Adsorption-desorption Behaviors Of As And Cu In Soil And Their Influencing Factors

Adsorption and desorption behaviors of heavy metals onto and from various soils help to evaluate soil disinfection capacity for different metals. In this study, two representative heavy metals, Arsenic (As) and Copper (Cu), were selected and six soil with contrasted properties were chosen. A set of static and dynamic batch experiments were conducted. The objectives of the study were to understand adsorption-desorption behaviors of Arsenic and Copper in various soils and to investigate their influencing factors. These results provide basic data and theoretical basis for establishing decision of environmental protection.Arsenic adsorption onto soil was largely determined by soil type, in which the contents of Fe- and Al-oxides in various soils played an important role. The adsorption capacity of various soils showed the decreasing order of laterite>red clay>yellow soil>sandy soil, probably because of the difference in the content of Fe- and Al-oxides. However, the aging crystalloid of these oxides and existence of mass soil organic matter inhibited the arsenate adsorption process in laterite. Adsorption of Arsenic decreased with increase in soil pH. With the increase of solution pH, descending positive ions on the soil colloid surface obviously reduced the Arsenic adsorption in yellow soil or sandy soil. Compared with As (V) and As (III), the former is much easier for adsorption in red clay, and the adverse tendency performed in their adsorption stability.As the cognation elements, phosphorus (P) and arsenic (As) presented similar environmental behavior, phosphorus has different effect on adsorption-desorption while As (V) in soil,but their adsorptive sites are not identical. When both simultaneously join in the soil, phosphorus is much prone to be absorbed during the competitive process, and has inhibitive effect on As (V) adsorption. After phosphorus occupies some adsorptive sites on the soil, the adsorption of As (V) on soil is under various degrees of suppression, with more adsorptive sites held by phosphorus, the effect becomes conspicuous. After the phosphorus holds most of the soil adsorptive sites, the limited adsorptive sites become the controlling factors for As (V) adsorption, especially on red clay with little aluminum oxide content. When As (V) takes up different adsorptive sites in soil, with phosphorus concentration elevated, arsenic concentration in the soil solution increases. Adsorption of phosphorus on soils has inhibition on As (V) adsorption, and reduces the quantity of total adsorptive sites on soil.As adsorption greatly correlated with soil type, copper was much easier for adsorption in alkaline soils compared with acid ones, which is ascribed to soil pH. The copper adsorbed on the alkaline soil was difficult to be desorbed by neutral salt.The addition of Humic Acid (HA) increased the adsorption of copper, and more considerable increase was observed in the alkaline soil than in the acid soil. On the other hand, Citric Acid (CA) decreased the copper adsorption in the alkaline soils, while in the acid soil, the effect of CA on the adsorption of copper varied with the concentration of added copper, with the effect changing from negative to positive when the concentration of added copper changed from less than 63.54mg·kg-1 to more than 63.54mg·kg-1. It was hypothesized that changes in copper hydrolysis with pH and the native properties of dissolved organic carbon (DOC) all contributed to the copper behaviors aforementioned.Along with precise determination for arsenic amount, effective obviation of disturbance of arsenic on phosphorous measurement according to the Bill Law provides a technical platform in the research and reliable theoretical basis for reasonable assessment of their environmental behavior.