Method for preparing ammonium dihydrogen phosphate by recovering phosphorus element based on ferrophosphorus waste residues

Abstract

The invention discloses a method for preparing ammonium dihydrogen phosphate by recovering phosphorus element on the basis of iron phosphate waste residue, which comprises the following steps of: promoting ferric iron in the iron phosphate waste residue to be continuously leached and reduced into zero-valent iron by adopting the synergistic effect of acid leaching and electrochemistry, further realizing the recovery and separation of iron and phosphorus, and reacting the separated phosphate radical with ammonia water to prepare the ammonium dihydrogen phosphate. And a sodium thiosulfate solution is continuously added in the electrolysis process, so that secondary oxidation of ferrous ions in the process that ferric iron is reduced to zero-valent iron is inhibited, and forward reaction from ferric iron to zero-valent iron is promoted. According to the method, iron and phosphorus in the iron phosphate waste residues are recycled, the acid leaching and electrochemical combination mode is adopted, the acid and alkali amount of raw materials is saved, iron and phosphorus can be recycled and separated from the iron phosphate waste residues to a great extent, and ammonium dihydrogen phosphate meeting the battery grade standard is prepared; and the iron phosphate waste residues are recycled at low cost and high efficiency.

Description

Technical Field

[0001] The invention belongs to the field of ferric phosphate waste slag recovery and treatment, and in particular relates to a method for preparing diammonium phosphate based on recovering phosphorus element from ferrophosphate waste slag. Background Art

[0002] With the rapid development of the new energy industry, the demand for lithium iron phosphate batteries is increasing, and the amount of scrapped lithium iron phosphate batteries is also growing rapidly. Iron phosphate accounts for 40% of the cost of lithium iron phosphate cathode materials, and the phosphorus source accounts for 53% of the cost of iron phosphate. As the main phosphorus source, ammonium dihydrogen phosphate plays an important role in the preparation of lithium iron phosphate. Therefore, how to reasonably and environmentally friendly dispose of scrapped lithium iron phosphate batteries is a major problem that needs to be solved in the industry.

[0003] At present, the recycling of waste lithium iron phosphate batteries is mainly carried out by selectively recovering lithium metal by oxidative acid leaching after pretreatment. In this process, a large amount of iron phosphate waste residue will be generated. If it cannot be properly treated and utilized, the large amount of valuable metal phosphorus and iron contained in it will cause waste of resources and environmental pollution. Therefore, the effective recycling of iron phosphate waste residue generated during the recycling process has considerable economic and environmental benefits.

[0004] In the prior art, for example, the patent with application number 2018102803135 discloses a method for treating waste battery-grade iron phosphate. The method collects the iron phosphate waste, adds sulfuric acid to wash, and then filters it. After the filter residue is dried, it is passed through an electromagnet to remove magnetic foreign matter, sieved, and the screened material is mixed with a dispersant solution, sand-milled, and then the slurry is released; the slurry is added with ammonia water for precipitation conversion to obtain iron hydroxide particles; hydrazine hydrate and high-pressure hydrogen are used for reduction to obtain nano iron powder, and the filtrate obtained by precipitation conversion is vacuum concentrated and crystallized to obtain battery-grade ammonium monohydrogen phosphate crystals. This method requires a large amount of acid and alkali washing and is supplemented by high temperature and high pressure treatment. The preparation process is complicated and cumbersome, the preparation time is long, and the preparation cost is high.

[0005] Based on this, a method for recycling ferrophosphorus waste slag is studied, and ammonium dihydrogen phosphate is prepared based on this method, which saves a lot of acid and alkali consumption, has a simpler process, is safe and environmentally friendly, is more conducive to large-scale preparation, has high economic value, and the prepared ammonium dihydrogen phosphate is of high quality and meets the battery-grade ammonium dihydrogen phosphate standards, realizing the reuse of ferrophosphate waste slag. Summary of the invention

[0006] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for preparing diammonium phosphate by recovering phosphorus from ferrophosphate waste slag. This method not only saves the amount of acid and alkali in raw materials, but also can recover and separate iron and phosphorus from ferrophosphate waste slag to a great extent to prepare diammonium phosphate that meets battery-grade standards.

[0007] Technical solution: The method for preparing diammonium phosphate by recovering phosphorus from electrolytic ferric phosphate waste residues according to the present invention comprises the following steps:

[0008] (1) stirring and slurrying the ferric phosphate waste residue and water to obtain a slurry after slurrying the ferric phosphate waste residue;

[0009] (2) setting positive and negative electrode plates in the slurry, adding acid to form an electrolyte after power is applied, and the amount of acid added is 1 to 1.1 times the theoretical amount of dissolved iron phosphate;

[0010] (3) Under the conditions of step (2), when the conversion rate of divalent iron ions obtained by electrolysis reaches 40-60%, continuously adding sodium thiosulfate solution to the electrolyte until the conversion of elemental iron reaches more than 90%, then adding ammonia water to continue the reaction for 0.5-2h, and obtaining a slurry of a mixture of diammonium phosphate aqueous solution and filter residue; wherein the amount of sodium thiosulfate solution added is equal to the amount of water added in step (1);

[0011] (4) filtering the slurry to obtain an aqueous solution of ammonium dihydrogen phosphate, and then cooling, crystallizing, filtering, and drying to obtain ammonium dihydrogen phosphate.

[0012] The present invention adopts acid leaching combined with electrochemistry to recover the byproduct of the selective lithium extraction process of lithium iron phosphate from the iron phosphate waste residue to prepare battery-grade ammonium dihydrogen phosphate. The method firstly mixes the iron phosphate waste residue with water to form a slurry, and adds a small amount of acid solution to the slurry to form an electrolyte. Then, positive and negative electrode plates are arranged in the electrolyte and electricity is applied. Under the combined action of the acid solution and the electrochemical reaction, the trivalent iron in the iron phosphate waste residue is reduced to divalent iron and then to elemental iron (Fe 3+ to Fe 2+ At the same time, when the conversion rate of divalent iron in the electrolyte reaches 40-60%, sodium thiosulfate solution is added continuously to react with a part of the acid solution in the electrolyte system to generate sulfur dioxide gas, which continuously provides a reducing atmosphere for the reaction of the electrolyte system and weakens the oxidizing atmosphere to inhibit the oxygen generated on the anode plate from reacting with the Fe in the solution. 2+ Further oxidation generates trivalent iron, which promotes the forward reaction of reducing divalent iron to elemental iron at the cathode, avoiding the reverse reaction of divalent iron to trivalent iron, making it difficult to separate trivalent iron and phosphate ions in the electrolyte system. On the other hand, sulfur dioxide as a reducing agent can also react with Fe in the electrolyte system.3+ Or the oxidized Fe 2+ The Fe generated 3+ Oxidation-reduction reaction occurs to generate Fe 2+ , which in turn promotes the reduction of trivalent iron ions to divalent iron ions, and then to elemental iron by the cathode. The reaction equation involved is as follows:

[0013] anode:

[0014] 2H2O-4e - →O2↑+4H + ;

[0015] Fe 2+ -e - →Fe 3+ ;

[0016] cathode:

[0017] Fe 3+ +e - →Fe 2+ ;

[0018] Fe 2+ +2e - →Fe;

[0019] 2H + +2e - →H2↑;

[0020] Reduction to Fe 2+ :

[0021] 2FePO4+H2SO4+H2O→FeSO4+Fe(H2PO4)2+0.5O2↑;

[0022] Reduction to Fe element:

[0023] FeSO4+Fe(H2PO4)2+2NH3H2O→2Fe+2NH4H2PO4+(NH4)2SO4+0.5O2↑+H2O;

[0024] Na2S2O3+2H + =2Na + +S↓+SO2+H2O;

[0025] 2Fe 3+ +2H2O+SO2=2Fe 2+ +SO4 2- +4H + ;

[0026] Furthermore, in step (1) of the method, the solid-to-liquid ratio of the ferric phosphate waste residue to water is 1:(1-10), and the slurry stirring time is 0.2-3h.

[0027] Furthermore, in step (2) of the method, the number of groups of the anode and cathode electrode plates is 1 to 50, and the anode and cathode electrode plates are carbon electrodes, metal platinum electrodes, metal titanium electrodes, stainless steel electrodes, oxide ceramic electrodes or coated electrodes of the above electrodes, and the coated metal includes ruthenium, iridium, gold or silver.

[0028] Furthermore, in step (2) of the method, the voltage applied during the power-on is 0.5 to 30 V and the current is 0.1 to 30 A.

[0029] Furthermore, in step (2) of the method, the acid solution is one or more of formic acid, citric acid, phosphoric acid, nitric acid, sulfuric acid, and hydrochloric acid.

[0030] Furthermore, in steps (2) and (3) of the method, the electrolyte is continuously stirred at a stirring speed of 50 to 500 r / min during the electrolysis process.

[0031] Furthermore, in step (3) of the method, the reaction temperature of the electrolysis is between room temperature and 95°C, and the amount of ammonia water added is such that the pH value of the electrolyte reaches 3 to 8.

[0032] Furthermore, in step (2) of the method, a coating material is provided on the anode electrode plate of the cathode and anode electrode plates, and the coating material includes filter cloth, non-woven fabric, or carbon cloth.

[0033] Furthermore, in step (3) of the method, the concentration of the sodium thiosulfate solution is 1 to 10%.

[0034] Furthermore, in step (4) of the method, the cooling crystallization temperature is 0 to 26°C.

[0035] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are: the method recovers iron and phosphorus from ferric phosphate waste slag, and adopts a combination of acid leaching and electrochemistry, which not only saves the amount of acid and alkali in the raw materials, but also can recover and separate iron and phosphorus from the ferric phosphate waste slag to a great extent, so as to prepare ammonium dihydrogen phosphate that meets battery-grade standards, thereby realizing the reuse of ferric phosphate waste slag at low cost and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the process of the preparation method of the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described in detail below in conjunction with embodiments.

[0038] It should be noted that the raw materials used in the present invention can be purchased from the market. The conversion rate of divalent iron ions in the present invention is the amount of divalent iron ions in the electrolyte / total iron × 100%, wherein the divalent iron ions can be measured by a known titration method, and the total iron is calculated by the amount of raw material added; the conversion rate of elemental iron is elemental iron content / total iron × 100%, wherein the iron content in the electrolyte can be obtained by ICP detection.

[0039] In step (3) of the preparation method of the present invention, sodium thiosulfate is continuously added during the entire electrolysis reaction until the electrolysis reaction is completed. The flow rate of its addition can be continuously adjusted according to actual needs to ensure that the amount of sodium thiosulfate during the entire electrolysis reaction is consistent with the amount of water added in step (1).

[0040] In addition, the amount of acid solution added is 1 to 1.1 times the theoretical amount of acid solution for dissolving the ferric phosphate waste slag, which is calculated based on the assumption that all the ferric phosphate waste slag is ferric phosphate.

[0041] Example 1

[0042] This embodiment 1 is a method for preparing ammonium dihydrogen phosphate based on ferrophosphorus waste slag, and its process is as follows Figure 1 As shown, the following steps are included:

[0043] (1) Take 150 g of ferric phosphate waste residue, add 500 g of water and stir for 0.5 h to slurry, and obtain a slurry of ferric phosphate waste residue.

[0044] (2) Two groups of graphite anode plates wrapped with non-woven fabrics and two groups of stainless steel cathode plates without coating are placed in the slurry obtained in step (1) and energized. The voltage is set to 2.0 V, the current is 0.8 A, the stirring speed is 100 r / min, and 50 g of sulfuric acid is added to the slurry.

[0045] (3) subjecting the electrolyte obtained in step (2) to an electrolytic reaction at room temperature, and performing a titration determination of the amount of divalent iron ions in the electrolyte every half hour, and when the divalent iron ion conversion rate reaches about 50%, adding 500 g of a 5% sodium thiosulfate solution under the condition that the stirring speed and voltage are unchanged, and the sodium thiosulfate solution is continuously added during the electrolytic reaction until the electrolytic reaction is completed.

[0046] (4) After adding the sodium thiosulfate solution, the elemental iron content in the electrolyte was measured. When the elemental iron conversion rate in the electrolyte was measured to be about 90%, ammonia water was added to adjust the pH of the electrolyte to 3.5, and the reaction was continued for 1 hour to obtain a slurry of a mixture of diammonium phosphate aqueous solution and filter residue, and elemental iron was obtained at the cathode.

[0047] (5) filtering the diammonium phosphate aqueous solution and the filter residue obtained in step (4) to obtain a diammonium phosphate aqueous solution and a filter residue, respectively; cooling the obtained diammonium phosphate aqueous solution at 5° C. for crystallization, filtering to obtain diammonium phosphate crystals with a lower water content, and low-temperature drying the crystals to obtain battery-grade diammonium phosphate.

[0048] After calculation, the iron phosphorus recovery rate of this embodiment is shown in the following Table 1.

[0049] Table 1 Phosphorus iron recovery rate after electrolysis of Example 1

[0050] Fe content of ferrophosphorus slag 28.56％ Phosphorus content of ferrophosphorus slag 15.67％ Phosphorus recovery rate 94.37％ Iron recovery rate 89.19％

[0051] The content of each element in the prepared ammonium dihydrogen phosphate is shown in Table 2 below, and the content of each element in the prepared iron element after drying is shown in Table 3 below.

[0052] Table 2 Content of each element in the diammonium phosphate prepared in Example 1

[0053]

[0054] Table 3 Composition detection of elemental iron recovered in Example 1

[0055]

[0056] Comparative Example 1

[0057] Comparative Example 1 The basic steps are the same as those of Example 1, except that sodium thiosulfate solution is not added in step (3), and specifically comprises the following steps:

[0058] (1) Take 150 g of ferric phosphate waste residue, add 500 g of water and stir for 0.5 h to slurry, and obtain a slurry of ferric phosphate waste residue.

[0059] (2) placing a graphite plate anode wrapped with non-woven fabric and a stainless steel plate cathode without coating into the slurry obtained in step (1) and applying power to them, setting the voltage to 2.0 V, the current to 0.8 A, the stirring speed to 100 r / min in a constant voltage mode, and adding 50 g of sulfuric acid to the slurry.

[0060] (3) The electrolyte obtained in step (2) is reacted at room temperature, and the amount of divalent iron ions in the electrolyte is titrated every half an hour. When the conversion rate of divalent iron ions is detected to be 45%, ammonia water is added under the condition that the stirring speed and voltage are unchanged. The addition of ammonia water is stopped when the pH of the electrolyte is adjusted to 3.5, and the reaction is continued for 24 hours to obtain a mixed slurry of diammonium phosphate aqueous solution and filter residue, and iron element is obtained at the cathode.

[0061] (4) filtering the diammonium phosphate aqueous solution and the filter residue obtained in step (3) to obtain a diammonium phosphate aqueous solution and a filter residue, respectively; cooling the obtained diammonium phosphate aqueous solution at 5° C. for crystallization, filtering to obtain diammonium phosphate crystals with a lower water content, and low-temperature drying the crystals to obtain diammonium phosphate.

[0062] After calculation, the iron-phosphorus recovery rate of this embodiment is shown in Table 4 below.

[0063] Table 4 Iron and phosphorus recovery rate after electrolysis of comparative example 1

[0064] Fe content of ferrophosphorus slag 28.56％ Phosphorus content of ferrophosphorus slag 15.67％ Phosphorus recovery rate 82.23％ Iron recovery rate 63.89％

[0065] The content of each element in the prepared ammonium dihydrogen phosphate is shown in Table 5 below, and the content of each element in the prepared iron element after drying is shown in Table 6 below.

[0066] Table 5 Content of each element in the diammonium phosphate prepared in Comparative Example 1

[0067]

[0068] Table 6 Component detection of elemental iron recovered in Comparative Example 1

[0069]

[0070] Example 2

[0071] The difference between Example 2 and Example 1 is that the pH value of the electrolyte is different. The specific preparation method includes the following steps:

[0072] (1) Take 150 g of ferric phosphate waste slag, the component contents of which are shown in Table 1 below, add 500 g of water and stir for 0.5 h to slurry, to obtain a slurry of ferric phosphate waste slag.

[0073] (2) Two groups of graphite anode plates wrapped with non-woven fabrics and two groups of stainless steel cathode plates without coating are placed in the slurry obtained in step (1) and energized. The voltage is set to 2.0 V, the current is 0.8 A, the stirring speed is 100 r / min, and 50 g of sulfuric acid is added to the slurry.

[0074] (3) subjecting the electrolyte obtained in step (2) to an electrolytic reaction at room temperature, and performing a titration determination of the amount of divalent iron ions in the electrolyte every half hour, and when the divalent iron ion conversion rate reaches about 50%, adding 500 g of a 5% sodium thiosulfate solution while keeping the stirring speed and voltage unchanged, and continuously adding the sodium thiosulfate solution during the electrolytic reaction.

[0075] (4) After adding the sodium thiosulfate solution, the elemental iron content in the electrolyte was measured. When the elemental iron conversion rate in the electrolyte was measured to be about 90%, ammonia water was added to adjust the pH of the electrolyte to 7, and the reaction was continued for 1 hour to obtain a slurry of a mixture of diammonium phosphate aqueous solution and filter residue, and elemental iron was obtained at the cathode.

[0076] (5) filtering the diammonium phosphate aqueous solution and the filter residue obtained in step (4) to obtain a diammonium phosphate aqueous solution and a filter residue, respectively; cooling the obtained diammonium phosphate aqueous solution at 5° C. for crystallization, filtering to obtain diammonium phosphate crystals with a lower water content, and low-temperature drying the crystals to obtain battery-grade diammonium phosphate.

[0077] After calculation, the iron-phosphorus recovery rate of this embodiment is shown in Table 7 below.

[0078] Table 7 Recovery of iron phosphorus after electrolysis of Example 2

[0079] Fe content of ferrophosphorus slag 28.56％ Phosphorus content of ferrophosphorus slag 15.67％ Phosphorus recovery rate 95.04％ Iron recovery rate 88.97％

[0080] The content of each element in the prepared ammonium dihydrogen phosphate is shown in Table 8 below, and the content of each element in the prepared iron element after drying is shown in Table 9 below.

[0081] Table 8 Content of each element in diammonium phosphate prepared in Example 2

[0082]

[0083]

[0084] Table 9 Composition detection of elemental iron recovered in Example 2

[0085]

[0086] Example 3

[0087] The specific preparation methods of this embodiment are basically the same as those of embodiment 1, except that in this embodiment, the pH value of the electrolyte in step (3) is 8.

[0088] After calculation, the iron-phosphorus recovery rate of this embodiment is shown in Table 10 below.

[0089] Table 10 Recovery of iron phosphorus after electrolysis of Example 3

[0090] Fe content of ferrophosphorus slag 28.56％ Phosphorus content of ferrophosphorus slag 15.67％ Phosphorus recovery rate 94.96％ Iron recovery rate 89.03％

[0091] The content of each element in the prepared ammonium dihydrogen phosphate is shown in Table 11 below, and the content of each element in the prepared iron element after drying is shown in Table 12 below.

[0092] Table 11 Content of each element in diammonium phosphate prepared in Example 3

[0093]

[0094]

[0095] Table 12 Composition detection of elemental iron recovered in Example 3

[0096]

[0097] Example 4

[0098] The method for preparing ammonium dihydrogen phosphate based on ferrophosphorus waste slag in Example 4 comprises the following steps:

[0099] (1) Take 1500 g of ferric phosphate waste residue, add 5000 g of water and stir for 0.5 h to slurry, and obtain a slurry of ferric phosphate waste residue.

[0100] (2) Place two groups of graphite anode plates that are not wrapped with non-woven fabrics and two groups of graphite cathode plates that are not coated into the slurry obtained in step (1) and energize them. Use a constant voltage mode to set the voltage to 3.0 V, the current to 1.2 A, the stirring speed to 200 r / min, and add 500 g of sulfuric acid to the slurry.

[0101] (3) subjecting the electrolyte obtained in step (2) to an electrolytic reaction at room temperature, and performing a titration determination of the amount of divalent iron ions in the electrolyte every half hour, and when the divalent iron ion conversion rate reaches about 40%, adding 5000 g of a sodium thiosulfate solution with a concentration of 8% under the condition that the stirring speed and voltage are unchanged, and the sodium thiosulfate solution is continuously added during the electrolytic reaction until the electrolytic reaction is completed.

[0102] (4) After adding the sodium thiosulfate solution, the elemental iron content in the electrolyte was measured. When the elemental iron conversion rate in the electrolyte was measured to be about 90%, ammonia water was added to adjust the pH of the electrolyte to 3.7, and the reaction was continued for 1 hour to obtain a slurry of a mixture of diammonium phosphate aqueous solution and filter residue, and elemental iron was obtained at the cathode.

[0103] (5) filtering the diammonium phosphate aqueous solution and the filter residue obtained in step (4) to obtain a diammonium phosphate aqueous solution and a filter residue, respectively; cooling the obtained diammonium phosphate aqueous solution at 5° C. for crystallization, filtering to obtain diammonium phosphate crystals with a lower water content, and low-temperature drying the crystals to obtain battery-grade diammonium phosphate.

[0104] After calculation, the iron-phosphorus recovery rate of this embodiment is shown in Table 13 below.

[0105] Table 13 Recovery of iron phosphorus after electrolysis of Example 4

[0106]

[0107]

[0108] The content of each element in the prepared ammonium dihydrogen phosphate is shown in Table 14 below, and the content of each element in the prepared iron element after drying is shown in Table 15 below.

[0109] Table 14 Content of each element in diammonium phosphate prepared in Example 4

[0110]

[0111] Table 15 Composition detection of elemental iron recovered in Example 4

[0112]

[0113] Comparative Example 2

[0114] Comparative Example 2 The basic steps are the same as those of Example 4, except that sodium thiosulfate solution is not added in step (3), and specifically comprises the following steps:

[0115] (1) Take 1500 g of ferric phosphate waste residue, add 5000 g of water and stir for 0.5 h to slurry, then obtain slurry of ferric phosphate waste residue.

[0116] (2) Place an uncoated graphite plate anode and an uncoated graphite plate cathode into the slurry obtained in step (1) and energize them. Use a constant voltage mode to set the voltage to 3.0 V, the current to 1.2 A, the stirring speed to 200 r / min, and add 500 g of sulfuric acid to the slurry at this time.

[0117] (3) The electrolyte obtained in step (2) is reacted at room temperature, and the amount of divalent iron ions in the electrolyte is titrated every half an hour. When the conversion rate of divalent iron ions is detected to be about 40%, ammonia water is added under the condition that the stirring speed and voltage are unchanged. The addition of ammonia water is stopped when the pH value of the electrolyte is adjusted to 3.7. The reaction is continued for 30 hours to obtain a mixed slurry of diammonium phosphate aqueous solution and filter residue, and iron element is obtained at the cathode.

[0118] (4) filtering the diammonium phosphate aqueous solution and filter residue obtained in step (3) to obtain a diammonium phosphate aqueous solution and a filter residue, respectively.

[0119] (5) Cooling the ammonium dihydrogen phosphate aqueous solution obtained in step (4) at 5° C. for crystallization, filtering to obtain ammonium dihydrogen phosphate crystals with a lower water content, and low-temperature drying the crystals to obtain battery-grade ammonium dihydrogen phosphate.

[0120] After calculation, the iron-phosphorus recovery rate of this embodiment is shown in Table 16 below.

[0121] Table 16 Recovery of iron phosphorus after electrolysis of comparative example 2

[0122] Fe content of ferrophosphorus slag 29.34％ Phosphorus content of ferrophosphorus slag 15.98％ Phosphorus recovery rate 83.73％ Iron recovery rate 62.16％

[0123] The content of each element in the prepared ammonium dihydrogen phosphate is shown in Table 17 below, and the content of each element in the prepared iron element after drying is shown in Table 18 below.

[0124] Table 17 Content of each element in diammonium phosphate prepared in Comparative Example 2

[0125]

[0126] Table 18 Component detection of elemental iron recovered in Comparative Example 2

[0127]

[0128] Example 5

[0129] The method for preparing ammonium dihydrogen phosphate based on ferrophosphorus waste residue in Example 5 comprises the following steps:

[0130] (1) Take 1500 g of ferric phosphate waste residue, add 7150 g of water and stir for 0.5 h to slurry, and obtain slurry of ferric phosphate waste residue.

[0131] (2) Place two groups of graphite anode plates wrapped with polyester filter cloth and two groups of uncoated graphite cathode plates into the slurry obtained in step (1) and energize them. Use a constant voltage mode to set the voltage to 2.5 V, the current to 1.0 A, the stirring speed to 150 r / min, and add 185 g of hydrochloric acid to the slurry.

[0132] (3) subjecting the electrolyte obtained in step (2) to an electrolytic reaction at room temperature, and performing a titration determination of the amount of divalent iron ions in the electrolyte every half hour, and when the divalent iron ion conversion rate reaches about 60%, adding 7150 g of a 3% sodium thiosulfate solution under the condition that the stirring speed and voltage are unchanged, and the sodium thiosulfate solution is continuously added during the electrolytic reaction until the electrolytic reaction is completed.

[0133] (4) After adding the sodium thiosulfate solution, the elemental iron content in the electrolyte was measured. When the elemental iron conversion rate in the electrolyte was measured to be about 90%, ammonia water was added to adjust the pH of the electrolyte to 3, and the reaction was continued for 2 hours to obtain a slurry of a mixture of diammonium phosphate aqueous solution and filter residue, and elemental iron was obtained at the cathode.

[0134] (5) filtering the diammonium phosphate aqueous solution and the filter residue obtained in step (4) to obtain a diammonium phosphate aqueous solution and a filter residue, respectively; cooling the obtained diammonium phosphate aqueous solution at 5° C. for crystallization, filtering to obtain diammonium phosphate crystals with a lower water content, and low-temperature drying the crystals to obtain battery-grade diammonium phosphate.

[0135] After calculation, the iron-phosphorus recovery rate of this embodiment is shown in Table 19 below.

[0136] Table 19 Component contents of iron phosphate waste residue in Example 5 and recovery rate of iron and phosphorus after reaction

[0137] Fe content of ferrophosphorus slag 29.34％ Phosphorus content of ferrophosphorus slag 15.98％ Phosphorus recovery rate 94.88％ Iron recovery rate 89.01％

[0138] The content of each element in the prepared ammonium dihydrogen phosphate is shown in Table 20 below, and the content of each element in the prepared iron element after drying is shown in Table 21 below.

[0139] Table 20 Content of each element in diammonium phosphate prepared in Example 5

[0140]

[0141]

[0142] Table 21 Composition detection of elemental iron recovered in Example 5

[0143]

[0144] It can be seen from Tables 1 to 21 above that the recovery method of the present invention can achieve a phosphorus recovery rate of more than 94%, an iron recovery rate of more than 88%, effectively recover phosphorus and iron, and effectively improve the recovery rate. At the same time, it can be seen from Comparative Examples 1 and 2 that in the recovery process, if sodium thiosulfate is not added, the iron loss rate is directly reduced to about 60%. It can be seen that the addition of sodium thiosulfate can effectively inhibit the conversion of divalent iron to trivalent iron, but can further promote the conversion of divalent iron to monoester iron, thereby improving the conversion rate of iron. At the same time, it can also promote the effective recovery and extraction of phosphorus.

[0145] In addition to the above embodiments, the preparation process and process parameter range of the present invention can achieve the above-mentioned technical effect of improving the effective recovery and separation of iron and phosphorus, so no further experimental description is given. For example:

[0146] In step (1) of the preparation method of the present invention, the solid-liquid ratio of the ferric phosphate waste residue and water can be 1:(1-10), and the slurry stirring time can be 0.2-3h.

[0147] In step (2) of the preparation method, the number of groups of the positive and negative electrode plates can be 1 to 50, and the positive and negative electrode plates can be carbon electrodes, metal platinum electrodes, metal titanium electrodes, stainless steel electrodes, oxide ceramic electrodes or coated electrodes of the above electrodes, and the coated metal includes ruthenium, iridium, gold or silver. The anode electrode plate of the positive and negative electrode plates can be provided with a coating material, and the coating material includes filter cloth, non-woven fabric, or carbon cloth. The voltage applied by power-on can be 0.5 to 30V, and the current can be 0.1 to 30A. The acid solution can be one or more of formic acid, citric acid, phosphoric acid, nitric acid, sulfuric acid, and hydrochloric acid. The amount of acid solution added can be 1 to 1.1 times the theoretical calculated amount of dissolved iron phosphate waste slag.

[0148] In step (3) of the preparation method, the reaction temperature of the electrolysis can be room temperature to 95° C. The concentration of the sodium thiosulfate solution can be 1 to 10%. After adding ammonia water, the reaction is continued for 0.5 to 2 hours.

[0149] In step (4) of the preparation method, the cooling crystallization temperature can be 0 to 26°C.

Claims

1. A method for recovering phosphorus from ferrophosphorus waste to prepare diammonium phosphate, characterized in that: The following steps are involved: (1) stirring and slurrying the ferric phosphate waste residue and water to obtain a slurry after slurrying the ferric phosphate waste residue; (2) arranging positive and negative electrode plates in the slurry, adding acid solution to form an electrolyte after power is applied, and the amount of the acid solution added is 1 to 1.1 times the theoretical calculated amount of the dissolved iron phosphate waste residue; (3) Under the conditions of step (2), when the conversion rate of divalent iron ions obtained by electrolysis reaches 40-60%, continuously adding sodium thiosulfate solution to the electrolyte until the conversion of elemental iron reaches more than 90%, then adding ammonia water and continuing the reaction for 0.5-2h to obtain a slurry of a mixture of diammonium phosphate aqueous solution and filter residue; wherein the amount of sodium thiosulfate solution added is equal to the amount of water added in step (1); (4) filtering the slurry to obtain an aqueous solution of ammonium dihydrogen phosphate, and then cooling, crystallizing, filtering, and drying to obtain ammonium dihydrogen phosphate.

2. The method for preparing diammonium phosphate based on recovering phosphorus from ferrophosphorus waste slag according to claim 1, characterized in that: In step (1), the solid-liquid ratio of the ferric phosphate waste residue and water is 1:(1-10), and the slurry stirring time is 0.2-3h.

3. The method for preparing diammonium phosphate based on recovering phosphorus from ferrophosphorus waste slag according to claim 1, characterized in that: In step (2), the number of groups of the anode and cathode electrode plates is 1 to 50, and the anode and cathode electrode plates are carbon electrodes, metal platinum electrodes, metal titanium electrodes, stainless steel electrodes, oxide ceramic electrodes or coated electrodes of the above electrodes, and the coated metal includes ruthenium, iridium, gold or silver.

4. The method for preparing diammonium phosphate based on recovering phosphorus from ferrophosphorus waste according to claim 1, characterized in that: In step (2), the voltage applied during the power-on is 0.5 to 30 V, and the current is 0.1 to 30 A.

5. The method for preparing diammonium phosphate by recovering phosphorus from electrolytic ferrophosphorus waste slag according to claim 1, characterized in that: In step (2), the acid solution is one or more of formic acid, citric acid, phosphoric acid, nitric acid, sulfuric acid, and hydrochloric acid.

6. The method for preparing diammonium phosphate based on recovering phosphorus from ferrophosphorus waste slag according to claim 1, characterized in that: In steps (2) and (3), the electrolyte is continuously stirred at a stirring speed of 50 to 500 r / min during the electrolysis process.

7. The method for preparing diammonium phosphate based on recovering phosphorus from ferrophosphorus waste slag according to claim 1, characterized in that: In step (3), the reaction temperature of the electrolysis is from room temperature to 95°C, and the amount of ammonia water added is such that the pH value of the electrolyte reaches 3 to 8.

8. The method for preparing diammonium phosphate based on recovering phosphorus from ferrophosphorus waste slag according to claim 1, characterized in that: In step (2), a coating material is provided on the anode electrode plate of the cathode and anode electrode plates, and the coating material includes filter cloth, non-woven fabric, or carbon cloth.

9. The method for preparing diammonium phosphate based on recovering phosphorus from ferrophosphorus waste slag according to claim 1, characterized in that: In step (3), the concentration of the sodium thiosulfate solution is 1 to 10%.

10. The method for preparing diammonium phosphate based on recovering phosphorus from ferrophosphorus waste slag according to claim 1, characterized in that: In step (4), the cooling crystallization temperature is 0 to 26°C.

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