General Guidelines for S/S of Wastes - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 16

types of cementing materials, or different interference effects on the same binder may
result from different concentrations of a given contaminant. Thus, matching a cement-
ing material with the waste or contaminant is important to avoid interference effects
that may compromise treatment. Because of differences in interaction, regulatory
agencies such as the USEPA have published regulations or guidance concerning the
degree of interaction between a contaminant and binder, because of the potential re-
release of the compound under various disposal conditions. 13 Physical forces such
as gravity or mechanical compression may cause release. Also, pH and redox changes
might affect future releases. The degree of interaction may be evaluated by physical
methods such as gravity (paint filter test) 14 and mechanical compression (liquids
release test). 15 Chemical extraction (solvents) or analytical techniques such as Fourier
transform infrared (FTIR) spectroscopy, energy-dispersive x-ray analysis (EDXA),
transmission electron microscopy (TEM), and x-ray diffraction (XRD) may be used
to assess the degree of interaction. 16-18

2.4.2 C HEMICAL F IXATION OF C ONTAMINANTS

Hardened cement and concrete are porous materials that allow free ions to transport
within and external to the binder matrix. In general, precipitation, absorption, or
adsorption fix or stabilize contaminants chemically, primarily by the following three
methods: (1) pH control of the system, (2) chemical reaction between contaminants
and hydration products of cement, and (3) use of special additives. A variety of
sorption processes have been evaluated for reducing the leachability of inorganic or
organic compounds in waste material. Applications and evaluations of commercial
processes based upon sorption are available in the literature. 19-21
S/S for inorganic contaminants has been well accepted by the regulatory com-
munity, but not for organic contaminants. Water-soluble organic compounds such
as phenol and ethylene glycol have been shown to chemically interact with cement,
but were not effectively immobilized. 16 Less-soluble organics such as naphthalene
were shown to be bound to quaternary ammonium compounds by stronger sorption
reactions. 22 In general, hydrophobic organic material is not compatible with inorganic
material such as cement. By substituting quaternary ammonium ions for group IA
and IIA metal ions in clays, however, the interplanar distance between aluminum
and silica can be increased, allowing clays to sorb organic compounds. For example,
quaternary ammonium ions (R 4 N + ) can be substituted for group IA and IIA metal
ions (such as Li + , Na + , K + , Mg 2t , Ca), yielding clays that have both organic and
inorganic interactive properties, enabling the clay to also sorb organic compounds. 22
An evaluation of the organophilic clays conducted with four polyaromatic com-
pounds, each with a concentration of less than 20 mg/kg, showed significant reduc-
tions in an organic extraction test and possible chemical reaction between the
organophilic clay and organic compounds. 18
Surfactants may be manufactured so as to have different chemical compatibilities
on each end of the molecule. In simple terms, this configuration allows organic waste
material to be sorbed on one end, while the other end is compatible with water
mixed with the inorganic cement. With the use of a surfactant to lower surface
tension, organic waste material can be dispersed with water in which the continuous