Colloid Release Process and Permeability Losses of Coastal Aquifer in Different SAR Conditions

On the basis of field investigation, batch experiments and column experiments have been conducted to elucidate dynamics of colloid release concentration and amount from the coastal aquifer under different sodium adsorption ratios (SAR). The differences of colloids release in different aqueous mediums are identified, and the permeability changes of aqueous mediums are investigated in the process of colloid release. The results show that the release capacity of colloidal particles from the aqueous mediums decrease with the increasing of sodium adsorption ratio (SAR) in the mixed solution system of NaCl and CaCl₂, and Ca²⁺ inhibits the release of the colloid. From the column experiment, it is found that a little colloid particles of silty soil are released at the SAR of influent is 0 and 8, and begin to release obviously when the SAR of influent is ∞, and the release amount of colloidal particles from the aqueous mediums increases gradually with the increasing of pore volumes, and reaches the maximum at pore volumes of 52, then the concentration reduces gradually. The total cumulative release amount of colloidal particles from silty soil is 0.13 mg/g. Very little colloid particles of the fine silty and medium sand are released. The permeability loss of silty soil, fine silty and medium sand are 98.2%, 86.7% and 95.9% respectively in the process of colloid release. The permeability losses of aqueous mediums are mainly due to the spatial redistribution of released colloidal particles in the media.