Phosphate, Lime and Bentonite Affect Heavy Metals and Phosphorus Availability in Acidic and Calcareous Soils

This work investigated the effect of soil amendments on the mobility of heavy metals and P in acidic and calcareous heavy metal polluted soils after incubated for one year. Compared to phosphate alone, the phosphate+bentonite amendment had lower available P concentrations (13.1 and 16.3% in the acidic and calcareous soils, respectively) and similar heavy metal immobilization capacity. The lime amendment increased soil P availability possibly by increasing the negative charges of soil particles in both soils. Lime amendment greatly reduced the DTPA-extractable concentrations of Cd, Cu, Mn, Ni, Pb and Zn in both soils; greater reductions were observed with higher rate compared to the lower rate and in the acidic soil compared to the calcareous soil, especially for Cd, Mn, Ni and Zn (23.9–95.3% lower than the control). The bentonite in the phosphate+bentonite treatment may have reduced soil P availability by adsorption of soluble P. Based on the results, phosphate+bentonite instead of phosphate alone may be used to reduce heavy metal and P availability in heavy metal contaminated soil. When only lime is used, caution should be taken with respect to potential soil P losses and subsequent off-site degradation in water and environmental quality.