Determination of total iron in carbon-coated lithium iron phosphate by potassium dichromate titrimetry

Lithium iron phosphate sample is usually coated with a layer of carbon which would possibly have certain effect on sample dissolution by acid.The sample was dissolved with hydrochloric acid through heating for 10min and filtered to remove carbon.Under acidic conditions,TiCl3was used as reductive agent to reduce a small amount of Fe3+.After the addition of 15mL of sulfuric acid and phosphoric acid mixture and three to four drops of 5g/L sodium diphenylaminesulfonate,total iron in carbon-coated lithium iron phosphate was determined by potassium dichromate titrimetry.The common impurity metal elements in practical lithium iron phosphate had no interference with the determination.When the experimental method was applied to determine total iron in practical sample,the relative standard deviation(RSD)was less than 0.2%,and the standard addition recovery(RSD)was 99.7%-100.3%.The method was suitable for the determination of total iron in carbon-coated lithium iron phosphate in practical production and scientific research.