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EDTA连续络合滴定钍和稀土存在的主要问题是在滴定钍后调节pH 5—6滴定稀土时,由于生成了Th-EDTA-指示剂有色三元配合物,指示剂被封闭,使终点无法辨认。Pribil甚至认为用EDTA或CDTA连续滴定稀土是不可能的。为了解决此问题,本文选择了指示剂和有关络合滴定条件以及矿石中常量钍和稀土的草酸盐沉淀分离条件。试验结果表明:草酸盐沉淀最佳酸度是pH1.5—2.5,此时回收率最高,以二甲酚橙为指示剂滴定钍最佳酸度是pH1.8—2.2,此时终点敏锐,高达15倍的稀土;尚无干扰;在连续滴定稀土时,本文首次提出以钙萤素及PAR为混合指示剂,在pH5.0—5.2的条件下以铜盐反滴定至萤光消失的方法测定稀土总量。由于采用了萤光滴定,所以钍量高达75mg对稀土的滴定尚无干扰,终点变化比其它指示剂明显,从而解决了钍对指示剂的封闭问题。可用以测定独居石、钍石等矿石中钍和稀土。
Continuous titration of EDTA with EDTA The major problem with thorium and rare earths is that when the titration of thorium is used to titrate rare earths with a pH of 5-6, a colored ternary complex of Th-EDTA-indicator is formed and the indicator is blocked, making the end point unrecognizable . Pribil even thought it impossible to titrate rare earths with EDTA or CDTA. In order to solve this problem, we selected the indicator and the conditions of the complexation titration and oxalate precipitation conditions of the thorium and rare earth in the ore. The results showed that the optimal acidity of oxalate precipitation was pH1.5-2.5, and the highest recovery was obtained at this time. The optimum acidity of thorium titration with xylenol orange as indicator was pH1.8-2.2, the endpoint was sharp at this time, 15 times the rare earth; there is no interference; in the continuous titration of rare earth, this paper for the first time put the calcitonin and PAR as a mixed indicator, under the conditions of pH5.0-5.2 copper titration to the disappearance of fluorescence measured The total amount of rare earth. As a result of the fluorescent titration, so thorium up to 75mg of rare earth titration has no interference, the end point change significantly than other indicators, thus addressing the sealing of the indicator of thorium. Can be used to determine monazite, thorium and other thorium ore and rare earth.