CN112340719A - Method for preparing battery-grade iron phosphate by taking chloride as medium - Google Patents
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Abstract
The invention discloses a method for preparing battery-grade iron phosphate by taking chloride as a medium, belonging to the field of preparation of lithium battery anodes. Aiming at the problems of low ion utilization rate and poor iron phosphate performance in the existing iron phosphate preparation, the invention provides a method for preparing battery-grade iron phosphate by taking chloride as a medium, which comprises the steps of dissolving ferrous sulfate serving as a titanium white byproduct, and adding a precipitator to remove Ti2+Impurities are obtained to obtain ferrous sulfate purifying liquid; oxidizing the ferrous sulfate purified liquid, and adding a mixed solution of phosphoric acid and chloride to obtain a pre-reaction liquid; heating the pre-reaction liquid, and diluting after heating to obtain white iron phosphate slurry; and washing, filtering, drying and roasting the white iron phosphate slurry to obtain the battery-grade iron phosphate. According to the invention, the chloride is added to replace alkaline substances in a conventional method, the pH value in the solution is adjusted by taking the chloride as a medium to generate the battery-grade high-purity high-specific-surface-area iron phosphate, the atom utilization rate in the whole process is high, the process method is simple and environment-friendly, and the industrial large-scale production is easy to realize.
Description
Technical Field
The invention belongs to the field of preparation of lithium battery anodes, and particularly relates to a method for preparing battery-grade iron phosphate by taking chloride as a medium.
Background
In recent years, lithium ion batteries for power have been developed vigorously, and lithium iron phosphate is widely applied in recent years due to low preparation cost and high safety performance. The iron source for preparing the lithium iron phosphate is mostly ferric phosphate, the ferric phosphate is usually prepared by using a cheap titanium dioxide byproduct ferrous sulfate, and the common ferrous sulfate has low purity and cannot meet the requirement of preparing the ferric phosphate, so the ferric phosphate can be utilized only after being purified. In addition, with the mature development of the iron phosphate preparation process, manufacturers for preparing battery grade iron phosphate are increasing in recent years, so that the superiority of the iron phosphate preparation process is more emphasized. At present, the byproduct ferrous sulfate in the titanium dioxide industry in China exceeds 100 million tons per year, and the price is low and the purity is high, so that the preparation of battery-grade iron phosphate by using the ferrous sulfate becomes a mainstream method for preparing low-price iron phosphate.
For example, chinese patent application No. CN202010023348.8, published as 26/6/2020, discloses a method for preparing high-purity iron phosphate from ferrous sulfate, which comprises dissolving ferrous sulfate, a byproduct of titanium dioxide, in deionized water to obtain a saturated solution, sequentially adding an impurity removing agent and a flocculating agent, filtering to obtain a deeply purified ferrous solution, adding phosphoric acid into the ferrous solution, adding an oxidizing agent to oxidize ferrous iron into ferric iron, adding a pH adjusting agent to precipitate iron phosphate to form an iron phosphate slurry, press-drying and pulp-washing the slurry for multiple times, aging, filtering, drying, dehydrating and scattering to obtain a high-purity iron phosphate product. The disadvantages of the patent are that: because a large amount of alkaline substances are required to be added in the process of preparing the iron phosphate to adjust the pH value of the solution, H is generated in the process+And OH-Are combined into H2The process of O is actually a dissociationThe method is wasted and the process is therefore to be further optimized.
Also, as shown in chinese patent application No. cn201810268409.x, published as 2018, 7, month and 24, the patent discloses a method for preparing battery grade anhydrous iron phosphate from sulfuric acid cinder, which comprises the following steps: feeding washing water containing hydrochloric acid in the iron phosphate production into an electrolytic cell to obtain chlorine; introducing chlorine into the yellow phosphorus water, and absorbing the chlorine by the yellow phosphorus water to obtain a mixture of phosphoric acid and hydrochloric acid; and reacting the mixture of phosphoric acid and hydrochloric acid with the sulfuric acid cinder to obtain crude iron phosphate. The disadvantages of the patent are that: on one hand, when the sulfuric acid cinder is adopted for preparing the iron phosphate, the impurity removal process is complex due to the fact that the content of impurity ions in the sulfuric acid cinder is high, and in addition, a large amount of hydrochloric acid in the process also provides great challenges for equipment preparation in reaction equipment.
Disclosure of Invention
1. Problems to be solved
Aiming at the problems of low ion utilization rate and poor iron phosphate performance in the prior art for preparing ferric phosphate, the invention provides a method for preparing battery-grade ferric phosphate by taking chloride as a medium. The method starts from the reaction essence in the iron phosphate generation process, adds chloride to replace alkaline substances in the conventional method, adjusts the pH value in the solution by taking chloride as a medium, and finally generates the battery-grade high-purity iron phosphate with high specific surface area.
2. Technical scheme
In order to solve the above problems, the present invention adopts the following technical solutions.
A method for preparing battery-grade iron phosphate by taking chloride as a medium comprises the following steps:
s1: dissolving ferrous sulfate as a titanium white byproduct, and adding a precipitator to remove Ti2+Impurities are obtained to obtain ferrous sulfate purifying liquid;
s2: oxidizing the ferrous sulfate purified liquid, and adding a mixed solution of phosphoric acid and chloride to obtain a pre-reaction liquid;
s3: heating the pre-reaction liquid, and diluting after heating to obtain white iron phosphate slurry;
s4: and washing, filtering, drying and roasting the white iron phosphate slurry to obtain the battery-grade iron phosphate.
Furthermore, the precipitant in step S1 is a mixture of phosphoric acid and sodium hydroxide, and the pH of the ferrous sulfate solution is maintained at 1.8-2.5, the reaction temperature is 60-80 ℃, and the reaction time is 0.5-1.5 h.
Further, phosphoric acid is added in an amount of Ti in the ferrous sulfate solution2+The amount of the substance is 1.5 to 2.0 times.
Further, in step S2, the chloride salt is one or more of sodium chloride, potassium chloride, and lithium chloride.
Furthermore, the ratio of the amount of the substances added in the phosphoric acid to the amount of the ferrous ion substances in the ferrous sulfate purifying solution is (1.0-1.3): 1; the ratio of the amount of the substance added in the chloride salt to the amount of the ferrous ion substance in the ferrous sulfate purifying solution is (1.0-1.3): 1.
furthermore, the molar concentration of the iron ions in the pre-reaction liquid is 1.0-2.0 mol/L.
Furthermore, in step S2, the ferrous sulfate purified liquid is oxidized by hydrogen peroxide, and the ratio of the amount of hydrogen peroxide to the amount of iron ion is (1.1-1.3): 1.
furthermore, in the step S3, the heating temperature is 100-150 ℃, and the heating time is 3-6 hours.
Furthermore, deionized water is introduced in the heating process, and the concentration of iron ions is maintained at 2.5-4.0 mol/L; after the heating process is finished, deionized water is passed through the furnace, and the concentration of iron ions is maintained at 0.8-1.5 mol/L.
Furthermore, in the step S4, the roasting temperature is 400-650 ℃, and the roasting time is 1-4 h.
3. Advantageous effects
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention dissolves ferrous sulfate, adds precipitator to remove impurities, adds the mixed solution of phosphoric acid and chloride into the ferrous solution after removing impurities, in the heating evaporation process, hydrogen ions in phosphoric acid and chloride ions in added chloride are combined and then escape from the system in a hydrogen chloride mode, the pH value in the system is gradually increased, battery-grade iron phosphate slurry is instantly and completely generated by diluting the slurry after the pH value of the iron phosphate precipitate is reached, the chloride salt is adopted to replace alkaline solution or acidic solution required by conventional reaction in the whole preparation process, and hydrogen ions in the phosphoric acid are added to escape from the system by a hydrogen chloride method to obtain a hydrochloric acid solution, the hydrogen ions in the solution are fully utilized to be converted into important industrial raw materials, the ion utilization rate is improved, the prepared iron phosphate has high purity and large specific surface area, and is beneficial to performance exertion of the subsequent preparation of the iron lithium material; the production cost of the iron phosphate is reduced while the effective utilization of resources is ensured;
(2) the method controls the pH value of a ferrous sulfate solution to be 1.8-2.5, and performs reaction for 0.5-1.5 h at the temperature of 60-80 ℃ to perform Ti2+The impurity removal operation of (2) and the control of the amount of phosphoric acid substance, facilitating Ti2+The precipitation is complete, and the effect of removing impurities from the ferrous sulfate solution is improved; meanwhile, mixed liquor of phosphoric acid and sodium hydroxide is used as a precipitator, so that phosphate ions and sodium ions contained in the ferrous sulfate purified liquor do not cause any influence on the preparation and performance of the iron phosphate, impurity ions in the precipitator are prevented from being contained in the prepared iron phosphate, and the prepared iron phosphate is ensured to have higher purity;
(3) the chloride salt adopted by the invention is one or more of sodium chloride, potassium chloride and lithium chloride, cations in the chloride salt cannot overflow a system, namely a pre-reaction liquid, in the reaction process, and the cations left in the system can be easily washed and removed in the subsequent process, and cannot be doped in the iron phosphate;
(4) the heating temperature is controlled to be 100-150 ℃, the heating time is 3-6 hours, the chlorine ions and the hydrogen ions are mainly combined to generate a hydrogen chloride escape system, the hydrogen chloride escape is not facilitated when the temperature is too low or too high, the heating is carried out within the temperature range, the complete reaction of the chlorine ions is facilitated, the hydrogen ions in the solution quickly escape in a hydrogen chloride mode, the iron phosphate can be completely generated, and the specific surface area is controlled to be a large level; meanwhile, after heating is finished, diluting the pre-reaction solution, wherein the diluting function is to reduce the concentration of iron ions and phosphate ions in the system, so that the ferric phosphate dihydrate slurry can be effectively generated in a combined manner;
(5) according to the invention, deionized water is introduced in the heating process to ensure that iron ions are maintained within a certain concentration range, namely, the concentrations of chloride ions and hydrogen ions in the pre-reaction liquid are maintained, so that hydrogen chloride can quickly and effectively escape from the system, and the reaction period is shortened; the reason why deionized water is introduced to maintain the iron ions within a certain concentration range after the heating process is finished is that the specific surface area of the generated iron phosphate is larger under the concentration.
Drawings
FIG. 1 is an electron micrograph of dehydrated iron phosphate at 5000 Xmagnification in example 1;
FIG. 2 is an electron micrograph of dehydrated iron phosphate at 2000 times magnification in example 1.
Detailed Description
The invention is further described with reference to specific embodiments and the accompanying drawings.
A method for preparing battery-grade iron phosphate by taking chloride as a medium comprises the following steps:
s1: dissolving ferrous sulfate as a titanium white byproduct, and adding a precipitator to remove Ti2+Impurities are obtained to obtain ferrous sulfate purifying liquid;
specifically, a mixed solution of phosphoric acid and sodium hydroxide is selected as a precipitator to remove Ti from a ferrous sulfate solution which is a titanium white byproduct2+Impurities; because the sodium sulfide is usually selected as the conventional precipitant, the ferrous sulfate solution after impurity removal contains a small amount of impurity ions, namely sulfide ions, and the purity and performance of the later-stage ferric phosphate are greatly influenced; the ferrous sulfate solution after the impurities of the mixed solution of phosphoric acid and sodium hydroxide are removed contains residual phosphate ions and sodium ions, so that the purity and performance of the iron phosphate are not affected, and the good performance of the iron phosphate is ensured. And controlling the concentration of ferrous ions after the ferrous sulfate is dissolved to be 1.5-2.5mol/L and the concentration of the ferrous ions to be too low,energy consumption for subsequent evaporation of water is increased, and cost is increased; at too high a concentration, ferrous ions are difficult to dissolve to form a solution. At the same time, in order to ensure Ti2+The impurities can be completely precipitated, the impurity removal effect and efficiency are improved, the pH value of the ferrous sulfate solution is kept to be 1.8-2.5, the reaction temperature is 60-80 ℃, and the reaction time is 0.5-1.5 h; and the amount of the substance added by the phosphoric acid is Ti in the ferrous sulfate solution2+The amount of the substance is 1.5 to 2.0 times of that of the substance, and the amount of the phosphoric acid substance is slightly higher than that of Ti2+Amount of substance ensuring Ti2+Complete reaction and complete precipitation.
S2: oxidizing the ferrous sulfate purified liquid, and adding a mixed solution of phosphoric acid and chloride to obtain a pre-reaction liquid;
specifically, the ferrous sulfate purified liquid is oxidized by hydrogen peroxide, and the ratio of the amount of hydrogen peroxide substances to the amount of iron ion substances is (1.1-1.3): 1, the hydrogen peroxide has good oxidation effect and wide sources; meanwhile, the quantity of the hydrogen peroxide is controlled within a certain proportion range, so that bivalent iron ions can be completely oxidized, and the purity of the iron phosphate prepared in the later period is high. And the chloride salt in the application meets the following requirements: cations in the chloride cannot escape from the system of the pre-reaction liquid in the reaction process, and the cations remained in the system can be easily washed and removed in the subsequent washing and filtering process of the iron phosphate, otherwise, the prepared iron phosphate has low purity and contains impurities. Therefore, the chloride salt is preferably one or more of sodium chloride, potassium chloride and lithium chloride, the chloride salt is cheap in price and wide in raw material source, and the preparation cost of the iron phosphate is effectively reduced. Meanwhile, the ratio of the amount of the substances added in the phosphoric acid to the amount of the ferrous ion substances in the ferrous sulfate purifying solution is (1.0-1.3): 1; the ratio of the amount of the substance added in the chloride salt to the amount of the ferrous ion substance in the ferrous sulfate purifying solution is (1.0-1.3): 1, for chloride, when the content of the chloride is too low, the acidity of the solution is too strong after subsequent heating and evaporation, and iron phosphate precipitation is difficult to generate; when the content is too large, the prepared slurry contains a large amount of chloride ions, and the wastewater treatment cost is increased. When the phosphoric acid content is too low, iron phosphate cannot be generated; too much content causes waste of resources. Therefore, the amount of the substances of the chloride and the phosphoric acid is strictly controlled, raw materials are saved under the condition of ensuring that hydrogen ions and chloride ions are completely combined, the cost of the raw materials is reduced, and the pressure of wastewater treatment is reduced. And controlling the molar concentration of iron ions in the pre-reaction liquid to be 1.0-2.0mol/L, and controlling the molar concentration of the iron ions in the range, so that the elements are kept existing in a solution mode, and the subsequent evaporation cost is reduced under a higher concentration.
S3: heating the pre-reaction liquid, and diluting after heating to obtain white iron phosphate slurry;
specifically, the heating temperature is controlled to be 100-150 ℃ in the step, the heating time is 3-6 hours, a hydrogen chloride escape system is generated by mainly combining chloride ions and hydrogen ions in the step, the temperature is too low or too high, the hydrogen chloride escape is not facilitated, heating is performed within the temperature range, complete reaction of the chloride ions is facilitated, the hydrogen ions in the solution escape in a hydrogen chloride mode quickly, meanwhile, the pH of the final solution is accurately controlled, iron phosphate can be generated completely, and the specific surface area of the iron phosphate can be controlled to a large level. Deionized water is added twice in the step, the deionized water is slowly introduced at a constant speed for the first time in the heating process, the concentration of iron ions is maintained at 2.5-4.0mol/L, and the concentrations of chloride ions and hydrogen ions in the pre-reaction liquid are maintained, so that hydrogen chloride can quickly and effectively escape from the system, and the reaction period is shortened; and slowly introducing deionized water at a constant speed for the second time after heating is finished, wherein the concentration of iron ions is maintained to be 0.8-1.5mol/L, and the specific surface area of the generated iron phosphate is larger at the concentration.
S4: and washing, filtering, drying and roasting the white iron phosphate slurry to obtain the battery-grade iron phosphate, wherein the roasting temperature is 400-650 ℃, and the roasting time is 1-4 h, so that the battery-grade iron phosphate with high purity and high specific surface is obtained.
Starting from the reaction essence in the iron phosphate generation process, the invention seeks a method which has relatively cheap raw materials and high ion utilization rate in the preparation process to prepare the high-purity iron phosphate with high specific surface area. Dissolving ferrous sulfate, adding a small amount of phosphoric acid, adjusting the pH value of the solution to remove Ti in the solution2+Impurities then willAfter the ferrous solution after impurity removal is oxidized, a mixed solution of chloride and phosphoric acid with a proper amount is added, in the heating evaporation reaction process, through reasonably controlling the concentration and reaction temperature of ferrous ions in the solution, hydrogen ions in the phosphoric acid and chloride ions in the added chloride are combined and then escape from the system in a hydrogen chloride mode, the pH value in the system is gradually increased, after the precipitation pH value of the iron phosphate is reached, battery-grade iron phosphate slurry is instantly and completely generated through diluting the slurry, and meanwhile, hydrogen chloride escaping from the system can be reused. The chloride salt is added in the preparation process to replace the alkaline solution or the acid solution required by the conventional reaction, and the ions of the chloride salt are unreasonably utilized because the hydroxide ions of the chloride salt are combined with the hydrogen ions in the solution to generate water by the conventional method. The method takes chloride as a medium to adjust the pH value in the solution to finally generate the battery-grade high-purity iron phosphate with high specific surface area, the ion utilization rate in the whole process is high, the process method is simple, the environment is protected, and the industrial large-scale production is easy to realize.
Example 1
As shown in fig. 1 and 2, a method for preparing battery grade iron phosphate by taking chloride as a medium comprises the following steps:
s1: taking 2mol of titanium white byproduct ferrous sulfate crystals, adding 1L of water for dissolving, heating in a water bath kettle at 70 ℃ for reaction, adding a sodium hydroxide solution and 0.04mol of phosphoric acid solution, adjusting the pH value to 2.0, reacting for 0.5h, filtering and washing to obtain a ferrous sulfate purified solution;
s2: adding 3.0mol of hydrogen peroxide into the ferrous sulfate purified solution for oxidation, then adding a mixed solution of 2.4mol of phosphoric acid and 2.5mol of sodium chloride, and fixing the volume to 1.8L of solution to obtain a pre-reaction solution;
s3: heating the pre-reaction liquid at 150 ℃, introducing deionized water at a constant speed during the heating to maintain the concentration of iron ions at 3.5mol/L, reacting for 5 hours, introducing deionized water at a constant speed after the heating is finished, and diluting to obtain 2L of white iron phosphate slurry;
s4: and washing, filtering and drying the white iron phosphate slurry, and roasting at 600 ℃ for 3h to obtain high-purity and high-specific surface iron phosphate powder.
Example 2
A method for preparing battery-grade iron phosphate by taking chloride as a medium comprises the following steps:
s1: taking 2mol of titanium white byproduct ferrous sulfate crystals, adding 1.33L of water for dissolving, heating in a water bath kettle at 85 ℃ for reaction, adding a sodium hydroxide solution and 0.05mol of a phosphoric acid solution, adjusting the pH value to 1.8, reacting for 1.0h, filtering and washing to obtain a ferrous sulfate purified solution;
s2: adding 2.5mol of hydrogen peroxide into the ferrous sulfate purified solution for oxidation, then adding a mixed solution of 2.0mol of phosphoric acid and 2.1mol of potassium chloride, and fixing the volume to 1.1L of solution to obtain a pre-reaction solution;
s3: heating the pre-reaction liquid at 100 ℃, introducing deionized water at a constant speed during the heating to maintain the concentration of iron ions at 4.0mol/L, reacting for 4 hours, introducing deionized water at a constant speed after the heating is finished, and diluting to obtain 1.5L of white iron phosphate slurry;
s4: and washing, filtering and drying the white iron phosphate slurry, and roasting at 500 ℃ for 3h to obtain high-purity and high-specific surface iron phosphate powder.
Example 3
A method for preparing battery-grade iron phosphate by taking chloride as a medium comprises the following steps:
s1: taking 2mol of titanium white byproduct ferrous sulfate crystals, adding 1.20L of water for dissolving, heating in a water bath kettle at 60 ℃ for reaction, adding a sodium hydroxide solution and 0.043mol of phosphoric acid solution, adjusting the pH to 1.9, reacting for 1.0h, filtering and washing to obtain a ferrous sulfate purified solution;
s2: adding 2.7mol of hydrogen peroxide into the ferrous sulfate purified solution for oxidation, then adding a mixed solution of 2.2mol of phosphoric acid and 2.2mol of lithium chloride, and fixing the volume to 1.5L of solution to obtain a pre-reaction solution;
s3: heating the pre-reaction liquid at 140 ℃, introducing deionized water at a constant speed during the heating to maintain the concentration of iron ions at 2.5mol/L, reacting for 6 hours, introducing deionized water at a constant speed after the heating is finished, and diluting to obtain 1.6L of white iron phosphate slurry;
s4: and washing, filtering and drying the white iron phosphate slurry, and roasting at 650 ℃ for 3.5 hours to obtain high-purity and high-specific surface iron phosphate powder.
Example 4
A method for preparing battery-grade iron phosphate by taking chloride as a medium comprises the following steps:
s1: taking 2mol of titanium white byproduct ferrous sulfate crystals, adding 1.30L of water for dissolving, heating in a water bath kettle at 75 ℃ for reaction, adding a sodium hydroxide solution and 0.05mol of a phosphoric acid solution, adjusting the pH value to 2.0, reacting for 0.8h, filtering and washing to obtain a ferrous sulfate purified solution;
s2: adding 2.6mol of hydrogen peroxide into the ferrous sulfate purified solution for oxidation, then adding a mixed solution of 2.3mol of phosphoric acid and 1.1mol of each of sodium chloride and lithium chloride, and fixing the volume to 1.4L of solution to obtain a pre-reaction solution;
s3: heating the pre-reaction liquid at 140 ℃, introducing deionized water at a constant speed during the heating to maintain the concentration of iron ions at 3.8mol/L, reacting for 4.5h, introducing deionized water at a constant speed after the heating is finished, and diluting to obtain 1.7L of white iron phosphate slurry;
s4: and washing, filtering and drying the white iron phosphate slurry, and roasting at 550 ℃ for 4h to obtain high-purity and high-specific surface iron phosphate powder.
Example 5
A method for preparing battery-grade iron phosphate by taking chloride as a medium comprises the following steps:
s1: taking 2mol of titanium white byproduct ferrous sulfate crystals, adding 1.25L of water for dissolving, heating in a water bath kettle at 70 ℃ for reaction, adding a sodium hydroxide solution and 0.05mol of a phosphoric acid solution, adjusting the pH value to 1.7, reacting for 0.8h, filtering and washing to obtain a ferrous sulfate purified solution;
s2: adding 2.6mol of hydrogen peroxide into the ferrous sulfate purified solution for oxidation, then adding a mixed solution of 2.3mol of phosphoric acid and 1.15mol of each of potassium chloride and lithium chloride, and carrying out constant volume to 1.4L of solution to obtain a pre-reaction solution;
s3: heating the pre-reaction liquid at 140 ℃, introducing deionized water at a constant speed during the heating to maintain the concentration of iron ions at 3.6mol/L, reacting for 4.0h, introducing deionized water at a constant speed after the heating is finished, and diluting to obtain 1.6L of white iron phosphate slurry;
s4: and washing, filtering and drying the white iron phosphate slurry, and roasting at 450 ℃ for 4h to obtain high-purity and high-specific surface iron phosphate powder.
Comparative example 1
In contrast to example 1, a method for preparing battery grade iron phosphate mediated by chloride salts comprises the following steps:
s1: taking 2mol of titanium white byproduct ferrous sulfate crystals, adding 1.0L of water for dissolving, heating in a water bath kettle at 70 ℃ for reaction, adding a sodium hydroxide solution and 0.04mol of phosphoric acid solution, adjusting the pH value to 2.0, reacting for 0.5h, filtering and washing to obtain a ferrous sulfate purified solution;
s2: adding 3.0mol of hydrogen peroxide into the ferrous sulfate purified solution for oxidation, then adding a mixed solution of 2.4mol of phosphoric acid and 2.5mol of sodium chloride, and fixing the volume to 1.8L of solution to obtain a pre-reaction solution;
s3: heating the pre-reaction liquid at 80 ℃, introducing deionized water at a constant speed during the heating to maintain the concentration of iron ions at 3.5mol/L, reacting for 5.0h, introducing deionized water at a constant speed after the heating is finished, and diluting to obtain 2.0L of white iron phosphate slurry;
s4: and washing, filtering and drying the white iron phosphate slurry, and roasting at 600 ℃ for 3h to obtain iron phosphate powder.
Conditions changed compared to example 1: the pre-reaction liquid is heated to a reaction temperature lower than 100 ℃. The comparative examples have the disadvantages that: when the pre-reaction temperature is lower than 100 ℃ in step S3, it is difficult for chloride ions and hydrogen ions to escape from the system in the form of hydrogen chloride during the heating evaporation, resulting in too low solution pH, partial generation of iron phosphate and small specific surface area.
Comparative example 2
In contrast to example 1, a method for preparing battery grade iron phosphate mediated by chloride salts comprises the following steps:
s1: taking 2mol of titanium white byproduct ferrous sulfate crystals, adding 1.0L of water for dissolving, heating in a water bath kettle at 70 ℃ for reaction, adding a sodium hydroxide solution and 0.04mol of phosphoric acid solution, adjusting the pH value to 2.0, reacting for 0.5h, filtering and washing to obtain a ferrous sulfate purified solution;
s2: adding 3.0mol of hydrogen peroxide into the ferrous sulfate purified solution for oxidation, then adding a mixed solution of 2.4mol of phosphoric acid and 1.6mol of sodium chloride, and fixing the volume to 1.8L of solution to obtain a pre-reaction solution;
s3: heating the pre-reaction liquid at 150 ℃, introducing deionized water at a constant speed during the heating to maintain the concentration of iron ions at 3.5mol/L, reacting for 5.0h, introducing deionized water at a constant speed after the heating is finished, and diluting to obtain 2.0L of white iron phosphate slurry;
s4: and washing, filtering and drying the white iron phosphate slurry, and roasting at 600 ℃ for 3h to obtain iron phosphate powder.
Conditions changed compared to example 1: the dosage of the chloride is less than 1.0 time of the molar weight of the ferrous. The comparative examples have the disadvantages that: when the amount of the chloride substance is less than 1.0 times the amount of the ferrous ion substance in step S2, even if all chloride ions escape from the system in the form of hydrogen chloride during the reaction, the pH of the system does not reach the pH at which the ferric phosphate is completely precipitated, so that the ferric phosphate is only partially formed and has a small specific surface area.
Comparative example 3
In contrast to example 1, a method for preparing battery grade iron phosphate mediated by chloride salts comprises the following steps:
s1: taking 2mol of titanium white byproduct ferrous sulfate crystals, adding 1.0L of water for dissolving, heating in a water bath kettle at 70 ℃ for reaction, adding a sodium hydroxide solution and 0.04mol of phosphoric acid solution, adjusting the pH value to 2.0, reacting for 0.5h, filtering and washing to obtain a ferrous sulfate purified solution;
s2: adding 3.0mol of hydrogen peroxide into the ferrous sulfate purified solution for oxidation, then adding a mixed solution of 3.0mol of phosphoric acid and 2.5mol of sodium chloride, and fixing the volume to 1.8L of solution to obtain a pre-reaction solution;
s3: heating the pre-reaction liquid at 150 ℃, introducing deionized water at a constant speed during the heating to maintain the concentration of iron ions at 3.5mol/L, reacting for 5.0h, introducing deionized water at a constant speed after the heating is finished, and diluting to obtain 2.0L of white iron phosphate slurry;
s4: and washing, filtering and drying the white iron phosphate slurry, and roasting at 600 ℃ for 3h to obtain iron phosphate powder.
Conditions changed compared to example 1: the amount of the phosphoric acid is 1.3 times more than the molar amount of the ferrous iron. The comparative examples have the disadvantages that: when the amount of the phosphoric acid substance exceeds 1.3 times of the amount of the ferrous ion substance in step S2, on one hand, the residual phosphate radical in the solution after the iron phosphate generation is excessive, which increases the treatment cost and raw material cost of the wastewater, and on the other hand, when the amount of the phosphoric acid is excessive, the pH in the system is too low, even if all chloride ions escape from the system in the form of hydrogen chloride, the pH of the system is too low, which does not reach the pH at which the iron phosphate is completely precipitated, so that the iron phosphate is only partially generated, and the specific surface area is small.
Comparative example 4
In contrast to example 1, a method for preparing battery grade iron phosphate mediated by chloride salts comprises the following steps:
s1: taking 2mol of titanium white byproduct ferrous sulfate crystals, adding 1.0L of water for dissolving, heating in a water bath kettle at 70 ℃ for reaction, adding a sodium hydroxide solution and 0.04mol of phosphoric acid solution, adjusting the pH value to 2.0, reacting for 0.5h, filtering and washing to obtain a ferrous sulfate purified solution;
s2: adding 3.0mol of hydrogen peroxide into the ferrous sulfate purified solution for oxidation, then adding a mixed solution of 2.4mol of phosphoric acid and 2.5mol of sodium chloride, and fixing the volume to 1.8L of solution to obtain a pre-reaction solution;
s3: heating the pre-reaction liquid at 150 ℃, introducing deionized water at a constant speed during the heating to maintain the concentration of iron ions at 2.0mol/L, reacting for 5.0h, introducing deionized water at a constant speed after the heating is finished, and diluting to obtain 2.0L of white iron phosphate slurry;
s4: and washing, filtering and drying the white iron phosphate slurry, and roasting at 600 ℃ for 3h to obtain iron phosphate powder.
Conditions changed compared to example 1: and in the process of continuously reacting the pre-reaction liquid to generate the iron phosphate, maintaining the concentration of iron ions at 2.0 mol/L. The comparative examples have the disadvantages that: in the process of continuing the reaction of the pre-reaction solution to generate iron phosphate in step S3, when the concentration of iron ions is too low, chloride ions and hydrogen ions in the solution are difficult to escape from the system in the form of hydrogen chloride, resulting in too low pH of the system, only partial generation of iron phosphate, and small specific surface area.
According to the invention, the physical parameters of the iron phosphate in the above examples and comparative examples are compared and analyzed to obtain the following table 1:
table 1: comparison of physical parameters of iron phosphate prepared in examples and comparative examples
As can be seen from table 1, when the pre-reaction solution is heated, the concentration and the reaction temperature of the ferrous ions in the pre-reaction solution and the amounts of the phosphoric acid and the chloride salt are reasonably controlled, so that the hydrogen ions in the phosphoric acid and the chloride ions in the added chloride are completely combined and escape from the system in the form of hydrogen chloride, the pH in the system gradually rises, and after the pH of the iron phosphate precipitate is reached, the slurry is diluted to instantly and completely generate the battery-grade iron phosphate slurry with high purity and high specific surface area. The whole process has high atom utilization rate, simple process method, environmental protection and easy industrial large-scale production.
The examples described herein are merely illustrative of the preferred embodiments of the present invention and do not limit the spirit and scope of the present invention, and various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the design concept of the present invention shall fall within the protection scope of the present invention.
Claims (10)
1. A method for preparing battery-grade iron phosphate by taking chloride as a medium is characterized by comprising the following steps: the method comprises the following steps:
s1: dissolving ferrous sulfate as a titanium white byproduct, and adding a precipitator to remove Ti2+Impurities are obtained to obtain ferrous sulfate purifying liquid;
s2: oxidizing the ferrous sulfate purified liquid, and adding a mixed solution of phosphoric acid and chloride to obtain a pre-reaction liquid;
s3: heating the pre-reaction liquid, and diluting after heating to obtain white iron phosphate slurry;
s4: and washing, filtering, drying and roasting the white iron phosphate slurry to obtain the battery-grade iron phosphate.
2. The method for preparing battery-grade iron phosphate mediated by chloride salt according to claim 1, characterized in that: and in the step S1, the precipitator is a mixed solution of phosphoric acid and sodium hydroxide, the pH value of the ferrous sulfate solution is kept to be 1.8-2.5, the reaction temperature is 60-80 ℃, and the reaction time is 0.5-1.5 h.
3. The method for preparing battery-grade iron phosphate mediated by chloride salt according to claim 2, characterized in that: the amount of the substance added into the phosphoric acid is Ti in the ferrous sulfate solution2+The amount of the substance is 1.5 to 2.0 times.
4. The method for preparing battery-grade iron phosphate mediated by chloride salt according to claim 1, characterized in that: in the step S2, the chloride salt is one or more of sodium chloride, potassium chloride and lithium chloride.
5. The method for preparing battery-grade iron phosphate mediated by chloride salt according to claim 4, characterized in that: the ratio of the amount of the substances added in the phosphoric acid to the amount of the ferrous ion substances in the ferrous sulfate purifying solution is (1.0-1.3): 1; the ratio of the amount of the substance added in the chloride salt to the amount of the ferrous ion substance in the ferrous sulfate purifying solution is (1.0-1.3): 1.
6. the method for preparing battery-grade iron phosphate mediated by chloride salt according to claim 5, characterized in that: the molar concentration of iron ions in the pre-reaction liquid is 1.0-2.0 mol/L.
7. The method for preparing battery grade iron phosphate mediated by chloride salt according to claim 1 or 5, characterized in that: in the step S2, the ferrous sulfate purified liquid is oxidized by hydrogen peroxide, and the ratio of the amount of hydrogen peroxide to the amount of iron ion substances is (1.1-1.3): 1.
8. the method for preparing battery-grade iron phosphate mediated by chloride salt according to claim 1, characterized in that: in the step S3, the heating temperature is 100-150 ℃, and the heating time is 3-6 h.
9. The method for preparing battery grade iron phosphate mediated by chloride salt according to claim 8, wherein: deionized water is introduced in the heating process, and the concentration of iron ions is maintained at 2.5-4.0 mol/L; after the heating process is finished, deionized water is passed through the furnace, and the concentration of iron ions is maintained at 0.8-1.5 mol/L.
10. The method for preparing battery-grade iron phosphate mediated by chloride salt according to claim 1, characterized in that: in the step S4, the roasting temperature is 400-650 ℃, and the roasting time is 1-4 h.
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