Importance of Mineralogy in the Geoenvironmental
Characterization and Treatment of Chromite Ore
Processing Residue
Maria Chrysochoou
1
; Dimitris Dermatas, M.ASCE
2
; Dennis G. Grubb, M.ASCE
3
; Deok Hyun Moon
4
; and
Christos Christodoulatos
5
Abstract: The geoenvironmental characterization of COPR at two deposition sites New Jersey and Maryland included geotechnical,
chemical, mineralogical, and leaching analyses of three main chromite ore processing residue COPR types gray-black GB, hard brown
HB, clayey C. Quantitative mineralogical analyses were instrumental in the delineation of the geochemical differences between the
three COPR types, which enabled a framework to predict COPR response to potential remediation schemes. Overall, COPR mineralogy
resembled cement, with hydration and pozzolanic reactions dominating its geochemistry. GB COPR was largely unreacted despite its
prolonged exposure to humid conditions, while HB COPR was completely hydrated and contained high CrVI concentrations. The two
materials were chemically similar, with dilution accounting for the chemical and density differences. While the total acid neutralization
capacity ANC of GB and HB was the same, the ANC at high pH 8–12 was higher in HB due to the dominance of hydrating materials,
leading to more buffering capacity and lower CrVI leaching levels. It is concluded that GB and HB were derived from the same ore and
process and that postdepositional transformations account for the emergence of HB layers in COPR sites. The physicochemical properties
of HB hardness, high and inaccessible CrVI, high ANC are complicating factors for in situ COPR reductive treatment in the presence
of HB.
DOI: 10.1061/ASCEGT.1943-5606.0000233
CE Database subject headings: Chromium; Mineralogy; Site investigation; Expansive soils; Hazardous wastes.
Author keywords: Chromium; Mineralogy; Site investigation; Expansive soils; Hazardous wastes.
Introduction
Chromite ore processing residue COPR is generated as a by-
product of chromite ore processing to isolate and extract chro-
mium. Numerous chromite ore processing plants operated
throughout the world, including England, Japan, Germany, and
the United States McKee 1998, as well as India, Pakistan,
China, and the former Soviet Union Darrie 2001. Chromite ore
of the general chemical formula Mg,FeCr,Al,Fe
2
O
4
is pro-
cessed by means of a high-temperature lime roasting process
1,200°C that separates metal impurities Fe, Mg, and Al and
isolates chromium as soluble sodium chromate Na
2
CrO
4
. Addi-
tion of lime CaO during the roasting process leads to the for-
mation of insoluble residuals, COPR, with a pH on the order of
11.5–12.5 and total chromium content up to 46,000 mg/kg, 30%
or more of which occurs as CrVILioy et al. 1992.
COPR was widely used as a structural fill because of its physi-
cal resemblance to a sandy soil that was considered suitable for
use as foundation material. As a result, COPR deposition sites are
commonly residential or commercial sites having high real estate
value. For example, the major deposition sites in the United
States are located in Maryland, New Jersey, New York, and Ohio
Public Health Service 1953. COPR was also commonly used as
fill for wetlands, sewerline, and roadway construction and con-
struction of tank berms. The two sites investigated in this study
are characteristic examples of in-filled wetlands that currently
constitute prime real estate in the metropolitan areas of New Jer-
sey and Maryland.
New Jersey is one of the states with the most COPR deposition
sites. Three high-lime chromite ore processing plants located in
Hudson County N.J. operated between 1905 and 1971 and pro-
duced over 2 million tons of COPR that were historically depos-
ited in over 160 sites in the Hudson and Essex counties, in most
cases as marshland fill New Jersey Department of Environmental
Protection NJDEP 1997. Increased public awareness during the
1980s drew attention to chromium-related hazards, and an exten-
sive investigation program was initiated by the NJDEP that is
ongoing today. NJDEP recently modified its soil clean-up criteria
for CrVI to 20 mg/kg for both residential and nonresidential
sites NJDEP 2007, “Chromium moratorium.” Memorandum
from DEP Commissioner Lisa Jackson, February 8, 2007. There
is no limit for CrIII for nonresidential sites, while there is a limit
1
Assistant Professor, Dept. of Civil and Environmental Engineering,
Univ. of Connecticut, Storrs, CT 06269 corresponding author. E-mail:
mchrysoc@engr.uconn.edu
2
Director, Waste Management Authority Eastern Macedonia-Thrace,
N. Plastira 6, Komotini 69100, Greece.
3
Senior Associate, Schnabel Engineering LLC, 510 East Gay St., West
Chester, PA 19380.
4
Lecturer, Chosun Univ., Gwangju 501-759, South Korea.
5
Director, Center for Environmental Systems, Stevens Institute of
Technology, Castle Point on Hudson, Hoboken, NJ 07030.
Note. This manuscript was submitted on August 18, 2009; approved
on August 28, 2009; published online on September 1, 2009. Discussion
period open until August 1, 2010; separate discussions must be submitted
for individual papers. This paper is part of the Journal of Geotechnical
and Geoenvironmental Engineering, Vol. 136, No. 3, March 1, 2010.
©ASCE, ISSN 1090-0241/2010/3-510–521/$25.00.
510 / JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING © ASCE / MARCH 2010
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