A process for recovering multiple valuable elements including lead, zinc, silver and potassium from steel mill ash

Abstract

The present invention provides a process for recovering multiple valuable elements, including lead, zinc, silver, and potassium, from steel mill fly ash. The process comprises the following steps: water leaching, fluorine removal, high-temperature concentration, primary cooling crystallization, secondary cooling crystallization, secondary leaching, ammonia leaching, and ammonia distillation. The recovery process of the present invention allows potassium from the steel mill fly ash to be recovered as potassium chloride, zinc as zinc sulfate, and silver as silver chloride. The entire recovery process utilizes only inexpensive auxiliary materials, such as sulfuric acid, aqueous ammonia, and calcium chloride, resulting in low costs. The entire process generates no wastewater or waste residue, and the direct recovery rates for lead and zinc exceed 95%, while the direct recovery rate for silver exceeds 98%, demonstrating practical application value.

Description

Technical Field

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

[0002] The generation of soot is inevitable during the steelmaking process. Volatile valuable elements such as lead, chlorine, potassium, zinc, fluorine, and silver are easily enriched in this soot. Since these soot contain chlorine, fluorine, lead, zinc, and silver, if not promptly or properly handled, these elements can easily enter the soil and water sources, leading to soil pollution and water eutrophication. Heavy metals such as lead and silver can accumulate in organisms, causing long-term impacts on ecosystems and even human health. Therefore, the proper disposal of steel mill soot and the comprehensive recovery of its valuable elements are currently key priorities. The rational recovery of these elements can achieve resource reuse while reducing environmental pollution. Summary of the Invention

[0003] In light of this, the present invention proposes a process for recovering multiple valuable elements, including lead, zinc, silver, and potassium, from steel mill fly ash to address the aforementioned technical issues. The entire process utilizes only inexpensive auxiliary materials, such as sulfuric acid, aqueous ammonia, and calcium chloride, resulting in low production costs and generating no wastewater or residue.

[0004] The technical solution of the present invention is achieved as follows:

[0005] A process for recovering multiple valuable elements including lead, zinc, silver, and potassium from steel mill fly ash, comprising the following steps:

[0006] S1. Water leaching: adding steel mill fly ash into water for leaching, filtering, and obtaining primary leachate and primary leach residue;

[0007] S2, defluorination: adding calcium oxide to the primary leachate 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 460-480g / L, and the process is stopped immediately to obtain a concentrated solution;

[0009] S4, primary cooling crystallization: The concentrated solution of S3 is subjected to primary cooling crystallization until the potassium chloride concentration in the concentrated solution reaches 280-285 g / L, and filtered to obtain potassium chloride and a 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 of 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 leachate;

[0012] The secondary leachate 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 distillation: the ammonia leaching liquid of S7 is heated in sections to obtain ammonia water and ammonia distillation mother liquor, the ammonia distillation mother liquor is filtered to obtain ammonia distillation mother liquor filtrate and silver chloride, wherein the ammonia water can be recycled and the ammonia distillation mother liquor filtrate can be used as the absorption liquid of the ammonia distillation 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 leachate contains potassium, sodium, lead, zinc and fluorine; and the primary leaching residue contains sodium chloride and potassium chloride.

[0016] The invention firstly leach 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 leachate is 2.5-3.5:1 g / L; and the reaction time is 1-2 h.

[0018] The present invention adds calcium oxide to 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% 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 mill fly ash are introduced into the leachate by water leaching. At the same time, 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 fly 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 using 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 chloride ions are present in the leachate, after the leachate is returned to the zinc oxide leaching system, it reacts with the zinc oxide ash. The chloride ions in the leachate react with the lead in the zinc oxide ash to form lead chloride, which remains in the zinc oxide leaching residue, achieving zero-cost removal of the chloride ions in the leachate.

[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. As a result, during the ammonia leaching treatment in step S7, all the silver chloride can enter the solution, and the result that zinc reacts with the 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 is low in cost and does not add other inorganic salts to the system.

[0032] (6) The recovery process of the present invention recovers potassium from steel mill ash 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. No wastewater or waste residue is generated in the entire process. 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 examples are provided below to further illustrate the present invention.

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

[0036] Unless otherwise specified, the materials, reagents, etc. used in the examples 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 for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill fly ash has the following specific steps:

[0040] S1, water leaching: 1000g of steel mill fly ash was added to 5L of water at a leaching temperature of 40°C for 2h. After the reaction was complete, filtration was performed to obtain 4.9L of primary leachate and 493.2g of primary leachate residue. The primary leachate contained 40.28g / L of potassium, 4.32g / L of sodium, 13.21mg / L of lead, 15.13mg / L of zinc, and 1.72g / L of fluorine.

[0041] S2, defluorination: add 15g of calcium oxide to the primary leachate of S1 and react for 2h, control the end point pH to 7.0±0.1, filter after reaction, and obtain 21.2g of calcium fluoride and 4.81L of 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 was subjected to primary cooling crystallization, and the temperature was lowered to 1-2°C at a cooling rate of 0.8°C / min until the potassium chloride concentration in the concentrated solution reached 282.32 g / L. Filter to obtain 164.35 g of potassium chloride and 382 mL of primary crystallization mother liquor, wherein the primary crystallization mother liquor was 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 1 hour, and then filtered to obtain 80.26 g of mixed salt and 385 mL 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 leachate, which contains 46.14g / L zinc. The secondary leachate can be sent to the zinc oxide leaching process to prepare zinc sulfate heptahydrate;

[0046] S7, ammonia leaching: the secondary leaching residue in S6 was added to 1300 mL of ammonia water and leached at room temperature for 2 h, filtered to obtain 392.3 g of ammonia leaching residue and 1200 mL of ammonia leaching solution, and the ammonia leaching residue was 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 1100 mL of ammonia water and ammonia evaporation mother liquor, filter the ammonia evaporation mother liquor to obtain ammonia evaporation mother liquor filtrate and 1.23 g 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 for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill fly ash has the following specific steps:

[0053] S1, water leaching: 1000g steel mill fly ash was added to 5.5L water, the leaching temperature was 45°C, and the leaching temperature was maintained for 3h. After the reaction was complete, 5230mL of primary leachate and 323.62g of primary leachate residue were obtained. The primary leachate 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 of calcium oxide to the primary leachate of S1 and react for 2h, control the end point pH to 7.0±0.1, filter after reaction, and obtain 20.91g of calcium fluoride and 5220mL of 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 was subjected to primary cooling crystallization, and the temperature was lowered to 1-2°C at a cooling rate of 0.9°C / min until the potassium chloride concentration in the concentrated solution reached 284.56 g / L. Filter to obtain 240.33 g of potassium chloride and 626 mL of primary crystallization mother liquor, wherein the primary crystallization mother liquor was 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 1.5 hours, and then filtered to obtain 83.25 g of mixed salt and 618 mL 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 leachate, which contains 55.75g / L zinc. The secondary leachate can be sent to the zinc oxide leaching process to prepare zinc sulfate heptahydrate;

[0059] S7, ammonia leaching: the secondary leaching residue in S6 was added to 1000 mL of ammonia water, leached at room temperature for 2.5 h, filtered to obtain 285.61 g of ammonia leaching residue and 960 mL of ammonia leaching solution, and the ammonia leaching residue was 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 910 mL of ammonia water and ammonia evaporation mother liquor, filter the ammonia evaporation mother liquor to obtain ammonia evaporation mother liquor filtrate and 1.26 g 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 scope of protection of the present invention.

Claims

1. A process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill fly ash, characterized in that: The specific steps include: S1. Water leaching: Add steel mill fly ash into water, leach at 35-45°C for 2-3 hours, filter, and obtain primary leachate and primary leach residue; S2, defluorination: adding calcium oxide to the primary leachate 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 of 85-95°C until the concentration of potassium chloride in the salt solution is 460-480g / L, and then the concentration is stopped immediately to obtain a concentrated solution; S4, primary cooling crystallization: The concentrated solution of S3 is subjected to primary cooling crystallization until the potassium chloride concentration in the concentrated solution reaches 280-285 g / L, and filtered to obtain potassium chloride and a primary crystallization mother liquor, wherein the primary crystallization mother liquor is returned to step S1 for circulation; The primary cooling crystallization is performed at a cooling rate of 0.5-1.0°C / min to 1-2°C; S5, secondary cooling crystallization: when the sodium content of 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; 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; S6, secondary leaching: the primary leaching residue of S1 is added to hydrogen peroxide, sulfuric acid is added to control the end point pH to 2.5-3.0, and secondary leaching is carried out at room temperature for 2-3 hours, and filtered to obtain secondary leaching residue and secondary leachate; S7, ammonia leaching: add the secondary leaching residue in S6 into ammonia water, leach at room temperature for 2-3 hours, filter, and obtain ammonia leaching residue and ammonia leaching liquid; S8, ammonia distillation: heating the ammonia leaching liquid in S7 in stages to obtain ammonia water and ammonia distillation mother liquor, filtering the ammonia distillation mother liquor to obtain ammonia distillation mother liquor filtrate and silver chloride; 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.

2. A process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill fly ash according to claim 1, characterized in that: In step S1, the steel mill fly ash contains potassium, zinc, lead, sodium, fluorine, iron and silver; the solid-liquid ratio of the steel mill fly ash to water is 1:4-6 g / mL; the primary leachate contains potassium, sodium, lead, zinc and fluorine; and the primary leachate residue contains sodium chloride and potassium chloride.

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

4. The process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill fly ash according to claim 1, wherein: In step S6, the mass of the hydrogen peroxide is 20%-40% of the mass of the primary leaching residue.

5. The process for recovering multiple valuable elements such as lead, zinc, silver and potassium from steel mill fly ash according to 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.

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