A method for reducing arsenic content by using low-grade lead-zinc ore and waste acid to cooperate with hydrothermal reaction

Abstract

This invention belongs to the field of non-ferrous metallurgy and hazardous waste treatment technology, proposing a method for reducing arsenic content using a synergistic hydrothermal reaction of low-grade lead-zinc ore and polluted acid. The method involves pre-decalcifying the low-grade lead-zinc ore with dilute hydrochloric acid to remove interfering calcium carbonate. Then, by controlling the mass ratio of active metals such as Pb, Zn, and Fe in the ore powder to As in the polluted acid, under specific hydrothermal conditions, the in-situ release and induced precipitation of metal ions within the ore are stimulated, constructing thermodynamically extremely stable onionite and onionite-like mineral phases. The arsenic removal rate of this invention is consistently above 95%, and the stability of the arsenic-fixed products far exceeds national hazardous waste landfill standards. This method not only solves the problem of arsenic pollution from polluted acid but also simultaneously realizes the resource utilization of low-grade ore, demonstrating significant environmental and economic benefits.

Description

Technical Field

[0001] This invention relates to the fields of non-ferrous metallurgy and hazardous waste treatment, and in particular to a method for reducing arsenic content by using a synergistic hydrothermal reaction of low-grade lead-zinc ore and waste acid. Background Technology

[0002] Waste acid, a metallurgical byproduct primarily composed of sulfuric acid and containing complex components (As, Cd, Cu, Pb, F, Cl, etc.), is highly acidic, corrosive, and toxic, posing significant environmental risks. Typical waste acid contains 1-15 g / L of arsenic and 1%-10% of sulfuric acid. Direct discharge without treatment will severely harm the ecological environment and human health. Existing waste acid treatment processes typically employ sulfidation or calcium salt precipitation methods. These methods suffer from high reagent consumption, complex operation, high processing costs, and poor stability of the resulting arsenic slag (sulfided arsenic slag or calcium arsenic slag), which can easily lead to secondary pollution. Therefore, achieving efficient purification of waste acid while controlling arsenic pollution is a pressing technical challenge in the metallurgical field.

[0003] Lead-zinc ore is an important basic metal resource. In recent years, with the depletion of high-quality mineral resources, the proportion of low-grade and difficult-to-process lead-zinc ores has gradually increased, among which oxygen-sulfur mixed ores account for a significant portion. These ores typically contain 1%-10% Zn, 1%-3% Pb, and 5%-10% Fe, with associated gangue components such as SiO2 and CaO. Their complex mineral structure and low beneficiation efficiency lead to long-term stockpiling, occupying land resources and posing potential environmental risks. Therefore, developing resource utilization pathways for low-grade lead-zinc ores has significant economic and environmental implications.

[0004] Existing research largely focuses on either treating polluted acid or utilizing low-grade ores individually, lacking effective technologies for the synergistic treatment of both. Particularly in acidic systems, how to utilize soluble metal ions in low-grade lead-zinc ores to efficiently stabilize arsenic while simultaneously promoting ore resource utilization remains a technological gap in this field. Therefore, there is an urgent need to provide a method for utilizing low-grade lead-zinc ores to solve the problem of arsenic pollution from polluted acid and to open up new avenues for the utilization of low-grade ores. Summary of the Invention

[0005] To address the problems of high arsenic content, high acidity, high treatment costs, and easy secondary pollution in existing waste acid, as well as the long-term stockpiling and low utilization rate of low-grade lead-zinc ore, the present invention aims to provide a method for reducing arsenic content by synergistic hydrothermal reaction of low-grade lead-zinc ore and waste acid. By pre-decalcifying the low-grade lead-zinc ore through dilute hydrochloric acid washing, the interference of calcium ions in the system on arsenate crystallization is reduced. Under closed hydrothermal conditions, the active metal ions in the mineral react with the arsenate ions in the waste acid to generate stable arsenate precipitates, thereby achieving the dual goals of waste acid purification and low-grade lead-zinc ore resource utilization.

[0006] To achieve the above objectives, the present invention provides a method for reducing arsenic content by synergistic hydrothermal reaction of low-grade lead-zinc ore and waste acid, comprising the following steps:

[0007] (1) Pretreatment of low-grade lead-zinc ore: The low-grade lead-zinc ore is subjected to dilute hydrochloric acid pickling, filtration, washing, drying, crushing and ball milling in sequence to obtain pretreated ore powder;

[0008] (2) The pretreated mineral powder and the pretreated arsenic-containing acid reaction liquid were placed in a closed system for hydrothermal reaction; after the reaction was completed, solid-liquid separation was carried out to obtain arsenic removal liquid and arsenic solid residue respectively.

[0009] Furthermore, the conditions for acid washing with dilute hydrochloric acid in step (1) are: hydrochloric acid concentration 0.2-0.5 mol / L, solid-liquid ratio 1:10 g / ml, and stirring time 10-30 min.

[0010] Furthermore, the composition of the low-grade lead-zinc ore mentioned in step (1) is: the mass percentage of Pb+Zn is 5%-10%.

[0011] Furthermore, the pretreatment of arsenic-containing waste acid in step (2) includes: adding an oxidant to the arsenic-containing waste acid and adjusting the pH value of the system to 0.25-1.0.

[0012] Furthermore, the oxidant is hydrogen peroxide, and the molar ratio of arsenic to hydrogen peroxide is 1:(1.1-1.2).

[0013] Furthermore, the mass ratio of the active metal element M contained in the low-grade lead-zinc ore to As in the waste acid is M / As≥5:1, and M is at least one of Zn, Pb, and Fe.

[0014] Furthermore, the mass ratio of the active metal element M / As is 5-15:1.

[0015] Furthermore, the hydrothermal reaction time in step (2) is 12-18 hours.

[0016] Furthermore, the reagent used to adjust the pH value is calcium carbonate.

[0017] Furthermore, the temperature of the hydrothermal reaction is 160-220℃.

[0018] Beneficial effects

[0019] 1. Highly efficient arsenic removal: Through hydrothermal reaction, metal ions are fully dissolved and combined with arsenate ions, achieving an arsenic removal rate of 90%-98%, and significantly reducing the residual arsenic content in waste acid to 0.05-0.5 g / L.

[0020] 2. Formation of stable solidified phase: The generated thermodynamically stable minerals such as 8PbO·As2O5, Zn3(AsO4)2, and Ca3(AsO4)2 have a dense structure. The leaching concentration of TCLP (Toxicity Characteristic Leaching Procedure) is less than 5 mg / L, which is far below the hazardous waste discharge standard, thus avoiding secondary pollution.

[0021] 3. Reduced acidity and resource reuse: During the reaction, some of the acid is neutralized, and the resulting purified liquid can be reused in hydrometallurgy or acid production systems, reducing the amount of waste acid discharged and the consumption of neutralizing agent.

[0022] 4. Promote the resource utilization of low-grade minerals: Use active metal ions in low-grade lead-zinc ores to replace added chemical agents to achieve "acid treatment with minerals", so that the originally stockpiled minerals participate in the reaction and are transformed into stable solid phases, thus achieving synergistic utilization.

[0023] 5. Simple process and strong applicability: The reaction system is closed and controllable, and the operating conditions are mild. No toxic reducing agents or sulfiding agents are required. It is suitable for arsenic-containing waste acid from different sources and various low-grade lead-zinc ores.

[0024] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0025] The above and other objects, features and advantages of this application will become more apparent from the more detailed description of exemplary embodiments thereof in conjunction with the accompanying drawings.

[0026] Figure 1 This is a schematic diagram of the basic process of a method for reducing arsenic content by using low-grade lead-zinc ore and waste acid in a synergistic hydrothermal reaction, according to the present invention.

[0027] Figure 2 The Xrd spectrum of the solidified arsenic slag in Example 6 is shown. Detailed Implementation

[0028] Embodiments of this application will now be described in more detail with reference to the accompanying drawings. While embodiments of this application are shown in the drawings, it should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0029] In the process of reducing arsenic content by synergistic hydrothermal reaction of low-grade lead-zinc ore and waste acid, the As content in the waste acid is reduced by controlling the mass ratio of Pb+Zn+Fe in low-grade lead-zinc ore to As in copper smelting waste acid, i.e., (Zn+Pb+Fe) / As. This forms a stable solidified As phase, efficiently removes arsenic, and promotes the resource utilization of low-grade lead-zinc ore.

[0030] The reaction principle of this invention is as follows: under closed hydrothermal conditions at 160-220℃, active metal elements (Fe, Zn, Pb) in low-grade lead-zinc ore undergo in-situ dissolution in an acidic system, releasing Fe. 3+ Zn 2+ Pb 2+ Plasma. In the pre-oxidized waste acid, arsenic is mainly present as AsO4. 3- It exists in form. According to thermodynamic principles, under high-temperature hydrothermal conditions, Fe... 3+ With AsO4 3- Preferential formation of crystalline ferric arsenate (FeAsO4·2H2O) is observed, with a Gibbs free energy far lower than that of amorphous ferric arsenate, making it a thermodynamically extremely stable solid arsenic mineral. Simultaneously, Zn dissolves into the system... 2+ Pb 2+ Metal ions can partially replace Fe in the stolonite lattice. 3+ Or, stable arsenate minerals with structures similar to schizocarpite, such as Zn3(AsO4)2 and 8PbO·As2O5, can be formed, collectively constituting a "schizocarpite-like mineral phase". The dilute hydrochloric acid washing pretreatment in step (1) first removes calcium carbonate from the ore, avoiding the formation of Ca... 2+ The interference with the crystallization process of arsenic-containing stone creates a favorable chemical environment for the construction of the aforementioned thermodynamically stable mineral phases. XRD pattern of the solidified arsenic slag in Example 6 ( Figure 2 The product's characteristic diffraction peaks are sharp and its crystallinity is high, confirming the formation of styrofoam and styrofoam-like mineral phases. The corresponding toxicity leaching results in Table 2 are excellent, further confirming from a macroscopic perspective that this mineral phase has extremely high long-term stability.

[0031] This embodiment uses an acidic arsenic-containing solution generated by a scrubber in the sulfuric acid production process of a low-grade lead-zinc ore stockpiled in Yunnan as the treatment object. The low-grade lead-zinc ore contains 1%-5% lead, 5%-20% zinc, and 3%-10% iron. The arsenic concentration in the waste acid is 1-10 g / L, and the sulfuric acid concentration is 1%-8%.

[0032] Example 1

[0033] A method for reducing arsenic content using a synergistic hydrothermal reaction of low-grade lead-zinc ore and waste acid includes the following steps:

[0034] (1) Pretreatment of low-grade lead-zinc ore:

[0035] Take a low-grade lead-zinc ore stockpile in Yunnan, acid wash it with 0.3 mol / L dilute hydrochloric acid at a solid-liquid ratio of 1:10 g / ml, stir for 20 min, filter and wash until neutral, dry in an oven at 60℃ for 12 h, then crush and ball mill it, pass it through a 200-mesh sieve (<75 μm), and collect the low-grade lead-zinc ore powder for later use.

[0036] (2) Pretreatment of waste acid:

[0037] Take 200 ml of waste acid (arsenic concentration of 5.42 g / L), add hydrogen peroxide (arsenic / hydrogen peroxide molar ratio of 1:2) to the waste acid, add calcium carbonate to adjust the pH of the reaction to 0.25, react for 2 hours, filter and separate to obtain calcium sulfate residue and waste acid pretreatment: reaction solution 1;

[0038] (3) Hydrothermal co-treatment of low-grade lead-zinc ore and waste acid:

[0039] Add 50 mL of reaction solution 1 to the hydrothermal reactor, then place the low-grade lead-zinc ore powder obtained in step (1) into the hydrothermal reactor. Add the low-grade lead-zinc ore powder prepared in step (1) at a solid-liquid ratio of 1:6.6 g / mL to reaction solution 1, controlling the M / As mass ratio in the hydrothermal co-treatment to be 5. Control the reaction temperature at 180℃ for 18 h. After the reaction, allow natural cooling and solid-filtration separation to obtain arsenic removal liquid and arsenic-fixed slag. Determine the arsenic content and sulfuric acid concentration in the arsenic removal liquid, and evaluate the toxicity of the arsenic-fixed slag through leaching. The results are shown in Tables 1 and 2. Among them:

[0040] Arsenic content was determined using inductively coupled plasma optical emission spectrometry (ICP-OES) in accordance with HJ 694-2014 standard. Arsenic removal rate was calculated using formula (1):

[0041]

[0042] In the formula: C0 is the mass concentration of arsenic in the waste acid reaction solution before the reaction (g / L), and C1 is the mass concentration of arsenic in the arsenic removal solution after the reaction (g / L).

[0043] The concentration of sulfuric acid was determined by acid-base titration, using methyl orange as an indicator and titration with sodium hydroxide standard solution, in accordance with GB / T 534-2014 standard.

[0044] The toxicity evaluation of arsenic-fixed slag was conducted using the TCLP (Toxicity Characteristic Leaching Procedure), and the specific operation was performed in accordance with the HJ / T 299-2007 standard "Solid Waste Leaching Toxicity Leaching Method - Sulfuric Acid and Nitric Acid Method". The arsenic concentration in the leachate was evaluated according to GB 18598-2019 "Standard for Pollution Control of Hazardous Waste Landfill", with a limit of 5 mg / L.

[0045] Example 2

[0046] A method for reducing arsenic content using a synergistic hydrothermal reaction of low-grade lead-zinc ore and waste acid includes the following steps:

[0047] (1) Pretreatment of low-grade lead-zinc ore:

[0048] The steps are the same as step (1) in Example 1;

[0049] (2) Pretreatment of waste acid:

[0050] Adjust the pH value to 0.5, and the remaining steps are the same as step (1) in Example 1;

[0051] (3) Hydrothermal co-treatment of low-grade lead-zinc ore and waste acid:

[0052] Add 50 mL of waste acid to the hydrothermal reactor, and then place the low-grade lead-zinc ore obtained in (1) into the hydrothermal reactor. The solid-liquid ratio of ore powder to reaction liquid is 1:6.6 g / ml. The mass ratio of M / As in the hydrothermal co-treatment is controlled to be 5. After thorough mixing, the reaction temperature is controlled to be 180℃ and the reaction time is 18h. A hydrothermal test is carried out. After the reaction is completed, the mixture is cooled, filtered and separated. The arsenic content and sulfuric acid concentration in the arsenic removal liquid are determined, and the toxicity leaching of the solidified arsenic residue is evaluated. The results are shown in Table 1 and Table 2.

[0053] Example 3

[0054] A method for reducing arsenic content using a synergistic hydrothermal reaction of low-grade lead-zinc ore and waste acid includes the following steps:

[0055] (1) Pretreatment of low-grade lead-zinc ore:

[0056] The steps are the same as step (1) in Example 1;

[0057] (2) Pretreatment of waste acid:

[0058] Adjust the pH value to 1, and the remaining steps are the same as step (1) in Example 1;

[0059] (3) Hydrothermal co-treatment of low-grade lead-zinc ore and waste acid:

[0060] Add 50 mL of waste acid to the hydrothermal reactor, and then place the low-grade lead-zinc ore obtained in (1) into the hydrothermal reactor. The solid-liquid ratio of ore powder to reaction liquid is 1:6.6 g / ml. The mass ratio of M / As in the hydrothermal co-treatment is controlled to be 5. After thorough mixing, the reaction temperature is controlled to be 180℃ and the reaction time is 18h. A hydrothermal test is carried out. After the reaction is completed, the mixture is cooled, filtered and separated. The arsenic content and sulfuric acid concentration in the arsenic removal liquid are determined, and the toxicity leaching of the solidified arsenic residue is evaluated. The results are shown in Table 1 and Table 2.

[0061] Example 4

[0062] A method for reducing arsenic content using a synergistic hydrothermal reaction of low-grade lead-zinc ore and waste acid includes the following steps:

[0063] (1) Pretreatment of low-grade lead-zinc ore:

[0064] The steps are the same as step (1) in Example 1;

[0065] (2) Pretreatment of waste acid:

[0066] Adjust the pH value to 0.5, and the remaining steps are the same as step (1) in Example 1;

[0067] (3) Hydrothermal co-treatment of low-grade lead-zinc ore and waste acid:

[0068] Add 50 mL of dirty acid to the hydrothermal reactor, and then place the low-grade lead-zinc ore obtained in (1) into the hydrothermal reactor. The solid-liquid ratio of ore powder to reaction liquid is 1:3.3 g / ml. The mass ratio of M / As in the hydrothermal co-treatment is controlled to be 10. After thorough mixing, the reaction temperature is controlled to be 180℃ and the reaction time is 18h. A hydrothermal test is carried out. After the reaction is completed, the mixture is cooled, filtered and separated. The arsenic content and sulfuric acid concentration in the arsenic removal liquid are determined, and the toxicity leaching of the solidified arsenic residue is evaluated. The results are shown in Table 1 and Table 2.

[0069] Example 5

[0070] A method for reducing arsenic content using a synergistic hydrothermal reaction of low-grade lead-zinc ore and waste acid includes the following steps:

[0071] (1) Pretreatment of low-grade lead-zinc ore:

[0072] The steps are the same as step (1) in Example 1;

[0073] (2) Pretreatment of waste acid:

[0074] Adjust the pH value to 0.5, and the remaining steps are the same as step (1) in Example 1;

[0075] (3) Hydrothermal co-treatment of low-grade lead-zinc ore and waste acid:

[0076] Add 50 mL of dirty acid to the hydrothermal reactor, and then place the low-grade lead-zinc ore obtained in (1) into the hydrothermal reactor. The solid-liquid ratio of ore powder to reaction liquid is 1:2.2 g / ml. The mass ratio of M / As in the hydrothermal co-treatment is controlled to be 15. After thorough mixing, the reaction temperature is controlled to be 180℃ and the reaction time is 18h. A hydrothermal test is carried out. After the reaction is completed, the mixture is cooled, filtered and separated. The arsenic content and sulfuric acid concentration in the arsenic removal liquid are determined, and the toxicity leaching of the solidified arsenic slag is evaluated. The results are shown in Table 1 and Table 2.

[0077] Example 6

[0078] A method for reducing arsenic content using a synergistic hydrothermal reaction of low-grade lead-zinc ore and waste acid includes the following steps:

[0079] (1) Pretreatment of low-grade lead-zinc ore:

[0080] The steps are the same as step (1) in Example 1;

[0081] (2) Pretreatment of waste acid:

[0082] The steps are the same as step (2) in Example 1;

[0083] (3) Co-treatment of low-grade lead-zinc ore and waste acid:

[0084] Add 50 mL of polluted acid to the hydrothermal reactor, then place the low-grade lead-zinc ore obtained in (1) into the hydrothermal reactor. The solid-liquid ratio of ore powder to reaction liquid is 1:3.3 g / ml. Control the mass ratio of M / As in the hydrothermal co-treatment to be 10. After thorough mixing, control the reaction temperature at 200℃ and the reaction time at 18 h for a hydrothermal test. After the reaction, cool and filter to separate the arsenic residue. The XRD pattern of the solidified arsenic slag is shown in [reference needed]. Figure 2 The arsenic content and sulfuric acid concentration in the arsenic removal solution were determined, and the toxicity leaching of the solidified arsenic residue was evaluated. The results are shown in Tables 1 and 2. XRD phase analysis was performed on the solidified arsenic residue obtained in this example. Figure 2 The reason for this is that this embodiment has the highest arsenic removal rate and the lowest TCLP leaching concentration in the solidified arsenic residue, representing the best technical effect of the method of the present invention, and its phase composition is the most representative. (See Tables 1 and 2 for results.) Figure 2 XRD pattern analysis shows that during the synergistic hydrothermal reaction in step (3), Pb dissolved from the low-grade lead-zinc ore... 2+ Zn 2+ Ca 2+ (Originating from the small amount of calcium remaining after acid washing in step (1) and the trace amount of calcium ions introduced by adjusting the pH with calcium carbonate in step (2)) and AsO4 in the dirty acid.3- A precipitation reaction occurs, producing thermodynamically stable minerals such as 8PbO·As2O5, Zn3(AsO4)2, and Ca3(AsO4)2. Figure 2 The characteristic diffraction peaks appearing at 2θ of 23.1°, 29.5°, and 39.4° in the XRD patterns of the minerals matched well with the standard cards (PDF# 26-0829, PDF#33-1468, PDF#26-0295, etc.) of the aforementioned minerals, confirming that these dense-structured solid arsenic mineral phases were formed during the hydrothermal reaction stage in step (3). Meanwhile, the TCLP leaching data in Table 2 showed that the arsenic leaching concentration in the solid arsenic residue of Example 6 was only 1.34 mg / L, far below the 5 mg / L limit, further verifying the dense structure and excellent stability of this type of mineral.

[0085] Example 7

[0086] A method for reducing arsenic content using a synergistic hydrothermal reaction of low-grade lead-zinc ore and waste acid includes the following steps:

[0087] (1) Pretreatment of low-grade lead-zinc ore:

[0088] The steps are the same as step (1) in Example 1;

[0089] (2) Pretreatment of waste acid:

[0090] The steps are the same as step (2) in Example 1;

[0091] (3) Hydrothermal co-treatment of low-grade lead-zinc ore and waste acid:

[0092] Add 50 mL of dirty acid to the hydrothermal reactor, and then place the low-grade lead-zinc ore obtained in (1) into the hydrothermal reactor. The solid-liquid ratio of ore powder to reaction liquid is 1:3.3 g / ml. The mass ratio of M / As in the hydrothermal co-treatment is controlled to be 10. After thorough mixing, the reaction temperature is controlled to be 160℃ and the reaction time is 12h. A hydrothermal test is carried out. After the reaction is completed, the mixture is cooled, filtered and separated to obtain arsenic removal liquid and arsenic solidification slag. The arsenic content and sulfuric acid concentration in the arsenic removal liquid are determined, and the toxicity leaching of the arsenic solidification slag is evaluated. The results are shown in Table 1 and Table 2.

[0093] Example 8

[0094] A method for reducing arsenic content using a synergistic hydrothermal reaction of low-grade lead-zinc ore and waste acid includes the following steps:

[0095] (1) Pretreatment of low-grade lead-zinc ore:

[0096] The steps are the same as step (1) in Example 1;

[0097] (2) Pretreatment of waste acid:

[0098] The steps are the same as step (2) in Example 1;

[0099] (3) Hydrothermal co-treatment of low-grade lead-zinc ore and waste acid:

[0100] Add 50 mL of waste acid to the hydrothermal reactor, and then place the low-grade lead-zinc ore obtained in (1) into the hydrothermal reactor. Control the mass ratio of M / As in the hydrothermal co-treatment to be 10. After thorough mixing, control the reaction temperature to be 220℃ and the reaction time to be 18 h. Conduct a hydrothermal test. After the reaction is completed, cool and filter to separate the arsenic removal liquid and solid arsenic residue. Determine the arsenic content and sulfuric acid concentration in the arsenic removal liquid, and evaluate the toxicity leaching of the solid arsenic residue. The results are shown in Table 1 and Table 2.

[0101] Table 1. Arsenic content (g / L) and sulfuric acid concentration (%) in the arsenic removal solutions of Examples 1-8

[0102]

[0103] Table 2 shows the toxicity leaching tests of Examples 1-8.

[0104]

[0105] Comparative Analysis of the Effects of Examples

[0106] Table 3. Effects of pH on arsenic removal and acid neutralization efficiency.

[0107]

[0108] As shown in the comparison of Examples 1-3, when the pH value of the waste acid pretreatment increased from 0.25 to 0.50 and 1.00, the arsenic concentration in the arsenic removal solution significantly decreased from 2.05 g / L to 1.05 g / L and 0.98 g / L, and the sulfuric acid concentration decreased dramatically from 0.92% to 0.02% and ≤0.01%. This is because, under lower pH conditions (0.25), excess hydrogen ions in the system react with Fe... 3+ Competition AsO4 3- This inhibits the formation of onionite precipitate, while excessively high acidity is detrimental to the complete hydrolysis and precipitation of metal ions. When the pH is adjusted to above 0.50, the acidity in the system is effectively controlled, which is beneficial for Fe... 3+ With AsO4 3- Directional bonding generates stable onionite and onionite-like mineral phases, significantly improving both arsenic removal and acid neutralization. However, as the pH value continues to rise to 1.00, the increase in arsenic removal rate slows down, and the risk of iron ion hydrolysis and precipitation in the system may increase. Considering all factors, the preferred pH value is 0.50-1.00, more preferably 0.50.

[0109] Table 4. Effect of M / As mass ratio on arsenic removal efficiency

[0110]

[0111] A comparison of Examples 2, 4, and 5 shows that as the M / As mass ratio increases from 5 to 10 and 15, the arsenic concentration in the arsenic removal solution gradually decreases from 1.05 g / L to 0.83 g / L and 0.56 g / L, respectively, indicating a continuous improvement in arsenic removal rate. This is because increasing the M / As mass ratio increases the amount of active metal ions (Fe2+, Fe2+, Fe3+, Fe2+) in the system. 3+ Zn 2+ Pb 2+ The total amount of AsO4 is 3- This provides more precipitation binding sites, promoting the formation of more arsenic and arsenic-like mineral phases. When M / As=15, the arsenic removal effect is optimal, but the amount of mineral powder required increases significantly (solid-liquid ratio reaches 0.45 g / mL). When M / As=10, the arsenic removal rate reaches a relatively good level (arsenic concentration in the de-arsenic solution 0.83 g / L), and the amount of mineral powder is moderate (solid-liquid ratio 0.30 g / mL), balancing treatment effect and economy. Considering both treatment effect and mineral powder usage, the preferred M / As mass ratio is 10-15, more preferably 10.

[0112] Table 5 Effect of reaction temperature on arsenic removal efficiency

[0113]

[0114] The comparison of Examples 6-8 shows that the reaction temperature has a significant impact on the arsenic removal efficiency. In Example 7 (160℃), the arsenic concentration in the dearsenic removal solution reached as high as 2.63 g / L, while in Example 6 (200℃) it decreased to 0.34 g / L, and in Example 8 (220℃) it was 0.47 g / L. The reason is that at too low a temperature (160℃), the dissolution rate of active metal ions in the minerals is insufficient, and the kinetic conditions for nucleation and crystal growth of the arsenic crystals are unfavorable, leading to incomplete arsenic precipitation. When the temperature rises to 200℃, the hydrothermal conditions promote the full dissolution of metal ions and the efficient crystallization of the arsenic crystals, resulting in the optimal arsenic removal rate. Further increases in temperature to 220℃ may cause thermal decomposition or crystal transformation of some arsenic crystals, which is detrimental to the stability of the fixed arsenic. Furthermore, the data in Table 2 show that the TCLP arsenic leaching concentration in Example 6 was only 1.34 mg / L, the lowest among all examples, further confirming that the solid arsenic mineral phase generated at 200°C has the best structural density and chemical stability. Therefore, the reaction temperature is preferably 180-220°C, more preferably 200°C.

[0115] (4) Summary of the optimal solution

[0116] Based on the above analysis, the optimal technical solution is Example 6, and its specific parameters are as follows:

[0117] Table 6 Specific parameters of Example 6

[0118]

[0119] Under this optimal condition:

[0120] The arsenic concentration in the arsenic removal solution was as low as 0.34 g / L, with an arsenic removal rate of 93.7%; the sulfuric acid concentration in the arsenic removal solution was reduced to 0.01%, demonstrating excellent acid neutralization; the arsenic leaching concentration in the solidified arsenic residue using TCLP was only 1.34 mg / L, far below the 5 mg / L limit specified in GB 18598-2019; XRD pattern ( Figure 2 It was confirmed that well-crystallized stolonite and stolonite-like mineral phases were formed, exhibiting excellent thermodynamic stability.

[0121] This scheme achieves efficient arsenic removal from wastewater while utilizing the active metal resources in low-grade lead-zinc ore for the construction of arsenic-fixing mineral phases, demonstrating significant technical effectiveness and economic efficiency. It is the preferred technical solution for which this invention seeks protection.

[0122] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for reducing arsenic content by synergistic hydrothermal reaction of low-grade lead-zinc ore and waste acid, characterized in that, Includes the following steps: (1) Pretreatment of low-grade lead-zinc ore: The low-grade lead-zinc ore is subjected to dilute hydrochloric acid pickling, filtration, washing, drying, crushing and ball milling in sequence to obtain pretreated ore powder; (2) The pretreated mineral powder and the pretreated arsenic-containing acid reaction liquid were placed in a closed system for hydrothermal reaction; after the reaction was completed, solid-liquid separation was carried out to obtain arsenic removal liquid and arsenic solid residue respectively.

2. The method according to claim 1, characterized in that, The conditions for acid washing with dilute hydrochloric acid in step (1) are: hydrochloric acid concentration 0.2-0.5 mol / L, solid-liquid ratio 1:10 g / ml, and stirring time 10-30 min.

3. The method according to claim 1, characterized in that, The composition of the low-grade lead-zinc ore mentioned in step (1) is: Pb + Zn mass percentage of 5%-10%.

4. The method according to claim 1, characterized in that, The pretreatment of arsenic-containing waste acid in step (2) includes: adding an oxidant to the arsenic-containing waste acid and adjusting the pH of the system to 0.25-1.

0.

5. The method according to claim 1 or 4, characterized in that, The oxidant is hydrogen peroxide, and the molar ratio of arsenic to hydrogen peroxide is 1:(1.1-1.2).

6. The method according to claim 1, characterized in that, The mass ratio of the active metal element M contained in the low-grade lead-zinc ore to As in the waste acid is M / As≥5:1, and M is at least one of Zn, Pb, and Fe.

7. The method according to claim 6, characterized in that, The mass ratio of the active metal element M / As is 5-15:

1.

8. The method according to claim 1, characterized in that, The hydrothermal reaction time in step (2) is 12-18 hours.

9. The method according to claim 1, characterized in that, The reagent used to adjust the pH value is calcium carbonate.

10. The method according to claim 1, characterized in that, The temperature of the hydrothermal reaction is 160-220℃.

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