Determination of calcium oxide in rare earth ore by EDTA titration method
EDTA滴定法测定稀土矿石中氧化钙

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 pH>13,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 %.