Method for stabilizing arsenic-containing residues by thermally stabilizing precipitated hydroarsenite

Abstract

The present invention discloses a method for stabilizing arsenic-containing residues by thermal stabilization of precipitated hydroarsenite, the method comprising the steps of: a first step of neutralization in which arsenic-containing wastewater is contacted with a first neutralizing agent to produce a first neutralized arsenic-containing wastewater; a second step of adjusting the Fe (III) / As (III) ratio, wherein the first neutralized arsenic-containing wastewater is mixed with a first iron solution to produce a third arsenic-containing wastewater; a third step of arsenic precipitation in which the pH of the third arsenic-containing wastewater is adjusted with a second neutralizer to produce a first arsenic-containing residue slurry; a fourth step of solid-liquid separation, wherein the first arsenic-containing residue slurry is separated to generate fourth arsenic-containing wastewater and a first arsenic-containing residue; a fifth step of calcining, wherein the first arsenic-containing residue is calcined to generate a second arsenic-containing residue; a sixth step of washing, wherein the second arsenic-containing residue is washed with an aqueous solution to generate a second arsenic-containing residue slurry; and a seventh step of solid-liquid separation, wherein the second arsenic-containing residue slurry is separated to produce a fifth arsenic-containing wastewater and a stable third arsenic-containing residue in the form of fisheyanite. The invention solves the technical problem of removing arsenic from arsenic-containing wastewater to produce stable arsenic-containing residues, and the synthesis of these arsenic-containing residues does not require an oxidation stage to oxidize arsenite ions into arsenate ions and does not require heating in a precipitation stage.

Description

Technical Field

[0001] The invention solves the technical problem of removing arsenic from arsenic-containing wastewater to produce stable arsenic-containing residues, the synthesis of which does not require an oxidation stage to oxidize arsenite ions into arsenate ions, nor does it require heating during the precipitation stage. Background Art

[0002] Since arsenic is widely distributed in more than 320 minerals, it is commonly found in the acid dissolution of arsenic-containing ores generated by dilute acid scrubbing flue gases from mining and metallurgical operations and calcination and smelting of copper concentrates. The wastewater generated by the above two processes has a very low pH value of about 1.0 and a high arsenic content in the range of 3g / L-10g / L, which is the most toxic inorganic form in polluted water and is considered to be 25-60 times more toxic than As(V). Compared with As(V), the removal of As(III) in water treatment is technically more difficult because As(III) has a higher mobility and solubility (Paikaray, S., J., & Peiffer, S. (2012). As(III) retention kinetics, equilibrium and redoxstability on biosynthesized schwertmannite and its fate and control on schwertmannite stability on acidic (pH 3.0) aqueous exposure. Chemosphere, 86 (6), 557-564.). Effective and direct removal of As(III) is a major challenge, especially at pH values ​​around 1. Various treatment methods have been used to remove arsenic in different media, such as precipitation, adsorption, ion exchange and membrane separation. For the removal of high-concentration arsenic, chemical precipitation seems to be more suitable and economical, while the other three methods are usually used when the arsenic concentration is low due to their cost and capacity. Traditional arsenic precipitation methods include neutralization with lime, co-precipitation with iron ions and sulfide precipitation. However, all of these methods are not suitable for the treatment of arsenic contents above 30% w / w. During the lime neutralization process, the pH must be adjusted to 12 to remove the arsenic in the form of calcium arsenate and calcium arsenite, where the arsenic content is relatively low, at 5%-15%. Therefore, large amounts of lime are required, and large amounts of sludge are generated, which is not completely safe to store, and the arsenic is subsequently released into the solution. Co-precipitation with iron ions is a special method for removing arsenates, however, large amounts of oxidants must be used to convert As(III) to As(V). Sulfide precipitation can directly remove As(III) in the form of As2S3, but this poses great operational challenges due to the formation of hydrogen sulfide and the need for additional treatment to provide environmental stability.

[0003] Copper smelters use various treatment operations to remove arsenic from WAWs, the most common of which is co-precipitation with iron (Fe:As molar ratio >3) and lime neutralization to form arsenic-containing ferrihydrite [As(V)-ferrihydrite: As(V)-Fh]. However, As(V)-Fh has been designated as the Best Available Demonstrated Technology (BDAT) for the removal of arsenic from acidic ore processing wastewater by the United States Environmental Protection Agency (US EPA). However, this treatment method involves the generation of large amounts of sludge, high iron demand, low As content (6%), and the need to oxidize As(III) to As(V) species prior to precipitation. In addition, the long-term stability of As(V)-Fh is also a concern, as the ferrihydrite contained in As(V)-Fh may convert to goethite and ultimately hematite, thereby releasing arsenic into solution. In addition, in anoxic environments, As(V)-Fh can be reduced, leading to the reductive dissolution of ferrihydrite or As(V) and the migration of arsenic (Pedersen, HD, Postma, D., & Jakobsen, R. (2006). Release of arsenic associated with the reduction and transformation of iron oxides. Geochimica et Cosmochimica Acta, 70(16), 4116-4129).

[0004] Scorodite (FeAsO4×2H2O) is generally considered to be the most suitable removal solution for As fixation because of its high arsenic removal efficiency, high arsenic content (30%), low iron requirement (Fe:As=1) and low solubility in the pH range of 2.8 to 5.3. In addition, scorodite has good sedimentation and filtration properties due to its crystalline nature. Professor George Demopoulos has developed a new method for fixing arsenic from metallurgical weak acidic wastewater by atmospheric precipitation of scorodite at 95°C under ambient pressure and supersaturation control conditions (Demopoulos, GP (2005). On the preparation and stability of scorodite. Arsenic metallurgy, 25-50), which has been implemented on an industrial scale by EcoMetales. This method is currently being operated in Calama, Chile, for the removal of arsenic from smelter dust leachate. However, given the high costs associated with energy supply and oxidant requirements, there is a need to investigate an alternative stabilization scheme with low solubility, low iron demand, high arsenic removal efficiency, and good filterability for arsenic removal from WAW in copper smelters.

[0005] Tooeleite, a ferrous sulfate arsenite hydrate ((Fe2O3)6(As2O3)5(SO3)2*12H2O), has been proposed as a potential removal solution for the removal and fixation of As(III) species from weakly acidic wastewater. Tooeleite can be considered as the scorodite equivalent of As(III) and is considered by the industry to be the most suitable medium for arsenic removal. Tooeleite has high arsenic content (25%), high arsenic removal efficiency, low iron demand (Fe:As=1.2), and is easily precipitated under ambient conditions. The structure of Tooeleite is formed by FeO6 octahedra (connected by AsO3 cones at corners and edges) and sulfate tetrahedra (which occupy the interlayer space), which lays a solid foundation for understanding the formation of Tooeleite and suggests a highly promising method for the removal and stabilization of high As(III) (up to 25% As content). According to Morin's research, the chemical structure of tooeleite is (Fe2O3)6(As2O3)5(SO3)2*12H2O, and its Fe / As ratio is 1.2. Synthesized tooeleite is stable between pH 2.0 and 3.5, and it will transform into arsenic ferrihydrite (As(III)-Fh) above pH 3.5. Since tooeleite is only stable within a narrow pH range, it is necessary to store it in a lined pool and continuously monitor and maintain acidic conditions (Morin, G., Rousse, G., & Elkaim, E. (2007). Crystal structure of tooeleite, Fe6(AsO3)4SO4(OH)4-×4H2O, a new iron arsenite oxyhydroxy-sulfate mineral relevant to acid mine drainage. American Mineralogist, 92(1), 193-197).

[0006] Hydrotalcite is a mineral belonging to the carbonate family. It is composed of carbonate, hydroxyl group, molecular water, magnesium and aluminum, arranged in a clear molecular crystal structure. In nature, it mainly coexists with dolomite deposits. The general chemical formula of hydrotalcite is ([M1-x2+Mx3+(OH)2]x+(An-)x / n-mH2O), where M corresponds to divalent (+2 charge) and trivalent (+3 charge) cations; A corresponds to -2 charge anions, and the value of x is defined by the ratio: x=M^(3+) / (M^(3+)+M^(2+)).

[0007] These compounds have a positively charged H2+(OH)2 layer surrounded by water molecules (H2O) and anions such as CO3 2- 、NO3 - , Cl - These types of structures are called double layer hydroxides (LDH). They have a structure derived from brucite (Mg(OH)2). The brucite layer is neutral and the Mg 2+ The cations are octahedrally coordinated via OH-groups, with the octahedra sharing edges. Residual positive charges are generated by replacing divalent cations (+2 charge) with trivalent cations (+3 charge) in these layers. For stability, these layers require anions to be incorporated between the layers for the removal of negatively charged impurities from the solution of interest. The large interlayer area, as well as the possibility of many exchangeable anions, makes hydrotalcites ideal for industrial applications in single adsorption and ion exchange operations.

[0008] Typical hydrotalcites contain Al as +3 charged cations and Mg as +2 charged cations, while typical anions are carbonate, CO3 2- In the case of these cations, the literature reports that they have a high affinity for removing arsenic from aqueous streams. Furthermore, hydrotalcite has a 10-fold higher affinity for removing arsenic than other minerals such as hematite and goethite.

[0009] Regarding the cations that make up the crystal structure, they can be of different types (Mg, Ni, Fe, Co, Cu, Zn, Mn as divalent cations, and Al, Fe, Sc, Ga, Cr, Mn, Ni, Co), while the typical anion is Cl - 、NO 3- 、SO4 2- and CO3 2- These ions determine the impurity removal or absorption capacity of the solid. Furthermore, the removal capacity of the target impurity will depend on the size of the anion in question, its charge density (higher charge density means higher interaction with the layer), pH, and temperature.

[0010] CL 2620-2001 is aimed at the thermal conversion of amorphous ferric arsenate [basic iron (III) arsenate] into scorodite [FeAsO4×2H2O] by thermal conversion of amorphous ferric arsenate precipitates generated in the treatment of arsenic-containing wastewaters, smelter dusts, refinery wastes, arsenic-containing sludges and other processes generating any arsenic-containing wastewaters. The document CL 2620-2001 represents the state of the art as it is directed to arsenic stabilization processes based on the formation of scorodite (FeAsO4×2H2O).

[0011] Document CL 50423 relates to a method for removing wastes and liquid wastewaters with a high content of pollutants, such as arsenic and other substances, in hydrometallurgical treatment plants. The document discloses a method for the removal of arsenic and antimony, for the environmental stabilization of liquid wastewaters and solid wastes with a high concentration of arsenic, comprising the following stages: leaching of furnace dust, oxidation of As(III) present in the rich stream to As(V), adjustment of the ratio of Fe(III) to As(T), adjustment of the pH of the solution by adding a neutralizing agent, solid-liquid separation, wherein a liquid stream free of arsenic (As) and rich in Cu is obtained, which passes through an electrowinning process, and the solids stabilized in the form of scorodite and gypsum are confined in a suitable waste dump. Document CL 50423 represents the prior art, since it is directed to an arsenic stabilization process based on the formation of scorodite (FeAsO4×2H2O).

[0012] Patent application CL 1684-2021 aims at obtaining a final residue with a high content of stable arsenic. The document CL1684-2021 discloses a method for obtaining a mining or industrial residue (comprising copper, arsenic and optionally iron, antimony and / or bismuth) containing iron arsenate and / or scorodite with a high arsenic content from a highly acidic solution having an acid concentration higher than 45 g / L, the method comprising the following stages: neutralization to produce gypsum, oxidation of arsenite ions to arsenate ions in two stages, adjustment of the molar ratio of iron ions to arsenate ions, recycling of scorodite slurry, heating to a temperature between 50°C and 90°C, acidity adjustment and solid-liquid separation. Document CL 1684-2021 represents the prior art, since it aims at an arsenic stabilization process based on the formation of scorodite (FeAsO4×2H2O).

[0013] Document CA 2066905 discloses a method for reducing the arsenic content in a solution containing sulfuric acid, water and arsenic acid, comprising the steps of producing copper arsenate, separating the precipitated copper arsenate from the resulting solution, adjusting the iron / arsenic molar ratio by adding soluble iron sufficient to reduce the amount of residual arsenic in the solution; separating the iron arsenate. CA 2066905 merely represents the prior art based on reducing the arsenic content in arsenic-containing solutions.

[0014] The paper Opio, FK (2013). Investigation of Fe(III)-As(III) bearing phases and their potential for arsenic disposal. Queen's University (Canada) describes the investigation of Fe(III)-As(III) bearing phases and their potential for arsenic disposal, and chapter 2.11 describes Tooeleite and its properties and synthesis. In other respects, this document only represents the state of the art based on the investigation of Fe(III)-As(III) bearing phases and their potential for arsenic disposal.

[0015] The present invention is novel and inventive, since none of the cited prior art documents relates to a method for forming a stable arsenic-containing residue based on Tooeleite, which is ferrous sulfate arsenite hydrate [(Fe2O3)6(As2O3)5(SO3)2×12H2O], from an initial stage comprising contact of arsenic-containing wastewater with a neutralizing slurry, and after a separation-leaching-separation stage, continuing with a stage of contact of the arsenic-containing solution with an iron solution and a neutralizing agent, wherein the arsenic-containing residue slurry begins to precipitate, after a solid-liquid separation step, an arsenic-containing residue is generated, the arsenic-containing residue is subjected to a continuous and necessary heat treatment at a temperature of 450° C. to 650° C., and then continues with washing and separation stages to obtain a stable arsenic-containing residue based on Tooeleite. The present invention solves the technical problem of generating a stable arsenic-containing residue, the precipitation of which involves a phase of a compound with arsenate ions. In the prior art, methods for precipitation of arsenite ions are known, such as calcium arsenite or arsenic trisulfide, which are arsenic-containing residues that are unstable in terms of As leaching in environmental stability tests (such as TCLP). The present invention makes it possible to precipitate arsenic-containing residues containing arsenite ions, and by a stabilization step including calcination, the resulting arsenic-containing residue is stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1A flow chart of a method for removing arsenic from arsenic-containing wastewater disclosed in the present invention is shown. Stage I shows the first step of neutralizing the arsenic-containing wastewater (1), to which a neutralizer solution or slurry prepared by a neutralizer (3) and water (2) from stage A is added. Next, by adding an iron solution (which is prepared in stage B by adding water (2), an iron source (5) and finally sulfuric acid (4)), the solution enters the second step of adjusting the Fe(III) / As(III) ratio. The adjusted solution is transported to the third step (iii) Tooeleite precipitation, and its slurry is separated in the fourth step (iv). The solid obtained in the fifth step (v) is transported to the calcination stage, and then to the sixth step (vi) water washing (2) and the seventh step (vii) solid-liquid separation to generate an arsenic-containing residue (6) of stabilized Tooeleite. In an optional aspect, the solution obtained in the fourth step (iv) is conveyed to the seventh step (vii) for purification, the metal solution prepared in step C by adding water (2), the first transition metal salt (7) and the second transition metal salt (8), and the neutralizer solution or slurry from step A are added, and the final slurry is conveyed to the ninth step (ix) for solid-liquid separation to generate a fourth arsenic-containing residue (9) and treated wastewater (10).

[0017] Figure 2 The X-ray diffraction pattern (XRD) of Tooeleite precipitated with NaOH by the method disclosed in the present invention is shown, wherein the XRD pattern obtained by synthesis with NaOH shows a broad band between 10°2θ and 34°2θ, which can be attributed to the adsorption of As(III). The XRD pattern shows that the diffraction peaks at 10.0°; 32.0° and 34.0° gradually increase, marked by the indices (020), (200) and (061) of the Tooeleite phase, indicating that the mineral composition changes from ferrihydrite to ferrihydrite.

[0018] Figure 3 The X-ray diffraction pattern (XRD) of Tooeleite precipitated with calcium carbonate by the method disclosed in the present invention is shown, wherein the XRD pattern obtained by synthesis with CaCO3 shows a broad band between 10°2θ and 34°2θ, which can be attributed to the adsorption of As(III). The XRD pattern shows that the diffraction peaks at 10.0°; 32.0° and 34.0° gradually increase, marked with the indices (020), (200) and (061) of the Tooeleite phase, indicating that the mineral composition changes from ferrihydrite to ferrihydrite. In addition, characteristic diffraction peaks of gypsum are observed at 14.0°2θ and 24.0°2θ, which is a natural phenomenon that sulfate is precipitated as gypsum in the presence of calcium. Summary of the invention

[0019] The present invention relates to a method for removing harmful elements, such as arsenic, which are generated from the leaching of metal concentrates or metallurgical residues, or from the smelting or roasting of concentrates, wherein the waste water is generated from sulfuric acid plants containing harmful elements, or from arsenic-contaminated water, wherein all these waste waters are treated to produce an arsenic-containing residue, which is precipitated in a stable manner.

[0020] In a more specific aspect, the present invention relates to an arsenic removal method, wherein a stable arsenic-containing residue is generated according to TCLP (Total characteristic leaching procedure) and SPLP (Syntetic precipitation leaching procedure) hazard tests.

[0021] In another variation of the invention, a method of recovering aqueous solutions is disclosed, with particular interest in aqueous streams generated from metallurgical operations having arsenic concentrations below 200 mg / L.

[0022] In another variation of the invention, a method of recovering aqueous solutions is disclosed, with particular interest in water streams generated from metallurgical operations having arsenic concentrations below 10 mg / L.

[0023] In a more specific aspect, the wastewater treated by the presently claimed method has an arsenic concentration of 1 g / L to 15 g / L total arsenic.

[0024] In a more specific aspect, arsenic present in the wastewater can have an arsenite ion concentration of 10 mg / L to 15 g / L.

[0025] In a more specific aspect, the wastewater can contain sulfuric acid at a concentration between 2 g / L and 200 g / L.

[0026] The method for removing arsenic includes a first step i, neutralization, in which the arsenic-containing wastewater is contacted with a neutralization initiator to generate a first neutralized arsenic-containing wastewater.

[0027] The method for removing arsenic includes a second step ii of adjusting the Fe(III) / As(III) ratio, wherein the first neutralized arsenic-containing wastewater is mixed with the first iron solution to generate a third arsenic-containing wastewater.

[0028] The method for removing arsenic includes a third step iii arsenic precipitation, wherein the pH of the third arsenic-containing wastewater is adjusted with a second neutralizing agent to generate a first arsenic-containing residue slurry.

[0029] The method for removing arsenic includes a fourth step iv of solid-liquid separation, wherein the first arsenic-containing residue slurry is separated to generate a fourth arsenic-containing wastewater and the first arsenic-containing residue.

[0030] The method for removing arsenic includes a fifth step v. calcination, wherein the first arsenic-containing residue is calcined to generate a second arsenic-containing residue.

[0031] The method for removing arsenic includes a sixth step vi of washing, wherein the second arsenic-containing residue is washed with an aqueous solution to form a second arsenic-containing residue slurry.

[0032] The method for removing arsenic includes a seventh step vii of solid-liquid separation, wherein the second arsenic-containing residue slurry is separated to generate a fifth arsenic-containing wastewater and a third arsenic-containing residue.

[0033] The method for removing arsenic includes an eighth step (vii) of purification, wherein the fourth arsenic-containing wastewater and the fifth arsenic-containing wastewater are treated with a precipitation solution and a third neutralizing agent to generate a third arsenic-containing residue slurry.

[0034] The method for removing arsenic includes a ninth step of solid-liquid separation, in which the third arsenic-containing residue slurry is separated to generate a fifth arsenic-containing wastewater and a fourth arsenic-containing residue.

[0035] In a preferred variant of the invention, in the neutralization step i, the pH value is adjusted to a value in the range from 0.5 to 2.

[0036] In another preferred variation 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 dolomitic limestone.

[0037] In another preferred variant of the present invention, the calcium-based neutralizer of step i is formulated into a neutralizer slurry with water (step A), wherein the concentration of the neutralizer in the neutralizer slurry is between 15% w / w and 25% w / w.

[0038] In another preferred variant of the present invention, in the neutralization step i, a first neutralized wastewater slurry is generated.

[0039] In another preferred variant of the invention, the first neutralized wastewater slurry is conveyed to a first separation stage to generate a first neutralized arsenic-containing wastewater and a first residue.

[0040] In another preferred variant of the invention, the first separation stage comprises a first concentrating, clarifying or centrifuging sub-stage, to which the first neutralized wastewater slurry is subjected to obtain a first overflow solution and a first concentrated slurry.

[0041] In another preferred variant of the invention, the first separation stage comprises a second filtration sub-stage, to which the first concentrated slurry is subjected to generate a first filtrate solution and a first residue.

[0042] In another preferred variant of the invention, the first separation stage comprises a third mixing sub-stage, in which the first overflow solution and the first filtration solution are provided to generate a first neutralized arsenic-containing wastewater.

[0043] In another preferred variant of the invention, the first residue is subjected to a leaching process to remove arsenic, thereby generating a second residue slurry.

[0044] In another preferred variant of the invention, the leaching process is carried out with an acid solution.

[0045] In another preferred variant of the invention, the acid solution comprises sulfuric acid.

[0046] In another preferred variant of the invention, the concentration of sulfuric acid in the acid solution is between 10 g / L and 75 g / L.

[0047] In another preferred variant of the invention, the leaching process is carried out at a temperature ranging from 40°C to 80°C.

[0048] In another preferred variant of the present invention, the leaching process is carried out at a solid content of 10% w / w to 40% w / w in the slurry obtained by mixing the first residue with the acid solution.

[0049] In another preferred variant of the invention, the second residue slurry is sent to a second separation stage to generate a second arsenic-containing wastewater and a second residue.

[0050] In another preferred variant of the invention, the second separation stage comprises a first concentrating, clarifying or centrifuging sub-stage to which the second residue slurry is subjected to obtain a second overflow solution and a second concentrated slurry.

[0051] In another preferred variant of the invention, the second separation stage comprises a second filtration sub-stage to which the second concentrated slurry is subjected to generate a second filtrate solution and a second residue.

[0052] In another preferred variant of the present invention, the second separation stage comprises a third mixing sub-stage, in which a second overflow solution and a second filtered solution are provided to generate a second arsenic-containing wastewater.

[0053] In another preferred variant of the invention, the second residue comprises gypsum and it constitutes a stable residue.

[0054] In another preferred variant of the present invention, the sodium-based neutralizing agent is prepared with water to a concentration between 1 mol / L and 10 mol / L.

[0055] In another preferred variant of the present invention, after adding the neutralizing agent, a first neutralized arsenic-containing wastewater is generated.

[0056] In another preferred variant of the present invention, in step ii, the adjustment of the Fe(III) / As(III) molar ratio is carried out by adding one of ferric sulfate, ferric sulfate heptahydrate, ferric chloride, or a leachate of an iron ore (e.g., hematite, goethite or magnetite) (step B).

[0057] In another preferred variant of the present invention, in step ii, the adjustment of the Fe(III) / As(III) molar ratio can be carried out using a leachate of magnetite, which has been oxidized with an oxidizing agent to convert all ferrous ions into ferric ions.

[0058] In another preferred variant of the present invention, the oxidizing agent of the leachate for oxidizing the magnetite is selected from one of hydrogen peroxide or sodium chlorite.

[0059] In another preferred variant of the present invention, in step ii. adjusting the Fe(III) / As(III) molar ratio, the Fe(III) / As(III) molar ratio is adjusted to be between 1.5 and 2.

[0060] In another preferred variant of the present invention, in step ii. adjusting the Fe(III) / As(III) molar ratio, the Fe(III) / As(III) molar ratio is adjusted to 1.8.

[0061] In another preferred variant of the invention, step iii. arsenic precipitation is carried out at a pH of 2 to 4.

[0062] In another preferred variant of the invention, step iii is performed for a period of time ranging from 1 hour to 24 hours.

[0063] In another preferred variant of the invention, step iii is carried out at a temperature between 15°C and 80°C.

[0064] In another preferred variant of the invention, step iii is carried out at a temperature of 20°C.

[0065] In another preferred variant of the present invention, the second neutralizing agent is 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 dolomitic limestone.

[0066] In another preferred variant of the present invention, in step iii, the second neutralizing agent is selected from one of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, magnesium oxide, magnesium hydroxide or magnesium carbonate.

[0067] In another preferred variant of the invention, in step iv, a first concentration, clarification or centrifugation sub-step is performed, to which the first arsenic-containing residue slurry is subjected to obtain a third overflow solution and a third concentrated slurry.

[0068] In another preferred variant of the invention, in step iv, a second filtration sub-step is performed, to which the third concentrated slurry is subjected to generate a third filtered solution and a first arsenic-containing residue.

[0069] In another preferred variant of the present invention, in step iv, a third mixing sub-stage is carried out, in which a third overflow solution and a third filtered solution are provided to generate a fourth arsenic-containing wastewater.

[0070] In another preferred variant of the invention, the first arsenic-containing residue is subjected to a drying process to produce the second arsenic-containing residue.

[0071] In another preferred variant of the invention, the drying process is carried out until the moisture content of the second arsenic-containing residue reaches 10% w / w to 25% w / w on a wet basis.

[0072] In another preferred variant of the invention, step v is carried out at a temperature of 450°C to 600°C.

[0073] In another preferred variant of the invention, step v is performed for a period of time ranging from 15 minutes to 60 minutes.

[0074] In another preferred variant of the invention, in step v, gypsum is added.

[0075] In another preferred variant of the invention, in step v, gypsum is added in a mass ratio of 10% w / w to 20% w / w relative to the total mass of the second arsenic-containing residue and gypsum.

[0076] In another preferred variant of the invention, the gypsum added in step v corresponds to the second residue.

[0077] In another preferred variant of the present invention, in step iii, the second neutralizing agent is selected from one of calcium oxide, calcium hydroxide, calcium carbonate or dolomitic limestone.

[0078] In another preferred variant of the invention, in step iv, a first concentration, clarification or centrifugation sub-step is performed, to which the first arsenic-containing residue slurry is subjected to obtain a third overflow solution and a third concentrated slurry.

[0079] In another preferred variant of the invention, in step iv, a second filtration sub-step is performed, to which the third concentrated slurry is subjected to generate a third filtered solution and a first arsenic-containing residue.

[0080] In another preferred variant of the present invention, in step iv, a third mixing sub-stage is carried out, in which a third overflow solution and a third filtered solution are provided to generate a fourth arsenic-containing wastewater.

[0081] In another preferred variant of the invention, the first arsenic-containing residue is subjected to a drying process to produce the second arsenic-containing residue.

[0082] In another preferred variant of the invention, the drying process is carried out until the moisture content of the second arsenic-containing residue reaches 10% w / w to 25% w / w on a wet basis.

[0083] In another preferred variant of the invention, step v is carried out at a temperature of 450°C to 600°C.

[0084] In another preferred variant of the invention, step v is performed for a period of time ranging from 15 minutes to 60 minutes.

[0085] In another preferred variant of the invention, in step vi, the washing of the second arsenic-containing residue is carried out with water at a washing ratio of 1 to 3 tonnes of water per tonne of the second arsenic-containing residue.

[0086] In another preferred variant of the invention, in step vii, a first concentration, clarification or centrifugation sub-step is performed, to which the second arsenic-containing residue slurry is subjected to obtain a fourth overflow solution and a fourth concentrated slurry.

[0087] In another preferred variant of the invention, in step vii, a second filtration sub-step is performed, to which the fourth concentrated slurry is subjected to generate a fourth filtered solution and a third arsenic-containing residue.

[0088] In another preferred variant of the present invention, in step vii, a third mixing sub-stage is performed, in which a fourth overflow solution and a fourth filtered solution are provided to generate a fifth arsenic-containing wastewater.

[0089] In another preferred variant of the invention, the fifth arsenic-containing wastewater is recycled to step iii.

[0090] In another preferred variant of the invention, the third arsenic-containing residue is a stable residue.

[0091] Alternatively, in another preferred variant of the invention, purification step viii is performed, which is carried out at a pH in the range of 11 to 13.

[0092] In another preferred variant of the invention, the third neutralizing agent added in step viii is selected from sodium hydroxide, potassium hydroxide, calcium oxide or calcium hydroxide.

[0093] In another preferred variant of the invention, the precipitation solution added in step viii comprises the first transition metal and the second transition metal (step C).

[0094] In another preferred variant of the present invention, the first transition metal added in step viii is added in the form of a ferrous salt selected from one of ferrous sulfate and ferrous chloride.

[0095] In another preferred variant of the present invention, the second transition metal added in step viii is added in the form of a zinc salt selected from one of zinc sulfate, zinc sulfate pentahydrate or zinc chloride.

[0096] In another preferred variant of the invention, the first transition metal added in step viii is added in a molar ratio of between 2:1 and 25:1 relative to the concentration of arsenite ions.

[0097] In another preferred variant of the invention, the second transition metal added in step viii is added in a molar ratio of between 6:1 and 20:1 relative to the concentration of arsenite ions.

[0098] Alternatively, in another preferred variant of the invention, in step ix, a first concentration, clarification or centrifugation sub-step is performed, to which the second arsenic-containing residue slurry is subjected to obtain a fifth overflow solution and a fifth concentrated slurry.

[0099] In another preferred variant of the invention, in step ix, a second filtration sub-step is performed, to which the fifth concentrated slurry is subjected to generate a fifth filtered solution and a fourth arsenic-containing residue.

[0100] In another preferred variant of the present invention, in step ix, a third mixing sub-stage is carried out, in which a fifth overflow solution and a fifth filtered solution are provided to generate a sixth arsenic-containing wastewater.

[0101] Those having ordinary knowledge in the art will appreciate that there may be a variety of solid-liquid separation steps that allow the solid phase to be separated from the liquid phase, thus being applicable to the present invention, wherein the application of any such alternatives will not depart from the subject matter claimed in the present invention. DETAILED DESCRIPTION

[0102] The following examples should be considered as forms of the invention and should not be considered as limiting the invention in any case, since various modifications thereof will be included in the subject matter claimed by the invention.

[0103] Neutralization

[0104] Examples 1 to 7

[0105] Prepare 3500mL of arsenic (III) concentration of 12g / L and sulfuric acid concentration of 70g / L and 150g / L arsenic solution, and place it in a 5L glass reactor, add limestone or lime slurry to adjust the pH to within the range of 1 to 2, and the pH is measured according to the Ag / AgCl pH electrode. The reactor was stirred at 300rpm for 2 hours at room temperature. When the reaction time ends, the slurry is subjected to solid-liquid separation by filtration. The solid is washed with an acidified solution of pH 1 for subsequent TCLP analysis. The results are shown in Table 1.

[0106] Table 1. Gypsum removal results of Examples 1-7

[0107]

[0108]

[0109] Examples 8 to 21

[0110] 3500 mL of arsenic solution with sulfuric acid concentration between 10 g / L and 150 g / L was prepared and mixed with gypsum obtained under the conditions of Example 7, adjusting the solid percentage between 10% w / w and 40% w / w. The reactor was stirred at 300 rpm for 2 hours at a temperature of 20°C to 80°C. At the end of the reaction time, the slurry was separated from the solid by filtration. The solid was washed with an acidified solution of pH 1 for subsequent TCLP analysis. The results are shown in Table 2.

[0111] Table 2. Gypsum leaching results of Examples 8-21

[0112]

[0113] Arsenic removal

[0114] Examples 22 to 28

[0115] Prepare 1000mL arsenic (III) concentration is 10g / L and sulfuric acid concentration is 2g / L arsenic solution (the solution of pH being 2 from Application Examples 1 to 5), and be placed in a 2L glass reactor, add 70g ferric sulfate heptahydrate to maintain Fe (III) / As (III) mol ratio equal to 2mol Fe (III) / mol As (III). By adding the sodium hydroxide solution that concentration is 10mol / L to adjust the pH of solution in the range of 2 to 6 (measured with Ag / AgCl pH electrode). At room temperature, the reactor is stirred for 5 hours to 20 hours with 300rpm. When the reaction time ends, the slurry is carried out solid-liquid separation by filtering. The acidified solution washing solid is used for subsequent TCLP analysis with pH being 3. The result is as shown in Table 3.

[0116] Table 3. As precipitation results of Examples 22-28

[0117] Variables / Examples unit 22 23 24 25 26 27 28 pH 2 3 3 3.5 4 5 6 Dwell time h 20 20 5 20 5 5 5 As removal rate ％ 18.0 98.9 95.0 98.3 98.7 98.5 98.6 As released from TCLP mg / L Not measured 13.1 12.6 20.1 24.6 162 236

[0118] Examples 29 to 34

[0119] Prepare 1000mL arsenic (III) concentration is 10g / L and sulfuric acid concentration is 2g / L arsenic solution, and be placed in 2L glass reactor, add ferric sulfate heptahydrate to keep Fe (III) / As (III) mol ratio equal to 1.5-2mol Fe (III) / mol As (III).By adding the sodium hydroxide solution that concentration is 10mol / L, the pH of solution is adjusted to 3 (measured with Ag / AgCl pH electrode).At room temperature, reactor is stirred 20 hours with 300rpm.When reaction time ends, slurry is carried out solid-liquid separation by filtering.Be 3 acidified solutions washing solid with pH, ​​be used for subsequent TCLP analysis.Result is as shown in Table 4.

[0120] Table 4. As precipitation results of Examples 29-34

[0121] Variables / Examples unit 29 30 31 32 33 34 pH 3 3 3 3 3 3 Dwell time h 20 20 20 20 20 20 Fe(III) / As(III) mol / mol 1.5 1.6 1.7 1.8 1.9 2.0 As removal rate ％ 93.7 97.7 97.7 99.3 99.1 98.7 As released from TCLP mg / L 27.3 19.7 16.1 16.8 20.1 23.2

[0122] Examples 35 to 41

[0123] 1000mL of arsenic solution with 10g / L arsenic (III) concentration and 2g / L sulfuric acid concentration was prepared and placed in a 2L glass reactor, and iron sulfate heptahydrate was added to keep the Fe(III) / As(III) molar ratio equal to 1.5-2mol Fe(III) / mol As(III). The pH of the solution was adjusted to a range of 2-4 by adding lime slurry with a concentration of 10-25% w / w, and the pH was measured according to an Ag / AgCl pH electrode. The reactor was stirred at 300rpm for 20 hours at room temperature. When the reaction time was over, the slurry was subjected to solid-liquid separation by filtration. The solid was washed with an acidified solution at pH 3 for subsequent TCLP analysis. The results are shown in Table 5.

[0124] Table 5. As precipitation results of Examples 35-41

[0125] Variables / Examples unit 35 36 37 38 39 40 41 pH 2 3 4 3 3 3 3 Dwell time h 20 20 20 20 20 20 20 Fe(III) / As(III) ratio mol / mol 2 2 2 1 1.5 2.0 2.5 As removal rate ％ 74 98 99 88 95 98 98 As released from TCLP mg / L 55 62 215 670 28.5 62.0 36.2

[0126] Application Examples 37 and 38 show that under their conditions it is not possible to obtain an arsenic residue with an As concentration of 25 mg / L to 70 mg / L (typical values ​​for Tooeleite) released in the TCLP test. The precipitation of the Fe / As molar ratio at pH 3 shows that, although As can be removed, the resulting phase is very unstable and has nothing to do with Tooeleite, which, according to its chemical structure, requires a Fe / As molar ratio equal to 1.5. In the case of precipitation at pH 4, the main phase observed is not Tooeleite, but iron oxyhydroxide, which has an As adsorption mechanism, rather than chemical bonds that fix As in the crystal structure (this is why unstable arsenic residues are generated).

[0127] Examples 42 to 43

[0128] 20000mL of arsenic-containing solution was prepared according to the method shown in Example 7 and placed in a 20L glass reactor, and iron sulfate heptahydrate was added to keep the Fe(III) / As(III) molar ratio equal to 1.8mol Fe(III) / mol As(III). The pH of the solution was adjusted to 3 by adding a NaOH solution with a concentration of 10mol / L and a lime slurry with a concentration of 25% w / w, and the pH was measured according to an Ag / AgCl pH electrode. The reactor was stirred at 300rpm for 18 hours at room temperature. 200mL of slurry samples were taken out at 1, 2, 4, 7, 10, 15 and 18 hours. For each slurry sample, solid-liquid separation was performed by filtration. The solid was washed with an acidified solution with a pH of 3 for subsequent TCLP analysis. The results are shown in Tables 6 and 7.

[0129] Table 6. Results of As precipitation with sodium hydroxide in Example 42

[0130] Reaction time h 1 2 4 7 10 15 18 pH 3 3 3 3 3 3 3 Fe(III) / As(III) ratio mol / mol 1.8 1.8 1.8 1.8 1.8 1.8 1.8 As removal rate ％ 97.9 98.1 98.6 98.8 99.0 99.5 99.5 As released from TCLP mg / L 34.9 18.0 20.7 17.6 16.8 18.7 19.5

[0131] Table 7. Results of As precipitation using lime slurry in Example 43 Reaction time

[0132] Reaction time h 1 2 4 7 10 15 18 pH 3 3 3 3 3 3 3 Fe(III) / As(III) ratio mol / mol 1.8 1.8 1.8 1.8 1.8 1.8 1.8 As removal rate ％ 96.0 96.5 97.5 98.0 98.2 98.3 98.3 As released from TCLP mg / L 58 63 64 63 59 60 62

[0133] Embodiment 44

[0134] 50 L of an arsenic solution having an arsenic (III) concentration of 8 g / L and a sulfuric acid concentration of 2 g / L was prepared from a sulfuric acid plant wastewater solution treated according to the conditions of Example 7 and placed in a 100 L glass reactor, with magnetite leachate added to maintain a Fe(III) / As(III) molar ratio of 1.8 mol Fe(III) / mol As(III). The pH of the solution was adjusted to 3 by adding a limestone slurry at a concentration of 18% w / w, as measured by an Ag / AgCl pH electrode. The reactor was stirred at 300 rpm for 6 hours at room temperature. The slurry was filtered in a plate filter and washed with an acidified solution at a pH of 3. The results are shown in Table 8.

[0135] Table 8. As precipitation results of Example 44

[0136] Reaction time h 6 pH 3 Fe(III) / As(III) ratio mol / mol 1.8 As removal rate ％ 97.9

[0137] Calcination

[0138] Examples 45 to 50

[0139] According to the conditions of Experiment 42, 10 g of the precipitated arsenic-containing residue was taken out at a residence time of 6 hours and placed in a zirconium crucible and reacted in a muffle furnace at a temperature of 400°C-650°C for 1 hour. When the reaction time was over, the crucible was taken out of the muffle furnace, and the solid was washed with water at a mass ratio of 2:1 for subsequent TCLP analysis. The test results are shown in Table 9.

[0140] Table 9. Calcination results of application examples 45 to 50

[0141] Variables / Examples unit 45 46 47 48 49 50 Reaction time h 1 1 1 1 1 1 temperature ℃ 400 450 500 550 600 650 Quality loss ％ 18 10.1 9.8 15.1 24 24.7 As released from TCLP mg / L 11.1 15.1 16.2 5.4 5.5 1.2

[0142] Application Examples 45-50 show that the calcination process of the arsenic-containing residue of Tooeleite precipitated with sodium hydroxide is not sufficient to stabilize this residue.

[0143] Examples 51 to 56

[0144] According to the conditions of Experiment 43, 10 g of the precipitated arsenic-containing residue was taken out at a residence time of 6 hours and placed in a zirconium crucible, and reacted at a temperature of 400°C-650°C in a muffle furnace for 1 hour. When the reaction time was over, the crucible was taken out of the muffle furnace, and the solid was washed with water at a mass ratio of 2:1 for subsequent TCLP analysis. The test results are shown in Table 10.

[0145] Table 10. Calcination results of application examples 51 to 56

[0146] Variables / Examples unit 51 52 53 54 55 56 Reaction time h 1 1 1 1 1 1 temperature ℃ 400 450 500 550 600 650 Quality loss ％ 11.0 16.8 15.0 10.7 16.0 18.0 As released from TCLP mg / L 4.2 3.4 2.9 5.4 5.9 13.9

[0147] Application Examples 51-53 show that stable arsenic residues can be obtained by calcining precipitated Tooeleite neutralized with calcium hydroxide. Unstable arsenic residues are formed in the temperature range of 550°C to 650°C due to the formation of arsenite and arsenate ions, which begin to volatilize in the form of arsenic trioxide and arsenic pentoxide.

[0148] Examples 57 to 61

[0149] According to the conditions of Experiment 42, 10 g of the precipitated arsenic residue was taken out at 6 hours and placed in a zirconium crucible and reacted at 550°C in a muffle furnace for 1-3 hours. After the reaction time was over, the crucible was taken out of the muffle furnace, and the solid was washed with water at a mass ratio of 2:1 for subsequent TCLP analysis. The test results are shown in Table 11.

[0150] Table 11. Calcination results of application examples 57 to 61

[0151]

[0152]

[0153] Application Examples 57-61 show that prolonged calcination does not improve the stability of the arsenic-containing residue, since the arsenic trioxide and arsenic pentoxide formed generate highly unstable gases.

[0154] Examples 62 to 65

[0155] According to the conditions of Experiment 43, 10 g of the precipitated arsenic residue was taken out at 6 hours and placed in a zirconium crucible, and reacted at 500°C in a muffle furnace for 15-60 minutes. When the reaction time was over, the crucible was taken out of the muffle furnace, and the solid was washed with water at a mass ratio of 2:1 for subsequent TCLP analysis. The test results are shown in Table 12.

[0156] Table 12. Calcination results of application examples 62-65

[0157] Variables / Examples unit 62 63 64 65 Reaction time min 15 30 45 60 temperature ℃ 500 500 500 500 Quality loss ％ 15.9 16.0 16.1 16.4 As released from TCLP mg / L 1.2 1.5 2.1 1.9

[0158] Application Examples 62-65 show that under the conditions provided herein, a stable arsenic-containing residue can be formed from Tooeleite precipitated with calcium hydroxide within a calcination time range of 15-60 minutes at 500°C.

[0159] Examples 66 to 71

[0160] According to the conditions of Experiment 42, 10 g of the precipitated arsenic residue was taken out at a residence time of 6 hours and placed in a zirconium crucible and reacted at 550° C. in a muffle furnace for 1 hour. The gypsum produced according to Example 7 was charged into the crucible so that the gypsum content in the total mixture of arsenic residue was between 10-20% w / w. After the reaction time was over, the crucible was taken out of the muffle furnace and the solid was washed with water at a mass ratio of 2:1 for subsequent TCLP analysis. The test results are shown in Table 13.

[0161] Table 13. Calcination results of application examples 66 to 71

[0162]

[0163] Application Examples 66-71 show that by calcining a mixture of Tooeleite precipitated with sodium hydroxide and gypsum produced in Application Example 7, a stable arsenic-containing residue can be obtained, compared to calcining Tooeleite in the absence of gypsum as disclosed in Application Examples 45-50.

[0164] Examples 72 to 73

[0165] Two arsenic removal tests were conducted according to the conditions of Experiment 42 with a residence time of 6 hours, but using mixtures containing 67% calcium hydroxide and 33% sodium hydroxide and 87% calcium hydroxide and 13% sodium hydroxide as neutralizers, respectively. Subsequently, 10 g of the arsenic-containing residue precipitated according to the aforementioned conditions was taken and placed in a zirconium crucible and reacted in a muffle furnace at 550° C. for 1 hour. When the reaction time was over, the crucible was removed from the muffle furnace and the solid was washed with water at a mass ratio of 2:1 for subsequent TCLP analysis. The test results are shown in Table 14.

[0166] Table 14. Calcination results of application examples 72-73

[0167]

[0168] Application Examples 72 and 73 show that by adding a mixture of sodium hydroxide neutralizer and lime slurry, a stable arsenic-containing residue can be obtained after calcination, which confirms that the presence of gypsum in the arsenic-containing residue is beneficial to its stabilization.

[0169] Embodiment 74

[0170] According to the conditions of Experiment 44, 10 g of the precipitated arsenic-containing residue was taken out at a residence time of 6 hours and placed in a zirconium crucible and reacted in a muffle furnace at 500°C for 1 hour. After the reaction time was over, the crucible was taken out of the muffle furnace, and the solid was washed with water at a mass ratio of 2:1 for subsequent TCLP analysis. The test results are shown in Table 15.

[0171] Table 15. Calcination results of Application Example 74

[0172] Variables / Examples unit 74 Reaction time h 1 temperature ℃ 500 Quality loss ％ 9.9 As released from TCLP mg / L 0.39

[0173] Examples 75 to 81

[0174] According to the conditions of Experiment 44, 10 g of the precipitated arsenic-containing residue was taken out and placed in a zirconium crucible, and reacted in a muffle furnace at a temperature of 400°C-500°C for 15-60 minutes. When the reaction time was over, the crucible was taken out of the muffle furnace, and the solid was washed with water at a mass ratio of 2:1 for subsequent TCLP analysis. The test results are shown in Table 16.

[0175] Table 16. Calcination results of Examples 75-80

[0176]

[0177]

[0178] Example 75 demonstrates that stabilization of arsenic-containing residues in the form of Tooeleite precipitated with a limestone slurry cannot be achieved at a temperature of 400° C. Application Examples 76-80 show how arsenic-containing residues can be stabilized by calcination, in contrast to Control Example 81, where the arsenic-containing residue was not subjected to calcination conditions.

[0179] Secondary arsenic removal

[0180] Examples 82 to 89

[0181] 2000mL of arsenic-containing solution was prepared according to the precipitation conditions of Example 74 and placed in a 5L glass reactor, and ferrous sulfate heptahydrate and zinc sulfate pentahydrate were added to adjust the molar ratios of Fe(II) / As(III) and Zn(II) / As(III), respectively. The pH of the solution was adjusted to between 11 and 13 by adding a sodium hydroxide solution having a concentration of 10mol / L and a lime slurry having a concentration of 25% w / w. The pH was measured using an Ag / AgCl pH electrode. The reactor was stirred at 300rpm for 1 hour at room temperature. The slurry was subjected to solid-liquid separation by filtration for subsequent TCLP analysis. The results are shown in Table 17.

[0182] Table 17. Arsenic precipitation results of Examples 82-89

[0183] Variables / Examples unit 82 83 84 85 86 87 88 89 Initial As g / L 1.0 1.0 0.15 0.15 0.20 0.20 0.20 0.20 <![CDATA[Initial H2SO4]]> g / L 1.7 1.7 0.8 0.8 2.0 2.0 2.0 2.0 Adjust pH 11 12 13 13 12 12 12 12 Dwell time h 1 1 1 1 1 1 1 1 Fe(II) / As(III) ratio mol / mol 3.0 3.0 3.0 3.0 3.0 3.0 3.4 3.4 Zn(II) / As(III) ratio mol / mol 6.0 6.0 6.0 6.0 6.0 6.0 6.0 20.0 As removal rate ％ 96 97 97 98 99 99 99 99 As released from TCLP mg / L 3.5 2.5 0.58 0.42 2.4 1.4 1.7 0.7

[0184] Application Examples 82 to 89 show that a stable arsenic-containing residue in the form of Tooeleite can be obtained from the solution by a precipitation process, thereby enabling an arsenic removal solution with an As concentration of less than 10 mg / L to be obtained.

[0185] Examples 90 to 96

[0186] 50L of arsenic-containing solution was prepared according to the precipitation conditions of Example 74 and placed in a 100L glass reactor, and ferrous sulfate heptahydrate and zinc sulfate pentahydrate were added to adjust the molar ratios of Fe(II) / As(III) and Zn(II) / As(III), respectively. The pH of the solution was adjusted to 12 by adding a sodium hydroxide solution having a concentration of 10 mol / L and a lime slurry having a concentration of 25% w / w. The pH was measured using an Ag / AgCl pH electrode. The reactor was stirred at 300 rpm for 1 hour at room temperature. The slurry was subjected to solid-liquid separation by filtration for subsequent TCLP analysis. The results are shown in Table 18.

[0187] Table 18. Results of As precipitation of Examples 90-96

[0188]

[0189]

[0190] Application Examples 90-96 show that a stable arsenic-containing residue in the form of Tooeleite can be obtained from the solution by a precipitation process, thereby enabling an arsenic removal solution with an As concentration of less than 10 mg / L to be obtained.

Claims

1. A method for removing arsenic from arsenic-containing wastewater to produce a stable arsenic-containing residue, characterized in that: It includes: i. a first neutralization step, wherein the arsenic-containing wastewater is contacted with a first neutralizing agent to generate a first neutralized arsenic-containing wastewater, ii. a second step of adjusting the Fe(III) / As(III) ratio, wherein the first neutralized arsenic-containing wastewater is mixed with the first iron solution to generate a third arsenic-containing wastewater, iii. a third step of arsenic precipitation, wherein the pH of the third arsenic-containing wastewater is adjusted with a second neutralizing agent to generate a first arsenic-containing residue slurry, iv. a fourth step of solid-liquid separation, wherein the first arsenic-containing residue slurry is separated to generate a fourth arsenic-containing wastewater and a first arsenic-containing residue, v. a fifth step of calcining, wherein the first arsenic-containing residue is calcined to form a second arsenic-containing residue, vi. a sixth step of washing, wherein the second arsenic-containing residue is washed with an aqueous solution to form a second arsenic-containing residue slurry, vii. The seventh step is solid-liquid separation, wherein the second arsenic-containing residue slurry is separated to generate a fifth arsenic-containing wastewater and a stable third arsenic-containing residue in the form of arsenic hydroxide ferroaluminate.

2. The method according to claim 1, characterized in that In the neutralization step i, the pH value is adjusted to be in the range of 0.5 to 2.

3. The method according to claims 1 to 2, characterized in that The first neutralizing agent is 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.

4. The method according to claims 1 to 3, characterized in that The calcium-based first neutralizer in step i is prepared into a neutralizer slurry with water, wherein the concentration of the neutralizer in the neutralizer slurry is between 15% w / w and 25% w / w.

5. The method according to claim 4, characterized in that In the neutralization step i, a first neutralized wastewater slurry is generated.

6. The method according to claim 5, characterized in that The first neutralized wastewater slurry is conveyed to a first separation stage to generate a first neutralized arsenic-containing wastewater and a first residue.

7. The method according to claim 6, characterized in that The first separation stage comprises a first concentrating, clarifying or centrifuging sub-stage to which the first neutralized wastewater slurry is subjected to obtain a first overflow solution and a first concentrated slurry.

8. The method according to any one of claims 6 to 7, characterized in that The first separation stage includes a second filtration sub-stage to which the first concentrated slurry is subjected to produce a first filtered solution and a first residue.

9. The method according to any one of claims 6 to 8, characterized in that The first separation stage includes a third mixing sub-stage in which a first overflow solution and a first filtration solution are provided to generate a first neutralized arsenic-containing wastewater.

10. The method according to any one of claims 6 to 9, characterized in that The first residue undergoes a leaching stage to remove arsenic, thereby generating a second residue slurry.

11. The method according to claim 10, characterized in that The leaching stage is carried out with an acidic solution comprising sulfuric acid, wherein the concentration of sulfuric acid in the acidic solution is between 10 g / L and 75 g / L.

12. The method according to any one of claims 10 to 11, characterized in that The leaching stage is carried out at a temperature ranging from 40°C to 80°C.

13. The method according to any one of claims 10 to 12, characterized in that The leaching stage is carried out at a solid content of 10% to 40% in the slurry obtained by mixing the first residue with the acidic solution.

14. The method according to any one of claims 10 to 13, characterized in that The second residue slurry is conveyed to a second separation stage to generate a second arsenic-containing wastewater and a second residue.

15. The method according to claim 14, characterized in that The second separation stage comprises a first concentrating, clarifying or centrifuging sub-stage to which the second residue slurry is subjected to obtain a second overflow solution and a second concentrated slurry.

16. The method according to any one of claims 14 to 15, characterized in that The second separation stage comprises a second filtration sub-stage to which the second concentrated slurry is subjected to produce a second filtration solution and a second residue; the second residue comprises gypsum and constitutes a stable residue.

17. The method according to any one of claims 14 to 16, characterized in that The second separation stage includes a third mixing sub-stage in which a second overflow solution and a second filtered solution are provided to generate a second arsenic-containing wastewater.

18. The method according to any one of claims 1 to 3, characterized in that The first sodium-based neutralizer is prepared with water to a concentration between 1 mol / L and 10 mol / L.

19. The method according to any one of claims 1 to 3 and 18, characterized in that After adding the neutralizing agent, the first neutralized arsenic-containing wastewater is generated.

20. The method according to any one of claims 1 to 19, characterized in that In step ii, the Fe(III) / As(III) molar ratio is adjusted by adding one of ferric sulfate, ferric chloride, or a leaching solution of an iron ore, such as hematite, goethite, or magnetite.

21. The method according to claim 20, characterized in that In step ii, the adjustment of the Fe(III) / As(III) molar ratio is carried out using a leachate of magnetite, wherein the leachate has been oxidized by an oxidant to convert all ferrous ions into ferric ions.

22. The method according to claim 21, characterized in that The oxidant used to oxidize the magnetite leachate is selected from one of hydrogen peroxide and sodium chlorite.

23. The method according to any one of claims 1 to 22, characterized in that In step ii of adjusting the Fe(III) / As(III) molar ratio, the Fe(III) / As(III) molar ratio is adjusted to be between 1.5 and 2.

24. The method according to claim 23, characterized in that In step ii of adjusting the Fe(III) / As(III) molar ratio, the Fe(III) / As(III) molar ratio is adjusted to 1.

8.

25. The method according to any one of claims 1 to 24, characterized in that Step iii. Arsenic precipitation is carried out at a pH of 2 to 4.

26. The method according to any one of claims 1 to 25, characterized in that Step iii is performed for 1 hour to 24 hours.

27. The method according to any one of claims 1 to 26, characterized in that Step iii is carried out at a temperature of 15°C to 80°C.

28. The method according to any one of claims 1 to 27, characterized in that The second neutralizing agent is 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.

29. The method according to claim 28, characterized in that The second neutralizing agent in step iii is selected from one of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, magnesium oxide, magnesium hydroxide or magnesium carbonate.

30. The method according to claim 29, characterized in that In step iv, a first concentration, clarification or centrifugation sub-step is performed, to which the first arsenic-containing residue slurry is subjected to obtain a third overflow solution and a third concentrated slurry.

31. The method according to claim 30, characterized in that In step iv, a second filtration sub-stage is performed, to which the third concentrated slurry is subjected to produce a third filtered solution and a first arsenic-containing residue.

32. The method according to any one of claims 29 to 31, characterized in that In step iv, a third mixing sub-stage is performed, in which a third overflow solution and a third filtered solution are provided to generate a fourth arsenic-containing wastewater.

33. The method according to any one of claims 29 to 32, characterized in that Step v is performed at a temperature of 450°C to 600°C.

34. The method according to any one of claims 29 to 33, characterized in that Step v is performed for a period of 15 to 60 minutes.

35. The method according to any one of claims 29 to 34, characterized in that Add the plaster in step v.

36. The method according to any one of claims 29 to 35, characterized in that In step v, gypsum is added in a mass ratio of 10% w / w to 20% w / w relative to the total mass of the second arsenic-containing residue and gypsum.

37. The method according to any one of claims 29 to 35, characterized in that The gypsum added in step v corresponds to the second residue.

38. The method according to claim 28, characterized in that The second neutralizing agent in step iii is selected from one of calcium oxide, calcium hydroxide, calcium carbonate or dolomitic limestone.

39. The method according to claim 38, characterized in that In step iv, a first concentration, clarification or centrifugation sub-step is performed, to which the first arsenic-containing residue slurry is subjected to obtain a third overflow solution and a third concentrated slurry.

40. The method according to any one of claims 38 to 39, characterized in that In step iv, a second filtration sub-step is performed, to which the third concentrated slurry is subjected to produce a third filtered solution and a first arsenic-containing residue.

41. The method according to any one of claims 38 to 40, characterized in that In step iv, a third mixing sub-stage is performed, in which a third overflow solution and a third filtered solution are provided to generate a fourth arsenic-containing wastewater.

42. The method according to any one of claims 38 to 41, characterized in that The first arsenic-containing residue is subjected to a calcination step to produce a second arsenic-containing residue.

43. The method according to claim 42, characterized in that The calcining step is performed until the moisture content of the second arsenic-containing residue reaches 10% w / w to 25% w / w on a wet basis.

44. The method according to any one of claims 38 to 43, characterized in that Step v is performed at a temperature of 450°C to 600°C.

45. The method according to any one of claims 38 to 44, characterized in that Step v is performed for a period of 15 to 60 minutes.

46. ​​The method according to any one of claims 1 to 45, characterized in that In step vi, the second arsenic-containing residue is washed with water at a washing ratio of 1-3 tonnes of water per tonne of the second arsenic-containing residue.

47. The method according to any one of claims 1 to 46, characterized in that In step vii, a first concentration, clarification or centrifugation sub-step is performed, to which the second arsenic-containing residue slurry is subjected, to obtain a fourth overflow solution and a fourth concentrated slurry.

48. The method according to claim 47, characterized in that In step vii, a second filtration sub-step is performed, to which the fourth concentrated slurry is subjected to produce a fourth filtered solution and a stabilized third arsenic-containing residue.

49. The method according to claim 48, characterized in that In step vii, a third mixing sub-stage is performed, in which a fourth overflow solution and a fourth filtered solution are provided to generate a fifth arsenic-containing wastewater.

50. The method according to any one of claims 1 to 49, characterized in that The fifth arsenic-containing wastewater is recycled to step iii.

51. The method according to claim 1, characterized in that A purification step viii is additionally performed, wherein the fourth arsenic-containing wastewater and the fifth arsenic-containing wastewater are treated with a precipitation solution and a third neutralizing agent to generate a third arsenic-containing residue slurry.

52. The method according to claim 51, characterized in that Purification step viii is carried out at a pH range of 11 to 13.

53. The method according to claim 51, characterized in that In step viii, the third neutralizing agent added is selected from sodium hydroxide, potassium hydroxide, calcium oxide or calcium hydroxide.

54. The method according to claim 51, characterized in that In step viii, the added precipitation solution comprises a first transition metal and a second transition metal.

55. The method according to claim 54, characterized in that In step viii, the first transition metal is added in the form of a ferrous salt, and the ferrous salt is selected from one of ferrous sulfate and ferrous chloride.

56. The method according to claim 55, characterized in that In step viii, the first transition metal is added in a molar ratio of 2:1 to 25:1 relative to the concentration of arsenite ions.

57. The method according to claim 51, characterized in that In step viii, the second transition metal is added in the form of a zinc salt, and the zinc salt is selected from zinc sulfate or zinc chloride.

58. The method according to claim 57, characterized in that In step viii, the second transition metal is added in a molar ratio of 6:1 to 20:1 relative to the concentration of arsenic ions.

59. The method according to claim 51, characterized in that A solid-liquid separation step ix is ​​additionally performed, wherein the third arsenic-containing residue slurry is separated to generate a sixth arsenic-containing wastewater and a fourth arsenic-containing residue.

60. The method according to claim 59, characterized in that In step ix, a first concentration, clarification or centrifugation sub-step is performed, to which the third arsenic-containing residue slurry is subjected to obtain a fifth overflow solution and a fifth concentrated slurry.

61. The method according to claim 59, characterized in that In step ix, a second filtration sub-step is performed, to which the fifth concentrated slurry is subjected to generate a fifth filtered solution and a fourth arsenic-containing residue.

62. The method according to claim 59, characterized in that In step ix, a third mixing sub-stage is performed, in which a fifth overflow solution and a fifth filtered solution are provided to generate a sixth arsenic-containing wastewater.

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