.80                                                    
______________________________________                                    
 
    
     Solvent Extraction 109 by a SX Process (FIG. 7) 
     The best metallurgical results are obtained with application of the following operating conditions: 
     
         ______________________________________                                    
No. of extraction stages                                                  
                    2                                                     
No. of stripping stages                                                   
                    2                                                     
No. of wash stages  2                                                     
______________________________________                                    
 
    
     
         ______________________________________                                    
             E1      E2      S1   S2   Wash (EL)                          
______________________________________                                    
             1.98    1.98    2.46 2.47 2.53                               
Specific flow                                                             
             2.06    2.06    1.66 1.65 1.61                               
(m.sup.3 /hr × m2)                                                  
Continuity of                                                             
             0       0       0    0    0                                  
phases                                                                    
O/A ratio Without                                                         
             1.04    1.04    2.0  2.0  1.87                               
recirculation (W/OR)                                                      
With recirculation                                                        
             W/OR    W/OR    1.73 1.75 1.00                               
(WR)                                                                      
______________________________________                                    
Operating temperature                                                     
                   Ambient                                                
Type and concentration                                                    
                   50% LIX 984                                            
of extractant      50% ACORGA PT5050                                      
                   25 O/V in Escaid 100                                   
______________________________________                                    
 
    
     For the conditions indicated, it is possible to ensure a minimum extraction of 90%. The rates of crud formation are around 300 liters for every 1,000 cubic meters of solution fed. 
     Electrolytic Extraction 114 (FIG. 7) 
     Electrodeposition of the copper contained in the solvent extraction advance solutions is technically feasible. For the conditions evaluated, it is possible to obtain current efficiencies of over 90% with electrolytes having FeT levels of up to 1.3 gpl, 98 ppm manganese, 90 ppm cobalt and 80 ppm chloride. In general, the cathodes obtained are of good chemical quality. With the exception of one yield in which chloride levels reached 128 ppm, the average content of impurities of five yields obtained are as listed below: 
     
         ______________________________________                                    
SPECIES        COMPOSITION                                                
______________________________________                                    
Copper         99.9592                                                    
Chloride (g/mg)                                                           
               18.25                                                      
Arsenic        0.20                                                       
Antimony       0.14                                                       
Iron           0.34                                                       
Nickel         0.10                                                       
Lead           2.32                                                       
Bismuth        0.10                                                       
Tellurium      0.10                                                       
Zinc           0.16                                                       
Tin            0.16                                                       
Cadmium        0.10                                                       
Silver         0.66                                                       
______________________________________                                    
 
    
     The addition of Guarfloc remained fixed at 200 g/ton cathode. 
     Secondary Leaching of Coarse Fraction (&gt;2 mm) Separated in the Sorting Stage 
     The coarse fractions present copper contents varying between 0.54 and 0.82%, which must be leached to increase overall recovery. Pile leaching at a high specific flow is possible since only the coarse fractions are leached separately. Recoveries of copper reach 65.07% with H 2  SO 4  consumption of 12.6 kg/MT when the following operating conditions are applied: 
     
         ______________________________________                                    
Preliminary classification mesh                                           
                      2 mm                                                
Leaching agent        SX process                                          
                      refined solution                                    
Average specific flow 110 liters/hr ×                               
                      m.sup.2                                             
Height of pile        278 m                                               
Leaching cycle        255 hours                                           
m.sup.3 leachant/MT solid                                                 
                      7.64                                                
______________________________________                                    
 
    
     Under these conditions the refined increases its concentration of copper by 0.56 gpl. 
     Extraction of Copper and Consumption of H 2  SO 4  in Primary Leaching, Secondary Leaching of Coarse Fractions and Total 
     Primary leaching is understood to mean the process and results obtained up until filtration of the pulp and without considering treatment of the coarse fractions. Secondary leaching comprises treatment of the coarse fractions with the refined solution from the SX process 109. Total extraction is the weighted sum of the above values according to the weights of each fraction. The average results are the following: 
     
         ______________________________________                                    
          EXTRACTION  CONSUMPTION OF                                      
          OF COPPER   FRESH H.sub.2 SO.sub.4                              
I T E M     (%)           (kg/MT)   (kg/kg)                               
______________________________________                                    
PRIMARY     58.22         98        13.33                                 
LEACHING                                                                  
SECONDARY   65.07          0        0                                     
LEACHING                                                                  
PROCESS TOTAL                                                             
            67.61         98        11.93                                 
______________________________________                                    
 NOTE:                                                                    
 Secondary leaching does not use fresh acid, it utilizes the acid         
 regenerated in the refining process.                                     
 
    
     It should be pointed out that when this ore is incorporated in the percolation pans, its recovery does not exceed 30%. Moreover, when it is treated by a conventional agitation leaching process, the separation of phases becomes critical and this process does not become technically feasible. 
     EXAMPLE 9 
     In this process, application of the process to the treatment of other oxidized sources of the Chuquicamata Division at pilot level is considered. 
     Using the same pilot plant already described above, the process was applied to the treatment of the following oxidized sources of the Division: 
     Mina Sur ore feed to percolation pans: Coming from the Mina Sur deposit and reduced to a grain size of (&lt;3/8&#34;). 
     New Mina Sur spalls: Coming from pan leaching process. Grain size 25-30% (&gt;3/8&#34;). 
     Old Mina Sur spalls: Coming from Mina Sur spall dumps. Grain size 20-25% (&gt;3/8&#34;). 
     Chuqui Norte ore: Coming from Chuqui Norte deposit and reduced to a grain size of (&gt;3/8&#34;). 
     El Abra ore: Coming from the &#34;El Abra&#34; deposit and reduced to a grain size of (&lt;1/2&#34;) (mixture of 20% feldspathic ore). 
     Summaries of the principal operating conditions employed and the metallurgical results obtained are presented in Tables 7 and 8 below. These results demonstrate the technical feasibility of application of the process to any type of oxidized copper source. 
     For Tables 7 and 8 below, Mina Sur ores are represented by I; New Mina Sur spalls are represented by II; Old Mina Sur spalls are represented by III; Chuqui norte ores are represented by IV; and El Abra ores are represented by V. 
     
                       TABLE 7                                                     
______________________________________                                    
OPERATING CONDITIONS IN PILOT EVALUATION                                  
ITEM        I        II     III    IV   V                                 
______________________________________                                    
Dose (kg/MT)                                                              
H.sub.2 SO.sub.4                                                          
            60       40     40     40   40                                
H.sub.2 O   50       0      50     60   40                                
Rest time   1        1      1      1    1                                 
(days)                                                                    
Classification mesh repulped product washing                              
drum (mm)   2        2      2      2    2                                 
Composition of initial ore in %                                           
Total copper:                                                             
            1.57     0.57   1.26   1.12 0.89                              
Soluble copper:                                                           
            1.19     0.36   0.82   0.73 0.82                              
Secondary leaching time, (&gt;2 mm) fraction                                 
(days)      30       30     --     30   34                                
______________________________________                                    
 
    
     
                       TABLE 8                                                     
______________________________________                                    
PRINCIPAL METALLUGRICAL RESULTS, PILOT TESTS                              
ITEM    I         II     III*     IV   V                                  
______________________________________                                    
Recovery of copper in primary leaching:                                   
61.70         47.40  73.80      46.20                                     
                                     56.60                                
Recovery of copper in secondary leaching:                                 
18.80         23.40  --         43.80                                     
                                     26.90                                
Total recovery of copper in the process:                                  
80.50         70.80  73.80      90.00                                     
                                     86.50                                
______________________________________                                    
 *Secondary leaching was not considered.                                  
 
    
     Accordingly to the provisions of the Patent Statutes, we have explained the principle, preferred construction and mode of operation of the invention and have illustrated and described what we now consider to represent its best embodiments. However, it should be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.