电导法测定粘土矿物的阳离子交换容量

用亚甲基蓝法测定粘土矿物和泥页岩阳离子交换容量CEC值时滴定终点不易判断，测定值准确度不高。本文提出用1mol/L BaCl2溶液充分置换矿岩样中可交换阳子（平衡5d），再用0．1mol/L MgSO4溶液进行电导滴定，滴定曲线明锐的拐点指示滴定终点。用此法测得基准钠蒙脱土和用化学纯高岭土精制的钠高岭土的CEC值分别为84．8和5．2mmol/100g土，而亚甲基蓝法测定值则分别为82．5和2．7mmol/100g土。对于膨胀性的钠蒙脱土，两种方法的测定结果一致，而对于非膨胀性的钠高岭土，亚甲基蓝法测定值明显偏低。对于胜利油田6个泥页岩样，电导滴定法测定的CEC值大大高于亚甲基蓝法测定值，而比较接近按矿物分析数据估算的CEC值。BaCl2-MgSO4电导滴定法对膨胀性和非膨胀性粘土矿物都适用，测定程序简便，测定值准确度高。

Determination of Cationic Exchange Capacity of Clay Minerals by Conductometric Titration

The real endpoint is difficult to ascertain and the determinations are not accurate enouph in determing the cationic exchang capacity ( CEC ) of clay minerals by using methylene blue (MB) method. In this study, the exchangeable cations in mineral/rock samples are displaced thoroughly by Ba 2+ in 1 mol/L BaCl 2 solution over 5 days and then titrated conductometrically with 0.1 mol/L MgSO 4 solution and the sharp inflection of titration curves indicates the endpoint. The CEC values determined by the suggested method for standard Na montmorillonite(Na M) and refined Na kaolinite (N K, from chemically pure kaolinite) account 84.8 and 5.2 mmol /100 g and by MB method-82.5 and 2.7 mmol/100 g, respectively. For Na M as swellable clay, the determinations by the two methods are similar; for Na K as non swellable clay, the determinations by MB method is too low. The CEC values of six shale samplex from Shengli oil fields determined by conductometric titration are much more higher than that by MB method and relatively approach to the values estimated from mineral analysis data. The BaCl 2 MgSO 4 conductometric titration can be applied to both swellable and non swellable clay minerals and is a simple and accurate method.