Study On Soil Environmental Criteria Of Silver Based On Groundwater Protection

The study on soil environmental criteria was an important prerequisite of standard setting of soil environment. Study on soil environmental criteria was still in the infancy, especially lack of the research on groundwater protection in China. Therefore, three types of soil--Hunan Red soil, Bei Jing Chao soil and Black soil which widely distributed and representative were chosen as the study soil, heavy metals silver (Ag) as the target pollutant, to study the soil environmental criteria for groundwater protection.Batch adsorption-desorption equilibrium test haved been used to study adsorption behavior of the heavy metal silver (Ag) in three soils. The results showed that, silver adsorption increased with the concentration of Ag+in balanced solution of three kinds of soils, the maximum adsorption capacity of silver expressed as Chao soil>Black soil>Red soil. The results of commonly used isotherm equation fit showed that the Langmuir equation and Freundlich equation could fitting isothermal adsorption process of silver in three soils, but Langmuir equation fitting better. The desorption amount of silver followed as Black>Chao soil>Red soil and desorption rate range of2.31%-28.04%, followed as Red soil> Black soil>Chao soil, which showed that the retaining capacity of chao soil was stronger than red soil and black soil and red soil had the weakest retaining capacity.The same adsorption isotherm experiment method was used in adsorption kinetics of silver. The speed of adsorption of silver was quickly in three soils,more than80%of the maximum adsorption amount had been reached within5min and reached adsorption saturation in about30min. Adsorption kinetics equation numerical fitting were-used in the kinetic adsorption, the adsorption kinetics process of silver in red soil and black soil were both in line with the pseudo-first order kinetic equation and the second-order kinetic equation, but second-order kinetic equation was more accurate.indicating that chemical adsorption was the dominant reaction in adsorption process; However, the adsorption kinetics of silver in chao soil consistented with the first order kinetic equation.The soil before and after the adsorption analysed by infrared spectroscopy and X-ray diffraction showed that the red soil mineral components belong to kaolinite minerals, black and chao soil mineral components belong to montmorillonite minerals.Differences among mineral composition would influence the adsorption and desorption processes of silver. View from the structure of mineral components, the adsorption capacity of silver of black and chao soil were stronger than red soil, which was consistent with the experimental results.SSL model based on the reference concentration limits in drinking water and RBCA model based on human health risk for adults were utilised to derived the criteria of silver in three soils. The results showed that risk-based soil level(RBSLs) of silver was higher than the water quality-based level(Cs). But the criteria complied with:Beijing Chao soil>Black soil>Hunan Red soil. For soil-water allocation factor (Ksw):Red soil>Black>Chao soil, lower Ksw meaned more component of object pollutant was adsorpted or fixed by soil and fewer quantity of soil leaching,which consistent with the result that the retaining capacity of silver of chao soil was greater than black soil and red soil in adsorption-desorption experiment.