正电荷胶体(赤铁矿)凝聚动力学机制的激光散射研究

Kinetics Mechanism of Aggregation of the Positively Charged Colloid(Hematite)by Laser Scattering Technology

赤铁矿胶体是可变电荷土壤的重要组成部分,其相互作用深刻影响可变电荷土壤团聚体的形成、稳定与分散,从而深刻影响土壤结构状态与物质迁移过程的发生.通常的土壤pH(pH<8)条件下,赤铁矿带净正电荷,其凝聚由溶液中的阴离子引发.目前,阴离子引发土壤胶体凝聚的相关研究鲜见报道.本研究以赤铁矿为试验材料,在pH=4的酸性条件下研究了NaCl溶液中Cl-引发赤铁矿凝聚的动力学特征.研究发现:1)NaCl溶液中,赤铁矿胶体的临界聚沉浓度为99.2mmol/L.2)NaCl溶液中,赤铁矿胶体的凝聚活化能与NaCl浓度间满足如下指数关系:ΔE=RTln{[0.35f0/(0.44f0-8.66)]}.3)当NaCl浓度小于99.2mmol/L时,赤铁矿胶体发生慢速的反应控制凝聚,即表现出RLCA凝聚机制;当NaCl浓度高于99.2mmol/L时,赤铁矿胶体发生快速的扩散控制凝聚,即表现出DLCA凝聚机制.本研究发现的带正电荷赤铁矿胶体的凝聚动力学规律对于进一步探索可变电荷土壤团聚体的形成与分散机制具有一定参考价值.

Hematite colloid is an important component of variable charge soil colloids.The interactions of hematite colloids profoundly influence the formation,stability and dispersion of variable charge soil aggregates,and then strongly affect the transfer process of soil particles.Under the normal soil pH（pH〈8）conditions,the net charge of hematite surface is positive,thus the aggregation of hematite colloids is triggered by the anions in the solution.Currently,there are few reports concerning researches of the aggregation of colloids induced by anions.In this study,the kinetics of aggregation of hematite affected by Cl-1in NaCl solution at pH=4was investigated.The critical coagulation concentration of hematite colloids in the NaCl solution was found to be 99.2mmol/L.The exponential function between the activation energy of hematite colloid aggregation and the NaCl concentration was observed asΔE =RTln{[0.35f0/（0.44f0-8.66）]}.When the NaCl concentration was lower than 99.2mmol/L,the reaction of hematite colloid aggregation was slow,an RLCA cohesion mechanism;in contrast,when the NaCl concentration was higher than 99.2mmol/L,the aggregation showed a rapid diffusion mechanism（DLCA）.The aggregation kinetics of hematite colloids with positive charges observed in the present study would provide a possible direction for the study of the mechanism of the formation and dispersion of soil aggregates with variable charges.