Abstract：During the determination of zinc in high-cobalt zinc concentrate by EDTA back-titration after precipitation separation, the amphoteric oxides of cobalt enter the testing solution together with zinc, which will influence on the determination results of zinc. The sample was dissolved with hydrochloric acid, nitric acid and sulfuric acid. The impurities were separated by ammonia precipitation. The solution containing cobalt and zinc were determined by EDTA back-titration method to obtain the total content of zinc and cobalt. Then the content of zinc in high-cobalt zinc concentrate could be obtained by deducting the content of cobalt. The results showed that when the content of cobalt in zinc solution was not less than 1.0 mg, there was no endpoint or the endpoint was hardly achieved in direct titration with EDTA. After precipitation separation with ammonia, the recoveries of cobalt were between 99.8% and 100.1%, which quantitatively interfered with the determination of zinc. When the acidity of titration solution was pH 5.5-6.0 or pH 10, the content of zinc in solution containing cobalt and zinc could not be directly titrated with EDTA. After adding 45 mL of EDTA standard solution (0.05 mol/L), the determination requirements of zinc in cobalt-bearing zinc concentrate could be met. After adding EDTA and placing for more than 10 min, the zinc and cobalt in solution could be completely complexed with EDTA. The content of zinc in high-cobalt zinc concentrate sample was determined according to the experimental method. The relative standard deviation (RSD, n=7) of determination results was less than 1%. The recoveries were between 99.84% and 100.06%. Certain amount of cobalt was added into certified reference material and actual sample of zinc concentrate. The content of zinc was determined according to the experimental method, and the found results were consistent with the certified values/standard values.
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