阅读说明：本技术 一种从砷渣中水热还原回收单质砷的方法 (Method for recovering simple substance arsenic from arsenic slag through hydrothermal reduction ) 是由 张静 时坚 刘峰 于 2021-07-21 设计创作，主要内容包括：本发明公开了一种从砷渣中水热还原回收单质砷的方法。金属冶炼产生的含砷污酸,常用沉淀剂初步处理并产生大量的含砷废渣。本发明采用还原的方法从砷渣中制得砷单质,甲酸盐和亚磷酸盐具有较好的还原性。本发明将砷渣与调节pH后的还原剂溶液,按照一定比例混合之后水热反应,砷元素被还原为单质砷。再经离心分离,洗涤干燥之后可制得黑色单质砷固体。在砷的各种存在形式中,单质砷不仅毒性最低,且具有一定的经济价值。本发明可实现一步法水热还原砷渣制得单质砷,反应过程短,能耗低,经济价值高,砷的回收率最高可达99%,固体含砷量大于95%。(The invention discloses a method for recovering simple substance arsenic from arsenic slag through hydrothermal reduction. Arsenic-containing waste acid produced by metal smelting is subjected to primary treatment by using a precipitator, and a large amount of arsenic-containing waste slag is produced. The invention adopts a reduction method to prepare the arsenic simple substance from the arsenic slag, and formate and phosphite have better reducibility. According to the invention, arsenic slag and a reducing agent solution with the pH adjusted are mixed according to a certain proportion and then undergo hydrothermal reaction, and the arsenic element is reduced into simple substance arsenic. And then the black simple substance arsenic solid can be prepared after centrifugal separation, washing and drying. Among various existing forms of arsenic, the simple substance arsenic has the lowest toxicity and certain economic value. The method can realize one-step hydrothermal reduction of arsenic slag to prepare simple substance arsenic, and has the advantages of short reaction process, low energy consumption, high economic value, arsenic recovery rate up to 99 percent and solid arsenic content higher than 95 percent.)

1. A method for recovering simple substance arsenic from arsenic slag through hydrothermal reduction mainly comprises the following steps:

(1) preparing a reducing agent solution: mixing a reducing agent with water according to a certain concentration, and adjusting the pH value;

(2) and (3) mixing and reacting: putting a certain amount of arsenic slag into a reaction kettle, adding a certain proportion of reducing agent solution, and heating and pressurizing for reaction for 2-10 hours;

(3) recovering simple substance arsenic: filtering or centrifuging to separate solid from liquid, washing and drying black solid to obtain simple substance arsenic.

2. The method for obtaining elemental arsenic by hydrothermal reduction of arsenic slag according to claim 1, wherein the method comprises the following steps: in step (1), the reducing agent is formic acid or formate, phosphorous acid or phosphite, including but not limited to formic acid, sodium formate, phosphorous acid, sodium hydrogen phosphite, potassium hydrogen phosphite, etc.

3. The method for obtaining elemental arsenic by hydrothermal reduction of arsenic sulfide slag according to claim 1, wherein the method comprises the following steps: when the reducing agent in the step (1) is formic acid or formate, the concentration range is 0.18 mmol/L-0.488 mmol/L, and the adjusted pH range is 4-5; when the reducing agent is phosphorous acid or phosphite, the concentration range is 0.122 mmol/L-0.488 mmol/L, and the adjusted pH range is 9-12.

4. The method for obtaining elemental arsenic by hydrothermal reduction of arsenic-calcium slag according to claim 1, wherein the method comprises the following steps: when the reducing agent in the step (1) is formic acid diluent, the concentration is higher than 5%.

5. The method for obtaining elemental arsenic by hydrothermal reduction of arsenic slag according to claim 1, wherein the method comprises the following steps: the arsenic slag in the step (1) is high-concentration arsenic-containing waste acid and high-concentration arsenic-containing electrolyte generated in the non-ferrous metal industry, and is generated by treatment through a precipitation process, including but not limited to arsenic sulfide slag and arsenic calcium slag.

6. The method for obtaining elemental arsenic by hydrothermal reduction of arsenic slag according to claim 1, wherein the method comprises the following steps: the molar ratio of the arsenic slag to the reducing agent in the step (1) is 1: 3-1: 20.

7. The method for obtaining elemental arsenic by hydrothermal reduction of arsenic slag according to claim 1, wherein the method comprises the following steps: when the reducing agent in the step (2) is formic acid or formate, the hydrothermal time is not less than 6 h, and the temperature is not less than 200 ℃; when the reducing agent is phosphorous acid or phosphite, the hydrothermal time is not less than 2h, and the temperature is not less than 180 ℃.

8. The method for obtaining elemental arsenic by hydrothermal reduction of arsenic slag according to claim 1, wherein the method comprises the following steps: and (4) the drying method in the step (3) adopts forced air heating drying or vacuum freeze drying, and the drying time is not more than 12 h.

Technical Field

The invention belongs to the field of metallurgical technology and environmental protection, and relates to a process for preparing simple substance arsenic by hydrothermal reduction of arsenic slag.

Background

Arsenic is widely present in various ores and large amounts of arsenic-containing contaminated acids and arsenic residues have been produced in connection with mining metallurgical activities. They are highly toxic and are likely to migrate in the environment when mishandled. The existing treatment methods for arsenic compounds mainly comprise curing treatment and stockpiling treatment. Although such curing process can be solved for a while, it not only has considerable potential risks to the natural environment and human health, but also causes a huge waste of resources. Arsenic has important applications in metallurgy, medical treatment, electronics, agriculture, and the like. Therefore, the simple substance arsenic with extremely low toxicity can be obtained from the arsenic sulfide slag, which is not only the detoxification treatment of the highly toxic substances, but also has important significance for the resource reutilization of the arsenic.

The current research on the resource utilization of arsenic slag mainly converts the arsenic slag into white arsenic or simple substance arsenic. White arsenic can be used as a preservative or as a raw material for the preparation of high purity elemental arsenic. White arsenic has high toxicity, and the production process can cause secondary pollution to the environment. The preparation of the simple substance arsenic adopts a vacuum distillation process, the equipment is complex, the energy consumption is high, and the separation of the simple substance arsenic can be realized only when the temperature reaches 600-900 ℃.

Patent CN108913915A discloses a process for obtaining elemental arsenic by reduction of arsenic trioxide. Uniformly mixing arsenic trioxide, low-melting-point substances, a reducing agent and soda ash, putting the mixture into a crucible, carrying out heat preservation reaction to obtain low-melting-point and nonvolatile arsenic alloy, and then carrying out vacuum recovery to obtain metal arsenic and low-melting-point metal. The process is long, the cost is high, and the energy consumption is high.

Patent CN106756113A discloses a method for directly producing metallic arsenic by reducing arsenic sulfide slag, fixing sulfur and roasting. Arsenic sulfide slag produced in a waste acid purification process of a copper smelting plant is used as a raw material, copper oxide powder and a reducing agent are added at the same time, low-temperature reduction sulfur fixation roasting is carried out after metallurgical calculation and mixed ingredients, and crude metal arsenic is obtained by performing vacuum separation on a roasted product in a reducing atmosphere by utilizing the volatility of arsenic. But the energy consumption is high, and the purity of the metal arsenic is not high.

Patent CN103388076A discloses a method for reducing arsenic sulfide slag by stannous chloride in two-step method. Firstly, arsenic sulfide slag is subjected to alkaline oxidation leaching, then concentrated arsenic liquid is enriched, and finally elemental arsenic is obtained by reduction under the condition of strong hydrochloric acid. The disadvantages are long process, great amount of hydrochloric acid needed and easy secondary pollution of acid. Therefore, a method for preparing the simple substance arsenic by one-step reduction is sought, so that the cost is effectively reduced, and the secondary pollution can be reduced.

Disclosure of Invention

The invention provides a new solution for solving the problem of resource treatment of arsenic slag. Particularly for arsenic sulfide slag, the method can simply and efficiently remove sulfur and extract arsenic from the arsenic slag, and realize harmless and resource utilization of the arsenic slag as much as possible.

In order to realize the purpose of the invention, the reducing agent is added, the initial pH value is adjusted, the reducing agent and a proper amount of arsenic slag are mixed and placed in a high-pressure reaction kettle for hydrothermal reaction, and the simple substance arsenic can be obtained by reduction. The method mainly comprises the following steps:

(1) preparation of a reducing agent: the reducing agent can be formate or phosphite, and solution with proper concentration and initial pH is prepared as the reducing agent.

(2) And (3) mixing and reacting: putting a certain amount of arsenic slag into a reaction kettle, adding a reducing agent, and then heating and pressurizing for reaction.

(3) Recovering simple substance arsenic: and (4) carrying out solid-liquid separation, washing and drying the black solid to obtain the simple substance arsenic.

The proportion of the arsenic slag and the reducing agent of phosphite in the step (1) is that the molar ratio of arsenic to phosphorus is 1: (2-6) metering, and adjusting the pH to be = 9-12; the prepared reducing agent has better reducing effect under the condition that the arsenic-phosphorus ratio is 1: 3.

The proportion of the formate reducing agent in the step (1) is that the molar ratio of arsenic to carbon is 1: (2-6) metering, and adjusting the pH = 4-5; the prepared reducing agent has better reducing effect under the condition that the arsenic-carbon ratio is 1: 3.

When the formate is used as a reducing agent in the step (2), the hydrothermal temperature is not lower than 200 ℃; when phosphite is used as a reducing agent, the hydrothermal temperature is not lower than 180 ℃.

When the formate is used as a reducing agent in the step (2), the hydrothermal time is not less than 8 h; when phosphite is used as a reducing agent, the hydrothermal time is not less than 2 h.

The preferable scheme is as follows: in the step (2), the arsenic slag and formate are hydrothermal for 10 hours, and the arsenic slag and phosphite are hydrothermal for 4 hours.

The preferable scheme is as follows: in the step (2), the plastid ratio of the arsenic slag to the reducing agent is 1 (50-100), stirring or ultrasonic treatment is carried out during mixing, and the hydrothermal temperature is set at 200 ℃.

The preferable scheme is as follows: and (3) centrifugally washing the solid sample for more than 3 times, and blowing, heating and drying the solid sample for 12 hours at the temperature of 60 ℃.

The following reactions may occur during phosphite reduction:

adjusting the pH of phosphite with sodium hydroxide and hydrochloric acid solution to produce sodium monohydrogen phosphite:

H₃PO₃+2NaOH=Na₂HPO₃+2H₂O

arsenic sulphide dissolves in alkaline, reactions (1) and (2) taking place:

（1）As₂S₃+6NaOH =Na₃AsS₃+Na₂S+3H₂O

（2）As₂S₅+8NaOH=Na₃AsS₄+Na₃AsO₄+Na₂S+3H₂O

sodium monohydrogen arsenite reduces the polysulphide of arsenic, reactions (3) and (4) taking place:

（3）3Na₂HPO₃+2Na₃AsS₃+3H₂O=2As↓+3Na₂HPO₄+3Na₂S+3H₂S↑

（4）5Na₂HPO₃+2Na₃AsS₄+5H₂O=2As↓+5Na₂HPO₄+3Na₂S+5H₂S↑

the generated hydrogen sulfide reacts under alkalinity to generate a reaction (5):

（5）2NaOH+H₂S=Na₂S+2H₂O

the following reaction may occur during the formic acid reduction:

（1）6NaCOOH+2As₂S₃+3H₂O=4As↓+3Na₂S+6CO₂↑+3H₂S↑

（2）3HCOOH+As₂S₃=2As↓+3H₂S↑+3CO₂↑

in conclusion, the invention realizes the one-step hydrothermal reduction of the simple substance arsenic. The recovery rate of arsenic reaches 99 percent, and the purity of simple substance arsenic is more than 95 percent. The by-product contains Na₂The S solution can be oxidized to generate elemental sulfur for recycling, and can also be used as a precipitator of arsenic-containing waste acid for recycling.

Drawings

FIG. 1 is a flow chart of a process for obtaining elemental arsenic by hydrothermal reduction of arsenic slag according to the present invention.

FIG. 2 shows the scanning electron microscope morphology of arsenic sulfide reduced to elemental arsenic.

Fig. 3 is the scan result of EDS spot 1 in fig. 2.

Fig. 4 is the scan result of EDS spot 2 in fig. 2.

Detailed Description

For better understanding and implementation, the comprehensive treatment method for resource utilization of the arsenic sulfide slag is described in detail as follows:

example 1

Simulating arsenic sulfide slag: (1) 1.04 g of sodium arsenite (NaAsO) is taken₂) Dissolved in 20 mL of deionized water, sodium sulfide nonahydrate (Na)₂S·9H₂O) is dissolved in 10 mL deionized water, the pH of the sodium arsenite solution is adjusted to be =1 by using 46% sulfuric acid solution, at the moment, the sodium sulfide solution is dropwise added into the sodium arsenite solution, and after reaction for 10 min, the simulated arsenic sulfide slag (As) is obtained₂S₃). Washing, centrifuging and drying the obtained product to obtain amorphous simulated arsenic sulfide slag.

(2) Phosphorous acid was used as a reducing agent, as arsenic: phosphite in a molar ratio equal to 1:3, adjusted to pH =10 as reducing agent solution. Weighing 0.1g of simulated arsenic sulfide slag, placing the slag in a reaction kettle, mixing 10 mL of sodium phosphite with the concentration of 0.244 mmol/L with the arsenic slag, placing the mixture in a high-pressure reaction kettle at 200 ℃ for hydrothermal for 4 hours, then carrying out solid-liquid separation, washing and drying black solids. And washing the solid for 3-4 times, and carrying out vacuum freeze drying for 10 hours to finally obtain the simple substance arsenic.

(3) The recovery rate of arsenic in the arsenic slag is more than 99 percent, and the arsenic content of the solid is more than 95 percent.

Example 2

Arsenic sulfide in example 1 was used as a treatment target, and phosphorous acid was used as a reducing agent, and the molar ratio of arsenic to phosphorous acid was equal to 1:3, and adjusted to pH =12 as a reducing agent solution. Weighing 0.1g of arsenic sulfide slag, placing the arsenic sulfide slag in a reaction kettle, mixing 10 mL of sodium phosphite with the concentration of 0.244 mmol/L with the arsenic slag, placing the mixture in a high-pressure reaction kettle, heating the mixture at 200 ℃ for 4 hours, then carrying out solid-liquid separation, washing and drying black solids. And washing the solid for 3-4 times, and carrying out vacuum freeze drying for 10 hours to finally obtain the simple substance arsenic, wherein the recovery rate is more than 99%, and the arsenic content of the solid is more than 95%.

Example 3

(1) The method is characterized in that the actual arsenic slag of a gold smelting plant is taken as a processing object, the arsenic content is about 29 percent, phosphorous acid is taken as a reducing agent, and the ratio of arsenic: phosphite in a molar ratio equal to 1:6, adjusted to pH =12, as reducing agent solution. Weighing 0.2g of arsenic sulfide slag, placing the arsenic sulfide slag in a reaction kettle, mixing 20 mL of reducing agent and the arsenic slag, placing the mixture in a high-pressure reaction kettle at 200 ℃ for hydrothermal for 10 hours, and carrying out solid-liquid separation and washing to obtain a dry black solid. And washing the solid for 3-4 times, and carrying out vacuum freeze drying for 10 hours to finally obtain the simple substance arsenic. The recovery rate of arsenic in the arsenic slag is more than 99 percent, and the arsenic content of the solid is more than 95 percent.

Example 4

Arsenic sulfide in example 1 was treated with sodium formate as a reducing agent, and the molar ratio of arsenic to formic acid was 1:3, adjusted to pH =4, as a reducing agent solution. Weighing 0.1g of arsenic sulfide slag, placing the arsenic sulfide slag in a reaction kettle, mixing 10 mL of reducing agent with the arsenic slag, placing the mixture in a high-pressure reaction kettle, performing hydrothermal treatment at 200 ℃ for 15 hours, performing solid-liquid separation, washing and drying black solids. And washing the solid for 3-4 times, and carrying out vacuum freeze drying for 10 hours to finally obtain the simple substance arsenic. The recovery rate of arsenic in the arsenic slag is more than 99 percent, and the arsenic content of the solid is more than 95 percent.

Example 5

The arsenic content of the actual arsenic slag of the gold smelting plant is about 29 percent as a treatment object. Sodium formate is used as a reducing agent, and the weight ratio of arsenic: the molar ratio of sodium formate was 1:3, adjusted to pH =4, as reducing agent solution. Weighing 0.1g of arsenic sulfide slag, placing the arsenic sulfide slag in a reaction kettle, mixing 10 mL of reducing agent arsenic slag, placing the mixture in a high-pressure reaction kettle at 200 ℃ for hydrothermal for 15 h, then carrying out solid-liquid separation, washing and drying black solids. And washing the solid for 3-4 times, and carrying out vacuum freeze drying for 10 hours to finally obtain the simple substance arsenic. The recovery rate of arsenic in the arsenic slag is more than 99 percent, and the purity of the obtained simple substance arsenic is more than 95 percent.

Example 6

After preparing the sodium hydrogen arsenate solution, adding calcium hydroxide as a precipitator, and adjusting the pH to 8.5 to obtain the calcium arsenate slag. Formic acid diluent is used as a reducing agent. Weighing 0.1g of calcium arsenate slag, placing the calcium arsenate slag in a reaction kettle, mixing 3 mL of formic acid reducing agent, 7 mL of ultrapure water and arsenic slag, placing the mixture in a high-pressure reaction kettle, performing hydrothermal treatment at 200 ℃ for 20 hours, performing solid-liquid separation, and washing and drying black solids. And washing the solid for 3-4 times, and carrying out vacuum freeze drying for 10 hours to obtain the simple substance arsenic. The recovery rate of arsenic is more than 99 percent, and the purity of the obtained simple substance arsenic is more than 95 percent.