EDTA滴定法测定高铋铅中铋

高铋铅中含有锑、锡、碲、银等干扰元素。按照常规溶解粗铅的方法,锑或锡在硝酸介质下易发生水解,生成不溶物,影响铋的测定;按照常规EDTA滴定铋含量的方法,高铋铅中碲或银的存在可使试液变黑而影响滴定颜色的观察,锡的存在会出现试液变亮黄色后颜色返红的现象,严重影响了铋含量的测定。试验使用硝酸-酒石酸溶解高铋铅试样,探讨了抗坏血酸加入量和加入顺序,考察了杂质元素锡、银和其他共存元素对铋测定的影响。结果表明,称取5.0000g高铋铅试样采用40mL酒石酸(100g/L)-80mL硝酸(1+1)溶解;抗坏血酸加入量是0.2g,加入顺序是调节pH值之后;锡量小于0.4mg时,对铋的测定无影响;锡量大于0.4mg时,分取试液后采取添加氢溴酸低温除锡的方法,消除锡对铋的影响;该实验条件下,银不会发生氧化还原反应;其他共存元素对铋的测定基本没有影响。实验方法用于测定5个高铋铅试样中铋,结果的相对标准偏差(RSD,n=5)为0.038%~1.3%。按照实验方法溶解其中1个高铋铅试样,分别采用实验方法和电感耦合等离子体原子发射光谱法(ICP-AES)测定铋含量,结果相吻合。按照实验方法对3个高铋铅试样进行加标回收试验,回收率为99.8%~101%。

Determination of bismuth in bismuth-riched lead by EDTA titrimetric method

The bismuth-riched lead contains some interference elements such as antimony, tin, tellurium and silver. When lead bullion is dissolved according to the traditional method, antimony or tin is easily hydrolyzed in nitric medium to form insoluble substances, which influences on the determination of bismuth. On the other hand, when the content of bismuth is determined according to the traditional EDTA titration method, the existing tellurium or silver in bismuth-riched lead can cause darkening of sample solution, which influences on the color observation in titration. Due to the presence of tin, the color of sample solution will be back to the red after appearing brilliant yellow, and the determination of bismuth is severely affected. The bismuth-riched lead sample was dissolved with nitric acid-tartaric acid. The dosage and addition sequence of ascorbic acid were discussed. The influence of impurity elements (tin and silver) and other coexisting elements on the determination of bismuth was investigated. The results showed that 5.0000g of bismuth-riched lead sample could be fully dissolved with 40mL of tartaric acid (100g/L) and 80mL of nitric acid (1+1). The dosage of ascorbic acid was 0.2g and it was added after pH adjustment. When the content of tin was less than 0.4mg, it had no influence on the determination of bismuth. When the content of tin was higher than 0.4mg, it was removed at low temperature by adding hydrobromic acid to eliminate its influence on the determination of bismuth. The redox reaction would not occur under this experimental condition. Other coexisting elements had no influence on the determination of bismuth. The proposed method was applied for the determination of bismuth in five high-bismuth lead samples. The relative standard deviations (RSD, n=5) of determination results were between 0.038% and 1.3%. One bismuth-riched lead sample was dissolved according to the experimental method. The content of bismuth was determined by the proposed method and inductively coupled plasma atomic emission spectrometry (ICP-AES), and the results were consistent. Three high-bismuth lead samples were used for the spiked recovery tests according to the experimental method. The recoveries were between 99.8% and 101%.