EDTA滴定法直接测定水氯镁石脱水产品中氧化镁

研究了用EDTA滴定法测定水氯镁石脱水产品中主体成分后用差减法求得杂质含量而间接测定水氯镁石脱水产品中Mg（OH）Cl、MgO含量（间接法）时产生很大误差的原因, 提出了通过用EDTA滴定法直接测定水氯镁石脱水产品样品的水溶渣中镁含量而得到产品中总MgO含量（直接法A）以及同时直接测定脱水产品样品的醇溶渣和水溶渣中镁含量而得到产品中Mg（OH）Cl、MgO含量(直接法B)的两种直接测定方法。醇或水溶渣中镁的测定是将渣用煮沸的5%（V/V）H₂SO₄溶解后用EDTA滴定。实验证明, 直接法测定脱水产品中氧化镁或碱式氯化镁的绝对误差很小（质量分数小于0.1%）。其中直接法A测得的脱水产品中总氧化镁含量更稳定、可靠, 具有更高的精密度和准确度（加标回收率在94%-117%）, 因此, 更适合于用盐酸苯胺(C₆H₅NH₂·HCl)作脱水剂的复盐法得到水氯镁石脱水产品中总MgO含量的准确测定。

Direct determination of magnesium oxide in dehydration products of bischofite by EDTA titrimetric method

The reason of error arising was examined in the determination of Mg(OH)Cl and MgO in bischofite dehydration product by indirect method, in which the impurity content of Mg(OH)Cl and MgO in bischofite dehydration was obtained by subtraction method after the major component was determined by EDTA titrimetric method. Two direct determination methods were proposed. Firstly, total MgO was obtained by using EDTA titration for determining the magnesium in aqueous-soluble residue of bischofite dehydration product(direct method A). Secondly, Mg(OH)Cl and MgO were obtained by simultaneous determination of magnesium in alcohol-soluble residue and the aqueous residue of dehydration product(direct method B). Magnesium in alcohol or aqueous residue was titratd by EDTA after the residue was dissolved in boiled 5%(V/V)H₂SO₄. The experiment indicated the absolute error for the determination of total magnesium oxide in dehydration product by direct method was quite small (with mass fraction of less than 0.1%). Among both methods, the direct method A which was used for determining total magnesium oxide in dehydration product was more stable and reliable, with high precision and accuracy (the recoveries were 94%-117%). Therefore, direct method A is more suitable for the accurate determination of total MgO in bischofite dehydration which was obtained by using C₆H₅NH₂·HCl as dehydrating agent.