Abstract:
A process for the extraction of copper from a sulphide ore or concentrate comprises the steps of subjecting the ore or concentrate to pressure oxidation in the presence of oxygen and an acidic solution containing halide and sulphate ions to obtain a resulting pressure oxidation slurry. The slurry is subjected to a liquid/solid separation step to obtain a resulting pressure oxidation filtrate and a solid residue containing an insoluble basic metal sulphate salt. The basic metal sulphate salt is leached in a second leaching with an acidic sulphate solution to dissolve the basic metal salt to produce a leach liquor containing a metal sulphate, e.g. copper sulphate, in solution and a resulting solid residue. The leach liquor is separated from the solid residue and subjected to a solvent extraction process to produce metal concentrate solution and a metal depleted raffinate. At least a portion of the raffinate is recycled to the pressure oxidation after being subjected to evaporation.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a division of U.S. patent application Ser. No. 09/452,431 filed Dec. 1, 1999 which in turn is a division of U.S. patent application Ser. No. 08/911,797 filed Aug. 15, 1997. The contents of the foregoing applications are incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to the hydrometallurgical treatment of metal ores or concentrates. In particular, it relates to the extraction of copper from sulphide ores or other concentrates in the presence of halogen ions, such as chloride ions.  
         BACKGROUND OF THE INVENTION  
         [0003]    The hydrometallurgical treatment of sulphide concentrates whereby the concentrate is subjected to pressure oxidation in the presence of chloride ions is known. See for example U.S. Pat. Nos. 4,039,406; 5,645,708; and 5,650,057.  
           [0004]    The purpose of the present invention is to provide an improved process for the extraction of metals from sulphide ores.  
         SUMMARY OF THE INVENTION  
         [0005]    According to the invention there is provided a process for the extraction of copper from a sulphide copper ore or concentrate, comprising the steps of subjecting the ore or concentrate to pressure oxidation in the presence of oxygen and an acidic solution containing halide and sulphate ions to obtain a resulting pressure oxidation slurry, subjecting the slurry to a liquid/solid separation step to obtain a resulting pressure oxidation filtrate and a solid residue containing an insoluble basic copper sulphate salt; leaching the basic copper sulphate salt produced by the pressure oxidation with an acidic sulphate solution in a second leaching to dissolve the basic copper salt to produce a leach liquor containing copper sulphate in solution and a resulting solid residue; separating the leach liquor from the solid residue; subjecting the leach liquor to a solvent extraction process to produce copper concentrate solution and a copper depleted raffinate; recycling at least a portion of the raffinate to the pressure oxidation; and wherein the raffinate is subjected to evaporation to remove water therefrom prior to the recycle thereof; and wherein the evaporation is effected by means of a direct-fired evaporation process comprising the submerged combustion of a fuel in the raffinate being recycled.  
           [0006]    The term “concentrate” in this specification refers to any material in which the metal value content has been increased to a higher percentage by weight as compared with the naturally occurring ore and includes man made artificial sulphide ore, such as matte, and metal values precipitated as solids such as hydroxides and sulphides.  
           [0007]    Further objects and advantages of the invention will become apparent from the description of preferred embodiments of the invention below.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a flow diagram of a hydrometallurgical metal extraction process according to one embodiment of the invention.  
         [0009]    [0009]FIG. 2 is a flow diagram of a hydrometallurgical metal extraction process according to another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0010]    The feed ore or concentrate to the process may contain one or more sulphide minerals of the base metals Cu, Ni, Co and Zn, frequently combined with Fe and sometimes with other elements, such as As, Sb, and Ag.  
         [0011]    In FIG. 1, reference numeral  10  generally indicates a hydrometallurgical process according to one embodiment of the invention. The process  10  comprises a pressure oxidation stage  12 , an atmospheric leach  14 , a liquid/solid separation  24 , a solvent extraction  16 , an evaporation stage  20  and a neutralization  22 .  
         [0012]    Prior to the pressure oxidation stage  12 , the copper concentrate is first subjected to a regrind to reduce the particle size to about 2 %+325 mesh.  
         [0013]    The concentrate is subjected to the pressure oxidation  12  in an autoclave in the presence of an acidic solution containing sulphate, chloride and preferably copper ions.  
         [0014]    The amount of acid introduced into the pressure oxidation  12  (by way of recycle after the initial startup, as will be described below) is sufficient to maintain the discharge solution from the autoclave, when operated in a continuous mode, at a pH of above 2.0, typically pH 2.3-3.8.  
         [0015]    The chloride ion concentration in the solution in the autoclave is maintained at about 8-20 g/L, preferably about 12 g/L.  
         [0016]    The pressure oxidation  12  is carried out at a temperature of from about 115° C. to about 175° C., preferably about 130° C. to about 155° C., under a pressure of about 100-300 psig. This is total pressure comprising oxygen pressure plus steam pressure.  
         [0017]    The retention time is about 0.5-2.5 hours and the process is normally carried out in a continuous fashion in the autoclave. However, the process can also be carried out in a batch-wise fashion, if desired.  
         [0018]    In the pressure oxidation stage  12 , all copper minerals are converted to basic copper sulphate CuSO 4 ·2Cu(OH) 2 , i.e. all the copper being recovered reports to the solid phase in the pressure oxidation  12 .  
         [0019]    The solids content in the autoclave is maintained at about 12-25%, i.e. 150-300 g/L solids as determined by the heat balance and viscosity limitations.  
         [0020]    The slurry produced in the autoclave is discharged through a series of one or more flash tanks (not shown) to reduce the pressure to atmospheric pressure and the temperature to about 90-100° C. The liquid part of the slurry is referred to as the product solution from the pressure oxidation stage  12  and is indicated by reference numeral  21 .  
         [0021]    The slurry from the flash tank(s)  22  is filtered, as shown at  24 , and the resultant filter cake is washed thoroughly to remove entrained liquor as much as possible.  
         [0022]    The solids from the pressure oxidation stage  12  after the filtration  24 , are treated in the atmospheric leaching stage  14  at about pH 1.2 to pH 2.2 using raffinate from the solvent extraction  16 , which is acidic, to dissolve the basic copper sulphate. The leaching  14  takes place at a temperature of about 40° C. for a retention time of about 15-60 minutes. The percentage solids in the feed to the leach  14  is typically about 3-15% or about 30-170 g/L, although it is possible to operate the process outside this range. The percentage solids drops substantially during the leach  14  as the basic copper sulphate dissolves. Thus, the product g/L solids may be as little as one half of the feed g/L solids.  
         [0023]    During the atmospheric leaching stage  14 , the basic copper salts dissolve almost completely with very little of the iron present in the concentrate going into solution, provided care is taken to maintain the pH in the range 1.2 to 2.2, preferably pH 1.5 to 2.0.  
         [0024]    The slurry  31  from the atmospheric leaching stage  14  is sometimes difficult if not impossible to filter, but settles well. In view of the need to wash the leach solids very thoroughly, the slurry  31  is pumped to a counter current decantation (CCD) wash circuit  34 . In the CCD circuit  34 , the solids are fed through a series of thickeners with wash water added in the opposite direction. By this method, the solids are washed and entrained solution removed, together with the soluble metals dissolved therein. About 3 to 7 thickeners (not shown) are required with a wash ratio (water to solids) of about 2 to 5 to reduce entrained liquor down to less than 100 ppm dissolved Cu in the final residue.  
         [0025]    The thickener underflow from the last thickener is the final residue stream  35  at about 50% solids. This can be treated for the recovery of precious metals, such as gold and silver, or sent to tailings.  
         [0026]    The main constituents of the stream  35  are hematite and elemental sulphur, which may also be recovered by a combination of other processes, such as flotation and leaching into a specific solvent for sulphur, e.g. perchloroethylene, if market conditions warrant.  
         [0027]    The thickener overflow from the first thickener is the product solution  33  which is fed to the solvent extraction stage  16 , as shown.  
         [0028]    Copper is extracted from the product solution  33  from the CCD circuit  34  in two stages of extraction in the solvent extraction stage  16  to produce a raffinate  37 .  
         [0029]    The raffinate  37  is split, as indicated at  38 , into three streams  40 ,  41  and  42 . The stream  40  which comprises about ⅔ of the raffinate  37  is recycled to effect the atmospheric leach  14 , as indicated above. The actual volume of  40  is determined by the acid needs of the leach  14 , to dissolve the basic copper sulphate as described, and maintain a slight excess of acid, i.e. pH 1.5-2.0 which corresponds to about 1-5 g/L H 2 SO 4 . The acid requirements for stream  40  are less than the total acid contained in  37 , and part of the remainder is used in the pressure oxidation  12  as an acid source for the reactions therein. This is supplied by stream  42 . Any acid still left over from  37 , not used by  40  or  42 , is considered excess, and is neutralized. This is stream  41 . Typically streams  41  and  42  are each about ⅙ of  37 . The stream  41  which comprises about ⅙ of the raffinate  37  is subjected to the neutralization  22  with lime rock and after liquid/solid separation  43  results in gypsum, which can be discarded, and wash water which is recycled as wash water to the CCD wash circuit  34 .  
         [0030]    The liquid  21  from the filtration  24 , along with the stream  42 , is subjected to the evaporation  20  to remove water and produce a more concentrated acid and chloride solution  44  which is recycled to the pressure oxidation  12 .  
         [0031]    The evaporation of the solution prior to recycling is problematical due to the very corrosive nature thereof, i.e. high acidity (50 g/L free acid), high chloride content (12 g/L) and high temperature in evaporation. This precludes the use of most if not all commercially available evaporators, which are normally based on indirect heat transfer through thin metal surfaces, such as shell and tube evaporators made typically of stainless steel. Titanium would be suitable but is too expensive if used in the large quantities which would be required for this type of application.  
         [0032]    However, the problem has been solved by direct-fired evaporation using submerged combustion of a fuel in the solution  44  and using titanium material.  
         [0033]    In order to keep the size of the evaporator down, and minimize operating and capital costs, the amount of water to be evaporated must be minimized. In order to achieve this, the copper concentration in the stream  31  is maintained at a more concentrated level, i.e. at about 35 g/L, compared with a value of 12 g/L in the absence of evaporation. This in turn generates a more concentrated acid stream  42  containing about 48 g/L H 2 SO 4  instead of only 18 g/L H 2 SO 4 . This effectively reduces the volume of the water to be evaporated by putting the same mass of acid in a smaller volume of water, thus reducing the size of the evaporator, hence justifying the use of titanium, and the fuel costs necessary to operate a direct fired evaporator. Direct fired evaporators do not have the advantage of multiple effect of the steam generated which can generally reduce fuel costs in indirect evaporators, and thus justify evaporating large volume of water.  
         [0034]    With reference to FIG. 2, a process  100  according to another embodiment of the invention is shown.  
         [0035]    The process  100  also comprises a pressure oxidation stage  12 , filtration  24 , atmospheric leach  14 , CCD wash circuit  34 , solvent extraction  16 , evaporation  20  and neutralization  22 .  
         [0036]    In the process  100  some of the metal values being recovered also report to the pressure oxidation liquid  21  in addition to the solid, which solid is subjected to the atmospheric leach  14  as described with reference to FIG. 1.  
         [0037]    The liquid  21  from the filtration  24  is subjected to a copper solvent extraction  50  in order to recover copper values therefrom.  
         [0038]    It should be noted that although the step  24  is referred to as a filtration, any suitable liquid/solid separation method can be employed.  
         [0039]    The filtration  24  is the separation point between the high chloride liquid used in the pressure oxidation  12 , which liquid is recycled as indicated, and a low chloride or chloride free liquid going to the atmospheric leach  14 . The filtration  24  is always accompanied by a wash with water or recycled low chloride water or a concentration of both to remove as much chloride from the solids (filter cake) as possible. The objective is to minimize transfer of chloride from the high chloride circuit to the low chloride circuit, to counteract chloride build up in the latter circuit.  
         [0040]    However, despite the washing of the solid residue produced by the filtration  24 , the chloride concentration is prone to increase in the low chloride circuit, because it is essentially a dead ended circuit with minimum bleed.  
         [0041]    This problem has been overcome by recycling a stream from the low chloride circuit to the high chloride circuit. This stream is indicated by reference numeral  42  in FIG. 2 to correspond with the stream  42  in FIG. 1 which also comprises a recycle from the low chloride circuit to the high chloride circuit.  
         [0042]    Again the stream  42  is subjected to the evaporation  20 , as described with reference to FIG. 1, prior to recycle to the pressure oxidation  12 . However, in this case, there is no need to recycle acid from the low chloride circuit because enough acid is generated by the copper solvent extraction  50  in the form of raffinate  63 . In fact, it is usually necessary to neutralize some of the acid in the raffinate  63 , as indicated at  64  prior to recycling the raffinate  63 . As indicated at  65 , the neutralization product is subject to a liquid/solid separation step to produce solid gypsum which can be discarded and a liquid  66  which is subjected to the evaporation  20  before recycle.  
         [0043]    Since there is no need to recycle acid from the low chloride circuit, the raffinate  37  from the solvent extraction  16  is split into only two streams, i.e. ⅔ into stream  40  which is used in the atmospheric leach  14 , and ⅓ into stream  41  which is subjected to the neutralization  22  and liquid/solid separation  43  to produce solid gypsum which can be discarded and a stream  45  which is split, as indicated at  46  into a stream which is recycled as wash water to the CCD circuit  34  and stream  42  which goes to the evaporation  20  for recycle to the pressure oxidation  12 . This serves to recycle chloride from the low chloride circuit back to the high chloride circuit.  
         [0044]    While only preferred embodiments of the invention have been described herein in detail, the invention is not limited thereby and modifications can be made within the scope of the attached claims.