Stabilization/Solidification Additives - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 189

leachability, but not for reduction in trichloroethane (TCA). 61 Particulate rubber is
not as effective in TCLP reduction, but is the only additive that was broadly useful
for TCA reduction, especially for the low-volatility compounds. Organoclays are
effective with select contaminants.
For solidification of moderate levels of non-hazardous organic contaminants,
surfactants have been used to disperse an organic phase in an aqueous phase before
the emulsion is solidified. Organic reagents tend to retard pozzolanic reactions and
may be easily leached from the resulting solidified waste form. 62 Organic modified
clays can overcome these limitations. 63 The modified organophilic clays are prepared
by exchanging ammonium ions for metal ions in the clay. The modified clay has
both inorganic and organic properties. The ammonium ions increase the distance
between the layers of alumina and silica in the clay, and this allows organics to
penetrate. Studies indicate that chemical bonding may occur between the organo-
philic clay binder and certain organic wastes. 64
For solidification of higher levels of non-hazardous organic wastes, a mixture
of lime and flyash or other cementitious additives is commonly used. The lime makes
oils and tars miscible with solidification/stabilization reagents. Lime/flyash processes
are able to accommodate large quantities of organics as well as the more common
inorganic sludges. Therefore, they are useful in the solidification of oily wastes 65
and other water-insoluble organic materials at organic levels of 20% or more. In
fact, this is a major use for these processes. Combining lime and flyash with water
forms a cementitious material. The reaction product formed is initially a non-
crystalline gel, but eventually becomes calcium silicate hydrate, a compound found
in hydrated portland cements. In general, however, these reactions are slower than
those of cement and do not produce exactly the same products in terms of chemical
and physical properties. Flyash used in lime/flyash processes is a by-product of coal-
burning power plants, and its composition, and thus its reactive property, is dependent
on not only the composition of the coal burned, but also how the plant is operated.

8.5 ADDITIVES AND TREATMENT METHODS FOR

ORGANOMETALLIC AND COMPLEXED
COMPOUNDS

Additive and treatment methods for metal/organic compounds are dependent on the
type of compound present. Simple complexes such as cyanides can often be treated
by alkaline chlorination. However, many industrial waste streams contain soluble
metal complexes that are very difficult to treat because of their stability.
Simple complexes such as metallo-cyanides, e.g., Cd(CN) 4 -2 , can be treated
using alkaline chlorination (e.g., sodium or calcium hypochlorite). Nickel cyanide
complexes can be broken with alkaline chlorination, leaving a nickel species that
can be stabilized to low leaching levels. In cases where a stable, soluble silver
complex is present in large amounts, several techniques are available. Magnesium
sulfate and lime can be used to precipitate a mixed sulfate-oxide. Alkaline chlori-
nation can be used to break the complex and precipitate silver chloride. Sulfides and
hydrosulfites are also used to treat silver complexes.