Effect of Phosphate Addition on Cadmium Precipitation and Adsorption in Contaminated Arable Soil with a Low Concentration of Cadmium

The objectives of this study were to determine (1) the phosphorus (P) level required to induce cadmium (Cd) precipitation in a contaminated arable soil with low concentrations of Cd and (2) the primary mechanism of Cd immobilization at different P levels. Phosphorus was added at levels of 0 800, 1600, and 16,000 mg P kg−1 to a soil containing 5.57 mg Cd kg−1. The concentration of 1 M NH4OAc extractable Cd decreased significantly with P levels up to 1600 mg kg−1 due to an increase in soil pH and negative charge of soil (p < 0.001). A further decrease in 1 M NH4OAc extractable Cd concentration was noted when P was increased to 16,000 mg P kg−1 and may have been the result of Cd precipitation. This study suggest that adding P at high levels may help in the formation of geochemically stable Cd minerals in soil containing low levels of this heavy metal.