镁钙锌铝四元类水滑石金属含量的测定研究

Determination of metal contents of Mg-Ca-Zn-Al tetra atomic synthetic hydrotalcite-like heat stabilizer

论述了镁-钙-锌-铝四元合成类水滑石中含量相差悬殊的4种金属元素含量的测定方法:第一份试液,以氟化铵掩蔽铝、镁、钙离子后,用乙二胺四乙酸二钠(EDTA)标准溶液滴定锌离子;第二份试液,用缓冲溶液调节pH为3.5,加过量EDTA煮沸处理,再调节pH为4.2,促使铝离子和锌离子全部与EDTA络合,以铜离子标准溶液滴定剩余的EDTA后,用取代络合滴定法测定铝离子;第三份试液,用小体积沉淀法处理,形成碳酸钙和氢氧化镁沉淀,与溶于水的偏锌酸根(ZnO22-)和偏铝酸根(A lO2-)分离,再使碳酸钙与氢氧化镁溶于盐酸溶液,用EDTA滴定钙-镁总量;向第四份钙-镁溶液中加入乙二醇二乙醚二胺四乙酸钡(Ba-EGTA)-硫酸钠溶液掩蔽钙离子,用EDTA标准溶液滴定镁离子,以差减法计算钙离子含量。该法准确度和精密度均较高,能满足工业分析要求。

There is a large disparity among the contents of Mg,Ca,Zn and Al in tetraatomic hydrotalcite-like heat stabilizer. Determination method of their contents was discussed. An analyte solution was first treated with an excess of NH4F, which masked Al^3＋ , Mg^2＋ ,and Ca^2＋ , thereby leaving only Zn2. was titrated with standard EDTA. Another analyte was buffered to a pH of 3.5,treated with excess EDTA and boiled,adjusted to pH = 4.2 to ensure complete complexation of Al^3＋ and Zn^2＋ with EDTA. Surplus EDTA was titrated with standard Cu^2＋ solution. Then,Al^3＋ was determined by displacement titration. Using little volume precipitation method, CaCO3 and Mg （OH）2 precipitates were separated from water-soluble ZnO2^2- and AlO^2- . Afterwards to dissolve CaCO3 and Mg（ OH） 2 in HCl solution,total content of Ca^2＋ and Mg^2＋ was titrated with standard EDTA. In order to mask Ca^2＋ with EGTA, Ba - EDTA - Na2 SO4 solution was added into Ca - Mg solution and Mg^2＋ was titrated with standard EDTA,content of Ca^2＋ could be obtained by subtraction. The method is accurate and precise and can meet the requirements of industry analysis.