Method for stabilizing arsenic by precipitating iron arsenate by blending with aluminum gel

Abstract

A method of precipitating iron arsenate to stabilize arsenic by blending with an aluminum gel, the method comprising the steps of: i) neutralizing an arsenic-containing wastewater with a first neutralizing agent to produce a neutralized arsenic-containing wastewater; ii) oxidizing the wastewater from step i by adding a first oxidizing agent, wherein As (III) is oxidized to As (V); iii) adjusting the molar ratio of Fe (III) / As (V), wherein the oxidized arsenic-containing wastewater of step ii is mixed with an iron solution; iv) arsenic precipitation, wherein the pH of the arsenic-containing wastewater of step iii is adjusted with a second neutralizing agent to produce an arsenic-containing residue slurry; v) separating the arsenic-containing residue slurry obtained in step iv) to produce wastewater and a first arsenic-containing residue; and vi) mixing the arsenic-containing residue obtained in step v) with a gel to produce a second arsenic-containing residue.

Description

Technical Field

[0001] The present invention solves the technical problem of generating a stable arsenic-containing residue which does not require a thermal stabilization step to generate the stable arsenic-containing residue.

[0002] The invention solves the technical problem of removing arsenic from arsenic-containing wastewater to produce a stable arsenic-containing residue, the synthesis of which does not require heating in the precipitation stage to produce a crystalline compound. Background Art

[0003] Since arsenic is widely distributed in more than 320 minerals, it is commonly found in the acid dissolution of arsenic-containing ores produced by mining and metallurgical operations, as well as in the dilute acid washing flue gases produced during the calcination and smelting of copper concentrates. The wastewater produced by the above two processes has an extremely low pH value of about 1.0 and a high arsenic content of between 3-10 g / 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.). In addition, arsenic exists mainly in the trivalent As(III) state, which is the most toxic inorganic form present in contaminated water and is considered to be 25-60 times more toxic than As(V). Removal of As(III) is technically more difficult in water treatment because As(III) has higher mobility and solubility than As(V) (Paikaray, S., 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.). Effective and direct removal of As(III) is a major challenge, especially at very low concentrations and pH values ​​around 1.0. 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 appears 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 lower, 5-15%. Therefore, large amounts of lime are required, while large amounts of sludge are produced, the storage of which is not completely safe, and the arsenic is subsequently released into the solution. Co-precipitation with iron ions is a special method for removing arsenates, however, this requires the use of oxidants 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 production of hydrogen sulfide and the need for additional treatment to provide environmental stability.

[0004] Copper smelters use various treatment operations to remove arsenic from weak acid wastewater, the most commonly used 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 requirements, low As content (6%), and the need to oxidize As(III) to As(V) before precipitation. In addition, the long-term stability of As(V)-Fh is also a concern because the ferrihydrite contained in As(V)-Fh may be converted 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).

[0005] Scorodite (FeAsO4×2H2O) is generally considered to be the most suitable removal solution for As fixation due to 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 acid wastewaters by atmospheric precipitation of scorodite at 95°C under ambient pressure and supersaturation controlled 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. Compared with high temperature pressure oxidation (HTPOX), this method has lower investment cost and is independent of process scale (Filippou, D., & Demopoulos, GP (1997). Arsenic immobilization by controlled scorodite precipitation. Jom, 49 (12), 52-55.). In addition, scorodite can be decomposed under anoxic conditions by carbonation with CO2 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, it is necessary to study an alternative treatment scheme with low solubility, low iron demand, high arsenic removal efficiency and good filtration performance for the removal and treatment of arsenic in weak acid wastewater in copper smelters.

[0006] In this sense, it is desirable to create a method for providing stability to amorphous arsenic precipitates containing iron at relatively low Fe / As dosages that does not require the use of heat to generate a crystalline phase to provide stability. The present invention improves upon the prior art in that amorphous iron arsenate can be stabilized without the need for excess Fe / As by using an aluminum gel to create a passivation layer to reduce arsenic release into the leaching medium, the aluminum gel allowing aluminum arsenate to form on the particle surface and precipitate as aluminum hydroxide or aluminum oxyhydroxide after a solidification process.

[0007] Patent application WO2019000091 discloses a method for stabilizing hazardous waste using aluminum gel. This application focuses in particular on the stabilization of scorodite, which contains crystalline ferric arsenate on which the aluminum gel coats the particles. In the present invention, amorphous ferric arsenate is used, which does not provide any crystallization by the precipitation method disclosed herein. Therefore, by the technology used in the present invention, by adding aluminum gel, an aluminum arsenate phase can be generated, which, according to our data, makes it possible to obtain a stable arsenic-containing precipitate, which is impossible to obtain by using a gel with scorodite, thus making the particles completely dependent on the mineralization of aluminum in the form of aluminum oxyhydroxide or aluminum hydroxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 The flow chart of the method disclosed in the present invention is shown. Stage a comprises neutralizing arsenic-containing wastewater A with a neutralizing agent B, and the resulting slurry is directed to a separation stage b, in which the slurry containing solids is directed to a stage c to obtain gypsum, and the solution is directed to an oxidation stage d by adding an oxidizing agent D. The solution obtained from stage d is directed to a precipitation stage e, in which an iron-based precipitant E and a neutralizing agent B are added. The obtained slurry is directed to a separation stage f, in which a solution F is obtained, which constitutes a treated arsenic-containing solution, and a slurry containing arsenic residues, which is reduced in humidity in stage g. In stage h, acidic and alkaline gelling agents G and H are mixed, respectively. In stage h, when the gelling agents G and H are mixed, the gel is directed to stage j, in which encapsulated arsenic-containing residues J are obtained.

[0009] Figure 2 The particle size distribution of the arsenic-containing residue obtained after precipitation is shown. Due to the amorphous nature of the precipitate, the particle size is very small, reaching an average of 11 microns.

[0010] Figure 3 The particle size distribution of the arsenic-containing residue obtained after encapsulation is shown. Due to the amorphous nature of the precipitate, the particle size is very small, reaching an average of 10 microns.

[0011] Figure 4 Figure 1 shows an SEM analysis of particles obtained by precipitation of arsenic with ferric arsenate followed by encapsulation with aluminum gel. XRD analysis of the resulting material shows that the solid is amorphous. The points marked with a cross in the figure represent the composition FeAs 1,1 S 0, 1Ca 0,02 Si 0,1 Al 0,3 O5, which is expanded into the following expression 0.95(FeAsO4)0.05(FeOOH)0.15(AlAsO4)0.1(AlOOH)0.02(CaSO4)0.1(SiO2)0.025(Al2(SO4)3).

[0012] By the method claimed in the present invention, it was observed that by adding aluminum as a stabilization source, a higher stability can be provided to amorphous ferric arsenate, maintaining the Fe / As molar ratio below 2. The stability is provided because the aluminum in the gel reacts with part of the arsenic to form aluminum arsenate, which constitutes a stable arsenic-containing residue at a molar ratio of aluminum to arsenic of 2: 1. In this sense, the formation of amorphous ferric arsenate and aluminum arsenate has a synergistic effect, reducing the release of As from the residue to the leaching medium in the TCLP test, which is confirmed in various application examples disclosed in this patent application. Summary of the invention

[0013] 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 that is deposited in a stable manner.

[0014] 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.

[0015] 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.

[0016] 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.

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

[0018] In a more specific aspect, the wastewater can contain sulfuric acid at a concentration between 2 g / L and 200 g / L.

[0019] The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue comprises a first step i) neutralization, wherein the arsenic-containing wastewater is contacted with a first neutralizing agent to generate a first neutralized arsenic-containing wastewater.

[0020] The method for removing arsenic includes a second step ii) oxidation, in which As(III) is oxidized to As(V) by adding a first oxidizing agent to generate a second oxidized arsenic-containing wastewater.

[0021] The method for removing arsenic includes a third step iii) adjusting the Fe(III) / As(V) ratio, wherein the second oxidized arsenic-containing wastewater is mixed with the first iron solution to generate a third arsenic-containing wastewater.

[0022] The method for removing arsenic includes a fourth step iv) 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.

[0023] The method for removing arsenic includes a fifth step v) solid-liquid separation, wherein the first arsenic-containing residue slurry obtained in step iv) is separated to generate a fourth arsenic-containing wastewater and the first arsenic-containing residue.

[0024] The method for removing arsenic comprises a sixth step vi) of encapsulation, wherein the first arsenic-containing residue obtained in step v) is mixed with a gel to generate a second arsenic-containing residue.

[0025] 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.

[0026] 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.

[0027] In another preferred variant of the present invention, the calcium-based neutralizing agent of step i) is formulated into a neutralizing agent slurry with water, wherein the concentration of the neutralizing agent in the neutralizing agent slurry is between 15% w / w and 25% w / w.

[0028] In another preferred variant of the invention, in the first step i), a first neutralized wastewater slurry is obtained, which is conveyed to a first separation stage to generate a first neutralized arsenic-containing wastewater and a first residue.

[0029] 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.

[0030] 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 filtration solution and a first residue.

[0031] 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.

[0032] In another preferred variant of the invention, the first residue obtained from step i) is subjected to a leaching stage to remove arsenic, thereby generating a second residue slurry.

[0033] In another preferred variant of the invention, the leaching stage is carried out with an acid solution.

[0034] In another preferred variant of the invention, the acid solution comprises sulfuric acid.

[0035] 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.

[0036] In another preferred variant of the invention, the leaching stage is carried out at a temperature ranging from 40°C to 80°C.

[0037] In another preferred variant of the invention, the leaching stage is carried out at a solids content of 10% w / w to 40% w / w in the slurry obtained by mixing the first residue with the acid solution.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] In another preferred variant of the invention, the second residue comprises gypsum and it constitutes a stable residue.

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

[0044] In another preferred variant of the present invention, after adding the neutralizing agent, a first neutralized arsenic-containing wastewater is generated.

[0045] In another preferred variant of the present invention, in step ii) oxidation, the first oxidant is hydrogen peroxide or sodium chlorite. In another preferred variant of the present invention, in step ii) oxidation, the hydrogen peroxide is carried out at a dosage of 1 mol to 2 mol H2O2 / mol As(III), or the sodium chlorite is carried out at a dosage of 0.5 mol to 1 mol NaClO2 / mol As(III).

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

[0047] In another preferred variant of the invention, in step iii) adjusting the Fe(III) / As(V) molar ratio, the first iron solution comprises a magnetite leachate which has been oxidized by a second oxidant to convert all ferrous ions into ferric ions.

[0048] In another preferred variation of the present invention, the first iron solution comprises magnetite leachate, and the second oxidant for oxidizing the first iron solution is selected from one of hydrogen peroxide and sodium chlorite.

[0049] In another preferred variant of the present invention, in step iii) adjusting the Fe(III) / As(V) molar ratio, the Fe(III) / As(V) molar ratio is adjusted between 1 and 1.3.

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

[0051] In another preferred variant of the present invention, in step iv) 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, calcium oxide, calcium hydroxide, calcium carbonate or dolomitic limestone.

[0052] In another preferred variant of the present invention, in step iv) arsenic precipitation, the second neutralizing agent is selected from one of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, magnesium oxide, magnesium hydroxide or magnesium carbonate.

[0053] In another preferred variant of the invention, step v) solid-liquid separation is performed by a first concentration, clarification or centrifugation sub-step, to which the first arsenic-containing residue slurry is subjected to obtain a third overflow solution and a third concentrated slurry.

[0054] In another preferred variant of the invention, step v) solid-liquid separation is followed by a second filtration sub-stage, to which the third concentrated slurry is subjected to generate a third filtered solution and a first arsenic-containing residue.

[0055] In another preferred variant of the present invention, step v) solid-liquid separation is followed by a third mixing sub-stage, in which a third overflow solution and a third filtered solution are provided to generate a fourth arsenic-containing wastewater.

[0056] In another preferred variant of the invention, in step vi) encapsulation, the gel mixed with the first arsenic-containing residue consists of 3 + The method is prepared by mixing an aqueous solution of a valent metal salt and an aqueous solution of an alkaline earth metal.

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

[0058] In a more specific aspect, 3 + The valent metal salt is aluminum sulfate.

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

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

[0061] In another preferred variant, the gel is prepared by adding a volume of 3 + The aqueous solution of the valent metal and a certain volume of the aqueous solution of the alkaline earth metal are prepared so that the alkaline earth metal and the 3 + The molar ratio of the valent metal is between 2 and 3.

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

[0063] 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

[0064] 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.

[0065] Neutralization

[0066] Examples 1 to 7

[0067] Prepare 3500mL of arsenic (III) concentration is 12g / L and sulfuric acid concentration is 70g / L and 150g / L arsenic solution, and place it in 5L glass reactor, wherein add CaCO or Ca (OH) to adjust pH to 1 to 2 range, pH is measured according to pH Ag / AgCl electrode. At room temperature, reactor is stirred for 2 hours with 300rpm. When reaction time ends, slurry is carried out solid-liquid separation by filtering. Wash solid with acidified solution of pH 1, for subsequent TCLP analysis. Result is as shown in Table 1.

[0068] Table 1. Gypsum removal results of Examples 1-7

[0069]

[0070] Examples 8 to 21

[0071] 3500 mL of arsenic solution with a 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 between 20°C and 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 at pH 1 for subsequent TCLP analysis. The results are shown in Table 2.

[0072] Table 2. Gypsum leaching results of Examples 8-21

[0073]

[0074] Oxidation of arsenite ions

[0075] Examples 22 and 23

[0076] 4500 mL of arsenic solution with an arsenic (III) concentration of 10 g / L and a sulfuric acid concentration of 2 g / L and a pH of 2 was prepared from Application Examples 1 to 5 and placed in a 5 L glass reactor, to which 30% w / w hydrogen peroxide was added at a dosage of 1.1 mol H2O2 / mol As(III) and 80% w / w sodium chlorite was added at a dosage 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.

[0077] Table 3. Results of Examples 22 and 23

[0078] test unit 22 23 Oxidants - Hydrogen Peroxide Sodium chlorite dose Oxidation mol / mol As(III) 1.1 0.5 Oxidation yield ％ 98 95

[0079] Examples 24 to 29

[0080] 4500 mL of sulfuric acid plant wastewater solution (pH 2 solution from Application Examples 1 to 5) with arsenic (III) concentration 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, wherein 50% w / w hydrogen peroxide was added at a ratio of 1.0 mol 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.

[0081] Table 4. Results of Examples 24 to 29

[0082] test unit 24 25 26 27 28 29 As(III) concentration g / L 12 12 12 8.5 8.5 8.5 dose Oxidation mol / mol As(III) 1.0 1.4 1.6 1.2 1.6 1.9 Oxidation yield ％ 80.2 99.1 99.9 66.9 95.3 99.9

[0083] Arsenic removal

[0084] Examples 30 to 45

[0085] 3500mL of arsenic solution with a concentration of 10g / L As(V) and a concentration of 2g / L sulfuric acid (from a solution with a pH of 2 of Application Examples 1 to 5 and oxidized according to the conditions of Test Example 28) was prepared and placed in a 5L glass reactor, to which magnetite leachate (with a concentration of 156g / L Fe and 40g / L Fe(II)) was added to maintain a Fe(III) / As(V) molar ratio between 1.1mol and 2mol Fe(III) / mol As(V). The pH of the solution was adjusted to a range of 2 to 4 (measured with an Ag / AgCl pH electrode) by adding a sodium hydroxide solution prepared at a concentration of 10mol / L, a 25% w / w lime slurry or a 18% w / w dolomite lime slurry. The reactor was stirred at 400rpm for 6 hours at 20°C. When the reaction time was over, the slurry was subjected to solid-liquid separation by filtration. The results are shown in Table 5.

[0086] Table 5. Precipitation results of Examples 30-45

[0087]

[0088]

[0089] Examples 46 to 51

[0090] 3500mL of arsenic solution (from Application Examples 1-5, pH 2 solution, oxidized according to the conditions of Test Example 28) with an As(V) concentration of 10g / L and a sulfuric acid concentration of 2g / L was prepared and placed in a 5L glass reactor, wherein aluminum sulfate tetradecahydrate was added to maintain the Al(III) / As(V) molar ratio between 1.1 and 2mol / mol. The solution was adjusted to a pH of 5 by adding a sodium hydroxide solution prepared at a concentration of 10mol / L and 25% w / w of Ca(OH)2 (depending on the situation). The reactor was stirred at 400rpm for 6 hours at room temperature. When the reaction time was over, the slurry was subjected to solid-liquid separation by filtration. The results are shown in Table 6.

[0091] Table 6. Precipitation results of Examples 46-51

[0092] Variables / Examples unit 46 47 48 49 50 51 Neutralizer - NaOH NaOH NaOH <![CDATA[Ca(OH)2]]> <![CDATA[Ca(OH)2]]> <![CDATA[Ca(OH)2]]> Al(III) / As(V) ratio mol / mol 1.2 1.5 2.0 1.2 1.5 2.0 As removal rate ％ 97.0 99.0 99.6 99.0 99.8 99.9 As released in TCLP mg / L 121 52.1 5.4 118 47.5 4.7

[0093] Stabilization

[0094] Examples 52 to 64

[0095] Take 10 mL of 2N aluminum sulfate solution and 10 mL of 5M sodium hydroxide solution and mix with a stainless steel impeller. After stirring for 10 to 20 seconds, when a gel is formed, add the arsenic-containing residue precipitated according to Examples 30 to 45 to maintain the ratio of gel volume to arsenic-containing residue mass between 0.09 mL / g and 0.48 mL / g. After mixing with a glass rod for 5 minutes, place the sample in a mold and dry it at humid and 20°C for 7 days. The results are shown in Table 7.

[0096] Table 7. Results of Examples 52-64

[0097]

[0098] Embodiment 65

[0099] The precipitation was carried out on a solution of sulphuric acid plant wastewater, which was pre-adjusted to pH 2 according to the conditions of Example 7 and oxidized at a ratio of 1.6 mol H2O2 / mol As(III). The arsenic concentration was 8.5 g / L. The solution was placed in a 100 L reactor, to which a magnetite leachate with a concentration of 156 g / L Fe and 40 g / L Fe(II) was added to obtain a Fe(III) / As(V) ratio of 1.1 mol / mol. The solution was kept at pH 4 for 6 hours, adjusted with 18% w / w CaCO3 and stirred at 400 rpm. Subsequently, the slurry was filtered on a plate filter and the solids with a moisture content of 20% were mixed with a gel prepared from equal volumes of 2N aluminium sulphate solution and 5M sodium hydroxide solution to give a gel volume:arsenic residue ratio (Gel / ReAs) of 0.1 mL / g and 0.2 mL / g. The results are shown in Tables 8-11.

[0100] Table 8. Composition of arsenic-containing precipitate in Example 65

[0101] element content% arsenic 14.7 iron 11.0 aluminum 0.21 silicon 0.05 calcium 9.1

[0102] Table 9. Composition of 0.1 mL / g of Gel / ReAs encapsulated arsenic compounds in Example 65

[0103] element content% arsenic 13.0 iron 10.0 aluminum 0.37 silicon 0.04 calcium 7.4

[0104] Table 10. Composition of wastewater discharged in Example 65

[0105] element Content mg / L arsenic 3.8 iron 0.1 Arsenite ion <370

[0106] Table 11. Stability test results of Example 65

[0107] solid Total As (TCLP) mg / L Total As (SPLP) mg / L Non-encapsulated ferric arsenate in continuous mode 9.04 9.32 Encapsulated ferric arsenate, Gel / ReAs=0.1mL / g <0.01 0.02 Encapsulated ferric arsenate, Gel / Reas=0.2mL / g <0.01 1.40

[0108] The results of Example 65 show that high removal rates can be obtained using a Fe / As molar dose equal to 1.1, and stability in the As concentration released in the TCLP test is achieved by encapsulating with aluminum gel at a dose of 0.1 mL-0.2 mL gel / g arsenic-containing residue.

Claims

1. A method for removing arsenic from arsenic-containing wastewater to produce a stable arsenic-containing residue, characterized in that: include: i) a first step i) neutralization, wherein the arsenic-containing wastewater is contacted with a first neutralizing agent to generate a first neutralized arsenic-containing wastewater; ii) a second step ii) oxidation, wherein As(III) is oxidized to As(V) by adding a first oxidizing agent to generate a second oxidized arsenic-containing wastewater; iii) the third step iii) adjusting the Fe(III) / As(V) molar ratio, wherein the second oxidized arsenic-containing wastewater is mixed with the first iron solution to generate a third arsenic-containing wastewater; iv) a fourth step iv) 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; v) a fifth step v) solid-liquid separation, wherein the first arsenic-containing residue slurry obtained in step iv) is separated to generate a fourth arsenic-containing wastewater and a first arsenic-containing residue; vi) A sixth step vi) packaging, wherein the first arsenic-containing residue obtained in step v) is mixed with a gel to generate a second arsenic-containing residue.

2. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to claim 1, characterized in that: In step i), the pH value is adjusted to be in the range of 0.5 to 2.

3. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to any one of 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 for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to claim 3, characterized in that: The calcium-based neutralizer of step i) is prepared 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.

5. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to claim 1, characterized in that: In the first step i), a first neutralized wastewater slurry is obtained, which is conveyed to a first separation stage to generate a first neutralized arsenic-containing wastewater and a first residue.

6. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to claim 5, characterized in that: The first separation stage includes a first concentration, clarification or centrifugation sub-stage, through which the first neutralized wastewater slurry undergoes to obtain a first overflow solution and a first concentrated slurry; the first separation stage includes a second filtration sub-stage, through which the first concentrated slurry undergoes to generate a first filtered solution and a first residue; the first separation stage includes a third mixing sub-stage, in which the first overflow solution and the first filtered solution are provided to generate a first neutralized arsenic-containing wastewater.

7. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to claim 5, characterized in that: The first residue obtained from step i) is subjected to a leaching stage to remove arsenic, thereby generating a second residue slurry.

8. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to claim 7, characterized in that: The leaching stage is carried out with a sulfuric acid solution, wherein the concentration of sulfuric acid in the solution is between 10 g / L and 75 g / L, and the leaching stage is carried out at a temperature range of 40° C. to 80° C. and a solid content of 10% w / w to 40% w / w in the slurry obtained by mixing the first residue with the sulfuric acid solution.

9. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to claim 7, 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.

10. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to claim 9, characterized in that: The second separation stage includes a first concentration, clarification or centrifugation sub-stage, through which the second residue slurry undergoes to obtain a second overflow solution and a second concentrated slurry; the second separation stage includes a second filtration sub-stage, through which the second concentrated slurry undergoes to generate a second filtered solution and a second residue; the second separation stage includes a third mixing sub-stage, in which the second overflow solution and the second filtered solution are provided to generate a second arsenic-containing wastewater.

11. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to claim 10, characterized in that: The second residue includes gypsum and constitutes a stable residue.

12. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to claim 3, characterized in that: The sodium-based neutralizing agent in step i) is prepared with water to a concentration between 1 and 10 mol / L.

13. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to any one of claims 1 to 12, characterized in that: After adding the neutralizing agent, the first neutralized arsenic-containing wastewater is generated.

14. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to claim 1, characterized in that: In the oxidation step ii), the first oxidizing agent is hydrogen peroxide or sodium chlorite.

15. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to claim 1, characterized in that: In step ii), the oxidation is carried out at a dosage of hydrogen peroxide in a ratio of 1 mol to 2 mol H2O2 / mol As(III), or at a dosage of sodium chlorite in a ratio of 0.5 mol to 1 mol NaClO2 / mol As(III).

16. The method of claim 1 for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue, characterized in that: In step iii) of adjusting the Fe(III) / As(V) molar ratio, the first iron solution comprises one of ferric sulfate, ferric chloride, or a leaching solution of an iron ore, such as hematite, goethite, or magnetite.

17. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to claim 16, characterized in that: In step iii) of adjusting the Fe(III) / As(V) molar ratio, the first iron solution comprises magnetite leachate, and all ferrous ions in the first iron solution have been converted into ferric ions by oxidation with a second oxidant.

18. The method for removing arsenic from arsenic-containing wastewater to generate a stable arsenic-containing residue according to claim 17, characterized in that: The first iron solution comprises magnetite leachate, and the second oxidant used to oxidize the first iron solution is selected from one of hydrogen peroxide and sodium chlorite.

19. The method of claim 1 for removing arsenic from arsenic-containing wastewater to produce a stable arsenic-containing residue, characterized in that: Step iii) adjusting the Fe(III) / As(V) molar ratio to between 1 and 1.

3.

20. The method of claim 1 for removing arsenic from arsenic-containing wastewater to produce a stable arsenic-containing residue, characterized in that: Step iv) arsenic precipitation is carried out at a pH of 2 to 4 and a temperature of 15° C. to 25° C. for 1 to 24 hours.

21. The method of claim 1 for removing arsenic from arsenic-containing wastewater to produce a stable arsenic-containing residue, characterized in that: In step iv) 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, calcium oxide, calcium hydroxide, calcium carbonate or dolomitic limestone.

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

23. The method of claim 1 for removing arsenic from arsenic-containing wastewater to produce a stable arsenic-containing residue, characterized in that: Step v) solid-liquid separation is performed by a first concentration, clarification or centrifugation sub-stage, the first arsenic-containing residue slurry undergoes this sub-stage to obtain a third overflow solution and a third concentrated slurry; and then a second filtration sub-stage is performed, the third concentrated slurry undergoes this sub-stage to generate a third filtered solution and the first arsenic-containing residue; and a third mixing sub-stage in which a third overflow solution and a third filtered solution are provided to generate a fourth arsenic-containing wastewater.

24. The method of claim 1 for removing arsenic from arsenic-containing wastewater to produce a stable arsenic-containing residue, characterized in that: In step vi) packaging, the gel mixed with the first arsenic-containing residue comprises 3 + The method is prepared by mixing an aqueous solution of a valent metal salt and an aqueous solution of an alkaline earth metal.

25. The method of claim 24 for removing arsenic from arsenic-containing wastewater to produce a stable arsenic-containing residue, characterized in that: 3 + The valent metal salt is selected from one of ferric sulfate, ferric chloride, anhydrous aluminum sulfate, aluminum sulfate tetradecahydrate, aluminum sulfate octadechydrate or aluminum chloride.

26. The method of claim 25 for removing arsenic from arsenic-containing wastewater to produce a stable arsenic-containing residue, characterized in that: 3 + The valent metal salt is preferably anhydrous aluminum sulfate, aluminum sulfate tetradecahydrate or aluminum sulfate octadecadecahydrate.

27. The method of claim 24 for removing arsenic from arsenic-containing wastewater to produce a stable arsenic-containing residue, characterized in that: The aqueous solution of the alkaline earth metal is equivalent to a sodium hydroxide solution.

28. The method of claim 24 for removing arsenic from arsenic-containing wastewater to produce a stable arsenic-containing residue, characterized in that: The gel was prepared by adding a certain volume of 3 + The aqueous solution of the valent metal and a certain volume of the aqueous solution of the alkaline earth metal are prepared so that the alkaline earth metal and the 3 + The molar ratio of the valent metal is between 2 and 3; preferably, the dosage of the gel is such that 3 + The molar ratio of the valence metal to the total As contained in the first arsenic-containing residue is in the range of 0.1 to 0.3.

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