Determination of cobalt in zinc electrolyte by complex adsorptioncatalytic wave polarography with EDTA-masking
DU Juan1,YANG Chun-hua2,LI Yong-gang2,ZHANG Tai-ming*1,ZHU Hong-qiu2
1. College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China; 2. School of Information Science and Engineering, Central South University, Changsha 410083, China
Abstract：A determination method of cobalt in zinc electrolyte by complex adsorption catalytic wave polarography was established in ammonia water-ammonium chloride buffer medium in presence of dimethylglyoxime (DMG) and sodium nitrite with EDTA as masking agent. The effect of EDTA amount was investigated. The results showed that the required amount of EDTA was related to the amount of zinc in solution. The ratio of the amount of substance for EDTA and zinc (nEDTA/nZn) at 1.15 was the optimal choice. At this time, the interference of high concentration zinc and other coexisting metal impurity ions in zinc electrolyte with the determination of trace cobalt could be eliminated. The acidity of base solution, the amount of ammonia water-ammonium chloride buffer solution, the amount of DMG ethanol solution, the amount of sodium nitrite solution, and the standing time were optimized. The results indicated that the concentration of cobalt (c, nmol/L) in range of 5.0×10-11-5.0×10-9 and 5.0×10-9-3.2×10-7mol/L had good linear relationship to the corresponding second derivative wave peak current (Ip, nA) under the optimized experimental conditions, respectively. The correlation coefficient was 0.9980 and 0.9997, respectively. The detection limit of method was 2.0×10-12 mol/L. The proposed method was applied for determination of actual samples of neutral supernatant liquor, zinc electrolyte before and after removal of cobalt. The determination results were compared with those obtained by national standard method GB/T 223.22—1994 (nitroso-R-salt spectrophotometry, NRS). The relative error (RE) in range of ±4.5%, and the relative standard deviation (RSD, n=6) was not more than 2.7%. The linear range of proposed method was wide. It had high selectivity to the determination of cobalt in zinc electrolyte, and was suitable for the control analysis of hydrometallurgical processes
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