重铬酸钾滴定法测定碳包覆磷酸铁锂中全铁

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

实际磷酸铁锂样品颗粒表面常包覆一层碳，碳的存在可能对酸溶解样品有一定的影响。通过试验确定试样经盐酸加热10min溶解后，过滤除碳，在酸性条件下以TiCl3为还原剂将少量的Fe抖还原，然后加入15mL硫磷混酸，滴加3～4滴5g／L二苯胺磺酸钠溶液后，采用重铬酸钾滴定法测定碳包覆磷酸铁锂中全铁含量。实际磷酸铁锂样品通常掺杂的金属元素对测定没有干扰。采用实验方法对实际样品的全铁含量进行测定，相对标准偏差（RSD）小于0．2%，加标回收率为99．7％～100．3％，适合于实际生产和科研中碳包覆磷酸铁锂中全铁含量的测定。

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 10 min and filtered to remove carbon. Under acidic conditions, TICl3 was used as reductive agent to reduce a small amount of Fe3＋. After the addition of 15 mL of sulfuric acid and phosphoric acid mixture and three to four drops of 5 g/L sodium diphenylaminesulfonate, total iron in carbon-coated lithium iron phosphate was determined by potassium dichromate titrimetry. The com- mon impurity metal elements in practical lithium iron phosphate had no interference with the determi- nation. When the experimental method was applied to determine total iron in practical sample, the rel- ative 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.