Abstract:
A method of removing aqueous phase residues and other contaminants from the organic phase used in hydrometallurgical extraction processes comprises passing the organic phase through a column or other vessel in which a porous bed of elements of suitable size and shape to permit flow therethrough is provided. The material making up the bed elements may be polyethylene, polypropylene, nylon, teflon, stainless steel, plastics in general and their derivatives, or combinations thereof. The aqueous phase coalesces on the surfaces of the materials making up the bed and forms droplets which drop to the bottom of the column or vessel which are thereafter removed.

Description:
TECHNICAL FIELD 
     This invention relates generally to the field of hydrometallurgical extraction of metals and more particularly to the separation of aqueous residues or other contaminants from an organic phase during solvent extraction of metals such as copper. 
     BACKGROUND OF THE INVENTION 
     In industrial extraction processes, residue from one phase of an extraction is typically carried over into the other phase. Such residues are typically present as micro-drops which fail to separate within the decanting vessels used for the extraction, or as residues of solids and other contaminants. The residue levels depend on a variety of factors, particularly the type and concentration of the active reagent in the solvent, the degree of agitation and the diameter of the agitator drive, the presence of solids in the feed stock, the continuity of the phases and the temperature, in addition to other significant variables well known in the art. 
     When copper is extracted, of particular importance are the aqueous residues which remain in the charged organic phase, inasmuch as when the charged organic phase advances to the reextraction stage, the electrotwinning electrolyte is gradually contaminated. Impurities often present in these residues include Fe, Mn, Cl, NO 3 , SiO 2  and Al. Such contamination directly affects the system operating costs as well as the cathodic quality of the final product. 
     In other types of extraction operations involving copper, aqueous phase contamination can cause contamination of the final product, thus leading to an undesirable increase in the operating costs for the process. The more impure the solutions are which feed into the extraction, the greater the impact on the operating costs. 
     In extraction operations in which it is necessary to operate in both acid and alkaline cycles respectively, steps for the intermediate washing of the organic phase have to be incorporated between these cycles to minimize the impact caused by the residues of aqueous phases as the organic passes from the acid cycle and vice-versa. Such washing steps significantly increase both the investment and operating costs for the system. Nevertheless, the inclusion of such intermediate treatment steps is common practice in uranium extraction as well as in the case of copper, where the extraction stage is carried out in an ammoniacal alkaline medium and the reextraction stage is carried out in an acid medium. A similar situation occurs with hydrometallurgical treatment of copper concentrates in a hydrochloric acid medium, where a significant amount of chlorine contamination is transmitted through the residues to the reextraction stage. 
     In other hydrometallurgical extraction operations, the transfer of electrolyte residues from the reextraction to the extraction stage can significantly affect the pH in the extraction stage, whereby the efficiency of extraction and, consequently, production can diminish. Additionally, any electrolyte lost as residue further adds to the cost of the process. 
     The presence of Fe (III) decreases the current efficiency; manganese can be oxidized to permanganate in the anode, whereby when the spent solution returns to extraction, the organic phase may be degraded. 
     Moreover, when it oxidizes in the anode, the potential for oxidation of the aqueous solution increases, thus increasing the amount of gaseous chlorine liberated in the electrolytic vessel, leading to a resultant increase in environmental contamination. 
     Nitrate ions also contribute to greater anode corrosion. Due to its low solubility in highly acidic solutions, SiO 2  passing over to the electrolyte can subsequently precipitate and lead to greater formation of residue commonly referred to in the art as &#34;crud&#34;. The presence of SiO 2  and Al together increase the viscosity of the electrolyte, thus affecting the transport properties in the electrolytic process. 
     The contamination level of the electrolyte can become critical, particularly when sea water is used as the leaching agent. Some mining installations, e.g., the Tocopilla and Lince Mining companies in Chile, have been forced to incorporate an additional washing stage to treat the charged organic phases in an additional decanting mixer, thus increasing both their investment and operating costs. This additional washing of the organic phase before the reextraction stage has been necessitated by the high residue level and high level of impurities in the solutions feeding the extraction. 
     World-wide, the levels of aqueous residues found in the charged organic during the hydrometallurgical extraction of copper fluctuate between 100 and 800 ppm, depending on the operating conditions. In specific cases, such as where a high concentration of reagent is used in the operation, these residues can exceed 1,000 ppm. A common technique for maintaining acceptable levels of impurities in the electrolyte comprises periodically purging a determined volume. The major disadvantage of this technique is that it often results in the undesirable discharge of copper, cobalt and additives from the cycle. 
     Another method of removing an aqueous residue from an organic phase is for the organic phase to undergo an extended period of decanting, which, however, prohibitively increases both the production rate and the inventory of organic in the plant. Although centrifuging is a technically feasible alternative, the investments involved limit the application of this technique to small-scale, low production rate processes. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an inexpensive, reliable method for separating aqueous material from an organic phase in hydrometallurgical extraction plants. Moreover, the presently described process is additionally capable of removing, from the organic phase, solids and/or crud or other contaminants. For convenience in describing the invention, the aqueous material, the &#34;crud&#34; and the other contaminants noted above are referred to collectively herein as &#34;contaminants&#34; or &#34;contaminating residues&#34;. 
     In accordance with the present invention, a method of filtering aqueous material and/or other contaminants from the organic phase (i.e., referred to herein as the &#34;contaminated&#34; organic phase) comprises passing the contaminated organic phase through a bed of material to facilitate coalescence of micro-drops of aqueous material upon the bed and then subsequently decanting the remaining, i.e. filtered, solution. The bed through which the contaminated organic phase containing the residues passes is comprised, for example, of strings, netting, shavings, fragments, spheres, spirals, twists, scraps or some body of similar form, formed of one or more of materials that are compatible with the organic phase. Depending on such features as the opening size, the apparent density and the thicknesses (i.e., when netting is used to form the bed) and otherwise generally on the granulometry of the material, any desired specific flow rate (i.e., the volume of organic phase that goes through the coalescing bed per unit of area and time) can be obtained by one of ordinary skill in the art. 
     The bed may be installed within any suitable container means e.g., a column, having an inlet for introducing the contaminated organic phase and an outlet for removing the resultant &#34;filtered&#34; organic phase after separation of the contaminants. 
     The equipment required to carry out the process thus comprises vessel means that contains the bed-forming material, which vessel means may, as noted above, typically comprise one or more columns of various shapes and/or sizes. Depending on the required capacities for removing the aqueous material, various configurations of liquid circuits can be established, in which the columns can operate in series, in parallel, or in series-parallel, in such a way that a substantially total removal of the trapped aqueous phase and/or other contaminants can be achieved. 
     In alternate embodiments of the invention, a coalescing bed in the form, e.g., of a net can be incorporated, for example, into the spillways for the organic phase in the decanters, in the charged organic accumulator, in the vessels that convey the organic phase, or in other vessels suitable for this purpose. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a flow chart illustrating a preferred embodiment of the process of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As illustrated in FIG. 1, a stream of contaminated organic material 1 containing, for example, an aqueous residue is fed by gravity or by pumping into the lower part of a column or other container means 2. Stream 1 may be fed through the column in continuous or batch fashion, depending upon the desired production rate and volumetric capacity of the container means utilized for a particular application. 
     As those skilled in the art will recognize, the precise dimensions and geometric configuration of container means 2 are not critical and may vary in accordance with the desired flow rate and volumetric capacity. Accordingly, container means 2 may have a circular, polygonal, or irregular cross section as desired. In the illustrated embodiment, container means 2 is provided in the form of a vertical column having an inlet proximate its lower end for introducing the mixture containing the contaminated organic phase, and an outlet proximate its upper end for removing the filtered organic phase. 
     Depending on the amount of organic phase being filtered, various configurations of liquid circuits can be established. For example, instead of a single large column, two or more columns may be operated in series with the second being located downstream, i.e., in the direction of the liquid flow, from the first, or in parallel, or in series-parallel, in such a way that a total removal of the trapped aqueous phase and/or other contaminants can be achieved. 
     The separation of the aqueous and organic phases which occurs within column 2 will now be described in further detail. As noted above, however, the presently described process can also effectively remove, e.g., other contaminants such as dispersed solids and/or &#34;crud&#34; from the organic phase. 
     A bed 3 made up of strings, netting, shavings, fragments, spheres, scraps or other objects having a variety of configurations is arranged within column 2 to define a labyrinth of surfaces upon which coalescence of the aqueous material may take place. Depending on the apparent densities of the bed elements (i.e. the degree of compaction) or, alternately, the thicknesses and openings of the nets, and in general on the granulometry of the bed material, the flow rate can be varied as desired. As would be well understood by one skilled in the art, the apparent density of the bed is affected by the type of material used and its real density, the grain size of the material, the porosity and degree of compaction in the bed, and the shape of the material used (i.e., threads, webbing, shavings, etc.). Bed 3 should have a low apparent density so as to maximize the surface area of the bed elements exposed to the passage of liquid stream 1 therethrough. 
     An optimal apparent density for a given specific flow rate exists for each type of material used to form the bed. To obtain an efficient system response, the apparent density is complemented by the height of the bed, which preferably varies between 2 and 5 times its diameter. Preferably, the system has an apparent density in the range of 0.02 to 0.20 gr/cc. In this range, specific flow rates will fluctuate between 8 and 30 m 3  /hr×m 2 . The system is perfectly capable of operating outside of these preferred ranges, however. 
     The objects comprising the bed may be formed, as noted above, from any materials compatible with the organic phase. These materials include, as non-limiting examples, polyethylene, polypropylene, polystyrene, polyvinyl chloride, teflon, stainless steel, other metals and their alloys, plastics, acrylic, ceramics and glasses. One of ordinary skill in the art would thus be readily be able to choose an appropriate material simply based upon knowledge of the compatibility of the liquid stream with the bed material. 
     As the organic material 1 flows upwardly through bed 3 of the column, micro-drops of aqueous material 5 coalesce on the surfaces of the bed elements, with these drops continuing to increase in size until a point at which they detach and drop to the bottom of the column. The formation of these drops and their separation from the bed elements occurs more readily at higher temperatures than at lower temperatures. The aqueous material 5 can then be removed from the column in batches or continuously. In the bottom of the column, drops will not be present until they have coalesced and formed an aqueous phase. This liquid can be purged continually through a suitable valve (not shown) by regulating the exit flow at a rate corresponding to the rate of aqueous formation. 
     Depending on the efficiency with which the aqueous material is filtered during treatment in a single column, more than one column may be utilized; i.e., in series, in parallel, or in series-parallel combination, to effect a substantially total removal of the residual aqueous phase and/or other contaminants from the organic phase. When a loss of efficiency in the column is detected because solids or other foreign material have been trapped therein, the operation of one column can be discontinued in order to permit backwashing. Alternatively, the contents of the filtration bed 3 may be removed and replaced with clean filter material before resuming the filtration process in that column. 
     Trapping of the aqueous phase will occur at any specific flow rate of the organic through the bed, although the efficiency of the removal of aqueous from the organic phase will vary. For a given size, efficiency will decrease as the flow rate increases. Maximum levels of aqueous removal have been obtained with a specific flow in the range of 8 to 30 m 3  /hr×m 2 . 
     The organic phase 4, now substantially free of residues of aqueous material and other contaminants, may be utilized in the normal fashion once it exits column 2. To facilitate the efficient removal of the residues and solids or other contaminants, it is preferred that the material forming the bed be previously wetted with water or a suitable aqueous solution. 
     EXAMPLES 
     The embodiments described herein and the specific examples of the present invention provided below are presented only 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 below. 
     EXAMPLE NO. 1 
     In this example, the presently disclosed process was implemented in a pilot extraction plant with a capacity of 0.5 gallons per minute by the Chuquicamata division of Codelco-Chile. 
     For treating the contaminated organic, an acrylic column was used in which the charged organic was fed through the lower lateral part of the column, gradually proceeding to the removal of the aqueous material accumulated in the bottom and below the feed line. 
     Different types of materials were evaluated as coalescing (i.e., bed forming) agents. 
     A summary of the operating conditions used and the results obtained are presented in Table No. 1. These results demonstrate that all the types of materials evaluated are capable of removing the aqueous phase trapped within the organic stream with greater or lesser efficiency depending on the operating conditions. 
     
                                           TABLE NO. 1__________________________________________________________________________EVALUATION OF COALESCING AGENTS FOR THEREMOVAL OF AQUEOUS RESIDUES FROM THE ORGANIC PHASE  Apparent         Height/            Removal of  Density of         Diameter               Specific Organic                       Operation                            Residues                                  Residence  the Material         Ratio -               Flow with                       Time -                            from the                                  Time in                                       SpecificType of  in the Column         Coalescing               Residues                       Column                            Organic                                  Column                                       Areacoalescent  (gr/cc)         Column               (m.sup.5 /hr × m.sup.2)                       (hours)                            (ppm) (minutes)                                       (cm.sup.2 /g)__________________________________________________________________________Strips of High  0.06   3.1   9.53    13   624   1.76 38DensityPolyethylenein the Form ofSpiralsMixture of  0.18   2.0   9.06    5    936   1.19 --PolypropyleneNet withStainless SteelMarienberg  0.05   2.0   8.21    12   1,149 1.32 --Netting(CommercialProduct)Polypropylene  0.10   2.0   10.31   9    511   1.05 47Balls (Used inElectro-Winning)Polypropylene  0.10   3.1   9.44    15   1,143 1.78 47Balls (Used inElectro-Winning)High density  0.14   2.0   9.50    120  885   1.15 --polyethylenein the Form ofShavings -sawmill typeHigh Density  0.06   2.0   16.90   96   1,192 0.63 38Polyethylenein the Form ofSpiralsTeflon Netting  0.09   2.0   9.53    9    697   1.13 --(Used in AcidPlants)__________________________________________________________________________ 
    
     EXAMPLE NO. 2 
     This example was also carried out in a solvent extraction pilot plant with a capacity of 0.5 gallons per minute. 
     In this example, the organic stream was fed to a first column 0.065 meters in diameter with a capacity of one liter. After passing through the first column, the stream was then fed to a second column in series with the first, measuring 0.09 meters in diameter with a capacity of 2.5 liters for the substantial removal of any residues still present therein. 
     The operating conditions and the results obtained are presented in Tables 2, 3 and 4 below. These results demonstrate the feasibility of totally removing the residual aqueous phase in the charged organic by suitably regulating the operating conditions and by using an appropriate number of columns. 
     
                       TABLE NO. 2______________________________________EVALUATION OF THE PROCESS IN A PILOT PLANTHAVING A CAPACITY OF 0.5 GALLONS PER MINUTE______________________________________Average specific flow              15.18 m.sup.3 /hr × m.sup.2Column diameter    0.065 metersHeight of bed      0.25 metersType of filler     polyester (material used(i.e., bed) material              to form filters used in              lateral walls of              refineriesApparent density   0.05 gr/cc______________________________________    AQUEOUS     AQUEOUS    RESIDUES    RESIDUESHOURS OF IN ORGANIC  IN ORGANIC  AQUEOUSOPERATION    ENTRANCE    EXIT        REMOVAL (%)______________________________________ 2       1,500       100         99.33 4       2,000       100         95.00 6       1,500       100         93.33 8       1,400       200         85.7110       1,500       100         93.3312       1,300       100         92.3114       1,400       100         92.8616       1,500       100         93.3318       1,200       100         91.6720         600        0          100.0022         400        0          100.0024       1,000       100         90.0026       1,100       200         81.8228         800       100         87.50______________________________________ 
    
     
                       TABLE NO. 3______________________________________EVALUATION OF THE PROCESS IN A PILOT PLANTHAVING A CAPACITY OF 0.5 GALLONS PER MINUTE______________________________________Average specific flow             16.5 m.sup.3 /hr × m.sup.2Column diameter   0.065 metersHeight of bed     0.25 metersType of filler    teflon netting (material used(i.e., bed) material             in acid plants)Apparent density  0.09 gr/cc______________________________________    AQUEOUS     AQUEOUS    RESIDUES    RESIDUESHOURS OF IN ORGANIC  IN ORGANIC  AQUEOUSOPERATION    ENTRANCE    EXIT        REMOVAL (%)______________________________________ 2       1,200       100         91.67 4         500       100         80.00 6         400        0          100.00 8       1.200       100         91.6710       1,000       100         90.0012         500       100         80.0014       1,000       100         90.0016       1,800       200         88.8918       1,100       100         90.9120       2,500        0          100.00______________________________________ 
    
     
                       TABLE NO. 4______________________________________EVALUATION OF THE PROCESS IN A PILOT PLANTHAVING A CAPACITY OF 0.5 GALLONS PER MINUTE______________________________________Average specific flow             9.02 m.sup.3 /hr × m.sup.2Column diameter   0.09 metersHeight of bed     0.40 metersType of filler    teflon netting (used in acid(i.e., bed) material             plants)Apparent density  0.09 gr/cc______________________________________    AQUEOUS     AQUEOUS    RESIDUES    RESIDUEHOURS OF IN ORGANIC  IN ORGANIC  AQUEOUSOPERATION    ENTRANCE    EXIT        REMOVAL (%)______________________________________1        917         20          97.822        740         60          91.893        775         63          91.874        625         75          88.005        1,425       225         84.216        950         50          94.747        540          0          100.008        583         67          88.519        1,200       92          92.3310       1,033       108         89.5511       1,117       208         81.3812       1,233       142         88.4813       1,333       25          98.1214       683         25          96.34______________________________________ 
    
     EXAMPLE NO. 3 
     Was carried out in a pilot plant for the solvent extraction of copper having a capacity of 50 gallons per minute. The process was implemented with two columns operating in series. 
     The bed material used in the column was made up of spiral strips of high density polyethylene. The degree of compaction of the HDPE in the column was such that the apparent density reached a value of 0.05 t/m 3 . 
     The operating conditions for the two columns in series are shown below: 
     Material used to form the two columns: HDPE 
     Type of feeding to the columns: by gravity in the lower lateral sector of each column 
     Flow of charged organic: 8.2 m 3  /hour 
     Average specific flow: 30 m 3  /hour×m 2   
     Diameter and area of each column: 0.58 m and 0.27 m 2   
     Height of each column: 2.50 m 
     Type of filler (i.e., bed) material: strips of HDPE 
     Width of HDPE strips: 12 mm 
     Thickness of HDPE strips: 1 mm 
     Length of HDPE strips: variable 
     Average specific surface: 38 cm 2  /gr. 
     Apparent density of the filler in the column: 0.05 t/m 3   
     Form of removal of the aqueous material accumulated: intermittent and/or continuous 
     Table No. 5 presents the results obtained when the columns were operated continuously for a period of 13 days with checks made every 4 hours of operation. 
     
                       TABLE NO. 5______________________________________EVALUATION OF THE PROCESS IN A PILOT PLANTHAVING A CAPACITY 50 GALLONS PER MINUTE    AVERAGE     AVERAGE    RESIDUE     RESIDUE    CONTENT (ppm)                CONTENT (ppm)    ENTRANCE    EXITDAY OF   FIRST       SECOND      RESIDUEOPERATION    COLUMN      COLUMN      REMOVAL (%)______________________________________1          850        50         94.122        1,092       158         85.533        1,183       100         91.554        1,125       150         86.675        1,517        92         93.946        1,225       158         87.107        1,125       133         88.188          733       117         84.049          792       133         83.2110         858       117         86.3611         850        75         91.1812         350        25         92.8613         675        50         92.59______________________________________ 
    
     These results demonstrate that with the present process it was possible to remove between 83% and 94% of the aqueous material contained in the initial flow of charged organic. 
     EXAMPLE NO. 4 
     Was carried out in a solvent extraction pilot plant having a capacity of 50 gallons per minute. 
     The process was evaluated by operating two columns in parallel. In this case the total flow of charged organic was divided into two equal streams, each independently feeding into a respective column. The filtered organics were subsequently joined, after which they proceed to the reextraction stage. 
     The bed material used in the column was strips of high density polyethylene. 
     The operating conditions for each column are shown below: 
     Construction material used to form the two columns: HDPE 
     Type of feeding to the columns: by gravity in the lower side 
     Flow of charged organic for each column: 4 m 3  /hour 
     Average specific flow for each column: 15 m 3  /hour×m 2   
     Diameter of each column: 0.58 m 
     Area of each column: 0.27 m 2   
     Height of each column: 2.5 m 
     Type of filler (i.e., bed) material: strips of HDPE 
     Width of HDPE strips: 12 mm 
     Thickness of HDPE strips: 1 mm 
     Length of HDPE strips: variable 
     Average specific surface: 38 cm 2  /gr. 
     Apparent density of the filler in the column: 0.05 t/m 3   
     Form of removal of the aqueous material accumulated: intermittent and/or continuous 
     Table No. 6 presents the principal average results obtained when the two columns were operated continuously for 8 days and with checks made every 4 hours of operation. 
     
                       TABLE NO. 6______________________________________EVALUATION OF THE PROCESS IN A PILOT PLANTHAVING A CAPACITY 50 GALLONS PER MINUTE  RESIDUE  RESIDUE  RESIDUEDAY    ENTER-   EXITING  EXITING                           RESIDUE                                  RESIDUEOF     ING THE  (ppm)    (ppm)  REMOV- REMOV-OPERA- COLUMN   COLUMN   COLUMN AL (%) AL (%)TION   (ppm)    1        2      COL 1  COL 2______________________________________1      550      142      117    74.18  78.732      758      100      67     86.81  91.163      750      75       33     90.00  95.604      525       0        0     100.00 100.005      692      58       17     91.62  97.546      758      92       25     87.86  96.707      817      75       75     90.82  90.828      650      33        0     94.92  100.00______________________________________ 
    
     These results demonstrate that with the circuit configuration described above it is also feasible to obtain very satisfactory results, with up to 100% of the aqueous material contained in the original organic being removed in the best cases. 
     As will be apparent to those skilled in the art, various modifications and adaptations of the embodiments described above will become readily apparent without departure from the spirit and scope of the invention, the scope of which is defined in the appended claims.