The adsorption characteristics of soils and removal of cadmium and nickel from wastewaters

The interactions between the adsorption characteristics of 27 experimental soils and the sorption of Cd and Ni from the municipal wastewaters were investigated in this study. The removal of these elements from soil solution was followed for 50 days. All the adsorption characteristics, except cation exchange capacity and organic matter, were significantly correlated to the sorption of Cd after one day shaking. After 7 days of shaking, none of the soil adsorption characteristics except free CaCO₃ was significantly correlated to Cd removal from wastewater. The soil saturated paste pH and suspension pH were strongly correlated to Cd sorption throughout this experiment. The behavior of Ni in soils was different from that of Cd. Surface area, total Fe, and total Al were significantly correlated to Ni sorption. The correlation between Ni removal and pH was the strongest than any other parameter studied. After 7 days shaking, clay content and total Ca were not significantly correlated to Ni sorption. The cation exchange capacity of the soils was not significantly correlated to Cd or Ni sorption in this experiment. It seems that in the experimental soils, concentration of Cd and Ni were probably not controlled by adsorption process. The precipitation process was probably playing a major role in the removal of these elements from the municipal wastewaters. As observed in this experiment, the cation exchange capacity of experimental soils was a poor parameter to define sorption capacity of these soils for Cd and Ni. The guidelines for determining the soil sludge load, which are mainly based on the cation exchange capacity of soils, should be revised.