Removal and Breakthrough of Lead, Cadmium, and Zinc in Permeable Reactive Concrete

Abstract

Heavy metal contamination of surface and ground waters from anthropogenic sources presents a significant risk to human health and the environment. Leaching of metals such as lead, cadmium, and zinc from historic mining residuals has led to extensive groundwater contamination, for example, the elevated concentrations found at the Oronogo-Duenweg Superfund site in Joplin, Missouri, United States. Excessive wastewater buildup and storage at historic mines have also caused the release of metal toxicants into river systems, as was the case in the catastrophic 2015 Gold King mine spill into the Animas River in Western Colorado. Prevention of metals contamination and the reclamation of contaminated water for human and agricultural use are compelling reasons to improve heavy metal remediation technologies. Permeable reactive concrete (PRC) is a novel, cementitious material that demonstrates substantial removal capacity for heavy metals from aqueous solutions at the bench scale. This study investigated breakthrough testing of PRC using a synthetic groundwater solution of lead, cadmium, and zinc at concentrations similar to reported values for the Oronogo-Duenweg site of ∼0.4 mg/L for lead and cadmium and 45 mg/L for zinc. Breakthrough testing elucidates removal mechanisms and reaction rates, but has never before been performed on PRC. Removal mechanisms documented in this study were precipitation of the hydroxide metals, complexation, and sorption of metals into the hydrated cement paste or metal precipitates. Demonstrated removal became more permanent over time, with total testing time around 260 days without breakthrough. Column breakthrough testing timeframes exceeded initial bench scale isotherm estimates by a factor of 20. Cost estimates for PRCs are ∼1/6th to 1/12th the cost of comparable technologies for similar site applications. PRC has been shown in this study to perform equal to, or greater than, comparable technologies and could significantly reduce remediation costs for other contamination sites.