Treatment method of ferrophosphorus waste

Abstract

The invention relates to a method for treating ferrophosphorus waste, which comprises the following steps: carrying out alkaline leaching on the ferrophosphorus waste to be treated, and carrying out solid-liquid separation to obtain a leaching solution and leaching residues; after the pH value of the leachate is adjusted to 6.5-8.0, standing is conducted, solid-liquid separation is conducted, and a solution A rich in phosphate radicals and a slag phase A are obtained; after the leaching residues react with inorganic acid, solid-liquid separation is conducted, and a solution B and a residue phase B are obtained; mixing the solution A and the solution B, and after the reaction is finished, carrying out solid-liquid separation to obtain iron phosphate dihydrate and residual liquid; and subsequently purifying and dehydrating the iron phosphate dihydrate to obtain a high-purity iron phosphate product. According to the method, through comprehensive impurity removal under common conditions of acid, alkali, neutrality and the like, effective removal of various impurity elements is finally achieved, a pure iron source and a pure phosphorus source can be stably obtained, then the iron phosphate dihydrate or iron phosphate product with uniform and stable properties is prepared, the process is simple and efficient, the applicability to raw materials is wide, and the method has good industrial application prospects.

Description

Technical Field

[0001] The invention relates to a method for treating ferrophosphorus waste, in particular to a method for preparing ferric phosphate by using ferrophosphorus waste, and belongs to the field of resource treatment of ferrophosphorus waste. Background Art

[0002] Lithium iron phosphate positive electrode materials have become the first choice for manufacturing lithium-ion batteries due to their ultra-long life, fast charging and discharging, high temperature resistance, large capacity, no memory, and safe use. With the rapid development of new energy vehicles, a wave of scrapped lithium iron phosphate battery materials has also come. At the same time, the rising price of lithium has led to the recycling of lithium-containing materials becoming popular. At present, the industry almost selectively recovers high-value lithium from lithium iron phosphate waste to obtain high-value-added lithium salt products. After lithium extraction, the impure iron phosphate has high impurity content, complex composition, difficult processing, and high recycling cost. The iron phosphate slag after lithium extraction from waste lithium iron phosphate batteries is mostly disposed of in the form of stockpiling, becoming solid waste that harms the environment, and the valuable phosphorus and iron resources therein cannot be fully recycled.

[0003] Although the prior art has carried out relevant research on the process and method for recovering waste iron phosphate residue, for example, Chinese invention patent application CN116581415A discloses a method for the combined recovery of waste phosphorus iron residue and waste lithium cobalt oxide produced by selective lithium extraction from waste lithium iron phosphate, which obtains phosphoric acid and sodium sulfate decahydrate by alkali leaching - leachate exchange resin purification - evaporation crystallization - concentrated sulfuric acid re-dissolution - low-temperature freezing - cold filtration, and the phosphorus extraction residue is supplemented with carbon powder for reduction calcination, and iron powder is obtained after magnetic separation, and ferrous sulfate is obtained by acid dissolution, which is mixed with waste lithium cobalt oxide powder and then oxidized and calcined by water leaching to obtain lithium sulfate, cobalt sulfate and ferric hydroxide, and lithium sulfate is converted into lithium hydroxide by alkali conversion, and then carbonation is performed to obtain lithium carbonate. The process steps are not only cumbersome, but also require high-input and high-equipment requirements such as ion exchange, crystallization re-dissolution, low-temperature freezing, and high-temperature roasting. The efficiency of the process is seriously dependent on the recovery of lithium in lithium cobalt oxide waste, and the phosphoric acid and iron powder produced by phosphorus extraction and iron extraction from waste phosphorus iron residue are poor in economic benefits. For another example, Chinese invention patent application CN115159490A discloses a method for recycling iron phosphate slag, which adopts acidolysis-acid leaching liquid reduction-chemical precipitation under protective atmosphere to remove aluminum-chemical precipitation under protective atmosphere to prepare ammonium ferrous phosphate. Although the process steps are simple, both impurity removal and precipitation need to be carried out under a protective atmosphere, the equipment requirements are high, the operation and control are difficult, and it is difficult to implement on a large scale industrially.

[0004] Furthermore, the solid iron phosphate waste after lithium extraction has a high and complex impurity content due to different lithium extraction processes and sources. The existing production process cannot achieve efficient and selective extraction of iron and phosphorus. For example, the method for recovering iron phosphate waste involved in Chinese invention patent application CN112320780A can regenerate battery-grade iron phosphate from iron phosphate waste by simple acid leaching-oxidation-alkali adjustment-washing, but it can only process iron phosphate waste slag with a single component and low impurity content, and cannot process iron phosphate waste with relatively complex impurity content and types; for another example, although Chinese invention patent application CN116534823A discloses a method for regenerating battery-grade iron phosphate from iron phosphate slag and battery-grade iron phosphate, the patent does not explain the core impurity removal means and steps of crude iron phosphate, and only proposes to precipitate and prepare iron phosphate products by hydrothermal evaporation of purified slag acid leaching liquid, which is also unable to process iron phosphate waste with relatively complex impurity content and types.

[0005] In addition, the value of the process output products also determines the feasibility of industrialization. Chinese invention patent application CN116692820A discloses a method for preparing graphite powder and ferrous manganese phosphate using ferrous phosphate waste residue. The method uses only nitric acid leaching to remove Al and Cu impurities, but the method cannot avoid the loss of Fe and P elements during implementation, and the Al content in the ferrous phosphate material after impurity removal still cannot reach the battery-grade standard level. The ferrous manganese phosphate material finally prepared is only of industrial grade purity, and the graphite powder is only recovered as an insoluble byproduct with a high impurity content. Although the process is short, the economic added value of the output product is relatively low, and the use of nitric acid puts higher requirements on equipment and environmental protection.

[0006] In summary, there is currently no mature industrial process in the industry to dispose of this type of ferrophosphorus waste. How to reuse this type of waste through a simple treatment process and regenerate it into high-value-added ferrophosphate materials is a process technology with great research value and development potential. Summary of the invention

[0007] In view of the deficiencies of the prior art, the object of the present invention is to provide a new method for treating ferrophosphorus waste.

[0008] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0009] A method for treating ferrophosphorus waste comprises the following steps:

[0010] S1. After alkali leaching of the ferrophosphorus waste to be treated, solid-liquid separation is performed to obtain leachate and leach residue;

[0011] Among them, ferrophosphorus waste contains Fe, P, and Al;

[0012] S2, adjusting the pH value of the leaching solution to 6.5-8.0, standing it, and separating the solid and liquid to obtain a phosphate-rich solution A and a slag phase A;

[0013] After the leached residue is reacted with sulfuric acid, solid-liquid separation is performed to obtain solution B and slag phase B;

[0014] S3, mixing the solution A and the solution B, performing iron precipitation treatment, and then separating the solid and the liquid to obtain ferric phosphate dihydrate and a residual liquid.

[0015] Further, in S1, the ferrophosphorus waste to be treated is mixed with alkali and / or alkali solution, alkali leaching is performed, and then solid-liquid separation is performed to obtain a leachate and a leaching residue;

[0016] Preferably, the amount of alkali added is 1.2-1.5 times, more preferably 1.3-1.4 times, the theoretical amount required to convert all Fe in the ferrophosphorus waste into hydroxide (i.e., iron hydroxide);

[0017] Preferably, during alkali leaching, the liquid-to-solid ratio of the leaching system is controlled to be 4:1-8:1 mL / g. More preferably, water is mixed with the ferrophosphorus waste and the alkali for alkali leaching, or the ferrophosphorus waste is mixed with the alkali solution for alkali leaching; when the ferrophosphorus waste is mixed with the alkali and / or the alkali solution, water or its solution may be added as needed so that the initial liquid-to-solid ratio meets the above requirements;

[0018] Preferably, the alkali comprises one or more of sodium hydroxide and potassium hydroxide, preferably solid caustic soda flakes; more preferably, solid caustic soda flakes are added gradually; in this way, the alkali leaching is performed using solid caustic soda flakes, and the overall reaction is a self-exothermic process without the need for additional heating, which helps to save energy consumption, reduce material volume, and improve processing efficiency and processing capacity;

[0019] Preferably, during the alkali leaching process, the reaction temperature is controlled to be 80-100°C, more preferably 85-95°C, and the reaction time is 1-4h, more preferably 1.5-3.5h; more preferably 1.6-3.4h.

[0020] Preferably, during solid-liquid separation, the temperature of the mixing system and the solid-liquid separation equipment are controlled to be greater than 50°C, more preferably 55-95°C. This can better prevent the formation of colloids and the precipitation of sodium phosphate, thereby achieving more effective separation of phosphorus and iron.

[0021] Further, in S2, the pH value of the leachate is adjusted with acid or acid gas;

[0022] Preferably, the pH value of the leachate is adjusted to 6.8-7.5;

[0023] Preferably, the solid-liquid separation is performed after the sedimentation and stratification and the upper solution is clarified. Generally, it takes more than 1 hour to achieve the above degree.

[0024] Preferably, the solid-liquid separation is performed after standing at 10-40°C for 1-6 hours; more preferably, the solid-liquid separation is performed after standing for 2-3 hours;

[0025] Preferably, the acid includes one or more of hydrochloric acid, sulfuric acid, and nitric acid; preferably, the acid gas includes carbon dioxide.

[0026] By allowing the flocculent precipitate to settle, it is helpful for it to fully grow and fully absorb and remove some of the organic matter in the solution. It can also effectively reduce the possibility of penetration in the subsequent solid-liquid separation process, thereby obtaining a solution A with a higher purity.

[0027] Further, in S2, the leached residue is reacted with an inorganic acid, a water-soluble carbonate and / or a bicarbonate, and then the solid and liquid are separated to obtain a solution B and a residue phase B;

[0028] Preferably, the inorganic acid includes one or more of sulfuric acid, hydrochloric acid, and nitric acid. More preferably, the inorganic acid includes sulfuric acid. In this way, impurities such as Ca in the leached slag can be retained in the slag phase, which helps to obtain a purer solution B and reduces the burden of impurity removal.

[0029] Preferably, the leached residue is mixed with an inorganic acid and a water-soluble carbonate and / or bicarbonate for reaction at the same time; or, the leached residue is first reacted with an inorganic acid and then with a water-soluble carbonate and / or bicarbonate; or, the leached residue is first reacted with a water-soluble carbonate and / or bicarbonate and then with an inorganic acid;

[0030] Preferably, the amount of water-soluble carbonate and / or bicarbonate added is 1.1-1.5 times the total molar amount of M in the leached residue, where M includes one or more of Mg, Mn, Cu, and Ca, and more preferably 1.2-1.4 times;

[0031] Preferably, the water-soluble carbonate includes one or more of sodium carbonate, potassium carbonate, and ammonium carbonate. Optionally, the bicarbonate includes one or more of sodium bicarbonate, potassium bicarbonate, and ammonium bicarbonate.

[0032] Thus, by adding water-soluble carbonates, Mg, Mn, Cu, Ca and other ions can be retained in the slag phase in the form of water-insoluble carbonates, which helps to obtain a solution B with higher purity.

[0033] After in-depth research, the applicant found that in the reaction system of S2, the introduction of carbonate will not lead to the loss of iron salts; and carbonates can form insoluble carbonates with impurity ions such as Mn, Mg, Zn, Cu, Ca, etc., thereby removing impurities and helping to obtain a solution B with higher purity.

[0034] Furthermore, in S2, the amount of inorganic acid used is 1-1.1 times, preferably 1.02-1.08 times, of the theoretical amount required to dissolve all Fe in the leached slag; this helps to ensure a better impurity removal effect and facilitates subsequent iron precipitation treatment;

[0035] Preferably, the concentration of the inorganic acid is 3-8 mol / L, more preferably 4-7 mol / L;

[0036] Preferably, when the leached residue reacts with the inorganic acid, the initial liquid-solid mass ratio is controlled to be (5:2)-(5:1); the use of a high-concentration leaching system helps to save water usage;

[0037] Preferably, when the leached residue reacts with the inorganic acid, the reaction temperature is controlled to be >50°C, more preferably 55-95°C; the reaction time is 1-8h, more preferably 2-6h;

[0038] Preferably, in solution B, Ca<0.02 g / L, Mg<0.02 g / L, and Al<0.05 g / L.

[0039] Further, in S3, after solution A and solution B are mixed, the initial molar ratio of Fe to P is 0.98-1:1;

[0040] Preferably, during the iron precipitation treatment, the pH value of the mixed system is controlled to be 1.5-2.5;

[0041] Preferably, during the iron precipitation treatment, ammonia water and / or alkaline solution are used to control the pH value of the mixed system; more preferably, the alkaline solution contains one or more of sodium hydroxide and potassium hydroxide; more preferably, the concentration of the ammonia water is 1-10 mol / L, and more preferably 3-6 mol / L; the concentration of the alkaline solution is 1-10 mol / L, and more preferably 3-6 mol / L.

[0042] Furthermore, in S1, the iron and phosphorus in the ferrophosphorus waste include iron phosphate, FeP, Fe 2 Furthermore, when the ferrophosphorus waste contains FeP, Fe 2 When one or more of P is present, the ferrophosphorus waste is first subjected to oxidation treatment and then to alkaline leaching; optionally, the oxidation treatment is oxidation roasting, or the ferrophosphorus waste is mixed with an oxidant in an aqueous solution for reaction; optionally, the oxidant is one or more of oxygen, oxygen-enriched air, hydrogen peroxide, and ozone. Optionally, the oxidation roasting temperature is 500-800°C, further 550-650°C; the oxidation roasting time is 1-5h, further 2-4h.

[0043] Furthermore, in S1, the ferrophosphorus waste includes one or more of ferrophosphorus slag after lithium extraction from waste lithium iron phosphate, iron phosphorus slag produced by electric furnace production of yellow phosphorus, and ferrophosphate byproducts; preferably, before S1, the ferrophosphorus waste to be treated is crushed to obtain ferrophosphorus waste powder. Optionally, the ferrophosphorus slag after lithium extraction from waste lithium iron phosphate is ferrophosphate waste slag with high Al content after lithium extraction from which aluminum foil is not completely separated; optionally, the ferrophosphate byproduct is ferrophosphate containing impurities such as Mn, Cr, Mg, and Al from a steel enterprise.

[0044] Furthermore, between S1 and S2, the leached residue is alkali washed; preferably, the number of alkali washings is more than 3 times, more preferably, the number of alkali washings is 4-8 times; preferably, a strong alkaline solution with a pH>11 is used for alkali washing, more preferably, the strong alkali is one or more of sodium hydroxide and potassium hydroxide; preferably, the washing water obtained after alkali washing is returned to S1 for alkali leaching. In this way, the aluminate ions, phosphate ions, etc. adsorbed on the surface of the leached residue can be effectively removed, which is helpful for obtaining a solution B with higher purity later. The washing water can be returned to S1 for recycling, so as to achieve reuse and reduce phosphorus loss.

[0045] Furthermore, after S3, the dihydrated ferric phosphate is washed, solid-liquid separation is performed, and pure dihydrated ferric phosphate is obtained, and then dehydration and impurity removal are performed to obtain ferric phosphate;

[0046] Preferably, the pH value of the acidic wash water is 0.5-2, more preferably 0.8-1;

[0047] Preferably, the acidic washing water is a phosphoric acid solution;

[0048] Preferably, the temperature of the acidic washing water is >80°C, more preferably 85-99°C;

[0049] Preferably, during washing, the liquid-to-solid mass ratio is controlled to be 3-5:1;

[0050] Preferably, the number of washings is ≥ 3 times, more preferably 5-8 times;

[0051] Preferably, the mixture is calcined at 600-650°C for more than 1 hour to achieve dehydration and impurity removal; more preferably, the mixture is calcined at 610-640°C for 1.5-2.5 hours to achieve dehydration and impurity removal;

[0052] Preferably, the purity of the iron phosphate is ≥99.9wt%.

[0053] Furthermore, in the ferrophosphorus waste to be treated, the Fe content is ≥20wt%, the P content is ≥15wt%, and the Al content is ≥0.05wt%; preferably, the total content of impurities is 0.5-40wt%, more preferably 1-20wt%, and further preferably 3-10wt%; preferably, the impurities include one or more of Al, Mn, Mg, Zn, Cu, Ca, and graphite.

[0054] Furthermore, in the ferrophosphorus waste to be treated, the Fe content is 25-70wt%, the P content is 16-30wt%, and the Al content is 0.1-20wt%.

[0055] Furthermore, in the ferrophosphorus waste to be treated, the Fe content is 30-65wt%, the P content is 17-28wt%, and the Al content is 0.5-5wt%.

[0056] In the present invention, the characteristic of aluminum as an amphoteric metal is utilized to separate iron and aluminum through alkaline leaching, and a leachate rich in aluminate and phosphate and a leach residue rich in iron hydroxide are obtained. In the present invention, since iron and aluminum enter the leach residue and leachate respectively, the loss of valuable elements caused by the coprecipitation and adsorption process of iron and aluminum can be effectively avoided. Subsequently, by adjusting the pH value of the leachate to 6.5-8.0, possible impurities such as Al and Zn can be converted into Al(OH) 3 、Zn(OH) 2 Amphoteric hydroxides such as iodine and iodine can be flocculated and settled to remove more than 99.9% of aluminum and zinc. At the same time, due to its good flocculation and adsorption properties, the flocculent precipitate can also simultaneously remove some organic matter in the leachate to obtain a pure solution A (the solute is mainly soluble phosphate, such as sodium phosphate, potassium phosphate, etc.); at the same time, phosphorus loss can also be avoided. In addition, the leached residue is reacted with an inorganic acid to dissolve iron hydroxide into the liquid phase to obtain a pure solution B (the solute is mainly water-soluble iron salt, such as iron sulfate, etc.). Thereafter, solution A is used as a phosphorus source and solution B is used as an iron source. They are mixed in proportion according to the needs of preparing dihydrated iron phosphate, and the pH value of the system is controlled in a suitable range to prepare high-purity dihydrated iron phosphate. The dihydrated iron phosphate is further subjected to simple washing, purification, dehydration and impurity removal treatment to prepare high-purity iron phosphate.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] (1) The present invention uses effective impurity removal and purification means, and adopts comprehensive impurity removal under common conditions such as acid, alkali, and neutrality to ultimately achieve effective removal of multiple impurity elements, thereby stably obtaining pure iron sources and phosphorus sources, and further preparing dihydrated ferric phosphate or ferric phosphate products with uniform and stable properties. The process is simple and efficient, and has wide applicability to raw materials, and can achieve good treatment of ferrophosphorus waste with complex sources and complex components.

[0059] (2) The present invention adopts a pure wet process, and the preparation of iron phosphate can be achieved only by adjusting the precipitation conditions, with low energy consumption and low pollution. Wastewater can also be recycled through a conventional MVR system, effectively avoiding the huge energy consumption, acid mist corrosion and environmental damage caused by the hydrothermal evaporation of acid leaching liquid in the prior art such as CN116534823A.

[0060] (3) In the treatment process of the present invention, the loss rate of Fe and P elements during the recovery process is low, and the output iron phosphate product can meet the battery grade standard and achieve a purity of more than 99.95wt%. In addition, the graphite in the ferrophosphorus waste will be enriched in the slag phase B during the treatment process, so the graphite can also be recovered, which can effectively reduce the volume of waste slag.

[0061] (4) At present, most existing technologies (such as CN116581415A, etc.) are only aimed at the recovery of lithium iron phosphate materials. While recovering lithium elements, they also realize the recovery of iron and phosphorus elements simultaneously. Most of these patents are mainly based on the recovery and conversion of lithium into battery-grade materials, while the recovery process of iron and phosphorus elements is not yet mature. The recovery method is often lengthy, with high energy consumption or low industrial feasibility, and the recovery added value is relatively low. However, the present invention can not only effectively treat such iron phosphate solid waste materials after lithium extraction, but also treat iron phosphate containing impurities from other sources. The comprehensive recovery rate of iron and phosphorus can be stabilized at more than 95%, and common impurity elements such as calcium, magnesium, aluminum, chromium, zinc, and organic matter can be effectively removed. Finally, iron phosphate products with stable component properties can be output with common and easily available chemical materials and mature industrial wet processes. The iron phosphate products can meet battery-grade standards, have high product added value, strong industrial feasibility, and have better prospects for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 This is the XRD pattern of the iron phosphate product obtained in Example 1.

[0063] Figure 2 This is a SEM image of the ferric phosphate product obtained in Example 1 (magnified 5000 times).

[0064] Figure 3 This is a SEM image of the ferric phosphate product obtained in Example 1 (magnified 10,000 times). DETAILED DESCRIPTION

[0065] The present invention will be described in detail below in conjunction with the embodiments. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. Unless otherwise specified, the relevant percentages refer to mass percentages.

[0066] Example 1

[0067] A method for treating ferrophosphorus waste comprises the following steps:

[0068] S1. 50 kg of ferrophosphorus waste to be treated is mixed with an alkaline solution, subjected to alkaline leaching, and then filtered while hot to obtain a leachate and a leach residue;

[0069] The ferrophosphorus waste is ferrophosphorus slag after lithium extraction in a waste lithium battery recycling enterprise; the ferrophosphorus waste to be treated has an Fe content of 34.545wt%, a P content of 18.253wt%, an Al content of 0.336wt%, and a total impurity content of 5.12wt%, wherein the impurities include Mn, Mg, Zn, Cu, Ca, and graphite; the amount of alkali in the alkaline solution is 1.2 times the theoretical amount required to convert all Fe in the ferrophosphorus waste into hydroxide; the alkaline solution is a sodium hydroxide solution;

[0070] During alkali leaching, the initial liquid-solid ratio of the mixed system was controlled to be 4:1 mL / g;

[0071] During the alkali leaching process, the reaction temperature was controlled at 95°C and the reaction time was 2h;

[0072] During filtration, the temperature of the mixing system and the filtration equipment was controlled to be 75±10°C.

[0073] Between S1 and S2, the leached residue is alkali washed three times with a sodium hydroxide solution having a pH value of 13.02 to obtain purified leached residue; the washing water obtained after the alkali washing is returned to S1 for alkali leaching.

[0074] S2, adjusting the pH value of the leaching solution to 7.0 with sulfuric acid, leaving it to stand for 2 hours at 35° C., and filtering it to obtain a phosphate-rich solution A (with an Al removal rate of 98.75% and an Al concentration of 0.011 g / L) and a slag phase A mainly composed of aluminum hydroxide;

[0075] The purified leached residue is reacted with 6 mol / L hydrochloric acid, and further reacted with water-soluble carbonate, and then filtered to obtain a solution B (Ca 0.005 g / L, Mg 0.003 g / L, Al 0.06 g / L) and a slag phase B mainly composed of graphite, calcium carbonate, magnesium carbonate, and manganese carbonate;

[0076] Among them, the amount of water-soluble carbonate (sodium carbonate) added is 1.2 times the total molar amount of Mg, Mn, Cu, and Ca in the leached residue;

[0077] When the leaching residue reacts with hydrochloric acid, the amount of hydrochloric acid used is 1.05 times the theoretical amount required to dissolve all the Fe in the leaching residue; the reaction temperature is controlled to be 85° C. and the reaction time is 2 h.

[0078] S3, mixing the solution A and the solution B, performing iron precipitation treatment, and then separating the solid and the liquid to obtain ferric phosphate dihydrate and a residual liquid;

[0079] During the iron precipitation treatment, ammonia water is used to control the pH value of the mixed system within the range of 1.65±0.15; the concentration of the ammonia water is 6 mol / L;

[0080] After solution A and solution B were mixed, the initial molar ratio of Fe to P was 0.98:1;

[0081] S4, washing the dihydrated ferric phosphate with acidic washing water, separating the solid and the liquid, obtaining pure dihydrated ferric phosphate, and roasting at 600° C. for 3 h to achieve dehydration and impurity removal, obtaining 45.6 kg of ferric phosphate product;

[0082] The acidic washing water is a phosphoric acid solution with a pH value of 0.8; the temperature of the acidic washing water is 90°C; during washing, the liquid-to-solid mass ratio is controlled to be 3:1; and the number of washing times is 6 times.

[0083] Example 2

[0084] A method for treating ferrophosphorus waste comprises the following steps:

[0085] S1. Mixing the ferrophosphorus waste to be treated with water and alkali, performing alkali leaching, and filtering while hot to obtain a leachate and a leach residue;

[0086] The ferrophosphorus waste is 80 kg of crude ferrophosphate byproducts of the steel industry; the ferrophosphorus waste to be treated has an Fe content of 30.641 wt%, a P content of 17.225 wt%, an Al content of 0.069 wt%, and a total impurity content of 8.341 wt%, wherein the impurities include Mn, Mg, Zn, Cu, Ca, and graphite; the amount of alkali added is 1.3 times the theoretical amount required to convert all Fe in the ferrophosphorus waste into hydroxide; the alkali is solid flake alkali of sodium hydroxide;

[0087] During alkaline leaching, the initial liquid-to-solid ratio of the leaching system was controlled to be 5:1 mL / g;

[0088] During the alkali leaching process, the reaction temperature was controlled at 92°C and the reaction time was 2h;

[0089] During filtration, the temperature of the mixing system and the filtration equipment was controlled to be 75±10°C.

[0090] Between S1 and S2, the leached residue is alkali washed three times with a sodium hydroxide solution having a pH value of 12.8 to obtain purified leached residue; the washing water obtained after the alkali washing is returned to S1 for alkali leaching.

[0091] S2, adjusting the pH value of the leaching solution to 7.5 with hydrochloric acid, standing and settling at 30° C. for 2 hours, and filtering to obtain a phosphate-rich solution A (with an Al removal rate of 98.08% and an Al concentration of 0.003 g / L) and a slag phase A;

[0092] The purified leached residue is reacted with sulfuric acid having a concentration of 5 mol / L, and further reacted with water-soluble carbonate, and then filtered to obtain a solution B (Ca=0.006 g / L, Mg=0.0021 g / L, Al=0.008 g / L) and a slag phase B;

[0093] Among them, the amount of water-soluble carbonate (sodium carbonate) added is 1.5 times the total molar amount of Mg, Mn, Cu and Ca in the leached residue;

[0094] When the leaching residue reacts with sulfuric acid, the amount of sulfuric acid used is 1.05 times the theoretical amount required to dissolve all the Fe in the leaching residue; the reaction temperature is controlled to be 70° C. and the reaction time is 4 h.

[0095] S3, mixing the solution A and the solution B, performing iron precipitation treatment, and then separating the solid and the liquid to obtain ferric phosphate dihydrate and a residual liquid;

[0096] During the iron precipitation treatment, an alkaline solution is used to control the pH value of the mixed system to 1.8±0.2; the alkaline solution is a sodium hydroxide solution, and the concentration of the alkaline solution is 5 mol / L;

[0097] After solution A and solution B were mixed, the initial molar ratio of Fe to P was 0.99:1;

[0098] S4, washing the dihydrated ferric phosphate with acidic washing water, separating the solid and the liquid, obtaining pure dihydrated ferric phosphate, and roasting at 650° C. for 1 h to achieve dehydration and impurity removal, obtaining 63.83 kg of ferric phosphate product;

[0099] The acidic washing water is a phosphoric acid solution with a pH value of 0.6; the temperature of the acidic washing water is 85°C; during washing, the liquid-solid mass ratio is controlled to be 5:1; and the number of washing times is 5 times.

[0100] Example 3

[0101] A method for treating ferrophosphorus waste comprises the following steps:

[0102] S1. 20 kg of ferrophosphorus waste to be treated is subjected to oxidation roasting treatment at 600° C. in an air atmosphere for 3 hours, mixed with water and alkali, subjected to alkali leaching, and filtered while hot to obtain a leachate and a leach residue;

[0103] Wherein, the ferrophosphorus waste contains FeP, Fe 2 P iron phosphorus slag; in the ferrophosphorus waste to be treated, the content of Fe is 64.01wt%, the content of P is 25.17wt%, the content of Al is 0.174wt%, and the total content of impurities is 6.82wt%, and the impurities include Mn, Mg, Zn, Cu, Ca, and graphite; the amount of alkali added is 1.5 times the theoretical amount required to convert all Fe in the ferrophosphorus waste into hydroxide; the alkali is solid flake alkali of sodium hydroxide;

[0104] During alkaline leaching, the liquid-to-solid ratio of the leaching system was controlled to be 6:1 mL / g;

[0105] During the alkali leaching process, the reaction temperature was controlled at 98°C and the reaction time was 2h;

[0106] During filtration, the temperature of the mixing system and the filtration equipment was controlled to be 80±10°C.

[0107] Between S1 and S2, the leached residue is alkali washed three times with a sodium hydroxide solution having a pH value of 13.57 to obtain purified leached residue; the washing water obtained after the alkali washing is returned to S1 for alkali leaching.

[0108] S2, introducing CO into the leachate 2 The gas was adjusted to pH 7, and then allowed to stand for 2 h at 45 °C, and then filtered to obtain a phosphate-rich solution A (with an Al removal rate of 97.7% and an Al content of 0.007 g / L) and a slag phase A;

[0109] The purified leached residue is reacted with sulfuric acid having a concentration of 4 mol / L, and further reacted with water-soluble carbonate, and then filtered to obtain a solution B (Ca=0.0012 g / L, Mg=0.003 g / L, Al=0.035 g / L) and a slag phase B;

[0110] Among them, the amount of water-soluble carbonate (sodium carbonate) added is 1.3 times the total molar amount of Mg, Mn, Cu and Ca in the leached residue;

[0111] When the leaching residue reacts with sulfuric acid, the amount of sulfuric acid used is 1.1 times the theoretical amount required to dissolve all the Fe in the leaching residue; the reaction temperature is controlled to be 60° C. and the reaction time is 6 h.

[0112] S3, mixing the solution A and the solution B, performing iron precipitation treatment, and then separating the solid and the liquid to obtain ferric phosphate dihydrate and a residual liquid;

[0113] During the iron precipitation treatment, an alkaline solution is used to control the pH value of the mixed system to 1.7±0.2; the alkaline solution comprises a sodium hydroxide solution, and the concentration of the alkaline solution is 4 mol / L;

[0114] After solution A and solution B were mixed, the initial molar ratio of Fe to P was 1:1;

[0115] S4, washing the dihydrated ferric phosphate with acidic washing water, separating the solid and the liquid, obtaining pure dihydrated ferric phosphate, and roasting at 650° C. for 1.5 h to achieve dehydration and impurity removal, obtaining 33.18 kg of ferric phosphate product;

[0116] The acidic washing water is a phosphoric acid solution with a pH value of 0.5; the temperature of the acidic washing water is greater than 80°C; during washing, the liquid-to-solid mass ratio is controlled to be 4:1; and the number of washing times is 5 times.

[0117] See also Figure 1 , XRD test shows that the ferric phosphate product obtained by the present invention has a good crystal form, accurately matches the standard ferric phosphate card, and has no impurity peaks; see Figure 2 and Figure 3 SEM detection shows that the microscopic surface of the iron phosphate product obtained by the present invention is uniform, the primary grains are nano-scale smooth particles with excellent morphology, and the whole has good morphology and crystal shape.

[0118] Example 4

[0119] A method for treating ferrophosphorus waste comprises the following steps:

[0120] S1, mixing 50 kg of ferrophosphorus waste to be treated with water and alkali, performing alkali leaching, and filtering while hot to obtain a leachate and a leach residue;

[0121] The ferrophosphorus waste is ferrophosphate slag after lithium extraction in a waste lithium battery recycling enterprise; the ferrophosphorus waste to be treated has an Fe content of 28.19wt%, a P content of 16.06wt%, an Al content of 5.21wt%, and a total impurity content of 10.18wt%, wherein the impurities include Mn, Mg, Zn, Cu, Ca, and graphite; the amount of alkali added is 1.2 times the theoretical amount required to convert all Fe in the ferrophosphorus waste into hydroxide; the alkali is solid flake alkali of sodium hydroxide;

[0122] During alkaline leaching, the liquid-to-solid ratio of the leaching system was controlled to be 5:1 mL / g;

[0123] During the alkali leaching process, the reaction temperature was controlled at 95°C and the reaction time was 3h;

[0124] During filtration, the temperature of the mixing system and the filtration equipment was controlled to be 85±10°C.

[0125] Between S1 and S2, the leached residue is alkaline washed three times with a sodium hydroxide solution having a pH value of 13.52 to obtain purified leached residue; the washing water obtained after the alkaline washing is returned to S1 for alkaline leaching.

[0126] S2, adding sulfuric acid to the leachate, adjusting the pH value thereof to 7.05, standing and settling at 35° C. for 3 h, filtering, and obtaining a phosphate-rich solution A (with an Al removal rate of 99.86% and an Al content of 0.016 g / L) and a slag phase A;

[0127] The purified leached residue is reacted with sulfuric acid having a concentration of 5 mol / L, and further reacted with water-soluble carbonate, and then filtered to obtain a solution B (Ca=0.0013 g / L, Mg=0.003 g / L, Al=0.045 g / L) and a slag phase B;

[0128] Among them, the amount of water-soluble carbonate (sodium carbonate) added is 1.5 times the total molar amount of Mg, Mn, Cu and Ca in the leached residue;

[0129] When the leaching residue reacts with sulfuric acid, the amount of sulfuric acid used is 1.01 times the theoretical amount required to dissolve all the Fe in the leaching residue; the reaction temperature is controlled to be 70° C. and the reaction time is 3 h.

[0130] S3, mixing the solution A and the solution B, performing iron precipitation treatment, and then separating the solid and the liquid to obtain ferric phosphate dihydrate and a residual liquid;

[0131] During the iron precipitation treatment, an alkaline solution is used to control the pH value of the mixed system to 1.85±0.2; the alkaline solution is ammonia water, and the concentration of the alkaline solution is 6 mol / L;

[0132] After solution A and solution B were mixed, the initial molar ratio of Fe to P was 1:1;

[0133] S4, washing the dihydrated ferric phosphate with acidic washing water, separating the solid and the liquid, obtaining pure dihydrated ferric phosphate, and roasting at 620° C. for 2 h to achieve dehydration and impurity removal, obtaining 36.65 kg of ferric phosphate product;

[0134] The acidic washing water is a phosphoric acid solution with a pH value of 0.5; the temperature of the acidic washing water is 85°C; during washing, the liquid-solid mass ratio is controlled to be 3:1; and the number of washing times is 5 times.

[0135] After testing, the recovery rate of Fe element was 97.75%, and the recovery rate of P element was 96.24%.

[0136] Comparative Example 1

[0137] Example 1 was repeated, except that in S2, the pH value of the leaching solution was adjusted to 5.5 and then allowed to stand.

[0138] After testing, the Al content of solution A was 0.604 g / L, and the aluminum removal rate was only 35.26%.

[0139] Comparative Example 2

[0140] Example 1 was repeated, except that in S2, the pH value of the leaching solution was adjusted to 9.5 and then allowed to stand.

[0141] After testing, the Al content of solution A was 0.515 g / L, and the aluminum removal rate was only 44.87%.

[0142] According to HG / T 4701-2021, the composition analysis results of the ferric phosphate products obtained in each embodiment and the Fe and P recovery rates are shown in Table 1.

[0143] Table 1 Composition analysis results of ferric phosphate products obtained in various embodiments and Fe and P recovery rates

[0144]

[0145] Note: Except for the "Fe:P" column in the above table, the units of other columns are %. The recovery rates of P and Fe elements are calculated based on the phosphorus content in solution A and the iron content in solution B, respectively.

[0146] The contents explained in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

Claims

1. A method for treating ferrophosphorus waste, It is characterized in that The steps include: S1. After alkali leaching of the ferrophosphorus waste to be treated, solid-liquid separation is performed to obtain leachate and leach residue; Among them, ferrophosphorus waste contains Fe, P, and Al; S2, adjusting the pH value of the leachate to 6.5-8.0, standing and settling, and performing solid-liquid separation to obtain a phosphate-rich solution A and a slag phase A; After the leached residue is reacted with an inorganic acid, solid-liquid separation is performed to obtain a solution B and a residue phase B; S3, mixing the solution A and the solution B, performing iron precipitation treatment, and then separating the solid and the liquid to obtain ferric phosphate dihydrate and a residual liquid.

2. The processing method according to claim 1, It is characterized in that In S1, the ferrophosphorus waste to be treated is mixed with alkali and / or alkali solution, alkali leaching is performed, and then solid-liquid separation is performed to obtain a leachate and a leach residue; Preferably, the amount of alkali added is 1.2-1.5 times, more preferably 1.3-1.4 times, the theoretical amount required to convert all Fe in the ferrophosphorus waste into hydroxide; Preferably, during alkali leaching, the initial liquid-solid ratio of the leaching system is controlled to be 4:1-8:1 mL / g; more preferably, water is mixed with ferrophosphorus waste and alkali to perform alkali leaching, or ferrophosphorus waste is mixed with alkali solution to perform alkali leaching; Preferably, the alkali includes one or more of sodium hydroxide and potassium hydroxide, preferably solid flake alkali; Preferably, during the alkali leaching process, the reaction temperature is controlled to be 80-100°C, more preferably 85-95°C, and the reaction time is 1-4h, more preferably 1.5-3.5h; Preferably, during solid-liquid separation, the temperature of the mixing system and the solid-liquid separation equipment are controlled to be >50°C, more preferably 55-95°C.

3. The processing method according to claim 1, It is characterized in that In S2, the pH value of the leachate is adjusted with acid or acid gas; Preferably, the pH value of the leachate is adjusted to 6.8-7.5; Preferably, the solid-liquid separation is performed after standing at 10-45°C for 1-6 hours; more preferably, the solid-liquid separation is performed after standing for 2-3 hours; Preferably, the acid includes one or more of hydrochloric acid, sulfuric acid and nitric acid; and the acidic gas includes carbon dioxide.

4. The processing method according to claim 1, It is characterized in that In S2, the leached residue is reacted with an inorganic acid, a water-soluble carbonate and / or a bicarbonate, and then the solid and liquid are separated to obtain a solution B and a residue phase B; Preferably, the inorganic acid comprises one or more of sulfuric acid, hydrochloric acid and nitric acid, and more preferably, the inorganic acid comprises sulfuric acid; preferably, the leached residue is mixed with the inorganic acid and the water-soluble carbonate for reaction at the same time; or, the leached residue is first reacted with the inorganic acid and then with the water-soluble carbonate and / or bicarbonate; or, the leached residue is first reacted with the water-soluble carbonate and / or bicarbonate and then with the inorganic acid; Preferably, the amount of water-soluble carbonate and / or bicarbonate added is 1.1-1.5 times the total molar amount of M in the leached residue, where M includes one or more of Mg, Mn, Cu, and Ca, and more preferably 1.2-1.4 times; Preferably, the water-soluble carbonate includes one or more of sodium carbonate, potassium carbonate and ammonium carbonate; the bicarbonate includes one or more of sodium bicarbonate, potassium bicarbonate and ammonium bicarbonate.

5. The processing method according to claim 1, It is characterized in that In S2, the amount of inorganic acid used is 1-1.1 times, preferably 1.02-1.08 times, the theoretical amount required to dissolve all Fe in the leaching residue; Preferably, the concentration of the inorganic acid is 3-8 mol / L, more preferably 4-7 mol / L; preferably, when the leached residue reacts with the inorganic acid, the reaction temperature is controlled to be greater than 50°C, more preferably 55-95°C; the reaction time is 1-8h, more preferably 2-6h; Preferably, in solution B, Ca<0.02 g / L, Mg<0.02 g / L, and Al<0.05 g / L.

6. The processing method according to claim 1, It is characterized in that In S3, after solution A and solution B are mixed, the initial molar ratio of Fe to P is 0.98-1:1; Preferably, during the iron precipitation treatment, the pH value of the mixed system is controlled to be 1.5-2.5; Preferably, during the iron precipitation treatment, ammonia water and / or alkaline solution are used to control the pH value of the mixed system; more preferably, the alkaline solution contains one or more of sodium hydroxide and potassium hydroxide; more preferably, the concentration of the ammonia water is 1-10 mol / L, and more preferably 3-6 mol / L; the concentration of the alkaline solution is 1-10 mol / L, and more preferably 3-6 mol / L.

7. The processing method according to any one of claims 1 to 6, It is characterized in that In S1, the ferrophosphorus waste includes one or more of ferrophosphorus slag after lithium extraction from waste lithium iron phosphate, iron phosphorus slag produced by electric furnace production of yellow phosphorus, and ferrophosphate by-products; preferably, before S1, the ferrophosphorus waste to be treated is crushed to obtain ferrophosphorus waste powder.

8. The processing method according to any one of claims 1 to 6, It is characterized in that Between S1 and S2, the leached residue is subjected to alkali washing; preferably, the number of alkali washings is 3 or more times; preferably, a strong alkali solution with a pH value greater than 11 is used for alkali washing, and more preferably, the strong alkali is one or more of sodium hydroxide and potassium hydroxide; preferably, the washing water obtained after alkali washing is returned to S1 for alkali leaching.

9. The processing method according to any one of claims 1 to 6, It is characterized in that After S3, the dihydrated ferric phosphate is washed, solid-liquid separation is performed, and pure dihydrated ferric phosphate is obtained, and then dehydration and impurity removal are performed to obtain ferric phosphate; Preferably, the pH value of the acidic wash water is 0.5-2, more preferably 0.8-1; Preferably, the acidic washing water is a phosphoric acid solution; Preferably, the temperature of the acidic washing water is >80°C, more preferably 85-99°C; Preferably, during washing, the liquid-to-solid mass ratio is controlled to be 3-5:1; Preferably, the number of washings is ≥ 3 times, more preferably 5-8 times; Preferably, the mixture is calcined at 600-650°C for more than 1 hour to achieve dehydration and impurity removal; more preferably, the mixture is calcined at 610-640°C for 1.5-2.5 hours to achieve dehydration and impurity removal; Preferably, the purity of the iron phosphate is ≥99.9wt%.

10. The processing method according to any one of claims 1 to 6, It is characterized in that In the ferrophosphorus waste to be treated, the content of Fe is ≥20wt%, the content of P is ≥15wt%, and the content of Al is ≥0.05wt%; preferably, the total content of impurities is 0.5-40wt%; preferably, the impurities include one or more of Al, Mn, Mg, Zn, Cu, Ca, and graphite; Preferably, the iron and phosphorus in the ferrophosphorus waste include iron phosphate, FeP, Fe 2 P one or more; in S1, the ferrophosphorus waste is first subjected to oxidation treatment and then to alkaline leaching; more preferably, the oxidation treatment is oxidative roasting, or the ferrophosphorus waste is mixed with an oxidant in an aqueous solution for reaction; more preferably, the oxidant is one or more of oxygen, oxygen-enriched air, hydrogen peroxide, and ozone.

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