CN114348984A - Method for preparing nano iron phosphate and nano ferrous phosphate by using titanium dioxide byproduct - Google Patents
Method for preparing nano iron phosphate and nano ferrous phosphate by using titanium dioxide byproduct Download PDFInfo
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Abstract
The invention belongs to the technical field of nano materials, and discloses a method for preparing nano ferric phosphate and nano ferrous phosphate by using titanium dioxide byproducts. The method comprises the following steps: dissolving ferrous sulfate as a byproduct of titanium white, adding iron, reacting, and carrying out solid-liquid separation to obtain a separation solution; adding phosphoric acid and a flocculating agent into the separation liquid, and filtering to obtain a purified ferrous sulfate solution; adding an oxidizing reagent into the ferrous sulfate solution, and reacting to prepare a ferric sulfate solution; and adding the purified ferrous sulfate solution or ferric sulfate solution and a phosphorus source into a multiphase interface reactor in a concurrent flow manner, reacting, aging, and filtering to remove filtrate to obtain the nano ferrous phosphate or the nano ferrous phosphate. The nano iron phosphate and the nano ferrous phosphate prepared by the method have high purity and high yield; the product obtained by continuous reaction has good batch stability and high production efficiency. The method reasonably recycles the titanium white byproduct, and is beneficial to full utilization of resources and environmental protection.
Description
Technical Field
The invention belongs to the technical field of nano materials, and particularly relates to a method for preparing nano iron phosphate and nano ferrous phosphate by using titanium dioxide byproducts.
Background
With the development of new energy automobiles, energy storage materials are also deeply researched. Compared with a ternary cathode material, the lithium iron phosphate cathode material has the advantages of high safety performance, long cycle life, small pollution, low cost and the like, and becomes one of important materials for research. The lithium iron phosphate industry will also be continually developing in order to achieve the goal of carbon neutralization. Because the lithium iron phosphate product is continuously iterated, the requirements on the compaction density and the energy density of a new product are increased year by year, and the requirements on cost control are higher and higher along with the downstream industry. Therefore, the continuous research and development capability, the process control capability and the cost control capability can become barriers for the development of the lithium iron phosphate positive electrode material industry. Because the lithium iron phosphate anode material has poor conductivity and low lithium ion diffusion coefficient, the doping process, the carbon coating process and the material nanocrystallization are the main development directions of the lithium iron phosphate anode material. The existing production process of the lithium iron phosphate anode material mainly comprises a ferrous oxalate process, an iron oxide red process, a full wet process and an iron phosphate process. The production process basically adopts a large reaction kettle to perform discontinuous production by regulating and controlling the pH value during the synthesis of the precursor, namely the synthesis of ferric orthophosphate and ferrous phosphate. Therefore, the defects of high process control difficulty, poor product batch stability, large particle size, serious agglomeration and the like exist in the production of ferric orthophosphate and ferrous phosphate, and the comprehensive performance of the anode material synthesized by the anode material is poor and the production cost is high.
In addition, with the enhancement of environmental awareness and the control of raw material cost, the development and utilization of the byproduct ferrous sulfate of titanium white become a trend.
Therefore, it is urgently needed to provide a preparation method of iron phosphate and ferrous phosphate, the batch stability of the produced product is strong, the particle size is small, and the specific capacity of the lithium iron phosphate cathode material prepared by using the method is high.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art described above. Therefore, the invention provides a method for preparing nano ferric phosphate and nano ferrous phosphate by using titanium dioxide byproducts, the batch stability of the produced product is strong, the particle size is small, and the specific capacity of the lithium iron phosphate anode material prepared by using the method is high.
The invention provides a method for preparing nano ferric phosphate and nano ferrous phosphate by using a titanium dioxide byproduct.
Specifically, the method for preparing nano iron phosphate and nano ferrous phosphate by using a titanium white byproduct, which is a titanium white byproduct ferrous sulfate, comprises the following steps:
(1) dissolving ferrous sulfate as a byproduct of titanium dioxide, adding iron, reacting, and after the reaction is finished, carrying out solid-liquid separation on a reaction liquid to obtain a separation liquid; adding phosphoric acid and a flocculating agent into the separation liquid, and filtering to remove filter residues to obtain a purified ferrous sulfate solution;
(2) adding an oxidizing reagent into the purified ferrous sulfate solution prepared in the step (1), and reacting to prepare a ferric sulfate solution;
(3) and (3) adding the purified ferrous sulfate solution prepared in the step (1) or the ferric sulfate solution prepared in the step (2) and a phosphorus source into a multiphase interface reactor in a concurrent flow manner, reacting, aging, and filtering to remove filtrate to obtain the nano ferrous phosphate or the nano ferric phosphate.
In the step (3), when the purified ferrous sulfate solution prepared in the step (1) and a phosphorus source are added into a multiphase interface reactor in parallel for reaction, the nano ferrous phosphate is finally prepared. And (3) when the ferric sulfate solution prepared in the step (2) and a phosphorus source are added into the multiphase interfacial reactor in a cocurrent manner for reaction, the nano ferric phosphate is finally prepared.
Preferably, in the step (1), the iron is iron powder, and the mass of the iron powder is 0.01-0.1% of the mass of the ferrous sulfate as the titanium dioxide byproduct; further preferably, the mass of the iron powder is 0.01-0.05% of the mass of the ferrous sulfate as the titanium white byproduct.
Preferably, in the step (1), after the addition of the iron, the pH of the reaction system is raised to 3.0 to 4.0 by replacing hydrogen ions with iron.
Preferably, in the step (1), the temperature of the reaction is 50-90 ℃, and the time of the reaction is 0.5-5 h; further preferably, the reaction temperature is 60-80 ℃, and the reaction time is 1-3 h.
Preferably, in the step (1), the mass of the phosphoric acid is 0.005-3% of the mass of the ferrous sulfate byproduct of the titanium white; further preferably, in the step (1), the mass of the phosphoric acid is 0.01-2% of the mass of the ferrous sulfate as the titanium white byproduct.
Preferably, in step (1), the flocculant is selected from at least one of polyacrylamide, sodium polyacrylate, polydimethyldiallylammonium chloride, polyethyleneimine, polyvinyl pyridinium salt or sodium carboxymethylcellulose.
Preferably, in the step (1), the mass of the flocculating agent is 0.01-0.3 per mill of the mass of the ferrous sulfate as the titanium white byproduct; further preferably, in the step (1), the mass of the flocculating agent is 0.01 to 0.1 per mill of the mass of the ferrous sulfate as the titanium white byproduct.
In the step (1), adding iron powder into the dissolved ferrous sulfate as a titanium white byproduct to increase the pH value of the reaction system to 3.0-4.0, so that the residual titanium ions in the ferrous sulfate as the titanium white byproduct are further hydrolyzed to generate a precipitate without introducing additional impurities; the removal rate of titanium ions by solid-liquid separation reaches more than 95 percent; and then the phosphoric acid and the flocculating agent are used in a matching way, wherein the phosphoric acid can effectively adsorb ferric ions and other heavy metal ions in the ferrous sulfate solution, and the flocculating agent can remove fine suspended matters and ferric hydroxide colloid existing in the ferrous sulfate solution. The three components have synergistic effect, so that the purity of the finally obtained purified ferrous sulfate reaches 98 percent or more.
Preferably, in step (2), the oxidizing agent comprises sulfuric acid, hydrogen peroxide and ferrous ions; further preferably, in step (2), the oxidizing reagent includes sulfuric acid and fenton's reagent. The sulfuric acid and the Fenton reagent are used in a matched mode, the ferrous sulfate solution can be rapidly oxidized into the ferric sulfate solution, the oxidation efficiency is high, and the consumption of hydrogen peroxide is saved by more than 70% compared with the traditional method.
Preferably, in the oxidizing reagent, the mol ratio of the divalent iron ions to the hydrogen peroxide in the fenton reagent is 1: 0.5-5; further preferably, the mol ratio of the divalent iron ions to the hydrogen peroxide of the fenton reagent is 1: 1-3, preparation.
Preferably, the molar ratio of ferrous ions to sulfate radicals is 1-3: 1, adding the sulfuric acid.
Preferably, the volume of the fenton reagent is 0.1-2% of the volume of the purified ferrous sulfate solution prepared in step (1); further preferably, the volume of the fenton's reagent is 0.5-1% of the volume of the purified ferrous sulfate solution prepared in step (1).
Preferably, in the step (2), the reaction time is 0.3-3h, and the reaction temperature is 25-60 ℃; further preferably, in the step (2), the reaction time is 0.5-1h, and the reaction temperature is 30-50 ℃.
Preferably, in the step (3), the concentration of the purified ferrous sulfate solution prepared in the step (1) or the ferric sulfate solution prepared in the step (2) is firstly adjusted to be 0.1-3 mol/L; further preferably; in the step (3), the concentration of the purified ferrous sulfate solution prepared in the step (1) or the ferric sulfate solution prepared in the step (2) is firstly adjusted to be 0.1-2 mol/L.
Preferably, in step (3), the phosphorus source is selected from at least one of phosphoric acid, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium phosphate, monoammonium phosphate, or diammonium phosphate.
Preferably, the molar concentration of phosphate radical in the phosphorus source is 0.03-3.0 mol/L; further preferably, the molar concentration of phosphate in the phosphorus source is 0.05-2.5 mol/L. More preferably, the molar concentration of phosphate in the phosphorus source is 0.068-2.14 mol/L.
Preferably, in step (3), the raw material added concurrently with the purified ferrous sulfate solution prepared in step (1) or the ferric sulfate solution prepared in step (2) further includes a dispersant and a surfactant. By adding the surfactant and the dispersing agent, the surface energy of the nano crystal particles can be reduced, the thickness of a double electric layer can be changed, and the steric effect between the crystal particles can be increased, so that the effect of inhibiting agglomeration between the nano crystal particles is achieved, and the monodispersity of the prepared nano iron phosphate and nano ferrous phosphate is improved.
Preferably, the dispersant is a non-ionic dispersant; further preferably, the dispersant is selected from at least one of polyvinyl alcohol, ethylene glycol, polyethylene glycol, polyacrylic acid, or carboxymethyl cellulose.
Preferably, the surfactant is an anionic surfactant; further preferably, the surfactant is selected from at least one of a sulfate, sulfonate or carboxylate. Such as sodium oleate.
Preferably, in the step (3), when the purified ferrous sulfate solution prepared in the step (1) is used for reaction, the amount of the surfactant is 1% -2% of the amount of the ferrous ion in the purified ferrous sulfate solution, and the amount of the dispersant is 0.1-0.5% of the amount of the ferrous ion in the purified ferrous sulfate solution. When the dosage of the surfactant is less than 1 percent and the dosage of the dispersant is less than 0.1 per thousand, the product has uneven particle size distribution and poor monodispersity; when the dosage of the surfactant is more than 1 percent and the dosage of the dispersant is more than 0.5 per mill, the carbon impurity content of the product is higher, and the product performance and the production cost are influenced.
Preferably, in the step (3), when the reaction is performed with the iron sulfate solution prepared in the step (2), the amount of the substance of the surfactant is 1% to 2% of the amount of the substance of the iron ion in the iron sulfate solution, and the amount of the substance of the dispersant is 0.1% to 0.5% of the amount of the substance of the iron ion in the iron sulfate solution. When the dosage of the surfactant is less than 1 percent and the dosage of the dispersant is less than 0.1 per thousand, the product has uneven particle size distribution and poor monodispersity; when the dosage of the surfactant is more than 1 percent and the dosage of the dispersant is more than 0.5 per mill, the carbon impurity content of the product is higher, and the product performance and the production cost are influenced.
In the step (3), the chemical reaction rate and the crystal nucleation and growth environment can be effectively regulated and controlled by controlling the dosage of the iron source (the purified ferrous sulfate solution prepared in the step (1) or the ferric sulfate solution prepared in the step (2)), the phosphorus source, the dispersing agent and the surfactant, so that the nano-scale iron phosphate and the nano-scale ferrous phosphate can be conveniently generated; and the formed crystals are more uniform.
Preferably, in step (3), the feedstock added concurrently with the phosphorus source further comprises a pH adjuster. Preferably, the pH regulator is selected from sodium hydroxide or \ and ammonia water.
Preferably, in the step (3), when the reaction is performed using the purified ferrous sulfate solution prepared in the step (1), the pH of the reaction system is adjusted to 6.0 to 7.0 using the pH adjuster. When the pH value of the reaction system is less than 6, the ferrous ions are not completely precipitated, and the material waste is caused; when the pH value of the reaction system is more than 7, ferrous ions are hydrolyzed, and then ferrous hydroxide and ferric hydroxide impurities are formed.
Preferably, in the step (3), when the reaction is performed using the iron sulfate solution prepared in the step (2), the pH of the reaction system is adjusted to 1.5 to 2.0 using the pH adjuster. When the pH value of the reaction system is less than 1.5, the reaction of iron ions and phosphate radicals is incomplete, and the material waste is caused; when the pH value of the reaction system is more than 2.0, the iron ions are hydrolyzed to form ferric hydroxide impurities.
Preferably, in step (3), the co-current addition is carried out at a flow rate of 0.005 to 3m3H; further preferably, in step (3), the flow rate of the concurrent addition is 0.006-2m3H is used as the reference value. Such as 0.1, 0.5, 0.8, 1.0, 1.2, 1.5, 1.8m3/h。
Preferably, in the reaction process of step (3), stirring treatment is performed, and the rotation speed of stirring is 1000-. After each reaction raw material enters a multiphase interface reactor, a large amount of close-packed mineralized foam can be formed under the stirring action, the nucleation, growth and curing of crystal grains are finished in a liquid film, the mass transfer and heat transfer efficiency is high, and the nanoscale ferrous phosphate and iron phosphate can be generated.
Preferably, in step (3), the temperature of the reaction is 20-50 ℃; further preferably, in step (3), the temperature of the reaction is 20 to 40 ℃. In the reaction, no additional heating is needed, and the reaction temperature (20-50 ℃) is maintained by the self-chemical reaction heat.
Preferably, in step (3), the pressure of the reaction is atmospheric pressure. The reaction is completed under normal pressure, the requirement on equipment is low, and the safety is high; and can reduce cost and save energy.
Preferably, in the step (3), when the nano iron phosphate is prepared, the aging temperature is 55-90 ℃, and the aging time is 0.5-3 h; further preferably, in the step (3), when the nano iron phosphate is prepared, the aging temperature is 60-80 ℃, and the aging time is 1-2 h.
Preferably, in the step (3), when the nano ferrous phosphate is prepared, the aging temperature is 20-40 ℃, and the aging time is 0.5-3 h; further preferably, in the step (3), when the nano iron phosphate is prepared, the aging temperature is 20-35 ℃, and the aging time is 1-2 h.
More specifically, the method for preparing nano iron phosphate by using titanium dioxide byproduct comprises the following steps:
(1) dissolving the titanium dioxide by-product waste ferrous sulfate in water to obtain a ferrous sulfate solution A; heating the ferrous sulfate solution A under a stirring state, adding iron powder, reacting, and after the reaction is finished, carrying out solid-liquid separation on the reaction liquid to obtain a separation liquid; adding phosphoric acid and a flocculating agent into the separation liquid under a stirring state, and filtering to remove filter residues to obtain a purified ferrous sulfate solution;
(2) sequentially adding sulfuric acid and Fenton reagent into the purified ferrous sulfate solution prepared in the step (1) under a stirring state, and reacting to prepare a ferric sulfate solution;
(3) and (3) adding a phosphorus source, a surfactant and a dispersing agent and the ferric sulfate solution prepared in the step (2) into a multiphase interface reactor in a concurrent flow manner, reacting, aging, filtering to remove filtrate, washing and drying to obtain the nano ferric phosphate.
More specifically, the method for preparing nano ferrous phosphate by using titanium white byproducts comprises the following steps:
(1) dissolving the titanium dioxide by-product waste ferrous sulfate in water to obtain a ferrous sulfate solution A; heating the ferrous sulfate solution A under a stirring state, adding iron powder, reacting, and after the reaction is finished, carrying out solid-liquid separation on the reaction liquid to obtain a separation liquid; adding phosphoric acid and a flocculating agent into the separation liquid under a stirring state, and filtering to remove filter residues to obtain a purified ferrous sulfate solution;
(2) and (2) adding a phosphorus source, a surfactant and a dispersing agent and the purified ferrous sulfate solution prepared in the step (1) into a multiphase interface reactor in a concurrent flow manner, reacting, aging, filtering to remove filtrate, washing and drying to obtain the nano ferrous phosphate.
The invention provides an application of the method for preparing nano ferric phosphate and nano ferrous phosphate by using titanium dioxide byproducts in preparing lithium iron phosphate anode materials.
The third aspect of the invention provides application of the method for preparing nano iron phosphate and nano ferrous phosphate by using the titanium white byproduct in recovery of the titanium white byproduct.
Compared with the prior art, the invention has the following beneficial effects:
(1) the invention provides a method for preparing nano ferric phosphate and nano ferrous phosphate by using titanium dioxide byproducts, and the prepared nano ferric phosphate and nano ferrous phosphate have small particle size, high purity and high yield; the product obtained by continuous reaction has good batch stability, strong product consistency and high production efficiency.
(2) In the method provided by the invention, a large amount of close-packed mineralized foam can be formed after each reaction raw material enters the multiphase interface reactor, the nucleation, growth and curing of crystal grains are completed in a liquid film, and the mass transfer and heat transfer efficiency is high; the reaction temperature is maintained by the self chemical reaction heat, the pressure is normal pressure, and the production efficiency is high, safe and energy-saving.
(3) The invention reasonably recycles the titanium white byproduct, which is beneficial to the full utilization of resources and the environmental protection; the lithium iron phosphate anode material prepared by the nano iron phosphate or the nano ferrous phosphate prepared by the method has high specific capacity and excellent low-temperature performance.
Drawings
FIG. 1 shows Fe obtained in example 13(PO4)2·8H2XRD pattern of O;
FIG. 2 shows Fe obtained in example 13(PO4)2·8H2SEM picture of O;
FIG. 3 shows FePO prepared in example 24·2H2XRD pattern of O;
FIG. 4 shows FePO prepared in example 24·2H2SEM image of O.
Detailed Description
In order to make the technical solutions of the present invention more apparent to those skilled in the art, the following examples are given for illustration. It should be noted that the following examples are not intended to limit the scope of the claimed invention.
The heterogeneous interfacial reactor used in the following examples is obtained according to International publication No. WO2021/217550A1, and other raw materials, reagents or apparatuses are conventionally commercially available or can be obtained by conventionally known methods, unless otherwise specified.
Example 1
Preparation of Fe by using titanium dioxide byproduct3(PO4)2·8H2A process of O comprising the steps of:
firstly, a titanium white byproduct FeSO is purified in an iron source purification tank4.7H2Preparing 1mol/L solution of O with deionized water, heating the solution to 65 ℃ under the stirring state, and adding iron powder (the mass is titanium dioxide byproduct FeSO)4.7H20.01 percent of the mass of O), replacing hydrogen ions in the system by the iron powder to increase the pH value in the system to 3.5, starting hydrolysis of titanium ions in titanium white byproducts, and removing precipitates by a vacuum filter after reaction for 1h to obtain separation liquid; into the separated liquidAdding phosphoric acid (the mass is titanium dioxide byproduct FeSO)4.7H20.02% of the mass of O), and continuously stirring for 30 min; then adding polyacrylamide (the mass is titanium dioxide byproduct FeSO)4.7H20.001 percent of the mass of O), and continuously stirring for 30 min; and filtering the suspended matters in the separation liquid by using a vacuum filter to obtain a pure and transparent purified ferrous sulfate solution. The purity of the prepared purified ferrous sulfate is tested to be 98.5%. Transferring the purified ferrous sulfate solution to a ferrous sulfate preparation tank, sequentially adding ascorbic acid (the mass is 0.01 percent of the mass of the purified ferrous sulfate) and polyethylene glycol (0.1 thousandth of the molar mass of the purified ferrous sulfate), and stirring until the ascorbic acid and the polyethylene glycol are completely dissolved for later use.
Preparing 85 percent phosphoric acid into 0.68mol/L solution by deionized water in a phosphorus source batching tank for later use. Preparing sodium hydroxide into a 2mol/L solution by using deionized water in a pH regulator dosing tank, adding sodium oleate (the mass is 1 percent of ferrous sulfate), and stirring until the sodium oleate is completely dissolved for later use.
Thirdly, the solution in the iron source purification tank, the phosphorus source batching tank and the pH regulator batching tank is continuously conveyed to the multiphase interface reactor in parallel flow by adopting a metering mode, and a reactor stirring motor is started to carry out continuous synthesis reaction. The delivery flow rate of each component solution is 0.006m3The stirring speed of the reactor is 4000 r/min.
After the reaction, continuously conveying the slurry into an aging tank, then aging at normal temperature for 1h, repeatedly filtering and rinsing the aged slurry by using a filter press to obtain a blue filter cake, wherein the water content is less than or equal to 50%; drying the filter cake to constant weight by adopting a freeze drying mode to obtain blue gray Fe3(PO4)2·8H2O powder, Fe3(PO4)2·8H2Purity of O98%, Fe3(PO4)2·8H2The yield of O was 97%. Fe3(PO4)2·8H2The XRD pattern of O is shown in FIG. 1, and the iron-phosphorus ratio by ICP is 1.51. Fe3(PO4)2·8H2The SEM image of O is shown in FIG. 2, and it is found that the thickness is about 80nm and the morphology is plate-like by SEM test.
The production is continued for 24 hours by adopting the method, samples are taken at intervals of 2 hours, and the prepared Fe3(PO4) 2.8H 2O is tested for purity, wherein the purity is 98.2%, 98.7%, 98.4%, 98.2%, 98.8%, 98.9%, 98.5%, 98.3%, 98.2%, 98.0%, 98.6% and 98.9% in sequence, and the relative standard deviation RDS is 0.31%.
The first, second, third and fourth batches of production were carried out by the above method, maintaining the same production conditions, and the purity of the prepared Fe3(PO4) 2.8H 2O was tested to be 98.2%, 98.8%, 98.4% and 99.0% in this order, with a relative standard deviation RDS of 0.37%.
Therefore, the Fe3(PO4) 2.8H 2O prepared by the method has good stability and strong product consistency no matter in batches or among batches.
Example 2
Preparation of FePO by using titanium white byproduct4·2H2An O process comprising the steps of:
firstly, a titanium white byproduct FeSO is purified in an iron source purification tank4.7H2Preparing solution with the concentration of 0.5mol/L from O by deionized water, heating the solution to 80 ℃ under the stirring state, and adding iron powder (the mass of the byproduct FeSO of the titanium dioxide)4.7H20.02 percent of the mass of O), replacing hydrogen ions in the system by iron powder to increase the pH value in the system to 4.0, starting hydrolysis of titanium ions in the titanium dioxide byproduct, and removing precipitates by a vacuum filter after 1 hour of reaction to obtain a separation solution. Adding phosphoric acid (by-product FeSO of titanium white in quality) into the separated liquid4.7H20.02% of the mass of O), and continuously stirring for 30 min; then adding polyacrylamide (the mass is titanium dioxide byproduct FeSO)4.7H20.001 percent of the mass of O), and continuously stirring for 30 min; and filtering the suspended matters in the solution by using a vacuum filter to obtain a pure and transparent purified ferrous sulfate solution, wherein the purity of the prepared purified ferrous sulfate is 98.5%. Transferring the solution into a ferric sulfate batching tank, and sequentially adding sulfuric acid and a Fenton reagent into the ferric sulfate batching tank, wherein the adding amount of the sulfuric acid is determined according to the molar ratio n (Fe) of ferrous ions to sulfate radicals2+):n(H2SO4) 2: 1, the Fenton reagent is prepared according to the molar ratio n (Fe) of ferrous ions to hydrogen peroxide2 +):n(H2SO4) 1: 3, preparing, namely adding Fenton reagent in an amount which is 1 percent of the total volume of the purified ferrous sulfate solution, reacting for 1 hour at the reaction temperature of 40 ℃, oxidizing the ferrous sulfate solution into ferric sulfate solution after the reaction is finished, adding polyethylene glycol (0.1 per mill of the molar mass of ferric sulfate) into the ferric sulfate solution, and stirring until the polyethylene glycol is completely dissolved for later use.
② preparing the phosphoric acid with the mass fraction of 85 percent into solution with the concentration of 0.535mol/L by deionized water in a phosphorus source batching tank for standby. Preparing sodium hydroxide into a 1.08mol/L solution by using deionized water in a pH-to-regulator dosing tank, adding sodium dodecyl benzene sulfonate (the mass is 1 percent of the mass of ferric sulfate) into the solution, and stirring the solution until the sodium dodecyl benzene sulfonate is completely dissolved for later use.
Thirdly, the solution in the iron source purification tank, the phosphorus source batching tank and the pH regulator batching tank is continuously conveyed to the multiphase interface reactor in parallel flow by adopting a metering mode, and a reactor stirring motor is started to carry out continuous synthesis reaction. The conveying flow of each component solution is 1m3The stirring speed of the reactor is 4000 r/min.
After the reaction, continuously conveying the slurry into an aging tank, aging at 70 ℃ for 1h, repeatedly filtering and rinsing the aged slurry by using a filter press to obtain a white filter cake with the water content less than or equal to 50%; drying the filter cake to constant weight by adopting a flash evaporation drying mode to obtain white FePO4·2H2O powder, FePO4·2H2Purity of O is 99.0%, FePO4·2H2The yield of O was 98.0%. FePO4·2H2The XRD pattern of O is shown in FIG. 3, and the iron-phosphorus ratio by ICP is 0.98. FePO4·2H2The SEM image of O is shown in FIG. 4, and it is found that the particle size is about 50nm and the morphology is spheroidal by SEM test.
Continuously producing for 24 hours by adopting the method, sampling every 2 hours, and taking the prepared FePO4·2H2The purity of the product is tested by O, and the purity is 99.1%, 98.7%, 99.2%, 99.3%, 98.7%, 98.9%, 99.0%, 99.1%, 99.6% and 98.6% in sequence98.9%, 99.0%, relative standard deviation RDS of 0.28%.
The method is adopted to carry out the production of the first batch, the second batch, the third batch and the fourth batch, the same preparation conditions are kept, and the prepared FePO is tested4·2H2The purity of O is 98.9%, 99.5%, 99.1% and 98.7% in sequence, and the relative standard deviation RDS is 0.34%.
Thus, the FePO prepared by the method provided by the invention4·2H2And O, the prepared product has good stability and strong product consistency no matter in batch or between batches.
Application example 1
Fe prepared in example 13(PO4)2·8H2O and Li2CO3、NH4H2PO4The molar ratio of the raw materials is 2: 3: 2, mixing the materials, and then carrying out solid-phase reaction for 8 hours at 650 ℃ to obtain the lithium iron phosphate anode material.
Uniformly mixing the lithium iron phosphate positive electrode material with acetylene black and PVDF (polyvinylidene fluoride) according to the mass ratio of 8:1:1, fully grinding the mixture in an agate mortar, adding a proper amount of NMP (N-methyl pyrrolidone) as a solvent, fully stirring the mixture to prepare uniform slurry, uniformly coating the uniform slurry on an aluminum foil at the thickness of 150 mu m by using a film coater, drying the coated aluminum foil in vacuum at 120 ℃ for 12 hours, and punching and cutting the dried electrode plate into a circular electrode plate with the diameter of 14 mm.
The electrode plate, the metal lithium plate and the electrolyte (1mol L) prepared in the above are mixed-1LiPF6-EC/EMC) and a diaphragm (Celgard 2400) are placed in an argon-protected glove box, and a button lithium ion battery is assembled from bottom to top according to a positive electrode shell, an electrode plate, the diaphragm, a lithium plate, a gasket, an elastic sheet and a negative electrode shell in sequence.
The assembled button cell is subjected to charge and discharge performance test on a blue light tester (CT2001A) in a constant current-constant voltage charge and constant current discharge mode, the voltage range is 2.5-4.2V, the multiplying power is 0.1C, and the specific capacity definite result is 150 mAh/g.
Application example 2
FePO prepared in example 24·2H2O and Li2CO3The molar ratio of the raw materials is 2: 1, mixing materials, and then carrying out solid-phase reaction for 10 hours at 650 ℃ to obtain the lithium iron phosphate anode material.
Uniformly mixing the lithium iron phosphate positive electrode material with acetylene black and PVDF (polyvinylidene fluoride) according to the mass ratio of 8:1:1, fully grinding the mixture in an agate mortar, adding a proper amount of NMP (N-methyl pyrrolidone) as a solvent, fully stirring the mixture to prepare uniform slurry, uniformly coating the uniform slurry on an aluminum foil at the thickness of 150 mu m by using a film coater, drying the coated aluminum foil in vacuum at 120 ℃ for 12 hours, and punching and cutting the dried electrode plate into a circular electrode plate with the diameter of 14 mm.
The electrode plate, the metal lithium plate and the electrolyte (1mol L) prepared in the above are mixed-1LiPF6EC/EMC) and a diaphragm (Celgard 2400) are placed in a glove box protected by argon gas, and a button lithium ion battery is assembled from bottom to top according to a positive electrode shell, an electrode plate, the diaphragm, a lithium plate, a gasket, an elastic sheet and a negative electrode shell in sequence.
The assembled button cell is subjected to charge and discharge performance test on a blue light tester (CT2001A) in a constant current-constant voltage charge and constant current discharge mode, the voltage range is 2.5-4.2V, the multiplying power is 0.1C, and the specific capacity definite result is 165 mAh/g.
Meanwhile, through tests, the button cell has excellent low-temperature performance, and the capacity retention rate can reach 71% when the button cell is discharged at the temperature of-25 ℃.
Claims (10)
1. A method for preparing nano ferric phosphate and nano ferrous phosphate by using titanium dioxide byproducts is characterized by comprising the following steps:
(1) dissolving ferrous sulfate as a byproduct of titanium dioxide, adding iron, reacting, and after the reaction is finished, carrying out solid-liquid separation on a reaction liquid to obtain a separation liquid; adding phosphoric acid and a flocculating agent into the separation liquid, and filtering to remove filter residues to obtain a purified ferrous sulfate solution;
(2) adding an oxidizing reagent into the purified ferrous sulfate solution prepared in the step (1), and reacting to prepare a ferric sulfate solution;
(3) and (3) adding the purified ferrous sulfate solution prepared in the step (1) or the ferric sulfate solution prepared in the step (2) and a phosphorus source into a multiphase interface reactor in a concurrent flow manner, reacting, aging, and filtering to remove filtrate to obtain the nano ferrous phosphate or the nano ferric phosphate.
2. The method according to claim 1, wherein in the step (1), the iron is iron powder, and the mass of the iron powder is 0.01-0.1% of the mass of the ferrous sulfate as the titanium dioxide byproduct; the mass of the phosphoric acid is 0.005-3% of the mass of the ferrous sulfate as the titanium white byproduct.
3. The method according to claim 1, wherein in step (1), the flocculant is selected from at least one of polyacrylamide, sodium polyacrylate, polydimethyldiallylammonium chloride, polyethyleneimine, polyvinyl pyridinium salt or sodium carboxymethylcellulose; preferably, the mass of the flocculating agent is 0.01-0.3 per mill of the mass of the ferrous sulfate as the titanium white byproduct.
4. The method of claim 1, wherein in step (2), the oxidizing agent comprises sulfuric acid, hydrogen peroxide, and ferrous ions.
5. The method of claim 1, wherein in step (3), the feedstock co-current added to the purified ferrous sulfate solution prepared in step (1) or the ferric sulfate solution prepared in step (2) further comprises a dispersant and a surfactant.
6. The method of claim 5, wherein in step (3), the feedstock co-current added to the purified ferrous sulfate solution prepared in step (1) or the ferric sulfate solution prepared in step (2) further comprises a pH adjusting agent.
7. The method according to claim 6, wherein, in the step (3), when the reaction is carried out using the purified ferrous sulfate solution prepared in the step (1), the pH of the reaction system is adjusted to 6.0 to 7.0 using the pH adjusting agent.
8. The method as claimed in claim 6, wherein, in the step (3), when the reaction is carried out using the iron sulfate solution prepared in the step (2), the pH of the reaction system is adjusted to 1.5 to 2.0 using the pH adjustor.
9. The method according to claim 1, wherein, in the step (3), when the reaction is performed with the purified ferrous sulfate solution prepared in the step (1), the amount of the substance of the surfactant is 1 to 2% of the amount of the substance of the ferrous ion in the ferrous sulfate solution, and the amount of the substance of the dispersant is 0.1 to 0.5% of the amount of the substance of the ferrous ion in the ferrous sulfate solution;
when the ferric sulfate solution prepared in the step (2) is selected for reaction, the amount of the surfactant is 1% -2% of the amount of the ferric ion in the ferric sulfate solution, and the amount of the dispersant is 0.1-0.5% of the amount of the ferric ion in the ferric sulfate solution.
10. The use of the method for preparing nano iron phosphate and nano ferrous phosphate by using the titanium white byproduct as claimed in any one of claims 1 to 9 in the recovery of the titanium white byproduct.
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