Immobilization of toxic metal cations on goethite-amended soils: a remediation strategy

The study investigates a simple and viable option to reduce toxic metals mobility and availability in four surface (0–30cm) soils with varying physicochemical properties amended by different percentages of goethite. Batch sorption experiments carried out to study the effectiveness of immobilizing Pb²⁺, Cu²⁺, Zn²⁺ and Cd²⁺ ions on these soils showed that goethite played vital role in the metals adsorption (≥10% increase in adsorption). Removal of soil iron oxides caused reduced Pb²⁺ adsorption on soils with high organic matter (£10% decrease in adsorption) with no significant increase in adsorption upon amendment, while soils having low organic matter had enhanced adsorption with amendment. Cu²⁺ and Cd²⁺ adsorptions were not enhanced even at 10% goethite amendment. However, Zn²⁺ adsorption was interestingly different: the soils showed ≥55 % increases upon removal of inherent soil iron oxides without goethite amendment. Goethite amendments further enhanced Zn²⁺ adsorption on these soils. Generally, both whole and amended soils showed higher preference for Pb²⁺; the sorption trend is – Pb²⁺ >Cu²⁺ >Zn²⁺ >Cd²⁺. Goethite amendment of these soils improved Pb²⁺ and Zn²⁺ adsorption. Hence, goethite amendment may be an effective method for immobilizing Pb²⁺ and Zn²⁺ on these soils and thus reducing their availability to biota. The quantity of goethite required by a soil to attain maximum immobilization varies depending on the metal and the soil’s physicochemical properties; however, Cu²⁺ and Cd²⁺ may not be effectively immobilized using goethite amendment.