Immobilization of Heavy Metals in Contaminated Soils—Performance Assessment in Conditions Similar to a Real Scenario

Abstract

Soil “health” is becoming an increasing concern of modern societies, namely, at the European level, considering its importance to the fields of food, clean water, biodiversity, and even climate change control. On the other hand, human activities are contributing more and more to induce contamination in soils, especially in industrialized societies. This experimental work studies different additives (carbon nanotubes, clay, and Portland cement) with the aim to evaluate their effect on heavy metals, HMs (lead, cooper, nickel, and zinc) immobilization in a contaminated soil in conditions similar to a real scenario. Suspension adsorption tests (fluid-like condition) were performed aiming to supply preliminary information about the adsorption capacity of the soil towards the different HMs tested, while percolation tests (solid-like conditions) were performed aiming to evaluate the HMs immobilization by different additives in conditions similar to a real situation of soil contamination. Results showed that soil particles alone were able to retain considerable amounts of HMs (especially Pb and Cu) which is linked to their fine grain size and the soil high organic matter content. In conditions of good dispersion of the additives, addition of carbon nanotubes or clay can rise the HMs adsorption, except in the case of Zn2+ due to its low electronegativity and high mobility. Moreover, the addition of cement to the soil showed a high capacity to immobilize the HMs which is due to the chemical fixation of the HMs to binder hydration products. In this case, HMs immobilization comes associated with a soil stabilization strategy. The results allow to conclude that the additives, carbon nanotubes and clay, have the potential to minimize HMs mobility in contaminated soils and can be a valid alternative to the usual additive, Portland cement, when tested in conditions similar to a real on-site situation, if the objective is not to induce also soil stabilization, for instance, to enable its use for construction purposes. The results obtained can help designers and decision-makers in the choice of the best materials to remediate HMs contaminated soils.

Special Issue on Heavy Metals in the Environment—Causes and Consequences

“…In the case of soils, immobilizing heavy metals that penetrated into the soil as a result of human activity is a major challenge. While conducting experimental research, Correia et al [15] have analyzed the impact of various additives (carbon nanotubes, clay, and Portland cement) on the mobility of Pb, Cu, Ni, and Zn in contaminated soils. Their findings indicate that these additives increase the soil's natural capacity to bind and retain heavy metals.…”

Assessment and Impacts of Metal Recycling on Groundwater Quality in Ogijo, Ogun State, Nigeria

“…Clay soils, however, have a high affinity for adsorbing heavy metals in their interlayers. The sorption of these toxic metals reduces their concentration in the environment (Correia et al, 2020;Ugwu & Igbokwe, 2019). The underlying strata in the studied area consist of a high percentage of clayey soils (Adebayo & Oloruntoba, 2016) and could account for both the reduced metal concentrations observed in this area and the trace concentrations from BH1 to BH6.…”

Risk Assessment of Soil Contamination with Heavy Metals from Municipal Sewage Sludge

“…Heavy metals entering the environment affect all links in the food chain, from microorganisms, through plants and animals, to humans [18,19]. Therefore, the accumulation of heavy metals in the ground is particularly dangerous [20].…”