Copper extraction
United States Patent 1 [111 3,878,071  
 Selby et al. i Apr. 15, 1975 COPPER EXTRACTION 885,622 4/l908 Jumau 204/108 1,19,47 l2l9l4 V Adl ..249 [76] Inventors: John Harold Selby, 2l Zaymel l 7 I an rs f O l 2 Gardens, Duchess Ave., Windsor Park, Randburg, Transvaal; George Primary Examiner.lohn H. Mack Stephen James, 5 13th Ave., Assistant ExaminerAaron Weisstuch Parktown North, Johannesburg,  
 Transvaal, both of South Africa [22] Filed: July 17, 1973 ABSTRACT PP NOJ 379,968 A process of precipitating Chevreul salt from a solution comprising copper dissolved in sulphurous acid including the steps of contacting the solution with a 30 F&#39;Al&#39;t&#39;P&#34;tDt orelgn pp &#34;on y a a pair of electrodes, the anode preferably being copper,  
  July 18, 1972 South Africa 72/4933 and a potential difference across the elec trodes effective to cause precipitation of the Chevreul [52] US. Cl. 204/92, 204/93, 204/108, Salt The potential difference is preferably Such that the cathode potential is between a few milllvolts and [51] Colb 17/00; Colb 17/96; Colg 3/00 about 250 millivolts. The copper containing solution is of Search 93, prsferably a pp rich leach solution resulting from the sulphurous acid leaching of a copper-containing [56] References Cited oxidic 0m UNITED STATES PATENTS 777,669 l2/l904 Frank 204/92 19 Claims, No Drawings coPPER EXTRACTION This invention relates to the extraction of copper from copper containing materials, particularly copper containing oxidic ores.  
  The copper values from copper-containing oxidic ores may be leached using any one of a number of known leach solutions. Sulphuric and sulphurous acid solutions are two examples of such leach solutions. A sulphurous acid leach solution has the particular advantage over a sulphuric acid leach solution that much less gangue material is leached.  
  The leaching of coppercontaining oxidic ores with sulphurous acid involves the slurrying of finely ground ore with water, passing a stream of sulphur dioxide through the slurry to form the sulphurous acid in situ, and separating the copper-rich leach solution from the ore. The copper is then recovered from the leach solution by precipitating it in the form of Chevreul salt (Cu (Cu SO .2H O). In the past Chevreul salt has been precipitated from such leach solutions in a number of ways, e.g., nitrogen, vacuum, steam or pressure stripping or by the addition of powdered copper to the solutions. The disadvantages of these methods are that there are high sulphur losses due to oxidation to sulphate; high circulating loads of copper; impracticability of obtaining vacuum conditions in corrosive gaseous atmospheres; and high energy consumptions.  
  It is an object of the present invention to provide another method of precipitating Chevreul salt from a solution comprising copper dissolved in sulphurous acid.  
  According to the invention, there is provided a process of precipitating Chevreul salt from a solution comprising copper dissolved in sulphurous acid including the step of contacting the solution with a pair of electrodes and applying a potential difference across the electrodes effective to cause precipitation of the Chevreul salt.  
  It has been found that the Chevreul salt precipitates mainly in the region of the cathode, although some precipitation does occur in the region of the anode. The precipitated salt may be recovered from the solution by filtering, centrifuging or other conventional method.  
  The potential difference applied across the electrodes must be such as to cause precipitation of Chevreul salt. This means that the potential is such as to ensure that the cathode potential is lower than that at which sulphide ions will be produced by electrolysis in the solution. The actual potential applied in any particular case will vary according to factors such as concentration of copper in the solution, and the temperature and pH of the solution. The selection of an applied potential for any particular set of conditions is however well within the skills of one skilled in the art.  
  The potential applied across the electrodes is preferably such that the cathode potential with respect to a standard saturated calomel electrode is in the range from a few millivolts to about 250 millivolts.  
  Sulphur dioxide is generated during the precipitation of the Chevreul salt. This makes the process particularly attractive in the sulphurous acid leaching of copper-containing materials in that the sulphur dioxide gas generated can be used in the preparation of leach solution. Thus, according to another aspect of the invention, there is provided a process of extracting copper from a copper-containing material including the steps of leaching copper values from the material using a sulphurous acid leach solution, contacting the copper-rich leach solution with a pair of electrodes, and applying across the electrodes a potential difference effective to cause precipitation of copper in the form of Chevreul salt from the solution. The copper containing material is preferably a copper containing oxidic ore. Further, the sulphur dioxide generated during the precipitation of Chevreul salt is preferably used in the preparation of sulphurous acid leach solution. In practice, the sulphur dioxide will dissolve in the spent electrolyte so producing sulphurous acid in situ which can be recycled back to the leach stage.  
  The electrodes may, for example, be copper, platinum, graphite or the like electrodes. It is preferred, however, to have a copper anode as it has been found that such an anode reduces the tendency for oxidation of the sulphur to sulphate to occur. This, in turn, means that more sulphur dioxide is available for use in sulphurous acid leach solutions.  
  The concentration of copper in the solution will generally be in the range from 1 to g/l. The preferred copper concentration is from 20 to 40 g/l.  
  The current and current density will be dependent on factors such as area of the electrodes, concentration of the solution and so on. It has been found preferable to effect periodic current reversal to reduce overvoltage problems.  
  A particular advantage of the invention is that Chevreul salt of high purity is obtained. There are well known techniques for recovering copper from Chevreul salt, e.g., the method given in Example 1. The higher the purity of the Chevreul salt the higher the purity of the recovered copper.  
 Embodiments of the invention will now be described.  
 EXAMPLE 1 A copper-containing oxidic ore from Zaire was finely ground and then slurred with water to produce a pulp density of 45%. Sulphur dioxide gas was passed through the slurry to form sulphurous acid in situ. Leaching was continued for about six hours during which time the sulphurous acid leach solution was maintained at about 10C. Thereafter, the ore was filtered from the leach solution which comprised copper and other metals dissolved in sulphurous acid. The assay of the leach solution was as follows:  
 Ca 2,3 g/l Mg 2,2 g/l FezLOg/l S:64g/l Standard electrolysis apparatus was used to precipitate Chevreul salt from this solution. The apparatus consisted of a vessel into which the solution was placed and two electrodes which were connected to a conventional source of DC electrical power. Both electrodes were made of platinum. The electrodes were placed in the vessel in contact with the solution and an initial potential difference of 550 millivolts applied across them. The cathode potential was 50 millivolts measured against a standard saturated calomel electrode. The cathode potential was maintained&#39;at this value for 250 minutes during which time 96 percent of the copper had precipitated as Chevreul salt. The average current density was 8.6 A/m&#34;.  
  During the electrolysis the solution was stirred to minimise polarisation. Most of the Chevreul salt was foundto have precipitated in the region of the cathode, but some of the salt precipitated in the region of the anode.  
 following assay:  
  The Chevreul salt in the solution was recovered by f 54 E gg filtration. Small quantities of salt collect on the elec- 5 Fe 0.4 g/l $140.0 g/l trodes and this may be recovered by scraping and washing the electrodes. Precipitation of Chevreul salt was achieved using the The Chevreul salt recovered had the following assay: same apparatus and conditions as those specified in Example 1. A 95% recovery of the copper as Chevreul salt was achieved.  
 Cu 48,85% Mg:0,0l% EXAMPLE 14 Co 0,02% Fe 0.09% Ca 1 0,06% s: 16.0% The spent electrolytes from the processes of examples l to 12 were analysed for sulphate concentration The copper was recovered from this Chevreul salt by 15 using the standard barium sulphate precipitation roasting the salt to produce copper oxide, dissolving method. This analysis gave an indication of the sulphur the copper oxide in sulphuric acid and then electrowinoxidation during the electrolysis. The figure obtained in ning the copper in the conventional manner. Very pure each case was converted into a weight of sulphur oxicopper was obtained and this was achieved because of dised per ton of copper recovered from the solution. the very pure Chevreul salt obtained by the electrolytic On this basis it was found that in the examples where method described above. a copper anode was used there was no sulphur oxidised During the electrolysis, sulphur dioxide was generper ton of copper recovered whereas in the case of exated and this dissolved in the spent electrolyte thereby amples 2 and 3 with platinum electrodes, 0.054 and producing sulphurous acid which was available for re- 0.133 tons of sulphur, respectively, were oxidised per cycling to the leach stage. ton of copper recovered. It was found that using the low cathode potential of example 1, resulted in only a EXAMPLES 2 to 12 small amount of sulphur oxidation per ton of copper Using the same copper-rich leach solution as that of recovered. Example 1, experiments were carried out using differ- We claim: ent electrodes, cathode and cell voltages and current l. A process of precipitating Chevreul salt from a sodensities. The time of electrolysis was in ea h s lution comprising copper dissolved in sulfurous acid inabout 250 minutes. The results of these experiments cluding the steps of contacting the solution in an elecare given in Table I. The recovered Chevreul salt was r ly 66 With a pair of electrodes a d applying a poanalysed in each case and these analyses ar iv n in tential difference across the electrodes which is such Table I. It will be noted that the Chevreul salt was in t the Ca pote ti W th e pect t a tandard each case extremely pure making it ossibl for v r saturated calomel electrode is in the range from a few pure copper to be roduced th r fr millivolts to about 250 millivolts to cause precipitation Furthermore, it will be noted from the last column Of the Che eul Saltthat the power consumption (i.e. Kwh) per kg of cop- 2. A process according to claim 1 wherein the anode per recovered as Chevreul salt was very low even at relis p atively high current densities. This makes the process A Process accordmg to Clalm 1 whel&#39;em the anode economically very attractive as the conversion of Chev- 1S PPP and the cathode 18 Selected from pp reul salt to copper is relatively inexpensive. Platmum and graphlte- TABLE I.  
  Cathode Potential (v) Average Power Exam- Electrode w.r.t. Max. Current CONCENTRATION OF CONSTITUENTS Conple Pair Std. Sat. Cell Density IN CHEVREUL SALT sumption Calomel Voltage (A/m&#39; -Cu Co Ca Mg Fe S Kwh/kg Electrode (v) Cu 2 Pn/Pr 0.10 1.30 62.4 48,75 0.02 0,06 0.01 0.09 16,0 0,70 3 0.15 2.40 12.70 48.60 0.03 0.05 0.01 0,08 15.8 2,19 4 Cu /Pr 0.05 0.70 2.7 48.60 0.03 0.09 0.01 0.12 16.24 0.11 5 0,10 2,0 49.5 49.48 0.03 0.12 0.01 0.25 17.02 0.85 6 0.15 3.2 113,0 49.48 0.03 0.10 0.01 0.15 15.75 2.23 7 Cu /Cu 0.10 0.83 72.1 50.04 0.03 0.45 0.01 0.31 15.30 0.69 8 0,15 1.45 161 47.95 0.02 0.11 0.01 0.11 16.83 1.55 9 0,20 1.70 167 48.16 0.02 1.32 0,01 0.24 13.86 2.13 10 Cu /C (graphite) 0,15 1,30 46.2 48.60 0,03 0.09 0.01 0,23 16.36 0.42 1 1 0,20 1,38 41.99 48.99 0.03 0,10 0.02 0.16 15.60 0.36 12 0.25 1,50 75.3 47,94 0,03 1.35 0,01 0.13 15.70 0.80  
 EXAMPLE 3 4. A process according to claim 1 wherein the solu- The same leaching procedure as in example 1 was adopted except that the pulp density of the slurry was 20% and a lesser amount of sulphur dioxide gas was used. The resulting copper-rich leach solution had the tion is a leach solution resulting from the sulphurous acid leaching of a copper-containing material.  
  5. A process according to claim 4 wherein the copper-containing material is a copper-containing oxidic ore.  
  6. A process according to claim 1 wherein the concentration of copper in the solution is in the range from 1 to 50 g/l.  
  7. A process according to claim 1 wherein the concentration of copper in the solution is in the range from to 40 g/l.  
  8. A process of precipitating Chevreul salt from a solution comprising copper dissolved in sulphurous acid, the solution having a copper concentration in the range of from 1 to 50 g/l, including the steps of contacting the solution with a pair of electrodes, the anode being copper, and applying a potential difference across the electrodes such that the cathode potential with respect to a standard saturated calomel electrode is in the range from a few millivolts to about 250 millivolts thereby causing the copper to precipitate from the solution in the form of Chevreul salt.  
  9. A process of extracting copper from a coppercontaining material including the steps of leaching copper values from the material using a sulphurous acid leach solution, contacting the copper-rich leach solution with a pair of electrodes, and applying across the electrodes a potential difference effective to cause precipitation from the solution of copper in the form of Chevreul salt. 7  
  10. A process according to claim 9 wherein sulphur dioxide generated during precipitation of the Chevreul salt is used in the preparation of sulphurous acid leach solution for the leach stage.  
  11. A process according to claim 9 wherein the copper-containing material is a copper-containing oxidic ore.  
  12. A process according to claim 9 wherein the anode is copper.  
  13. A process according to claim 9 wherein the anode is copper and the cathode is selected from copper, platinum and graphite.  
  14. A process according to claim 9 wherein the applied potential is such that the cathode potential with respect to a standard saturated calomel electrode is in the range from a few millivolts to about 250 millivolts.  
  15. A process according to claim 9 wherein the copper-rich leach solution has a copper concentration in the range of from 1 to 50 g/l.  
  16. A process according to claim 9 wherein the copper-rich leach solution has a copper concentration in the range of from 20 to 40 g/l.  
  17. A process for extracting copper from a coppercontaining material including the steps of leaching copper values from the material using a sulphurous acid leach solution to produce a copper-rich leach solution having a copper concentration of in the range from 1 to SOg/l, contacting the copper-rich leach solution with a pair of electrodes, the anode being copper, applying a potential difference across the electrodes such that the cathode potential with respect to a saturated calomel electrode is in the range from a few millivolts to about 250 millivolts to cause precipitation from the solution of copper in the form of Chevreul salt, and recovering the copper from the Chevreul salt.  
  18. A process according to claim 17 wherein the copper-containing material is a copper-containing oxidic ore.  
  19. A process according to claim 18 wherein sulphur dioxide generated during the precipitation of Chevreul salt is used in the preparation of sulphurous acid leach solution for the leach stage.