Experimental immobilization of Zn, Pb and Cd by additives to highly contaminated soils

The immobilization effect of soil amendments on leaching and bioavailability of Pb, Zn and Cd in highly contaminated soils under industrial impact was studied by collecting the soils in the surroundings of Zn-Pb Smelter “Miasteczko Śląskie” in southern Poland as an example. Various amounts of four additives (phosphate fertilizer, limestone powder, bentonite rock and bog iron ore) were tested in laboratory experiments to compare the effectiveness of three dominant mechanisms of immobilization: precipitation of phosphates, pH increase, and sorption. The contents of metals before immobilization were determined by extraction in CaCl₂, EDTA and aqua regia. Cadmium and zinc are mainly represented by soluble, bio-available forms extractable in CaCl₂, while lead by potentially bioavailable speciations extractable by EDTA. Most effective in the immobilization of these metals were the amendments increasing soil pH: limestone powder and phosphate fertilizer. Bog iron ore and bentonite were less effective because the soil pH was too low for efficient cation adsorption.