Effect of porous hydrated calcium silicate on sorption and desorption of cadmium by soils

Abstract

Chemical immobilization of cadmium in soil by alkaline materials is a low-cost and non-destructive method to clean-up soils polluted by cadmium. However, much more attention has been paid to the sorption than desorption of metals from treated soils. Batch experiments were carried out to investigate the effect of porous hydrated calcium silicate (PS) on the sorption and desorption of cadmium from an Andosol and an Alluvial soil, which were collected from paddy fields. Samples of the two soil types were incubated with 0, 0.5, and 2.0% of PS under flooded and cultivated conditions for 2 months, and air-dried. PS treatment increased the soil pH. The sorption experiments showed that the amount of Cd sorbed by the two soil types increased with the increase of the percentage of PS. Sorption isotherms were described by the linear Langmuir equation. The increased q _m (sorption maximum) and k values (binding strength) of the PS treated soil samples suggested that the higher sorption capacity and stronger complex between cadmium and soils were caused by the PS treatment. The desorption experiments also showed that less cadmium was released from PS treated soils. There was no obvious difference in the cadmium sorption between the soils with and without PS treatment at the same pH value. It was concluded that PS, which can increase the soil pH, is very effective in stabilizing Cd in soils.