Process for recovering and preparing battery-grade iron phosphate from phosphorus iron slag

Abstract

The application provides a process for preparing battery-grade iron phosphate from phosphorus-iron slag, and belongs to the field of iron phosphate preparation, and specifically comprises the following steps: step 1, one-stage leaching to obtain one-stage leaching solution and one-stage leaching residue; step 2, two-stage leaching to obtain two-stage leaching solution and graphite residue; step 3, one-stage precipitation to obtain one-stage mother liquor and one-stage white residue; step 4, one-stage dissolution to obtain one-stage dissolution solution; step 5, two-stage precipitation or / and stirring washing of the two-stage white residue: two-stage precipitation to obtain two-stage mother liquor and two-stage white residue; stirring washing of the two-stage white residue to obtain post-stirring two-stage mother liquor and post-stirring two-stage white residue; step 6, two-stage dissolution to obtain refined iron phosphate solution; and step 7, iron phosphate synthesis to obtain anhydrous iron phosphate product. The iron phosphate prepared by the recycling process provided by the application has low impurity content, which is consistent with the impurity content of raw material prepared iron phosphate, and the process cost is low; meanwhile, the various indexes of the recycled iron phosphate are qualified, and the requirements for preparing high-capacity high-compaction lithium iron phosphate can be met.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of iron phosphate preparation, and particularly relates to a process for preparing battery-grade iron phosphate from phosphorus-iron slag. BACKGROUND

[0002] The large-scale application of lithium iron phosphate materials in the field of electrochemical energy storage will generate a large number of retired batteries. Recycling and re-preparing the batteries into lithium iron phosphate materials can not only realize the closed loop of the industrial chain, but also avoid environmental pollution caused by the retired batteries. Since the lithium iron phosphate positive material has a high requirement for the content of impurities, a wet recovery process with a high impurity removal depth has become the industry mainstream. Meanwhile, considering that the value of lithium is higher than that of phosphorus and iron, preferential lithium extraction can maximize the lithium recovery rate to ensure economic benefits. However, the phosphorus-iron slag after lithium extraction has a high content of impurities, which makes it difficult to recover phosphorus and iron. The main phase of the phosphorus-iron slag is FePO4, and the valuable element in the phosphorus-iron slag is phosphorus, with a content of 13-18%, which is equivalent to high-grade phosphate rock. In view of the actual situation that the phosphate rock grade in China is low and the phosphate resources are dependent on imports, it is of great significance to replace phosphate rock with phosphorus-iron slag to extract phosphorus. Therefore, developing a phosphorus-iron slag recovery process with cost advantages is a key link in the recovery of lithium iron phosphate.

[0003] The main challenge in the recovery and utilization of phosphorus-iron slag is how to effectively separate iron, aluminum, nickel, cobalt, manganese and lithium and the like from the phosphorus-iron slag while controlling the cost, especially the separation of aluminum and iron. Aluminum mainly comes from the aluminum foil current collector and the separator coating in the phosphorus-iron slag. If not completely separated, the aluminum will be mixed into the lithium iron phosphate product with the iron phosphate precursor, which may weaken the electrochemical performance of the regenerated lithium iron phosphate.

[0004] As for the influence of aluminum ions on lithium iron phosphate materials, researches have pointed out that aluminum ions can not only occupy the lithium site in lithium iron phosphate, but also occupy the iron site. A proper amount of aluminum ion doping can reduce the unit cell volume of lithium iron phosphate and shorten the lithium ion diffusion path, thereby improving the specific capacity and rate performance of the material. However, when the aluminum ion doping is excessive, the inert aluminum ions will reduce the specific capacity of the material.

[0005] Zhang et al. analyzed the existence form of aluminum ions in the synthesis process of the iron phosphate precursor and lithium iron phosphate through phase characterization and electrochemical tests, and clearly pointed out that aluminum ions cannot really be doped into the crystal lattice of lithium iron phosphate, but form inert aluminum phosphate with a trigonal system. This means that although the doping of aluminum ions does not directly affect the electrical performance of lithium iron phosphate, excessive aluminum ions will still reduce the overall performance of the material.

[0006] Under the background of increasingly fierce competition in the current lithium iron phosphate market, the quality requirements for lithium iron phosphate are becoming more and more strict. Therefore, for the recovered lithium iron phosphate, solving the problem of deep aluminum removal has become a technical difficulty that must be overcome before entering the market. In the phosphate system, the chemical properties of aluminum ions and trivalent iron ions are similar, making it difficult to directly achieve the requirements of iron phosphate product through conventional selective leaching or selective precipitation. CN116588909A proposes a method for preparing iron phosphate from lithium-extracted phosphorus iron slag. The method obtains a ferrous phosphate solution and a graphite slag by reducing leaching of the phosphorus iron slag, then adjusts the pH of the ferrous phosphate solution to remove aluminum and copper impurities to obtain a purified ferrous phosphate solution. After acidifying the purified solution with phosphoric acid and sulfuric acid, an oxidizing agent is added to synthesize iron phosphate. This type of reduction impurity removal-oxidation synthesis method has good impurity removal depth, but the use of a large amount of reducing agent and oxidizing agent can lead to high cost. In order to reduce the cost of the oxidizing agent, CN116581415B proposes a method for recovering lithium-extracted phosphorus iron slag and waste lithium cobalt oxide. The method first leaches the phosphorus iron slag with sodium hydroxide to obtain a sodium phosphate solution and carbon-containing iron hydroxide. The sodium phosphate solution is prepared into a phosphoric acid solution by freeze crystallization, and the carbon-containing iron hydroxide is reduced to iron powder by calcination. Further, the iron powder reacts with sulfuric acid to produce ferrous sulfate, and the ferrous sulfate is then calcined with lithium cobalt oxide to produce lithium sulfate, cobalt sulfate, and ferric oxide. This method uses lithium cobalt oxide to oxidize ferrous iron and graphite powder to reduce trivalent iron, saving the consumption of oxidizing agent and reducing agent. However, there are problems such as long process flow, high energy consumption for calcination reduction and freeze crystallization, and low product value. SUMMARY

[0007] To solve the above technical problems, the present application proposes a lithium-extracted phosphorus iron slag recovery process in a sulfuric acid system. The advantage of this process is that it can deeply remove aluminum ions from phosphorus iron slag through simple acid leaching and precipitation operations. At the same time, the process has low acid and alkali consumption. After introducing a cheap alkali source to replace traditional sodium / ammonium alkali, not only is there a cost advantage, but the "competition" effect of metal ions can also improve the separation efficiency of iron and aluminum. Finally, a refined phosphorus iron solution with good controllability is obtained, which can be used to prepare high-performance iron phosphate precursors, thus breaking through the key link of industrialized recovery and reconstruction of lithium iron phosphate from phosphorus iron slag. The specific process is as follows:

[0008] A process for recovering and preparing battery-grade iron phosphate from phosphorus iron slag, comprising the following steps:

[0009] Step 1, one-stage leaching: take the lithium-extracted phosphorous iron slag / phosphorous iron slag and mix with pure water to prepare a first slurry, and heat to 30-70℃, add sulfuric acid to the first slurry for acid leaching reaction, after 1-2h of reaction, filter to obtain a one-stage leaching solution and one-stage leaching residue;

[0010] Step 2, two-stage leaching: take the one-stage leaching residue above and mix with pure water to prepare a second slurry, and heat to 30-70℃, add concentrated sulfuric acid to the second slurry for acid leaching reaction, after 1-2h of reaction, filter to obtain a two-stage leaching solution and graphite residue;

[0011] Step 3, one-stage precipitation: heat the one-stage leaching solution of step 1 to 30-90℃, add ferrous sulfate and hydrogen peroxide to adjust the Fe / P molar ratio of the solution to 0.90-1.20, then add an alkali source slurry for precipitation reaction for 0.5-2.0h, then filter to obtain a one-stage mother liquor and one-stage white residue;

[0012] Step 4, one-stage dissolution: mix the one-stage white residue with pure water to prepare a third slurry, and heat to 30-90℃, add concentrated sulfuric acid to dissolve the one-stage white residue, control the pH value of the dissolution solution to 0.5-1.0, and after complete dissolution, obtain a one-stage dissolution solution;

[0013] Step 5, two-stage precipitation or / and two-stage white residue stirring washing:

[0014] Two-stage precipitation: heat the one-stage dissolution solution to 30-90℃, then add an alkali source slurry again, after 0.5-2.0h of reaction, filter to obtain a two-stage mother liquor and two-stage white residue;

[0015] Two-stage white residue stirring washing: take the two-stage white residue above and mix with pure water to prepare a fourth slurry, heat to 30-90℃ and add an eluent, adjust the pH value to 1.0-2.0 with sulfuric acid, react for 0.1-2.0h, and filter to obtain a two-stage mother liquor after stirring washing and a two-stage white residue after stirring washing;

[0016] Step 6, two-stage dissolution: dissolve the two-stage white residue after stirring washing in the two-stage leaching solution obtained in step 2, the reaction temperature is 30-90℃, the reaction time is 0.1-2.0h, adjust the density of the dissolution solution to 1.15-1.30g / mL by supplementing the two-stage white residue after stirring washing, and after passing, obtain a refined phosphorous iron solution by fine filtering;

[0017] Step 7, iron phosphate synthesis:

[0018] (1) add ferrous sulfate, hydrogen peroxide and pure water to the refined phosphorous iron solution to adjust the Fe / P molar ratio of the solution to 0.90-1.10 and the Fe concentration to 0.5-1.5M to obtain an adjusted solution;

[0019] (2) The adjusting liquid is heated to 30-90℃, and is put into the lye to react for 1.0-3.0h to generate iron phosphate precipitate, and the iron phosphate yellow material is obtained by filtration, and the iron phosphate yellow material is washed with pure water;

[0020] (3) The washed iron phosphate yellow material is put into pure water to make pulp into slurry, and 0.1-0.8 times of FePO4 molar amount of phosphoric acid is put in to carry out conversion reaction at 60-100℃ for 1.0-3.0h;

[0021] (4) The iron phosphate white material is filtered out, and is washed and dried to obtain iron phosphate dihydrate powder;

[0022] (5) The iron phosphate dihydrate powder is calcined at 550-650℃ for 1.0-5.0h to be dehydrated and crystallized into anhydrous iron phosphate product.

[0023] Further, in step 1, the solid content of the primary slurry adjusting liquid is 10-25%, and the amount of sulfuric acid added is 0.3-0.7 times the theoretical amount.

[0024] Further, in step 2, the solid content of the secondary slurry adjusting liquid is 10-25%, and the amount of sulfuric acid added is 0.8-1.2 times the theoretical amount.

[0025] Further, in step 3, the Fe / P molar ratio of the first leaching liquid is controlled in the range of 0.90-1.20, the alkali source is magnesium, calcium, manganese, nickel, iron oxide, hydroxide and carbonate, the concentration of the alkali source slurry is 5-25%, the feeding mode is single feeding (the first leaching liquid is used as the bottom layer, and the lye is fed into the low liquid) or simultaneous feeding (a small amount of the first leaching liquid is used as the bottom layer, and the first leaching liquid and the lye are simultaneously fed into the low liquid), and the reaction end point pH value is 1.5-2.5.

[0026] Further, in step 4, the liquid-solid ratio of the third slurry adjusting liquid is 1:1-10:1, and the pH value of the first dissolution liquid is 0.5-1.0.

[0027] Further, in step 5, during the secondary precipitation, the alkali source is magnesium, calcium, manganese, nickel, iron oxide, hydroxide and carbonate, the concentration of the alkali source slurry is 5-25%, the feeding mode is single feeding or simultaneous feeding, and the reaction end point pH value is 1.5-2.5.

[0028] Further, in step 5, during the stirring washing of the secondary precipitation white residue, the solid content of the fourth slurry adjusting liquid is 5-25%, the eluent is iron, calcium and magnesium sulfate or phosphate, and the amount of the eluent added is 0.1-5.0% of the mass of the fourth slurry adjusting liquid.

[0029] Further, in step 6, after dissolution, the pH value is 0.5-1.0, and the density of the refined phosphorus iron liquid is controlled in the range of 1.15-1.30 g / mL.

[0030] Further, in step 7, in step (2), the alkali liquor is one or more combinations of ammonia, sodium hydroxide, magnesium hydroxide, ammonium carbonate, sodium carbonate, magnesium carbonate, the amount of the alkali liquor added is adjusted to the pH value of the slurry to 1.6-2.2; the iron phosphate yellow material is washed with pure water until the conductivity of the washing liquid is 3500-4000us / m;

[0031] In step (3), the solid content of the slurry is 5-25%, and the slurry temperature is 70-100℃.

[0032] Further, in step 7, in step (3), the solid content of the slurry is 5-25%, and the slurry temperature is 70-100℃.

[0033] Compared with the prior art, the beneficial effects of the present application are:

[0034] 1、The process adopts multi-step impurity removal to separate impurity elements in the phosphorus iron slag, first, the impurities are preliminarily separated by staged leaching, and the impurities are leached into the first-stage leaching liquid, and the clean second-stage leaching liquid is obtained; secondly, in the precipitation process, the impurities are opened from the mother liquor by selectively precipitating iron phosphate, since the ksp of iron phosphate and aluminum phosphate is similar, the precipitation pH value of the two is close, and the local over-alkaline in the reaction process will increase the aluminum content in the iron phosphate slag; therefore, the present application uses weak base as a precipitant and changes the feeding mode to parallel feeding to maintain stable and uniform pH value in the precipitation reaction process, avoiding the local over-alkaline phenomenon leading to aluminum phosphate precipitation. At the same time, through the "competition effect" of ions, the cations compete with the dihydrogen phosphate, further reducing the aluminum ion precipitation rate. In addition, in the two-sedimentation and one-washing process, the present application converts the aluminum phosphate on the surface of the iron phosphate white slag into iron phosphate through the precipitation conversion reaction of the eluent, realizing the multiple deep removal of aluminum and other impurity ions. Finally, the impurities are deeply removed by the "two-sedimentation and one-washing" impurity removal method.

[0035] 2、The recovery process provided by the present application can prepare phosphorus iron slag with low impurity content, which can achieve the same impurity content as the raw material for preparing phosphorus iron, and the process cost is low, the comprehensive recovery cost of the phosphorus iron slag can be reduced to less than 8000 yuan / t FePO4, and the indicators of the recovered phosphorus iron meet the requirements for preparing high-capacity and high-compaction lithium iron phosphate.

[0036] 3、The present application effectively realizes the deep removal of aluminum ions in the phosphorus iron slag by two-stage leaching in the sulfuric acid system combined with multiple cycles of precipitation and dissolution, not only improves the removal efficiency of aluminum, but also ensures the purity of the phosphorus iron product, and meets the high-quality requirements of battery-grade phosphorus iron.

[0037] 4、The process does not need to reduce or high temperature roasting of phosphorus iron slag, only using conventional acid and base leaching precipitation reaction can deeply purify phosphorus iron slag, its equipment is simple, operability is strong, safety is high, and it is easy for industrial production.

[0038] 5、The process uses the way of segmented leaching and precipitation slag back to save the acid and alkali consumption of the whole process by using residual acid to dissolve amorphous iron phosphate.

[0039] 6、The process introduces crude alkali source instead of traditional sodium / ammonium alkali, which not only has cost advantage but also improves the iron and aluminum separation efficiency by using the "competition" effect of ions.

[0040] 7、The process has high phosphorus iron recovery rate, in the segmented precipitation process, most of the precipitation slag of the open circuit mother liquor can be dissolved and utilized in the system again, and the recovery rate of phosphorus iron elements is >95% without increasing the acid consumption. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 SEM image of regenerated iron phosphate prepared for example 1;

[0042] Figure 2 SEM image of lithium iron phosphate prepared from regenerated iron phosphate prepared for example 1. DETAILED DESCRIPTION

[0043] In the following examples of the present application, the lithium-extracted phosphorus iron slag is obtained from the black powder of waste lithium iron phosphate battery after oxidation and lithium extraction by hydrogen peroxide, and the solid content of the slag is 60%, and the composition is shown in Table 1:

[0044] Table 1 Composition of raw material phosphorus iron slag

[0045]

[0046] Example 1

[0047] (1) Take 1500g of lithium-extracted phosphorus iron slag, add 2100g of pure water and stir to pulp, then add 283.7g of concentrated sulfuric acid and react, the reaction temperature is 60℃, the reaction time is 2h, after the reaction is completed, filter to obtain a first leaching liquid and a first leaching residue, and then wash the first leaching residue with 2L of water and then rinse with 2L of water.

[0048] (2) Take 600g of the first leaching residue, add 840g of pure water and stir to pulp, then add 279.6g of concentrated sulfuric acid and react, the reaction temperature is 60℃, the reaction time is 2h, after the reaction is completed, filter to obtain a second leaching liquid and a graphite residue, and then rinse the graphite residue with 500mL of water.

[0049] (3) Take 0.75L of the first leaching solution into a 5L beaker, turn on the stirring motor, set the stirring speed to 300rpm, set the water bath temperature to 40°C, add 1.2M ferrous sulfate solution 0.325L, add 27.5% hydrogen peroxide 44.0mL, stir and react for 10min, set the flow rate of the first leaching solution to 37.5mL / min, continue to add 2.25L of the first leaching solution, at the same time, configure 20% magnesium oxide slurry as the alkali solution, the flow rate of the alkali solution is 10.7mL / min, and the alkali solution and the first leaching solution are added into the bottom solution, and the addition is continued for 60min, after which the alkali solution is continued to be added to adjust the pH of the slurry to 1.60. Filter the slurry to obtain a first white residue and a first mother liquor, and the first white residue is washed with 1L of water.

[0050] (4) Take 1250g of the first white residue and 1250g of pure water to slurry, adjust the pH to 0.8-1.0 by adding concentrated sulfuric acid to obtain a first dissolution solution;

[0051] (5) Take 2.0L of the first dissolution solution into a 3L beaker, turn on the stirring motor, set the stirring speed to 300rpm, set the water bath temperature to 40°C, configure 20% magnesium oxide slurry as the alkali solution, the flow rate of the alkali solution is 5.0mL / min, and the alkali solution is added into the first dissolution solution, the addition is continued for 60min, after which the alkali solution is continued to be added to adjust the pH of the slurry to 1.60. Filter the slurry to obtain a second white residue and a second mother liquor, and the second white residue is washed with 1L of water.

[0052] (6) Mix 1000g of pure water with 135mL of the second leaching solution, heat to 40°C, then add 1000g of the second white residue, stir and react for 1h, filter the slurry to obtain a washed second white residue and a second mother liquor, and the washed second white residue is washed with 1L of water.

[0053] (7) Mix 1000g of the washed second white residue with 1690mL of the second leaching solution, heat to 40°C, and react for 1h, the iron phosphate white residue is completely dissolved to obtain a refined phosphorus iron liquid.

[0054] (8) Take 2L of the refined phosphorus iron liquid, adjust Fe / P=1.000 with ferrous sulfate and hydrogen peroxide, and dilute to 0.8M iron concentration, after completion, heat to 40°C, control the feeding time to be 60min, add 20% ammonia water, after the feeding is completed, react for 1h and age for 1h, filter out the yellow phosphorus iron material, wash with pure water to a conductivity of 3500-4000μs / m; then the yellow material is added into pure water to make a slurry, control the slurry solid content to be 20%, add 0.6 times the molar amount of FePO4 of phosphoric acid, heat to 95°C, react for 3h and age for 1h, then filter to obtain a white phosphorus iron material, wash with pure water to a conductivity of 200-400μs / m; dry the white material, place it in a muffle furnace and calcine at 570°C for 4h to obtain anhydrous phosphorus iron.

[0055] The physical indicators and morphology of the anhydrous iron phosphate prepared in this example are shown in Table 2, Figure 1

[0056] Table 2 Physical indicators of anhydrous iron phosphate

[0057]

[0058] Further, the lithium iron phosphate prepared from the anhydrous iron phosphate has the indicators and morphology shown in Table 3, Figure 2

[0059] Table 3 Compaction density and electrical performance indicators of regenerated lithium iron phosphate

[0060]

[0061] As can be seen from Tables 2, 3, Figure 1 , Figure 2 the iron phosphate prepared by the recycling process meets the battery-grade iron phosphate raw material standard, and the lithium iron phosphate prepared from the iron phosphate exhibits high levels in capacity and compaction.

[0062] Example 2

[0063] The difference between this example and Example 1 is that the secondary precipitation process is cancelled, and the technical solution of this example is as follows:

[0064] (1) Take 1500g of lithium-extracted iron phosphate slag, add 2100g of pure water to stir and beat the pulp, then add 283.7g of concentrated sulfuric acid to react, the reaction temperature is 60℃, the reaction time is 2h, after the reaction is completed, filter to obtain a first-stage leaching liquid and a first-stage leaching residue, and then wash the first-stage leaching residue with 2L of water and then rinse it with 2L of water.

[0065] (2) Take 600g of the first-stage leaching residue, add 840g of pure water to stir and beat the pulp, then add 279.6g of concentrated sulfuric acid to react, the reaction temperature is 60℃, the reaction time is 2h, after the reaction is completed, filter to obtain a second-stage leaching liquid and a graphite residue, and then rinse the graphite residue with 500mL of water.

[0066] ​​(3) Take 0.75L of the first leaching solution into a 5L beaker, turn on the stirring motor, the stirring speed is 300rpm, set the water bath temperature to 40℃. Add 1.2M ferrous sulfate solution 0.325L, add 27.5% hydrogen peroxide 44.0mL, stir and react for 10min. Set the flow rate of the first leaching solution to 37.5mL / min, continue to add 2.25L of the first leaching solution, at the same time, configure 20% magnesium oxide slurry as the alkali solution, the flow rate of the alkali solution is 10.7mL / min, and the alkali solution and the first leaching solution are added into the bottom solution, and the addition is continued for 60min, after the end, continue to add the alkali solution, and adjust the pH of the slurry to 1.60. Filter the slurry to obtain a first sediment white residue and a first sediment mother liquor, wherein the first sediment white residue is rinsed with 1L of water.

[0067] (4) Take 1250g of the first sediment white residue and 1250g of pure water to slurry, and adjust the pH to 0.8-1.0 by adding concentrated sulfuric acid to obtain a first dissolution solution;

[0068] (5) Take 1000g of pure water and mix with 135mL of the first leaching solution, heat to 40℃, then add 1000g of the first sediment white residue, stir and react for 1h, filter the slurry to obtain a first sediment white residue after stirring and washing and a first sediment mother liquor, wherein the first sediment white residue after stirring and washing is rinsed with 1L of water.

[0069] (6) Take 1000g of the first sediment white residue after stirring and washing and mix with 1690mL of the second leaching solution, heat to 40℃, and react for 1h, the iron phosphate white residue is completely dissolved, to obtain a refined phosphorus iron liquid.

[0070] (7) Take 2L of the refined phosphorus iron liquid, adjust the Fe / P to 1.000 with ferrous sulfate and hydrogen peroxide, and dilute to 0.8M iron concentration, after completion, heat to 40℃, control the feeding time to be 60min, add 20% ammonia water, after the end of feeding, react for 1h and age for 1h, filter out the yellow phosphorus iron material, and wash the yellow phosphorus iron material with pure water until the conductivity is 3500-4000μs / m; then the yellow material is put into pure water to make a slurry, the solid content of the slurry is controlled to be 20%, 0.6 times the molar amount of FePO4 of phosphoric acid is added, heated to 95℃, reacted for 3h and aged for 1h, then filtered to obtain a white phosphorus iron material, and the white phosphorus iron material is washed with pure water until the conductivity is 200-400μs / m; the white material is dried, then placed in a muffle furnace and calcined at 570℃ for 4h to obtain anhydrous phosphorus iron.

[0071] The impurity content of the anhydrous phosphorus iron prepared in this example is compared with the impurity content of the anhydrous phosphorus iron prepared in example 1, to illustrate that the secondary precipitation process of the process can be increased or cancelled according to the required impurity removal depth, and the results are shown in table 4.

[0072] Table 4 Influence of secondary precipitation on the impurity content of regenerated phosphorus iron

[0073]

[0074] As can be seen from Table 4, the prepared iron phosphate recovered by the recovery process provided in Example 2 has no obvious difference in Cu, Ni, Co, Mn, Ti content from Example 1, and the increase of secondary precipitation mainly realizes the deep removal of Al impurities, both of which meet the battery-grade iron phosphate raw material standard, indicating that the secondary precipitation process of the process can be increased or cancelled according to the Al content requirement of the product.

[0075] Example 3

[0076] The difference between this example and Example 1 is that the stirring washing process of the secondary white residue is cancelled, which is as follows:

[0077] (1) Take 1500g lithium-extracted iron phosphate residue, add 2100g pure water to stir and beat, then add 283.7g concentrated sulfuric acid to react, the reaction temperature is 60℃, the reaction time is 2h, after the reaction is completed, filter to obtain a first leaching liquid and a first leaching residue, and then wash the first leaching residue with 2L water and then rinse it with 2L water.

[0078] (2) Take 600g of the first leaching residue, add 840g of pure water to stir and beat, then add 279.6g of concentrated sulfuric acid to react, the reaction temperature is 60℃, the reaction time is 2h, after the reaction is completed, filter to obtain a second leaching liquid and a graphite residue, and then rinse the graphite residue with 500mL of water.

[0079] (3) Take 0.75L of the first leaching liquid and pour it into a 5L beaker, turn on the stirring motor, the stirring speed is 300rpm, and the water bath temperature is set to 40℃. Add 1.2M ferrous sulfate solution 0.325L, add 27.5% hydrogen peroxide 44.0mL, and stir and react for 10min. Set the flow rate of the first leaching liquid to 37.5mL / min, continue to pour in 2.25L of the first leaching liquid, and at the same time, configure 20% magnesium oxide slurry as the alkali liquid, the flow rate of the alkali liquid is 10.7mL / min, and pour it into the bottom liquid together with the first leaching liquid, pour for 60min, after the pouring is completed, continue to pour in the alkali liquid, and adjust the pH of the slurry to 1.60. Filter the slurry to obtain a first white residue and a first mother liquor, and then rinse the first white residue with 1L of water.

[0080] (4) Take 1250g of the first white residue and 1250g of pure water to slurry, and adjust the pH to 0.8-1.0 by adding concentrated sulfuric acid to obtain a first dissolution liquid;

[0081] (5) Take 2.0L of the first dissolution liquid and pour it into a 3L beaker, turn on the stirring motor, the stirring speed is 300rpm, and the water bath temperature is set to 40℃. Configure 20% magnesium oxide slurry as the alkali liquid, the flow rate of the alkali liquid is 5.0mL / min, and pour it into the first dissolution liquid, pour for 60min, after the pouring is completed, continue to pour in the alkali liquid, and adjust the pH of the slurry to 1.60. Filter the slurry to obtain a second white residue and a second mother liquor, and then rinse the second white residue with 1L of water.

[0082] (6) Take 1000g of the stirred and washed second-stage white residue and mix it with 1690 mL of the second-stage leaching solution. After heating to 40°C, react for 1 h. The iron phosphate white residue is completely dissolved to obtain refined phosphorus iron liquid.

[0083] (7) Take 2 L of the refined phosphorus iron liquid, adjust Fe / P = 1.000 with ferrous sulfate and hydrogen peroxide, and dilute to 0.8 M iron concentration. After completion, heat to 40°C, control the feeding time to be 60 min, and feed 20% ammonia water. After the feeding is completed, react for 1 h and age for 1 h. Filter out the iron phosphate yellow material, and wash it with pure water until the conductivity is 3500-4000 μs / m. Then, pulp the yellow material in pure water, control the slurry solid content to be 20%, and feed 0.6 times the molar amount of FePO4 of phosphoric acid. Heat to 95°C, react for 3 h and age for 1 h after reaction, and then filter to obtain the iron phosphate white material. Wash it with pure water until the conductivity is 200-400 μs / m. After drying the white material, place it in a muffle furnace and calcine at 570°C for 4 h to obtain anhydrous iron phosphate.

[0084] The impurity content of the anhydrous iron phosphate prepared in this example is compared with that of the anhydrous iron phosphate prepared in Example 1 to illustrate that the white residue stirring and washing process of the process of the application can also be increased or cancelled according to the required impurity removal depth. The results are shown in Table 5.

[0085] Table 5 Effect of whether stirring and washing on the impurity content of regenerated iron phosphate

[0086]

[0087] As can be seen from Table 5, the phosphorus iron prepared by the recycling process provided in Example 3 still differs from Example 1 in the Al index, which illustrates that the white residue stirring and washing process of the process of the application can also be increased or cancelled according to the Al content requirement of the product.

[0088] Comparative Examples 1-3

[0089] Comparative Examples 1-3 have the same operation method as step (3) in Example 1, only the type of liquid alkali is changed, and the feeding mode is compared to the aluminum removal effect. The order feeding mode is that the first-stage leaching solution is first fed into the reaction kettle, and then the alkali solution is added to adjust the pH. The simultaneous feeding mode is that the first-stage leaching solution and the alkali solution are simultaneously fed into the reaction kettle. The results are shown in Table 6.

[0090] Table 6 Effect of the feeding mode and the type of alkali in the precipitation process on the impurity removal effect

[0091]

[0092] From Table 6, it can be seen that the comparative example 1 only changes the feeding method relative to the example 1, and the aluminum content in the white residue of one-sink has no obvious difference, which shows that the feeding method of magnesium oxide has no effect on the aluminum removal effect; the comparative examples 2 and 3 use sodium hydroxide for parallel feeding, and the aluminum content in the white residue of one-sink is significantly improved compared with the result of example 1, which shows that the magnesium salt as alkali source has better aluminum removal effect. In addition, the parallel feeding of sodium hydroxide can improve the aluminum removal effect.

[0093] Comparative examples 4-6

[0094] The operation method of comparative examples 4-6 and step (6) in example 1 is the same, only the slurry solid content, acid / charge ratio and aluminum removal agent dosage in the stirring washing process of two-sink white residue are changed to compare the aluminum removal effect, and the results are shown in Table 7.

[0095] Table 7 Influence of solid content, acid / charge ratio and aluminum removal agent dosage in stirring washing process of white residue on impurity removal effect

[0096]

[0097] The results of comparative example 4 and example 1 show that if a small amount of sulfuric acid is added in the stirring washing process, the aluminum content of the product is lower, and the aluminum removal effect is more significant; the results of comparative example 5 and example 1 show that only adding sulfuric acid without adding aluminum removal agent will weaken the aluminum removal effect; the results of comparative example 6 and example 1 show that the liquid / solid ratio has no significant effect on the impurity removal effect.

Claims

1. A process for recovering ferrophosphate slag to prepare battery-grade ferrophosphate, characterized in that, Comprising the following steps: Step 1, one-stage leaching: take the lithium extraction phosphorus iron slag / phosphorus iron slag and mix with pure water to prepare a first slurry, and heat to 30-70℃, add sulfuric acid to the first slurry for acid leaching reaction, after reaction for 1-2h, filter to obtain a first leaching solution and a first leaching residue; Step 2, two-stage leaching: take the first leaching residue and mix with pure water to prepare a second slurry, and heat to 30-70℃, add concentrated sulfuric acid to the second slurry for acid leaching reaction, after reaction for 1-2h, filter to obtain a second leaching solution and graphite residue; Step 3, first precipitation: heat the first leaching solution of step 1 to 30-90℃, adjust the Fe / P molar ratio of the solution to 0.90-1.20 by adding ferrous sulfate and hydrogen peroxide, and then add the alkali source slurry for precipitation reaction for 0.5-2.0h, then filter to obtain a first mother liquor and a first white residue; The alkali source is magnesium, calcium, manganese, nickel, iron oxide, hydroxide and carbonate, the concentration of the alkali source slurry is 5-25%, the feeding mode is single feeding or simultaneous feeding, and the reaction end point pH value is 1.5-2.5; Step 4, first dissolution: mix the first white residue with pure water to prepare a third slurry, heat to 30-90℃, and then add concentrated sulfuric acid to dissolve the first white residue, control the pH value of the dissolution solution to 0.5-1.0, and after complete dissolution, obtain a first dissolution solution; Step 5, second precipitation or / and stirring washing of the second white residue: Second precipitation: heat the first dissolution solution to 30-90℃, then add the alkali source slurry again, react for 0.5-2.0h, then filter to obtain a second mother liquor and a second white residue; The alkali source is magnesium, calcium, manganese, nickel, iron oxide, hydroxide and carbonate, the concentration of the alkali source slurry is 5-25%, the feeding mode is single feeding or simultaneous feeding, and the reaction end point pH value is 1.5-2.5; Stirring washing of the second white residue: take the second white residue and mix with pure water to prepare a fourth slurry, heat to 30-90℃ and add an eluent, adjust the pH value to 1.0-2.0 with sulfuric acid, react for 0.1-2.0h, then filter to obtain a second mother liquor after stirring washing and a second white residue after stirring washing; the eluent is iron, calcium, magnesium sulfate or phosphate; Step 6, second dissolution: add the second white residue after stirring washing to the second leaching solution obtained in step 2 for dissolution, the reaction temperature is 30-90℃, the reaction time is 0.1-2.0h, the density of the dissolution solution is adjusted to 1.15-1.30g / mL by supplementing the second white residue after stirring washing, and after passing, the refined phosphorus iron liquid is obtained by precision filtration; Step 7, synthesis of iron phosphate: (1) Add ferrous sulfate, hydrogen peroxide and pure water to the refined phosphorus iron liquid to adjust the Fe / P molar ratio to 0.90-1.10 and the Fe concentration to 0.5-1.5M to obtain an adjusted solution; (2) Heat the adjusted solution to 30-90℃, add alkali solution to generate iron phosphate precipitate after 1.0-3.0h, filter to obtain iron phosphate yellow material, and then wash the iron phosphate yellow material with pure water; (3) Add the washed iron phosphate yellow material to pure water to prepare a slurry, and then add 0.1-0.8 times the molar amount of phosphoric acid of FePO4 to perform conversion reaction at 60-100℃ for 1.0-3.0h. (4) filtering out the iron phosphate white material, washing and drying to obtain iron phosphate dihydrate powder; (5) roasting the iron phosphate dihydrate powder at 550-650°C for 1.0-5.0h, dehydrating and crystallizing to obtain the iron phosphate anhydride product.

2. The process for recovery of phosphorous iron slag for preparation of battery grade iron phosphate as claimed in claim 1 wherein, In step 1, the solid content of the primary slurry is 10-25%, and the amount of sulfuric acid added is 0.3-0.7 times the theoretical amount.

3. The process of claim 1, wherein the phosphorus iron slag is recovered and prepared into battery grade iron phosphate, characterized in that, In step 2, the solid content of the secondary slurry is 10-25%, and the amount of sulfuric acid added is 0.8-1.2 times the theoretical amount.

4. The process of claim 1, wherein the phosphorus iron slag is recovered and prepared into battery grade iron phosphate, characterized in that, In step 4, the liquid-solid ratio of the third slurry is 1:1-10:1, and the pH value of the primary dissolution liquid is 0.5-1.

0.

5. The process of claim 1, wherein the phosphorous iron slag is recovered to produce battery grade iron phosphate, characterized by, In step 5, when the white residue is stirred and washed, the solid content of the fourth slurry is 5-25%, and the amount of eluent added is 0.1-5.0% of the mass of the fourth slurry.

6. The process of claim 1, wherein the phosphorous iron slag is recovered to produce battery grade iron phosphate, characterized by, In step 6, after dissolution, the pH value is 0.5-1.0, and the density of the refined phosphorus iron liquid is controlled in the range of 1.15-1.30 g / mL.

7. The process of claim 1, wherein the phosphorous iron slag is recovered and prepared into battery grade iron phosphate, characterized in that, In step 7, in step (2), the alkali solution is a combination of one or more of ammonia, sodium hydroxide, magnesium hydroxide, ammonium carbonate, sodium carbonate, and magnesium carbonate, and the amount of alkali solution added is adjusted to a slurry pH value of 1.6-2.2; the iron phosphate yellow material is washed with pure water until the conductivity of the washing liquid is 3500-4000 μs / m; In step (3), the solid content of the slurry is 5-25%, and the slurry temperature is 70-100°C.

8. The process of claim 1, wherein the phosphorous iron slag is recovered and prepared into battery grade iron phosphate, characterized in that, In step 7, in step (3), the solid content of the slurry is 5-25%, and the slurry temperature is 70-100°C.

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