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萤石中CaF_2和CaCO_3的分相是用10%乙酸溶解CaCO_3和CaSO_4。实践证明,这种方法并不理想。其原因在于乙酸也能溶解部分CaF_2。因此,它只基本适用于CaCO_3含量>1%的萤石样品,对于CaF_2含量较高的试样(>97%)则偏差较大。资料推荐计算CaF_2含量时加校正值的办法,但由于10%乙酸对CaF_2的溶解量因CaCO_3含量的不同而异,所以校正值不应该是一个固定值。特别是当校正值接近或大于CaCO_3的含量时,难以保证CaCO_3等不出现成倍超差现象。因此,在考虑分析方法时应力求使校正值缩小到可以忽略的程度,或使不同性质的试样有相对恒定的校正值。资料推荐用含40%乙酸铵的2.5%乙酸分相。由于溶液中大量NH_4~+存在使CaF_2的溶解度增大,经我们测定CaF_2在该溶液中的溶解度为2.3×10~(-3)M因此,该法对CaCO_3%<2%的样品偏差很大。笔者用Ca~(2+)的同离子效应,以降低CaF_2的溶解度的方法来解决萤石中CaF_2和CaCO_3(包括CaSO_4)的分相(即在10%乙酸中加入适量乙酸钙)。试验证明本法适应性强,准确度、精密度令人满意。
Fluorite CaF_2 and CaCO_3 phase separation is the use of 10% acetic acid dissolved CaCO_3 and CaSO_4. Practice has proved that this method is not ideal. The reason is that acetic acid can also dissolve part of CaF 2. Therefore, it is only applicable to fluorite samples with CaCO_3 content> 1%, while those with higher CaF_2 content (> 97%) have larger deviations. It is recommended to add the correction value when calculating the CaF_2 content. However, the correction value should not be a fixed value since the dissolution amount of CaF_2 by 10% acetic acid varies with CaCO_3 content. Especially when the correction value is close to or greater than the content of CaCO_3, it is difficult to ensure that CaCO_3 and so on will not appear double overshoot phenomenon. Therefore, when considering the analysis method, the correction value should be minimized to a negligible level or a relatively constant correction value should be given to different types of specimens. Data recommended with 40% ammonium acetate 2.5% acetic acid phase. Due to the presence of a large amount of NH 4 + in the solution, the solubility of CaF 2 increased and the solubility of CaF 2 in this solution was 2.3 × 10 -3 M. Therefore, the method deviates from the sample with CaCO 3% <2% . The author uses the same ion effect of Ca ~ (2+) to reduce the solubility of CaF_2 to solve the phase separation of CaF_2 and CaCO_3 (including CaSO_4) in fluorite (ie adding the proper amount of calcium acetate into 10% acetic acid). Tests prove that this law adaptability, accuracy and precision are satisfactory.