Determination of chlorine in alumina and aluminum hydroxide by silver nitrate potentiometric titration with microwave digestion
TANG Dongmei1, MA Bingbing*2, XIAO Fei3, HU Yi3
1. CEPREI Innovation (Chongqing) Technology Co., Ltd., Chongqing 401332, China; 2. Chongqing Geology and Mineral Exploration and Development Group Inspection and Test Co., Ltd., Chongqing 400707, China; 3. Chongqing CEPREI Industrial Technology Research Institute Co., Ltd., Chongqing 401332, China
Abstract：The cumulative damage of chloride ions in the production process of alumina and aluminum hydroxide is great. It can cause the reduction of seed decomposition rate and the corrosion of production equipment, and also affect the quality of final products of alumina and aluminum hydroxide. Therefore, it is of great significance to determine the chlorine content in alumina and aluminum hydroxide efficiently and accurately. After the sample was treated by microwave digestion with phosphoric acid, and the silver nitrate standard solution was selected as the titrant, a method for determination of chlorine in alumina and aluminum hydroxide was established by silver nitrate potentiometric titration. The results showed that the samples of alumina and aluminum hydroxide could be completely decomposed in 10 mL of phosphoric acid by microwave digestion at 220 ℃ for 50 min. The addition of hydrogen peroxide could eliminate the interference of sulfide, sulfite and thiosulfate in the sample. The effect of phosphoric acid concentration on the titration results of chlorine was investigated. The results showed that the dosage of phosphoric acid had no obvious influence on the determination when it reached 10 mL. The detection limit of the method was 0.002%. The contents of chlorine in the samples of alumina and aluminum hydroxide were determined according to the proposed method. The relative standard deviations (RSD, n=6) of determination results were between 0.65% and 9.2%, and the recoveries were between 97% and 103%.
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