Procedure for stabilizing arsenic by precipitation of ferric arsenate in a mixture with aluminum gel

Abstract

A procedure for stabilizing arsenic by precipitation of ferric arsenate in a mixture with aluminum gel, comprising the following steps: (i) neutralization of arsenic wastewater using a first neutralizing agent to produce neutralized arsenic wastewater; (ii) oxidation of the wastewater from step i to As(V) by adding a first oxidizing agent; (iii) adjustment of the Fe(III) / As(V) molar ratio by mixing the oxidized arsenic wastewater from step ii with a ferric solution; (iv) arsenic precipitation by adjusting the pH of the arsenic wastewater from step iii with a second neutralizing agent to produce an arsenic residue slurry; (v) separation of the arsenic residue slurry obtained from step iv) to produce wastewater and a first arsenic residue; and (vi) mixing of the arsenic residue with the gel obtained in step v) to produce a second arsenic residue.

Description

Detailed description of the invention

[0001] [Field of Invention] This invention solves the technical problem of producing a stable arsenic residue without requiring a thermal stabilization process for producing a stable arsenic residue.

[0002] This invention solves the technical problem of removing arsenic from arsenic wastewater and producing stable arsenic wastewater without requiring heating in the precipitation stage for generating crystalline compounds.

[0003] [Current technology] Arsenic is widely distributed in over 320 types of minerals, and is therefore present everywhere, including in mining and metallurgical operations, as well as in calcination and smelting, and in the acid dissolution of arsenic-containing ore in copper concentrate, resulting from the washing of exhaust gases with dilute acids. Wastewater from the two processes mentioned above is characterized by an extremely low pH of around 1.0 and a high arsenic content of 3g / L to 10g / L (Luo, T., Cui, J., Hu, S., Huang, Y., & Jing, C. (2010). Arsenic removal and recovery from copper smelting wastewater using TiO2. Environmental science & technology, 44(23), 9094-9098.). Furthermore, arsenic in this form is mainly in the trivalent As(III) state, which is the most toxic inorganic form present in polluted water, and its toxicity is suggested to be 25 to 60 times that of As(V). The removal of As(III) in water treatment is technically more difficult than that of As(V) due to its higher mobility and solubility (Paikaray, S., Gottlicher, J., & Peiffer, S. (2012). As(III) retention kinetics, equilibrium and redox stability on biosynthesized schwertmannite and its fate and control on schwertmannite stability on acidic (pH 3.0) aqueous exposure. Chemosphere, 86(6), 557-564.). Efficient and direct removal of As(III) is a particularly significant challenge at extremely low concentrations and around pH 1.0. Various treatment processes have been employed for arsenic removal in various media, including precipitation, sorption, ion exchange, and membrane separation. Chemical precipitation appears to be more suitable and economical for the removal of high concentrations of arsenic, while the other three are typically used for low concentrations due to their cost and capacity. Traditional methods for arsenic precipitation include neutralization with lime, co-precipitation with iron ions, and sulfide precipitation.However, none of these methods are very suitable for treating arsenic with a content exceeding 30% w / w. In lime neutralization, in order to remove arsenic as calcium arsenate and calcium arsenite, which have moderately low arsenic concentrations of 5% to 15%, the pH needs to be adjusted to 12. This requires a large amount of lime, which simultaneously generates a large amount of sludge, and its storage is not entirely safe, as the arsenic is subsequently released into the solution. Coprecipitation with ferric ions is a special method for arsenate removal, but it requires the use of an oxidizing agent to convert As(III) to As(V). Sulfide precipitation can directly remove As(III) as As2S3, but it presents significant operational challenges due to the generation of hydrogen sulfide and the additional process required to ensure environmental stability.

[0004] Copper smelters employ various treatment methods to remove arsenic from weakly acidic wastewater, the most commonly used being the coprecipitation method, which forms arsenic ferrihydrite [As(V)-ferrihydrite: As(V)-Fh] by neutralizing iron (Fe:As molar ratio > 3) and lime. However, As(V)-Fh has been designated as the Best Validated Technology (BDAT) by the U.S. Environmental Protection Agency (US EPA) for removing arsenic from acidic ore treatment wastewater. However, this treatment option involves high sludge production, high iron requirements, low As content (6%), and the need to oxidize As(III) to species such as As(V) before precipitation. In addition, there are concerns about the long-term stability of As(V)-Fh because the ferrihydrite contained in As(V)-Fh can change to goetite and eventually hematite, potentially releasing arsenic into the solution. Furthermore, in an oxygen-free environment, the reduction of As(V)-Fh can lead to the reductive dissolution of ferrihydrite or As(V), potentially resulting in arsenic migration (Pedersen, HD, Postma, D., & Jakobsen, R. (2006). Release of arsenic associated with the reduction and transformation of iron oxides. Geochimica et Acta, 70(16), 4116-4129).

[0005] Scorodite (FeAsO4×2H2O) is generally considered the most suitable removal option for arsenic fixation due to its high arsenic removal efficiency, high arsenic content of 30%, low iron requirement (Fe:As=1), and low solubility in the pH range of 2.8 to 5.3. Furthermore, because scorodite is crystalline, it has good settling and filterability. Professor George Demopoulos developed a new process for immobilizing arsenic from weakly acidic metallurgical wastewater by atmospheric precipitation of scorodite at 95°C under atmospheric pressure and supersaturated controlled conditions (Demopoulos, GP (2005). On the preparation and stability of scorodite. Arsenic metallurgy, 25-50). This process is being implemented on an industrial scale by EcoMetales. This process is currently in operation in Calama, Chile, to remove arsenic from leachate of smelting dust. This process has lower capital costs than high-temperature, high-pressure oxidation (HTPOX) and is independent of process scale (Filippou, D., & Demopoulos, GP (1997). Arsenic immobilization by controlled scorodite precipitation. Jom, 49(12), 52-55.). Furthermore, scorodite can be decomposed under anaerobic conditions, by CO2 carbonation, or in the presence of reducing bacteria (Riveros, PA, Dutrizac, JE, & Spencer, P. (2001). Arsenic disposal practices in the metallurgical industry. Canadian Metallurgical Quarterly, 40(4), 395-420). Therefore, there is an incentive to investigate alternative disposal options that have low solubility, require less iron, have high arsenic removal efficiency, and possess good filtration properties, which can be used by copper smelters for the removal and disposal of arsenic from weakly acidic wastewater.

[0006] In this sense, there is a need to develop a procedure that provides stability to amorphous arsenic precipitates containing iron with relatively low Fe / As donations, without requiring the use of heat to generate a crystalline phase that provides stability. The present invention improves the current technological situation by stabilizing amorphous ferric arsenate without requiring excessive Fe / As donations by creating a passivation layer that reduces the release of arsenic into the leaching medium, by using an aluminum gel in which aluminum arsenate is formed on the particle surface and precipitates as aluminum hydroxide or aluminum oxyhydroxide after the hardening process.

[0007] Patent application WO2019000091 discloses a method for stabilizing hazardous waste using an aluminum gel. This application particularly focuses on the stabilization of scorodite containing crystalline ferric arsenate, to which particles are coated by an aluminum gel. In the present invention, amorphous ferric arsenate is used, and amorphous ferric arsenate does not impart any crystallinity by the precipitation method disclosed herein. As a result, it is possible to generate an aluminum arsenate phase by the technique used in the present invention by adding an aluminum gel, which, according to our data, can yield a stable arsenic precipitate, which cannot be obtained by using a gel containing scorodite, and as a result the particles are no longer dependent on the mineralization of aluminum in the form of aluminum oxyhydroxide or hydroxide.

[0008] [Description of the drawing] Figure 1 shows a flowchart of the procedure disclosed in the present invention. Step a consists of neutralization of arsenic waste liquid A with neutralizing agent B to produce pulp, which is transported to separation step b, where the pulp containing solids is transported to step c to obtain gypsum, and the solution is transported to oxidation step d by the addition of oxidizing agent D. The solution obtained from step d is transported to precipitation step e to which iron-based precipitating agent E and neutralizing agent B are added. The obtained pulp is transported to separation step f, where solution F constituting the treated arsenic solution is obtained, and pulp containing arsenic residue is obtained, with the humidity reduced in step g. In step h, an acidic gelling agent G and a basic gelling agent H are mixed. When gelling agents G and H are mixed in step h, the gel is transported to step j to obtain encapsulated arsenic residue J.

[0009] Figure 2 shows the particle size distribution of the arsenic residue obtained after precipitation. Since the precipitate is amorphous, the particle size is fine, reaching an average of 11 microns.

[0010] Figure 3 shows the particle size distribution of the arsenic residue obtained after encapsulation. Since the precipitate is amorphous, the particle size is fine, reaching an average of 10 microns.

[0011] Figure 4 shows the SEM analysis of particles obtained by the arsenic precipitation process with ferric arsenate and subsequent encapsulation with aluminum gel. XRD analysis of the obtained material shows that the solid is amorphous. In the figure, the points highlighted with crosses are composed of FeAs, created by the formula 0.95(FeAsO4)0.05(FeOOH)0.15(AlAsO4)0.1(AlOOH)0.02(CaSO4)0.1(SiO2)0.025(Al2(SO4)3). 1,1 S 0,1 Ca 0,02 Si 0,1 Al 0,3 Give O5

[0012] The process claimed in this invention has shown that by adding aluminum as a stabilizing source, it is possible to provide greater stability to amorphous ferric arsenate while maintaining a Fe / As molar ratio of less than 2. The stabilization is achieved because the aluminum in the gel reacts with some of the arsenic to form aluminum arsenate, which constitutes a stable arsenic residue with a molar ratio of aluminum to arsenic of 2:1. In this sense, both the amorphous ferric arsenate and aluminum arsenate forms result in a synergistic effect that reduces the release of As from the residue to the leaching medium in TCLP tests, as demonstrated in the various applications disclosed in this application.

[0013] [Summary of the Invention] The present invention relates to a process for removing hazardous elements such as arsenic generated from the leaching of metal concentrates or metallurgical residues, or from the smelting or roasting processes of concentrates. These processes generate wastewater from sulfuric acid plants containing hazardous elements, or from arsenic-contaminated water, but all such wastewater is treated to produce arsenic residue that precipitates in a stable manner.

[0014] In a more specific embodiment, the present invention deals with a procedure for reducing arsenic, thereby generating a stable arsenic residue according to hazard testing of TCLP (Total Characteristic Leaching Procedure) and SPLP (Synthetic Precipitation Leaching Procedure).

[0015] In another modification of the present invention, a procedure for recovering an aqueous solution is disclosed, with particular focus on aqueous solutions derived from metallurgical operations that generate flows with an arsenic concentration of less than 10 mg / L.

[0016] In a more specific embodiment, the waste liquid treated by the method claimed in the present invention has a total arsenic concentration in the range of 1 g / L to 15 g / L.

[0017] In a more specific embodiment, the arsenic present in the wastewater may have an arsenite ion concentration in the range of 10 mg / L to 15 g / L.

[0018] In a more specific embodiment, the waste liquid may contain sulfuric acid at a concentration that can vary between 2 g / L and 200 g / L.

[0019] The procedure for removing arsenic from arsenic waste liquid to produce stable arsenic residue includes a first step of neutralization i) in which the arsenic waste liquid is contacted with a first neutralizing agent to produce a first neutralized arsenic waste liquid.

[0020] The arsenic removal procedure includes a second step of oxidation ii) in which As(III) is oxidized to As(V) by the addition of a first oxidizing agent to produce a second oxidized arsenic waste liquid.

[0021] The arsenic removal procedure consists of a third step of Fe(III) / As(V) ratio adjustment iii) in which the second oxidized arsenic waste liquid is mixed with a first ferric solution to produce a third arsenic waste liquid.

[0022] The arsenic removal procedure consists of a fourth step of arsenic precipitation iv) in which the pH of the third arsenic waste liquid is adjusted with a second neutralizing agent to produce a first arsenic residue slurry.

[0023] The arsenic removal procedure includes a fifth step of solid-liquid separation v) in which the first arsenic residue slurry obtained in step iv) is separated to produce a fourth arsenic waste liquid and a first arsenic residue.

[0024] The arsenic removal procedure includes a sixth step of encapsulation vi) in which the first arsenic residue obtained in step v) is mixed with a gel to produce a second arsenic residue.

[0025] In a preferred modification of the present invention, in the neutralization step i), the pH is adjusted to a value that varies within the range of 0.5 to 2.

[0026] In another preferred modification of the present invention, the first neutralizing agent may be selected from one of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, magnesium oxide, magnesium hydroxide, magnesium carbonate, calcium oxide, calcium hydroxide, calcium carbonate or dolomite limestone.

[0027] In another preferred modification of the present invention, the calcium-based neutralizing agent in step i) is prepared as a neutralizing agent slurry in combination with water, and the concentration of the neutralizing agent in the neutralizing agent slurry varies between 15% w / w and 25% w / w.

[0028] In another preferred modification of the present invention, in the first step i), a first neutralized waste liquid slurry is obtained, and the first neutralized waste liquid slurry is sent to a first separation stage to produce a first neutralized arsenic waste liquid and a first residue.

[0029] In another preferred modification of the present invention, the first separation stage includes sub-steps of first concentration, clarification or centrifugation, and the first neutralized waste liquid pulp is subjected to the sub-steps of first concentration, clarification or centrifugation to obtain a first overflow solution and a first concentrated pulp.

[0030] In another preferred modification of the present invention, the first separation stage includes a second filtration sub-step, and the first concentrated pulp is subjected to the second filtration sub-step to produce a first filtration solution and a first residue.

[0031] In another preferred modification of the present invention, the first separation stage consists of a third mixing sub-step in which the first overflow solution and the first filtration solution are supplied to produce a first neutralized arsenic waste liquid.

[0032] In another preferred modification of the present invention, the first residue obtained from step i) is subjected to a leaching step for removing arsenic to produce a second residue slurry.

[0033] In another preferred modification of the present invention, the leaching process is carried out using an acid solution.

[0034] In another preferred modification of the present invention, the acid solution contains sulfuric acid.

[0035] In another preferred modification of the present invention, the concentration of sulfuric acid in the acid solution varies between 10 g / L and 75 g / L.

[0036] In another preferred modification of the present invention, the leaching step is carried out in a temperature range of 40°C to 80°C.

[0037] In another preferred modification of the present invention, the leaching step is carried out when the solid content in the pulp resulting from the mixing of the first residue with the acid solution is 10% w / w to 40% w / w.

[0038] In another preferred modification of the present invention, the second residue pulp is sent to a second separation step to produce a second arsenic waste liquid and a second residue.

[0039] In another preferred modification of the present invention, the second separation step comprises a first concentration, clarification, or centrifugation substep, wherein the second residue pulp is subjected to the first concentration, clarification, or centrifugation substep to obtain a second overflow solution and a second concentrated pulp.

[0040] In another preferred variation of the present invention, the second separation step comprises a second filtration substep, wherein the second concentrated pulp is subjected to the second filtration substep to produce a second filtered solution and a second residue.

[0041] In another preferred modification of the present invention, the second separation step comprises a third mixing sub-step in which a second overflow solution and a second filtration solution are supplied to produce a second arsenic waste liquid.

[0042] In another preferred variation of the present invention, the second residue contains gypsum and constitutes a stable residue.

[0043] In another preferred modification of the present invention, the sodium-based neutralizing agent of step i) is prepared with water at a concentration ranging from 1 mol / L to 10 mol / L.

[0044] In another preferred modification of the present invention, a first neutralized arsenic waste liquid is generated after the addition of a neutralizing agent.

[0045] In another preferred modification of the present invention, in oxidation step ii), the first oxidizing agent is hydrogen peroxide or sodium chlorite. In another preferred modification of the present invention, oxidation step ii) is carried out by supplying hydrogen peroxide in a ratio of 1 mol to 2 mol H2O2 / mol As(III), or sodium chlorite in a ratio of 0.5 mol to 1 mol NaClO2 / mol As(III).

[0046] In another preferred modification of the present invention, in step iii) of adjusting the Fe(III) / As(V) molar ratio, the first ferric solution comprises one of ferric sulfate, ferric chloride, or an iron ore leachate such as hematite, goetite, or magnetite.

[0047] In another preferred modification of the present invention, in step iii) of adjusting the Fe(III) / As(V) molar ratio, the first ferric solution includes a magnetite iron ore leachate in which all ferrous ions have been converted to ferric ions by oxidation with a second oxidizing agent.

[0048] In another preferred modification of the present invention, the second oxidizing agent used to oxidize the ferrous solution containing magnetite iron ore leachate is selected from hydrogen peroxide or sodium chlorite.

[0049] In another preferred modification of the present invention, step iii) of adjusting the Fe(III) / As(V) molar ratio is carried out so that the Fe(III) / As(V) molar ratio is 1 to 1.3.

[0050] In another preferred modification of the present invention, step iv) of arsenic precipitation is carried out at a pH of 2 to 4, for a period of 1 to 24 hours, and at a temperature of 15°C to 25°C.

[0051] In another preferred modification of the present invention, step iv) of arsenic precipitation is performed by selecting a second neutralizing agent from one of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, magnesium oxide, magnesium hydroxide, magnesium carbonate, magnesium carbonate, calcium oxide, calcium hydroxide, calcium carbonate, or dolomite limestone.

[0052] In another preferred modification of the present invention, step iv) of arsenic precipitation is performed by selecting a second neutralizing agent from one of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, magnesium oxide, magnesium hydroxide, or magnesium carbonate.

[0053] In another preferred modification of the present invention, step v) of solid-liquid separation is carried out in a first concentration, clarification or centrifugation substep, and the first arsenic residue pulp is subjected to the first concentration, clarification or centrifugation substep to obtain a third overflow solution and a third concentrated pulp.

[0054] In another preferred modification of the present invention, step v) of solid-liquid separation is performed after a second filtration sub-step, and a third concentrated pulp is subjected to the second filtration sub-step to produce a third filtered solution and a first arsenic residue.

[0055] In another preferred modification of the present invention, step v) of solid-liquid separation is carried out after a third mixing sub-step in which a third overflow solution and a third filtration solution are supplied to produce a fourth arsenic wastewater.

[0056] In another preferred modification of the present invention, in step vi) encapsulation, the gel into which the first arsenic residue is mixed is 3 + It is prepared from a mixture containing an aqueous solution of a valence metal salt and an aqueous solution of an alkaline earth metal.

[0057] In a more specific embodiment, 3 +The metal salt of valence is selected from one of ferric sulfate, ferric chloride, anhydrous aluminum sulfate, aluminum sulfate tetradecahydrate, aluminum sulfate octadecahydrate or aluminum chloride.

[0058] In a more specific embodiment, 3 + The metal salt of valence is aluminum sulfate.

[0059] In another specific embodiment, the aqueous solution of aluminum sulfate is prepared at a concentration equal to 2N.

[0060] In another specific embodiment, the aqueous solution of the alkaline earth metal, corresponding to a solution of sodium hydroxide, is prepared at a concentration equal to 5M.

[0061] In another preferred variant, the gel is prepared by adding an aqueous solution of a metal salt of valence 3 and an aqueous solution of an alkaline earth metal in a volume such that the molar ratio of the alkaline earth metal to the metal salt of valence 3 is 2 to 3. + In another preferred variant, the gel is provided such that the molar ratio of the metal of valence 3 to the total As contained in the first arsenic residue is within the range of 0.1 to 0.3. + In another preferred variant, the gel is prepared by adding an aqueous solution of a metal salt of valence 3 and an aqueous solution of an alkaline earth metal in a volume such that the molar ratio of the alkaline earth metal to the metal salt of valence 3 is 2 to 3.

[0062] In another preferred variant, the gel is provided such that the molar ratio of the metal of valence 3 to the total As contained in the first arsenic residue is within the range of 0.1 to 0.3. + In another preferred variant, the gel is provided such that the molar ratio of the metal of valence 3 to the total As contained in the first arsenic residue is within the range of 0.1 to 0.3.

[0063] Those having average knowledge in the technical field understand that there may be a plurality of solid-liquid separation steps applicable to the present invention that enable separation of the solid phase from the liquid phase, and here, even if such alternatives are applied, they do not depart from the subject matter claimed by the present invention.

[0064] 〔Application Examples〕 The following application examples should be considered as aspects of the present invention, and since possible different applications are covered within the scope of the claims of this application, in no case should they be considered as limiting the present invention.

[0065] 〔Neutralization〕 Application Examples 1 to 7 3500 mL of arsenic solution was prepared with arsenic(III) concentrations of 12 g / L and sulfuric acid concentrations of 70 g / L and 150 g / L. These solutions were placed in a 5 L glass reactor, and CaCO3 or Ca(OH)2 was added to adjust the pH to a range of 1-2. The pH was then measured using an Ag / AgCl electrode. The reactor was stirred at 300 rpm for 2 hours at room temperature. After the reaction time, the pulp was subjected to a solid-liquid separation process by filtration. The solid was washed with an acidic solution at pH 1, and subsequent TCLP analysis was performed. The results are shown in Table 1.

[0066] [Table 1]

[0067] Application Examples 8-21 3500 mL of arsenic solution with a sulfuric acid concentration of 10 g / L to 150 g / L was prepared and mixed with gypsum obtained under the conditions of Application Example 7 to adjust the solid content to 10% w / w to 40% w / w. The reactor was stirred at 300 rpm for 2 hours at a temperature between 20°C and 80°C. At the end of the reaction time, the pulp was subjected to a solid-liquid separation process by filtration. The solid was washed with an acidic solution at pH 1, and subsequent TCLP analysis was performed. The results are shown in Table 2.

[0068] [Table 2]

[0069] [Oxidation of arsenite ions] Application Examples 22 and 23 4500 mL of a pH 2 arsenic solution with an arsenic(III) concentration of 10 g / L and a sulfuric acid concentration of 2 g / L, prepared according to Application Examples 1-5), was placed in a 5 L glass reactor. 30% w / w hydrogen peroxide was added at a rate of 1.1 mol H2O2 / mol As(III), and 80% w / w sodium chlorite was added at a rate of 0.5 mol NaClO2 / mol As(III). The solution was stirred at 400 rpm for 30 minutes at 20°C. The results are shown in Table 3.

[0070] [Table 3]

[0071] Application Examples 24-29 4500 mL of sulfuric acid plant wastewater (pH 2 solution from Application Examples 1-5) with arsenic(III) concentrations of 8.5 g / L to 12 g / L and sulfuric acid concentration of 2 g / L was prepared and placed in a 5 L glass reactor. 50% w / w hydrogen peroxide was added at a ratio of 1.0 to 1.9 mol H2O2 / mol As(III). The solution was stirred at 400 rpm for 30 minutes at 20°C. The results are shown in Table 4.

[0072] [Table 4]

[0073] [Arsenic Reduction] Application Examples 30-45 3500 mL of arsenic solution (derived from Application Examples 1-5, oxidized according to the conditions of Test 28, pH 2) with an As(V) concentration of 10 g / L and a sulfuric acid concentration of 2 g / L was prepared and placed in a 5 L glass reactor. Magnetite leachate (concentrations of 156 g / L Fe and 40 g / L Fe(II)) was added to maintain the Fe(III) / As(V) molar ratio at 1.1 mol to 2 mol Fe(III) / mol As(V). The pH of the solution was adjusted to within the range of 2 to 4 by adding a sodium hydroxide solution prepared to a concentration of 10 mol / L, a 25% w / w lime slurry, or an 18% w / w dolomite limestone slurry, as measured using an Ag / AgCl pH electrode. The reactor was stirred at 400 rpm for 6 hours at 20°C. After the reaction time, the pulp was subjected to a solid-liquid separation process by filtration. The results are shown in Table 5.

[0074] [Table 5]

[0075] Application Examples 46-51 3500 mL of arsenic solution (oxidized according to the conditions of Test 28, from Application Examples 1-5, with pH 2) containing 10 g / L As(V) and 2 g / L sulfuric acid was prepared and placed in a 5 L glass reactor. Aluminum sulfate tetrahydrate was added to maintain the Al(III) / As(V) molar ratio at 1.1 mol to 2 mol / mol. The solution was adjusted to pH 5 by adding a 10 mol / L sodium hydroxide solution and 25% w / w Ca(OH)2 as needed. The reactor was stirred at 400 rpm for 6 hours at room temperature. After the reaction time, the pulp was subjected to a solid-liquid separation process by filtration. The results are shown in Table 6.

[0076] [Table 6]

[0077] [Stabilization] Application Examples 52-64 Ten milliliters of 2N aluminum sulfate solution and ten milliliters of 5M sodium hydroxide solution were taken and stirred with a stainless steel impeller. After stirring for 10 to 20 seconds, once a gel had formed, the arsenic residue precipitated according to Application Examples 30 to 45 was added, maintaining the ratio of gel volume to arsenic residue mass at 0.09 mL / g to 0.48 mL / g. After mixing with a glass rod for 5 minutes, the sample was placed in a mold and dried at humidity and 20°C for 7 days. The results are shown in Table 7.

[0078] [Table 7]

[0079] Application Example 65 Precipitation of sulfuric acid plant wastewater, which had been pre-oxidized to pH 2 with a ratio of 1.6 mol H2O2 / mol As(III) according to the conditions of Application Example 7, was carried out. The arsenic concentration was 8.5 g / L. This solution was placed in a 100 L reactor, and magnetite leachate with a Fe concentration of 156 g / L and an Fe(II) concentration of 40 g / L was added to adjust the Fe(III) / As(V) ratio to 1.1 mol / mol. The solution was adjusted with 18% w / w CaCO3 and maintained at pH 4 for 6 hours while stirring at 400 rpm. Subsequently, the pulp was filtered through a plate filter, and the solid with a water content of 20% was mixed with gels prepared from equal volumes of 2N aluminum sulfate solution and 5M sodium hydroxide solution, so that the gel volume:arsenic residue ratio (Gel / ReAs) was 0.1 mL / g to 0.2 mL / g. The results are shown in Tables 8 to 11.

[0080] [Table 8] [Table 9] [Table 10] [Table 11]

[0081] The results of Application Example 65 demonstrate that a high removal yield can be obtained using a donated molar amount with an Fe / As ratio equal to 1.1, which indicates that encapsulation of the aluminum gel with a donated amount of 0.1 mL to 0.2 mL gel / g arsenic residue provides stability in terms of the As concentration released in the TCLP test. [Brief explanation of the drawing]

[0082] [Figure 1]A flowchart of the procedure disclosed by the present invention is shown. Step a consists of neutralization of arsenic waste liquid A with neutralizing agent B to produce pulp, which is transported to separation step b, where the pulp containing solids is transported to step c to obtain gypsum, and the solution is transported to oxidation step d by the addition of oxidizing agent D. The solution obtained from step d is transported to precipitation step e to which iron-based precipitating agent E and neutralizing agent B are added. The obtained pulp is transported to separation step f to obtain solution F which constitutes the treated arsenic solution, and in step g the humidity is reduced to obtain pulp containing arsenic residue. In step h, an acidic gelling agent G and a basic gelling agent H are mixed. When gelling agents G and H are mixed in step h, the gel is transported to step j to obtain encapsulated arsenic residue J. [Figure 2] The particle size distribution of the arsenic residue obtained after precipitation is shown. Since the precipitate is amorphous, the particle size is fine, reaching an average of 11 microns. [Figure 3] The particle size distribution of the arsenic residue obtained after encapsulation is shown. Since the precipitate is amorphous, the particle size is fine, reaching an average of 10 microns. [Figure 4] This figure shows SEM analysis of particles obtained by the arsenic precipitation process with ferric arsenate and subsequent encapsulation with aluminum gel. XRD analysis of the obtained material reveals that the solid is amorphous. The points highlighted with crosses in the figure represent the composition FeAs1,1S0,1Ca0,02Si0,1Al0,3O5, generated by the formula 0.95(FeAsO4)0.05(FeOOH)0.15(AlAsO4)0.1(AlOOH)0.02(CaSO4)0.1(SiO2)0.025(Al2(SO4)3).

Claims

1. A procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue: i) A first neutralization step i) to bring the arsenic waste liquid into contact with a first neutralizing agent to produce a first neutralized arsenic waste liquid; ii) The second oxidation step ii) is in which As(III) is oxidized to As(V) by the addition of the first oxidizing agent, producing a second oxidized arsenic waste liquid; iii) The third step of adjusting the Fe(III) / As(V) molar ratio involves mixing the second arsenic oxide waste liquid with the first ferric solution to produce a third arsenic waste liquid; iv) The fourth step of arsenic precipitation, in which the pH of the third arsenic waste liquid is adjusted with the second neutralizing agent to produce the first arsenic residue slurry; v) A fifth solid-liquid separation step v) to separate the first arsenic residue slurry obtained from step iv) to produce a fourth arsenic waste liquid and a first arsenic residue; and The procedure is characterized by comprising a sixth step vi) of encapsulation, in which the first arsenic residue obtained in step v) is mixed with the gel to produce a second arsenic residue.

2. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, as described in claim 1, characterized in that in the neutralization step i), the pH is adjusted to a value that changes within the range of 0.5 to 2.

3. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claims 1 to 2, characterized in that the first neutralizing agent may be selected from one of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, potassium carbonate, magnesium oxide, magnesium hydroxide, magnesium carbonate, magnesium carbonate, calcium oxide, calcium hydroxide, calcium carbonate, or dolomite limestone.

4. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 3, characterized in that the calcium-based neutralizing agent of step i) is prepared as a neutralizing agent slurry with water (step A), and the concentration of the neutralizing agent in the neutralizing agent slurry changes from 15% w / w to 25% w / w.

5. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, characterized in that in the first step i), a first neutralization wastewater slurry is obtained and sent to a first separation step to produce a first neutralized arsenic wastewater and a first residue, as described in claim 1.

6. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 5, characterized in that the first separation step comprises a first concentration, clarification or centrifugation substep to which the first neutralized wastewater slurry is supplied to obtain a first overflow solution and a first concentrated pulp; a second filtration substep to which the first concentrated pulp is supplied to produce a first overflow solution and a first filtered solution; and a third mixing substep to which the first overflow solution and the first filtered solution are supplied to produce the first neutralized arsenic wastewater.

7. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 5, characterized in that the first residue obtained from step i) is subjected to a leaching step for removing arsenic in order to produce a second residue slurry.

8. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, as described in claim 7, characterized in that the leaching step is carried out using a sulfuric acid solution, the concentration of sulfuric acid in the solution varies from 10 g / L to 75 g / L, the leaching step is carried out at a temperature that varies from 40°C to 80°C, and the solid content in the pulp obtained by mixing the first residue with the sulfuric acid solution varies from 10% w / w to 40% w / w.

9. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 7, characterized in that the second waste slurry is sent to a second separation step to produce a second arsenic wastewater and a second waste.

10. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 9, characterized in that the second separation step comprises a first concentration, clarification or centrifugation substep to which the second waste slurry is supplied to obtain a second overflow solution and a second concentrated pulp; a second filtration substep to which the second concentrated pulp is supplied to produce a second filtered solution and a second residue; and a third mixing substep to which the second overflow solution and the second filtered solution are supplied to produce a second arsenic wastewater.

11. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 10, characterized in that the second waste contains gypsum and constitutes a stable waste.

12. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, as described in claim 3, characterized in that the sodium-based neutralizing agent in step i) is prepared with water to a concentration in the range of 1 mol / L to 10 mol / L.

13. A procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claims 1 to 12, characterized in that the first neutralized arsenic wastewater is produced after the addition of the neutralizing agent.

14. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, as described in claim 1, characterized in that the first oxidizing agent in step ii) is hydrogen peroxide or sodium chlorite.

15. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, as described in claim 1, characterized in that in step ii) of oxidation, the amount of hydrogen peroxide donated is 1 mol to 2 mol H₂O₂ / mol As(III), and in the case of the amount of sodium chlorite donated, it is 0.5 mol to 1 mol NaClO₂ / mol As(III).

16. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 1, characterized in that, in step iii) adjusting the Fe(III) / As(V) molar ratio, the first ferric solution contains one of ferric sulfate, ferric chloride, or an iron ore leachate such as hematite, goetite, or magnetite.

17. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 16, characterized in that, in step iii) adjusting the Fe(III) / As(V) molar ratio, the first ferric solution contains a magnetite iron ore leachate in which all ferrous ions have been converted to ferric ions by oxidation with a second oxidizing agent.

18. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 17, characterized in that the second oxidizing agent involved in oxidizing the first ferric solution containing magnetite iron ore leachate is selected from one of hydrogen peroxide or sodium chlorite.

19. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 1, characterized in that step iii) is carried out with a Fe(III) / As(V) molar ratio of 1 to 1.

3.

20. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, characterized in that step iv) arsenic precipitation is carried out at a pH of 2 to 4; over a period of 1 to 24 hours; and at a temperature of 15°C to 25°C, according to claim 1.

21. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 1, characterized in that in step iv) of arsenic precipitation, the second neutralizing agent is selected from one of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, magnesium oxide, magnesium hydroxide, magnesium carbonate, magnesium carbonate, calcium oxide, calcium hydroxide, calcium carbonate, or dolomite limestone.

22. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 1, characterized in that in step iv) of arsenic precipitation, the second neutralizing agent is selected from sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, potassium carbonate, magnesium oxide, magnesium hydroxide, or magnesium carbonate.

23. Step v) of solid-liquid separation is characterized by comprising: a first sub-step of concentration, clarification or centrifugation to obtain a third overflow solution and a third concentrated pulp; a second filtration sub-step to produce a third filtered solution and the third concentrated pulp; and a third mixing sub-step to produce a fourth arsenic wastewater, the procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 1.

24. In the encapsulation step vi), the gel into which the first arsenic residue is mixed is 3 ＋ A procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 1, characterized in that it is prepared from a mixture containing an aqueous solution of a valence metal salt and an aqueous solution of an alkaline earth element.

25. The third ＋ The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 24, characterized in that the valence metal salt is selected from one of ferric sulfate, ferric chloride, anhydrous aluminum sulfate, aluminum sulfate tetrahydrate, aluminum sulfate octahydrate, or aluminum chloride.

26. The third ＋ The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 25, characterized in that the valence metal salt is preferably anhydrous aluminum sulfate, aluminum sulfate tetrahydrate, or aluminum sulfate octahydrate.

27. The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 24, characterized in that the aqueous solution of the alkaline earth metal corresponds to a sodium hydroxide solution.

28. Alkaline earth metals 3 ＋ The molar ratio of the valence to the metal is 2 to 3. ＋ The gel is prepared by adding the volume of an aqueous solution of a valence metal and the volume of an aqueous solution of an alkaline earth metal; preferably, 3 ＋ The procedure for removing arsenic from arsenic wastewater to produce a stable arsenic residue, according to claim 24, characterized in that the gel is provided such that the molar ratio of the valence metal to the total arsenic contained in the first arsenic residue is within the range of 0.1 to 0.3.

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