66    EXTRACTION, RECOVERY, AND IMMOBILIZATION OF
CHROMIUM FROM CONTAMINATED SOILS
Edwin F. Barth, Environmental Engineer
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
Michael L. Taylor, Director
Research and Development
IT Corporation
Cincinnati, Ohio 45268
John A. Wentz, Environmental Engineer
Civil and Environmental Consultants
Cincinnati, Ohio 45268
Steve Giti-Pour, Graduate Research Student
University of Cincinnati
Department of Civil and Environmental Engineering
Cincinnati, Ohio 45268
INTRODUCTION
Chromium is a widely utilized heavy metal in industry because of its refractory, catalytic, decorative, fungicidal, and corrosion-resistant properties. Unfortunately, uncontrolled disposal practices
utilized in conjunction with mining, production, and manufacturing operations have caused soil,
sediment, and groundwater to become contaminated with chromium and chromium compounds at
many sites.
Several technologies have been utilized to remediate chromium-contaminated soil and groundwater.
Solidification/stabilization (immobilization), vitrification, in-situ chemical reduction, electrokinetic
separation, and soil flushing are examples of remediation technologies that have been employed.
Extraction using acidic or alkaline solutions offers recovery options for chromium. The type of soil
(mineralogy, texture), pH, water chemistry, and redox conditions influence the soil/chromium interactions and, in turn, the effectiveness of some treatment options.
The chemistry of chromium and potential remediation processes have been described in numerous
publications. For example, extraction studies performed at the New Jersey Institute of Technology
revealed that sand did not adsorb either chromium (III) or chromium (VI) regardless of pH.1 Certain
clays adsorbed more chromium (III) than chromium (VI), however, until saturation occurred. Less
chromium (VI) was adsorbed on clays below a pH of 4 units or greater than 10 units. Approximately
35% of chromium was removed from a soil containing between 10,000 to 22,000 mg/kg of chromium
after pH adjustment to 10 units. More removal was noted if a chelating agent such as EDTA was used
in the extractant fluid.
Less chromium was released during acid extraction of a synthetically contaminated soil containing
Cr(N03)3, relative to other heavy metals, in a study designed to evaluate several soil treatment
processes.2 These data suggest that chromium (III) may be strongly sorbed to a soil, even after limited
contact time.
The United States Environmental Protection Agency has evaluated acid leaching processes (using
H2S04) for extracting heavy metals from wood preserving solid waste.3 The concentrations of chromium remaining in the acid-treated solids (as determined by an acetic acid extraction test) were
reduced from 0.12 mg/L for the untreated waste to 0.02 mg/L for the treated waste.
The Bureau of Mines has evaluated management strategies for minimizing the leaching of chromium from chromium-bearing slags (waste) under acidic conditions.4 The CaO:Si02 ratio and/or the
49th Purdue Industrial Waste Conference Proceedings, 1994 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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