Process for recovering iron and zinc from iron-zinc-containing sludge

Abstract

A kind of process method for recovering iron and zinc from iron-zinc-containing sludge, which is carried out in the following steps: roasting the iron-zinc-containing sludge at 600-800 ℃ in an oxidizing environment, Zn(OH)2 is decomposed into ZnO, and Fe(OH)3 is decomposed into Fe2O3, obtaining an oxidized roasting product; reducing roasting 1 of the oxidized roasting product at 500-700 ℃, obtaining a reduced roasting product; grinding the reduced roasting product to a content of 65%-85% of -0.025 mm; weak magnetic roughing and cleaning of the ground product at a magnetic intensity of 79.62-131.34 kA / m, obtaining a final concentrate with an iron grade of more than 55%; and reducing roasting 2 of the tailings with coke as a reducing agent at 1100-1200 ℃, distillation to obtain elemental zinc, with a zinc recovery rate of more than 90%, a zinc content in the roasting slag of less than 0.5%, and the roasting slag being treated as waste slag. The method is used for treating iron-zinc-containing sludge obtained by chemical precipitation of electroplating zinc wastewater, and recovers iron and zinc by combined beneficiation and smelting, reduces the content of heavy metals in the iron-zinc-containing sludge, recovers valuable metals, solves the problem of environmental pollution, and provides a zinc recovery method for solid waste resources.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically a process for recovering iron and zinc from iron-zinc sludge. Background Technology

[0002] Untreated zinc-containing industrial wastewater poses a serious threat to human health and industrial and agricultural activities. This harm is characterized by its persistence, high toxicity, and severe pollution. Once zinc enters the food chain, it accumulates in organisms. Excessive zinc accumulation in animals can negatively impact the immune, hematopoietic, nervous, and reproductive systems in humans. High zinc levels in plants can inhibit growth and induce disease. Therefore, treating zinc-containing industrial wastewater is of great importance to the health of plants and animals.

[0003] Iron-zinc sludge is obtained by chemical precipitation of electroplating wastewater and quicklime. The electroplating wastewater contains Fe. 3+ Zn 2+ Metal ions, in an alkaline environment, Fe 3+ Zn 2+ A chemical reaction occurs to form Fe(OH)3 and Zn(OH)2 precipitates, with Zn grade of 5%–15% and TFe grade of 15%–25%, making it a secondary resource for zinc utilization.

[0004] Electroplating iron-zinc sludge mainly consists of hydroxide precipitates of metals such as zinc, iron, and calcium. These metal hydroxides decompose under high-temperature conditions, generating corresponding metal oxides. The chemical decomposition reactions of zinc and iron under high-temperature conditions are as follows:

[0005] Zn(OH)2=O2(g)+ZnO

[0006] 2Fe(OH)3=O2(g)+3Fe2O3

[0007] Iron oxides obtained from high-temperature decomposition undergo reduction reactions in hydrogen or carbon monoxide atmospheres to form strongly magnetic Fe3O4. Zinc oxides are difficult to reduce to elemental zinc in hydrogen or carbon monoxide atmospheres, as evidenced by the Gibbs free energy of the chemical reaction between zinc oxide and hydrogen or carbon monoxide, which remains greater than zero at temperatures between 0-1300℃. The reduction reactions of iron oxides are as follows:

[0008] 3Fe₂O₃ + H₂ = 2Fe₃O₄ + H₂O

[0009] 3Fe₂O₃ + CO = 2Fe₃O₄ + CO₂

[0010] Zinc metal oxides undergo a reduction reaction at temperatures of 1100–1200℃ with coke as a reducing agent. The zinc metal oxides are then separated from zinc-containing tailings as zinc vapor, realizing the resource utilization of iron-zinc mud. Based on the Gibbs free energy of the reaction between zinc metal oxides and carbon, it is known that when the temperature is above 1050℃, the Gibbs free energy is less than zero, and the chemical reaction can proceed spontaneously. The chemical reaction of zinc oxide in the environment of coke as a reducing agent is as follows:

[0011] 2ZnO + C = 2Zn(g) + CO2(g)

[0012] ZnO + C = Zn(g) + CO(g)

[0013] Chemical reactions of zinc and iron compounds under conditions of 0–1500℃, such as Figure 1 As shown.

[0014] In existing technologies, precipitation methods can treat electroplating wastewater to meet wastewater discharge requirements, but the precipitated wastewater contains high levels of heavy metals such as iron and zinc, and its storage still leads to environmental pollution. Summary of the Invention

[0015] This invention relates to a process for recovering iron and zinc from iron-zinc sludge, with the aim of recovering zinc and iron metals from the iron-zinc sludge, making resource utilization of heavy metal emissions, reducing environmental pollution, and providing a new direction for the resource utilization of iron-zinc chemical precipitation sludge from electroplating.

[0016] To achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0017] A process for recovering iron and zinc from iron-zinc sludge includes the following steps:

[0018] Step 1: Oxidize and roast the iron-zinc mud for 30-50 minutes, then reduce and roast the oxidized product to obtain product 1;

[0019] Step 2: Grind the product from reduction roasting 1. The ground product is first subjected to a weak magnetic roughing separation, and then to a weak magnetic cleaning separation to obtain iron concentrate and zinc-containing tailings.

[0020] Step 3: The zinc-containing tailings obtained in Step 2 are subjected to reduction roasting 2 using coke as a reducing agent, and distilled at 1100-1200℃ for 20-40 minutes to obtain elemental zinc and roasting residue.

[0021] Furthermore, the zinc mud containing iron in step 1 contains 5% to 15% Zn and 15% to 25% total iron. Zinc exists in the form of Zn(OH)2 and iron exists in the form of Fe(OH)3.

[0022] Furthermore, the oxidative roasting temperature in step 1 is 600–800°C, the time is 30–50 min, the oxygen concentration is 20%, and the total gas flow rate is 600 mL / min.

[0023] Furthermore, the reduction roasting 1 described in step 1 is carried out at a temperature of 500-700°C for 20-50 minutes, using hydrogen or carbon monoxide as the reducing gas with a concentration of 30-60% and a total gas flow rate of 600 mL / min.

[0024] Furthermore, the grinding fineness of the reduction roasting product 1 described in step 2 is -0.025 μm, and the content is 65% to 85%.

[0025] Furthermore, the magnetic field strength for magnetic separation in step 2 is 79.62–131.34 kA / m.

[0026] Preferably, the grinding product described in step 2 undergoes a coarse separation followed by a fine separation.

[0027] Furthermore, the total iron grade of the iron concentrate described in step 2 is greater than 55%.

[0028] Furthermore, in step 3, the ratio of coke to zinc-containing tailings in the reduction roasting 2 is 1.0 to 1.5.

[0029] Furthermore, the elemental zinc recovery rate in step 3 is greater than 90%, and the zinc grade of the roasting slag is less than 0.5%.

[0030] Beneficial effects: This invention is used to treat iron-zinc sludge, providing a new approach to resource recycling in the electroplating zinc industry. The first-stage reduction roasting uses hydrogen, carbon monoxide, or a mixture of both to reduce the iron content in zinc-containing tailings, thereby reducing the amount of carbon used and emissions in the second-stage roasting. The second-stage reduction roasting distillation of zinc is mainly based on the fact that zinc oxide can be reduced to elemental zinc under carbon as a reducing agent, converting heavy metals in the waste into resources, recovering iron while recovering zinc, and reducing the degree of environmental pollution caused by waste emissions. Attached Figure Description

[0031] Figure 1 It is the Gibbs free energy (ΔG) of the reaction of zinc and iron compounds. θ Relationship between ) and temperature (T);

[0032] Figure 2 This is a schematic flow diagram of a process for recovering iron and zinc from iron-zinc sludge according to the present invention.

[0033] Figure 3 This is a process flow diagram of a method for recovering iron and zinc from iron-zinc sludge according to the present invention. Detailed Implementation

[0034] In the description of this invention, it should be noted that unless specific conditions are specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0035] This invention provides a schematic flow diagram of a process for recovering iron and zinc from iron-zinc sludge, as shown in the figure below. Figure 2 As shown in the diagram, the process flow chart is as follows: Figure 3 As shown.

[0036] The roasting furnace used in this invention is a horizontally placed quartz tube roasting furnace, with one end of the quartz tube serving as the air inlet and the other end as the air outlet.

[0037] A process for recovering iron and zinc from iron-zinc sludge includes the following steps:

[0038] Step 1: Drying and sample preparation of iron-zinc mud. Take a quantitative amount of iron-zinc mud sample and place it in a quartz tube for oxidation roasting. After the roasting furnace temperature reaches the preset temperature of 600-800℃, place the quartz tube into the roasting furnace cavity. Introduce a nitrogen-oxygen mixed gas (nitrogen or other oxidizing or neutral gas) into one end of the quartz tube. The oxygen concentration is 20% and the total gas flow rate is 600mL / min. Keep the temperature for the preset time of 30-50min and then stop introducing oxygen.

[0039] After the oxidation roasting is completed, nitrogen gas is continued to be introduced to purge the oxygen in the quartz tube. When the temperature of the roasting furnace reaches the preset temperature of 500-700℃, hydrogen or carbon monoxide is introduced from the gas inlet end of the quartz tube at a concentration of 30-60% and a total gas flow rate of 600mL / min. The oxidized roasted product is then subjected to reduction roasting 1. After holding at the preset time of 20-50min, the introduction of hydrogen or carbon monoxide is stopped. The quartz tube is removed and nitrogen gas is continued to be introduced until the sample temperature is cooled to room temperature. The roasted sample formed by reduction roasting 1 is then removed.

[0040] Step 2: The roasted sample obtained in Step 1 is ground to a fineness of -0.025mm and a content of 65% to 85% using a three-roll four-cylinder rod mill. The ground product is then subjected to a weak magnetic roughing separation under a magnetic field strength of 79.62 to 131.34 kA / m, followed by a weak magnetic cleaning separation to obtain iron concentrate and zinc-bearing tailings.

[0041] Step 3: Add the dried zinc-containing tailings to coke and mix well. Place the mixture in a quartz tube for reduction roasting 2. The mass ratio of coke to zinc-containing tailings is 1.0 to 1.5. Place the quartz tube into the roasting furnace cavity and keep it at a temperature of 1100 to 1200°C for 20 to 40 minutes. Then, remove the quartz tube and let it cool naturally to room temperature. First, recover the zinc metal from the gas outlet of the quartz tube, and then remove the roasting slag.

[0042] Example 1

[0043] The iron-zinc sludge is sludge produced by chemical precipitation of quicklime from electroplating industrial wastewater. Iron exists in the form of ferric hydroxide, and zinc exists in the form of zinc hydroxide. The total iron content of the iron-zinc sludge is 24.94%, and the zinc content is 14.92%.

[0044] Step 1: Dry and prepare iron-zinc mud samples. Take a quantitative amount of iron-zinc mud sample and place it in a quartz tube for oxidation roasting. After the roasting furnace temperature reaches the preset temperature of 800℃, place the quartz tube into the roasting furnace cavity. Introduce nitrogen gas at 600mL / min into one end of the quartz tube. After holding for 50 minutes, set the roasting furnace temperature to 600℃. After the roasting furnace temperature reaches the preset temperature, introduce hydrogen gas at 240mL / min and nitrogen gas at 360mL / min into one end of the quartz tube to perform reduction roasting 1 on the sample. After holding for 30 minutes, stop introducing hydrogen gas. Remove the quartz tube and continue to introduce nitrogen gas until the sample temperature cools to room temperature. Take out the roasted sample obtained from reduction roasting 1.

[0045] Step 2: The roasted sample obtained in Step 1 is ground to 85% content in -0.025mm using a three-roller four-cylinder rod mill. Roughing and cleaning are carried out under magnetic field strengths of 131.34kA / m and 87.56kA / m to obtain iron concentrate and zinc-bearing tailings.

[0046] Step 3: After drying and mixing the zinc-containing tailings from the two weak magnetic separation stages, coke with a carbon-to-ore ratio (coke to iron-zinc mud ratio) of 1.5 is added. The ore is then placed in a quartz tube for reduction roasting. The quartz tube is placed inside the roasting furnace cavity and kept at a temperature of 1180℃ for 40 minutes. After this time, the quartz tube is removed and allowed to cool naturally to room temperature. The zinc metal condensed at the outlet of the quartz tube is recovered first, and then the roasting slag is removed.

[0047] The obtained iron concentrate had a total iron grade of 56.86% and a zinc metal recovery rate of 98.82%. The roasted slag had a total iron grade of 11.58% and a zinc grade of 0.38%.

[0048] Example 2

[0049] The method is the same as in Implementation Case 1, the difference being:

[0050] Iron-zinc sludge is sludge obtained by chemical precipitation of quicklime from wastewater from the electroplating zinc industry. Iron exists in the form of ferric hydroxide and zinc exists in the form of zinc hydroxide. The total iron content of the iron-zinc sludge is 23.76% and the zinc content is 9.68%.

[0051] The oxidative calcination temperature was 600℃, the holding time was 30min, and an oxygen-nitrogen mixture with a 20% oxygen concentration was introduced into one end of the quartz tube, with a total gas flow rate of 600mL / min.

[0052] The reduction roasting 1 was carried out at a roasting temperature of 700℃ for 50 min, with carbon monoxide at a flow rate of 360 mL / min and nitrogen at a flow rate of 240 mL / min introduced into one end of the quartz tube.

[0053] The product obtained by reduction roasting 1 has a grinding fineness of -0.025mm and a content of 65%. The magnetic field strength of the grinding product for weak magnetic roughing is 119.42kA / m, and the magnetic field strength of the weak magnetic cleaning is 79.62kA / m.

[0054] The reduction roasting 2 produced coke at a roasting temperature of 1200℃, a holding time of 20 min, and a carbon-to-ore ratio of 1.1.

[0055] The obtained iron concentrate had a total iron grade of 55.08% and a zinc metal recovery rate of 95.33%. The roasted slag had a total iron grade of 13.66% and a zinc grade of 0.16%.

[0056] Example 3

[0057] The method is the same as in Implementation Case 1, the difference being:

[0058] Iron-zinc sludge is sludge obtained by chemical precipitation of quicklime from wastewater from the electroplating zinc industry. Iron exists in the form of ferric hydroxide and zinc exists in the form of zinc hydroxide. The total iron content of the iron-zinc sludge is 20.59% and the zinc content is 7.42%.

[0059] The oxidative calcination temperature was 700℃, the holding time was 40min, and an oxygen-nitrogen mixed gas with an oxygen concentration of 20% was introduced into one end of the quartz tube, with a total gas flow rate of 600mL / min.

[0060] The reduction roasting 1 was carried out at a roasting temperature of 500℃ for 40 min, with carbon monoxide at a flow rate of 360 mL / min and nitrogen at a flow rate of 240 mL / min introduced into one end of the quartz tube.

[0061] The product obtained by reduction roasting 1 has a grinding fineness of -0.025mm and a content of 75%. The magnetic field strength of the weak magnetic roughing is 103.51kA / m, and the magnetic field strength of the weak magnetic cleaning is 79.62kA / m.

[0062] The reduction roasting 2 produced coke with a roasting temperature of 1100℃, a holding time of 30 min, and a carbon-to-ore ratio of 1.3.

[0063] The obtained iron concentrate had a total iron grade of 56.23% and a zinc metal recovery rate of 97.38%. The roasted slag had a total iron grade of 9.79% and a zinc grade of 0.28%.

[0064] Example 4

[0065] The method is the same as in Implementation Case 1, the difference being:

[0066] Iron-zinc sludge is sludge obtained by chemical precipitation of quicklime from wastewater in the electroplating zinc industry. Iron exists in the form of ferric hydroxide and zinc exists in the form of zinc hydroxide. The total iron content of the iron-zinc sludge is 22.89% and the zinc content is 10.77%.

[0067] The oxidative calcination temperature was 750℃, the holding time was 30min, and an oxygen-nitrogen mixture with a 20% oxygen concentration was introduced into one end of the quartz tube, with a total gas flow rate of 600mL / min.

[0068] The reduction roasting 1 was carried out at a roasting temperature of 650℃ for 30 min, with carbon monoxide at a flow rate of 240 mL / min and nitrogen at a flow rate of 360 mL / min introduced into one end of the quartz tube.

[0069] The product obtained by reduction roasting 1 has a grinding fineness of -0.025mm and a content of 85%. The magnetic field strength of the weak magnetic roughing is 131.34kA / m, and the magnetic field strength of the weak magnetic cleaning is 87.56kA / m.

[0070] The reduction roasting 2 produced coke at a roasting temperature of 1100℃, a holding time of 40 min, and a carbon-to-ore ratio of 1.5.

[0071] The obtained iron concentrate had a total iron grade of 57.93% and a zinc metal recovery rate of 96.66%. The roasted slag had a total iron grade of 8.53% and a zinc grade of 0.33%.

Claims

1. A process for recovering iron and zinc from iron-zinc sludge, characterized in that, Includes the following steps: Step 1: Oxidize and roast the iron-zinc mud for 30-50 minutes, then reduce and roast the oxidized product to obtain product 1. Step 2: Grind the product from reduction roasting 1. The ground product is first subjected to a weak magnetic roughing separation, and then to a weak magnetic cleaning separation to obtain iron concentrate and zinc-containing tailings. Step 3: The zinc-containing tailings obtained in Step 2 are subjected to reduction roasting 2 using coke as a reducing agent, and distilled at 1100~1200℃ for 20~40 min to obtain elemental zinc and roasting residue; The zinc mud containing iron in step 1 contains 5% to 15% Zn and 15% to 25% total iron. Zinc exists in the form of Zn(OH)2 and iron exists in the form of Fe(OH)3. The oxidation roasting temperature in step 1 is 600~800℃, the time is 30~50min, the oxygen concentration is 20%, and the total gas volume is 600mL / min; The reduction roasting 1 described in step 1 is carried out at a temperature of 500~700℃ for 20~50min, using hydrogen or carbon monoxide as the reducing gas with a concentration of 30~60% and a total gas flow rate of 600mL / min.

2. The process for recovering iron and zinc from iron-zinc sludge as described in claim 1, characterized in that, The grinding fineness of the product from the reduction roasting step 2 is -0.025 μm, and the content is 65%~85%.

3. The process for recovering iron and zinc from iron-zinc sludge as described in claim 1, characterized in that, The magnetic field strength for magnetic separation in step 2 is 79.62~131.34 kA / m.

4. The process for recovering iron and zinc from iron-zinc sludge as described in claim 1, characterized in that, The grinding product described in step 2 undergoes a coarse separation followed by a fine separation.

5. The process for recovering iron and zinc from iron-zinc sludge as described in claim 1, characterized in that, The iron concentrate described in step 2 has a total iron content greater than 55%.

6. The process for recovering iron and zinc from iron-zinc sludge as described in claim 1, characterized in that, In step 3, the reduction roasting 2, the ratio of coke to zinc-containing tailings is 1.0 to 1.

5.

7. The process for recovering iron and zinc from iron-zinc sludge as described in claim 1, characterized in that, The elemental zinc recovery rate in step 3 is greater than 90%, and the zinc grade in the roasting slag is less than 0.5%.

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