次亚磷酸钠还原-碘滴定法测定矿石样品中砷含量

Hypophosphite Reduction-Iodometric Titration of Arsenic in Ore Samples

矿石样品(0.5g)溶于硝酸-盐酸(3+1)混合酸(20mL)中,加硫酸(5mL)并蒸发至冒三氧化硫白烟,冷却后加入盐酸(1+1)溶液70mL,温热至盐类溶解后,用硫酸铜(0.1g)作催化剂,加入次亚磷酸钠至过量约1~2g,使砷(Ⅲ)还原至单体砷析出,过滤。将带有单体砷沉淀的滤纸投入烧杯中,加入过量碘标准溶液使砷溶解。在20g·L-1碳酸氢钠溶液中,用硫代硫酸钠标准溶液滴定过量的碘;根据两标准溶液的消耗量计算样品中砷的含量。应用此方法分析了3个标准样品,所得结果与认定值相符,测定值的相对标准偏差(n=5)在1.5%~2.1%之间。

The ore sample(0.5g)is dissolved in 20mL of HNO3-HCl(3+1)mixed acid and fumed with5mL of H2SO4.After cooling,the salts are dissolved with 70mL of warm HCl(1+1)solution.Arsenic(Ⅲ orⅤ)in the solution is reduced to elementary state by adding sodium hypophosphite with 1to 2g in excess using 0.1g of CuSO4as catalyst.After filtration and washing,the precipitate of elementary arsenic together with the filter paper is removed to the beaker and an excess and definite amount of iodine standard solution is added to dissolve the As°completely,and the excess amount of iodine is titrated with Na2S2O3standard solution in a medium of 20g·L-1 NaHCO3solution.Based on the volume of the 2standard solutions consumed in dissolution of As°and titration of excess of iodine,content of arsenic in the sample is calculated.Three standard samples were analyzed by the proposed method,and contents of arsenic found were in consistency with the certified values,with values of RSD′s(n=5)ranged from 1.5%to 2.1%.