Zinc sorption by different soils as affected by selective removal of carbonates and hydrous oxides

Zinc is relatively abundant compared to other trace elements and can be highly mobile in the soil-plant system. We aimed to determine the importance of CaCO3 and oxides as two important soil constituents which affect Zn sorption in eight soils of the Southeastern Mediterranean varying in stage of weathering, origin, and properties. We removed CaCO3 and Al, Fe, Mn, and Si oxides from the soils and compared Zn sorption in the untreated soils with that in the CaCO3- and the oxides-removed soils. We found that sorption decreased considerably from 83 to 98% with CaCO3 removal in all soils and decreased further when oxides were removed from 85 to over 99% as compared to the control. The lowered sorption was confirmed by comparing Zn distribution coefficient, Kd,mean, among treated and untreated soils. This revealed that Kd,mean decreased by approximately two orders of magnitude with CaCO3 and oxides removal. Maximum Kd,mean value in untreated soils was 4886 L kg−1 (lacustrine soil); in the CaCO3-removed soils maximum Kd,mean was 143 (Histosols), and in the oxides-removed soils it was 126.5 L kg−1 (Vertisols). Zinc sorption was less affected by oxides removal in the low amorphous (oxalate-extracted) oxides-content soils, due to the reactive nature of these oxides. In the CaCO3-removed soils, Al and Fe amorphous oxides were the soil constituents that mainly affected Zn sorption. We conclude that in acidic soils with low oxides content, the addition of Fe and Al amorphous reactive oxides may result in reduced metal mobility due to enhanced sorption. This approach might be useful for future remediation options of Zn-contaminated soils.