RECOVERY OF SOIL AND METAL RESOURCES USING A SUSTAINABLE REMEDIATION APPROACH BY COMBINING ZERO VALENT IRON AND MAGNETIC SEPARATION TECHNOLOGIES

Abstract

In metal impacted environments, both soils and aquatic systems tend to behave as sinks, and several techniques have been proposed to help protect or restore such systems. As essential natural resources, soils are the basis for human life, and soil’s pollution with toxic levels of metals such as those found in superfund sites in the USA tends to overcome the resilience of impacted systems, and therefore, their sustainability. Accordingly, research in this field follows two main tracks: (i) protection of soil resources (pro-active pollution prevention), and (ii) remediation of impacted soils to restore ecosystem functions (a reactive response). The latter is the topic of this study, but with emphasis on both the restoration soil’s essential ecosystem functions such as plant growth, and the recovery of metal resources. The overarching hypothesis of this study is that “the ability of metal-contaminated soils to support plant growth without metal bioaccumulation and phyto-toxicity can be restored through use of metal sorption onto corroded metallic iron particles and retrieval from soil’s matrices by magnetic separation techniques. This treatment would then allow for the recovery of metal resources from the retrieved sorbents”. Laboratory studies were conducted using a predictive approach to remediate soils contaminated with selected representative of type-A (beryllium), type-B (mercury), and borderline (lead) metals based on the following steps. First, corroded ZVI particles were incorporated into metal-contaminated soils at a 2.5% application rate to capture metals through sorption. Second, metals sorbed onto ZVI particles were retrieved from treated soils, and third, metals were recovered from ZVI, and treated soils used in plant growth studies. The results showed a significant decrease in total metal concentrations of the treated soils, with removal efficiencies of 80% for Be, 90% for Pb, and 97% for Hg. The acid leaching of Be and Pb sorbed onto ZVI particles followed by chemical precipitation using oxyanion ligands resulted in recoveries of up to 99.79% of Be and 90.63% of Pb initially present in the aqueous solutions prior to precipitation. The X‐ray diffraction (XRD) analysis of the produced solid phases confirmed the presence of crystalline PbSO4(s), while BeCO3(s) appears to occur primarily in the amorphous form. Finally, plant studies were used to investigate the uptake, accumulation, and translocation of Be and Pb by the hyper tomato plant (Solanum lycopersicum), when grown in treated and Be and Pb contaminated soils. The results showed that the proposed remediation method can decrease Be and Pb bio-accumulation in plants.