Method for preparing iron phosphate by recycling renewable phosphorus resource

Abstract

The invention belongs to the field of resource recycling, and particularly relates to a method for preparing iron phosphate by recycling renewable phosphorus resources. The method comprises the following steps: by taking phosphorus-containing solid waste as a raw material, carrying out alkaline leaching and calcification to obtain a phosphorus-calcium compound and iron-containing waste residue; reacting the phosphorus-calcium compound with concentrated sulfuric acid and water to obtain a phosphoric acid solution; iron-containing waste slag or ferrophosphorus slag is used as a raw material and reacts with a phosphoric acid solution or ammonia water to prepare iron phosphate. According to the method, the solid waste phosphorus resource with extremely low cost is recycled to prepare high-purity phosphoric acid and produce high-purity and high-value iron phosphate, so that the waste of the phosphoric acid resource is effectively reduced, and the efficient recycling of phosphorus is realized; the cost of phosphoric acid and iron phosphate is effectively reduced, and the cost advantage is relatively high; the whole technological process is relatively simple, the generated wastewater can be recycled after phosphorus recovery and calcium and magnesium removal, environmental protection is facilitated, and the iron phosphate obtained by the method has the same performance as iron phosphate obtained by a standard iron method.

Description

Technical Field

[0001] The invention belongs to the field of resource recycling, and in particular relates to a method for preparing ferric phosphate by recycling renewable phosphorus resources. Background Art

[0002] Ferric phosphate, also known as ferrous phosphate and ferric orthophosphate, is an inorganic compound with the chemical formula FePO 4 It is a white or light red crystalline powder, an orthophosphate generated by the reaction of trivalent iron oxide and phosphoric acid solution, in which iron is trivalent. It is mainly used to produce lithium iron phosphate battery positive electrode materials, catalysts and ceramics. The iron phosphate used in the manufacture of lithium iron phosphate positive electrode materials is called battery grade iron phosphate (purity> 99.7%, iron-phosphorus ratio 0.985±0.2).

[0003] At present, the main iron phosphate production processes include iron method (the main raw materials are high-purity phosphoric acid and iron source), sodium method (the main raw materials are industrial-grade phosphoric acid, liquid alkali and iron source), and ammonium method (the main raw materials are industrial-grade phosphoric acid, synthetic ammonia and iron source). No matter which method is used, phosphorus is an extremely important raw material. Affected by the rapid development of new energy vehicles and energy storage industries, the demand for phosphate ore has increased, but the scale of phosphate mining has not increased further due to the influence of policies and environmental protection. Therefore, the supply capacity of phosphate ore has been weakened to a certain extent, and the contradiction between supply and demand in the industry has intensified. In addition, phosphate ore is non-renewable and non-recyclable. At the 2024 World New Energy Vehicle Conference, Zeng Yuqun, chairman of CATL, said that by 2042, half of the batteries produced globally will use recycled lithium and half will use minerals to meet social needs. Therefore, in the iron phosphate production process, phosphorus source occupies the first place in cost items (accounting for more than 53%). The competition in the iron phosphate market is the competition for phosphorus. How to obtain and efficiently use low-cost renewable phosphorus sources is the cost lifeline of battery-grade iron phosphate.

[0004] Lithium battery recycling refers to the centralized recycling of scrapped lithium batteries, recycling batteries or extracting valuable metal elements such as lithium, cobalt, and nickel from batteries through physical and chemical recycling processes. The market pays little attention to the phosphorus iron slag after lithium extraction from lithium iron phosphate. Due to the limitations of lithium iron phosphate pole piece black powder lithium extraction process equipment, a large amount of phosphorus iron slag from lithium iron phosphate extraction is currently stored, resulting in a large amount of phosphorus and iron elements being idle. How to recycle renewable iron and phosphorus elements has become a problem in the industry. Summary of the invention

[0005] In view of the problems in the prior art, the present invention proposes a method for preparing iron phosphate by recycling renewable phosphorus resources, which not only solves the problem of phosphorus iron slag left over from lithium extraction after disassembly of lithium batteries and calcium phosphate sludge produced by sewage dephosphorization, but also reduces the production cost of iron phosphate.

[0006] The method for preparing ferric phosphate by recycling renewable phosphorus resources of the present invention comprises preparing a phosphoric acid solution and preparing ferric phosphate, wherein the process of preparing the phosphoric acid solution is:

[0007] (1-1) Phosphorus-containing solid waste is subjected to alkali leaching and calcification to obtain phosphorus-calcium compounds and iron-containing waste slag;

[0008] (1-2) adding concentrated sulfuric acid and water to the phosphate calcium compound for reaction, and performing post-treatment I to obtain a phosphoric acid solution;

[0009] The phosphorus-containing solid waste is ferrophosphorus slag or calcium phosphate sludge. Ferrophosphorus slag is a black mixture of iron phosphate and graphite remaining after lithium extraction from lithium iron phosphate positive electrode black powder; calcium phosphate sludge is a phosphate-rich byproduct produced by chemical dephosphorization or sewage dephosphorization, with a dry basis phosphorus pentoxide content of more than 30%, and the main components are high-iron calcium phosphate, high-magnesium calcium phosphate, and high-organic calcium phosphate.

[0010] The specific process of alkali leaching is: mixing phosphorus-containing solid waste with liquid alkali for reaction. During the alkali leaching process, the mass ratio of phosphorus-containing solid waste: liquid alkali = 1: (6-9); the liquid alkali is a sodium hydroxide aqueous solution with a mass fraction of 15-25%; the temperature of alkali leaching is 60-95°C, and the alkali leaching time is 0.5-3h. After the alkali leaching is completed, filter pressing and hot water washing are performed to obtain filter cake, filtrate and washing liquid. Under normal circumstances, 90°C hot water washing is used for four times or depending on the specific process conditions, and the sodium content in the filter cake after washing needs to be less than 0.05%. The last two washing liquid is used for the first washing, the last three washing liquid is used for the second washing, the three washings are used for the third washing, and the four washings are used for the fourth washing. The low-concentration washing liquid obtained can be concentrated into a high-concentration washing liquid to supplement the evaporated water during alkali leaching. The filtrate and the first washing liquid will enter the subsequent process flow.

[0011] If the phosphorus-containing solid waste used is ferrophosphorus slag, ferric phosphate reacts with sodium hydroxide to produce ferric hydroxide and sodium phosphate. The sodium phosphate exists in the filtrate and the washing liquid, especially the primary washing liquid. The filter cake mainly becomes ferric hydroxide and graphite, which is called carbon iron slag.

[0012] If the phosphorus-containing solid waste used is high-impurity calcium phosphate, the components therein react with sodium hydroxide to form sodium phosphate and calcium hydroxide, magnesium hydroxide, and iron hydroxide. Sodium phosphate exists in the filtrate and the washing liquid, especially the primary washing liquid, and the filter cake mainly becomes calcium hydroxide, magnesium hydroxide, and iron hydroxide, which is called calcium-iron slag.

[0013] The filtrate and the first washing liquid obtained from the alkaline leaching are decolorized by activated carbon adsorption to obtain a transparent and colorless decolorized sodium phosphate solution, which enters the calcification process.

[0014] The specific process of calcification is: add calcium hydroxide (calcium carbonate content <0.5%, pH of 10 grams of calcium hydroxide dissolved in 200 grams of water cannot be lower than 12) to the decolorized sodium phosphate solution, react at room temperature and pressure for 1 hour, filter, wash with hot water, and obtain filter cake, filtrate and washing liquid. In terms of mass ratio, sodium phosphate solution: calcium hydroxide = 1: (0.055-0.095). The reaction in this process is that sodium phosphate reacts with calcium hydroxide to generate calcium phosphate, monocalcium phosphate and sodium hydroxide. The filter cake is a calcium phosphate compound (a mixture of calcium phosphate and monocalcium phosphate), and the main component of the filtrate and washing liquid is sodium hydroxide.

[0015] During the calcification process, generally, the product is washed with hot water 7 times (the first washing uses the last three washing solutions, the second washing uses the last four washing solutions, the third washing uses the last five washing solutions, the fourth washing uses the last six washing solutions, the fifth washing uses the last six washing solutions, and the sixth and seventh washings use clean water) until the sodium hydroxide content is less than 0.05%. The number of washings depends on the specific process conditions. The filtrate + the first washing solution + the second washing solution are mixed and then impurities are removed (dealuminization and calcium removal, aluminum removal with sodium silicate, calcium removal with sodium carbonate, and aluminum-calcium impurity removal agent is added according to the theoretical amount based on the detection value of the filtrate). The low-concentration sodium hydroxide solution after impurities removal is pumped to the evaporation concentration system to evaporate into a 20% sodium hydroxide solution, and the distilled water is returned to the pure water tank for standby use.

[0016] Add concentrated sulfuric acid and water to the phosphate calcium compound obtained after calcification to react and obtain phosphoric acid. In terms of mass ratio, the phosphate calcium compound: concentrated sulfuric acid: water = 1:1-1.2:4-5, the reaction temperature is 75-160°C, and the reaction time is 1-3h.

[0017] The phosphoric acid concentration obtained at 75-95°C is 20-25%; the phosphoric acid concentration obtained at 100-130°C is 25-33%; the phosphoric acid concentration obtained at 130-160°C is 33-40%, and the reaction pressure is 0-0.5Mpa (compressed air is used to supplement the pressure when the steam pressure cannot be reached).

[0018] In this process, dihydrate gypsum is produced, and its molecular formula is CaSO 4 ·2H 2 O, its chemical structure is a calcium sulfate crystal with two crystal waters. Its crystal water is easily released during heating treatment under different conditions to become various crystals of hemihydrate gypsum and anhydrous gypsum.

[0019] When heated at 65°C, dihydrate gypsum begins to release crystal water, but the dehydration rate is relatively slow. At around 107°C and when the water vapor pressure reaches 971 mmHg, the dehydration rate rapidly increases. As the temperature continues to rise, the dehydration is accelerated. At 170-190°C, dihydrate gypsum dehydrates at a very fast rate to become α-hemihydrate gypsum or β-hemihydrate gypsum. When the temperature continues to rise to 220°C and 320-360°C, the hemihydrate gypsum continues to dehydrate to become α-soluble anhydrous gypsum. However, the anhydrous gypsum generated under 220°C conditions is easier to absorb water in the air to become hemihydrate gypsum. The volume of dihydrate gypsum is larger than that of hemihydrate gypsum. If less water is added, the gypsum absorbs water and turns into dihydrate gypsum, which will cause the slurry to thicken and increase the difficulty of stirring. The present invention uses temperature to control the crystal water form of gypsum to achieve the concentration of phosphoric acid.

[0020] The post-treatment I includes filtration, hot water washing, desulfurization, impurity removal, resin column filtration, and activated carbon decolorization.

[0021] After the reaction is completed, filter and wash with hot water to obtain filter cake, filtrate and washing liquid. Usually, 90℃ hot water is used for washing 3-5 times until the phosphorus content of the filter cake is less than 0.5%. The filtrate and washing liquid are combined and successively subjected to coarse desulfurization, fine desulfurization, impurity removal, resin column filtration, and activated carbon decolorization to obtain phosphoric acid solution.

[0022] The specific process of crude desulfurization is: add a phosphate-calcium mixture to the filtrate and the water washing liquid, filter press, and obtain a crude desulfurization filtrate; the amount of the phosphate-calcium mixture is determined based on the sulfur detection value.

[0023] The specific process of fine desulfurization is as follows: barium carbonate is added to the crude desulfurization filtrate until no bubbles are generated, sulfuric acid reacts with barium carbonate to form barium sulfate, and calcium reacts with carbon dioxide to form calcium carbonate. After the reaction is completed, it is heated to a boiling state for 30 minutes to 60 minutes to allow the residual magnesium carbonate and calcium carbonate to precipitate due to heat, and then filtered and washed three times with water to obtain a fine desulfurization filtrate.

[0024] The specific process of impurity removal is: detect the content of iron, magnesium, aluminum and calcium impurity ions in the desulfurization filtrate and add oxalic acid or oxalate (sodium oxalate, ammonium oxalate) to the desulfurization filtrate to react at 60°C for 1-3 hours to generate ferrous oxalate and divalent metal oxalate precipitates such as magnesium oxalate, calcium oxalate, aluminum oxalate and ferrous oxalate. After the reaction is completed, filter press and wash with water three times to obtain the impurity-removed filtrate and water washing liquid.

[0025] The specific process of resin column filtration is: the impurity removal filtrate and the first water washing liquid are mixed and evaporated to a concentration of 20-25%, and then filtered through a 5-stage resin column to remove monovalent and divalent metal ions, and the sodium potassium ions and divalent metal ions are reduced to less than 0.005%, and the resin column filtration filtrate is obtained. After the resin is saturated, it is regenerated and reduced with a 5% sulfuric acid solution and washed with water to pH = 7, and the sulfur content of the washing liquid is less than 0.005%. The resin used is T-42H resin or T-62H resin or a mixture of T-42H resin and T-62H resin (in terms of volume ratio, T-42H resin: T-62H resin = 6:4)

[0026] The filtrate from the resin column is decolorized with activated carbon to obtain a phosphoric acid solution, which is pumped to a phosphoric acid storage tank for standby use.

[0027] An appropriate amount of calcium hydroxide or calcium oxide is added to the phosphorus-containing washing liquid obtained in the above reaction and post-treatment process to generate calcium dihydrogen phosphate to recover the phosphorus component, and the calcium dihydrogen phosphate is returned to the phosphoric acid preparation process for recycling. The reclaimed water is recycled, and the excess reclaimed water is discharged after precipitation.

[0028] The raw materials used in the preparation process of ferric phosphate can be ferrophosphorus slag or carbon iron slag or calcium iron slag generated in the process of preparing phosphoric acid.

[0029] When ferrophosphorus slag or the carbon iron slag obtained in step (1-1) is used as a raw material to prepare ferric phosphate, the specific process is as follows:

[0030] (2-1) reacting the iron-containing slag with iron powder and phosphoric acid solution, and performing post-treatment II to obtain ferrophosphorus liquid and carbon slag;

[0031] In terms of mass ratio, iron slag: iron powder: phosphoric acid solution = 1: (0.01-0.04): (5-7), the mass fraction of phosphoric acid solution is 20%. The reaction time is 10-60 minutes, the carbon slag (mainly graphite) is separated by filter pressing, the carbon slag is washed twice with hot water at 90°C, the washing liquid is added to the filtrate, the main components of the filtrate are ferrous dihydrogen phosphate and ferrous dihydrogen phosphate, which is called crude ferrophosphorus liquid. The addition of iron powder also inhibits the leaching of aluminum.

[0032] The post-treatment II includes fluoride impurity removal, sulfide impurity removal, and resin adsorption of sodium and potassium ions.

[0033] The specific process of fluoride impurity removal is: detecting the aluminum, calcium, magnesium and zinc content in the crude ferrophosphorus liquid, adding fluoride to the crude ferrophosphorus liquid, reacting for 30 minutes, heating to 98°C and maintaining for 1 hour to evaporate and remove residual hydrogen fluoride. The fluoride is selected from any one of potassium fluoride, sodium fluoride, ammonium fluoride, ammonium hydrogen fluoride, ferric fluoride and ferrous fluoride.

[0034] The specific process of sulfide impurity removal is: detect the content of manganese, copper, nickel, chromium and lead in the liquid after fluoride impurity removal, add sulfide, react for 30 minutes, heat to 98°C and keep for 1 hour to evaporate and remove residual hydrogen sulfide. The sulfide is selected from any one of potassium sulfide, sodium sulfide, ammonium sulfide and ferrous sulfide.

[0035] The specific process of resin adsorption of sodium and potassium ions is: the liquid after sulfide impurities are removed is passed through the resin to adsorb sodium and potassium ions until the sodium and potassium contents in the total liquid content are less than 50 ppm respectively, to obtain ferrophosphorus liquid, wherein the flow rate of the liquid passing through the resin is 0.5V liters / minute (V is the volume of the resin).

[0036] (2-2) detecting the iron-phosphorus ratio in the ferrophosphorus solution, adding phosphoric acid solution to a specified iron-phosphorus ratio, oxidizing, heating to 85° C.-95° C. and keeping warm for precipitation after oxidation, filtering, washing with water until pH = 3.5, obtaining dihydrate ferric phosphate, and performing post-treatment III to obtain anhydrous ferric phosphate;

[0037] Specifically, the iron ion and phosphorus ion content in the ferrophosphorus liquid is detected, and phosphoric acid solution is added according to the iron-phosphorus ratio (iron: phosphorus) = 1:2.6-3.0 to adjust the iron-phosphorus ratio to the specified iron-phosphorus ratio. After adjusting the iron-phosphorus ratio, hydrogen peroxide (hydrogen peroxide concentration 7.5%-30%) is added to oxidize the divalent iron ions to trivalent iron ions (metal ion online analyzer detects divalent iron ions <0.1%). After the oxidation is completed, it is heated to 85°C-95°C and kept warm for precipitation for 3 hours to obtain a nearly white or pink dihydrate iron phosphate slurry. The dihydrate iron phosphate slurry after the reaction is completed is filtered and washed with hot water to pH = 3-4. The filtrate and washing liquid are pumped to the phosphate concentrate pre-treatment process and then neutralized and used as recycled water. The amount of hydrogen peroxide is usually 1.2-1.5 times the molar amount of ferrous ions.

[0038] The post-treatment III includes processes such as drying and calcination.

[0039] The ferric phosphate dihydrate filter cake is transported to a flash evaporator and heated to 110-150℃ for drying. After drying and dehydration to a moisture content of <5%, it is put into an electrically heated rotary kiln for calcination. After calcination at 550-650℃ in a rotary kiln for 2-4 hours, anhydrous ferric phosphate is generated. The anhydrous ferric phosphate is ground to 2500-4000 mesh by air separation and ultrafine grinding, and the magnetic particles are removed by electromagnetic and then packed in ton bags.

[0040] When the carbon iron slag or calcium iron slag obtained in step (1-1) is used as a raw material to prepare ferric phosphate, the specific process is as follows:

[0041] (3-1) The iron-containing slag is reacted with concentrated sulfuric acid, filtered and washed with water to obtain a filter cake and a filtrate. The main component of the filter cake is calcium sulfate dihydrate or graphite, and the main component of the filtrate is ferric sulfate or ferric sulfate and magnesium sulfate, that is, a solution containing ferric sulfate. In terms of mass ratio, the iron-containing slag: concentrated sulfuric acid = 100: (120-200); the reaction time is 30-60 min.

[0042] (3-2) adding iron powder to a solution containing ferric sulfate to react, filtering, and performing post-treatment IV to obtain a ferrous sulfate solution;

[0043] In this process, ferric sulfate is reduced to ferrous sulfate, magnesium sulfate is hydrolyzed into ferrous sulfate and magnesium hydroxide, and after the hydrolysis is completed, the solid and liquid are separated by filtration. The main component of the filter cake is magnesium hydroxide, and the main component of the filtrate is ferrous sulfate. The amount of iron powder used is based on the Fe 3+ 、Al 3+ Mg 2+ The amount of metal ions can be determined.

[0044] The post-processing IV process is the same as post-processing II.

[0045] (3-3) Mix ferrous sulfate solution and phosphoric acid solution to a specified iron-phosphorus ratio, heat to 75-80° C., aerate (use an online metal ion analyzer to detect the content of divalent iron ions and trivalent iron ions, and stop aeration when the divalent iron ions are less than 2%), add hydrogen peroxide to finalize oxidation (use an online metal ion analyzer to detect the content of divalent iron ions is less than 0.1%), detect and adjust the iron-phosphorus ratio to 0.96-0.98, adjust the pH to 1.7-2.2, heat to 90-95° C. for reaction for 3-5 hours, filter press, and wash with hot water to obtain a phosphorus-iron complex.

[0046] Specifically, the phosphorus content in the phosphoric acid solution and the iron content in the ferrous sulfate solution are detected respectively, and the iron-phosphorus ratio of the ferrous phosphate (0.965-0.985) is generated as required (calculation formula X=iron / phosphorus*0.5545). The phosphoric acid solution and the ferrous sulfate solution are measured respectively, and a certain amount of phosphoric acid solution is first added into the ferrous phosphate reactor, and then a certain amount of ferrous sulfate solution is added. After the addition is completed, the iron-phosphorus ratio of the solution is detected after stirring and reacting for 30 minutes. If the iron-phosphorus ratio does not meet the requirements, the iron-phosphorus ratio is adjusted with ammonium dihydrogen phosphate solution. The reaction solution after the initial adjustment of the iron-phosphorus ratio is heated to 75-80°C. After the temperature is reached, the heating is maintained and the aeration fan (500 cubic meters / hour) is turned on. The divalent iron solution is aerated for 0.5-6 hours to obtain a trivalent iron solution. After the aeration is completed, a small amount of 7.5% hydrogen peroxide is added for final oxidation. After the final oxidation is completed, the iron-phosphorus ratio of the solution is detected. If the iron-phosphorus ratio does not meet the requirements, phosphoric acid is used for adjustment. The solution with the secondary iron-phosphorus ratio is adjusted to pH 1.7-2.2 with ammonia water. After the addition of ammonia water, it is heated to 90-95°C and reacted for 3-5 hours to obtain the phosphorus-iron complex. It is filtered and washed with hot water at 80-90°C for 5 times until the sulfate and ammonia content is less than 0.001%. The washing liquid is directly pumped to the ammonia synthesis system for the preparation of ammonia water.

[0047] (3-4) The ferrophosphorus complex is aged and subjected to post-treatment V to obtain anhydrous ferric phosphate;

[0048] The post-treatment V includes filtration, washing, drying, calcination and the like.

[0049] Specifically, the ferrophosphorus complex filter cake is put into a 10%-15% phosphoric acid solution for aging for 3-5 hours to obtain ferric phosphate dihydrate, which is then filtered and washed with hot water at 80°C. The filtrate is aged once and then passed through a phosphoric acid resin column for impurity removal and then pumped to a ferrophosphorus slag acid / carbon iron slag hydrolysis process for standby use. Afterwards, all the washing liquid is collected as calcium dihydrogen phosphate with calcium hydroxide and then returned to the phosphoric acid preparation link.

[0050] The aged filter cake is transported to the flash evaporator for drying and powdering at 110-150℃. The dry ferric phosphate dihydrate powder is transported to the rotary kiln for electric heating and calcined at 550-700℃ for 3-4 hours to produce anhydrous ferric phosphate. The anhydrous ferric phosphate is ground, sorted and demagnetized before being packed in ton bags.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] 1. Use waste or high-impurity phosphorus resources to recycle and prepare high-purity phosphoric acid for the manufacture of iron phosphate, effectively reducing the waste of phosphoric acid resources and achieving efficient recycling of phosphorus.

[0053] 2. The preparation of iron phosphate from waste or high-impurity phosphorus resources has a lower cost advantage, which effectively reduces the cost of phosphoric acid. It utilizes extremely low-cost waste or high-impurity phosphorus resources, uses only a small amount of impurity removers in the production process, and does not use other agents. It produces high-purity and high-value phosphate products, achieving the same performance as standard iron-based iron phosphate.

[0054] 3. Make full use of the tailings after dismantling and extracting lithium from waste lithium batteries and the high-impurity calcium phosphate sludge produced by sewage dephosphorization to reduce the pollution of the complex composition of phosphorus tailings to the environment.

[0055] 4. The whole process of the present invention is relatively simple, and no sodium alkali is needed to adjust the pH value, thereby reducing the complexity of the chemical reaction and improving the production efficiency. In addition, the process has little impact on the environment during the production process, and almost no waste gas is discharged. The waste water generated can be recycled after phosphorus recovery and decalcification and magnesium removal, which is beneficial to environmental protection. It also has the characteristics of high product purity and high raw material utilization rate, and has its unique advantages.

[0056] 5. The ferric phosphate produced by this process has high purity, and many impurity elements are not detected in the finished ferric phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a schematic diagram of the process flow of the present invention;

[0058] Figure 2-Figure 3 The iron phosphate test report of the present invention;

[0059] Figure 4-Figure 5 This is a SEM photo of the iron phosphate described in the present invention. DETAILED DESCRIPTION

[0060] Example 1 Preparation of phosphoric acid solution using ferrophosphorus slag as raw material

[0061] The process for preparing phosphoric acid solution is:

[0062] (1-1) The ferrophosphorus slag is subjected to alkali leaching and calcification to obtain phosphate-calcium compounds and carbon-iron slag;

[0063] The specific process of alkali leaching is: mixing ferrophosphorus slag with liquid alkali for reaction. During the alkali leaching process, the ferrophosphorus slag: liquid alkali = 1:6 in terms of mass ratio; the liquid alkali is a sodium hydroxide aqueous solution with a mass fraction of 25%; the alkali leaching temperature is 90°C and the alkali leaching time is 0.5h. After the alkali leaching is completed, filter pressing and hot water washing are performed to obtain filter cake, filtrate and washing liquid.

[0064] Hot water washing is done by washing with 90℃ hot water four times. The sodium content in the filter cake after washing must be less than 0.05%. The first washing uses the last second washing liquid, the second washing uses the last third washing liquid, the third washing uses clean water, and the fourth washing uses clean water. The low-concentration washing liquid obtained can be concentrated into a high-concentration washing liquid to supplement the evaporated water during alkali leaching. The filtrate and the first washing liquid will enter the subsequent process flow.

[0065] During the alkaline leaching process, ferric phosphate reacts with sodium hydroxide to form ferric hydroxide and sodium phosphate. Sodium phosphate exists in the filtrate and water washing liquid, especially the primary water washing liquid. The filter cake mainly becomes ferric hydroxide and graphite, which is called carbon iron slag.

[0066] The filtrate and the first washing liquid obtained from the alkaline leaching are decolorized by activated carbon adsorption to obtain a transparent and colorless decolorized sodium phosphate solution, which enters the calcification process.

[0067] The specific process of calcification is: add calcium hydroxide (calcium carbonate content <0.5%, pH of 10 grams of calcium hydroxide dissolved in 200 grams of water cannot be lower than 12) to the decolorized sodium phosphate solution, react at 25°C for 1 hour, filter, wash with hot water, and obtain filter cake, filtrate and washing liquid. In terms of mass ratio, sodium phosphate solution: calcium hydroxide = 1: 0.055. Sodium phosphate reacts with calcium hydroxide to generate calcium phosphate, monocalcium phosphate and sodium hydroxide. The filter cake is a calcium phosphate compound (a mixture of calcium phosphate and monocalcium phosphate), and the main component of the filtrate and washing liquid is sodium hydroxide.

[0068] During the calcification process, the product is washed with hot water for 7 times (the first washing is done with the last three washing solutions, the second washing is done with the last four washing solutions, the third washing is done with the last five washing solutions, the fourth washing is done with the last six washing solutions, the fifth washing is done with the last six washing solutions, and the sixth and seventh washings are done with clean water) until the sodium hydroxide content is less than 0.15%. The filtrate + the first washing solution + the second washing solution are mixed and then impurities are removed (dealuminization and calcium removal, aluminum removal with sodium silicate, calcium removal with sodium carbonate, and aluminum-calcium impurity removal agent is added according to the theoretical amount based on the detection value of the filtrate). The low-concentration sodium hydroxide solution after impurities removal is pumped to the evaporation concentration system to evaporate into a 20% sodium hydroxide solution, and the distilled water is returned to the pure water tank for standby use.

[0069] (1-2) adding concentrated sulfuric acid and water to the phosphate calcium compound for reaction, and performing post-treatment I to obtain a phosphoric acid solution;

[0070] Add concentrated sulfuric acid and water to the phosphate calcium compound obtained after calcification to react and obtain a phosphoric acid solution. In terms of mass ratio, iron phosphate: concentrated sulfuric acid: water = 1:1:4, the reaction temperature is 80°C, and the reaction time is 3 hours. The post-treatment I includes filtration, hot water washing, desulfurization, impurity removal, resin column filtration, and activated carbon decolorization.

[0071] After the reaction is completed, filter and wash with hot water to obtain filter cake, filtrate and washing liquid. Wash with 90℃ hot water for 5 times until the phosphorus content of the filter cake is less than 0.5%. The filtrate and washing liquid are combined and then desulfurized, impurity removed, filtered by resin column, and decolorized with activated carbon to obtain phosphoric acid solution.

[0072] The specific process of desulfurization is: add barium carbonate until no more bubbles are generated, heat to boiling state for 60 minutes, then filter press and wash three times to obtain desulfurization filtrate.

[0073] The specific process of impurity removal is: add oxalic acid to the desulfurization filtrate, heat to 60°C for reaction for 3 hours, and impurities such as iron, magnesium, aluminum, and calcium react with oxalic acid to form precipitates. After the reaction is completed, filter press and wash three times with water to obtain impurity-removed filtrate and water washing liquid.

[0074] The specific process of resin column filtration is: the impurity removal filtrate and the first water washing liquid are mixed and evaporated to 25% concentration, and then filtered through a 5-stage resin column to remove monovalent and divalent metal ions, and reduce sodium potassium ions and divalent metal ions to less than 0.005%, and obtain the resin column filtration filtrate. The resin used is T-42H resin.

[0075] The filtrate from the resin column is decolorized with activated carbon to obtain a phosphoric acid solution, which is pumped to a phosphoric acid storage tank for standby use.

[0076] Example 2 Preparation of phosphoric acid solution using phosphorus-containing calcium compounds as raw materials

[0077] The process for preparing phosphoric acid solution is:

[0078] (1-1) Phosphorus-calcium compounds are leached with alkali and calcified to obtain phosphorus-calcium compounds and calcium-iron slag;

[0079] The specific process of alkali leaching is: mixing phosphorus-containing solid waste with liquid alkali for reaction. During the alkali leaching process, the phosphorus-containing calcium compound: liquid alkali = 1:9 in terms of mass ratio; the liquid alkali is a sodium hydroxide aqueous solution with a mass fraction of 15%; the temperature of alkali leaching is 60°C, and the alkali leaching time is 3h. After the alkali leaching is completed, filter pressing and hot water washing are performed to obtain filter cake, filtrate and washing liquid. Use 90°C hot water to wash four times, and the sodium content in the filter cake after washing must be less than 0.05%. Use the last two washing liquid for the first washing, the last three washing liquid for the second washing, clean water for the third washing, and clean water for the fourth washing. The main components of the filtrate and washing liquid, especially the first washing liquid, are sodium phosphate, and the filter cake mainly becomes calcium hydroxide, magnesium hydroxide, and iron hydroxide, which is called calcium iron slag.

[0080] The filtrate and the first washing liquid obtained from the alkaline leaching are decolorized by activated carbon adsorption to obtain a transparent and colorless decolorized sodium phosphate solution, which enters the calcification process.

[0081] The specific process of calcification is: add calcium hydroxide (calcium carbonate content <0.5%, pH of 10 grams of calcium hydroxide dissolved in 200 grams of water cannot be lower than 12) to the decolorized sodium phosphate solution, react at 20°C for 0.5h, filter, wash with hot water, and obtain filter cake, filtrate and washing liquid. In terms of mass ratio, sodium phosphate solution: calcium hydroxide = 1: 0.095. The reaction in this process is that sodium phosphate reacts with calcium hydroxide to generate calcium phosphate, monocalcium phosphate and sodium hydroxide. The filter cake is a calcium phosphate compound (a mixture of calcium phosphate and monocalcium phosphate), and the main component of the filtrate and washing liquid is sodium hydroxide.

[0082] During the calcification process, the mixture is washed with hot water for 7 times (the first washing is done with the last three washing solutions, the second washing is done with the last four washing solutions, the third washing is done with the last five washing solutions, the fourth washing is done with the last six washing solutions, the fifth washing is done with the last six washing solutions, and the sixth and seventh washings are done with clean water) until the sodium hydroxide content is less than 0.15%. The filtrate + the first washing solution + the second washing solution are mixed and then impurities are removed (dealuminization and calcium removal, aluminum removal with sodium silicate, calcium removal with sodium carbonate, and aluminum-calcium impurity removal agent is added according to the theoretical amount based on the detection value of the filtrate). The low-concentration sodium hydroxide solution after impurities removal is pumped to the evaporation concentration system to evaporate into a 20% sodium hydroxide solution, and the distilled water is returned to the pure water tank for standby use.

[0083] (1-2) adding concentrated sulfuric acid and water to the phosphate calcium compound for reaction, and performing post-treatment I to obtain a phosphoric acid solution;

[0084] Add concentrated sulfuric acid and water to the phosphate calcium compound obtained after calcification to react and obtain phosphoric acid. In terms of mass ratio, phosphorus-containing solid waste: concentrated sulfuric acid: water = 1:1.2:6, the reaction temperature is 150°C, and the reaction time is 1h. The post-treatment I includes filtration, hot water washing, desulfurization, impurity removal, resin column filtration, and activated carbon decolorization.

[0085] After the reaction is completed, the mixture is filtered and washed with hot water to obtain a filter cake, a filtrate and a washing liquid. The filter cake is washed with hot water at 90°C for 3 times until the phosphorus content of the filter cake is less than 0.5%. The filtrate and the washing liquid are combined and then subjected to desulfurization, impurity removal, resin column filtration, and activated carbon decolorization in sequence to obtain a phosphoric acid solution, and the process is the same as in Example 1.

[0086] Example 3 Preparation of ferric phosphate using ferrophosphorus slag and phosphoric acid solution as raw materials

[0087] The specific process of preparing iron phosphate is:

[0088] (2-1) reacting ferrophosphorus slag with iron powder and phosphoric acid solution, and performing post-treatment II to obtain ferrophosphorus liquid and carbon slag;

[0089] In terms of mass ratio, ferrophosphorus slag: iron powder: phosphoric acid solution = 1: 0.04: 5, and the mass fraction of phosphoric acid solution is 20%. The reaction time is 60 minutes, the carbon slag is separated by filtration, and the carbon slag is washed twice with 90°C hot water. The washing liquid is added to the filtrate. The main components of the filtrate are ferrous dihydrogen phosphate and ferrous dihydrogen phosphate, which is called crude ferrophosphorus liquid. The addition of iron powder also inhibits the leaching of aluminum.

[0090] The post-treatment II includes fluoride impurity removal, sulfide impurity removal, and resin adsorption of sodium and potassium ions.

[0091] The specific process of fluoride impurity removal is: detecting the aluminum, calcium, magnesium and zinc content in the crude ferrophosphorus liquid, adding fluoride to the crude ferrophosphorus liquid, reacting for 30 minutes, heating to 98°C and maintaining for 1 hour. The fluoride is selected from potassium fluoride.

[0092] The specific process of sulfide impurity removal is: detecting the content of manganese, copper, nickel, chromium and lead in the liquid after fluoride impurity removal, adding sulfide, reacting for 30 minutes, heating to 98°C and maintaining for 1 hour. The sulfide is selected from sodium sulfide.

[0093] The specific process of resin adsorption of sodium and potassium ions is: the liquid after sulfide impurities are removed is passed through the resin to adsorb sodium and potassium ions until the sodium and potassium contents in the total liquid content are less than 50 ppm respectively, to obtain ferrophosphorus liquid, wherein the flow rate of the liquid passing through the resin is 0.5V liters / minute (V is the volume of the resin).

[0094] (2-2) detecting the iron-phosphorus ratio in the ferrophosphorus solution, adding phosphoric acid solution to a specified iron-phosphorus ratio, oxidizing, heating to 85° C. and keeping warm for precipitation after oxidation, filtering, washing with water until pH=3, obtaining dihydrate ferric phosphate, and performing post-treatment III to obtain anhydrous ferric phosphate;

[0095] Specifically, the iron ion and phosphorus ion content in the ferrophosphorus liquid is detected, phosphoric acid solution is added according to the iron-phosphorus ratio (iron: phosphorus) = 1:2.6, hydrogen peroxide (hydrogen peroxide concentration 30%) is added for oxidation, and after oxidation, it is heated to 85°C and kept warm for precipitation for 3 hours to obtain dihydrated ferrous phosphate slurry. The dihydrated ferrous phosphate slurry after the reaction is completed is filtered and washed with hot water to pH = 3. The filtrate and washing liquid are pumped to the phosphate concentrate pre-treatment process and then neutralized and used as recycled water. The amount of hydrogen peroxide is determined according to the ferrous ion, which is 1.2 times the molar amount of the ferrous ion.

[0096] The ferric phosphate dihydrate filter cloth is transported to the dryer and heated to 150℃ for drying. After drying and dehydration to a moisture content of 5%, it is pulverized with a pulverizer to 80-90 mesh and then put into an electrically heated rotary kiln for calcination. After calcination at 550℃ in the rotary kiln for 4 hours, anhydrous ferric phosphate is generated. The anhydrous ferric phosphate is extruded by double rollers, sieved, and ground by a jet mill to a particle size of less than 5 microns, mixed and demagnetized by electromagnetic, and then packed in ton bags.

[0097] Example 4 Preparation of iron phosphate using carbon iron slag and phosphoric acid solution as raw materials

[0098] The specific process of preparing iron phosphate is:

[0099] (2-1) reacting carbon iron slag with iron powder and phosphoric acid solution, and performing post-treatment II to obtain ferrophosphorus liquid and carbon slag;

[0100] In terms of mass ratio, iron slag: iron powder: phosphoric acid solution = 1: 0.01: 7, and the mass fraction of phosphoric acid solution is 35%. The reaction time is 30 minutes, and the carbon slag (mainly graphite) is separated by filter pressing, and the carbon slag is washed twice with 90°C hot water, and the washing liquid is added to the filtrate. The main components of the filtrate are ferrous dihydrogen phosphate and ferrous dihydrogen phosphate, which is called crude ferrophosphorus liquid.

[0101] The post-processing II is the same as the post-processing II in Example 3.

[0102] (2-2) detecting the iron-phosphorus ratio in the ferrophosphorus solution, adding phosphoric acid solution to a specified iron-phosphorus ratio, oxidizing, heating to 95° C. and keeping warm for precipitation after oxidation, filtering, washing with water until pH=4, obtaining dihydrated ferric phosphate, and performing post-treatment III to obtain anhydrous ferric phosphate;

[0103] Specifically, the iron ion and phosphorus ion content in the ferrophosphorus liquid is detected, and phosphoric acid solution is added according to the iron-phosphorus ratio (iron: phosphorus) = 1:3.0. After adjusting the iron-phosphorus ratio, hydrogen peroxide (hydrogen peroxide concentration 30%) is added, and the oxidation is completed, heated to 95°C and kept warm for precipitation for 3 hours to obtain a nearly white or pink dihydrate ferric phosphate slurry. The dihydrate ferric phosphate slurry after the reaction is completed is filtered and washed with hot water to pH = 4. The filtrate and washing liquid are pumped to the phosphate concentrate pre-treatment process and then neutralized and used as recycled water. The amount of hydrogen peroxide is determined according to the ferrous ion, which is 1.5 times the molar amount of the ferrous ion.

[0104] The ferric phosphate dihydrate filter cloth is transported to the dryer and heated to 150℃ for drying. After drying and dehydration to a moisture content of 10%, it is pulverized with a pulverizer to 80-100 mesh and then put into an electrically heated rotary kiln for calcination. After calcination at 650℃ in the rotary kiln for 3 hours, anhydrous ferric phosphate is generated. The anhydrous ferric phosphate is extruded by double rollers, sieved, and ground by a jet mill to a particle size of less than 5 microns, mixed batched, and electromagnetically demagnetized before packaging in ton bags.

[0105] Example 5 Preparation of ferric phosphate using calcium iron slag and ammonia water as raw materials

[0106] The specific process of preparing iron phosphate is:

[0107] (3-1) The calcium iron slag is reacted with concentrated sulfuric acid, filtered and washed with water to obtain a filter cake and a filtrate. The main component of the filter cake is calcium sulfate dihydrate or graphite, and the main component of the filtrate is ferric sulfate or ferric sulfate and magnesium sulfate, that is, a solution containing ferric sulfate. In terms of mass ratio, the calcium iron slag: concentrated sulfuric acid = 100:200; the reaction time is 30 minutes.

[0108] (3-2) adding iron powder to a solution containing ferric sulfate to react, filtering, and performing post-treatment IV to obtain a ferrous sulfate solution;

[0109] The amount of iron powder used is based on the Fe 3+ 、Al 3+ Mg 2+ Just wait to determine the amount.

[0110] The post-treatment IV process is the same as the post-treatment II in Example 3.

[0111] (3-3) Mix ferrous sulfate solution and phosphoric acid solution to a specified iron-phosphorus ratio, heat to 75° C., aerate, add 7.5% by mass of hydrogen peroxide to complete oxidation, detect the iron-phosphorus ratio, adjust the pH to 1.7, heat to 90° C. for reaction for 3 hours, filter press, and wash with hot water to obtain a phosphorus-iron complex.

[0112] Specifically, the phosphorus content in the phosphoric acid solution and the iron content in the ferrous sulfate solution are detected respectively, and the iron-phosphorus ratio (0.971) of the ferric phosphate is generated as required (the calculation formula X=iron / phosphorus*0.5545), the phosphoric acid solution and the ferrous sulfate solution are respectively measured, and the phosphoric acid solution and the ferrous sulfate solution are simultaneously added to the ferrous phosphate synthesis reactor in the same proportion by using an electric valve PID control according to the ratio between the weighing values;

[0113] After the addition is completed, the solution is stirred for reaction for 30 minutes and the iron-phosphorus ratio is tested. If the iron-phosphorus ratio does not meet the requirements, the iron-phosphorus ratio is adjusted with diammonium phosphate solution. After the adjustment is completed, it is heated to 75°C. After the temperature is reached, the heating is maintained and the aeration fan (500 cubic meters / hour) is turned on for aeration for 3 hours to obtain a trivalent iron solution. After the aeration is completed, a small amount of 7.5% hydrogen peroxide is added to finish the oxidation. After the final oxidation is completed, the iron-phosphorus ratio of the solution is tested. If the iron-phosphorus ratio does not meet the requirements, phosphoric acid is used for preparation. The solution with the secondary adjustment of the iron-phosphorus ratio is adjusted to a pH of 1.7 with ammonia water. After the addition of ammonia water is completed, it is heated to 95°C and reacted for 3 hours to obtain a phosphorus-iron complex. Press filter and wash with 80°C hot water 5 times, wash until the sulfate and ammonia content is less than 0.001%, and the washing liquid is directly pumped to the ammonia synthesis system for the preparation of ammonia water.

[0114] (3-4) The ferrophosphorus complex is aged and subjected to post-treatment V to obtain anhydrous ferric phosphate;

[0115] The post-treatment V includes filtration, washing, drying, calcination and the like.

[0116] The ferrophosphorus complex filter cake was placed in a 10% phosphoric acid solution and aged for 3 hours, filtered and washed with 80°C hot water. The filtrate was aged once and then passed through a phosphoric acid resin column to remove impurities and then pumped to the ferrophosphorus slag acidification process for standby use. After that, all the washing liquid was collected with calcium hydroxide as dicalcium phosphate and returned to the phosphoric acid preparation link.

[0117] The aged filter cake is conveyed to the flash evaporator for drying and powdering at 100℃. The dry ferric phosphate dihydrate powder is conveyed to the rotary kiln for electric heating and calcined at 550℃ for 3 hours to produce anhydrous ferric phosphate. The anhydrous ferric phosphate is ground, screened and demagnetized before being packed in ton bags.

[0118] Example 6 Preparation of ferric phosphate using carbon iron slag and ammonia water as raw materials

[0119] The specific process of preparing iron phosphate is:

[0120] (3-1) The carbon iron slag is reacted with concentrated sulfuric acid, filtered and washed with water to obtain a filter cake and a filtrate. The main component of the filter cake is calcium sulfate dihydrate or graphite, and the main component of the filtrate is ferric sulfate or ferric sulfate and magnesium sulfate, that is, a solution containing ferric sulfate. In terms of mass ratio, the carbon iron slag: concentrated sulfuric acid = 100:120; the reaction time is 60 minutes.

[0121] (3-2) adding iron powder to a solution containing ferric sulfate to react, filtering, and performing post-treatment IV to obtain a ferrous sulfate solution;

[0122] The amount of iron powder used is based on the Fe 3+ 、Al 3+ Mg 2+ Just wait to determine the amount.

[0123] The post-treatment IV process is the same as the post-treatment II in Example 3.

[0124] (3-3) Mix ferrous sulfate solution and phosphoric acid solution to a specified iron-phosphorus ratio, heat to 80° C., aerate, add 7.5% by mass of hydrogen peroxide to complete oxidation, detect the iron-phosphorus ratio, adjust the pH to 2.1, heat to 95° C. for reaction for 4 hours, filter press, and wash with hot water to obtain a phosphorus-iron complex.

[0125] Specifically, the phosphorus content in the phosphoric acid solution and the iron content in the ferrous sulfate solution are detected respectively, and the iron-phosphorus ratio (0.968) of the ferric phosphate is generated as required (the calculation formula X=iron / phosphorus*0.5545), the phosphoric acid solution and the ferrous sulfate solution are respectively measured, and the phosphoric acid solution and the ferrous sulfate solution are simultaneously added to the ferrous phosphate synthesis reactor in the same proportion by using an electric valve PID control according to the ratio between the weighing values;

[0126] After the addition is completed, the solution is stirred for 30 minutes and then the iron-phosphorus ratio is tested. If the iron-phosphorus ratio does not meet the requirements, the iron-phosphorus ratio is adjusted with diammonium phosphate solution. After the adjustment is completed, it is heated to 80°C. After the temperature is reached, the heating is maintained and the aeration fan (500 cubic meters / hour) is turned on for aeration for 2 hours to obtain a trivalent iron solution. After the aeration is completed, a small amount of 7.5% hydrogen peroxide is added to finish the oxidation. After the final oxidation is completed, the iron-phosphorus ratio of the solution is tested. If the iron-phosphorus ratio does not meet the requirements, phosphoric acid is used for preparation. The solution with the secondary adjustment of the iron-phosphorus ratio is adjusted to a pH of 2.1 with ammonia water. After the addition of ammonia water is completed, it is heated to 95°C and reacted for 3 hours to obtain a phosphorus-iron complex. Press filter and wash with hot water at 80°C 5 times, wash until the sulfate and ammonia content is less than 0.001%, and the washing liquid is directly pumped to the ammonia synthesis system for the preparation of ammonia water.

[0127] (3-4) The ferrophosphorus complex is aged and subjected to post-treatment V to obtain anhydrous ferric phosphate;

[0128] The post-treatment V includes filtration, washing, drying, calcination and the like.

[0129] The ferrophosphorus complex filter cake was placed in a 15% phosphoric acid solution and aged for 5 hours, filtered and washed with 80°C hot water. The filtrate was aged once and then passed through a phosphoric acid resin column to remove impurities and then pumped to the ferrophosphorus slag acidification process for standby use. After that, all the washing liquid was collected with calcium hydroxide as dicalcium phosphate and returned to the phosphoric acid preparation link.

[0130] The aged filter cake is transported to a flash evaporator for drying and powdering at 120°C. The dry ferric phosphate dihydrate powder is transported to a rotary kiln for electric heating and calcined at 700°C for 3 hours to produce anhydrous ferric phosphate. The anhydrous ferric phosphate is ground, screened, demagnetized and then packed in ton bags.

[0131] Example 7 Ammonia synthesis

[0132] Calcium hydroxide was added to the ammonium sulfate solution (filtrate + washing liquid) [derived from the filter press and hot water washing procedure of step (3-3) of Example 5 or 6)] until pH = 12, and the reaction was carried out at room temperature for 30 minutes and then the filter press was carried out. After the filter press, the filter cake was washed three times with water at room temperature. The filter cake was dihydrate gypsum. The filtrate + washing liquid was pumped into the ammonia still, which was a jacketed structure (201 stainless steel internal scraping anti-corrosion putty), and steam was passed into the ammonia still to heat it to 98 ° C, and ammonia water was stirred and heated. Ammonia gas passed through a 6-stage ammonia dissolving still (5 for 1 standby, and the standby was ammonia water cached and utilized after reaching the concentration) (jacket cooling, 201 stainless steel internal scraping anti-corrosion putty, maintaining the temperature at 25 ° C, and the circulating cooling water needed to be equipped with a cold water pool and a cooler), and the concentration of ammonia water was determined by density detection. After the ammonia water concentration reached 25%, the ammonia dissolving still was switched. Ammonia gas was used for ammonia water preparation after activated carbon adsorption, and the tailings were dihydrate gypsum.

Claims

1. A method for preparing ferric phosphate by recycling renewable phosphorus resources, comprising preparing a phosphoric acid solution and preparing ferric phosphate, characterized in that: The process of preparing phosphoric acid solution is: (1-1) Phosphorus-containing solid waste is subjected to alkali leaching and calcification to obtain phosphorus-calcium compounds and iron-containing waste slag; (1-2) adding concentrated sulfuric acid and water to the phosphate calcium compound to react to obtain a phosphoric acid solution; The phosphorus-containing solid waste is ferrophosphorus slag or calcium phosphate sludge.

2. The method for preparing ferric phosphate by recycling renewable phosphorus resources according to claim 1, characterized in that: In step (1-1), during the alkali leaching process, the mass ratio of phosphorus-containing solid waste: liquid alkali is 1: (6-9); the liquid alkali is a sodium hydroxide aqueous solution with a mass fraction of 15-25%; the alkali leaching temperature is 60-95°C, and the alkali leaching time is 0.5-3h.

3. The method for preparing ferric phosphate by recycling renewable phosphorus resources according to claim 1, characterized in that: In step (1-1), during the calcification process, the mass ratio of sodium phosphate solution to calcium hydroxide is 1: (0.055-0.095); the temperature is 20-25° C., and the calcification time is 0.5-1 h.

4. The method for preparing ferric phosphate by recycling renewable phosphorus resources according to claim 1, characterized in that: In step (1-2), the mass ratio of calcium phosphate compound: concentrated sulfuric acid: water is 1:1-1.2:4-6, the reaction temperature is 75-160°C, and the reaction time is 1-3h.

5. The method for preparing ferric phosphate by recycling renewable phosphorus resources according to claim 1, characterized in that: The process of preparing iron phosphate includes: (2-1) reacting the iron-containing slag with iron powder and phosphoric acid solution to obtain ferrophosphorus liquid and carbon slag; (2-2) detecting the iron-phosphorus ratio in the ferrophosphorus solution, adding phosphoric acid solution to a specified iron-phosphorus ratio, oxidizing, heating to 85° C.-95° C. and keeping warm for precipitation after oxidation, filtering, washing with water until the pH value is 3-4, and obtaining ferric phosphate dihydrate; The iron-containing slag is ferrophosphorus slag or the iron-containing waste slag in step (1-1).

6. The method for preparing ferric phosphate by recycling renewable phosphorus resources according to claim 5, characterized in that: In step (2-1), the mass ratio of iron slag: iron powder: phosphoric acid solution is 1: (0.01-0.04): 5-7, and the mass fraction of the phosphoric acid solution is 20%-25%.

7. The method for preparing ferric phosphate by recycling renewable phosphorus resources according to claim 4, characterized in that: In step (2-2), the iron-phosphorus ratio is iron:phosphorus=1:2.6-3.0; hydrogen peroxide is used for oxidation, and the mass fraction of hydrogen peroxide is 7.5-30%.

8. The method for preparing ferric phosphate by recycling renewable phosphorus resources according to claim 1, characterized in that: The process of preparing iron phosphate includes: (3-1) reacting the iron-containing slag with concentrated sulfuric acid, filtering by pressure, and washing with water to obtain a solution containing iron sulfate; (3-2) adding iron powder to a solution containing ferric sulfate to react, and filtering to obtain a ferrous sulfate solution; (3-3) mixing ferrous sulfate solution and phosphoric acid solution to a specified iron-phosphorus ratio, heating to 75-80° C., aerating, oxidizing, detecting the iron-phosphorus ratio, adjusting pH to 1.7-2.1, heating to 90-95° C. for reaction, filtering, washing with hot water, and obtaining a phosphorus-iron complex; (3-4) Aging of the ferrophosphorus complex to obtain ferric phosphate dihydrate; The iron-containing slag is the iron-containing waste slag in step (1-1).

9. The method for preparing ferric phosphate by recycling renewable phosphorus resources according to claim 7, characterized in that: In step (3-1), the mass ratio of iron-containing slag: concentrated sulfuric acid = 100: (120-200); the reaction time is 30-60 min.

10. The method for preparing ferric phosphate by recycling renewable phosphorus resources according to claim 7, characterized in that: In step (3-4), the ferrophosphorus complex filter cake is placed in a 10%-15% phosphoric acid solution and aged for 3-5 hours.

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