硫酸氢钾沉淀分离—2-(5-溴-2-吡啶偶氮)-5-二乙氨基苯酚光度法测定矿石中铅

2-(5-溴-2-吡啶偶氮)-5-二乙氨基苯酚(5-Br-PADAP)光度法应用于矿石中铅的测定时,Cu、Zn、Fe、Ni、Bi、Mn、Cd、Co、V、Ti、Nb和Ta等多种元素的干扰不容忽视。针对这一问题,实验提出了采用KHSO₄沉淀法对样品进行前处理,5-Br-PADAP光度法测定矿石中Pb的方法。实验表明,采用盐酸-硝酸体系溶解矿石后,加入10 mL 200 g/L KHSO₄溶液,放置20 min后即可见样品中的铅沉淀完全从而与上述离子分离;将沉淀过滤后,采用pH 5.6的HAc-NaAc缓冲溶液溶解沉淀,可使K₂SO₄·PbSO₄复盐沉淀溶解,从而与Ba、W、Sr和Ca等元素分离。在样品溶液中依次加入0.4 mL pH 9.3 H₃BO₃-KCl-NaOH缓冲溶液、0.4 mL饱和KI溶液、0.4 mL 10%(V∶V)Trion X-100溶液、1.0 mL 0.03 g/L 5-Br-PADAP乙醇溶液,于1 cm比色皿中,在波长558 nm处进行测定,Pb质量浓度在0.02～2 μg/mL范围内符合比尔定律,线性回归方程的相关系数为0.998。方法检出限为0.02 μg/mL。采用实验方法分别对铅矿、锌矿、铅锌矿标准物质中的Pb进行分析,测得结果与认定值基本一致,相对标准偏差(RSD,n=11)为2.3%～5.8%。

Determination of lead in ore by 2-[(5-bromine-2-pyridine)-azo]-5-diethylaminophenol spectrophotometry with potassium bisulfate precipitation separation

During the determination of lead in ore by 2-(5-bromine-2-pyridine)-azo]-5-diethylaminophenol (5-Br-PADAP) spectrophotometry, the interference of many elements (such as Cu, Zn, Fe, Ni, Bi, Mn, Cd, Co, V, Ti, Nb and Ta) could not be ignored. To solve this problem, the sample was pretreated by KHSO₄ precipitation method. Then, the content of lead in ore was determined by 5-Br-PADAP spectrophotometry. The results showed that the lead in sample could be fully precipitated and separated from ions above by adding 10 mL 200 g/L KHSO₄ solution and placing for 20 min after dissolving the ore with hydrochloric acid-nitric acid system. After filtration, the K₂SO₄·PbSO₄ composite salt precipitation was dissolved with HAc-NaAc buffer solution at pH 5.6, realizing the separation from Ba, W, Sr and Ca. Then, 0.4 mL of H₃BO₃-KCl-NaOH buffer solution at pH 9.3, 0.4 mL of saturated KI solution, 0.4 mL of 10% (V∶V) Trion X-100 solution and 1.0 mL of 0.03 g/L 5-Br-PADAP ethanol solution were added into sample solution successively. The content of lead was determined in 1 cm cuvette at 558 nm. The Beer's law was obeyed for Pb with mass concentration in range of 0.02-2 μg/mL. The correlation coefficient of linear regression equation was 0.998. The detection limit was 0.02 μg/mL. The proposed method was applied to the determination of Pb in certified reference materials of lead ore, zinc ore and lead-zinc ore. The found results were basically consistent with the certified values. The relative standard deviations (RSD, n=11) were between 2.3% and 5.8%.