Site Remediation via Dispersion By Chemical Reaction (DCR)
GILES M. MARION, JAMES R. PAYNE, AND GURDARSHAN S. BRAR
INTRODUCTION
cipitate potentially toxic metals and neutralize
acids (Lewis and Boynton 1976, Boynton 1980).
Lime-based technologies
Lime application for metal precipitation requires
Lime (CaO) is one of the oldest chemicals used
pH adjustment to produce lowest solubility. Most
on Earth (Wray 1991). Although history does not
potentially toxic metals (e.g., cadmium, chrom-
record its discovery, lime is mentioned in the
ium, lead and nickel) are amphoteric, a process
Bible and in documents from ancient China as
where metal hydroxides show increased solubil-
well as Egypt, dating back about 6000 years. Lime
ity at very low and high pH values. Weeter and
and its by-products used in the waste treatment
Jones (1987) concluded that a lime/fly ash addi-
industry are summarized in Table 1. Many lime
tive significantly reduced the chromium (Cr) con-
products and by-products behave differently.
centration of industrial sludge high in copper
Chemically these by-products are poorly defined,
(Cu), nickel (Ni), and Cr. The concentrations of
and their use in place of lime requires extensive
Cu and Ni were reduced by solidification. Fur-
analysis to determine the equivalent quantity of
thermore, they stated that a lime/fly ash admix-
lime. Most common forms of lime used in waste
ture is more cost effective than other agents such
treatment are quicklime or unslaked lime (CaO)
as portland cement, lime, or sodium silicate. On
and hydrated or slaked lime [Ca(OH)2]. In 1989,
more than 1.54 1010 kg (34 billion lb) of lime
the other hand, Malone et al. (1987) found that the
fly ash/lime additive produced a product which
were produced in the United States (Chemical and
lowered the overall hydraulic conductivity of the
Engineering News, 18 June 1990).
leachate but did not significantly lower the losses
Lime is often used in water treatment to pre-
Table 1. Characteristics of major lime, limestone products, and
by-products used in waste treatment (Malone and May 1991).
Formula
Bulk density
(kg m3)
Reagent
or composition
pH
High calcium quicklime
CaO
7691121
10.512.4
Dolomitic quicklime
CaOMgO
7901400
9.0
High calcium hydrate
Ca(OH)2
400641
10.512.4
Normal dolomitic hydrate
Ca(OH)2.Mg(OH)2
400560
9.0
Dolomitic pressure hydrate
Ca(OH)2.Mg(OH)2
480640
9.0
High calcium limestone
CaCO3
--
6.5
Dolomitic limestone
CaCO3.MgCO3
--
--*
Lime kiln dust
1015% lime
--
~ 12.4
Cement kiln dust
Lime varies
--
~ 12.4
Fly ash†
Lime varies
--
~ 12.4
Waste lime
Lime varies
--
~ 12.4
* Nonreactive.
† High calcium fly ash may have up to 2.4% uncombined CaO.
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