Process for recovering various valuable elements such as lead, zinc, silver and potassium from soot of steel mill

Abstract

The invention provides a process for recovering various valuable elements such as lead, zinc, silver and potassium from soot of a steel mill. The process comprises the following steps of water leaching, fluorine removal, high-temperature concentration, primary cooling crystallization, secondary cooling crystallization, secondary leaching, ammonia leaching and ammonia distillation. According to the recovery process, potassium in the soot of the steel mill is recovered in the form of potassium chloride, zinc is recovered in the form of zinc sulfate, silver is recovered in the form of silver chloride, only auxiliary materials such as sulfuric acid, ammonia water and calcium chloride which are low in price are used in the whole recovery process, the cost is low, no waste water or waste residues are generated in the whole process, the direct recovery rate of lead and zinc is 95% or above, and the production cost is low. The direct recovery rate of silver is 98% or above, and the method has practical application value.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgical waste slag recovery, and in particular to a process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel plant ash. Background Art

[0002] In the process of steel smelting, the generation of soot is an inevitable phenomenon. Volatile valuable elements such as lead, chlorine, potassium, zinc, fluorine, and silver are easily enriched in the soot of steel smelting. Since these soot contain chlorine, fluorine, lead, zinc, and silver, if not handled in time or improperly, these elements are very likely to flow into the soil and water sources, causing soil pollution and eutrophication of water bodies. Heavy metals such as lead and silver will accumulate in organisms, causing long-term impacts on the ecosystem and even affecting human health. Therefore, the proper disposal of steel mill soot and the comprehensive recovery of valuable elements therein are also the focus of current work. Reasonable recovery of these elements can achieve resource reuse and reduce environmental pollution. Summary of the invention

[0003] In view of this, the present invention proposes a process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill ash to solve the above technical problems. The whole process only uses low-priced auxiliary materials such as sulfuric acid, ammonia water and calcium chloride, the production cost is low, and the whole process does not produce wastewater and waste residue.

[0004] The technical solution of the present invention is achieved in this way:

[0005] A process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill ash, the specific steps of which include:

[0006] S1. Water leaching: adding steel mill ash into water for leaching, filtering, and obtaining primary leaching liquid and primary leaching slag;

[0007] S2, defluorination: adding calcium oxide to the primary leaching solution of S1 to react, controlling the end point pH to 7±0.1, filtering after the reaction to obtain calcium fluoride and salt solution;

[0008] S3, high temperature concentration: the salt solution of S2 is concentrated at a constant temperature until the concentration of potassium chloride in the salt solution is 460-480 g / L, and the concentration is stopped immediately to obtain a concentrated solution;

[0009] S4, primary cooling crystallization: cooling the concentrated solution of S3 for primary crystallization until the potassium chloride concentration in the concentrated solution reaches 280-285 g / L, filtering to obtain potassium chloride and primary crystallization mother liquor, wherein the primary crystallization mother liquor is returned to step S1 for circulation;

[0010] S5, secondary cooling crystallization: when the sodium content in the primary crystallization mother liquor returned to step S1 for circulation in S4 is higher than 300 g / L, the primary crystallization mother liquor is subjected to secondary cooling crystallization and filtered to obtain a mixed salt and a secondary crystallization mother liquor, wherein the secondary crystallization mother liquor is returned to step S1 for circulation;

[0011] S6, secondary leaching: adding the primary leaching residue of S1 into hydrogen peroxide, adding sulfuric acid to control the end point pH to 2.5-3.0, performing secondary leaching, filtering, and obtaining secondary leaching residue and secondary leaching solution;

[0012] The secondary leaching solution can be sent to the zinc oxide leaching process to prepare zinc sulfate heptahydrate;

[0013] S7, ammonia leaching: adding the secondary leaching residue in S6 into ammonia water for leaching, filtering, and obtaining ammonia leaching residue and ammonia leaching liquid, wherein the ammonia leaching residue is sent to the lead smelting system;

[0014] S8, ammonia evaporation: the ammonia leaching liquid of S7 is heated in stages to obtain ammonia water and ammonia evaporation mother liquor, the ammonia evaporation mother liquor is filtered to obtain ammonia evaporation mother liquor filtrate and silver chloride, wherein the ammonia water can be recycled and the ammonia evaporation mother liquor filtrate can be used as an absorption liquid for the ammonia evaporation system.

[0015] Furthermore, in step S1, the steel mill ash contains potassium, zinc, lead, sodium, fluorine, iron and silver; the solid-liquid ratio of the steel mill ash to water is 1:4-6 g / mL; the leaching is carried out at 35-45° C. for 2-3 hours; the primary leaching solution contains potassium, sodium, lead, zinc and fluorine; and the primary leaching residue contains sodium chloride and potassium chloride.

[0016] The invention firstly leaches out the sodium chloride and potassium chloride in the steel plant ash by water leaching, and more than 99% of the lead chloride and more than 99% of the zinc chloride remain in the leaching residue without being leached out.

[0017] Furthermore, in step S2, the solid-liquid ratio of the calcium oxide to the primary leaching solution is 2.5-3.5:1 g / L; and the reaction time is 1-2 h.

[0018] The present invention adds calcium oxide into the leaching solution to precipitate fluorine and obtain a relatively pure potassium chloride solution.

[0019] Furthermore, in step S3, the temperature of the constant temperature concentration is 85-95°C.

[0020] Furthermore, in step S4, the primary cooling crystallization is performed at a cooling rate of 0.5-1.0°C / min to 1-2°C.

[0021] Furthermore, in step S5, the secondary cooling crystallization is performed by cooling the mixture to 1-2°C at a cooling rate of 0.5-1.0°C / min and stirring the mixture for 1-1.5h.

[0022] The present invention obtains more than 90% of potassium chloride products through high-temperature concentration and low-temperature segmented cooling crystallization treatment, which can be sold to the fertilizer industry.

[0023] Furthermore, in step S6, the mass of the hydrogen peroxide is 20%-40% of the mass of the primary leaching residue; and the secondary leaching is carried out at room temperature for 2-3 hours.

[0024] Furthermore, in step S7, the solid-liquid ratio of the secondary leaching residue to the ammonia water is 0.25-0.35:1 g / mL; and the leaching is performed at room temperature for 2-3 hours.

[0025] Furthermore, in step S8, the staged heating treatment is firstly heating to 85-90°C and maintaining for 2-3 hours, and then heating to 98-102°C and maintaining for 1-1.5 hours.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) In step S1 of the present invention, inorganic salts such as potassium chloride and sodium chloride in the steel plant fly ash are introduced into the leaching solution through water leaching treatment, and more than 99% of the lead chloride and more than 99% of the zinc chloride in the fly ash are retained in the leaching residue without being leached, so that heavy metals such as lead and zinc do not enter the potassium chloride recovery system.

[0028] (2) Steps S3-S5 of the present invention recover potassium chloride by high-temperature heating concentration-stage cooling, and can recover more than 90% of the potassium in the steel plant ash in the form of potassium chloride product.

[0029] (3) In step S6 of the present invention, the pH of the leaching is controlled by hydrogen peroxide and sulfuric acid, so that the zinc in the ash enters the leachate, and the iron remains in the leaching residue in the form of trivalent iron. Although there are chloride ions in the leachate, after the leachate is returned to the zinc oxide leaching system, it will react with the zinc oxide ash, and the chloride ions in the leachate and the lead in the zinc oxide ash will form lead chloride and remain in the zinc oxide leaching residue, so that the chloride ions in the leachate can be removed at zero cost.

[0030] (4) The present invention uses water leaching in step S1 and secondary leaching in step S6 to allow elements such as potassium, sodium, and zinc in the steel plant fly ash to enter the solution and be separated from the fly ash, so that during the ammonia leaching treatment in step S7, all silver chloride can enter the solution, and the result that zinc reacts with ammonia water first will not occur.

[0031] (5) The ammonia evaporation process in step S8 of the present invention allows the ammonia in the solution to be recovered in the form of ammonia water for recycling, while the silver chloride is directly precipitated. The entire silver recovery process only adds reusable ammonia water without adding a silver replacement agent or reducing agent, which has a low cost and does not add other inorganic salts to the system.

[0032] (6) The recovery process of the present invention recovers potassium in the steel plant smoke ashes in the form of potassium chloride, zinc in the form of zinc sulfate, and silver in the form of silver chloride. The entire recovery process uses only inexpensive auxiliary materials such as sulfuric acid, ammonia water and calcium chloride, which is low in cost. The entire process does not generate wastewater and waste residue. The direct recovery rates of lead and zinc are above 95%, and the direct recovery rate of silver is above 98%, which has practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0034] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0035] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0036] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0037] Example 1

[0038] Take 1000g of steel plant fly ash, which contains 20.14% potassium, 7.02% zinc, 10.28% lead, 2.16% sodium, 0.92% fluorine, 3.26% iron and 655.47g / t silver.

[0039] The process of recovering multiple valuable elements such as lead, zinc, silver and potassium from steel plant ash has the following specific steps:

[0040] S1, water leaching: add 1000g steel mill smoke ash to 5L water, leaching temperature 40℃, continue for 2h, filter after reaction is complete, obtain 4.9L primary leaching solution and 493.2g primary leaching slag, the primary leaching solution contains 40.28g / L potassium, 4.32g / L sodium, 13.21mg / L lead, 15.13mg / L zinc, 1.72g / L fluorine;

[0041] S2, defluorination: add 15g calcium oxide to the primary leaching solution of S1 and react for 2h, control the end point pH to 7.0±0.1, filter after the reaction, and obtain 21.2g calcium fluoride and 4.81L salt solution;

[0042] S3, high temperature concentration: the salt solution of S2 is concentrated at a constant temperature of 95°C until the concentration of potassium chloride in the salt solution is 465.12 g / L, to obtain a concentrated solution;

[0043] S4, primary cooling crystallization: The concentrated solution of S3 is subjected to primary cooling crystallization, and the temperature is reduced to 1-2°C at a cooling rate of 0.8°C / min, until the potassium chloride concentration in the concentrated solution reaches 282.32 g / L, and filtered to obtain 164.35 g potassium chloride and 382 mL primary crystallization mother liquor, wherein the primary crystallization mother liquor is returned to step S1 for circulation;

[0044] S5, secondary cooling crystallization: when the sodium content in the primary crystallization mother liquor returned to step S1 for circulation in S4 is higher than 300 g / L, the primary crystallization mother liquor is subjected to secondary cooling crystallization, cooled to 1-2°C at a cooling rate of 0.8°C / min, stirred for 1h and then filtered to obtain 80.26g of mixed salt and 385mL of secondary crystallization mother liquor, wherein the secondary crystallization mother liquor is returned to step S1 for circulation;

[0045] S6, secondary leaching: add 100g hydrogen peroxide to the primary leaching residue of S1, add 1500mL water, add sulfuric acid to control the end point pH to 2.8, carry out secondary leaching at room temperature for 2.5h, filter, and obtain 401.2g secondary leaching residue and 1450mL secondary leaching solution, which contains 46.14g / L zinc. The secondary leaching solution can be sent to the zinc oxide leaching process to prepare zinc sulfate heptahydrate;

[0046] S7, ammonia leaching: the secondary leaching residue in S6 is added into 1300 mL ammonia water for leaching at room temperature for 2 h, filtered to obtain 392.3 g ammonia leaching residue and 1200 mL ammonia leaching solution, and the ammonia leaching residue is sent to the lead smelting system;

[0047] S8, ammonia evaporation: put the ammonia leaching liquid of S7 into a closed container with an absorption device, first heat it to 90°C and keep it for 3 hours, then heat it to 100°C and keep it for 1.5 hours, collect 1100mL of ammonia water and ammonia evaporation mother liquor, filter the ammonia evaporation mother liquor to obtain ammonia evaporation mother liquor filtrate and 1.23g of silver chloride (containing 52.76% silver), wherein the ammonia water can be recycled and the ammonia evaporation mother liquor filtrate can be used as the absorption liquid of the ammonia evaporation system.

[0048] The valuable element recovery effect of this embodiment is:

[0049] lead Zinc silver Potassium 99.94％ 95.30％ 99％ 97.46％

[0050] Example 2

[0051] Take 1000g of steel plant fly ash, which contains 30.26% potassium, 5.32% zinc, 9.12% lead, 3.33% sodium, 0.88% fluorine, 8.22% iron and 852.33g / t silver.

[0052] The process of recovering multiple valuable elements such as lead, zinc, silver and potassium from steel plant ash has the following specific steps:

[0053] S1. Water leaching: 1000g of steel plant fly ash was added into 5.5L of water, the leaching temperature was 45°C, and the leaching was continued for 3h. After the reaction was complete, 5230mL of primary leaching solution and 323.62g of primary leaching residue were obtained. The primary leaching solution contained 57.27g / L of potassium, 6.3g / L of sodium, 15.26mg / L of lead, 16.18mg / L of zinc, and 1.51g / L of fluorine.

[0054] S2, defluorination: add 15g calcium oxide to the primary leaching solution of S1 and react for 2h, control the end point pH to 7.0±0.1, filter after the reaction, and obtain 20.91g calcium fluoride and 5220mL salt solution;

[0055] S3, high temperature concentration: the salt solution of S2 is concentrated at a constant temperature of 90°C until the concentration of potassium chloride in the salt solution is 470.33 g / L, to obtain a concentrated solution;

[0056] S4, primary cooling crystallization: The concentrated solution of S3 is subjected to primary cooling crystallization, and the temperature is reduced to 1-2°C at a cooling rate of 0.9°C / min, until the potassium chloride concentration in the concentrated solution reaches 284.56 g / L, and filtered to obtain 240.33 g potassium chloride and 626 mL primary crystallization mother liquor, wherein the primary crystallization mother liquor is returned to step S1 for circulation;

[0057] S5, secondary cooling crystallization: when the sodium content in the primary crystallization mother liquor returned to step S1 for circulation in S4 is higher than 300 g / L, the primary crystallization mother liquor is subjected to secondary cooling crystallization, cooled to 1-2°C at a cooling rate of 0.9°C / min, stirred for 1.5h and then filtered to obtain 83.25g of mixed salt and 618mL of secondary crystallization mother liquor, wherein the secondary crystallization mother liquor is returned to step S1 for circulation;

[0058] S6, secondary leaching: add 110g hydrogen peroxide to the primary leaching residue of S1, add 1000mL water, add sulfuric acid to control the end point pH to 2.8, carry out secondary leaching at room temperature for 2h, filter, and obtain 291.25g secondary leaching residue and 950mL secondary leaching solution, which contains 55.75g / L zinc. The secondary leaching solution can be sent to the zinc oxide leaching process to prepare zinc sulfate heptahydrate;

[0059] S7, ammonia leaching: add the secondary leaching residue in S6 into 1000 mL ammonia water, leach for 2.5 h at room temperature, filter, and obtain 285.61 g ammonia leaching residue and 960 mL ammonia leaching solution. The ammonia leaching residue is sent to the lead smelting system;

[0060] S8, ammonia evaporation: put the ammonia leaching liquid of S7 into a closed container with an absorption device, first heat it to 85°C and keep it for 3 hours, then heat it to 100°C and keep it for 1.5 hours, collect 910mL of ammonia water and ammonia evaporation mother liquor, filter the ammonia evaporation mother liquor to obtain ammonia evaporation mother liquor filtrate and 1.26g of silver chloride (containing 66.96% silver), wherein the ammonia water can be recycled and the ammonia evaporation mother liquor filtrate can be used as the absorption liquid of the ammonia evaporation system.

[0061] The valuable element recovery effect of this embodiment is:

[0062] lead Zinc silver Potassium 99.91％ 95.36％ 98.99％ 96.12％

[0063] 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 in the protection scope of the present invention.

Claims

1. A process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill ash, characterized in that: The specific steps include: S1. Water leaching: adding steel mill ash into water for leaching, filtering, and obtaining primary leaching liquid and primary leaching slag; S2, defluorination: adding calcium oxide to the primary leaching solution of S1 to react, controlling the end point pH to 7±0.1, filtering after the reaction to obtain calcium fluoride and salt solution; S3, high temperature concentration: the salt solution of S2 is concentrated at a constant temperature until the concentration of potassium chloride in the salt solution is 460-480 g / L, and the process is stopped immediately to obtain a concentrated solution; S4, primary cooling crystallization: cooling the concentrated solution of S3 for primary crystallization until the potassium chloride concentration in the concentrated solution reaches 280-285 g / L, filtering to obtain potassium chloride and primary crystallization mother liquor, wherein the primary crystallization mother liquor is returned to step S1 for circulation; S5, secondary cooling crystallization: when the sodium content in the primary crystallization mother liquor returned to step S1 for circulation in S4 is higher than 300 g / L, the primary crystallization mother liquor is subjected to secondary cooling crystallization and filtered to obtain a mixed salt and a secondary crystallization mother liquor, wherein the secondary crystallization mother liquor is returned to step S1 for circulation; S6, secondary leaching: adding the primary leaching residue of S1 into hydrogen peroxide, adding sulfuric acid to control the end point pH to 2.5-3.0, performing secondary leaching, filtering, and obtaining secondary leaching residue and secondary leaching solution; S7, ammonia leaching: adding the secondary leaching residue in S6 into ammonia water for leaching, filtering, and obtaining ammonia leaching residue and ammonia leaching liquid; S8, ammonia evaporation: the ammonia leaching solution of S7 is heated in stages to obtain ammonia water and ammonia evaporation mother liquor, and the ammonia evaporation mother liquor is filtered to obtain ammonia evaporation mother liquor filtrate and silver chloride.

2. A process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill ash as claimed in claim 1, characterized in that: In step S1, the steel mill ash contains potassium, zinc, lead, sodium, fluorine, iron and silver; the solid-liquid ratio of the steel mill ash to water is 1:4-6g / mL; the leaching is carried out at 35-45°C for 2-3h; the primary leaching solution contains potassium, sodium, lead, zinc and fluorine; and the primary leaching residue contains sodium chloride and potassium chloride.

3. A process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill ash as claimed in claim 1, characterized in that: In step S2, the solid-liquid ratio of the calcium oxide to the primary leaching solution is 2.5-3.5:1 g / L; and the reaction time is 1-2 h.

4. A process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill ash as claimed in claim 1, characterized in that: In step S3, the temperature of the constant temperature concentration is 85-95°C.

5. A process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill ash as claimed in claim 1, characterized in that: In step S4, the primary cooling crystallization is performed at a cooling rate of 0.5-1.0°C / min to 1-2°C.

6. A process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill ash as claimed in claim 1, characterized in that: In step S5, the secondary cooling crystallization is performed by cooling the temperature to 1-2°C at a cooling rate of 0.5-1.0°C / min and stirring for 1-1.5h.

7. A process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill ash as claimed in claim 1, characterized in that: In step S6, the mass of the hydrogen peroxide is 20%-40% of the mass of the primary leaching residue; and the secondary leaching is carried out at room temperature for 2-3 hours.

8. A process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill ash as claimed in claim 1, characterized in that: In step S7, the solid-liquid ratio of the secondary leaching residue to the ammonia water is 0.25-0.35:1 g / mL; and the leaching is performed at room temperature for 2-3 hours.

9. A process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill ash as claimed in claim 1, characterized in that: In step S8, the staged heating treatment is to first raise the temperature to 85-90°C and maintain it for 2-3 hours, and then raise the temperature to 98-102°C and maintain it for 1-1.5 hours.

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