Procedure for obtaining scorodite with a high arsenic content from acidic solutions with high content of sulfuric acid

Abstract

The present invention provides a process that allows the oxidation of trivalent arsenic and ferrous ion, simultaneous with neutralization of the acid solution to be treated, the precipitation of arsenic and oxidized ferric iron added in a molar ratio Fe:As determined at a defined pH, all of the above with a high efficiency of precipitation of arsenic as ferric arsenate or scorodite, obtaining a final residue stable in the long term, characterized by their higher content of arsenic in a lower volume compared with the procedures described in the state of the prior art.

Claims

1. A procedure for obtaining a mining or industrial waste, comprising ferric arsenate and/or scorodite with a high arsenic content from highly acidic solutions, superior in concentration of acid to 45 g/L, which include copper, arsenic and optionally iron, antimony and/or bismuth, the procedure comprising: i. contacting a first highly acidic solution rich in arsenic, and optionally containing iron, with a first slurry of neutralizer so that the acid concentration of the resulting solution is 35-45 g/L, obtaining a second acidic solution rich in arsenic with acid reduced solution, and optionally containing iron, and a first solid that includes gypsum with low arsenic content; ii. contacting said second acidic solution rich in arsenic with a first oxidant that simultaneously oxidizes arsenite ion to arsenate ion and oxidizes the ferrous ion to ferric ion to obtain a third acidic solution rich in arsenic; iii. contacting the third acidic solution rich in arsenic with a second oxidant that simultaneously oxidizes arsenite ion to arsenate ion and oxidizes the ferrous ion to ferric ion to obtain a fourth acidic solution rich in arsenic; iv. regulating a molar ratio of ferric ion: arsenate ion in the fourth acidic solution rich in arsenic between 1.0 and 2.0, by adding a solution rich in ferric ion to obtain a fifth acidic solution rich in arsenic; v. adding a portion of a pulp of ferric arsenate and/or scorodite consisting of a solid with an arsenic content higher than 15% and content of less than 54% gypsum recirculated from step x and further consisting of a portion of a 30% wt of ferric arsenate and/or scorodite to the fifth acidic solution rich in arsenic, as the basis for nucleation and growth of particle size and/or ferric arsenate scorodite during precipitation to obtain a first pulp of ferric arsenate and/or scorodite; vi. heating the first pulp of ferric arsenate and/or scorodite at a temperature between 50 and 90° C.; vii. adding a second slurry of neutralizer consisting of a neutralizer based on magnesium, calcium and water, reaching a concentration of free acid of between 5 and 33 g/L, to generate a second pulp of ferric arsenate and/or scorodite comprising a sixth acidic solution and impoverished in arsenic, ferric arsenate and/or scorodite and with low content of gypsum; viii. maintaining the second pulp of ferric arsenate and/or scorodite at the temperature in step vi for a time of between 5 and 48 h; ix. sending the second pulp of ferric arsenate and/or scorodite up to a stage of solid liquid separation to obtain a pulp of ferric arsenate and/or scorodite consisting of a solid with an arsenic content higher than 15% and content of less than 54% gypsum and sixth acidic solution and impoverished in arsenic; and x. recirculating a portion of the pulp of ferric arsenate and/or scorodite consisting of a solid with an arsenic content higher than 15% and content of less than 54% gypsum to step v.

2. The process of claim 1, wherein the first slurry of neutralizer in step i consists of calcium hydroxide slurry and water.

3. The process of claim 1, wherein the first slurry of neutralizer is added at room temperature.

4. The process of claim 1, wherein the first oxidant used in step ii is hydrogen peroxide.

5. The process of claim 1, wherein the second oxidant used in step iii is sodium chlorite.

6. The process of claim 1, wherein the first oxidant of step ii is added so that 40% of arsenic is oxidized in the second acidic solution rich in arsenic.

7. The process of claim 1, wherein the second oxidant in step iii is added so that 60% of arsenic is oxidized in the third acidic solution rich in arsenic.

8. The process of claim 1, wherein the molar ratio of ferric ion:arsenate ion in step iv is set to 1.2.

9. The process of claim 8, wherein the molar ratio of ferric ion:arsenate ion is adjusted with a solution rich in ferric ion obtained from a leaching magnetite and/or hematite solution.

10. The process of claim 1, wherein the second slurry of step vii contains a 47% by weight of calcium carbonate and a 53% by weight of magnesium carbonate.

11. The process of claim 1, wherein the second slurry of step vii is dolomitic limestone.

12. The process of claim 10, wherein the second slurry of step vii is dolomitic limestone.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows the performance of the oxidation of arsenite ion in percentage based on the addition of sodium chlorite per mass unit of arsenite ion in g/g.

(2) FIG. 2 shows the performance of the oxidation of ferrous ion in percentage based on the addition of sodium chlorite per mass unit of ferrous ion in g/g.

(3) FIG. 3 shows the oxidation of PLS with an arsenite ion concentration of 1.33 g/L of sodium chlorite (circle) and hydrogen peroxide (triangle), in the tests of Example 4.

(4) FIG. 4 shows the oxidation of PLS with an arsenite ion concentration of 2.61 g/L of sodium chlorite (circle) and hydrogen peroxide (triangle), in the tests of Example 4.

(5) FIG. 5 shows the oxidation of PLS with an arsenite ion concentration of 3.96 g/L of sodium chlorite (circle) and hydrogen peroxide (triangle), in the tests of Example 4.

(6) FIG. 6 shows the oxidation of leach solution of Magnetite with a ferrous ion concentration of 42.9 g/L with sodium chlorite, on the evidence of the Example 31. Experimental data (empty circle), theoretical calculation (filled circle).

(7) FIG. 7 shows the oxidation of arsenite ion in solution of leaching of Magnetite with a ferrous ion concentration of 12.4 g/L and arsenite ion of 0.95 g/L with sodium chlorite, on the evidence of the Example 32.

(8) FIG. 8 shows the oxidation of ferrous ion in solution of leaching of Magnetite with a ferrous ion concentration of 12.4 g/L and arsenite ion of 0.95 g/L with sodium chlorite, on the evidence of the Example 32. Experimental data (empty circle), theoretical calculation (filled circle).

(9) FIG. 9 shows the SEM morphology of the arsenic precipitate obtained by the method of the invention. Number 1 shows crystals of scorodite, number 2 shows gypsum crystals.

(10) FIG. 10 shows the spectrum of x-ray diffraction of the arsenic precipitate.

(11) FIG. 11 shows the Raman spectrum of the arsenic precipitate.

SUMMARY OF THE INVENTION

(12) The invention discloses a procedure for obtaining a mining or industrial waste, comprising ferric arsenate and/or scorodite with a high arsenic content from highly acidic solutions, superior in concentration of acid to 45 g/L, which include arsenic and optionally copper, iron, antimony and/or bismuth, considering that a solution rich in arsenic is a concentration greater than 7 g/L, in that the procedure comprises the following stages:

(13) i.—Contact a highly acidic solution rich in arsenic, and optionally containing iron, with a neutralizing slurry so that the acid concentration of the resulting solution is of at least 35-45 g/L, to obtain a solution reduced in acid and rich in arsenic, and optionally containing iron, and a solid that includes plaster with low arsenic content,

(14) ii.—contacting said solution reduced in acid and rich in arsenic, and optionally including iron, with an oxidant that simultaneously oxide arsenite ion in the arsenate ion and oxide the ferrous ion to ferric ion,

(15) iii.—contact a highly acidic solution rich in arsenic, and optionally including iron, with a second oxidizer that simultaneously oxide arsenite ion in the arsenate ion and oxide the ferrous ion to ferric ion,

(16) iv.—regulating the molar ratio of ferric ion:arsenate ion, in the highly acid solution, between 1.0 and 2.0, by the addition of a volume of a solution of ferric ion, such as a leach solution of a material that contains iron, for this molar ratio,

(17) v.—add a portion of a 30% ferric arsenate and/or scorodite to the reduced acid solution, as basis of nucleation and growth of particle size of ferric arsenate and/or scorodite during its precipitation,

(18) vi.—heat the highly acidic solution at a temperature between 50 and 90° C.,

(19) vii—Add a neutralizing slurry based on magnesium and calcium, until reaching a concentration of free acid of between 5 and 33 g/L, to generate a pulp comprising a neutralized highly acidic solution, ferric arsenate and/or scorodite and with low content of gypsum, as, for example, less than 54% of gypsum;

(20) viii.—Maintain the pulp at the temperature indicated in step vi for a time of between 5 and 48 h,

(21) ix. Send the pulp to a stage of solid liquid separation for obtaining a first stream of a solid comprising ferric arsenate and/or scorodite with an arsenic content higher than 15% and content of less than 54% plaster and a second stream comprising the neutralized highly acidic solution and impoverished in arsenic,

(22) x.—recirculating a part of the solid comprising ferric arsenate and/or scorodite to stage iii.

(23) In a preferential option, the pulp of neutralizer of stage i consists of calcium hydroxide slurry.

(24) In an even more preferential option, the pulp of neutralizer is added at room temperature.

(25) In a preferential option, in stage II the oxidizer used is hydrogen peroxide.

(26) In a preferential option, in stage iii the oxidizer used is sodium chlorite.

(27) In an even more preferential option, in stage ii hydrogen peroxide is added in such a way as to oxidize between a 0.1 to a 40 percent of the arsenic in the solution reduced in acid and rich in arsenic.

(28) In an even more preferential option, in stage iii sodium chlorite is added in such a way as to oxidize between a 60% and 99.9% of the arsenic in the solution reduced in acid and rich in arsenic.

(29) In a preferential option, in stage iv the ratio of ferric ion:arsenate ion is set to 1.2.

(30) In an even more preferential option, the ratio of ferric ion:arsenate ion is adjusted with a solution rich in ferric ion which comes from a leach solution of magnetite and/or hematite.

(31) In a preferential option, the slurry of phase vii contains between 0.1% to 47% by weight of calcium carbonate and a 53% to 99.9% by weight of magnesium carbonate.

(32) In an even more preferential option, the slurry of stage vii is dolomitic limestone.

DETAILED DESCRIPTION OF THE INVENTION

(33) The following examples should be considered as embodiments of the present invention, and in no case should be considered as constraints of the invention, as the different adaptations that can be made of the same will be covered within the claimed subject matter by this invention.

Example 1

(34) 300 mL were placed in an acid solution containing 55 g/L of sulfuric acid at pH 0.49, with a ferrous ion concentration of 9.27 g/L, a concentration of arsenite ion of 1.93 g/L and a copper concentration of 45 g/L, in a beaker of 500 mL stirring at 300 rpm at room temperature, to which a fixed amount of sodium chlorite was added. The mixture is kept in constant agitation during 30 min and then the concentration of arsenite ion and ferrous ion measured in solution using volumetric analysis with sulphate of cerium(IV) tartrate tetrahydrate 0.1 N from Merck.

(35) The results of the various tests are presented in Table 1

(36) TABLE-US-00001 Ratio Oxidation efficiency, NaClO.sub.2/ Concentration, ppm % As(III) g/g As.sup.3+ Fe.sup.2+ As.sup.3+ Fe.sup.2+ Final pH 0.48 1.26 7.18 35% 23% 0.52 0.62 1.14 6.95 41% 25% 0.55 0.73 0.96 6.77 50% 27% 0.58 0.90 0.57 5.57 70% 40% 0.67 1.36 0.37 4.74 81% 49% 0.76 1.51 0.37 4.03 91% 57% 0.77 1.66 0.13 2.94 93% 68% 0.75 1.81 0.09 2.35 95% 75% 0.76 1.96 0.04 1.46 98% 84% 0.66 2.11 0.04 1.06 98% 89% 0.81 2.27 0.04 0.55 98% 94% 0.76 3.01 0.05 0.55 97% 94% 0.75

Example 2

(37) 300 mL of an acid solution containing 55 g/L of sulfuric acid at pH 0.49, with a ferrous ion concentration of 9.27 g/L, a concentration of arsenite ion of 1.93 g/L and a copper concentration of 45 g/L, were placed in a 500 mL beaker stirring at 300 rpm at room temperature, to which a fixed amount of sodium chlorite was added. The mixture is kept in constant agitation during 30 min and then the concentration of arsenite ion and ferrous ion in solution is measured using volumetric analysis with sulphate of cerium(IV) tartrate tetrahydrate 0.1 N from Merck.

(38) The results of the various tests are presented in Table 2.

(39) TABLE-US-00002 Ratio NaClO.sub.2/ Concentration, ppm Oxidation efficiency, % As(III) g/g As.sup.3+ As.sup.3+ 0.08 8.68 11% 0.30 6.74 31% 0.60 4.73 52% 0.75 3.47 64% 0.92 3.19 67% 1.51 0.46 95% 2.26 0.44 95% 3.02 0.52 95%

Example 3

(40) 300 mL of an acid solution containing less than 500 ppm of sulfuric acid at pH 2.85, with a ferrous ion concentration less than 0.55 g/L, a concentration of arsenite ion of 9.76 g/L and a copper concentration of 200 ppm, were placed in a beaker of 500 mL stirring at 300 rpm at room temperature, to which a fixed amount of sodium chlorite was added. The mixture is kept in constant agitation during 30 min and then the concentration of arsenite ion and ferrous ion in solution is measured using volumetric analysis with sulphate of cerium(IV) tartrate tetrahydrate 0.1 N from Merck.

(41) The results of the various tests are presented in Table 2.

(42) TABLE-US-00003 Ratio NaClO.sub.2/ Concentration, ppm Oxidation efficiency, % As(III) g/g As.sup.3+ As.sup.3+ 0.21 5.97 26% 0.43 4.24 48% 0.66 2.64 67% 0.89 0.80 90%

Example 4

(43) Six tests of PLS oxidation were made with variable concentrations of arsenic and iron, and a fixed concentration of copper equal to 35 g/L. Various sodium chlorite and hydrogen peroxide additions were made to tests in order to compare the performance of the oxidation of arsenic.

(44) TABLE-US-00004 TABLE 1 Test conditions of PLS oxidation with sodium chlorite and hydrogen peroxide Test Unit P01 P02 P03 P04 P05 P06 Concentration g/L 1.32 2.45 3.98 1.32 2.45 3.98 of As(III) Concentration g/L 6.68 5.49 3.93 6.68 5.49 3.93 of Fe(II) Concentration g/L 35.5 35.5 35.5 35.5 35.5 35.5 of Cu Acidity g/L 45 45 45 45 45 45 Sodium g 14.8 28.8 39.5 — — — chlorite Hydrogen mL — — — 21 65 107 Peroxide

(45) Results show that the oxidation with sodium chlorite was linear throughout the range of the oxidation, however, for hydrogen peroxide is observed an asymptotic profile in higher concentrations of arsenite ion, losing efficiency in the oxidation of arsenite ion.

Example 5

(46) 3.76 L were placed in an acid solution with a concentration of sulfuric acid of 60 g/L with an arsenic total content of 18.55 g/L, arsenite ion less than 0.02 g/L, total iron of 15.45 g/L and ferrous ion of 0.17 g/L, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.12 mol:mol in a reactor of 5 L agitated at 400 rpm and at a temperature of 90° C. Once this temperature is reached, 1,779 mL of calcium carbonate slurry is added, prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to 2.2. The pulp was kept in constant agitation for a time of 5 h. After said time, pulp was left to decant during 16 h and was further filtered with a Kitasato system filter with filter paper of 80 g/m.sup.2. 806 g of dry solid were obtained, with an arsenic content of 8.63%, 7.02% of iron and copper of 2.64%, while the resulting solution contained 20 g/L of copper, 110 ppm of total arsenic and 430 ppm total iron.

Example 6

(47) 3.76 L were placed in an acid solution with a concentration of sulfuric acid of 60 g/L with an arsenic total content of 18.55 g/L, arsenite ion less than 0.02 g/L, total iron of 15.45 g/L and ferrous ion of 0.17 g/L, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.12 mol:mol in a reactor of 5 L agitated at 400 rpm and at a temperature of 90° C. Once this temperature is reached, 1,779 mL of magnesium carbonate slurry is added, prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to 2.2. The pulp was kept in constant agitation for a time of 5 h. After said time, pulp was left to decant during 16 h and was further filtered with a Kitasato system filter with filter paper of 2.5 μm. 274 g of dry solid were obtained with a content of 26.3% arsenic, 18.2% iron, 1.47% copper and 0.24% magnesium, while the resulting solution contained 26 g/L of copper, 60 ppm of total arsenic and 480 ppm total iron.

Example 7

(48) 3.76 L were placed in an acid solution with a concentration of sulfuric acid of 55.7 g/L with a copper content of 31.8 g/L, 19.3 g/L total arsenic, arsenite ion less than 0.02 g/L, 18.0 g/L total iron and ferrous ion of 340 ppm, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.25 mol:mol in a reactor of 5 L agitated at 400 rpm and at a temperature of 90° C. Once this temperature was reached, 1,640 mL neutralizing slurry was added characterized because it has a 52% by weight of calcium carbonate and a 48% by weight of magnesium carbonate, where the slurry was prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp that contains the acid solution to a pH equal to 2.2. The pulp was kept in constant agitation for a time of 5 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 475 g of dry solid were obtained with a content of 15.2% arsenic, 14.0% iron, 0.61% copper and 0.01% magnesium, while the resulting solution contained 26.6 g/L of copper, 110 ppm of total arsenic and 200 ppm total iron.

Example 8

(49) 3.76 L were placed in an acid solution with a concentration of sulfuric acid of 55.7 g/L with a copper content of 32.5 g/L, total arsenic of 20.4 g/L, arsenite ion less than 0.02 g/L, total iron of 18.9 g/L and ferrous ion of 110 ppm, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.24 mol:mol in a reactor of 5 L agitated at 400 rpm and at a temperature of 50° C. Once this temperature was reached, 1,630 mL neutralizing slurry was added characterized because it has a 52% by weight of calcium carbonate and a 48% by weight of magnesium carbonate, where the slurry was prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp that contains the acid solution to a pH equal to 2.2. The pulp was kept in constant agitation for a time of 5 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 471 g of dry solid were obtained with a content of 16.4% arsenic, 12.6% iron, 0.32% copper and 0.02% magnesium, while the resulting solution contained 25.8 g/L of copper, 40 ppm of total arsenic and 230 ppm total iron.

Example 9

(50) 3.5 L were placed in an acid solution with a concentration of sulfuric acid of 49.5 g/L with a copper content of 32.9 g/L, total arsenic of 20.0 g/L, arsenite ion less than 0.02 g/L, total iron of 10.04 g/L and ferrous ion of 0.17 g/L in an agitated reactor of 5 L, to which 256 mL of a solution of magnetite leaching was added with 34.1 g/l sulfuric acid, 111.5 g/L iron and 2.65 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.22 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 90° C. Once this temperature was reached, 1,115 mL of magnesium carbonate slurry was added, prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a pH equal to 1.2. The pulp was kept in constant agitation for a time of 5 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 220 g of dry solid were obtained with a content of 27.3% arsenic, 21.5% iron, 0.56% copper and 0.02% magnesium, while the resulting solution contained 24.2 g/L of copper, 1,230 ppm of total arsenic and 1,460 ppm total iron.

Example 10

(51) 3.5 L were placed in an acid solution with a concentration of sulfuric acid of 49.5 g/L with a copper content of 32.9 g/L, total arsenic of 20.0 g/L, arsenite ion less than 0.02 g/L, total iron of 10.04 g/L and ferrous ion of 0.17 g/L in an agitated reactor of 5 L, to which 256 mL of a solution of magnetite leaching was added with 34.1 g/l sulfuric acid, 111.5 g/L iron and 2.65 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.22 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 90° C. Once this temperature was reached, 1,295 mL of magnesium carbonate slurry was added, prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a pH equal to 1.5. The pulp was kept in constant agitation for a time of 5 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 266 g of dry solid were obtained with a content of 25.7% arsenic, 20.7% iron, 0.68% copper and 0.12% magnesium, while the resulting solution contained 22.5 g/L of copper, 300 ppm of total arsenic and 920 ppm total iron.

Example 11

(52) 3.5 L were placed in an acid solution with a concentration of sulfuric acid of 49.5 g/L with a copper content of 32.9 g/L, total arsenic of 20.0 g/L, arsenite ion less than 0.02 g/L, total iron of 10.04 g/L and ferrous ion of 0.17 g/L in an agitated reactor of 5 L, to which 256 mL of a solution of magnetite leaching was added with 34.1 g/l sulfuric acid, 111.5 g/L iron and 2.65 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.22 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 90° C. Once this temperature was reached, 1,245 mL of slurry was added, characterized because it has a 52% by weight of calcium carbonate and a 48% by weight of magnesium carbonate, where the slurry was prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a pH equal to 1.2. The pulp was kept in constant agitation for a time of 5 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 393 g of solid dry were obtained with a content of 16.8% arsenic, 12.9% iron, 0.26% copper, 13.4% calcium and 0.01% magnesium, while the resulting solution contained 25.4 g/L of copper, 1,010 ppm of total arsenic and 3,100 ppm total iron.

Example 12

(53) 3.5 L were placed in an acid solution with a concentration of sulfuric acid of 49.5 g/L with a copper content of 32.9 g/L, total arsenic of 20.0 g/L, arsenite ion less than 0.02 g/L, total iron of 10.04 g/L and ferrous ion of 0.17 g/L in an agitated reactor of 5 L, to which 256 mL of a solution of magnetite leaching was added with 34.1 g/l sulfuric acid, 111.5 g/L iron and 2.65 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.22 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 90° C. Once this temperature was reached, 1,460 mL of slurry were added, characterized because it has a 52% by weight of calcium carbonate and a 48% by weight of magnesium carbonate, where the slurry was prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a pH equal to 1.5. The pulp was kept in constant agitation for a time of 5 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 456 g of solid dry were obtained with a content of 15.6% arsenic, 13.1% iron, 0.36% copper, 14.9% calcium and 0.01% magnesium, while the resulting solution contained 24.5 g/L of copper, 160 ppm of total arsenic and 870 ppm total iron.

Example 13

(54) 3.5 L were placed in an acid solution with a concentration of sulfuric acid of 49.5 g/L with a copper content of 32.9 g/L, total arsenic of 20.0 g/L, arsenite ion less than 0.02 g/L, total iron of 10.04 g/L and ferrous ion of 0.17 g/L in an agitated reactor of 5 L, to which 256 mL of a solution of magnetite leaching was added with 34.1 g/l sulfuric acid, 111.5 g/L iron and 2.65 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.22 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 90° C. Once this temperature was reached, 1,385 mL of calcium carbonate slurry was added, prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a pH equal to 1.2. The pulp was kept in constant agitation for a time of 5 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 640 g of solid dry were obtained with a content of 10.0% arsenic, 8.9% iron, 0.23% copper, 17.8% calcium and 0.02% magnesium, while the resulting solution contained 27.9 g/L of copper, 1,380 ppm of total arsenic and 1,640 ppm total iron.

Example 14

(55) 3.5 L were placed in an acid solution with a concentration of sulfuric acid of 49.5 g/L with a copper content of 32.9 g/L, total arsenic of 20.0 g/L, arsenite ion less than 0.02 g/L, total iron of 10.04 g/L and ferrous ion of 0.17 g/L in an agitated reactor of 5 L, to which 256 mL of a solution of magnetite leaching was added with 34.1 g/l sulfuric acid, 111.5 g/L iron and 2.65 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.22 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 90° C. Once this temperature was reached, 1,699 mL of calcium carbonate slurry was added, prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a pH equal to 1.5. The pulp was kept in constant agitation for a time of 5 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 810 g of solid dry were obtained with a content of 8.5% arsenic, 7.8% iron, 0.28% copper, 17.6% calcium and 0.02% magnesium, while the resulting solution contained 25.6 g/L of copper, 190 ppm of total arsenic and 990 ppm total iron.

Example 15

(56) 3.5 L were placed in an acid solution with a concentration of sulfuric acid of 49.5 g/L with a copper content of 32.9 g/L, total arsenic of 20.0 g/L, arsenite ion less than 0.02 g/L, total iron of 10.04 g/L and ferrous ion of 0.17 g/L in an agitated reactor of 5 L, to which 256 mL of a solution of magnetite leaching was added with 34.1 g/l sulfuric acid, 111.5 g/L iron and 2.65 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.22 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 50° C. Once this temperature was reached, 1,295 mL of magnesium carbonate slurry was added, prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a pH equal to 1.5. The pulp was kept in constant agitation for a time of 5 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 175 g of dry solid were obtained with a content of 33.1% arsenic, 28.7% iron, 0.72% copper and 0.13% magnesium, while the resulting solution contained 25.9 g/L of copper, 1,120 ppm of total arsenic and 1,430 ppm total iron.

Example 16

(57) 3.5 L were placed in a acid solution with a concentration sulfuric acid of 45.2 g/L with a copper content of 32.1 g/L, total of 20.0 g/l arsenic, arsenite ion less than 0.04 g/L, total iron of 18.2 g/L and ferrous ion of 0.08 g/L in an agitated reactor of 5 L, to which were added 143 mL of a leaching solution of magnetite of 59.6 g/l sulfuric acid, 145.6 g/L total iron and 0.11 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.20 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 50° C. Once this temperature was reached, 1,210 mL of slurry were added, characterized because it has a 52% by weight of calcium carbonate and a 48% by weight of magnesium carbonate, where the slurry was prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a pH equal to 1.5. The pulp was kept in constant agitation for a time of 5 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 332 g of solid dry were obtained with a content of 18.0% arsenic, 15.3% iron, 0.17% copper, 9.9% calcium and 0.02% magnesium, while the resulting solution contained 26.1 g/L of copper, 850 ppm of total arsenic and 1,300 ppm total iron.

Example 17

(58) 3.5 L were placed in a acid solution with a concentration sulfuric acid of 49.5 g/L with a copper content of 32.9 g/L, total of 20.0 g/l arsenic, arsenite ion less than 0.02 g/L, total iron of 10.04 g/L and ferrous ion of 0.17 g/L in an agitated reactor of 5 L, to which were added 143 mL of a leaching solution of magnetite of 59.6 g/l sulfuric acid, 145.6 g/L total iron and 0.11 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.20 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 50° C. Once this temperature was reached, 1,295 mL of calcium carbonate slurry was added, prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a pH equal to 1.5. The pulp was kept in constant agitation for a time of 5 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 454 g of dry solid were obtained with a content of 13.0% arsenic, 11.6% iron, 0.31% copper, 10.7% of calcium from 0.02% magnesium, while the resulting solution contained 25.6 g/L of copper, 990 ppm of total arsenic and 1,000 ppm total iron.

Example 18

(59) 3.5 L of an a acid solution with a concentration sulfuric acid of 54.5 g/L with a copper content of 59.0 g/L, total of 12.2 g/L, arsenite ion less than 0.37 g/L, total iron of 13.4 g/L and ferrous ion less than 0.56 g/L were placed in an agitated reactor of 5 L1, to which were added 37 mL of a leaching solution of magnetite of 59.6 g/l sulfuric acid, 145.6 g/L total iron and 0.11 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.63 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 90° C. Once this temperature was reached, 580 mL of calcium carbonate slurry were added, prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a free acidity of 30 g/L. The pulp was kept in constant agitation for a time of 5 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 229 g of solid dry were obtained with a content of 16.8% arsenic, 12.5% iron, 0.78% copper, 12.1% calcium and 0.01% magnesium, while the resulting solution contained 49.5 g/L of copper, 1,060 ppm of total arsenic and 5,560 ppm total iron.

Example 19

(60) 3.5 L of an a acid solution with a concentration sulfuric acid of 54.5 g/L with a copper content of 59.0 g/L, total of 12.2 g/L, arsenite ion less than 0.37 g/L, total iron of 13.4 g/L and ferrous ion less than 0.56 g/L were placed in an agitated reactor of 5 L1, to which were added 37 mL of a leaching solution of magnetite of 59.6 g/l sulfuric acid, 145.6 g/L total iron and 0.11 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.63 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 90° C. Once this temperature was reached, 530 mL of calcium carbonate slurry were added, prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a free acidity of 30 g/L. The pulp was kept in constant agitation for a time of 44 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 218 g of solid dry were obtained with a content of 19.5% arsenic, 14.5% iron, 0.74% copper, 8.9% calcium and 0.01% magnesium, while the resulting solution contained 52.2 g/L of copper, 130 ppm of total arsenic and 5,140 ppm total iron.

Example 20

(61) 3.5 L of an a acid solution with a concentration sulfuric acid of 54.5 g/L with a copper content of 59.0 g/L, total of 12.2 g/L, arsenite ion less than 0.37 g/L, total iron of 13.4 g/L and ferrous ion less than 0.56 g/L were placed in an agitated reactor of 5 L1, to which were added 40 mL of a leaching solution of magnetite of 59.6 g/l sulfuric acid, 145.6 g/L total iron and 0.11 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.62 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 90° C. Once this temperature was reached, 530 mL of magnesium carbonate slurry were added, prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a free acidity of 30 g/L. The pulp was kept in constant agitation for a time of 48 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 218 g of solid dry were obtained with a content of 29.4% arsenic, 26.0% iron, 0.84% copper, 0.07% calcium and 0.01% magnesium, while the resulting solution contained 57.4 g/L of copper, 150 ppm of total arsenic and 5,280 ppm total iron.

Example 21

(62) 3.5 L of an a acid solution with a concentration sulfuric acid of 54.5 g/L with a copper content of 59.0 g/L, total of 12.2 g/L, arsenite ion less than 0.37 g/L, total iron of 13.4 g/L and ferrous ion less than 0.56 g/L were placed in an agitated reactor of 5 L1, to which were added 40 mL of a leaching solution of magnetite of 59.6 g/l sulfuric acid, 145.6 g/L total iron and 0.11 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.62 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 90° C. Once this temperature was reached, 530 mL of magnesium carbonate slurry were added, prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a free acidity of 30 g/L. The pulp was kept in constant agitation for a time of 48 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 218 g of solid dry were obtained with a content of 23.0% arsenic, 18.9% iron, 0.67% copper, 4.9% calcium and 0.02% magnesium, while the resulting solution contained 53.4 g/L of copper, 160 ppm of total arsenic and 4,860 ppm total iron.

Example 22

(63) 3.5 L of an a acid solution with a concentration sulfuric acid of 54.5 g/L with a copper content of 59.0 g/L, total of 12.2 g/L, arsenite ion less than 0.37 g/L, total iron of 13.4 g/L and ferrous ion less than 0.56 g/L were placed in an agitated reactor of 5 L1, to which were added 40 mL of a leaching solution of magnetite of 59.6 g/l sulfuric acid, 145.6 g/L total iron and 0.11 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.62 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 90° C. Once this temperature was reached, 530 mL of slurry were added, characterized because it has a 52% by weight of calcium carbonate and a 48% by weight of magnesium carbonate, where the slurry was prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a free acidity of 30 g/L. The pulp was kept in constant agitation for a time of 48 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 218 g of solid dry were obtained with a content of 23.0% arsenic, 18.9% iron, 0.67% copper, 4.9% calcium and 0.02% magnesium, while the resulting solution contained 53.4 g/L of copper, 160 ppm of total arsenic and 4,860 ppm total iron.

Example 23

(64) 3.5 L of an acid solution with a concentration sulfuric acid of 41.1 g/L with a copper content of 50.9 g/L, total of 12.1 g/L, arsenite ion less than 0.37 g/L, total iron of 13.4 g/L and ferrous ion of 5.7 g/L were placed in an agitated reactor of 5 L, previously oxidized with a solution of 63 g/L of sodium chlorite stabilized in sodium hydroxide at pH 12. To that solution, 42 mL of a leaching solution were added of magnetite of 59.6 g/l sulfuric acid, 145.6 g/L total iron and 0.11 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.1 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 90° C. Once this temperature was reached, 286 mL of calcium carbonate slurry were added, prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a free acidity of 30 g/L. The pulp was kept in constant agitation for a time of 48 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 162 g of solid dry were obtained with a content of 24.9% arsenic, 17.1% iron, 1.34% copper, 5.9% calcium and 0.03% magnesium, while the resulting solution contained 57.2 g/L of copper, 480 ppm of total arsenic and 7,000 ppm total iron.

Example 24

(65) 3.5 L of an acid solution with a concentration sulfuric acid of 41.1 g/L with a copper content of 50.9 g/L, total of 12.1 g/L, arsenite ion less than 0.37 g/L, total iron of 13.4 g/L and ferrous ion of 5.7 g/L were placed in an agitated reactor of 5 L, previously oxidized with a solution of 63 g/L of sodium chlorite stabilized in sodium hydroxide at pH 12. To that solution, 42 mL of a leaching solution were added of magnetite of 59.6 g/l sulfuric acid, 145.6 g/L total iron and 0.11 g/L of ferrous ion, in such a way that the molar ratio of ferric ion and arsenate ion is equal to 1.1 mol:mol. The reactor was agitated at 400 rpm and at a temperature of 90° C. Once this temperature was reached, 253 mL of slurry were added, characterized because it has a 52% by weight of calcium carbonate and a 48% by weight of magnesium carbonate, where the slurry was prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp to a free acidity of 30 g/L. The pulp was kept in constant agitation for a time of 48 h. After that time, the pulp was left to decant during 16 h and was filtered using a Kitasato system filter with filter paper of 2.5 μm. 147 g of solid dry were obtained with a content of 27.5% arsenic, 18.3% iron, 2.21% copper, 4.5% calcium and 0.03% magnesium, while the resulting solution contained 58.6 g/L of copper, 520 ppm of total arsenic and 7,300 ppm total iron.

Example 25

(66) A continuous oxidation and precipitation test was performed for scorodite for a period of 10 days, to an acidic solution containing 8.0 g/L of total arsenic, 1.4 g/L of arsenite ion and 10.0 g/L total iron. The acid solution was oxidized with 2.1 g of sodium chlorite per 1 g of arsenate ion, reaching a arsenate ion concentration below 370 ppm. The acid solution had a molar ratio of ferric ion to arsenate ion of 1.69 mol:mol, so there was no need to adjust with a leaching solution of magnetite. The system was disposed with two reactors of 20 L agitated at 700 rpm L connected in series, with a residence time of 24 h per reactor. A slurry was supplied, characterized because it has a 52% by weight of calcium carbonate and a 48% by weight of magnesium carbonate, where the slurry was prepared at a rate of 15 g of neutralizer for every 100 mL of distilled water, in order to bring the pH of the pulp in the first reactor to a free acidity of 35 g/L and 35 g/L in the second reactor. The system was connected to a online system of decantation and filtration, from where 30 percent of the thickened pulp was recirculated to the reactor 1, to serve as a surface for the generation of crystals of scorodite. The system is operated during a course of 10 days resulting in an acid solution that on average had a concentration of 600 g/L of total arsenic and a solid that had an average content of 24% As.

Example 26

(67) There were four neutralization tests of PLS with a volume of 4,120 mL and a arsenic concentration of 12.5 g/L and sulfuric acid of 45 g/L. A slurry was added to the 25% p/p of calcium hydroxide, reaching pH 0.7, 0.9, 1.1 and 1.3, respectively.

(68) TABLE-US-00005 Test Unit P01 P02 P03 P04 Concentration of g/L 12.5 12.5 12.5 12.5 As Sulfuric acid — — — — — concentration Before the g/L 45 45 45 45 neutralization After g/L 31.9 17.8 11.1 6.84 neutralization Arsenic Removal % 0.06 2.81 24.8 26.3 Gypsum generated g 70 149 213 233

(69) The test P01 obtained the lower arsenic removal, with only a 0.06 percent of arsenic present in the head, generating 70 g of gypsum with a minimum of arsenic.

Example 27

(70) A test was conducted with 3,000 mL of 8.8 g/L of arsenic (3.0 g/L As(III)) solution, oxidizing with 4.8 mL of hydrogen peroxide 50% p/p, followed by 13.6 g of sodium chlorite, equivalent to oxidize 25% of As(III) with hydrogen peroxide and 75% of the As(III) with sodium chlorite. Subsequently, the solution was adjusted with a magnetite leaching solution to adjust the Fe(III)/As(V) to 1.2, heated to 90° C. and adding artificial dolomitic limestone slurry with 47% of magnesium carbonate and 53% calcium carbonate, to bring the solution to an acidity of 30 g/L. It was kept under agitation at 400 rpm for 48 h, and subsequently the solid was filtered and washed with distilled water.

Example 28

(71) A test was conducted with 3,000 mL of 8.8 g/L of arsenic (3.0 g/L As(III)) solution, oxidizing with 20 g of sodium chlorite. Subsequently, the solution was adjusted with a magnetite leaching solution to adjust the Fe(III)/As(V) to 1.2, heated to 90° C. and adding artificial dolomitic limestone slurry with 47% of magnesium carbonate and 53% calcium carbonate, to bring the solution to an acidity of 30 g/L. It was kept under agitation at 400 rpm for 48 h, and subsequently the solid was filtered and washed with distilled water.

Example 29

(72) A test was conducted with 3,000 mL of 8.8 g/L of arsenic (3.0 g/L As(III)) solution, oxidizing with 260 mL of sodium hypochlorite at a concentration of 100 g/L. Subsequently, the solution was adjusted with a magnetite leaching solution to adjust the Fe(III)/As(V) to 1.2, heated to 90° C. and adding artificial dolomitic limestone slurry with 47% of magnesium carbonate and 53% calcium carbonate, to bring the solution to an acidity of 30 g/L. It was kept under agitation at 400 rpm for 48 h, and subsequently the solid was filtered and washed with distilled water.

Example 30

(73) A test was conducted with 3,000 mL of the neutralization solution of example 26, Test P01 (0.9 g/L As(III)). The solution was oxidized with 6.8 g of sodium chlorite. Subsequently, the solution was adjusted with a magnetite leaching solution to adjust the Fe(III)/As(V) to 1.2, heated to 90° C. and adding artificial dolomitic limestone slurry with 47% of magnesium carbonate and 53% calcium carbonate, to bring the solution to an acidity of 30 g/L. It was kept under agitation at 400 rpm for 48 h, and subsequently the solid was filtered and washed with distilled water.

Example 31

(74) A test was conducted with 2,000 mL of a magnetite leaching solution containing 90 g/L of sulfuric acid and 42.9 g/l Fe(II) at room temperature. Sodium chlorite was added at different doses in order to oxidize the ferrous ion to ferric ion. Samples were taken 30 min after each addition of sodium chlorite. The results showed a linear behavior of the oxidation of Fe(II), with a very similar performance to the theoretical consumption.

(75) TABLE-US-00006 TABLE 2 Efficiency of oxidation of ferrous ion in magnetite leaching solution using sodium chlorite Theoretical NaClO.sub.2 Oxidation oxidation accumulated Fe(II) Efficiency efficiency g g/L % % 0.0 12.42 0.0% 0.0% 2.3 11.18 10.0% 11.4% 4.6 9.9 20.3% 23.0% 6.8 8.47 32.0% 34.7% 9.0 7.42 40.5% 46.6% 11.2 5.67 54.7% 58.5% 13.2 3.64 71.1% 70.4% 15.2 2.35 81.4% 82.3% 17.0 1.19 90.7% 94.2% 18.7 0.15 98.8% 106.0%

Example 32

(76) A test was conducted with 2,000 mL of a leaching of foundry powders containing 46 g/L of sulfuric acid, 12.8 g/l Fe(II) and 0.95 g/L As(III) at room temperature. Sodium chlorite was added at different doses in order to oxidize the ferrous ion to ferric ion and arsenite ion ion to arsenate. Samples were taken 30 min after each addition of sodium chlorite. The results showed a linear behavior of the oxidation of Fe(II) and As(III), with a very similar performance to the theoretical consumption.

(77) TABLE-US-00007 TABLE 3 Efficiency of oxidation of arsenoso ion in leaching solution of foundry powders using sodium chlorite Theoretical NaClO.sub.2 Oxidation oxidation accumulated As(III) Efficiency efficiency g g/L % % 0.0 0.95 0.0% 0.0% 2.3 0.7 26.3% 100.3% 4.6 0.53 44.3% 201.1% 6.8 0.26 72.8% 300.2% 9.0 0.08 91.7% 395.5% 11.2 0.04 95.9% 485.0% 13.2 0 100.0% 567.5% 15.2 0 100.0% 641.7% 17.0 0.03 97.0% 707.1% 0 100.0% 763.4%

(78) TABLE-US-00008 TABLE 4 Efficiency of oxidation of ferrous ion in leaching solution of foundry powders using sodium chlorite Theoretical NaClO.sub.2 Oxidation oxidation accumulated Fe(II) Efficiency efficiency g g/L % % 0.0 12.42 0.0% 0.0% 2.3 11.18 10.0% 11.4% 4.6 9.9 20.3% 23.0% 6.8 8.47 32.0% 34.7% 9.0 7.42 40.5% 46.6% 11.2 5.67 54.7% 58.5% 13.2 3.64 71.1% 70.4% 15.2 2.35 81.4% 82.3% 17.0 1.19 90.7% 94.2% 0.15 98.8% 106.0%

Example 33

(79) 3,500 mL of a PLS solution were taken with 12.5 g/L, 20 g/l Fe, 35.9 g/L Cu and 46.6 g/L of sulfuric acid. Lime slurry was added at 25% p/v to neutralize the pulp up to 33 g/L at room temperature. We obtained a gypsum that had efficiency of arsenic removal copper, and iron of less than 0.1%.

Example 34

(80) 3,500 mL of a PLS solution were taken, with 12.5 g/L (0.9 g/L As(III)), 20 g/l Fe, 35.9 g/L Cu and 46.6 g/L of sulfuric acid. Lime slurry was added at 25% p/v to neutralize the pulp up to 36 g/L at room temperature. We obtained a gypsum that had efficiency of arsenic removal copper, and iron of less than 0.05%.

Example 35

(81) The previously neutralized PLS solution of the exercise 33, was subjected to a precipitation process of scorodite, oxidizing the As(III) and Fe(II) present with sodium chlorite adding 6.8 g NaClO.sub.2 80%, raising the temperature to 90° C., neutralizing with a slurry of dolomitic limestone to 15% p/v to reach 30 g/L and maintaining such acidity, and in constant agitation for 48 h. The results showed a precipitation efficiency of 99.3% As and only a 0.9% of Cu. The residue was scorodite with gypsum precipitate, with a content of 28% As. The chloride concentration was 0.7 g/L.

Example 36

(82) A PLS solution with 46.6 g/L of sulfuric acid, 7.4 g/L (3.0 g/L As(III)), 13.5 g/L Cu and 14 g/l Fe was subjected to a process of precipitation of gypsum to bring the mixture to 33 g/L of sulfuric acid as in the example 33. Then scorodite was precipitated, oxidizing the As(III) and Fe(II) present with sodium hypochlorite, adding 130 mL NaClO 100 g/L, raising the temperature to 90° C., neutralizing with a slurry of dolomitic limestone to 15% p/v to reach 30 g/L and maintaining such acidity, and in constant agitation for 48 h. The results showed an efficiency of precipitation of 97% As and only a 1.2% of Cu. The residue was scorodite with gypsum precipitate, with a content of 24% As. The chloride concentration was 4 g/L.

Example 37

(83) A PLS solution with 46.6 g/L of sulfuric acid, 7.4 g/L (3.0 g/L As(III)), 13.5 g/L Cu and 14 g/l Fe was subjected to a process of precipitation of gypsum to bring the mixture to 33 g/L of sulfuric acid as in the example 33. Then scorodite was precipitated, oxidizing the As(III) and Fe(II) with 12 g of sodium chlorite, and then raising the temperature to 90° C., neutralizing with a slurry of dolomitic limestone to 15% p/v to reach 30 g/L and maintaining such acidity, and in constant agitation for 48 h. The results showed an efficiency of precipitation of 98% As and only a 1.2% of Cu. The residue was scorodite with gypsum precipitate, with a content of 25% As. The chloride concentration was 1.6 g/L.

Example 38

(84) A PLS solution with 46.6 g/L of sulfuric acid, 7.4 g/L (3.0 g/L As(III)), 13.5 g/L Cu and 14 g/l Fe was subjected to a process of precipitation of gypsum to bring the mixture to 33 g/L of sulfuric acid as in the example 33. Then scorodite was precipitated, oxidizing the As(III) and Fe(II) present adding in a first stage hydrogen peroxide to 50% v/v and in a second stage with sodium chlorite. Hydrogen peroxide was added at a rate of 0.44 mol of hydrogen peroxide per mol of As(III), and then 0.4 mol of sodium chlorite per mol of initial As(III) in the solution, in order to oxidize 40% of As(III) with hydrogen peroxide and the rest with sodium chlorite. After the oxidation, temperature was increased to 90° C., neutralizing with a slurry of dolomitic limestone to 15% p/v to reach 30 g/L and maintaining such acidity, and in constant agitation for 48 h. The results showed an efficiency of precipitation of 97% Ass and only a 1.2% of Cu.

(85) The residue was scorodite with gypsum precipitate, with a content of 25% As. The chloride concentration was 1.0 g/L.

(86) The figures show the oxidizing potential of sodium chlorite on hydrogen peroxide when working with leaching solutions of foundry powders. The Figures I and II show the efficiency of oxidation of As(III) as well as that of the Fe(II) having a linear behavior with regard to the provided dose of sodium chlorite.

Example 39

(87) An analysis of scanning electron microscopy was performed to arsenical precipitates obtained in example 35. The proportions of As, Fe and O generate crystals with the proportion of chemical speciation of the scorodite FeAsO.sub.4, as well as the presence of gypsum in the precipitates.

(88) TABLE-US-00009 TABLE 4 Spectrum of scanning electron microscopy of arsenical precipitates Spectrum O S Ca Fe Cu As 1 41.74 2.07 0.34 22.14 1.72 32 2 45.9 2.14 0.54 20.23 1.64 29.55 3 26.07 27.09 42.74 1.08 — 3.02 4 36.25 1.97 0.25 24.76 1.88 34.89

Example 40

(89) Chemical stability tests were conducted for the precipitate obtained under the procedure described in Example 35. The results show a very low release of As, which gives an account of the stability of the generated residue.

(90) TABLE-US-00010 TABLE 5 Concentration of As released in stability analysis of solid wastes generated in neutralization tests with dolomitic limestone Test Batch test precipitate TCLP 0.46 ppm SPLP 0.29 ppm IMP 0.15 ppm

Example 41

(91) Analysis of x-ray diffraction (FIG. 10) and Raman spectrometry (FIG. 11) were performed. Both analyzes confirmed the presence of scorodite and gypsum in the arsenic precipitates of the Example 35. For the Raman spectrum peaks in 428, 487, 629, 669 and 1018 cm correspond to bassanita mineral (CaSO.sub.4.0.5H.sub.2O), while the peaks in 335, 807 and 893 cm correspond to the mineral scorodite (FeAsO.sub.4.2H.sub.2O).

(92) The stoichiometric consumption of As(III) is calculated as follows

(93) Sodium Chlorite

(94) ${\mathrm{HAsO}}_2+H_{2}O+1\text{/}2{\mathrm{NaClO}}_2.fwdarw.H_3{\mathrm{AsO}}_4+\mathrm{NaCl}\mathrm{Stoichiometric}\mathrm{consumption}=200\frac{\mathrm{moles}{\mathrm{NaClO}}_2}{\mathrm{moles}{\mathrm{As}\left(\mathrm{III}\right)}_{\mathrm{start}}}\%$

(95) Hydrogen Peroxide

(96) ${\mathrm{HAsO}}_2+H_2{O}_2.fwdarw.H_3{\mathrm{AsO}}_4\mathrm{Stoichiometric}\mathrm{consumption}=100.Math.\frac{\mathrm{moles}{H}_2{O}_2}{\mathrm{moles}{\mathrm{As}\left(\mathrm{III}\right)}_{\mathrm{start}}}\%$

(97) The stoichiometric consumption of Fe(II) is calculated as follows

(98) Sodium Chlorite

(99) ${\mathrm{FeSO}}_4+1\text{/}2H_2{\mathrm{SO}}_4+1\text{/}4{\mathrm{NaClO}}_2.fwdarw.1\text{/}2{{\mathrm{Fe}}_2\left({\mathrm{SO}}_4\right)}_3+1\text{/}2\mathrm{NaCl}+1\text{/}2H_{2}O\mathrm{Stoichiometric}\mathrm{consumption}=25\frac{\mathrm{moles}{\mathrm{NaClO}}_2}{\mathrm{moles}{\mathrm{Fe}\left(\mathrm{II}\right)}_{\mathrm{start}}}\%$

(100) Hydrogen Peroxide

(101) ${\mathrm{FeSO}}_4+1\text{/}2H_2{\mathrm{SO}}_4+1\text{/}2H_2{O}_2.fwdarw.1\text{/}2{{\mathrm{Fe}}_2\left({\mathrm{SO}}_4\right)}_3+H_{2}O\mathrm{Stoichiometric}\mathrm{consumption}=50.Math.\frac{\mathrm{moles}{H}_2{O}_2}{\mathrm{moles}{\mathrm{Fe}\left(\mathrm{II}\right)}_{\mathrm{start}}}\%$

(102) FIG. 3 shows that for concentrations of As in the order of 1.33 g/L, the stoichiometric consumption in the oxidation reaction of As(III) is more efficient for the sodium chlorite than that for hydrogen peroxide. As the concentration of As(III) increases to 2.61 g/L (FIG. 4) and 3.96 g/L (FIG. 5), the stoichiometric consumption of sodium chlorite becomes more efficient in respect to the consumption of hydrogen peroxide. It is important to note that the stoichiometric consumption of Figures I, II, III, IV and V are calculated with respect to the oxidation of As(III), however, in the experiments there was also the presence of Fe(II) which also consumes oxidizer to produce Fe(III), which makes the plotted consumption of stoichiometric As(III) greater than 100%.

(103) In the case of the Figures VI and VIII it is noted that the performance of oxidation of ferrous ion in the presence of low concentrations of arsenite ion is highly efficient, and approaching 100% stoichiometric performance with sodium chlorite.

(104) The precipitation with dolomitic limestone is beneficial, in that the magnesium in this type of carbonates neutralize acid without generating gypsum, which allows to increase the content of arsenic in the precipitate, compared with the precipitation of calcium carbonate or limestone.

(105) The oxidation with sodium chlorite is more beneficial than using sodium hypochlorite, since more moles of sodium hypochlorite are needed in order to oxidize As(III) and Fe(II), increasing the concentration of chloride in the final solution rich in copper. The greater presence of chloride can be harmful to the downstream process. That is why the combinations of oxidizing agents such as hydrogen peroxide and sodium chlorite allow to reduce the content of chloride in the solution rich in copper, but even so, maximizes the oxidation of arsenite ion. The oxidation with hydrogen peroxide should be performed at an initial stage, where the oxidative behavior shows a linear behavior, while the sodium chlorite can be used as a second oxidizer allowing to complete the oxidation.

(106) The analysis of physical characterization such as XRD, Raman and scanning electron microscopy confirmed that in the arsenic precipitates there is presence of scorodite.