Abstract:
A process for extracting iron, copper, and nickel from a solution containing iron, copper, nickel, and at least one contaminent selected from the group comprising magnesium, aluminum, calcium and sodium, wherein each of said solutes is present at its respective chloride. In the process, calcium oxide or calcium hydroxide are added as a precipitating agent in incremental steps to cause incremental increases in the pH of the solution. At each increasing pH, one of the aforesaid metals will precipitate as the corresponding metal hydroxide while leaving the remaining metals in solution. The metal hydroxide precipitate is separated from the remaining solution prior to the subsequent addition of the precipitating agent.

Description:
FIELD OF THE INVENTION 
     This invention relates to metal recovery processes, and more particularly, to processes to extract iron, copper and nickel from a solution in which the aforesaid metal solutes are present as their respective chlorides. 
     BACKGROUND OF THE INVENTION 
     Previous methods for recovering precious metals from a flotation concentrate involve smelting the concentrate to produce a &#34;matte&#34; in which metals values are further concentrated. The matte is then subjected to a series of leaching steps to leach out the base metals. Generally, a separate leaching step is used for each base metal to be removed. The precious metals are then leached out and removed from each of the leaching solutions in subsequent recovery steps. 
     The traditional process described above has several shortcomings. Firstly, smelting is generally an environmentally undesirable process because of the gasses given off and the problem of disposal of solid residue. Furthermore, if the concentrate has a high magnesia content, the melting temperature of the concentrate may be too high to be effectively smelted. Still furthermore, using a plurality of leaching steps is relatively costly and some of these steps also contribute to further environmental contaminants. 
     U.S. patent application Ser. No. 08/089,088, filed on Jul. 8, 1993 and now issued as U.S. Pat. No. 5,364,444, which is hereby incorporated by reference herein, discloses a process (hereinafter referred to as the &#34;new process&#34;) in which all of the precious metals and various additional metals are dissolved as one of the process steps. The precious metals are separated from solution leaving a solution containing iron, copper, nickel and various contaminants such as magnesium, aluminium, calcium and sodium. Each of the solutes is present as the respective metal chloride in an acidic solution. It is an object of the present invention to remove the iron, copper, and nickel individually from the solution, subsequently to remove the contaminants from the solution and then to convert the remaining solution to hydrochloric acid which may be re-used in the initial process. 
     SUMMARY OF THE INVENTION 
     A process for extracting iron, copper, nickel from a solution containing iron, copper, nickel and at least one contaminant selected from the group consisting of magnesium, aluminium, calcium and sodium wherein each of said solutes is present as a metal chloride and said solution has a pH of less than 1.0, said process comprising the steps of: 
     i) adding a precipitating agent selected from the group consisting of calcium oxide and calcium hydroxide to raise the pH of said solution to approximately 1.0 thereby causing said iron to precipitate as ferric hydroxide; 
     ii) separating said ferric hydroxide precipitate from the remaining solution; 
     iii) adding more of said precipitating agent to said remaining solution to raise the pH of said remaining solution from step ii to approximately 3.0 thereby causing said copper to precipitate as cupric hydroxide; 
     iv) separating said cupric hydroxide precipitate from the remaining solution; 
     iv) adding more of said precipitating agent to said remaining solution to increase the pH of said remaining solution from step iv to about 4.0 thereby causing said nickel to precipitate as nickel hydroxide; 
     vi) separating said nickel hydroxide precipitate from the remaining solution; 
     vii) adding more of said precipitating agent to said remaining solution to increase the pH of said remaining solution from step vi to approximately 8.8 thereby causing said contaminants to precipitate as their respective hydroxides; 
     viii) separating said precipitated contaminants from the remaining solution; 
     ix) adding a sufficient amount of sulphuric acid to said remaining solution from step viii to convert said remaining solution from step viii to calcium sulphate and hydrochloric acid; and 
     x) separating said calcium sulphate from said hydrochloric acid. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of the new process referred to above; and 
     FIG. 2 is a flow chart showing the treatment of barren leach solution according to the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The process of the present invention was developed to treat the resulting solution after recovering gold, platinum, palladium, copper and nickel from bulk sulfide concentrates obtained from Lac Des Iles flotation mill through the use of acid leaching procedures. A typical range of analysis for the valuable metals and impurities contained in the concentrates are set out in Table 1 below. 
     
                                           TABLE 1__________________________________________________________________________Element  g/t; %        Element %    Element %__________________________________________________________________________Gold   4-6 g/t        Barium  0.002                     Sodium  0.20Platinum  4-6 g/t        Beryllium                &lt;0.0001                     Neodymium                             &lt;0.005Palladium  50-80 g/t        Calcium 0.31 Phosphorus                             &lt;0.002Copper 2.5-3.0        Cadmium 0.001                     Lead    &lt;0.082Nickel 1.8-2.5        Cobalt  0.13 Tin     &lt;0.002Iron   12.0-12.5        Chromium                0.020                     Tellurium                             &lt;0.003Sulphur  6-8   Arsenic 0.008                     Antimony                             &lt;0.001Aluminium  1-3   Lanthanum                &lt;0.001                     Selenium                             0.008Magnesium  3-6   Manganese                0.044                     Yttrium &lt;0.001Silica 30-40 Molybdenum                &lt;0.01                     Zinc    0.26__________________________________________________________________________ 
    
     The main metal values contained in the concentrates are the Platinum Group Metals (PGM), gold (Au), copper (Cu), and nickel (Ni). The PGM are constituted by more or less complex sulphides, tellurides, arsenides, and alloys; Au appears native and as a telluride. The main sulphide constituents are chalchopyrite and pentlandite, but there are also minor amounts of pyrite and pyrrhotite. 
     Previous commercial procedures used in the leaching of PGM and Au consisted generally of an intermediate smelting stage, prior to leaching, to obtain a &#34;matte&#34; in which the metal values are further concentrated. 
     The first step of the new process is to roast the concentrate by heating the concentrate in an oxygen-containing environment such as air to oxidize a portion of the sulfur. It has been found that the roasting is best carried out at between 900° and 1200° F. The oxidation of sulfur during the roasting stage can be enhanced by agitating the concentrate (&#34;rabbling&#34;) to better expose the sulfur in the concentrate to the oxidizing atmosphere. The roasting should be carried out until the sulfur content is reduced to about two percent. 
     It has been found that if roasting is carried out at too high or too low a temperature, the leachability of PGM in subsequent steps of the process is adversely affected. Although exact maximum and minimum temperatures have not been determined, effective results may be obtained by roasting in air within the temperature range set out above. 
     After the concentrate has been roasted, it is leached with an acid solution which is a blend of hydrochloric and nitric acids. The leaching is carried out in a glass-lined autoclave, heated to a moderate temperature and pressurized with a moderate pressure of oxygen gas. 
     When the initial development work was commenced for treatment of the above concentrates, the initial test work was directed at directly leaching the metals values from the concentrate. Direct leaching of the metal values provided Au recovery of 94-98%; Pt 29-38%; Pd, 90-93%; Cu, 98-99%; Ni, 93-96%. Leaching of the roasted concentrate gave an Au recovery of 95-98%; Pt, 94-95%; Pd, 87-91%; Cu, 78-96%; Ni, 82-92%. Surprisingly, and quite unexpectedly, the roasting process resulted in an almost three-fold increase in Pt recovery. As Pt is a very valuable metal, such an increase is very significant as it favourably impacts on the economics of the process. 
     It has been found that the rate of dissolution of metal sulphides in a slurry is greatly enhanced if the slurry carries oxygen in the solution. One way of providing the oxygen is to add small amounts of nitric acid in a closed vessel. Providing oxygen gas at a moderate pressure of around 50 p.s.i.g. enables the nitric acid to be continuously regenerated by the oxygen gas being applied. 
     Satisfactory results have been achieved with a hydrochloric acid to nitric acid ratio of around 50:1. It is expected that leaching may be carried out with a hydrochloric to nitric acid ration of from 100:1 to 3:1. 
     Moderately heating the acid and roasted concentrate mixture assists the leaching process. Effective results have been achieved at a temperature of around 190° F. The temperature should be kept below the melting temperature of sulfur as it has been found that poor recovery of precious metals in the solution occurred at reaction temperatures of 135° C. or higher (288.5° F.). 
     Satisfactory results have been obtained using oxygen at approximately 50 p.s.i.g. It may be possible to substitute oxygen for air in the autoclave, if the autoclave is designed with enough free space to contain the necessary amount of air and to withstand the higher pressure requirements. 
     Once the leaching operation is substantially completed, the solution of acid and metal sulphides is separated from any undissolved portion of the roasted concentrate. The above leaching process is capable of forming solutions of gold, palladium, platinum, copper and nickel. 
     The final step of the new process is to retrieve the dissolved metals from the solution. Gold may be collected on activated carbon in an acidic solution. Similarly, the palladium and platinum may also be collected on activated carbon. 
     Palladium may be removed from the solution by solvent extraction, for example by mixing with dioctyl or dihexyl sulfide. At this stage, the solution may contain copper, platinum, nickel and iron. Platinum may be removed by cementation with a copper powder or the solution may be electrolyzed in an electrolytic cell to collect both the copper and platinum on the cathode. 
     The remaining nickel and iron solution may be treated by precipitating the nickel and iron together as a hydroxide which may then be sold to a smelter. Alternatively, a portion of the iron may be oxidized in an autoclave to form a ferric oxide precipitate which may be separated. The balance of the dissolved iron may be precipitated outside of the autoclave as a ferric hydroxide. 
     If the iron is removed separately from the nickel, the solution will still contain nickel. Nickel may be removed as a hydroxide, as a carbonate or through electrolysis as nickel plate. If calcium is used as a precipitating agent, this will leave a spent solution of calcium chloride. 
     It is desirable to regenerate the hydrochloric acid used in the process. This may be accomplished by reacting the calcium chloride solution with sulphuric acid to give hydrochloric acid and calcium sulfate as products. The calcium sulfate may be separated as a solid from the hydrochloric acid and sold as such, for example, for use in the building industry as gypsum. The hydrochloric acid may then be reused in the process. 
     As an alternative to the above, platinum may be removed through solvent extraction using known solvent extraction techniques. This would leave a solution containing iron, copper, nickel and various contaminants. The contaminants would mainly comprise magnesium and aluminium, however calcium and sodium may also be present. 
     Iron can be precipitated from the latter solution by adding calcium oxide or calcium hydroxide as a precipitating agent to increase the pH of the solution to 1.0. At pH 1.0, over 99% of the iron would typically precipitate as ferric hydroxide. The ferric hydroxide may be removed through solid/liquid separation. 
     A further increase of pH from 1.0to 3.0 by adding more calcium oxide or calcium hydroxide will cause the copper to precipitate as cupric hydroxide. The cupric hydroxide precipitate may be removed by solid/liquid separation. 
     Further increasing the pH to 4.0 by adding more calcium oxide or calcium hydroxide will cause nickel to precipitate as nickel hydroxide. The nickel hydroxide may be removed through a solid/liquid separation step. 
     Still further increasing the pH to 8.8 by adding more calcium oxide or calcium hydroxide will result in the majority of the remaining contaminants being removed as hydroxides. Once again, solid/liquid separation may be performed to remove the hydroxides. 
     At this stage, the solution will be primarily calcium chloride, as most of the metals were present in the solution as chlorides. The addition of calcium hydroxide would therefore yield calcium chloride plus a metal hydroxide. As suggested above, sulphuric acid may be added to the calcium chloride solution to yield calcium sulphate and hydrochloric acid. The hydrochloric acid may be reused in the extraction process. The calcium sulphate may be sold to the construction industry as plaster. 
     The calcium oxide/calcium hydroxide precipitation technique is preferably performed in each step at a temperature from 50° C. to boiling however it is believed that the technique may work at lower typical ambient temperatures. 
     Various aspects of the present invention may be more fully described by reference to the examples set out below. 
     EXAMPLE 1 
     FIG. 2 is a flow chart showing the treatment of barren leach solution with lime to remove iron, recover copper and nickel and remove magnesium. The analysis of the solution at various stages in the process, and experimental conditions are set out below with reference to the reference numerals in FIG. 2. 
     
         ______________________________________Reference Number inFIG. 2        Analysis and Experimental Conditions______________________________________1             Concentration:         18.6 g/L Cu, 10.1 g/L Ni,         44.7 g/L Fe, 161 g/L Cl,         48 g/L SO.sub.4, 8.5 g/L Al,         4.6 g/L Mg, 0.52 g/L Ca,         0.43 g/L Na         pH &lt;0, EMF 830 mV2             pH: ˜1         EMF: ˜680 mV (natural)         Temperature: ˜85° C.         Lime: 129 kg/m.sup.33             Solution Concentration:         19.1 g/L Cu, 10.2 g/L Ni,         0.15 g/L Fe, 163 g/L Cl,         0.53 g/L SO.sub.4, 7.7 g/L Al,         5.1 g/L Mg, 49 g/L Ca,         0.51 g/L Na         pH 0.9, EMF 680 mV4             Solid Composition:         32% Fe, 0.05% Cu, 0.005% Ni,         1% Al, 0.003% Mg, 10% Ca,         0.03% Na, ˜33% SO.sub.4         Weight: 143 kg/m.sup.3 feed         Estimated Removal:         99.7% Fe, 9.2% Al, 99% SO.sub.45             pH: ˜3         EMF: ˜550 mV (natural)         Temperature: ˜85° C.         Lime: 42 kg/m.sup.36             Solution Concentration:         0.58 g/L Cu, 6.9 g/L Ni         0.04 g/L Fe, ˜140 g/L Cl,         0.5 g/L SO.sub.4, ˜3 g/L Al,         ˜5 g/L Mg, ˜65 g/L Ca,         0.50 g/L Na         pH 3, EMF 550 mV7             Solid Composition:         35% Cu, 4.6% Ni, 0.25% Fe,         7.8% Al, 0.62% Mg, 0.12% Ca,         0.05% Na, ˜0.1% SO.sub.4         Weight: 51 kg/m.sup.3 feed         Estimated Recovery:         97% Cu, 32% Ni, 0.2% Fe         43% Al, 6% Mg8             pH: ˜4         EMF: ˜365 mV (natural)         Temperature: ˜85° C.         Lime: 14 kg/m.sup.39             Solution Concentration:         0.13 g/L Cu, 0.21 g/L Ni,         &lt;1 mg/L Fe, 123 g/L Cl,         0.4 g/L SO.sub.4, 0.03 g/L Al,         4.8 g/L Mg, 75 g/L Ca,         0.50 g/L Na         pH 4, EMF 365 mV10            Estimated Solid Composition:         29% Ni, 2% Cu, 13% Al,         1% Mg, 0.5% SO.sub.4         Weight: 23 kg/m.sup.3 feed         Estimated Recovery:         66% Ni, 2% Cu, 47% Al,         3% Mg11            pH: ˜8.8         EMF: ˜-28 mV (natural)         Temperature: ˜85° C.         Lime: 18 kg/m.sup.312            Solution Concentration:         0.002 g/L Cu, &lt;1 mg/L Ni,         &lt;1 mg/L Fe, 120 g/L Cl,         0.36 g/L SO.sub.4, 0.002 g/L Al,         0.01 g/L Mg, 93 g/L Ca,         0.33 g/L Na         pH 8.8, EMF -28 mV13            Solid Composition:         37% Mg, 1% Cu, 1.6% Ni,         0.06% Fe, 0.3% Al, 1.3% Ca,         0.1% Na         Weight: 15 kg/m.sup.3 feed         Estimated Removal:         1% Cu, 2% Ni, 0.3% Al, 91% Mg______________________________________ 
    
     EXAMPLE 2 
     A test was designed to purify the barren solution from a carbon loading test. 
     A feed solution (1000 mL) was placed in a two liter beaker. The test was conducted at a temperature of 80°-90° C. Agitating and heating were provided with a magnetic stirrer/heater. 
     Lime slurry was added to the solution to raise the pH and to precipitate iron and copper. Deionized water was added as required to compensate for evaporation. A thief sample was taken during the test to determine intermediate removal of impurities. 
     Following the test, the slurry was filtered and the filter cake was washed several times with hot deionized water. The first part of the wash which contained most of the trapped solution was added to the filtrate to adjust the volume back to approximately the starting volume less volume of thief sample. A sample was submitted for chemical analysis and the remainder of the wash was saved. The results are shown in table 2. 
     
                                           TABLE 2__________________________________________________________________________Lapsed             Cuml wt. of LimeTime Temp.    EMF  Added    Estim. Sol. Vol.                                      Amounth    °C.     pH  mV   g        mL       Samples                                      mL, g__________________________________________________________________________0    50   &lt;0  830   0       10000.5  92   &lt;0       101    90    0.03         810  35       1000     Sol 1 25                                Solid 1                                      0.62    90   0.7      53        9752.5  88   0.8      1163    88   1.3      1293.5  85   0.9 680  129       975     Sol. 2                                      20                                Cake  143__________________________________________________________________________LapsedTime    Analyses (mg/L, %)h   Fe  Cu  Ni  Al  Mg  Ca  Na  SO4 Cl  Comments__________________________________________________________________________0   44650   18580       10130           8500               4590                   520 430 48000                               160580                                   Sol. bright green0.5                                     Sol. slight brown1   44820   18410       10080    0.13*   0.006*       0.004*           0.011*               0.003*                   27.7*                       0.082*      White ppl.2                                       Lot of ppt.2.53.5 152 19070       10230           7720               5140                   49250                       510 530 162850                                   Sol. bright green    32.2*   0.051*       0.005*           1.0*               0.003*                   10.4*                       0.033*      Brown ppl.                                   Wash 710 mL__________________________________________________________________________ *Semi-quantitative  Solid collected from 25 mL sample   Total weight of filter cake 
    
     EXAMPLE 3 
     A test was designed to recover copper and nickel from purified barren solution from the test in Example 2. 
     The purified solution from the test in Example 2 (955 mL) was placed in a two liter beaker. The test was conducted at a temperature of 80°-90° C. Agitation and heating were provided with a magnetic stirrer/heater. 
     Lime slurry was added to the solution to raise the pH and to precipitate nickel. Dionized water was added as required to compensate for evaporation. Thief samples were taken during the test to determine the intermediate recoveries of copper and nickel. 
     Following the test, the slurry was filtered, the filter cake was washed several times with hot deionized water. The first part of the wash which contained most of the trapped solution was added to the flitrate to adjust the volume back to approximately the starting volume less volume of thief samples. A sample was then submitted for chemical analysis. The remainder of the wash was saved. The precipitate was submitted for Cu, Ni, and Fe, analysis, and for a semi-quantitative ICP scan. 
     Test results are show in Table 3. 
     
                                           TABLE 3__________________________________________________________________________Lapsed          Cuml wt. of LimeTime    Temp.   EMF Added    Estim. Sol. Vol.                                  Amounth   °C.    pH mV  g        mL      Samples                                  mL, g__________________________________________________________________________0   85   0.4       620 0        9550.5 90   0.9    151.5 90   2.1       640 34       955     Sol. 1                                  25                            Solid 1                                  0.53   88   3.0       550 40       930     Sol. 2                                  25                            Solid 2                                  1.254.5 90   4.0       386 53       900     Sol. 3                                  50                            Cake  67.5__________________________________________________________________________LapsedTime    Analyses (mg/L, %)h   Fe Cu  Ni  Al Mg Ca  Na SO4                          Cl  Comments__________________________________________________________________________0   152  19070      10230          7720             5140                49250                    510                       530                          162850                              Sol. bright green0.51.5 74 9040      7880          490       Sol. bright green    0.36*  30.4*      4.3*          8.3*             0.93*                0.30*                    0.11*     Green ppt.3   43 580 6920          500       Sol. bright green    0.25*  35.4*      4.6*          7.8*             0.62*                0.12*                    0.05*     Green ppt.4.5 0.2  128 208 26 4760                75250                    500                       408                          122560                              Sol. almost clear    0.24  24.1      12.9          9.1*             0.61*                0.13*                    0.05*     Green ppt                              Wash 210 mL__________________________________________________________________________ *Semi-quantitative  Solid collected from 25 mL sample   Total weight of filter cake 
    
     EXAMPLE 4 
     The purpose of this test was to remove magnesium from the nickel-barren solution from the test of Example 3. 
     The solution from Example 3 (850 mL) was placed in a two liter beaker. The test was conducted at a temperature of 80°-90° C. Agitation and heating were provided with a magnetic stirrer/heater. 
     Lime slurry was added to the solution to raise the pH and to precipitate Al and Mg. Deionized water was added as required to compensate for evaporation. A thief sample was taken during the test to determine the intermediate removal of Mg. 
     Following the test, the slurry was filtered. The filter cake was washed several times with hot deionized water. The first part of the wash which contained most of the trapped solution was added to the flitrate to adjust the volume back to approximately the starting volume less volume of thief sample. A sample was then submitted for chemical analysis. The remainder of the wash was saved. The precipitates were submitted for a semi-quantitative ICP scan. 
     Test results are reported in Table 4. 
     
                                           TABLE 4__________________________________________________________________________Lapsed          Cuml wt. of LimeTime    Temp.   EMF Added    Estim. Sol. Vol.                                 Amounth   °C.   pH  mV  g        mL      Samples                                 mL, g__________________________________________________________________________0   87  4.6  410           0        8500.2 80  7.5     40.25    80  8.3 -60 130.5 82  8.6 -75 150.75    82  8.8 -28 15       850     Sol. 1                                 30                            Solid 1                                 0.451   85  9.0     181.25    85  9.05    371.5 87  9.1     893   87  9.05       -44 142      820     Sol. 2                                 60                            Cake 135__________________________________________________________________________LapsedTime    Analyses (mg/L, %)h   Fe Cu Ni Al  Mg Ca  Na SO4                         Cl  Comments__________________________________________________________________________0   0.2  128     208        26  4760               75250                   500                      408                         122560                             Sol. almost clear0.2                               Green ppt.0.25                              Grey ppt.0.50.75    0.2  2.1     0.2        2.3 8.9               93500                   327                      357                         110350                             Sol. clear    0.06*  1.0*     1.6*        0.27*            37.1*               1.3*                   0.80*     Grey ppt.1.251.53   0.8  1.7     &lt;0.2        4.5 1.6               92500                   370                      305                         131350                             Sol. clear    0.4*  0.8*     0.12*        0.06*            3.2*               49* 0.05*     White ppt.                             Wash 310 mL__________________________________________________________________________ *Semi-quantitative  Solid collected from 25 mL sample   Total weight of filter cake 
    
     Tables 5 and 6 summarize the results of the tests of Example 2, 3 and 4. Example 2 is identified as Test R1, Example 3 is identified as Test R2, and Example 4 is identified as Test R3. 
     
                                           TABLE 5__________________________________________________________________________Concentration (%)     Test R1        Test R2   Test R3Test R1     Final          Test R2               Test R2                    Final                         Test R3                              FinalElementsSolid 1     Solid          Solid 1               Solid 2                    Solid                         Solid 1                              Solid__________________________________________________________________________Al   0.011     1.0  8.3  7.8  9.1  0.27 0.065As   &lt;0.001     &lt;0.02          &lt;0.05               &lt;0.05                    &lt;0.06                         &lt;0.002                              &lt;0.001Ba   0.001     &lt;0.0005          0.0005               &lt;0.0005                    &lt;0.0005                         &lt;0.0005                              &lt;0.0005Be   &lt;0.0001     &lt;0.0001          &lt;0.0001               &lt;0.0001                    &lt;0.0001                         &lt;0.0001                              &lt;0.0001Ca   27.7 10.4 0.30 0.12 0.13 1.3  49.0Cd   &lt;0.0005     &lt;0.005          &lt;0.0005               &lt;0.0005                    &lt;0.0005                         &lt;0.005                              &lt;0.0005Co   &lt;0.0005     0.002          0.12 0.19 0.45 0.10 0.008Cr   0.004     0.078          0.006               0.005                    0.006                         0.002                              0.001Cu   0.006     0.051          30.4 35.4 24.5 1.0  0.083Fe   0.13 32.2 0.36 0.25 0.25 0.063                              0.038La   &lt;0.001     &lt;0.001          &lt;0.0005               &lt;0.0005                    &lt;0.0005                         &lt;0.0005                              &lt;0.0005Mg   0.003     0.003          0.93 0.62 0.61 37.1 3.2Mn   &lt;0.0005     &lt;0.0005          0.006               0.012                    0.070                         0.10 0.009Mo   &lt;0.002     &lt;0.002          &lt;0.02               &lt;0.02                    &lt;0.02                         &lt;0.04                              &lt;0.005Na   0.082     0.033          0.11 0.053                    0.054                         0.088                              0.047Ni   0.004     0.005          4.3  4.6  13.6 1.6  0.12Pb   0.003     0.008          0.015               0.016                    0.042                         0.027                              0.002P    0.003     0.013          &lt;0.001               &lt;0.001                    &lt;0.001                         0.013                              0.006Sb   &lt;0.001     &lt;0.003          &lt;0.001               &lt;0.001                    &lt;0.001                         &lt;0.001                              &lt;0.001Se   &lt;0.005     &lt;0.02          &lt;0.005               &lt;0.005                    &lt;0.005                         &lt;0.005                              &lt;0.005Sn   &lt;0.002     &lt;0.02          &lt;0.002               &lt;0.002                    &lt;0.002                         &lt;0.002                              &lt;0.002Te   &lt;0.001     &lt;0.005          &lt;0.02               &lt;0.02                    &lt;0.02                         &lt;0.001                              &lt;0.001Y    &lt;0.0005     &lt;0.0005          &lt;0.0005               &lt;0.0005                    &lt;0.0005                         &lt;0.0005                              &lt;0.0005Zn   0.001     0.001          0.021               0.026                    0.18 0.86 0.063__________________________________________________________________________ 
    
     
                                           TABLE 6__________________________________________________________________________          Cumu.              Total          Lime              Vol.,Test       EMF Added              Wt.  Analyses (mg/L, %)Products   pH mV  g   mL, g                   Fe  Cu  Ni  Al  Mg  Ca  Na  SO4 NO3                                                      Cl__________________________________________________________________________Test R1 - Iron RemovalFeed    &lt;0 830 0   1000 44650                       18580                           10130                               8500                                   4590                                       520 430 48000                                                   NA 160580Intermediate SampleSol. 1  0.03      810 35  1000 44820                       18410                           10080                               NA  NA  NA  NA  NA  NA NASolid 1            24   0.13*                       0.006*                           0.004*                               0.011*                                   0.003*                                       27.7*                                           0.082*                                               NA  NA NARemoval** (%)           --  0.9 0.5 --  --  --  --  --  -- --Final ProductsSol. 2  0.9      680 129 975  152 19070                           10230                               7720                                   5140                                       49250                                           510 530 NA 162850Solid 2            143  32.2*                       0.051*                           0.005*                               1.0*                                   0.003*                                       10.4*                                           0.033*                                               NA  NA NARemoval** (%)           99.7                       --  --  9.2 --  --  --  98.9                                                   -- --Test R2 - Nickel RecoveryFeed    0.4      620 0   955  152 19070                           10230                               7720                                   5140                                       49250                                           510 530 NA 162850Intermediate SamplesSol. 1  2.1      640 34  955  74  9040                           7880                               NA  NA  NA  490 NA  NA NASolid 1            19   0.36*                       30.4*                           4.3*                               8.3*                                   0.93*                                       0.30*                                           0.11*                                               NA  NA NARemoval** (%)           51.3                       52.6                           23.0                               --  --  --  3.9 --  -- --Sol. 2  3.0      550 40  930  43  580 6920                               NA  NA  NA  500 NA  NA NASolid 2            47   0.25*                       35.4*                           4.6*                               7.8*                                   0.62*                                       0.12*                                           0.05*                                               NA  NA NARemoval** (%)           71.7                       97.0                           32.4                               --  --  --  2.0 --  -- --Final ProductsSol. 3  4.0      365 53  900  0.2 128 208 26  4760                                       75250                                           500 408 NA 122560Cake               67.5 0.24                       24.1                           12.9                               9.1*                                   0.61*                                       0.13*                                           0.05*                                               NA  NA NARemoval** (%)           99.9                       99.3                           98.0                               99.7                                   7.4 --  2.0 23.0                                                   -- 24.7Test R3 - Magnesium RemovalFeed    4.6      410 0   850  0.2 128 208 26  4760                                       75250                                           500 408 NA 122560Intermediate SampleSol. 1  8.8      -28 15  850  0.2 2.1 0.2 2.3 8.9 93500                                           327 357 NA 110350Solid 1            13   0.06*                       1.0*                           1.6*                               0.27*                                   37.1*                                       1.3*                                           0.09*                                               NA  NA NARemoval** (%)           0   98.4                           99.9                               91.3                                   99.8                                       --  34.6                                               12.5                                                   -- 10.0Final ProductsSol. 2  9.05      -44 142 820  0.8 1.7 &lt;0.2                               4.5 1.6 92500                                           370 305 1900                                                      131350Cake               135  0.04*                       0.08*                           0.12*                               0.06*                                   3.2*                                       49* 0.05*                                               NA  NA NARemoval** (%)           --  98.6                           100.0                               82.6                                   100.0                                       --  26.0                                               25.3                                                   -- --Overall Removal** (%)          203 g    100.0                       100.0                           100.0                               100.0                                   99.8                                       --  24.0                                               99.3                                                   -- 31.3(Feed R1 to Inter.Sample R3)Overall Removal** (%)          353 g    100.0                       100.0                           100.0                               99.9                                   100.0                                       --  14.0                                               99.4                                                   -- 18.2(Feed R1 to Final R3)__________________________________________________________________________ Feed to R1: barren sol. from carbon adsorption Test C1. Temperature: 80-90° C. NA: not analyzed *Semiquantitative **Based on sol. assay data  Estimated   Actual from filtration 
    
     EXAMPLE 6 
     This test related to the regeneration of hydrochloric acid. 
     A feed was prepared by dissolving 5 grams of NaCl, 370 gams CaCl 2  in deionized water in a two liter volumetric flask to 2000 mL. The feed composition therefore contained approximately 120 g/L Cl, 1 g/L Na, 70 g/L Ca. 
     The test was carried out in a 500 mL beaker. Agitation and stirring were provided by a heater/magnetic stirrer. 
     Four tests were run in which different amounts of sulphuric acid were added. In the first three tests, the sulphuric acid was added directly to the feed solution. In the fourth test, 2.5 g/L CaSO 4  was added as a seed. 
     The slurry was heated as required to maintain a 40° C. temperature for thirty minutes. A final pH reading was obtained. The slurry was filtered and the flitrate assayed. The filter cake was washed, re-pulped, filtered and washed free of acid. The filter cake was then dried and weighed. Test results are shown in Tables 7 and 8. 
     
                                           TABLE 7__________________________________________________________________________Conditions           Actual       Check            Seed                Feed                    H2SO4        Init.    H2SO4    Temp.        Time            CaSO4                Vol 97%  CaSO4   Temp.Test    % Stoi.    °C.        min g/L mL  g/L  g   pH  °C.__________________________________________________________________________Feed                              9.21    87  40  30  none                200 148  none                             &lt;0  422   108  40  30  none                200 185  none                             &lt;0  423   130  48  30  none                200 222  none                             &lt;0  534   108  40  30  2.5 200 185  0.5 &lt;0  41__________________________________________________________________________Check       Titration (Methyl Red)Vol.    Cake       Vol. NaOH Equiv.Filtr.  Wt. Aliquot            2.45%                 H2SO4                      Assay (g/L)Test    mL  g   mL   mL   g/L  Ca  Na  Cl  SO4__________________________________________________________________________Feed                       64.3                          0.91                              114 --1   80  34  5    25.4 152  8.15                          0.88                              114 6.782   83  39  5    31.6 190  1.91                          0.88                              112 28.93   74  39  5    36.7 220  0.89                          0.83                              107 59.74   97  37  1     8.3 189  1.94                          0.87                              117 28.6__________________________________________________________________________ 
    
     
                                           TABLE 8__________________________________________________________________________Conditions               Test (Used 200 mL Feed)               Seed H2SO4         Init.H2SO4     Temp.          Time CaSO4                    97%  CaSO4                              Sol.                                  Temp.Test 4% Stoi.     °C.          min  g/L  g/L  g    pH  °C.__________________________________________________________________________Feed                               9.21     87  40   30   none 148  none &lt;0  422    108  40   30   none 185  none &lt;0  423    130  40   30   none 222  none &lt;0  534    108  40   30   2.5  185  0.5  &lt;0  41__________________________________________________________________________Concentration (g/L, %)                        Total      HCl    Vol.       Cake             Equiv.                            Calc.                               Calc.                                   Rege-    Filtr.       Wt.              H2SO4                            HCl                               H2SO4                                   neratedTest 4    Product    mL g   Ca Na  Cl SO4                        g/L g/L                               g/L*                                   %__________________________________________________________________________Feed            64.3              0.91                  114                     -- --  -- --  --1   Filtrate    80 --  8.15              0.88                  114                     6.78                        152 108                               6.9 92    Cake**    -- 34  32.6              -0.03  78.42   Filtrate    83 --  1.91              0.88                  112                     28.9                        190 119                               29.5                                   102    Cake**    -- 39***           31.9              -0.03  73.83   Filtrate    74 --  0.89              0.83                  107                     59.7                        220 119                               60.9                                   101    Cake**    -- 39  32.5              -0.011 73.84   Filtrate    97 --  1.94              0.87                  117                     28.6                        189 119                               29.2                                   102    Cake**    -- 37  33.6              -0.03  78.0__________________________________________________________________________ *Assume all SO4 present as H2SO4 and all Ca present as CaCl2 **Calculated based on solution analyses. ***Analyzed 26.6% Ca and 65.4% SO4 (CaSO4.0.5 H2O) 
    
     The above description should be interpreted in an illustrative rather than a restrictive sense as modifications to the above description may be apparent to those skilled in the relevant art without departing from the spirit and scope of the present invention as defined by the claims set out below.