氯化钠-自动电位滴定法测定分银渣中银含量

采用火试金将分银渣、熔剂（Na₂CO₃、Na₂B₄O₇·H₂O、SiO₂）、PbO及淀粉按一定比例配好,在900～1 100 ℃的温度条件下于坩埚中加热熔融,形成铅扣,铅扣经灰吹得到合粒,用硝酸溶解合粒得到测试溶液,最后用电位滴定法分析测试溶液中银含量。探讨发现试样的质量为3.0 g、溶液的酸度pH 2～5、室温和乙醇的加入量为20 mL时分银渣中银含量的测定效果最佳。取不同样品进行精密度试验,结果的相对标准偏差（RSD,n=6）均在0.10%～0.56%之间；回收率试验结果表明,样品的加标回收率在96%～100%之间。对不同的分银渣样品进行测定,并与火试金-硫氰酸钾滴定法进行对照实验,结果一致。

Determination of silver in silver separating residue by sodium chloride-automatic potentiometric titration

Silver separating residue, flux (Na₂CO₃, Na₂B₄O₇·H₂O and SiO₂), PbO and starch were mixed in an appropriate ratio by adopting fire assay method. Then the mixed substance was heated to dissolve and form lead button in crucible at the temperature of 900-1 100 ℃. Alloy particle was obtained by cupellation of lead button. Then testing solution was gotten by dissolving the alloy particle with nitric acid. Finally, the content of silver in testing solution was determined by potentiometric titration.After testing, it was found that 3.0 g of sample, pH 2-5, room temperature and 20 mL of ethanol were the best choice to determine silver in silver separating residue. Different samples were used for precision test, with RSD (n=6) between 0.10% and 0.56%. Recovery test result indicated that the addition recovery rate of the sample was 96%-100%. Testing was conducted on different silver separating residue sample. In addition, contrast test was conducted by using fire assay - potassium thiocyanate titration. Both test results were consistent with each other.