Effects Of Colloid Size And Molar Ratio On The Transport Of Colloids In Mixed Ca-Na Electrolyte Solutions

Colloids are widely distributed in soil and groundwater:some mobile colloids are contaminants themselves,representing threats to soil and groundwater;while others can absorb some contaminants and then facilitate or inhabitant the transport of contaminants.Thus,the behavior of colloid in underground environment will affect the quality of soil and groundwater,and studying the transport of colloid is critical to prevent and repair soil and groundwater pollution.In this paper,polystyrene latex microspheres,with size of 300 nm,500 nm and1000 nm,were used as colloid,and quartz sands with sizes ranging from 200?m to 425?m were used as porous media,and laboratory sand column experiments were conducted to investigate the retention and remobilization of three-sized colloids in mixed Ca-Na electrolyte systems under four Ca²⁺/Na⁺molar ratios.Colloid concentration breakthrough curves were obtained based on the measurements of colloid concentration in samples from column experiments,and the retention and remobilization of colloid were analyzed.Besides,based on the results of colloid transport experiments,the colloid transport model in saturated porous media was established through COMSOL Multiphysics 3.5 software to simulate colloid breakthrough curves,and adsorption coefficient and desorption coefficient were obtained.The study results showed:?1?The smaller the colloid size was,the greater the retention occurred on the surface of quartz sands.The change range of the deposition rate of three-sized colloids was the smallest when molar ratio was equal to 0,while when molar ratios were equal to 0.5,1 and?,the change ranges of the deposition rate were similar.The deposition rates of colloid decreased from 38.14%to 19.56%when molar ratio was equal to 0,respectively when colloid size increased from 300 nm to 1000 nm.?2?The retention of three sized colloids in sand column increased when the molar ratio increased;when molar ratio increased from 0 to?,the change range of the deposition rate of three-sized colloids decreased with the increase of colloid size.The deposition rates of colloid increased from 30.91%to 77.22%for colloid with size of500 nm,respectively when molar ratio increased from 0 to?.?3?Colloid remobilization occurred during the injection of solution with IS equals to 1 mM and the injection of ultrapure water,and the total recovery rates decreased with the increasing of molar ratio;the change range of the total recovery rates of colloids with size of 300 nm and 500 nm were similar and greater than that of colloids with size of 1000 nm.The total recovery rates of colloids with size of 1000 nm decreased from62.58%to 23.79%when the molar ratio increased from 0 to?.?4?The advection-dispersion-retention-release model considering the processes of Langmuirian dynamics blocking and the straining effects was successfully developed to simulate the transport process of all the experiments.Parameters obtained from simulation can present colloid transport.The value of adsorption coefficient and maximum colloidal concentration in the solid phase increased as the molar ratio increased and the colloid size decreased,while the desorption coefficient decreased as the molar ratio increased and the colloid size decreased.This trend agreed with the trend observed from the experiment.