Methods for Comprehensive Recovery of Valuable Elements from Waste Acid in Non-ferrous Smelting

Abstract

This invention belongs to the field of metallurgical technology and relates to a method for the comprehensive recovery of valuable elements from waste acid in non-ferrous smelting. The method includes the following steps: S1, mixing waste acid with pyrrhotite and reacting under a sulfur dioxide atmosphere; after the reaction, copper slag and copper-removing liquid are obtained through solid-liquid separation; S2, introducing H2S gas into the copper-removing liquid obtained in step S1; after the reaction, arsenic sulfide slag and arsenic-removing liquid are obtained through solid-liquid separation. This invention utilizes the selective reaction of FeS in pyrrhotite with CuSO4 in the waste acid to form insoluble copper sulfide precipitate. Simultaneously, under the protection of a sulfur dioxide atmosphere, arsenic in the waste acid remains dissolved and does not precipitate. The synergistic effect of these two factors effectively separates copper and arsenic elements from the waste acid, and the separation steps are simple and efficient.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for the comprehensive recovery of valuable elements from waste acid in non-ferrous smelting. Background Technology

[0002] Non-ferrous metals refer to all metals except iron, chromium, manganese, and their alloys. They typically possess unique colors, good electrical and thermal conductivity, ductility, and corrosion resistance, and are widely used in industry and daily life. Non-ferrous metal smelting refers to the process of extracting and refining non-ferrous metals from ores or secondary resources (such as waste) using physical, chemical, or electrochemical methods. The flue gas generated during non-ferrous metal smelting must first undergo a purification process to remove impurities before being sent to the acid production process. To avoid excessively high impurity concentrations in the washing water, the purification process must discharge some waste acid, which is called waste acid. For example, in the acid production process using pyrite as raw material, approximately 50 kilograms of waste acid are generated for every ton of sulfuric acid produced. The flue gas contains a large amount of fine particulate matter, as well as metallic pollutants such as arsenic, mercury, lead, zinc, and cadmium, and gases such as SO2 and SO3. During the washing process, these substances enter the waste acid, making its composition extremely complex and unusable directly. This not only wastes valuable sulfuric acid resources but also harms the environment; therefore, the waste acid must be treated to render it harmless. Traditional methods for treating waste acid include chemical precipitation and lime neutralization. However, these methods produce a large amount of neutralization sludge, require a lot of storage space, and generate a large amount of greywater after treatment, thus increasing the amount of wastewater discharged by enterprises.

[0003] Currently, the main methods for treating waste acid in China include lime neutralization, neutralization-iron salt coprecipitation, and sulfidation. Lime neutralization involves directly adding lime to the waste acid for neutralization; neutralization-iron salt coprecipitation involves adding iron salts after adjusting the pH of the waste acid; and sulfidation involves adding a sulfiding agent, such as sodium sulfide or hydrogen sulfide, to the waste acid. All three methods can effectively remove arsenic and heavy metals. However, during the purification process, valuable metals in the waste acid precipitate along with the waste residue, resulting in a large amount of waste residue with low-grade valuable metals, making recovery difficult and leading to resource waste.

[0004] Sulfide precipitation is widely used in industrial production due to its simple operation and low production cost. However, this method faces challenges in achieving effective separation and recovery of copper and arsenic. At present, the separation of copper and arsenic in waste acid mainly adopts the following methods: (1) Using arsenic sulfide or arsenic sulfide slag to replace copper in waste acid, which is the most widely used method. However, there is a problem that the concentration of copper and arsenic in waste acid must be strictly controlled. Arsenic sulfide or arsenic sulfide slag reacts with copper in waste acid, and copper precipitates in the form of copper sulfide, while arsenic exists in waste acid in the form of arsenic trioxide. Since the solubility of arsenic trioxide in waste acid is small (usually less than 20 g / L), when the concentration of copper and arsenic in waste acid is high, the generated arsenic trioxide will be supersaturated and precipitate in the form of solid arsenic trioxide, which mixes with copper sulfide, resulting in a high arsenic content in copper sulfide, which is not conducive to subsequent treatment. (2) Directly sulfiding waste acid produces copper sulfide arsenic slag, which is then added to an alkaline solution. Arsenic sulfide dissolves in the alkaline solution, while copper sulfide remains in the slag. However, this method produces high-arsenic alkaline wastewater that is more difficult to treat, requiring acid neutralization. The arsenic removal process is cumbersome, with a large volume of wastewater and high costs. (3) Using slow-release sulfiding waste acid, copper sulfide is precipitated first, followed by arsenic sulfide. Although this method is better, the preparation cost of the slow-release sulfiding agent is high, the sulfidation control conditions are stringent, and there are problems such as low separation efficiency of copper and arsenic and the generation of a large amount of H2S gas. (4) Using oxalic acid selective precipitation, copper precipitates as copper oxalate, while arsenic remains in the waste acid. On the one hand, this method is greatly affected by pH, and the separation effect is poor when the acidity is high. On the other hand, oxalic acid is introduced into the waste acid, requiring further removal of oxalic acid, resulting in high production costs. Summary of the Invention

[0005] To address the shortcomings of the existing technology, this invention provides a method for the comprehensive recovery of valuable elements from waste acid in non-ferrous smelting.

[0006] The specific technical solution is as follows:

[0007] A method for the comprehensive recovery of valuable elements from waste acid in non-ferrous smelting includes the following steps:

[0008] S1 mixes waste acid with pyrrhotite and reacts it under a sulfur dioxide atmosphere. After the reaction, copper slag and copper removal liquid are obtained through solid-liquid separation.

[0009] S2 H2S gas is introduced into the copper removal liquid obtained in step S1. After the reaction, arsenic sulfide slag and arsenic removal liquid are obtained by solid-liquid separation.

[0010] In step S1, sulfur dioxide is continuously introduced during the reaction process.

[0011] Among them, the non-ferrous smelting sludge comes from the acidic wastewater generated by the washing of sulfur-containing flue gas in non-ferrous smelting. Its main components are: As content 0.5~20g / L, Cu content 0.1~5g / L, and acidity (pH) 0.5~1.5.

[0012] The reaction mechanism of this invention is as follows:

[0013] This invention utilizes the selective reaction of FeS in pyrrhotite with CuSO4 in waste acid to form insoluble copper sulfide precipitate. At the same time, under the protection of sulfur dioxide atmosphere, arsenic in waste acid remains in a dissolved state and does not precipitate. After the removal of copper, the arsenic in the solution reacts with hydrogen sulfide to form arsenic sulfide, thereby achieving efficient separation of arsenic and copper in waste acid.

[0014] In step S1, pyrrhotite reacts in an acidic solution to release hydrogen sulfide. Sulfur dioxide gas reacts with hydrogen sulfide in the acidic solution to generate elemental sulfur. This process effectively prevents the possibility of hydrogen sulfide reacting with arsenic to form arsenic sulfide precipitate. Furthermore, during the reaction, the continuous introduction of sulfur dioxide gas into the solution reduces the small amount of pentavalent arsenic present in the solution to trivalent arsenic, preventing pentavalent arsenic from combining with iron ions to form insoluble ferric arsenate precipitate, thus ensuring the thoroughness and selectivity of the copper-arsenic separation process. These two key mechanisms work synergistically to guarantee the high efficiency and selectivity of copper-arsenic separation from waste acid. The main reactions are:

[0015] FeS + CuSO4 → CuS↓ + FeSO4;

[0016] FeS + H2SO4 → H2S + FeSO4;

[0017] SO2 + H2O → H2SO3;

[0018] 2H₂S + H₂SO₃ → 3S↓ + 3H₂O;

[0019] H3AsO4+H2SO3→H3AsO3+H2SO4.

[0020] The copper content in the copper removal solution is ≤0.1 mg / L, and the arsenic content in the copper slag is ≤0.10 wt%.

[0021] Furthermore, in step S1, the mesh size of the pyrrhotite is less than 200 mesh.

[0022] Furthermore, in step S1, the reaction temperature is 5~25℃ and the reaction time is 2~6h.

[0023] Furthermore, in step S1, the molar ratio of sulfur in pyrrhotite to the total amount of copper in the waste acid is (1.1~1.5):1.

[0024] Further, in step S1, sulfur dioxide is introduced to displace the air in the reaction vessel, allowing the reaction to proceed under a sulfur dioxide atmosphere. Simultaneously, sulfur dioxide is continuously introduced during the reaction to maintain a slightly positive pressure. This slightly positive pressure ensures that some sulfur dioxide dissolves in the water to form sulfurous acid. Excessive pressure would lead to more dissolved sulfur dioxide and the formation of a large amount of sulfurous acid. This large amount of sulfurous acid reacts with dissolved hydrogen sulfide in the solution to form elemental sulfur, promoting the reaction of ferrous sulfide with sulfuric acid to form hydrogen sulfide, thus reducing the utilization rate of ferrous sulfide. Preferably, the slightly positive pressure is 0.01~0.03 MPa.

[0025] Preferably, in step S1, the copper slag is returned to the copper smelting system to recover copper.

[0026] In step S2, after copper removal, hydrogen sulfide reacts with arsenic in the copper removal solution to form arsenic sulfide precipitate. The main reaction is as follows:

[0027] 2H3AsO3+3H2S→As2S3↓+6H2O.

[0028] Among them, the arsenic sulfide slag contains ≤0.30wt% iron and ≤0.10wt% copper, and the arsenic removal liquid contains ≤0.1mg / L arsenic.

[0029] Furthermore, in step S2, the molar ratio of sulfur in the H2S gas to the total amount of arsenic in the copper removal solution is (1.5~1.8):1.

[0030] Furthermore, in step S2, the reaction temperature is 5~25℃ and the reaction time is 0.5~2h.

[0031] Preferably, in step S2, the arsenic sulfide slag is returned to the arsenic smelting system to recover arsenic, and the arsenic removal liquid is neutralized by the neutralization system to obtain iron-calcium slag and neutralized water. The iron-calcium slag is returned to the copper smelting system, and the neutralized water is reused industrially.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] This invention utilizes pyrrhotite to selectively remove copper from polluted acid, and avoids the formation of arsenic sulfide and ferric arsenate precipitates by the action of sulfur dioxide. The synergistic effect of the two can effectively separate copper and arsenic from polluted acid, and the separation steps are simple and efficient. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of a method for the comprehensive recovery of valuable elements from waste acid in non-ferrous smelting, as described in a specific implementation. Detailed Implementation

[0035] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention. Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0036] Example 1

[0037] A method for the comprehensive recovery of valuable elements from waste acid in non-ferrous smelting, among which...

[0038] The non-ferrous smelting sludge comes from the acidic wastewater generated by washing sulfur-containing flue gas in non-ferrous smelting. Its main components are: As content 19.52g / L, Cu content 4.68g / L, and acidity (pH) 0.5.

[0039] The steps are as follows:

[0040] S1. Add waste acid and pyrrhotite with a mesh size of less than 200 to the reactor. Then, introduce sulfur dioxide gas into the reactor to replace the air inside, creating a sulfur dioxide protective atmosphere. React at 5°C for 6 hours. During the reaction, sulfur dioxide is continuously introduced to maintain the reaction pressure in the reactor at 0.03 MPa. After the reaction, copper slag and copper removal liquid are obtained through solid-liquid separation. The copper slag is returned to the copper smelting system to recover cathode copper. The molar ratio of sulfur in the pyrrhotite to copper in the waste acid is 1.5:1.

[0041] S2 H2S gas is introduced into the copper removal liquid obtained in step S1, and the reaction is carried out at 25°C for 2 hours. After the reaction is completed, arsenic sulfide slag and arsenic removal liquid are obtained by solid-liquid separation. The arsenic sulfide slag is returned to the arsenic smelting system to recover arsenic trioxide. The arsenic removal liquid is neutralized to obtain iron-calcium slag and neutralized water. The iron-calcium slag is returned to the copper smelting system, and the neutralized water is reused industrially. The molar ratio of sulfur in H2S gas to the total amount of arsenic in the copper removal liquid is 1.5:1.

[0042] Example 2

[0043] A method for the comprehensive recovery of valuable elements from waste acid in non-ferrous smelting, among which...

[0044] The non-ferrous smelting sludge comes from the acidic wastewater generated by washing sulfur-containing flue gas in non-ferrous smelting. Its main components are: As content 0.52g / L, Cu content 0.14g / L, and acidity (pH) 1.5.

[0045] The steps are as follows:

[0046] S1. Add waste acid and pyrrhotite with a mesh size of less than 200 to the reactor. Then, introduce sulfur dioxide gas into the reactor to replace the air inside, creating a sulfur dioxide protective atmosphere. React at 15°C for 4 hours. During the reaction, sulfur dioxide is continuously introduced to maintain the reaction pressure in the reactor at 0.02 MPa. After the reaction, copper slag and copper removal liquid are obtained through solid-liquid separation. The copper slag is returned to the copper smelting system to recover cathode copper. The molar ratio of sulfur in the pyrrhotite to copper in the waste acid is 1.3:1.

[0047] S2 H2S gas is introduced into the copper removal liquid obtained in step S1, and the reaction is carried out at 5°C for 1 hour. After the reaction is completed, arsenic sulfide slag and arsenic removal liquid are obtained by solid-liquid separation. The arsenic sulfide slag is returned to the arsenic smelting system to recover arsenic trioxide. The arsenic removal liquid is neutralized to obtain iron-calcium slag and neutralized water. The iron-calcium slag is returned to the copper smelting system, and the neutralized water is reused industrially. The molar ratio of sulfur in H2S gas to the total amount of arsenic in the copper removal liquid is 1.7:1.

[0048] Example 3

[0049] A method for the comprehensive recovery of valuable elements from waste acid in non-ferrous smelting, among which...

[0050] The non-ferrous smelting sludge comes from the acidic wastewater generated by washing sulfur-containing flue gas in non-ferrous smelting. Its main components are: As content 10.57g / L, Cu content 2.39g / L, and acidity (pH) 1.2.

[0051] The steps are as follows:

[0052] S1. Add waste acid and pyrrhotite with a mesh size of less than 200 into the reactor. Then, introduce sulfur dioxide gas into the reactor to replace the air inside, creating a sulfur dioxide protective atmosphere. React at 25°C for 2 hours. During the reaction, sulfur dioxide is continuously introduced to maintain the reaction pressure in the reactor at 0.01 MPa. After the reaction, copper slag and copper removal liquid are obtained through solid-liquid separation. The copper slag is returned to the copper smelting system to recover cathode copper. The molar ratio of sulfur in the pyrrhotite to copper in the waste acid is 1.1:1.

[0053] S2 H2S gas is introduced into the copper removal liquid obtained in step S1, and the reaction is carried out at 10°C for 0.5 h. After the reaction is completed, arsenic sulfide slag and arsenic removal liquid are obtained by solid-liquid separation. The arsenic sulfide slag is returned to the arsenic smelting system to recover arsenic trioxide. The arsenic removal liquid is neutralized to obtain iron-calcium slag and neutralized water. The iron-calcium slag is returned to the copper smelting system, and the neutralized water is reused industrially. The molar ratio of sulfur in H2S gas to the total amount of arsenic in copper removal liquid is 1.8:1.

[0054] Comparative Example 1

[0055] Referring to Example 1, the difference is that in step S1, the reactor is in an inert gas protective atmosphere and sulfur dioxide is not introduced during the reaction. The inert gas is used to make the reaction pressure in the reactor 0.03 MPa during the reaction.

[0056] test

[0057] The copper content in the copper removal solution obtained in Example 1-3 and Comparative Example 1 in step S1, the arsenic content in the copper slag, the arsenic content in the arsenic removal solution obtained in step S2, and the copper and iron content in the arsenic sulfide slag were tested, and the results are shown in Table 1. The recovery rate of each valuable element in Example 1-3 and Comparative Example 1 was calculated, and the results are shown in Table 2.

[0058] The copper and arsenic contents in the solution were tested according to the national standard "Determination of 32 Elements in Water by Inductively Coupled Plasma Atomic Emission Spectrometry (HJ 776-2015)" and the copper, arsenic, and iron contents in the residue were tested according to the standard "Determination of Copper, Iron, Arsenic, Zinc, Cadmium, Mercury and Silver Contents in Mixed Materials by Inductively Coupled Plasma Atomic Emission Spectrometry (SN / T 5266-2020)".

[0059] Table 1. Elemental content in copper removal solution, copper slag, arsenic removal solution, and arsenic sulfide slag.

[0060]

[0061] Table 2 Recovery rate of valuable elements

[0062]

[0063] As shown in Tables 1 and 2, using the technical solutions of this invention (Examples 1-3), the Cu content in the copper removal liquid is ≤0.10 mg / L, the As content in the copper slag is ≤0.10 wt%, and the Cu content in the arsenic sulfide slag is ≤0.05 wt%. The Cu recovery rate is above 97% and the As recovery rate is above 90%. In contrast, the Cu content in the copper removal liquid of Comparative Example 1 is 652.36 mg / L, the As content in the copper slag is 2.54 wt%, and the Cu content in the arsenic sulfide slag is 1.95 wt%. The Cu recovery rate is only 83.91% and the As recovery rate is only 88.91%. This indicates that the introduction of sulfur dioxide during copper precipitation can effectively inhibit the reaction between sulfur and arsenic in pyrrhotite and achieve the separation of copper and arsenic in the waste acid.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the comprehensive recovery of valuable elements from waste acid in non-ferrous smelting, characterized in that, Includes the following steps: S1 mixes waste acid with pyrrhotite and reacts it under a sulfur dioxide atmosphere. After the reaction, copper slag and copper removal liquid are obtained through solid-liquid separation. S2 H2S gas is introduced into the copper removal liquid obtained in step S1. After the reaction, arsenic sulfide slag and arsenic removal liquid are obtained by solid-liquid separation. The non-ferrous smelting wastewater comes from the acidic wastewater generated by washing sulfur-containing flue gas in non-ferrous smelting. Its main components are: As content 0.5~20g / L, Cu content 0.1~5g / L, and pH 0.5~1.

5. In step S1, the molar ratio of sulfur in pyrrhotite to the total amount of copper in the wastewater is (1.1~1.5):

1. In step S1, during the reaction process, sulfur dioxide is continuously introduced to maintain the reaction pressure at a slightly positive pressure of 0.01~0.03MPa. In step S2, the molar ratio of sulfur in H2S gas to the total amount of arsenic in the copper removal liquid is (1.5~1.8):

1.

2. The method according to claim 1, characterized in that, In step S1, the mesh size of the pyrrhotite is less than 200 mesh.

3. The method according to claim 1, characterized in that, In step S1, the reaction temperature is 5~25℃ and the reaction time is 2~6h.

4. The method according to claim 1, characterized in that, In step S1, the copper slag is returned to the copper smelting system to recover copper.

5. The method according to claim 1, characterized in that, In step S2, the reaction temperature is 5~25℃ and the reaction time is 0.5~2h.

6. The method according to claim 1, characterized in that, In step S2, the arsenic sulfide slag is returned to the arsenic smelting system to recover arsenic.

7. The method according to claim 1, characterized in that, In step S2, the arsenic removal liquid is neutralized to obtain iron-calcium slag and neutralized water. The iron-calcium slag is returned to the copper smelting system, and the neutralized water is reused industrially.

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