Preparation of battery-grade iron phosphate using the by-product ferrous sulfate of titanium dioxide
Battery-grade iron phosphate was synthesized by liquid-phase precipitation using ferric sulphate as the source of iron,which was obtained from purification of by-product ferrous sulfate of titanium dioxide.The effects of iron to phosphorus feed ratio(Fe/P feed ratio),reaction temperature,pH,CTAB addition on Fe/P,grain size and yield of iron phosphate were investigated.The optimal synthesis conditions for high-yield iron phosphate obtained by response surface methodology were Fe/P feed ratio of 1.33,80℃,pH of 1.6 and CTAB addition of 2%.Through the response surface optimization experiment,the feed ratio of raw materials was reduced and the cost of materials decreased while ensuring the high yield of 90.98%.The product obtained was determined to be amorphous iron phosphate dehydrate,which was transformed into α-quartz type after calcination.The primary particle size of iron phosphate dihydrate was about 100nm and the average particle size D50 of secondary particles was 8.4μm.The formation mechanism of amorphous iron phosphate was analyzed according to the theory of crystal nucleus formation and crystal growth.The nucleation rate of iron phosphate was much higher than its growth rate and a large number of micro-nuclei were formed in the system.These micro-nuclei were irregularly aggregated because their radius was less than the critical nucleus radius and then amorphous iron phosphate was formed.The element content of the product(FePO4·2H2O)was determined to meet the technical index of battery grade iron phosphate.
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