Method for preparing ferric trichloride and / or phosphoric acid from slag obtained after lithium extraction of invalid lithium iron phosphate

Abstract

The invention discloses a method for preparing ferric trichloride and / or phosphoric acid from residues obtained after lithium extraction of failed lithium iron phosphate, which comprises the following steps: S1, taking the residues obtained after lithium extraction, and adding a leaching agent for leaching to obtain a leachate 1 and residues 1; s2, an extraction agent is added into the leachate 1 for extraction, the pH of an oil-water mixed homogeneous phase is controlled to be 0.2-1.0, and phosphorus-containing extraction raffinate 1 and an organic phase containing ferric trichloride are obtained; then the organic phase containing ferric trichloride is subjected to reverse extraction, and a ferric trichloride solution is obtained; the leaching agent in S1 is a hydrochloric acid solution, and the extracting agent in S2 is a tributyl phosphate solution. By the adoption of the method, iron and phosphorus in the slag obtained after lithium extraction are extracted respectively, ferric trichloride and wet-process phosphoric acid can be used for water treatment and chemical production respectively, and recycling of the slag obtained after lithium extraction is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium iron phosphate recycling, and in particular relates to a method for preparing ferric chloride and / or phosphoric acid by using the residue after lithium extraction from spent lithium iron phosphate. Background Art

[0002] After the spent lithium iron phosphate (LFP) cathode material is oxidized and leached under acidic conditions, the lithium element with high value can be basically extracted to prepare battery-grade lithium carbonate. However, it is difficult to obtain sustainable profit margins by simply recycling the lithium element in spent LFP. Therefore, the recycling of spent LFP needs to create other profit points.

[0003] The residue after lithium extraction from failed LFP - post-lithium extraction slag, is a solid waste mainly composed of iron phosphate, containing a large amount of carbon, binder, aluminum and other impurities. The current treatment method in the industry is generally to transport it as solid waste, which not only requires a high treatment cost, but also has a significant impact on the environment. However, the iron and phosphorus in the post-lithium extraction slag are also a resource, especially phosphorus. If it can be used as a resource, it will bring additional profits to the company's production. Summary of the invention

[0004] Based on the above technical problems, the present invention provides a method for preparing ferric chloride and / or wet-process phosphoric acid using the residue after lithium extraction from spent lithium iron phosphate. Ferric chloride and wet-process phosphoric acid can be used for water treatment and chemical production, respectively, to realize the resource utilization of the residue after lithium extraction.

[0005] The specific scheme of the present invention is as follows:

[0006] The present invention provides a method for preparing ferric chloride and / or phosphoric acid from spent lithium iron phosphate residue after lithium extraction, comprising the following steps: S1, taking the residue after lithium extraction, adding a leaching agent for leaching, and obtaining a leachate 1 and a residue 1; S2, adding an extractant to the leachate 1 for extraction, controlling the pH of the oil-water mixed homogeneous phase to be 0.2-1.0, and obtaining a phosphorus-containing extraction residue 1 and an organic phase containing ferric chloride; then stripping the organic phase containing ferric chloride to obtain a ferric chloride solution;

[0007] The leaching agent in S1 is hydrochloric acid solution, and the extracting agent in S2 is tributyl phosphate solution.

[0008] Preferably, the method further comprises S3, adding an extractant to the phosphorus-containing extract raffinate 1 for extraction to obtain a phosphorus-containing organic phase and an extract raffinate 2; and washing the phosphorus-containing organic phase with water to remove impurities and then stripping to obtain a dilute phosphoric acid solution.

[0009] Preferably, in S3, during extraction, the pH of the oil-water mixed homogeneous phase is -0.1 to -0.5.

[0010] The lithium slag of the present invention refers to the residue after lithium extraction from spent lithium iron phosphate, which is a solid waste with iron phosphate as the main component. The residue 1 obtained after S1 leaching treatment is mainly composed of carbon, which can be directly landfilled or used as incineration fuel. The obtained ferric chloride solution is treated by a conventional evaporation crystallization method to obtain ferric chloride crystals. The obtained dilute phosphoric acid is concentrated to obtain industrial phosphoric acid.

[0011] Preferably, in S1, the amount of HCl added to the leaching agent is 3 to 6 times the molar amount of phosphorus in the slag after lithium extraction; more preferably, the amount of HCl added to the leaching agent is 6 times the molar amount of phosphorus in the slag after lithium extraction.

[0012] Preferably, in S1, the weight ratio of the leaching agent to the slag after lithium extraction is 2:1 to 10:1; further, the weight ratio of the leaching agent to the slag after lithium extraction is 3:1 to 5:1.

[0013] Preferably, in S1, the leaching temperature is 30-80°C, and the leaching time is 30-120 min; preferably, in S1, the leaching temperature is 40-50°C, and the leaching time is 60 min.

[0014] Preferably, in S2, the tributyl phosphate solution (TBP) is tributyl phosphate diluted with solvent oil; more preferably, the volume fraction of tributyl phosphate in the solvent oil is 32% to 60%, and the solvent oil is any one of 200# and 260# solvent oil.

[0015] Preferably, in S2, the volume ratio of the tributyl phosphate solution to the leaching solution 1 is 2:1 to 10:1; preferably, the volume ratio of the tributyl phosphate solution to the leaching solution 1 is 4:1.

[0016] Preferably, in S2, during the extraction process, the mixing time is 2 to 10 minutes; more preferably, the mixing time is 6 minutes.

[0017] Preferably, in S2, during stripping, water is used as the stripping aqueous phase, the ratio of the organic phase to the aqueous phase is 10 to 30:1, and the pH of the mixed homogeneous phase is 2 to 3.

[0018] Preferably, in S2, the stripping temperature is 25-35°C, and the stripping time is 5-10 min.

[0019] Preferably, in S3, the extractant is tributyl phosphate solution; preferably, the tributyl phosphate solution is obtained by diluting tributyl phosphate with solvent oil as a diluent, and the volume fraction of the diluent is 20-30%. More preferably, the solvent oil is any one of 200# solvent oil, 260# solvent oil, and methyl isobutyl ketone.

[0020] Preferably, in S3, during extraction, the volume ratio of the extractant to the phosphorus-containing extract residue 1 is 3 to 6:1, the extraction temperature is 40 to 60° C., and the extraction time is 5 to 10 min.

[0021] Preferably, in S3, during stripping, pure water is used for stripping, and the volume ratio of the organic phase to the aqueous phase is 5 to 20:1.

[0022] Preferably, in S3, the stripping temperature is 20 to 40°C, and the stripping time is 8 to 20 min.

[0023] The beneficial effects of the present invention are:

[0024] The invention provides a novel method for recycling slag after lithium extraction, which respectively extracts iron and phosphorus from the slag after lithium extraction by means of acid leaching-impurity removal-extraction, prepares ferric chloride powder suitable for the field of water treatment and wet-process phosphoric acid that can be used in chemical production, and realizes the recycling of slag after lithium extraction. DETAILED DESCRIPTION

[0025] The present invention provides a method for preparing ferric chloride and / or phosphoric acid by using the residue after lithium extraction from spent lithium iron phosphate, comprising the following steps:

[0026] S1. Take the residue after lithium extraction, add a leaching agent solution to leaching, and obtain a leachate 1 and a residue 1; wherein the leaching agent is a hydrochloric acid solution.

[0027] The following reaction occurs in step S1 (1):

[0028] FePO4+3HCl=FeCl3+H3PO4 (1)

[0029] S2, adding an extractant to the leaching solution 1 for extraction, controlling the pH of the oil-water mixed homogeneous phase to be 0.2-1.0, and obtaining a phosphorus-containing extract raffinate 1 and an organic phase containing ferric chloride; then stripping the organic phase containing ferric chloride to obtain a ferric chloride solution; wherein the extractant is a tributyl phosphate solution (TBP).

[0030] S2 utilizes the complexation of trivalent iron by the extractant under extremely low pH conditions to selectively extract iron ions from the leachate into the organic phase to achieve separation and purification of iron. Under strong acid and high chlorine conditions, it can undergo the following reaction (2), where: (o) indicates that the substance is in the organic phase, and (a) indicates that the substance is in the aqueous phase.

[0031] 2TBP(o)+FeCl3(a)+HCl(a)=(TBP)2·HFeCl4(o) (2)

[0032] Preferably, S2 is subjected to multi-stage countercurrent extraction to achieve deep extraction of Fe, using 1 to 10 stages of countercurrent extraction to extract iron, and more preferably, using 5 stages of countercurrent extraction to deeply extract iron.

[0033] The organic phase containing FeCl3 obtained in S2 needs to be stripped to obtain a high-purity concentrated ferric chloride solution, and the principle is shown in formula (3):

[0034] (TBP)2·HFeCl4(o)+OH - (a)=2TBP(o)+FeCl3(a)+H2O(a)+Cl - (a) (3)

[0035] When the pH in the aqueous phase is ≥ 2, the above reaction will occur spontaneously. Therefore, during the stripping process, it is necessary to provide OH - Ensure complete stripping; in order to provide sufficient alkalinity for the stripping solution, S2 can add a certain amount of sodium hydroxide, sodium bicarbonate or sodium carbonate to the mixed homogeneous phase, but in this process it is necessary to ensure that the pH of the mixed homogeneous phase is ≤3 to prevent Fe precipitation.

[0036] Preferably, pure water is used as the solution to receive FeCl3 from the organic phase during S2 stripping, and the pH of the mixed homogeneous phase is controlled to be maintained between 2 and 3 during stripping.

[0037] S3, adding an extractant to the phosphorus-containing extract raffinate 1 for extraction to obtain a phosphorus-containing organic phase and an extract raffinate 2; washing the phosphorus-containing organic phase with water to remove impurities and then stripping to obtain a dilute phosphoric acid solution.

[0038] The extractant tributyl phosphate (TBP) used in the present invention is a neutral phosphorus oxygen extractant, a typical Lewis hard base in the experiment, and contains a P=O double bond in its molecule. Since the electronegativity of P and O is very different, the electron cloud of the P=O double bond is largely biased towards the O atom, which makes it easier for the O atom to form a complex with the phosphoric acid molecule through hydrogen bonds. The order of the extraction acid is related to the Lewis acid strength of the acid, and is generally ranked as follows: H2C2O4≈CH3COOH>HF>HClO3>H3PO4>HCl>H2SO4. Phosphoric acid, as a medium-strong acid, has a strong complexing ability with TBP.

[0039] During the S3 extraction process, in order to keep phosphoric acid in a molecular state, hydrochloric acid needs to be added to adjust the pH of the solution to -0.1 to -0.5 to inhibit the dissociation of phosphoric acid molecules. There is still a lot of hydrochloric acid remaining in the residual extract obtained after extraction. In order to make full use of it, the residual extract can be returned to the leaching section to achieve the purpose of saving water and utilizing hydrochloric acid.

[0040] Preferably, the organic phase obtained by phosphoric acid extraction needs to be washed to remove the entrained hydrochloric acid impurities; according to the difference in the affinity of TBP to different acid molecules, the binding ability of HCl molecules to TBP molecules is weaker than that of H3PO4 molecules, and they will be preferentially eluted during the water washing process. Therefore, as long as the washing conditions are well controlled, the hydrochloric acid impurities entrained in the organic phase can be eluted to ensure the purity of the final phosphoric acid product.

[0041] Preferably, the washing process uses a hydrochloric acid solution with a pH of 0.1 to 0.5 as the washing aqueous phase. This is to suppress the dissociation of phosphoric acid molecules while also allowing them to be washed away due to the relative unsaturation of hydrochloric acid in the aqueous solution.

[0042] Preferably, the volume ratio of the organic phase to the aqueous phase in the washing process is 20 to 40:1;

[0043] Preferably, the number of stages in the washing process is 1 to 3 stages of countercurrent washing;

[0044] Preferably, the aqueous solution after washing is a dilute hydrochloric acid solution, which can be returned to the leaching section for leaching.

[0045] Through the above steps, a purified phosphoric acid-containing organic phase can be obtained, and high-purity phosphoric acid can be obtained after stripping; preferably, the stripping stage is 3 to 5 countercurrent stripping stages.

[0046] Preferably, the mass concentration of the phosphoric acid solution obtained after stripping is 10-20%. In order to obtain industrial phosphoric acid that meets national standards, it needs to be further concentrated.

[0047] The technical solutions of the present invention are described in detail below through specific embodiments. However, it should be clearly stated that these embodiments are for illustration only and are not to be construed as limiting the scope of the present invention.

[0048] Example 1

[0049] A method for preparing ferric chloride and phosphoric acid from spent lithium iron phosphate residues, comprising the following steps:

[0050] S1. Take 100 g of the slag after lithium extraction and grind it to a particle size that passes through an 80-mesh sieve. Use 500 mL of a 5.8 mol / L hydrochloric acid solution for leaching (the molar ratio of phosphorus to HCl in the slag after lithium extraction is 1:6). The leaching temperature is 50 ° C. The reaction time is 60 min. After the reaction is completed, filter to obtain a leachate 1 and a residue 1.

[0051] The concentration of each element in the leaching solution 1 is: Ca 0.3043 g / L, Na 0.1186 g / L, Cu 0.0135 g / L, K 0.0254 g / L, Mg 0.0241 g / L, Al 0.1290 g / L, Fe 53.68 g / L, Li 0.2860 g / L, F 0.0462 g / L, P 29.59 g / L. In this step, 98.8% of iron and 99.2% of phosphorus in the slag after lithium extraction are extracted into the leaching solution 1;

[0052] S2, extracting the leachate 1, using 260# solvent oil as a diluent to dilute TBP to prepare a TBP solution with a volume fraction of 40 vol%, the volume ratio of the TBP solution to the leachate 1 is 4:1, the pH of the oil-water mixed homogeneous phase is always controlled to be maintained at 0.5, the single-stage extraction time is 6 minutes, and after 5-stage countercurrent extraction, the Fe in the leachate 1 is basically completely extracted;

[0053] The concentrations of the elements in the raffinate 1 are: Ca 0.2963 g / L, Na 0.1143 g / L, Cu 0.0129 g / L, K 0.0244 g / L, Mg 0.0221 g / L, Al 0.0090 g / L, Fe 0.0782 g / L, Li 0.2858 g / L, F 0.0072 g / L, P 28.23 g / L. In this step, more than 99.5% of Fe in the leaching solution 1 is extracted into the organic phase, and the amount of P extracted does not exceed 5%.

[0054] The iron-containing organic phase was stripped to obtain ferric chloride. Pure water was used as the stripping aqueous phase. The ratio of the organic phase to the aqueous phase was maintained at 10:1. The Fe in the organic phase was completely stripped at 35°C through 5 stages of countercurrent stripping. The stripping time for each stage was 6 minutes.

[0055] During this period, the pH of each phase was closely monitored. Since the second stage, the pH of the mixed phase has been less than 2, indicating that the OH provided by water is - Therefore, a small amount of sodium hydroxide needs to be further added to maintain the pH of the mixed homogeneous phase above 2 to ensure the stripping process;

[0056] After stripping, the ferric chloride in the organic phase can be completely extracted into the new aqueous phase. The contents of the main elements in the solution are as follows: Ca 0.0023g / L, Na 9.6523g / L, Cu 0.0052g / L, K 0.0025g / L, Mg 0.0062g / L, Al0.0590g / L, Fe 130.6g / L, Li 0.0809g / L, F 0.1126g / L, P 0.9233g / L. The overall stripping rate reaches more than 99%.

[0057] The solution is further concentrated to 60% volume and then filtered to remove iron phosphate. It is then evaporated and crystallized to obtain ferric chloride of a certain purity, the main components of which are: FeCl3 93.65%, FeCl2 0%, insoluble matter 0%, As 0%, heavy metals (Pb, Hg, Cd, Cr) 0%, meeting the requirements of GB 4482-2006 for Class II water treatment flocculants.

[0058] S3, using tributyl phosphate solution as an extractant, wherein the tributyl phosphate solution is obtained by diluting tributyl phosphate with methyl isobutyl ketone as a diluent, and the volume of the diluent accounts for 30%. Using the extractant, phosphoric acid is extracted from the extract residue 1 of step S2.

[0059] The extraction conditions were as follows: extraction temperature was 40°C, mixing time was 10 min, volume ratio of organic phase to aqueous phase was 5:1, extraction stages were 8, and hydrochloric acid was used in each stage to adjust the pH of the mixed homogeneous phase to -0.15 to inhibit the dissociation of phosphate molecules.

[0060] After extraction, the phosphoric acid in the solution is extracted into the organic phase. The content of each element in the extract 2 of this step is as follows: Ca 0.2898g / L, Na 0.1053g / L, Cu 0.0095g / L, K 0.0255g / L, Mg 0.0282g / L, Al0.0001g / L, Fe 0.0005g / L, Li 0.2848g / L, F 0.0001g / L, P 0.13g / L; in this step, more than 99% of PO4 3- are extracted into the organic phase, and only a small amount of impurities are extracted into the organic phase;

[0061] In order to reduce the impurity content of the phosphorus-containing organic phase, the organic phase needs to be washed to a certain extent. The process uses a hydrochloric acid solution with a pH of 0.15 as the washing water phase. The volume ratio of the organic phase to the water phase is 20:1. After one level of washing, the hydrochloric acid impurities in the organic phase are eluted. After washing, the pH of the hydrochloric acid solution further drops to 0.02, indicating that the hydrochloric acid is eluted, but a small amount of phosphorus is also eluted. The P content reaches 4.695g / L, accounting for 4% of the phosphoric acid in the organic phase. The loss is low and acceptable. The aqueous solution after washing is a dilute acid solution, which can be returned to the leaching section for continued leaching.

[0062] The impurity content of the phosphoric acid-containing organic phase obtained in the above steps is relatively low, and high-purity phosphoric acid can be obtained only after back extraction. Pure water is used for back extraction, and the volume ratio of the organic phase to the aqueous phase during back extraction is 10:1. The time for each back extraction is 10 minutes, and the back extraction temperature is 30°C. After 5 levels of countercurrent back extraction, a high-purity dilute phosphoric acid solution can be obtained.

[0063] The elements of the dilute phosphoric acid solution are: Ca 0.0005g / L, Na 0.0004g / L, Cu 0.0001g / L, K0.0001g / L, Mg 0.0001g / L, Al 0.0168g / L, Fe 0.112g / L, Li 0.0001g / L, F 0.0136g / L, P53.46g / L. Further calculation shows that the phosphoric acid content of the solution is 169.0g / L. Continuing to concentrate to 20% of the original volume, 75% phosphoric acid can be obtained. The impurity content of the product is: Fe 0.046%, Cl 0.054%, F 0.0056%, heavy metal 0%. It has reached the qualified level of 75% purity of industrial wet-process phosphoric acid.

[0064] Example 2

[0065] A method for preparing ferric chloride from the residue after lithium extraction from spent lithium iron phosphate comprises the following steps:

[0066] S1, same as in Example 1, obtaining leachate 1 and residue 1;

[0067] S2, extracting the leachate 1, using 260# solvent oil as a diluent to dilute TBP to prepare a TBP solution with a volume fraction of 32 vol%, the volume ratio of the TBP solution to the leachate 1 is 4:1, the pH of the oil-water mixed homogeneous phase is always controlled to be maintained at 0.2, the single-stage extraction time is 8 minutes, and after 5-stage countercurrent extraction, the Fe in the leachate 1 is basically completely extracted;

[0068] The concentrations of the elements in the raffinate 1 are: Ca 0.1758 g / L, Na 0.0964 g / L, Cu 0.0069 g / L, K 0.0144 g / L, Mg 0.0245 g / L, Al 0.0050 g / L, Fe 0.0158 g / L, Li 0.2584 g / L, F 0.0032 g / L, P 27.56 g / L. In this step, more than 99.7% of Fe in the leaching solution 1 is extracted into the organic phase, and the amount of P extracted does not exceed 5%.

[0069] The iron-containing organic phase was stripped to obtain ferric chloride. Pure water was used as the stripping aqueous phase. The ratio of the organic phase to the aqueous phase was maintained at 10:1. The Fe in the organic phase was completely stripped at 35°C through 5 stages of countercurrent stripping. The stripping time for each stage was 8 minutes.

[0070] During this period, the pH of each phase was closely monitored. Since the second stage, the pH of the mixed phase has been less than 2, indicating that the OH provided by water is -Therefore, a small amount of sodium hydroxide needs to be further added to maintain the pH of the mixed homogeneous phase above 2 to ensure the stripping process;

[0071] After stripping, the ferric chloride in the organic phase can be completely extracted into the new aqueous phase. The contents of the main elements in the solution are as follows: Ca 0.0043g / L, Na 10.5548g / L, Cu 0.0084g / L, K 0.0036g / L, Mg 0.0085g / L, Al 0.0845g / L, Fe 133.5g / L, Li 0.0707g / L, F 0.1366g / L, P 0.7533g / L. The overall stripping rate reaches more than 99%.

[0072] The solution is further concentrated to 60% volume and then filtered to remove iron phosphate. It is then evaporated and crystallized to obtain ferric chloride of a certain purity, the main components of which are: FeCl3 94.47%, FeCl2 0%, insoluble matter 0%, As 0%, heavy metals (Pb, Hg, Cd, Cr) 0%, meeting the requirements of GB 4482-2006 for Class II water treatment flocculants.

[0073] Example 3

[0074] A method for preparing ferric chloride and phosphoric acid from spent lithium iron phosphate residues, comprising the following steps:

[0075] S1, same as in Example 1, obtaining leachate 1 and residue 1;

[0076] S2, the same as in Example 2, obtaining phosphorus-containing extract raffinate 1 and ferric chloride;

[0077] S3, using tributyl phosphate solution as an extractant, wherein the tributyl phosphate solution is obtained by diluting tributyl phosphate with 260# solvent oil as a diluent, and the volume of the diluent accounts for 30%. Using the extractant, phosphoric acid is extracted from the extract residue 1 of step S2.

[0078] The extraction conditions were as follows: extraction temperature was 40°C, mixing time was 6 min, volume ratio of organic phase to aqueous phase was 6:1, extraction stages were 10, and hydrochloric acid was used in each stage to adjust the pH of the mixed homogeneous phase to -0.5 to inhibit the dissociation of phosphate molecules.

[0079] After extraction, the phosphoric acid in the solution is extracted into the organic phase. The content of each element in the extract 2 of this step is as follows: Ca 0.2922g / L, Na 0.1165g / L, Cu 0.0082g / L, K 0.0260g / L, Mg 0.232g / L, Al0.0001g / L, Fe 0.0001g / L, Li 0.2914g / L, F 0.0001g / L, P 0.0582g / L; in this step, more than 99.5% of PO4 3- are extracted into the organic phase, and only a small amount of impurities are extracted into the organic phase;

[0080] In order to reduce the impurity content of the phosphorus-containing organic phase, the organic phase needs to be washed to a certain extent. The process uses a hydrochloric acid solution with a pH of 0.10 as the washing water phase, and the volume ratio of the organic phase to the water phase is 15:1. After two levels of washing, the hydrochloric acid impurities in the organic phase are eluted. After washing, the pH of the hydrochloric acid solution further drops to 0.04, indicating that the hydrochloric acid has been eluted, but a small amount of phosphorus has also been eluted, with a content of 3.25g P / L, accounting for 3% of the phosphoric acid in the organic phase. The loss is low and acceptable. The aqueous solution after washing is a dilute acid solution, which can be returned to the leaching section for continued leaching.

[0081] The impurity content of the phosphoric acid-containing organic phase obtained in the above steps is relatively low, and high-purity phosphoric acid can be obtained only after back extraction. Pure water is used for back extraction, and the volume ratio of the organic phase to the aqueous phase during back extraction is 12:1. The time for each back extraction is 8 minutes, and the back extraction temperature is 30°C. After 10 levels of countercurrent back extraction, a high-purity dilute phosphoric acid solution can be obtained.

[0082] The elements of the dilute phosphoric acid solution are: Ca 0.0001g / L, Na 0.0010g / L, Cu 0.0001g / L, K0.0001g / L, Mg 0.0001g / L, Al 0.0097g / L, Fe 0.092g / L, Li 0.0001g / L, F 0.0115g / L, P54.66g / L. Further calculation shows that the phosphoric acid content of the solution is 174.0g / L. Continue to concentrate to 20% of the original volume to obtain 75% phosphoric acid. The impurity content of the product is: Fe 0.029%, Cl 0.034%, F 0.0049%, heavy metal 0%. It has reached the qualified level of 75% purity of industrial wet-process phosphoric acid.

[0083] Comparative Example 1

[0084] A method for preparing ferric chloride and phosphoric acid from the residue after lithium extraction from spent lithium iron phosphate is the same as that in Example 1, except that the operation order of step S2 and step S3 is reversed, that is, phosphoric acid is extracted first and then iron is extracted, and the main components of the obtained dilute phosphoric acid solution are as follows: Ca 0.0019g / L, Na 7.1511g / L, Cu 0.0033g / L, K 0.0019g / L, Mg 0.0052g / L, Al 0.0488g / L, Fe 93.76g / L, Li 0.0702g / L, F 0.0926g / L, P 20.8564g / L. It can be seen that it is impossible to extract high-purity phosphoric acid without first removing iron, mainly because TBP has a stronger binding ability for Fe.

[0085] Comparative Example 2

[0086] A method for preparing ferric chloride and phosphoric acid from the residue after lithium extraction from spent lithium iron phosphate is the same as that in Example 1 except that the pH of the iron extraction process in step S2 is adjusted to -0.1, and the contents of the main elements of the final ferric chloride solution obtained are as follows: Ca 0.0021 g / L, Na 10.4542 g / L, Cu 0.0040 g / L, K 0.0034 g / L, Mg 0.0072 g / L, Al 0.0665 g / L, Fe 129.5 g / L, Li 0.0912 g / L, F 0.1416 g / L, P 26.2233 g / L. Although the extraction of Fe is not affected under too low pH conditions, the phosphoric acid is inhibited from dissociating and presenting a molecular state, and is entrained during the iron extraction process, so a good separation effect cannot be achieved.

[0087] Comparative Example 3

[0088] A method for preparing ferric chloride and phosphoric acid from the residue after lithium extraction from spent lithium iron phosphate is the same as that in Example 1, except that the pH of the iron extraction process in step S2 is adjusted to 2.0, and the contents of the main elements of the final ferric chloride solution are as follows: Ca 0.0010g / L, Na 4.2586g / L, Cu 0.0004g / L, K 0.0014g / L, Mg 0.0041g / L, Al 0.0684g / L, Fe 24.61g / L, Li 0.10024g / L, F 0.1137g / L, P 0.0841g / L. Under the condition of too high pH, ​​the extraction efficiency of iron is poor because the formation of (TBP)2·HFeCl4 structure cannot be well promoted.

[0089] Comparative Example 4

[0090] A method for preparing ferric chloride and phosphoric acid from the residue after lithium extraction from spent lithium iron phosphate is the same as that of Example 1 except that the pH of the phosphorus extraction process in step S3 is adjusted to 0.5, and the contents of the main elements of the final dilute phosphoric acid solution obtained are as follows: Ca 0.0001 g / L, Na 0.0002 g / L, Cu 0.0001 g / L, K 0.0001 g / L, Mg 0.0001 g / L, Al 0.01548 g / L, Fe 0.121 g / L, Li 0.0001 g / L, F 0.0142 g / L, P 20.88 g / L. Under the condition of high pH, ​​a considerable proportion of phosphoric acid is always in an ionic state, which is not conducive to combining with TBP and being extracted into the organic phase, so the efficiency of phosphorus extraction is poor.

[0091] Comparative Example 5

[0092] A method for preparing ferric chloride and phosphoric acid from spent lithium iron phosphate residue, the other conditions are the same as those of Example 1, except that the pH of the extracted phosphorus in step S3 is adjusted to -0.6. Since the amount of added acid is several times that of the example, the phosphorus extraction efficiency is not improved, but the chlorine content of the final product exceeds the standard, so it is neither economical nor reasonable to adjust the pH too low during the extraction of phosphoric acid.

[0093] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing ferric chloride and / or phosphoric acid using the residue after lithium extraction from spent lithium iron phosphate, characterized in that: The method comprises the following steps: S1, taking the residue after lithium extraction, adding a leaching agent to perform leaching, and obtaining a leachate 1 and a residue 1; S2, adding an extractant to the leachate 1 to perform extraction, controlling the pH of the oil-water mixed homogeneous phase to be 0.2-1.0, and obtaining a phosphorus-containing extract residue 1 and an organic phase containing ferric chloride; then stripping the organic phase containing ferric chloride to obtain a ferric chloride solution; The leaching agent in S1 is hydrochloric acid solution, and the extracting agent in S2 is tributyl phosphate solution.

2. The method for preparing ferric chloride and / or phosphoric acid from the residue after lithium extraction from spent lithium iron phosphate according to claim 1, characterized in that: The method further comprises S3, adding an extractant to the phosphorus-containing extract residue 1 for extraction to obtain a phosphorus-containing organic phase and an extract residue 2; washing the phosphorus-containing organic phase with water to remove impurities and then stripping to obtain a dilute phosphoric acid solution; preferably, in S3, during extraction, the pH of the oil-water mixed homogeneous phase is -0.1 to -0.

5.

3. The method for preparing ferric chloride and / or phosphoric acid from the residue after lithium extraction from spent lithium iron phosphate according to claim 1 or 2, characterized in that: In S1, the amount of HCl added in the leaching agent is 3 to 6 times the molar amount of phosphorus in the slag after lithium extraction; the weight ratio of the leaching agent to the slag after lithium extraction is 2:1 to 10:

1.

4. The method for preparing ferric chloride and / or phosphoric acid from the residue after lithium extraction from spent lithium iron phosphate according to claim 1 or 2, characterized in that: In S1, the leaching temperature is 30-80°C, and the leaching time is 30-120 min; preferably, the leaching temperature is 40-50°C, and the leaching time is 60 min.

5. The method for preparing ferric chloride and / or phosphoric acid from the residue after lithium extraction from spent lithium iron phosphate according to any one of claims 1 to 4, characterized in that: In S2, the tributyl phosphate solution is tributyl phosphate diluted with solvent oil; preferably, the volume fraction of tributyl phosphate in the solvent oil is 32% to 60%, and the solvent oil is any one of 200# and 260# solvent oil.

6. The method for preparing ferric chloride and / or phosphoric acid from the residue after lithium extraction from spent lithium iron phosphate according to any one of claims 1 to 5, characterized in that: In S2, the volume ratio of tributyl phosphate solution to leaching solution 1 is 2:1 to 10:1; preferably, in S2, during the extraction process, the mixing time is 2 to 10 minutes.

7. The method for preparing ferric chloride and / or phosphoric acid from the residue after lithium extraction from spent lithium iron phosphate according to any one of claims 1 to 6, characterized in that: In S2, during the stripping, water is used as the stripping aqueous phase, the ratio of the organic phase to the aqueous phase is 10-30:1, and the pH of the mixed homogeneous phase is 2-3; preferably, the stripping temperature is 25-35° C., and the stripping time is 5-10 min.

8. The method for preparing ferric chloride and / or phosphoric acid from the residue after lithium extraction from spent lithium iron phosphate according to claim 2, characterized in that: In S3, the extractant is a tributyl phosphate solution; preferably, the tributyl phosphate solution is obtained by diluting tributyl phosphate with solvent oil as a diluent, and the volume fraction of the diluent is 20-30%; preferably, the solvent oil is any one of 200# solvent oil, 260# solvent oil, and methyl isobutyl ketone.

9. The method for preparing ferric chloride and / or phosphoric acid from the residue after lithium extraction from spent lithium iron phosphate according to any one of claims 2 or 8, characterized in that: In S3, during extraction, the volume ratio of the extractant to the phosphorus-containing extract residue 1 is 3 to 6:1, the extraction temperature is 40 to 60° C., and the extraction time is 5 to 10 minutes.

10. The method for preparing ferric chloride and / or phosphoric acid from the residue after lithium extraction from spent lithium iron phosphate according to claim 2, characterized in that: In S3, during the stripping, pure water is used for stripping, and the volume ratio of the organic phase to the aqueous phase is 5 to 20:1; preferably, in S3, the stripping temperature is 20 to 40° C., and the stripping time is 8 to 20 min.