Remediation of Chromium-Contaminated Soils: Bench-Scale Investigation

Abstract

A feasibility study was performed to remediate chromium-contaminated soil by cold top ex situ vitrification. This paper describes the initial conceptualization of the research demonstration and the results from the bench-scale study. Hexavalent chromium is a well known Group A human carcinogen. There are more than two million tons of leftover chromite ore residues from chromate extraction manufacturing in Hudson County, New Jersey. They contain both unleached hexavalent and unoxidized trivalent chromium. Both forms are considered an environmental and health hazard. In this demonstration study, the cold top ex situ vitrification process was used to remediate the chromium-contaminated soils. This technology evolved from the glass melting industry. Here, the chemical chromate is reduced and immobilized in a siliceous matrix. The bench-scale study included site selection, lab-scale vitrification, physical and chemical characterization of contaminated soils and vitrified soil, evaluation of potential reuse of vitrified soils as construction aggregates, and selection of two potential sites for pilot-scale testing. Nine chromium-contaminated sites were selected for this bench-scale study. The total chromium concentration in soil from the above sites ranged from 0.2 to 2.6% by weight, and the hexavalent chromium in toxicity characteristic leaching procedure (TCLP) leachate was above 30 ppm in some sites. The lab-scale vitrified soils had hexavalent chromium in TCLP leachate below 5 ppm, the regulatory limit, and could be used as construction aggregates. The pilot-scale test performed from soils obtained from two of the above sites demonstrated the cold top ex situ vitrification technology and the potential reuse of vitrified soil in highway construction application as asphalt concrete.