Study On The Process Of Preparing Battery-grade Iron Phosphate From Yellow Phosphorus By-product Ferrophosphorus Sla

As people pay more and more attention to the safety of new energy vehicles,lithium iron phosphate stands out among the many lithium battery materials due to its high safety features,and is sought after by the market.And iron phosphate,the main raw material for lithium iron phosphate,is therefore in great demand.Yellow phosphorus by-product iron phosphate slag as a solid waste,which is enriched with a large amount of iron and phosphorus elements(usually 50% to 75% iron and 18-30% phosphorus),if the iron and phosphorus elements in it are used rationally to prepare battery-grade iron phosphate,not only can turn waste into treasure,but also can meet the huge demand of the iron phosphate market,further promote the popularity of new energy vehicles and benefit the country’s This will further promote the popularisation of new energy vehicles and contribute to the country’s strategic goal of "carbon peaking" and "carbon neutral".In this paper,a spherical battery-grade ferric phosphate was prepared in a simple and efficient way using a three-stage process of "dissolution-co-precipitation-calcination",which shortens the production process and maximises the use of iron and phosphorus in ferric phosphate slag,thus solving environmental problems and achieving efficient use of solid waste resources.The process has been developed by using XRD,SEM,and other methods.Firstly,the physicochemical properties of the raw iron phosphate slag were determined by XRD,SEM and ICP tests,and the dissolution of the slag with a strong oxidising acid to obtain a solution of iron phosphate containing iron and phosphorus was determined by the test results and literature review.The optimum process conditions were derived.The optimum conditions were found to be: solid-liquid ratio of 1:12,nitric acid concentration of 7.6 mol/L,dissolution time of 5 h and dissolution temperature of 90°C.The dissolution rate of iron phosphate slag under these conditions was 96.39 %.Secondly,the prepared ferric phosphate solution was studied to generate hydrated ferric phosphate by co-precipitation,and the bound water was removed by drying and calcination to finally generate anhydrous ferric phosphate.The effects of the four process conditions of solution iron-phosphorus molar ratio,reaction temperature,reaction time and reaction p H in the co-precipitation process and the two process conditions of calcination time and calcination temperature in the calcination and dehydration process on the iron-phosphorus ratio,particle size and morphology of iron phosphate were investigated respectively.The optimum process conditions were determined to be: 1:1molar ratio of iron to phosphorus in solution,the reaction temperature of 80 °C,reaction time of 4 h,p H of 1,calcination temperature of 500 °C and calcination time of 1 h.the anhydrous iron phosphate material produced under these conditions met the requirements of the industry standard HG/T 4701-2021 in terms of iron content,phosphorus content,iron to phosphorus ratio,impurity element content and particle size.In addition,the process of washing wastewater treatment in the preparation process was explored.Through secondary treatment of wastewater,XRD and ICP testing of intermediate products and treated wastewater,nitric acid and barium sulphate were prepared from the hazardous waste product ammonium nitrate in washing wastewater,reducing the environmental hazards and enabling the reuse of nitric acidFinally,a carbon coated lithium iron phosphate cathode material was synthesised from home-made iron phosphate and assembled into a button cell to test the electrochemical performance,with a first discharge specific capacity of 142.37 m Ah g-1at a charge/discharge rate of 1 C.After 200 cycles,the specific capacity was still 143.09 m Ah g-1 with no degradation and good cycling stability;the highest discharge specific capacity at a charge/discharge rate of 0.1 C was 152.12 m Ah g-1.The highest discharge specific capacity at 0.1 C charge/discharge multiplier was 152.12 m Ah g-1 with a Coulomb efficiency of 95.35%;the discharge specific capacities at 0.1,1 and 5 C were152.01,138.07 and 107.87 m Ah g-1,respectively,and after charging and discharging at different current densities,the battery capacity was 146.8 m Ah g-1 after re-charging and discharging at 0.1 C,which was still 96% higher than the discharge specific capacity of the first cycle.of capacity,proving that the prepared cathode material has high specific capacity,stable structure,good reversibility and cycling performance,and has certain commercial value.