有机修饰剂对塿土的离子交换修饰研究

Ionic Exchange Modification Mechanism Between Organic Modifier and Lou Soil

研究了有机修饰剂十六烷基三甲基溴化铵（CTMAB）对于塿土2层次土样修饰的离子交换机制.结果表明,土壤表面的CTMAB和Ca^2＋/2的总和（SCC）可以作为一个简便有效的指标用来判断修饰机制的实质,它的研究证实了CTMAB对于塿土2层次土样的修饰是离子交换修饰和疏水键修饰共存的机制.疏水键修饰机制开始出现于修饰比例20%-28%CEC范围内,并随修饰比例和CTMAB摩尔分数的增大而线性增大,但直到50%CEC修饰比例时疏水键修饰机制才显现出其对于土壤性质的影响,100%CEC左右修饰比例是疏水键修饰超过离子交换修饰而成为主要修饰机制的转折点.Vanselow离子选择性系数表明塿土土样对于CTMAB的吸附偏好要远远大于对Ca^2＋的吸附.热力学研究结果表明,随总浓度增加,在25%-100%CEC比例区间,修饰反应由放热、熵减反应转变为吸热熵增反应,而在100%-200%CEC区间,表观焓变和表观熵变表现出焓、熵趋于减小的趋势,总体上表现出由25%-100%CEC区间的熵变控制的自发性反应向100%-200%CEC区间的焓变控制的自发性过程转换的热力学特征,佐证了上述修饰机制的合理性.

The ionic exchange modification mechanism between cationic organic modifier, cetyhrimethylammonium bromide （CTMAB）, and two layers of Lou soil, tillage layer （TLLS） and clay layer （CLLS）, were studied. The results show that a simple and effective index, sum of amounts of CTMAB and Ca^2＋/2 （Scc）, can be used to judge the essence of modification mechanism between CTMAB and Lou soil. SCC demonstrates that the modification of CTMAB to two layers of Lou soil is the coexist of both ionic exchange and hydrophobic bond mechanism. The hydrophobic bond modification appears in the range of modification ratio 20%-28 % CEC and linearly increases with an increase of both modification ratio and molar fraction of CTMAB, but its effects on the properties of soil become emergence just until 50% CEC modification ratio, and the hydrophobic bond mode exceeds the ionic exchange mode at about 100% CEC modification ratio and becomes main modification mechanism. The Vanselow selectivity coefficients show that the adsorption preference of Lou soil to CTMAB is stronger than that to calcium ion. The results of thermodynamics indicate that with an increase of modification ratio, the modification reaction transform from exothermic and entropy decrease to endothermic and entropy increase in the range of modification ratio 25 %-100% CEC, while both pseudo enthalpy change and pseudo entropy change display a decrease trend in the range of modification ratio 100%-200% CEC, and in total, the modification reaction is a spontaneous reaction which controlled by entropy change in range of modification ratio 25 %-100 % CEC but controlled by enthalpy change in range of modification ratio 100%-200% CEC. The rationality of modification mechanism could be demonstrated by the results of thermodynamics.