Grey-iron foundry slags as reactive media for removing trichloroethylene from groundwater

A feasibility study was conducted using slags from six grey-iron foundries to evaluate their potential as reactive media for permeable reactive barriers (PRBs) to remove aqueous trichloroethylene (TCE) from groundwater. Batch tests indicated that the slags exhibit varying degrees of reactivity ranging from nonreactive to reactivity comparable to that obtained with commercially available granular zerovalent iron on a surface-area-normalized basis. TCE removal follows pseudo-first-order kinetics, and produces lesser-chlorinated ethene byproducts (e.g., 1,1-DCE, cis-DCE). Greater reactivity was obtained with the slags having the highest iron content and the lowest reactivity was obtained with the slag having the lowest iron content, suggesting that iron is a primary reductant in the slags. Batch tests on the two most reactive slags indicated that the rate coefficients are linearly related to surface area over the range tested, and are sensitive to initial TCE concentration. Column studies showed that reactivity is lower under flow-through conditions than anticipated based on batch tests. Calculations indicate a 2-m-thick slag PRB can degrade TCE to less than 0.005 mg/L for influent concentrations less than 2 mg/L at seepage velocities below 0.1 m/d.