EDTA滴定法测定锌精矿中锌含量方法的改进

依次加入15 mL盐酸、15 mL硝酸溶解样品,在加入氯化铵的情况下,形成了锌胺络合物,然后在水中快速冷却,用沉淀分离方法分离铁、锰、铅等共存元素。在pH 5.5的乙酸-乙酸铵缓冲溶液中,用饱和硫脲、抗坏血酸和氟化钾溶液掩蔽Cu²⁺、Hg²⁺、Al³⁺、Ca²⁺等离子的干扰,最后,以二甲酚橙为指示剂,用EDTA标准溶液滴定出锌的含量。试验发现,采用盐酸和硝酸溶解样品,代替国标法的盐酸、硝酸、硫酸溶解样品,溶样较快;此外,两种方法溶解样品后都需要沉淀分离干扰元素,其中国标法采用的热液过滤可减免移液过程,但溶样和煮沸时间过长,实验方法采用冷却过滤避免了二次过滤,从而简化了分析步骤。精密度试验中,两个标准样品测定结果的相对标准偏差分别为0.23%和0.12%(n=10);采用国标法和实验方法对不同的锌精矿样品进行测定,测定结果基本一致。

Method improvement on the determination of zinc in zinc concentrate by EDTA titrimetry

The sample was dissolved by adding 15 mL of HCl and 15 mL of HNO₃ in sequence. Coexisting element such as Fe, Mg and Pb was separated through forming zinc amine complex when the sample was rapidly cooled in water after ammonium chloride was added. In the buffer of acetic acid-ammonium acetate at pH 5.5, the content of zinc was titrated by EDTA standard solution by masking interference ions such as Cu²⁺, Hg²⁺, Al³⁺ and Ca²⁺ with saturated thiourea, ascorbic acid and potassium fluoride and with xylenol range as indicator. It was found that the sample was dissolved faster when HCl and HNO₃ was used instead of HCl, HNO₃ and H₂SO₄ in national standard. Besides, both dissolution methods needed to separate interfering elements through precipitation. Though thermal fluid filter adopted in national standard method could avoid liquid transfer process, but sample dissolution and boiling time was too long. While the cooling filter adopted in the proposed method could avoid secondary filter, which could simplify the analytical procedure. In precision test, the relative standard deviation of the determination results of both standard samples were 0.23% and 0.12% (n=10). Different zinc concentrates were determined with national standard method and the proposed method. The results were basically consistent.