Determination of magnesium during producing electrolytic manganese by manganese dioxide precipitation-EDTA titration

Mn2+ in manganese electrolyte was oxided to MnO2 precipitation by ammonium persulfate,while small amounts of Mn2+ and other impurities in the sample solution were masked by hydroxylamine hydrochloride and triethnolamine respectively.Total amounts of Mg and Ca in the sample solution were determined by EDTA titration with acid chrome blue K and naphthol green B as titration indicator at pH10,while Ca was detected by EDTA titration with calcium titration indicator at pH≥12.The content of Mg was obtained by taking a difference.The influence of factors including dosage of oxidant,pH value,temperature and reaction time on removal rate of manganese was investigated.Optimal operation conditions were following as:(NH4)2S2O8 amount was 2.2 times more than stoichiometric one,the pH value was from 5 to 6 and the test solution was heated in boiling water bath for 1h.In the above condition,the removal rate of manganese was over 99.8%.Mg in samples including neutralized solution,sulfurized solution,electrolyte and waste electrolyte from electrolytic manganese plant were determined by this method,with the relative standard deviations(RSDs) of 0.42%-0.72%,the recovery rates in the range of 99.6%-100.4% and the determination results were coincident with that of the atomic absorption spectrometry(AAS).