Abstract：Manganese could interfere with the determination of cobalt by potentiometric titration. Since the content of manganese (mass fraction up to 8%) in crude cobalt hydroxide was relatively high, the interference of manganese should be considered during the determination of cobalt in crude cobalt hydroxide by potentiometric titration. The pretreatment of standard determination method for cobalt in industrial cobalt hydroxide (HG/T 4506-2013) was modified. After dissolving the sample with hydrochloric acid, manganese (II) in solution was oxidized to manganese (III) by perchloric acid in the solution containing phosphoric acid. Manganese (III) was complexed and marked by ammonium bifluoride to eliminate the interference of manganese. In ammonia environment, cobalt (II)-ammonium complex ion was oxidized to cobalt (III)-ammonium complex ion by excessive potassium ferricyanide. Then, the excessive potassium ferricyanide was back-titrated by cobalt standard titration solution. Consequently, a determination method of cobalt in crude cobalt hydroxide by potentiometric titration was established. According to the mass ratio of manganese to cobalt in crude cobalt hydroxide, the simulated sample of crude cobalt hydroxide was prepared with the mass ratio of manganese to cobalt in range of 13.7%-52.0% and determined according to the proposed method. The recoveries of cobalt were between 99% and 101%, which indicated that the interference of manganese could be ignored. The proposed method was applied to the determination of crude cobalt hydroxide. The relative standard deviations (RSD, n=10) were between 0.19% and 0.26%, and the recoveries were between 99% and 104%. The actual samples of crude cobalt hydroxide were determined by the proposed method, and the results were basically consistent with those obtained by potentiometric titration combined with inductively coupled plasma atomic emission spectrometry.
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