离子交换分离-Na2EDTA滴定法测定含镍钴锌精矿中锌的改进

随着锌资源的日益枯竭,锌精矿的成分也越来越复杂化,准确测定锌精矿中锌含量具有重要意义。试验以盐酸-氟化铵-硝酸-硫酸-高氯酸溶解样品,在盐酸(1+5)的介质中,用大孔型强碱性阴离子树脂分离镍、钴、铁、锰、铝等,用氨水-氯化铵溶液洗脱Zn²⁺,在分离杂质后的溶液中加入少量氟化铵掩蔽残余的铁,硫代硫酸钠溶液掩蔽微量铜,用Na₂EDTA标准滴定溶液直接滴定锌、镉合量,扣除镉量即为锌量,建立了离子交换分离-Na₂EDTA滴定法测定含镍钴锌精矿中11%～62%锌的方法。研究了金属离子在3种典型强碱性阴离子树脂上,不同酸度下的分配系数K_d,最终选择了在D296型大孔型强碱性阴离子交换树脂上、盐酸(1+5)介质中进行离子交换分离。试验结果表明少量NH⁺₄的存在不影响Zn²⁺的吸附,离子交换柱柱高为30 cm时吸附损失率小于0.10%,样品溶液通过离子交换柱的流速为8～10 mL/min时工作效率较高,吸附损失率低。方法用于测定3个含镍钴锌精矿样品中锌,测定结果与使用氢氧化钠沉淀分离-EDTA滴定法及丁二酮肟沉淀分离-EDTA滴定法结果基本一致,结果的相对标准偏差(RSD,n=11)为1.6%～5.6%。

Improvement of ion exchange separation-Na2EDTA titration for the determination of zinc in nickel-cobalt-zinc concentrate

With the increasing depletion of zinc resources, the composition of zinc concentrates becomes more and more complex. It is of great significance to accurately determine the content of zinc in zinc concentrate. In experiments, the sample was dissolved with hydrochloric acid- ammonium fluoride-nitrate acid-sulfuric acid-perchloric acid. In the medium of hydrochloric acid (1+5), the metal elements including nickel, cobalt, iron, manganese and aluminum were separated with macro-reticular type strong alkaline anionic resin. Zn²⁺ was eluted with ammonia-ammonium chloride solution. A small amount of ammonium fluoride and sodium hyposulfite was added into the solution after impurity separation to mask the residual iron and trace copper, respectively. The total contents of zinc and cadmium were directly titrated with Na₂EDTA standard titration solution. The content of zinc could be obtained by deducting the cadmium content. Consequently, a method for determination of zinc (11%-62%) in nickel-cobalt-zinc concentrate by Na₂EDTA titration with ion exchange separation was established. The partition coefficients (K_d) of metal ions on three typical strong alkaline anion resins with different acidity were investigated. The ion exchange separation conditions were finally selected as follows: D296 macro-reticular type strong alkaline anionic exchange resin and hydrochloric acid (1+5) medium. The test results showed that the presence of little NH⁺₄ would not influence on the adsorption of Zn²⁺. The adsorption loss rate was less than 0.10% when the height of ion exchange column was 30 cm. The working efficiency was high and adsorption loss rate was low when the flow rate of sample solution through ion exchange column was in range of 8-10 mL/min. The proposed method was applied for the determination of zinc in three nickel-cobalt-zinc concentrate samples, and the found results were basically consistent with those obtained by sodium hydroxide precipitation separation-EDTA titration and dimethylglyoxime precipitation separation-EDTA titration. The relative standard deviations (RSD, n=11) of determination results were between 1.6% and 5.6%.