2︰1和1︰1型黏土矿物胶体凝聚中Hofmeister效应的比较研究

土壤胶体是土壤具备肥力与生态功能的物质基础,土壤胶体凝聚与分散影响着土壤中一系列微观过程和宏观现象。采用动态光散射技术比较研究三种碱金属阳离子(Li+、Na+、K+)引发不同类型黏土矿物(2︰1型蒙脱石和1︰1型高岭石)胶体凝聚中的Hofmeister效应。研究发现,Li+、Na+、K+作用下蒙脱石、高岭石胶体的凝聚速率、临界聚沉浓度及活化能都存在明显差异,表现出强烈的Hofmeister效应。当电解质浓度为20 mmol·L–1时,K+引发蒙脱石胶体凝聚的速率为66.61 nm·min–1,远高于Na+、Li+引发蒙脱石胶体凝聚速率(5.93、4.41 nm·min–1);而与之对应的临界聚沉浓度则呈现K+(蒙脱石21.8 mmol·L–1、高岭石34.6 mmol·L–1)低于Na+(蒙脱石57.6 mmol·L–1、高岭石85.8 mmol·L–1)低于Li+(蒙脱石81.8 mmol·L–1、高岭石113.9 mmol·L–1)规律,胶体凝聚中活化能可合理解释此现象。电解质浓度为25 mmol·L–1时,Li+、Na+、K+引发蒙脱石、高岭石胶体凝聚的活化能分别为1.97 kT、1.43 kT、0 kT和2.94 kT、1.71 kT、0.49 kT,说明蒙脱石、高岭石胶体凝聚过程中Hofmeister效应序列均为Li+

Hofmeister Effects of 2:1 and 1:1 Clay Minerals in Agglomeration: A Comparative Study

【Objective】Soil colloid is the material foundation of soil fertility and soil ecological function.Agglomeration and dispersion of soil colloids influences a series of microscopic processes and macroscopic phenomena in soil.The purpose of this paper was to compare Hofmeister effects of 2︰1-typed montmorillonite and 1︰1-typed kaolinite mineral colloids in agglomeration triggered by alkali cations(Li+,Na+and K+),and analyze sources of the Hofmeister effects.【Method】To that end,ultrasonic dispersion and centrifugation of soil samples was performed to extract montmorillonite and kaolinite colloids,and dynamic light scattering was to determine separately,effects of Li+,Na+and K+on agglomeration of the mineral colloidal particles.And then comparison was made between agglomerations of the mineral colloids in three different alkali solutions in kinetic process and activation energy.【Result】Results show that the agglomeration varied sharply in rate,critical coagulation concentration and activation energy as affected by Li+,Na+or K+,demonstrating strong Hofmeister effects.In solutions with electrolyte concentration being 20 mmol·L–1,the aggregation of montmorillonite colloid triggered by K+reached 66.61 nm·min–1 in rate,much higher than that triggered by Na+(5.93 nm·min–1)and by Li+(4.41 nm·min-1).And in solutions with electrolyte concentration being 30 mmol·L–1,the agglomeration of kaolinite colloid activated by K+reached 32.43 nm·min–1 in rate,which was far too much higher than that triggered by Na+(7.28 nm·min–1)and by Li+(1.90 nm·min–1).The effect of Hofmeister effects on aggregation rate of montmorillonite and kaolinite colloids varied with the cation in the solution in an order of Li+Na+(1.43 kT)>K+(0 kT),while for kaolinite it did in the same order(2.94 kT,1.71 kT and 0.49 kT).All demonstrated that the Hofmeister effects in agglomeration of montmorillonite and kaolinite did vary with the cation in the solution in the order of Li+