EDTA滴定法测定稀土矿石中氧化钙

Determination of calcium oxide in rare earth ore by EDTA titration method

根据稀土矿石的特性,以氢氧化钠、过氧化钠、碳酸钠熔融分解试样,经过强碱分离铝、硅、氟、磷等杂质元素,氨水分离铁等元素后,用EDTA滴定法测定稀土矿石中氧化钙含量。试验发现经过强碱分离后硅、氟、磷等元素不影响钙的测定结果。讨论了少量铝、钡、锰元素的干扰情况及其干扰消除方法:用三乙醇胺和硫酸钾掩蔽剩余少量Al、Ba等干扰元素,盐酸羟铵掩蔽锰的干扰,加入硫酸镁来改善滴定终点的颜色变化;并实验得出空白值对不同称样量的贡献值也不一样,因为必须做空白实验。在pH>13的氢氧化钾介质中,以钙指示剂为指示剂,EDTA标准溶液滴定稀土矿石中氧化钙,测定值与ICP-AES法值相一致,RSD在0.8%～4.3%之间。

Based on the characters of rare earth ore,the sample was melted and decomposed with sodium hydroxide,sodium peroxide and sodium carbonate.The impurity elements including aluminum,silicon,fluorine and phosphorus are separated with strong alkali.The iron was separated with ammonia water.Then,the content of calcium oxide in rare earth ore was determined by EDTA titration.It was found that the silicon,fluorine and phosphorus after separation with strong alkali did not influence the determination results of calcium.The interference of a little aluminum,barium and manganese and its elimination method were discussed： the interference elements including a little residual aluminum and barium could be masked with triethanolamine and potassium sulfate;the interference of manganese could be masked with hydroxylamine hydrochloride;the color change in endpoint could be improved by adding magnesium sulfate.It was also found in experiments that,the blank showed different contribution to samples with various amount.Therefore,the blank test must be conducted.In potassium hydroxide medium at pH13,the calcium oxide in rare earth ore could be determined by EDTA titration using calcon-carboxylic acid as indicator.The results were consistent with those obtained by ICP-AES method.The RSD was 0.8 %-4.3 %.