Abstract：The cobalt residue leaching solution in zinc hydrometallurgy contained high concentrations of Fe2+ and Mn2+. During the determination of Co2+ and Ni2+ by spectrophotometry, Fe2+-EDTA had serious interference. On the other hand, when the total content of Zn2+ and Co2+ was determined by photometric titration, Ni2+ had blocking effect of xylenol orange indicator and Mn2+ could chelate with EDTA ,resulting in higher titration results. In order to eliminate the interference of Fe2+ and Mn2+ on the determination of Zn2+, Co2+ and Ni2+, the pretreatment of Fe2+ and Mn2+ was conducted by oxidization separation in experiments. Co2+ and Ni2+ were determined by spectrophotometry using EDTA as coloring reagent in NaAc/HAc buffer solution. The concentration of Co2+ in range of 50-500mg/L was linear to the absorbance at 466nm and the correlation coefficient was R2=0.9992. The concentration of Ni2+ in range of 50-500mg/L was linear to the absorbance at 384nm and the correlation coefficient was R2=0.9998. The molar amount of Ni2+ was determined by spectrophotometry. Then Ni2+ was removed by adding 1.1 times of dimethylglyoxime. The total content of Zn2+ and Co2+ was determined by EDTA chelation-photometric titration using xylenol orange as indicator. The content of Zn2+ was calculated by deducting the content of Co2+. Four actual samples of cobalt residue leaching solution in zinc hydrometallurgy were selected. The content of Co2+ and Ni2+ was determined by spectrophotometry according to the experimental method. The total content of Zn2+ and Co2+ was determined by photometric titration. The relative standard deviations (RSD, n=6) of Zn2+, Co2+ and Ni2+ were all less than 0.70%. The spiked recoveries were 99.59%-100.41%, 99.69%-100.64% and 99.92%-100.08%, respectively.
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