Method for preparing battery-grade iron phosphate from zinc-containing dust

Abstract

The invention discloses a method for preparing battery-grade iron phosphate by using zinc-containing dust, which comprises the following steps: carrying out acid leaching treatment on the zinc-containing dust by using a mixed acid solution of sulfuric acid and phosphoric acid, and then carrying out solid-liquid separation to obtain a leaching solution and leaching residues; adjusting the pH value of the leachate to 1.2-1.8, then carrying out precipitation reaction, aging, and carrying out solid-liquid separation to obtain a zinc-containing solution and crude iron phosphate; and removing impurities from the crude iron phosphate, and calcining to obtain the battery-grade iron phosphate. The mixed acid solution of sulfuric acid and phosphoric acid is adopted to perform acid leaching treatment on the zinc-containing dust, so that selective separation of zinc and lead can be effectively realized; by adjusting the pH value of the leachate, iron can be separated out from the leachate in the form of crude iron phosphate. According to the method, the crude iron phosphate is subjected to impurity removal and calcination, so that the battery-grade iron phosphate with high additional value can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial solid waste resource utilization, and particularly to a method for preparing battery-grade iron phosphate using zinc-containing dust. Background Art

[0002] A large amount of solid waste is generated during the steel production process, posing challenges to resource utilization and environmental protection. Zinc-containing dust is one of the typical solid wastes in steel production, mainly including gas ash, converter OG sludge, electric arc furnace dust, etc., with a huge production volume. Zinc-containing dust contains various valuable elements, such as 15% - 60% zinc, 10% - 30% iron, and heavy metals such as lead, chromium, and manganese. Due to the complex occurrence forms of zinc and iron, it is difficult to achieve efficient separation by conventional methods. Currently, the treatment of zinc-containing dust mainly relies on stacking, which not only causes waste of valuable resources such as zinc and iron but also seriously pollutes the soil and water bodies. Developing an efficient and environmentally friendly zinc-containing dust recovery process not only helps improve resource utilization efficiency but also reduces environmental pollution.

[0003] Currently, the recovery of zinc-containing dust mainly includes pyrometallurgical processes and hydrometallurgical processes. Among them, the pyrometallurgical process utilizes the characteristics of zinc having a relatively low boiling point (907°C) and being easily volatilized at high temperatures. Through high-temperature reduction smelting, the zinc in the dust is volatilized and enriched for recovery, but it has disadvantages such as high energy consumption, large pollution, and high investment. The hydrometallurgical process transfers zinc and iron into the leaching solution in ionic form through acid leaching, and then removes iron by precipitation. The hydrometallurgical process has significant energy consumption advantages compared to the pyrometallurgical process, with its energy consumption being only about 30% of that of the pyrometallurgical process, and the equipment is simple and the investment cost is low. However, conventional leaching and iron precipitation technologies often cause varying degrees of waste of resources such as zinc and iron. There is still entrainment loss of zinc in the iron precipitation slag and the utilization value of this iron precipitation slag is low.

[0004] Therefore, there is an urgent need to provide a new method for recovering zinc-containing dust to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies and propose a method for preparing battery-grade iron phosphate using zinc-containing dust, so as to solve the technical problems of difficult zinc-iron separation, easy resource waste, and low added value of iron precipitation slag in the existing wet recovery process of zinc-containing dust.

[0006] The present invention provides a method for preparing battery-grade iron phosphate using zinc-containing dust, comprising the following steps: Performing acid leaching treatment on the zinc-containing dust with a mixed acid solution of sulfuric acid and phosphoric acid, and then obtaining a leaching solution and a leaching residue through solid-liquid separation; Adjusting the pH of the leaching solution to 1.2 - 1.8, then performing a precipitation reaction, and then obtaining a zinc-containing solution and crude iron phosphate through aging and solid-liquid separation; Impurities are removed from and the crude iron phosphate is calcined to obtain battery-grade iron phosphate.

[0007] Compared with the prior art, the beneficial effects of the present invention include: The present invention uses a mixed acid solution of sulfuric acid and phosphoric acid to leach zinc-containing dust, which can effectively achieve the selective separation of zinc and lead; by adjusting the pH value of the leachate, iron can be precipitated from the leachate in the form of crude iron phosphate. This iron removal method can efficiently remove more than 96% of the iron in the leachate, and the zinc recovery rate can reach more than 97%, and the yield of crude iron phosphate can reach more than 75%. By removing impurities from and calcining the crude iron phosphate, the present invention can obtain battery-grade iron phosphate with high added value. Compared with the existing process, the present invention can reduce energy consumption compared with the pyrometallurgical recovery process, greatly improve the resource utilization rate and product added value of the traditional hydrometallurgical recovery, and has important practical significance for the comprehensive recovery and utilization of zinc-containing dust. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a process flow chart of an embodiment of the method for preparing battery-grade iron phosphate using zinc-containing dust provided by the present invention; Figure 2 is an XRD pattern of the battery-grade iron phosphate prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0009] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0010] The reaction temperature of the pyrometallurgical process for zinc-containing dust is high, and at the same time, a large amount of carbonaceous reducing agent needs to be consumed and a large amount of carbon dioxide emissions will be caused. The hydrometallurgical process is a recovery technology for leaching zinc-containing dust with high-concentration acid. Since part of the zinc in the zinc-containing dust is present in the phases of spinel structures such as zinc ferrite, the conventional sulfuric acid leaching cannot destroy its structure, resulting in the loss of zinc resources. Existing processes often strengthen the leaching effect by heating under pressure or adding a reducing agent, which will lead to the co-leaching of Zn and Fe. In order to achieve the recovery of zinc, an iron removal step needs to be added subsequently. The existing iron precipitation processes mainly include the jarosite process, the goethite process and the hematite process. Among them, the iron vitriol slag and goethite slag produced by the jarosite process and the goethite process will entrain metal elements such as zinc and lead, and are all hazardous wastes, resulting in resource losses and being difficult to further dispose of. The hematite process is complex, and the hematite slag produced belongs to general solid waste with low utilization value.

[0011] Please refer to Figure 1 , the present invention provides a method for preparing battery-grade iron phosphate using zinc-containing dust, including the following steps: S1. Acid-leach the zinc-containing dust with a mixed acid solution of sulfuric acid and phosphoric acid, and then obtain the leachate and leach residue through solid-liquid separation. The main chemical reactions in the leaching step are as follows: ZnO + H2SO4 → ZnSO4 + H2O ZnFe2O4 + 4H2SO4 → ZnSO4 + Fe2(SO4)3 + 4H2O 3ZnFe2O4 + 2H3PO4 → Zn3(PO4)2 + 3Fe2O3 + 3H2O PbO + H2SO4 → PbSO4 + H2O In this step, zinc oxide is dissolved by sulfuric acid, and zinc ions enter the solution; a part of zinc ferrite is dissolved by sulfuric acid, and zinc and iron enter the solution in the form of ions together, and another part is dissolved by phosphoric acid, zinc enters the solution, while iron exists in the form of iron oxide; lead oxide is dissolved by sulfuric acid to form lead sulfate precipitation.

[0012] S2. Adjust the pH of the leachate to 1.2 - 1.8, then carry out a precipitation reaction, and then obtain the zinc-containing solution and crude iron phosphate through aging and solid-liquid separation. The main chemical reactions in the iron precipitation step are as follows: Fe2(SO4)3 + 2H3PO4 → 2FePO4 + 3H2SO4 In this step, ferric sulfate is converted into iron phosphate precipitation to achieve the separation of iron and zinc.

[0013] S3. Remove impurities from the crude iron phosphate and calcine it to obtain battery-grade iron phosphate.

[0014] In this embodiment, the phase composition of the zinc-containing dust is mainly zinc ferrite and zinc oxide. In addition, it may contain phases such as lead oxide and potassium chloride, but the content is relatively low.

[0015] In this embodiment, by mass percentage, the elements of the zinc-containing dust include: zinc 15% - 60%, iron 10% - 30%, calcium 2% - 10%, potassium 0.5% - 10%, silicon 0.5% - 10%, lead 0.1% - 10%, sodium 0% - 5%, magnesium 0% - 5%, chromium 0% - 3%, manganese 0% - 2%.

[0016] In this embodiment, in step S1, in the mixed acid solution, the concentration of sulfuric acid is 2 - 3.5 mol / L, further 2.5 - 3 mol / L; the concentration of phosphoric acid is 0.3 - 0.6 mol / L, further 0.4 - 0.6 mol / L.

[0017] In this embodiment, in step S1, during the acid leaching process, the liquid-solid ratio is 5 - 15 mL / g, further 9 - 10 mL / g.

[0018] In this embodiment, in step S1, the temperature of acid leaching is 50-90°C, further 80-90°C; the time of acid leaching is 30-180 min, further 100-120 min, and the stirring speed is 200-600 r / min.

[0019] In this embodiment, in step S2, the pH of the leaching solution is adjusted to 1.4-1.8.

[0020] In this embodiment, in step S2, ammonia water is used to adjust the pH of the leaching solution.

[0021] In this embodiment, in step S2, the temperature of the precipitation reaction is 40-110°C, further 80-110°C; the time of the precipitation reaction is 30-480 min, further 60-180 min; the stirring speed is 10-800 r / min, further 200-500 r / min.

[0022] In this embodiment, in step S2, the temperature of aging is 25-110°C, further 80-110°C; the time of aging is 10-180 min, further 20-90 min.

[0023] In this embodiment, in step S3, the process of impurity removal includes: Mixing and reacting crude iron phosphate and hydrochloric acid solution, and then obtaining refined iron phosphate through solid-liquid separation and drying.

[0024] Furthermore, the concentration of the hydrochloric acid solution is 0.5-4 mol / L, further 0.5-2 mol / L; the liquid-solid ratio is 1-10 mL / g, further 1-3 mL / g.

[0025] In this embodiment, in step S3, the temperature of the mixing reaction is 140-180°C, further 160-180°C; the time of the mixing reaction is 180-240 min, further 180-200 min. If the temperature is too high, energy consumption will be lost; if the temperature is too low, a better impurity removal effect cannot be guaranteed.

[0026] In this embodiment, in step S3, the drying temperature is 40-80°C, and the drying time is 100-600 min.

[0027] In this embodiment, in step S3, the calcination temperature is 500-800°C, further 700-800°C, and the calcination time is 60-600 min, further 100-120 min.

[0028] To avoid repetition, some of the raw materials or parameters involved in the following examples and comparative examples of the present invention are uniformly described as follows: The raw material is zinc-containing dust taken from a steel plant, and its chemical analysis results are shown in Table 1.

[0029] Table 1 Chemical composition of zinc-containing dust (wt.%)

[0030] Example 1 (1) Mix 10 g of zinc-containing dust with a mixed acid of sulfuric acid concentration of 2.5 mol / L and phosphoric acid concentration of 0.4 mol / L at a liquid-solid ratio of 10 mL / g, and leach at 90 °C for 100 min with a stirring speed of 400 r / min. After the leaching is completed, use a vacuum filtration device for solid-liquid separation to obtain a leachate and a leaching residue. The zinc leaching rate during the leaching process can reach 98.69%, the iron leaching rate reaches 80.07%, while the lead leaching rate is only 0.58%.

[0031] (2) Take 100 mL of the leachate obtained in step (1) and place it in a beaker. Adjust its pH to 1.5 with ammonia water, then stir at 90 °C at a speed of 400 r / min for 120 min, and then age for 30 min. Perform solid-liquid separation to obtain a zinc-containing solution and crude iron phosphate. The iron removal rate during the iron precipitation process is 97.25%, and the zinc loss rate is 0.43%.

[0032] (3) Place the crude iron phosphate obtained in step (2) in a reactor, add a hydrochloric acid solution with a concentration of 1.5 mol / L at a liquid-solid ratio of 2 mL / g, react at 160 °C for 180 min and then perform solid-liquid separation. Dry the separated solid and calcine it at 700 °C for 120 min to obtain battery-grade iron phosphate with an iron-phosphorus ratio of 0.983 and a purity of 99.68%.

[0033] Example 2 (1) Mix 10 g of zinc-containing dust with a mixed acid of sulfuric acid concentration of 3.0 mol / L and phosphoric acid concentration of 0.6 mol / L at a liquid-solid ratio of 10 mL / g, and leach at 90 °C for 100 min with a stirring speed of 400 r / min. After the leaching is completed, use a vacuum filtration device for solid-liquid separation to obtain a leachate and a leaching residue. The zinc leaching rate during the leaching process can reach 99.38%, the iron leaching rate reaches 83.81%, while the lead leaching rate is only 0.66%.

[0034] (2) Take 100 mL of the leachate obtained in step (1) and place it in a beaker. Adjust its pH to 1.5 with ammonia water, then stir at 90 °C at a speed of 400 r / min for 120 min, and then age for 30 min. Perform solid-liquid separation to obtain a zinc-containing solution and crude iron phosphate. The iron removal rate during the iron precipitation process is 96.72%, and the zinc loss rate is 0.83%.

[0035] (3) Place the crude iron phosphate obtained in step (2) in a reactor, add a hydrochloric acid solution with a concentration of 1.5 mol / L according to a liquid-solid ratio of 2 mL / g, react for 180 min at 180 °C, then perform solid-liquid separation. After drying the separated solid, calcine it at 800 °C for 100 min to obtain battery-grade iron phosphate with an iron-to-phosphorus ratio of 0.987 and a purity of 99.59%.

[0036] Example 3 (1) Mix 10 g of zinc-containing dust with a mixed acid with a sulfuric acid concentration of 2.5 mol / L and a phosphoric acid concentration of 0.4 mol / L according to a liquid-solid ratio of 9 mL / g, leach at 90 °C for 120 min with a stirring speed of 400 r / min. After the leaching is completed, use a vacuum filtration device for solid-liquid separation to obtain a leachate and a leach residue. During the leaching process, the zinc leaching rate can reach 98.83%, the iron leaching rate reaches 80.31%, while the lead leaching rate is only 0.60%.

[0037] (2) Take 100 mL of the leachate obtained in step (1) and place it in a beaker. Adjust its pH to 1.5 with ammonia water, then stir at a speed of 400 r / min at 90 °C for 120 min, and then age for 30 min. Perform solid-liquid separation to obtain a zinc-containing solution and crude iron phosphate. During the iron precipitation process, the iron removal rate is 97.48% and the zinc loss rate is 0.73%.

[0038] (3) Place the crude iron phosphate obtained in step (2) in a reactor, add a hydrochloric acid solution with a concentration of 1.5 mol / L according to a liquid-solid ratio of 2 mL / g, react for 180 min at 160 °C, then perform solid-liquid separation. After drying the separated solid, calcine it at 700 °C for 120 min to obtain battery-grade iron phosphate with an iron-to-phosphorus ratio of 0.985 and a purity of 99.63%.

[0039] Example 4 (1) Mix 10 g of zinc-containing dust with a mixed acid with a sulfuric acid concentration of 2.5 mol / L and a phosphoric acid concentration of 0.4 mol / L according to a liquid-solid ratio of 9 mL / g, leach at 90 °C for 100 min with a stirring speed of 400 r / min. After the leaching is completed, use a vacuum filtration device for solid-liquid separation to obtain a leachate and a leach residue. During the leaching process, the zinc leaching rate can reach 98.46%, the iron leaching rate reaches 78.68%, while the lead leaching rate is only 0.54%.

[0040] (2) Take 100 mL of the leachate obtained in step (1) and place it in a beaker. Adjust its pH to 1.6 with ammonia water, then stir at a speed of 400 r / min at 100 °C for 120 min, and then age for 30 min. Perform solid-liquid separation to obtain a zinc-containing solution and crude iron phosphate. During the iron precipitation process, the iron removal rate is 96.52% and the zinc loss rate is 0.81%.

[0041] (3) Place the crude iron phosphate obtained in step (2) in a reactor, add a hydrochloric acid solution with a concentration of 1.5 mol / L at a liquid-solid ratio of 2 mL / g, react at 160 °C for 180 min, then perform solid-liquid separation. After drying the separated solid, calcine it at 700 °C for 120 min to obtain battery-grade iron phosphate with an iron-to-phosphorus ratio of 0.988 and a purity of 99.71%.

[0042] Comparative Example 1 Compared with Example 1, the only difference is that the phosphoric acid concentration in step (1) of Comparative Example 1 is 0.1 mol / L, specifically: (1) Mix 10 g of zinc-containing dust with a mixed acid with a sulfuric acid concentration of 2.5 mol / L and a phosphoric acid concentration of 0.1 mol / L at a liquid-solid ratio of 10 mL / g, and leach at 90 °C for 100 min with a stirring speed of 400 r / min. After the leaching is completed, perform solid-liquid separation using a vacuum filtration device to obtain a leachate and a leached residue. The zinc leaching rate during the leaching process can be 92.28%, the iron leaching rate reaches 58.01%, while the lead leaching rate is only 0.73%.

[0043] (2) Take 100 mL of the leachate obtained in step (1) and place it in a beaker. Adjust its pH to 1.5 with ammonia water, then stir at a speed of 400 r / min at 90 °C for 120 min, and then age for 30 min. Perform solid-liquid separation to obtain a zinc-containing solution and crude iron phosphate. The iron removal rate during the iron precipitation process is 77.25%, and the zinc loss rate is 0.42%.

[0044] (3) Place the crude iron phosphate obtained in step (2) in a reactor, add a hydrochloric acid solution with a concentration of 1.5 mol / L at a liquid-solid ratio of 2 mL / g, react at 160 °C for 180 min, then perform solid-liquid separation. After drying the separated solid, calcine it at 700 °C for 120 min. The obtained product has an iron-to-phosphorus ratio of 1.074 and does not meet the battery-grade iron phosphate standard.

[0045] Comparative Example 2 Compared with Example 1, the only difference is that the phosphoric acid concentration in step (1) of Comparative Example 2 is 0.7 mol / L, specifically: (1) Mix 10 g of zinc-containing dust with a mixed acid with a sulfuric acid concentration of 2.5 mol / L and a phosphoric acid concentration of 0.7 mol / L at a liquid-solid ratio of 10 mL / g, and leach at 90 °C for 100 min with a stirring speed of 400 r / min. After the leaching is completed, perform solid-liquid separation using a vacuum filtration device to obtain a leachate and a leached residue. The zinc leaching rate during the leaching process can be 99.13%, the iron leaching rate reaches 81.38%, while the lead leaching rate is only 0.62%.

[0046] (2) Take 100 mL of the leachate obtained in step (1) and place it in a beaker. After adjusting its pH to 1.5 with ammonia water, stir it at a speed of 400 r / min at 90 °C for 120 min, then age for 30 min, and perform solid-liquid separation to obtain a zinc-containing solution and crude iron phosphate. During the iron precipitation process, the iron removal rate is 99.06%, and the zinc loss rate is 0.92%.

[0047] (3) Place the crude iron phosphate obtained in step (2) in a reactor, add a hydrochloric acid solution with a concentration of 1.5 mol / L according to a liquid-solid ratio of 2 mL / g, react at 160 °C for 180 min, then perform solid-liquid separation. After drying the separated solid, calcine it at 700 °C for 120 min. The obtained product has an iron-to-phosphorus ratio of 0.952, which does not meet the battery-grade iron phosphate standard.

[0048] Comparative Example 3 Compared with Example 1, the only difference is that the sulfuric acid concentration in step (1) of Comparative Example 3 is 0.5 mol / L, specifically: (1) Mix 10 g of zinc-containing dust with a mixed acid with a sulfuric acid concentration of 0.5 mol / L and a phosphoric acid concentration of 0.4 mol / L according to a liquid-solid ratio of 10 mL / g, and leach at 90 °C for 100 min with a stirring speed of 400 r / min. After the leaching is completed, perform solid-liquid separation using a vacuum filtration device to obtain a leachate and leach residue. During the leaching process, the zinc leaching rate can reach 35.24%, the iron leaching rate is only 0.73%, and the lead leaching rate is 0.11%.

[0049] (2) Take 100 mL of the leachate obtained in step (1) and place it in a beaker. After adjusting its pH to 1.5 with ammonia water, stir it at a speed of 400 r / min at 90 °C for 120 min, then age for 30 min, and perform solid-liquid separation to obtain a zinc-containing solution and crude iron phosphate. During the iron precipitation process, the iron removal rate is 99.41%, and the zinc loss rate is 0.23%.

[0050] (3) Place the crude iron phosphate obtained in step (2) in a reactor, add a hydrochloric acid solution with a concentration of 1.5 mol / L according to a liquid-solid ratio of 2 mL / g, react at 160 °C for 180 min, then perform solid-liquid separation. After drying the separated solid, calcine it at 700 °C for 120 min. The obtained product has an iron-to-phosphorus ratio of 0.737, which does not meet the battery-grade iron phosphate standard, and the purity is 77.56%.

[0051] Comparative Example 4 Compared with Example 1, the only difference is that the sulfuric acid concentration in step (1) of Comparative Example 4 is 5 mol / L, specifically: (1) Mix 10 g of zinc-containing dust with a mixed acid with a sulfuric acid concentration of 5 mol / L and a phosphoric acid concentration of 0.4 mol / L at a liquid-solid ratio of 10 mL / g, and leach at 90 °C for 100 min with a stirring speed of 400 r / min. After the leaching is completed, use a vacuum filtration device for solid-liquid separation to obtain a leachate and leaching residue. The zinc leaching rate can reach 99.71% during the leaching process, the iron leaching rate reaches 97.26%, while the lead leaching rate is 16.22%.

[0052] (2) Take 100 mL of the leachate obtained in step (1) and place it in a beaker. After adjusting its pH to 1.5 with ammonia water, stir at a speed of 400 r / min at 90 °C for 120 min, and then age for 30 min. After solid-liquid separation, a zinc-containing solution and crude iron phosphate are obtained. The iron removal rate during the iron precipitation process is 84.37%, and the zinc loss rate is 0.96%.

[0053] (3) Place the crude iron phosphate obtained in step (2) in a reactor, add a hydrochloric acid solution with a concentration of 1.5 mol / L at a liquid-solid ratio of 2 mL / g, react at 160 °C for 180 min and then perform solid-liquid separation. After drying the separated solid, calcine it at 700 °C for 120 min to obtain battery-grade iron phosphate with an iron-to-phosphorus ratio of 0.991 and a purity of 98.89%.

[0054] Comparative Example 5 Compared with Example 1, the only difference is that: in step (2) of Comparative Example 5, the pH is adjusted to 1.0, specifically: (2) Take 100 mL of the leachate obtained in step (1) of Example 1 and place it in a beaker. After adjusting its pH to 1.0 with ammonia water, stir at a speed of 400 r / min at 90 °C for 120 min, and then age for 30 min. After solid-liquid separation, a zinc-containing solution and crude iron phosphate are obtained. The iron removal rate during the iron precipitation process is 63.17%, and the zinc loss rate is 0.47%.

[0055] (3) Place the crude iron phosphate obtained in step (2) in a reactor, add a hydrochloric acid solution with a concentration of 1.5 mol / L at a liquid-solid ratio of 2 mL / g, react at 160 °C for 180 min and then perform solid-liquid separation. After drying the separated solid, calcine it at 700 °C for 120 min to obtain battery-grade iron phosphate with an iron-to-phosphorus ratio of 0.984 and a purity of 99.70%.

[0056] Comparative Example 6 Compared with Example 1, the only difference is that: in step (2) of Comparative Example 6, the pH is adjusted to 2.0, specifically: (2) Take 100 mL of the leachate obtained in step (1) of Example 1 and place it in a beaker. After adjusting its pH to 2.0 with ammonia water, stir it at a speed of 400 r / min at 90 °C for 120 min, then age for 30 min, and perform solid-liquid separation to obtain a zinc-containing solution and crude iron phosphate. The iron removal rate during the iron precipitation process is 99.45%, and the zinc loss rate is 12.19%.

[0057] (3) Place the crude iron phosphate obtained in step (2) in a reactor, add a hydrochloric acid solution with a concentration of 1.5 mol / L according to a liquid-solid ratio of 2 mL / g, react at 160 °C for 180 min, then perform solid-liquid separation. After drying the separated solid, calcine it at 700 °C for 120 min to obtain battery-grade iron phosphate with an iron-to-phosphorus ratio of 0.964 and a purity of 99.54%.

[0058] Comparative Example 7 Compared with Example 1, the only difference is that: in step (3) of Comparative Example 7, the reaction temperature is 120 °C. Specifically: (3) Place the crude iron phosphate obtained in step (2) of Example 1 in a reactor, add a hydrochloric acid solution with a concentration of 1.5 mol / L according to a liquid-solid ratio of 2 mL / g, react at 120 °C for 180 min, then perform solid-liquid separation. After drying the separated solid, calcine it at 700 °C for 120 min. The obtained product has an iron-to-phosphorus ratio of 0.953, does not meet the battery-grade iron phosphate standard, and has a purity of 94.68%.

[0059] Comparative Example 8 Compared with Example 1, the only difference is that: in step (3) of Comparative Example 8, the reaction temperature is 200 °C. Specifically: (3) Place the crude iron phosphate obtained in step (2) of Example 1 in a reactor, add a hydrochloric acid solution with a concentration of 1.5 mol / L according to a liquid-solid ratio of 2 mL / g, react at 200 °C for 180 min, then perform solid-liquid separation. After drying the separated solid, calcine it at 700 °C for 120 min to obtain battery-grade iron phosphate with an iron-to-phosphorus ratio of 0.989 and a purity of 99.39%.

[0060] Comparative Example 9 Compared with Example 1, the only difference is that: in step (1) of Comparative Example 9, 3 mol / L sulfuric acid is used for leaching, and in step (2), the jarosite process is used for iron removal. Specifically: (1) Mix 10 g of zinc-containing dust with sulfuric acid with a concentration of 3 mol / L according to a liquid-solid ratio of 10 mL / g, and leach at 90 °C for 100 min with a stirring speed of 400 r / min. After the leaching is completed, use a vacuum filtration device for solid-liquid separation to obtain a leachate and a leaching residue. The zinc leaching rate during the leaching process reaches 92.44%, the iron leaching rate reaches 69.58%, and the lead leaching rate is 0.64%.

[0061] (2) Take 100 mL of the leaching solution obtained in step (1) and place it in a beaker. After adjusting its pH to 1.9 with potassium hydroxide, add potassium sulfate to the solution according to a dosing coefficient of 1.5, and add jarosite seeds to the solution, with an addition amount of 10 g / L. Stir at a speed of 400 r / min at 90 °C for 120 min. During the stirring process, gradually add dilute sulfuric acid to adjust the pH value of the solution so that the pH value at the end of the reaction is about 3.0. After the reaction ends, perform solid-liquid separation to obtain a zinc-containing solution and jarosite slag. During this process, the iron removal rate is 92.45%, and the zinc loss rate is 6.11%.

[0062] Comparative Example 10 Compared with Example 1, the only difference is that in step (1) of Comparative Example 10, sulfuric acid leaching at 2.5 mol / L is used, and in step (2), the jarosite method is used for iron removal, specifically: (1) Mix 10 g of zinc-containing dust with a mixed acid of sulfuric acid at a concentration of 2.5 mol / L according to a liquid-solid ratio of 10 mL / g, and leach at 90 °C for 100 min, with a stirring speed of 400 r / min. After the leaching ends, perform solid-liquid separation using a vacuum filtration device to obtain a leaching solution and leaching slag. During the leaching process, the zinc leaching rate reaches 91.68%, the iron leaching rate reaches 61.37%, and the lead leaching rate is 0.85%.

[0063] (2) Take 100 mL of the leaching solution obtained in step (1) and place it in a beaker. After adjusting its pH to 1.85 with potassium hydroxide, add potassium sulfate to the solution according to a dosing coefficient of 1.5, and add jarosite seeds to the solution, with an addition amount of 10 g / L. Stir at a speed of 300 r / min at 95 °C for 120 min. During the stirring process, gradually add dilute sulfuric acid to adjust the pH value of the solution so that the pH value at the end of the reaction is about 2.5. After the reaction ends, perform solid-liquid separation to obtain a zinc-containing solution and jarosite slag. During this process, the iron removal rate is 90.52%, and the zinc loss rate is 7.07%.

[0064] In the present invention, the calculation formulas for the above-mentioned leaching rate, iron removal rate, zinc loss rate, zinc recovery rate, crude ferric phosphate yield, ferric phosphate purity, and iron-phosphorus ratio are as follows: Leaching rate E 浸出 =

[0065] Iron removal rate E 除铁 =

[0066] Zinc loss rate E 锌损失 =

[0067] Zinc recovery rate E 锌回收 = E 浸出(Zn) ×(1 - E 锌损失 ) Yield of crude iron phosphate E 粗制磷酸铁 = E 浸出 × E 除铁 Purity of iron phosphate P =

[0068] In the formula, is the concentration of Zn, Fe or Pb in the leaching solution, g / L; is the volume of the leaching solution, L; is the mass of the leached material, g; is the mass fraction of Zn, Fe or Pb in the raw material, %; and are the concentrations of Fe and Zn in the solution after iron precipitation, g / L; is the volume of the solution after iron precipitation, L; and are the concentrations of Fe and Zn in the solution before iron precipitation, g / L; is the volume of the solution before iron precipitation, L; is the iron content in battery-grade iron phosphate, %.

[0069] The iron-to-phosphorus ratio is the molar ratio of iron and phosphorus elements in iron phosphate.

[0070] The process effects of Examples 1 - 4 and Comparative Examples 1 - 10 are shown in Table 2.

[0071] Table 2

[0072] Please refer to Table 1. It can be seen from the results of Examples 1 - 4 that the present invention uses a mixed acid solution of sulfuric acid and phosphoric acid to acid-leach zinc-containing dust, which can effectively achieve the selective separation of zinc and lead; by adjusting the pH of the leaching solution to 1.2 - 1.8, iron can be precipitated in the form of crude iron phosphate. This iron removal method can efficiently remove more than 96% of the iron in the leaching solution, and the zinc recovery rate can reach more than 97%. After impurity removal and calcination of the crude iron phosphate, high-value-added battery-grade iron phosphate ( Figure 2 ) can be obtained. The battery-grade iron phosphate prepared by the present invention meets the requirements of the chemical industry standard HG / T4701 - 2021 "Iron Phosphate for Batteries" and can be used to manufacture the cathode material of lithium iron phosphate (LiFePO4) batteries.

[0073] It can be seen from Example 1 and Comparative Examples 1-2 that the concentration of phosphoric acid in the mixed acid solution has a significant impact on the technical effect of the present invention. Too low a concentration of phosphoric acid will not only reduce the leaching rate of zinc, but also decrease the precipitation rate of iron, and the iron-precipitated slag cannot be converted into battery-grade iron phosphate through subsequent impurity removal and calcination. Too high a concentration of phosphoric acid will result in too low an iron-to-phosphorus ratio of the iron phosphate obtained after impurity removal and calcination, and the product does not meet the battery-grade iron phosphate index.

[0074] It can be seen from Example 1 and Comparative Examples 3-4 that the concentration of sulfuric acid in the mixed acid solution has a significant impact on the technical effect of the present invention. Too low a concentration of sulfuric acid will significantly reduce the leaching rates of zinc and iron during the leaching process; while too high a concentration of sulfuric acid will cause the leaching of lead, consume a large amount of alkali liquor during the pH adjustment process, and lead to a decrease in the iron removal rate.

[0075] It can be seen from Example 1 and Comparative Examples 5-6 that the iron precipitation pH has a significant impact on the technical effect of the present invention. Too low an iron precipitation pH will significantly reduce the yield of iron phosphate, while too high an iron precipitation pH will cause zinc loss.

[0076] It can be seen from Example 1 and Comparative Examples 7-8 that the purification temperature of the crude iron phosphate has a great impact on the technical effect of the present invention. Too low a purification temperature will reduce the product purity, while too high a purification temperature will increase the reaction energy consumption and cause unnecessary waste.

[0077] It can be seen from Example 1 and Comparative Examples 9-10 that the traditional acid leaching and iron removal processes will significantly cause the loss of zinc resources, and the generated iron-precipitated slag is difficult to further process. Compared with the traditional process, the present invention can effectively reduce the energy consumption, simplify the iron removal operation process, and greatly improve the resource utilization rate and product added value, which has important practical significance for the comprehensive recycling of zinc-containing dust.

[0078] The specific embodiments of the present invention described above do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing battery-grade iron phosphate using zinc-containing dust, characterized in that, It includes the following steps: The zinc-containing dust is subjected to acid leaching treatment with a mixed acid solution of sulfuric acid and phosphoric acid, and then the leaching solution and the leaching residue are obtained through solid-liquid separation; The pH of the leaching solution is adjusted to 1.2 - 1.8, then a precipitation reaction is carried out, and after aging and solid-liquid separation, a zinc-containing solution and crude iron phosphate are obtained; The crude iron phosphate is purified and calcined to obtain battery-grade iron phosphate.

2. The method for preparing battery-grade iron phosphate using zinc-containing dust according to claim 1, characterized in that, By mass percentage, the elements of the zinc-containing dust include: zinc 15% - 60%, iron 10% - 30%, calcium 2% - 10%, potassium 0.5% - 10%, silicon 0.5% - 10%, lead 0.1% - 10%, sodium 0% - 5%, magnesium 0% - 5%, chromium 0% - 3%, manganese 0% - 2%.

3. The method for preparing battery-grade iron phosphate using zinc-containing dust according to claim 1, wherein In the mixed acid solution, the concentration of sulfuric acid is 2 - 3.5 mol / L, and the concentration of phosphoric acid is 0.3 - 0.6 mol / L; and / or, During the acid leaching process, the liquid-solid ratio is 5 - 15 mL / g; and / or, The temperature of the acid leaching is 50 - 90 °C, the time of the acid leaching is 30 - 180 min, and the stirring speed is 200 - 600 r / min.

4. The method for preparing battery-grade iron phosphate using zinc-containing dust according to claim 1, characterized in that, In the mixed acid solution, the concentration of sulfuric acid is 2.5 - 3 mol / L, and the concentration of phosphoric acid is 0.4 - 0.6 mol / L; and / or, During the acid leaching process, the liquid-solid ratio is 9 - 10 mL / g; and / or, The temperature of the acid leaching is 80 - 90 °C, the time of the acid leaching is 100 - 120 min.

5. The method for preparing battery-grade iron phosphate using zinc-containing dust according to claim 1, characterized in that, The pH of the leaching solution is adjusted to 1.4 - 1.

8.

6. The method for preparing battery-grade iron phosphate using zinc-containing dust according to claim 1, wherein, The temperature of the precipitation reaction is 40 - 110 °C, the time of the precipitation reaction is 30 - 480 min, and the stirring speed is 10 - 800 r / min; and / or, The temperature of the aging is 25 - 110 °C, the time of the aging is 10 - 180 min.

7. The method for preparing battery-grade iron phosphate using zinc-containing dust according to claim 1, characterized in that, The temperature of the precipitation reaction is 80 - 110 °C, the time of the precipitation reaction is 60 - 180 min, and the stirring speed is 200 - 500 r / min; and / or, The temperature of the aging is 80 - 110 °C, the time of the aging is 20 - 90 min.

8. The method for preparing battery-grade iron phosphate using zinc-containing dust according to claim 1, characterized in that, The purification process includes: The crude iron phosphate and the hydrochloric acid solution are mixed and reacted, and then after solid-liquid separation and drying, refined iron phosphate is obtained; wherein, The concentration of the hydrochloric acid solution is 0.5 - 4 mol / L; and / or, The liquid-solid ratio is 1 - 10 mL / g; and / or, The temperature of the mixed reaction is 140 - 180 °C, the time of the mixed reaction is 180 - 240 min.

9. The method for preparing battery-grade iron phosphate using zinc-containing dust according to claim 1, wherein The purification process includes: The crude iron phosphate and the hydrochloric acid solution are mixed and reacted, and then after solid-liquid separation and drying, refined iron phosphate is obtained; wherein, The concentration of the hydrochloric acid solution is 0.5 - 2 mol / L; and / or, The liquid-solid ratio is 1 - 3 mL / g; and / or, The temperature of the mixed reaction is 160 - 180 °C, the time of the mixed reaction is 180 - 200 min.

10. The method for preparing battery-grade iron phosphate using zinc-containing dust according to claim 1, wherein The temperature of the calcination is 500 - 800 °C, the time of the calcination is 60 - 600 min.

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