NaOH沉淀—KF置换—酸碱滴定法快速测定高岭土中氧化铝

Study on Rapid Method of Determining Aluminum Oxide Content in Kaolin by NaOH Precipitation-KF Displacement-Acid-Base Titration

本文研究了快速测定高岭土中氧化铝含量的Na OH沉淀—KF置换的酸碱滴定法。试样与碱性混合熔剂Na2CO3+MgO半熔融,熔块以水浸取并消除干扰离子后,先在pH值7～8时,用稀NaOH溶液将Al3+沉淀为Al(OH)3,再加入KF,反应中释放出的游离KOH溶液,以酚酞为指示剂,用HCl标准溶液滴定至终点。测定结果的相对标准偏差(RSD)为0.30%(n=5),其加标回收率(R)在97.8%～101.6%。结果表明,改进后的本法具有简单、快捷、准确度高、干扰小等特点,可满足生产要求。

The study deals with rapid method of determining aluminum oxide content in kaolin by NaOH precipitation-KF displacement-acid-base titration. Sample is semi-melted with NaECO3＋MgO. The melt is then soaked with water and the disturbance eliminated, the Al^3＋ is deposited as Al（OH）3 by using thin solution of NaOH, while that remains pH 7～8.Then,KF is added and dissociated KOH is released. With phenolphthalein as the indicator and HCl as the standard solution, dissociated KOH is titrated to end point. The recovery of standard addition is between 97.80% and 101.64% with precision of 0.30%（n=5）.The results show that the improved method is a easy-operating way with the fast determination, high accuracy and with little disturbance. It can meet the demand of production.