Production of scorodite from solutions comprising arsenic and sulfuric acid

Abstract

The invention relates to a method for producing scorodite from a solution comprising arsenic and sulfuric acid without the use of a neutralizing agent, comprising the following steps: i. Subjecting a first arsenic solution comprising arsenic and sulfuric acid in the form of a mixture of arsenite ions and arsenate ions to an oxidation treatment, oxidizing the arsenite ions into arsenate ions, a second arsenic solution is obtained; ii, adding a first solution containing ferrous ions into the second arsenic solution to generate a third arsenic solution; iii. Adding a first portion of magnetite to the third arsenic solution to adjust the molar ratio of iron ions to arsenate ions to 0.3-1 to generate a first arsenic slurry; iv. Adding to the first arsenic slurry a portion of the scorodite slurry recycled from step viii as a nucleation matrix for scorodite particles, obtaining a first scorodite slurry of from 2% w / w to 15% w / w; v, heating the first scorodite slurry to 80 DEG C to 90 DEG C; vi, the first scorodite slurry is kept at the temperature of 80 DEG C to 90 DEG C for 5 h to 48 h, and second scorodite slurry is obtained; vii, conveying the second scorodite slurry to a solid-liquid separation step to obtain third scorodite slurry and a treated solution; viii. Recycling a first portion of the third scorodite slurry to step iv; and (ix) filtering a second portion of the third scorodite slurry.

Description

Technical Field

[0001] This invention relates to a method for preparing scorodite (ferric arsenate hydrate), which eliminates the need for a neutralizing agent to adjust the pH value during preparation. The method uses a solution containing a high concentration of arsenic as raw material. This solution can originate from various types of mining waste treatment processes, where the obtained arsenic is a major impurity and requires long-term stabilization treatment. This method yields arsenic residue mainly composed of scorodite and an arsenic-depleted solution. Background Technology

[0002] Patent application WO2020237361 (D1) discloses a method for producing crystalline arsenic trioxide that is essentially free of gypsum, comprising adding an iron oxyhydroxide (FeOOH) compound to a pentavalent arsenic solution to form the arsenic trioxide. In D1, by adding iron oxyhydroxide, the iron source implicitly contains a base, which acts as an acidity regulator to neutralize the arsenic solution. D1 mentions that a base (such as magnesium oxide) needs to be added to produce iron oxyhydroxide, which is significantly different from this patent application, which explicitly states that no base is used. Furthermore, D1 does not mention, as claimed in this application, the addition of ferrous sulfate to catalyze the precipitation reaction.

[0003] Invention patent CL N°50423 (D2) aims to remove high concentrations of contaminants (such as arsenic and other substances used in the production of arsenic) from waste and liquid wastewater in hydrometallurgical processing plants. D2 discloses steps including oxidation, adjusting the Fe(III) / As(V) molar ratio to at least 1.0 by adding magnetite leaching solution, and adjusting the pH by adding a neutralizing agent. D2 co-precipitates gypsum from arsenic residue using a calcium-based neutralizing agent. D2 does not mention utilizing the recycling of arsenic seed crystals to improve precipitation kinetics.

[0004] CL patent No. 66875 (CL application No. 202101684, D3) discloses a method for obtaining mining or industrial residues of arsenic-containing spodumene with an arsenic content exceeding 15% from a highly acidic solution (acid concentration greater than 45 g / L), said solution containing copper, arsenic, and optionally iron, antimony, and / or bismuth. In its steps, D3 discloses that the method requires adjusting the acidity by generating a first gypsum residue, a two-stage As(III) oxidation, adjusting the Fe(III) / As(V) ratio by adding an iron-containing solution, recycling a portion of the spodumene slurry, acidity adjustment, and heating. The difference between D3 and this application is that this patent application does not require an acidity adjustment step and adjusts the Fe(III) / As(V) molar ratio by adding solid magnetite, rather than adding an iron-containing solution.

[0005] CA 2066905 (D4) discloses a method for reducing arsenic levels in a solution containing sulfuric acid, water, and arsenic acid. The method includes the steps of: reacting the solution with sufficient copper or a copper-containing compound at a sufficiently high temperature to generate copper arsenate; adding an alkaline solution to precipitate copper arsenate; and adding an iron ion compound to precipitate ferric arsenate. Document D4 does not conflict with this patent application because it only discloses reducing the arsenic content in arsenic-containing solutions. Summary of the Invention

[0006] Technical issues The problem with existing technology is that there is currently no method for producing arsenic residues from styrofoam containing more than 25% wt. of As, which does not require the addition of a neutralizing agent when treating solutions with sulfuric acid concentrations of 10 g / L to 80 g / L.

[0007] The advantage of this invention is that it can generate arsenic residue with an arsenic content greater than 25% wt. without the need for a neutralizing agent. Furthermore, the method claimed in this patent application allows for the oxidation of some arsenite and ferrous ions present in the solution. The remaining acid in the arsenic-poor solution can be used as an oxidant for other resources (e.g., copper oxides).

[0008] The oxidation of arsenic acid and ferrous sulfate occurs in the presence of naturally dissolved oxygen in arsenic solution, through the generation of free radicals on the surface of magnetite.

[0009] The reaction for precipitating styrofoam from magnetite is as follows:

[0010] Therefore, the overall response is as follows:

[0011] For the reasons mentioned above, the entire reaction consumes sulfuric acid, thus eliminating the need for neutralization with alkali. Adding alkali introduces complexity because the addition of a sodium-based neutralizing agent generates sodium sulfate, a salt that is difficult to remove and can hinder solution reuse in water-scarce environments. Furthermore, the presence of sodium promotes the formation of natrojarosite, which can exchange arsenate ions to form unstable arsenic-containing compounds. On the other hand, using a calcium-based neutralizing agent generates gypsum, which has the disadvantages of increasing the amount of arsenic waste generated due to co-precipitation with onionite and thus increasing treatment costs.

[0012] Precipitating arsenite from magnetite also offers other advantages related to controlling iron supersaturation. By keeping the iron source in a solid state, magnetite slowly dissolves, generating ferrous sulfate and ferric sulfate. The latter reacts rapidly at the boundary layer between the magnetite and the liquid sinus to form ferric arsenate. This ferric arsenate then evolves into crystalline ferric arsenate, i.e., arsenite. In this way, the iron ion concentration is maintained at a low level, and a concentration gradient favorable to arsenite formation is always present between arsenate and iron ions, as documented in the literature. This saturation control method differs significantly from adding soluble iron salts, which require a chain precipitation system to control iron supersaturation and thus maintain a relatively high gradient between arsenate and iron ions.

[0013] Adding ferric hydroxide, produced by dissolving iron ions (such as magnetite and / or ferric sulfate), requires leaching the magnetite with sulfuric acid to obtain ferrous sulfate and ferric sulfate, especially when using magnetite. Secondly, a neutralizing agent based on ferric hydroxide is needed, specifically a sodium and / or magnesium-based neutralizing agent, to generate ferric hydroxide without forming gypsum. This is because calcium and soluble sodium and / or magnesium sulfates are absent, making process water difficult to reuse. Ferric hydroxide readily dissolves in high-temperature environments and sulfuric acid concentrations greater than 10 g / L, causing an immediate drop in the solution's pH.

[0014] The precipitation reaction of ferric hydroxide to form styrolith is shown below:

[0015] Therefore, the overall response is as follows:

[0016] As can be clearly seen from the above, the difference between Eq.3 and Eq.8 in the overall relationship of producing independent stinky onion stones lies in the consumption of neutralizing agent. Eq.8 requires the consumption of neutralizing agent, while Eq.3 does not require the addition of neutralizing agent.

[0017] Overall, the novelty and inventiveness of this application are as follows: A. Precipitate arsenic-containing stone under high concentrations of sulfuric acid (greater than 35 g / L). This method allows for the acquisition of stable arsenic-containing residues with an As content greater than 25% wt., with virtually no gypsum formation.

[0018] B. Precipitate stinky onion stone in a sulfuric acid concentration range of 35 g / L-80 g / L without using a neutralizing agent to adjust the sulfuric acid concentration.

[0019] C. In the process of precipitating arsenic in the form of arsenite using magnetite, arsenite ions are oxidized, which reduces the need for oxidant to oxidize arsenite ions to arsenate ions. The oxidation rate of arsenite ions varies between 20% wt. and 30% wt.

[0020] D. Using ferrous ions as a catalyst for the precipitation reaction of styrax allows the precipitation system to proceed under conditions where the Fe(III) / As(V) molar ratio is less than 1.0. Attached Figure Description

[0021] Figure 1 The effect of varying the solid percentage on the kinetics of arsenic (V) precipitation in the form of arsenic trioxide is shown under conditions of arsenic solution concentration of 10 g / L, sulfuric acid concentration of 70 g / L, and ferrous ion concentration of 20 g / L.

[0022] Figure 2 The effects of sulfuric acid concentrations ranging from 5 g / L to 25 g / L and ferrous ion concentrations on the precipitation kinetics of styrofoam in sulfuric acid plant effluent—molar ratio Fe(III)—are shown. Mag / As(V)=1.0. The figure shows the curves of ferrous ion concentration change under the same sulfuric acid concentrations (5 g / L and 25 g / L).

[0023] Figure 3 The effects of sulfuric acid concentrations of 40 g / L–70 g / L and ferrous ion concentration on the precipitation kinetics of styrofoam in sulfuric acid plant effluent—molar ratio Fe(III)—are shown. Mag / As(V)=1.0. The figure shows the curve of ferrous ion concentration change under the same sulfuric acid concentration.

[0024] Figure 4 The effect of ferrous ion concentrations of 0.5 g / L, 2 g / L, and 5 g / L on the precipitation kinetics of styrofoam in sulfuric acid plant effluent—molar ratio Fe(III)—is shown. Mag / As(V)=1.0. The figure shows the curves for H2SO4 concentrations of 5 g / L, 25 g / L, 40 g / L and 70 g / L at the same ferrous ion concentration.

[0025] Figure 5 The effect of ferrous ion concentration on the residual sulfuric acid concentration in EPAS solution (sulfuric acid plant effluent) is shown—molar ratio Fe(III). Mag / As(V)=1.0.

[0026] Figure 6The effect of sulfuric acid concentrations from 5 g / L to 25 g / L and ferrous ion concentrations on the As concentration of arsenic residues (ReAs) in TCLP (Toxicity Characteristic Leaching Procedure) tests—molar ratio Fe(III)—is shown. Mag / As(V)=1.0.

[0027] Figure 7 The effect of sulfuric acid concentrations from 40 g / L to 70 g / L and ferrous ion concentrations on the As concentration of arsenic residues (ReAs) in TCLP (Toxicity Characteristic Leaching Procedure) tests—molar ratio Fe(III)—is shown. Mag / As(V)=1.0.

[0028] Figure 8 The effect of sulfuric acid concentrations from 5 g / L to 25 g / L and ferrous ion concentrations on the As content in arsenic residue ReAs—molar ratio Fe(III)—is shown. Mag / As(V)=1.0.

[0029] Figure 9 The effect of sulfuric acid concentrations from 40 g / L to 70 g / L and ferrous ion concentrations on the As content in arsenic residue ReAs—molar ratio Fe(III) is shown. Mag / As(V)=1.0.

[0030] Figure 10 The effect of sulfuric acid concentrations from 5 g / L to 25 g / L and ferrous ion concentrations on the Fe content in arsenic residue ReAs—molar ratio Fe(III) is shown. Mag / As(V)=1.0.

[0031] Figure 11 The effect of sulfuric acid concentrations from 40 g / L to 70 g / L and ferrous ion concentrations on the Fe content in arsenic residues (ReAs) is shown—molar ratio Fe(III). Mag / As(V)=1.0.

[0032] Figure 12 The effect of sulfuric acid and ferrous ion concentrations on the precipitation kinetics of spatholite in EPAS solution is shown as the ferrous ion concentration increases from 5 g / L to 20 g / L—molar ratio Fe(III). Mag / As(V)=1.0.

[0033] Figure 13 The effects of high concentrations of sulfuric acid and ferrous ions on the As and Fe contents in arsenic residue ReAs—molar ratio Fe(III)—are shown. Mag / As(V)=1.0.

[0034] Figure 14 The effect of sulfuric acid concentrations from 0 g / L (pH 2) to 10 g / L on the As concentration in slaked sulfuric acid plant effluent—with a ferrous concentration of 5 g / L and Fe(III) concentration—is shown. Mag / As(V) molar ratio = 0.5.

[0035] Figure 15 This demonstrates the reduction of Fe(III) Mag Effect of / As(V) molar ratio and ferrous ion concentration on As concentration in the treated EPAS solution—sulfuric acid concentration 5.0 g / L.

[0036] Figure 16 This demonstrates the reduction of Fe(III) Mag Effects of / As(V) molar ratio and ferrous ion concentration on the As(III) concentration in the treated EPAS solution—sulfuric acid concentration 5.0 g / L.

[0037] Figure 17 This demonstrates the reduction of Fe(III) Mag Effect of / As(V) molar ratio and ferrous ion concentration on Fe concentration in treated EPAS solution—sulfuric acid concentration 5.0 g / L.

[0038] Figure 18 This demonstrates the reduction of Fe(III) Mag Effects of / As(V) molar ratio and ferrous ion concentration on Fe(II) concentration in treated EPAS solution—sulfuric acid concentration 5.0 g / L.

[0039] Figure 19 This demonstrates the reduction of Fe(III) Mag Effects of / As(V) molar ratio and ferrous ion concentration on As and Fe content in arsenic residue ReAs—sulfuric acid concentration 5.0 g / L.

[0040] Figure 20 The diagram shows the application of Fe(III) Mag The effect of decreasing the / As(V) molar ratio from 0.5 to 0.3 on the concentrations of As and As(III) in the treated EPAS solution—ferrous iron concentration of 5.0 g / L and sulfuric acid concentration of 5.0 g / L.

[0041] Figure 21 The diagram shows the application of Fe(III) Mag The effect of decreasing the / As(V) molar ratio from 0.5 to 0.3 on the Fe and Fe(II) concentrations in the treated EPAS solution—with ferrous iron concentration of 5.0 g / L and sulfuric acid concentration of 5.0 g / L.

[0042] Figure 22 The diagram shows the application of Fe(III) Mag The effect of decreasing the / As(V) molar ratio from 0.5 to 0.3 on the As and Cd concentrations released from the scorched stone residue in the TCLP (Toxicity Characteristic Leaching Procedure) test—with ferrous iron concentration of 5.0 g / L and sulfuric acid concentration of 5.0 g / L.

[0043] Figure 23 The diagram shows the application of Fe(III) Mag Effect of decreasing the / As(V) molar ratio from 0.5 to 0.3 on the As and Fe concentrations in the scorched onion stone residue—ferrous iron concentration of 5.0 g / L and sulfuric acid concentration of 5.0 g / L.

[0044] Figure 24 The effect of reducing the initial As(III) concentration on the As and As(III) concentrations in the treated EPAS solution—Fe(III) is shown. Mag / As(V) molar ratio is 0.5 — sulfuric acid concentration is 5.0 g / L — ferrous ion concentration is 5 g / L.

[0045] Figure 25 The effect of increasing the initial As(III) concentration on the As and As(III) concentrations in the treated EPAS solution—Fe(III) is shown. Mag / As(V) molar ratio is 1.0 — sulfuric acid concentration is 5.0 g / L — ferrous ion concentration is 5 g / L.

[0046] Figure 26 The effect of increasing the initial As(III) concentration on the Fe and Fe(II) concentrations in the treated EPAS solution is shown. Mag / As(V) molar ratio is 0.5 — sulfuric acid concentration is 5.0 g / L — ferrous ion concentration is 5 g / L.

[0047] Figure 27 The effect of reducing the initial As(III) concentration on the Fe and Fe(II) concentrations in the treated EPAS solution is shown. Mag / As(V) molar ratio is 1.0 — sulfuric acid concentration is 5.0 g / L — ferrous ion concentration is 5 g / L.

[0048] Figure 28 The effect of reducing the initial Fe(II) concentration on the As and As(III) concentrations is shown—Fe(III) Mag / As(V) molar ratio is 1.0 — sulfuric acid concentration is 25 g / L to 75 g / L — ferrous ion concentration is 0.5 g / L.

[0049] Figure 29 The effect of reducing the initial Fe(II) concentration on the As and As(III) concentrations is shown—Fe(III) Mag / As(V) molar ratio is 1.0 — sulfuric acid concentration is 5 g / L — ferrous ion concentration is 1.0 g / L to 2.0 g / L.

[0050] Figure 30 The effect of initial Fe(II) concentrations of 3 g / L to 4 g / L on As and As(III) concentrations is shown—with a sulfuric acid concentration of 5.0 g / L—Fe(III) concentration. Mag The / As(V) ratio is 0.50 mol / mol (equivalent to Fe(III)). Mag / As(V) is 0.50 mol / mol).

[0051] Figure 31 The arsenic concentrations in the formation tests of scorched onion stone with only magnetite and only ferrous sulfate as the iron source are shown.

[0052] Figure 32 The following is shown in Fe(III) Mag Diffraction pattern of arsenic residue ReAs precipitated after 24 h under conditions of / As(V) molar ratio of 1.0, ferrous ion concentration of 5 g / L and sulfuric acid concentration of 5 g / L.

[0053] Figure 33 The following is shown in Fe(III) Mag Scanning electron microscope image of arsenic residue ReAs precipitated after 24 h under conditions of / As(V) molar ratio of 1.0, ferrous ion concentration of 5 g / L and sulfuric acid concentration of 5 g / L.

[0054] Figure 34 The following is shown in Fe(III) Mag The particle size distribution of arsenic residue ReAs produced after 48 h of precipitation under conditions of / As(V) molar ratio of 0.5, ferrous ion concentration of 4 g / L and sulfuric acid concentration of 5 g / L.

[0055] Figure 35 A scanning electron microscope image of magnetite used in the styrofoam precipitation test is shown. Detailed Implementation

[0056] In the field of stabilization of harmful elements, one of the ways to generate stable arsenic waste is related to the optimization of the generation of concentrated arsenic stone, and the applicant of this patent application is dedicated to this.

[0057] To achieve these optimizations, one proposed approach is to use magnetite as a direct input, utilizing a solution from the EcoMetales plant for onionite precipitation, thereby consuming sulfuric acid in the pregnant leach solution (PLS) while reducing limestone consumption during process acidity adjustment. More efficient sulfuric acid consumption helps reduce gypsum formation and thus the mass of arsenic residue produced, while maintaining or even increasing arsenic precipitation rates during emission reduction. Based on experience gained from the PLS arsenic removal process design at EcoMetales, alternatives to this technology for removing arsenic from sulfuric acid plant effluent generated during smelting and / or roasting processes are proposed and evaluated.

[0058] Specifically, this application discloses a method for obtaining arsenic-containing onion stone from a solution containing arsenic and sulfuric acid without the use of a neutralizing agent, the method comprising the following steps: i. Oxidize a first arsenic solution containing arsenic and sulfuric acid in the form of a mixture of arsenite ions and arsenate ions to oxidize the arsenite ions to arsenate ions, thereby obtaining a second arsenic solution; ii. Add a first solution containing ferrous ions to the second arsenic solution to generate a third arsenic solution; iii. Add a first portion of magnetite to the third arsenic solution to adjust the molar ratio of iron ions to arsenate ions, thereby generating a first arsenic slurry; iv. Add a portion of the arsenic slurry recycled from step (viii) to the first arsenic slurry as a nucleation matrix for the arsenic particles to obtain the first arsenic slurry; v. Heat the first stinky onion stone slurry to 80°C to 90°C; vi. The first stinky onion stone slurry is kept at a temperature of 80°C to 90°C for 5 h to 48 h and continuously stirred to obtain the second stinky onion stone slurry; vii. The second stinky onion stone slurry is sent to a solid-liquid separation step to obtain the third stinky onion stone slurry and the treated solution; viii. Recycle the first portion of the third stinky onion slurry to step (iv); and ix. Filter the second portion of the third stinky onion stone slurry to obtain stinky onion stone filter cake, and send the stinky onion stone filter cake to the final processing.

[0059] In a preferred embodiment, the arsenic concentration of the first arsenic solution is from 1 g / L to 15 g / L.

[0060] In another preferred embodiment, the sulfuric acid concentration of the first arsenic solution is from 5 g / L to 80 g / L. In another preferred embodiment, the oxidation treatment described in step (i) consists of the addition of one of hydrogen peroxide or sodium chlorite, or a photo-oxidation treatment.

[0061] In another preferred embodiment, the first solution described in step (ii) comprises ferrous sulfate.

[0062] In another preferred embodiment, the concentration of ferrous ions described in step (ii) is adjusted to 0.5 g / L to 25 g / L.

[0063] In another preferred embodiment, magnetite is added so that the molar ratio of iron ions to arsenate ions in step (iii) is adjusted to 0.3 to 1.

[0064] In another preferred embodiment, 80% of the magnetite portion added in step (iii) has a particle size of less than 75 micrometers.

[0065] In another preferred embodiment, the portion of the stinky onion stone slurry added in step (iv) makes the solid content of the first stinky onion stone slurry range from 2% wt. to 15% wt.

[0066] In another preferred embodiment, the temperature of step (v) is 85°C.

[0067] Example The following embodiments should be considered as implementations of the present invention, but are by no means limitations on the present invention, as various modifications that can be made thereto will be included within the scope of protection claimed by the present invention.

[0068] Example 1 Changes in solid percentage 3800 g of arsenic solution was placed in a 5000 mL reactor. The sulfuric acid concentration in the arsenic solution was 70 g / L. Magnetite with a purity of 96% was added to the reactor to increase the Fe(III) content. Mag The ratio of As(V) to Fe (expressed as the number of moles of iron ions in magnetite) was equal to 1, and the mixture was mechanically stirred at a constant speed of 600 rpm at 85°C while maintaining reflux using a condenser for 48 h. A certain amount of styrax seed crystals was added to adjust the percentage of test solids to 4% to 15%. Slurry samples were collected at different time points, and the concentrations of As, As(III), Fe, Fe(II), and H2SO4 in the liquid phase were analyzed. The solid composition was analyzed at the end of the test, and the results are as follows: Figure 1 As shown.

[0069] The results showed that adding a higher amount of arsenic seed crystals could significantly improve the precipitation kinetics of arsenic (V), with the best effect achieved when the amount of recycled arsenic seed crystals was 15% wt.

[0070] Example 2 Precipitate onion stone from sulfuric acid plant effluent (EPAS) 3800 g of arsenic solution was placed in a 5000 mL reactor. The concentration of sulfuric acid in the arsenic solution was 0 g / L (pH 2) to 5 g / L. The concentration of As in the arsenic solution was 5 g / L to 12 g / L. As(III) was oxidized with peroxide until the solution contained 100 mg / L to 300 mg / L of As(III). In applications where the As(III) concentration was higher than this range, arsenic trioxide (Pa) was added to increase the initial concentration. Magnetite with a purity of 96% was added to the reactor to increase the Fe(III) concentration. Mag The molar ratio of As(V) (expressed as the number of moles of iron ions in magnetite) (represented as RM in the figure) varies between 0.3 and 1.2. This molar ratio can also be expressed as Fe(III). Mag / As(V), this value multiplied by Fe(III) Mag The / As(V) molar ratio was 1.5 times because every two moles of iron ions in the magnetite mineral (chemical formula FeOFe2O3) used in the experiment contained two moles of ferrous ions. The concentration was adjusted by adding ferrous sulfate heptahydrate, varying the ferrous ion concentration between 0.5 g / L and 20 g / L. The initial percentage of onionite seed solids was 15 wt.%, provided as pre-precipitated magnetite. The slurry was kept under constant reflux for 24 h to 72 h using a condenser at a constant mechanical stirring of 600 rpm and a temperature of 85 °C. Slurry samples were collected at different time points to analyze the concentrations of As, As(III), Fe, Fe(II), and H2SO4 in the liquid phase, and the solid composition was analyzed at the end of the test. The results are as follows. Figures 2 to 35 As shown.

[0071] The effects of H2SO4 concentration and ferrous ion concentration.

[0072] Figure 2 , Figure 3 and Figure 4 The following is shown in Fe(III) MagThe variation of arsenic concentration during the precipitation of arsenic from styrax was investigated using different sulfuric acid and ferrous ion concentrations under a / As(V) magnetite molar ratio of 1.0. The results confirmed that the kinetics of arsenic precipitation (particularly the As concentration measured after 12 h of precipitation) slowed down with increasing acidity. Very slow removal kinetics were observed over 48 h when the sulfuric acid concentration was 100 g / L. The results indicate that the ferrous ion concentration has a positive effect on the arsenic removal kinetics, as lower As concentrations were observed after 12 h of precipitation using a ferrous ion concentration of 5 g / L compared to concentrations of 0.5 g / L and 2 g / L in all tests with sulfuric acid concentrations ranging from 5 g / L to 40 g / L.

[0073] Figure 5 The results show that the initial sulfuric acid concentration was 5 g / L, the initial ferrous ion concentration was 0.5 g / L to 5 g / L, and the Fe(III) concentration was... Mag The changes in sulfuric acid and ferrous ion concentrations during the precipitation of stolonite were investigated under the condition that the molar ratio of As(V) to magnetite was 1.0. The results showed that the sulfuric acid concentration changed very little (except for some analytical differences), indicating that there is an equilibrium between the acid consumed by magnetite leaching and / or ferrous sulfate oxidation and the acid generated when As(V) is removed in the form of stolonite.

[0074] Figure 6 and Figure 7 The figures show Fe(III) at different sulfuric acid concentrations and with and without ferrous ions. Mag The concentration of As released during the arsenic removal test was determined by TCLP under the condition of As(V) = 1.0 molar ratio. The results showed that the concentration of As released by TCLP was less than 1 mg / L in all the generated solids, indicating that the residue was stable.

[0075] Figure 8 , Figure 9 , Figure 10 and Figure 11 The effects of increased sulfuric acid and ferrous ion concentrations on the As and Fe contents in arsenic residues (ReAs) are shown—molar ratio Fe(III). Mag / As(V)=1.0. The results show that the As grade in the arsenic residue (ReAs) varies between 26% and 29%, while the Fe grade varies between 21% and 24%. Although a decrease in Fe content was observed in the arsenic residue, which is related to the low magnetite content in the sample, the results indicate that magnetite cannot be completely converted in the presence of high concentrations of ferrous ions. Therefore, using high concentrations of ferrous ions accelerates the reaction kinetics, but some magnetite may not react and thus exist as impurities, reducing the As grade. On the other hand, lower ferrous ion concentrations slow down precipitation kinetics but are beneficial to the complete conversion of magnetite, resulting in arsenic residue with a higher arsenic content.

[0076] Effect of increasing ferrous ion concentration to 20 g / L Figure 12 The effects of sulfuric acid concentration and ferrous ion concentration are shown when the ferrous ion concentration increases from 5 g / L to 20 g / L. Increasing the ferrous ion concentration to 20 g / L showed a positive effect on arsenic removal kinetics; however, this effect was more limited compared to the sulfuric acid concentration changes mentioned in previous sections, and also more limited compared to the ferrous ion concentrations observed in previous sections from 0.5 g / L to 5.0 g / L.

[0077] Figure 13 The effects of increased sulfuric acid concentration and ferrous ion concentration on the As and Fe content in arsenic slag ReAs—molar ratio Fe(III)—are shown. Mag / As(V)=1.0. The results show that the As grade of the ReAs in the arsenic residue varies around 26% to 29%, while the Fe grade varies between 24% and 26%. Although a decrease in Fe content was observed in the arsenic residue, which is related to the decrease in magnetite content in the sample, the results indicate that magnetite cannot be completely converted in the presence of high concentrations of ferrous ions. Therefore, there is a trade-off between the improved precipitation kinetics and the As content in the arsenic residue in the presence of both ferrous ions and magnetite.

[0078] Under conditions of pH 2 and sulfuric acid concentration of 10 g / L, Fe(III) Mag The effect of reducing the / As(V) molar ratio from 1.0 to 0.5.

[0079] Figure 14 This demonstrates the reduction of Fe(III) MagThe effects of the / As(V) molar ratio and ferrous ion concentration on the As concentration in the treated EPAS solution—with a sulfuric acid concentration of 5.0 g / L. The results showed that the most significant effect was reducing the ferrous ion concentration to 2.5 g / L, but this did not completely eliminate arsenic from the solution. Similar kinetics were observed, but the curve for a ferrous ion concentration of 2.5 g / L showed that the total arsenic concentration tended to stabilize between 300 mg / L and 700 mg / L.

[0080] Fe(III) Mag Effects of decreasing the / As(V) molar ratio from 1.0 to 0.5 and decreasing the ferrous ion concentration from 5 g / L to 2.5 g / L. Figure 15 The results show Fe(II) concentrations of 2.5 g / L and 5.0 g / L, as well as Fe(III) concentrations. Mag The comparison of the / As(V) molar ratios of 0.5 and 1.0 shows that the ferrous ion concentration has the most significant impact on arsenic removal kinetics, while no significant kinetic differences were observed at molar ratios of 0.5 and 1.0.

[0081] In particular, Figure 16 This demonstrates a significant effect of the technique: the As(III) concentration was reduced from 130 mg / L to below 20 mg / L, indicating that the system is capable of oxidizing a portion of the As(III) in the solution.

[0082] Figure 17 and Figure 18 This demonstrates the reduction of Fe(III) Mag Effects of the / As(V) molar ratio and ferrous ion concentration on Fe and Fe(II) concentrations in the treated EPAS solution—with a sulfuric acid concentration of 5.0 g / L. The results showed that when operating at a Fe(II) concentration of 2.5 g / L, the system was in a ferrous ion-deficient state, with ferrous ions being depleted within the first 12 h. This resulted in relatively slow reaction kinetics and ultimately incomplete removal due to the lack of iron in the system. Figure 15 As shown in the figure. All tests showed a decrease in FeT concentration, indicating that at least some ferrous iron was consumed for arsenic precipitation, and therefore the system precipitates arsenic in the form of arsenic trioxide via ferrous ion oxidation reaction.

[0083] Figure 19 Lower Fe(III) levels were observed. MagEffects of Fe(III) / As(V) molar ratio and ferrous ion concentration on As and Fe content in arsenic residue ReAs—with a sulfuric acid concentration of 5.0 g / L. The results show that even when the Fe(III) / As(V) molar ratio is less than 1.0, precipitates with high As concentrations can still be formed, and the Fe / As molar ratio in the residue is close to 1.0 compared to the Fe content, which is consistent with the chemical formula of arsenic.

[0084] Under conditions of sulfuric acid concentration of 0.5 g / L and ferrous ion concentration of 0.5 g / L, Fe(III) Mag Effect of reducing the / As(V) molar ratio from 0.5 to 0.3 Figure 20 The diagram shows the application of Fe(III) Mag The effect of decreasing the As(V) molar ratio from 0.5 to 0.3. The results show that the oxidation yield of As(III) is affected because the initial As(III) concentration is low, about 130 mg / L, so this decrease in reaction rate has little effect on the precipitation yield of arsenic.

[0085] Figure 21 The concentrations of Fe, Fe(II), and Fe(III) in the treated EPAS solution are shown. For the two Fe(III) groups... Mag Similar behavior was observed in the Fe(III) / As(V) molar ratio, with decreasing Fe concentration and decreasing ferrous ion concentration in the solution. These results indicate that the precipitation process can proceed under conditions where the Fe(III) / As(V) molar ratio is less than 1, where the required Fe(III) is generated by the oxidation of ferrous ions and the leaching of magnetite. The consistently low Fe(III) concentration supports the fact that the system can proceed under nucleation conditions where the concentration gradient between As(V) and Fe(III) is high enough to trigger the precipitation of stolonite. Therefore, stolonite precipitation can be carried out under low-dose ferric ion conditions without the need for a series of reactors in series, as the oxidation of magnetite and ferrous ions continuously provides ferric ions to the system, which are immediately consumed by As(V) in the solution to form stolonite.

[0086] Figure 22 The concentrations of As and Cd released during the TCLP (Toxicity Characteristic Leaching Procedure) test are shown, both below the limits for determining the hazardousness of this type of waste. In particular, Fe(III) was observed. Mag The precipitated solid with an As(V) molar ratio of 0.3 released higher values ​​of As and Cd than Fe(III) in TCLP testing. Mag The case where the / As(V) molar ratio is 0.5 is likely due to lower crystallinity at lower molar ratios, as the reaction is more dependent on the As(V) precipitation produced by the oxidation of ferrous ions.

[0087] Figure 23 Fe(III) is shown. Mag The As and Fe contents of the arsenic residues produced by the precipitation of arsenic from arsenic trioxide (Fe / As) were determined when the Fe / As molar ratio was 0.3 and 0.5. The results showed that the Fe / As ratio was close to 1, which is attributed to the precipitation of arsenic trioxide.

[0088] Effect of initial concentration of As(III) Figure 24 and Figure 25 The effect of increasing the initial As(III) concentration on the As and As(III) concentrations in the treated EPAS solution—with a sulfuric acid concentration of 5.0 g / L and a ferrous ion concentration of 5 g / L—is shown. The results indicate that when Fe(III)... Mag Magnetite concentrations of 0.5 mol / mol and 1.0 mol / mol can oxidize As(III) in solution. Furthermore, since oxidation is required to remove As(V), the reaction kinetics are slightly slowed in the presence of As(III). This result is significant because it indicates that for arsenic removal from solutions containing high concentrations of As(III), the residual As(III) concentration requirement for the arsenic oxidation process is not excessively high. This is because, under conditions of coexistence of magnetite and ferrous sulfate, the arsenic-oxidizing system can oxidize some of the As(III) in solution, thereby maximizing arsenic removal in the form of arsenic-oxidizing stone.

[0089] Figure 26 and Figure 27 The effect of increasing the initial As(III) concentration on the concentrations of Fe and Fe(II) in the treated EPAS solution—with a sulfuric acid concentration of 5.0 g / L and a ferrous ion concentration of 5 g / L—is shown. The results indicate that ferrous ion consumption exists in these tests, and this consumption is more pronounced at higher As(III) concentrations compared to solutions with lower As(III) concentrations, likely due to the activation of the oxidation cycle of the ferrous sulfate-magnetite assemblages. In all cases, the arsenic removal kinetics of this process are slow because the oxidation of arsenous ions must be completed before they can be precipitated as arsenite.

[0090] Effect of ferrous ion concentration on arsenic precipitation Figure 28 and Figure 29The effect of decreasing the initial Fe(II) concentration on the concentrations of As and As(III) is shown—from sulfuric acid concentrations of 25 g / L to 75 g / L—and from ferrous ion concentrations of 0.5 g / L to 2 g / L. The results indicate that when the Fe(II) concentration is 0.5 g / L, As(V) precipitation cannot be initiated, possibly because the ferrous ion concentration is too low to facilitate the catalytic reaction. Therefore, the concentration difference between As(V) and Fe(III) is sufficiently high to initiate the precipitation reaction. Increasing the Fe(II) concentration to 1.0 g / L and 2.0 g / L also supports this conclusion, as shown in the figure. Figure 29 As shown, although the effect did not reach the level observed in the previous section when the Fe(II) concentration was greater than 3.0 g / L, the precipitation kinetics were improved within 48 h. In the test without As(III) oxidation (i.e., As(III) concentration of approximately 10 g / L), arsenic could not precipitate when the ferrous ion concentration was 2.0 g / L. These results indicate that the oxidation of arsenous ions is necessary for precipitation because the ferrous ion-magnetite system is insufficient to oxidize all arsenous ions in the solution, but only a portion of them. On the other hand, the critical concentration of ferrous ions required to achieve an arsenic concentration of less than 100 mg / L in the treated solution is approximately 3 g / L. Effect of increasing ferrous ion concentration to 3 g / L to 4 g / L Tests were conducted to adjust the dosage of magnetite and ferrous ions to minimize the total iron content in the system. The dosage used in this test protocol was Fe(III). Mag / As(V) is 0.5 mol / mol, equivalent to FeT Mag The molar ratio of Fe(II) / As(V) is 0.75, the molar ratio of Fe(II) / As(V) is 0.63 mol / mol to 0.84 mol / mol, and the total FeT / As(V) molar ratio is in the range of 1.38 mol / mol to 1.59 mol / mol.

[0091] Figure 30 The effect of initial Fe(II) concentrations from 3 g / L to 4 g / L on As and As(III) concentrations is shown—for a sulfuric acid concentration of 5.0 g / L—Fe(III) Mag The As(V) / As ratio was 0.5 mol / mol. The results indicate that, as described in previous sections, a higher ferrous ion concentration can improve precipitation kinetics. However, after 48 h of precipitation, the total As concentration ranged from 100 mg / L to 200 mg / L, while the As(III) concentration was approximately 10 mg / L to 20 mg / L.

[0092] The synergistic effect of adding magnetite and ferrous ions To investigate the effects of adding magnetite and ferrous ions separately on the precipitation of As(V) in the form of spodumene, three groups of experiments were conducted with only magnetite added and one group with only ferrous ions added. The results are as follows: Figure 31 As shown, this indicates that arsenic in the solution was not removed under any conditions. These results demonstrate that the addition of magnetite and ferrous ions has a synergistic effect on the removal of arsenic in the form of arsenic trioxide. The arsenic removal mechanism in the presence of both elements may be very complex, but it must be related to a Fenton-type effect between ferrous ions and magnetite in the mixture. This effect generates an electron flow capable of oxidizing ferrous ions in the solution, thereby initiating a reaction that precipitates As(V) in the form of arsenic trioxide.

[0093] Figure 32 The following is shown in Fe(III) Mag The diffraction pattern of the arsenic residue ReAs generated after precipitation for 24 h under the conditions of an As(V) molar ratio of 1.0, a ferrous ion concentration of 5 g / L, and a sulfuric acid concentration of 5 g / L; it can be observed from the figure that the content of arsenic in the residue is greater than 95% wt.

[0094] Figure 33 The following is shown in Fe(III) Mag Scanning electron microscopy image of arsenic residue ReAs generated after precipitation for 24 h under the conditions of an As(V) molar ratio of 1.0, a ferrous ion concentration of 5 g / L, and a sulfuric acid concentration of 5 g / L; it can be observed from the image that the arsenic crystals exhibit a typical spherical aggregate particle morphology.

[0095] Figure 34 The following is shown in Fe(III) Mag The particle size distribution of arsenic residue ReAs generated after precipitation for 48 h under the conditions of / As(V) molar ratio of 0.5, ferrous ion concentration of 4 g / L and sulfuric acid concentration of 5 g / L; it can be observed from the figure that 80% of the particles are smaller than 30 µm.

[0096] Figure 35 A scanning electron microscope image of magnetite used in the styrofoam precipitation test is shown.

[0097] In summary, based on the results obtained using the method of this invention, the following conclusions can be drawn: • Magnetite can be used as Fe 3+ The source precipitates or generates arsenic residue in EPAS (sulfuric acid plant effluent) solution, producing arsenic removal solution with an As concentration of less than 100 mg / L and arsenic residue with an arsenic content of more than 25% wt.

[0098] To precipitate styraxite from EPAS, at least 0.3 mol of FeT / As(V) and a ferrous ion concentration of 5 g / L are required from magnetite. Furthermore, the method necessitates the use of 15% wt. seed crystals to accelerate reaction kinetics.

[0099] The combination of ferrous ions and magnetite exhibits a synergistic effect on the precipitation of spheroidite. Based on the results, it can be concluded that both reagents participate in the precipitation of As(V); according to XRD (X-ray diffraction) analysis, the As(V) precipitation is mainly spheroidite. Therefore, a redox reaction must occur, causing the ferrous ions in the solution to be oxidized and precipitated together with As(V) in the form of spheroidite.

[0100] The combination of ferrous ions and magnetite can oxidize the remaining As(III) in EPAS solution. Using a system containing ferrous ions and magnetite, As(III) at a concentration of up to 1.4 g / L can be oxidized to an As(III) concentration of less than 50 mg / L.

[0101] • The kinetics of stinking onion stone precipitation depends on a variety of factors, the most significant of which are: ○ Sulfuric acid concentration: The lower the concentration, the better the removal kinetics.

[0102] ○ Ferrous ion concentration: Fe 2+ The limiting concentration was set at 3 g / L to promote the kinetics of precipitating styrofoam using magnetite.

[0103] ○Fe(III) Mag / As(V) ratio: A higher amount of magnetite favors the precipitation kinetics of arsenic; however, it leaves unreacted magnetite in the arsenic residue. Under conditions where sufficient ferrous ions are added, Fe(III) Mag The conversion rate of magnetite to styrax is highest when the / As(V) molar ratio is 0.5.

[0104] ○ Percentage of seed solids: A higher percentage of solids is beneficial to precipitation kinetics. It has been confirmed that a solid percentage of 15% wt. is sufficient to accelerate the precipitation kinetics of styrofoam.

[0105] Depending on the amounts of magnetite and ferrous sulfate used, the precipitation of spatholite produces and / or consumes sulfuric acid. Systems favoring magnetite conversion consume acid, while systems reacting by converting ferrous ions in the solution release acid. For systems evaluated using EPAS solution, in a solution of 6.3 g / L AsT (0.6 mol of sulfuric acid per mole of As(V)), the spatholite precipitate produces acid at a rate of 5 g / L.

[0106] • The arsenic residue generated using EPAS solution was stable in TCLP tests for As and Cd concentrations, which were less than 5 mg / L and 1 mg / L, respectively.

[0107] The arsenic-containing residue generated using the proposed method represents the residue with the highest As grade and best environmental stability among all residues evaluated by EcoMetales to date. These results were obtained using a real sulfuric acid plant effluent solution.

Claims

1. A method for obtaining orpiment from a solution containing arsenic and sulfuric acid without using a neutralizing agent, characterized by, The process comprises the following steps: i. subjecting a first arsenic solution comprising arsenic in the form of a mixture of arsenite ions and arsenate ions and sulfuric acid to an oxidation treatment to oxidize the arsenite ions to arsenate ions, to obtain a second arsenic solution; ii. adding to the second arsenic solution a first solution containing ferrous ions to obtain a third arsenic solution; iii. adding to the third arsenic solution a first portion of magnetite to adjust the molar ratio of iron ions to arsenate ions, to obtain a first arsenic slurry; iv. adding to the first arsenic slurry a portion of the orpiment slurry recycled from step (viii) as nucleation matrix for orpiment particles, to obtain a first orpiment slurry at 2%wt. to 15%wt.; v. heating the first orpiment slurry to 80°C to 90°C; vi. maintaining the first orpiment slurry at a temperature of 80°C to 90°C for 5 h to 48 h, with continuous stirring, to obtain a second orpiment slurry; vii. subjecting the second orpiment slurry to a solid-liquid separation step to obtain a third orpiment slurry and a treated solution; viii. recycling a first portion of the third orpiment slurry to step (iv); and ix. filtering a second portion of the third orpiment slurry to obtain an orpiment filter cake, which is subjected to a final treatment.

2. The method of claim 1, wherein, The concentration of arsenic in the first arsenic solution is 1 g / L to 15 g / L.

3. The method of claim 1, wherein, The concentration of sulfuric acid in the first arsenic solution is 5 g / L to 80 g / L.

4. The method of claim 1, wherein, The oxidation treatment in step (i) comprises the addition of one of hydrogen peroxide or sodium chlorite, or a photo-oxidation treatment.

5. The method of claim 1, wherein, The first solution in step (ii) comprises ferrous sulfate.

6. The method of claim 1, wherein, The concentration of ferrous ions in step (ii) is adjusted to 0.5 g / L to 20 g / L.

7. The method of claim 1, wherein, The portion of magnetite added in step (iii) has 80% of the particles having a size of less than 75 microns.

8. The method of claim 1, wherein, The temperature in step (v) is 85°C.

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