高钴镍物料中镍含量的准确测定对镍冶炼提纯工艺研究和行业发展具有重要意义.高钴镍物料中钴的质量分数为10％～20％,甚至更高,采用丁二酮肟沉淀分离-EDTA滴定法测定其中镍时,钴对测定存在干扰.实验通过先加入过硫酸铵将钴(Ⅱ)氧化为钴(Ⅲ)使其以钴氨离子[Co(NH3)6]3+的形式存在溶液中,从而避免了钴(Ⅱ)对丁二酮肟与镍反应生成沉淀的干扰;再采用丁二酮肟沉淀分离EDTA滴定法对沉淀中镍进行测定,同时用电感耦合等离子体原子发射光谱法(ICP-AES)测定滤液中镍对滴定法结果进行补正,实现了高钴镍物料中镍的测定.考察了不同含量的钴对镍测定的影响及通过增加丁二酮肟乙醇溶液用量消除干扰的可能性,结果表明,样品中钴对镍测定有干扰,且该干扰不能通过增加丁二酮肟用量的方法来消除.对过硫酸铵氧化钴(Ⅱ)的条件进行优化,结果表明,用氨水(1+1)调节溶液pH 6～10后加入10 mL 50 g/L过硫酸铵溶液小火煮沸10 min,可确保钴(Ⅱ)被氧化完全且过量的过硫酸铵被分解完全.按照实验方法测定两个高钴镍物料样品中镍并进行加标回收试验,镍测定结果的相对标准偏差(RSD,n=7)为0.14％～0.59％,回收率为99.8％～100.8％.分别采用实验方法和标准方法GB/T 30072-2013测定两个高钴镍物料样品中镍的含量,用t检验法对两种方法得到的结果进行统计分析,结果表明,t＜t7,0.05=2.18,说明两种方法无显著差异.
Discussion on determination method of nickel in high-cobalt-nickel material by EDTA titration with ammonium persulfate masking cobalt and dimethylglyoxime precipitation separation
Accurate determination of nickel content in high-cobalt-nickel material is of great significance for the purification technology study and industry development of nickel smelting.The mass fraction of cobalt in high-cobalt-nickel material is usually in range of 10％-20％or even higher.When nickel in this sample is determined by EDTA titration with dimethylglyoxime precipitation separation,cobalt will have interfer-ence.In this paper,ammonium persulfate was added to oxidize cobalt(Ⅱ)to cobalt(Ⅲ),which would exist in solution in the form of[Co(NH3)6]3+.Thus,the interference of cobalt(Ⅱ)with the precipitation reaction between dimethylglyoxime and nickel would be avoided.Then the content of nickel in precipitate was determined by EDTA titration with dimethylglyoxime precipitation separation.Meanwhile,the con-tent of nickel in filtrate was determined by inductively coupled plasma atomic emission spectrometry(ICP-AES)to correct the results of titration.Therefore,the determination of nickel in high-cobalt-nickel mate-rial was realized.The influence of cobalt content on the determination of nickel was investigated.The pos-sibility of increasing dimethylglyoxime ethanol solution dosage to eliminate this interference was also stud-ied.The results showed that cobalt in the sample had interference with nickel determination,and the inter-ference could not be eliminated by increasing dimethylglyoxime dosage.The oxidization conditions of co-balt(Ⅱ)by ammonium persulfate were optimized.The results showed that cobalt(Ⅱ)could be complete-ly oxidized and the excessive ammonium persulfate could be fully decomposed under such conditions:the pH of solution was adjusted to 6-10 with ammonium hydroxide(1+1);after adding 10 mL of 50 g/L am-monium persulfate solution,the solution was boiled with soft fire for 10 min.The contents of nickel in 2 samples of high-cobalt-nickel material were determined according to the proposed method.Moreover,the standard addition tests were conducted.The relative standard deviations(RSD,n=7)of determination re-sults were between 0.14％and 0.59％,and the recoveries were between 99.8％and 100.8％.The con-tents of nickel in 2 samples of high-cobalt-nickel material were determined according to the proposed meth-od and standard method of GB/T 30072-2013.The statistical analysis of the results by two methods was conducted by t test.The results showed that t＜t7,0.05=2.18,indicating that there was no significant difference between the two above methods.
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