General Guidelines for S/S of Wastes - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 15

TABLE 2.1 (CONTINUED)
RCRA Wastes for Which S/S is Identified as Best Demonstrated Available
Technology (BDAT) 6

BDAT Treatment/
Treatment Train Code Waste Description Reference

U204 Selenious acid S/S 55 FR 22574

U205 Selenium disulfide S/S 55 FR 22574

U214 Thallium (1) acetate S/S or Thermal Recovery 55 FR 3891

U215 Thallium (1) carbonate S/S or Thermal Recovery 55 FR 3891

U216 Thallium (1) chloride S/S or Thermal Recovery 55 FR 3891

U217 Thallium (1) nitrate S/S or Thermal Recovery 55 FR 3891

P074 Nickel cyanide Electrolytic oxidation +

alkaline chlorination +
precipitation + S/S

55 FR 26600

P099 Argenate (1-), bis(cyano-C)-potassium Electrolytic oxidation +

alkaline chlorination +
precipitation + S/S

55 FR 26600

2.4 DESIGN OF S/S FORMULATIONS

Once S/S technology is selected, the design of a proper S/S formulation is critical
in successful treatment of wastes or remediation of contaminated sites. S/S of
contaminants by cements includes the following three aspects: (a) chemical fixation
of contaminants (chemical interaction between the hydration products of the cement
and the contaminants); (b) physical adsorption of the contaminants on the surface
of hydration products of the cements; and (c) physical encapsulation of contaminated
waste or soil (low permeability of the hardened pastes). 9,10 The first two aspects
depend on the nature of the hydration products, and the third aspect relies on both
the nature of the hydration products and the density and physical structure of the
pastes. Thus, from all aspects, the selection of cementing materials for S/S of wastes
may have to consider the following aspects based on the characteristics of the wastes:
(1) compatibility between cement and waste materials; (2) chemical fixation of
contaminants; (3) physical encapsulation of contaminated waste and soils; (4) leach-
ability of contaminants from the treated waste or soil; (5) durability of the treated
waste or contaminated materials; and (6) cost-effectiveness of S/S. These aspects
are discussed in the subsections that follow.

2.4.1 C OMPATIBILITY B ETWEEN C EMENT AND W ASTE M ATERIALS

Many substances can significantly affect the hydration of cement. 11,12 The intent of
using admixtures, such as retarders, accelerators, or superplasticizers, is to affect
one or more properties of cements and concrete in a manner that is beneficial for a
given application. The interferences between contaminants and binders are discussed
in Chapter 7. The same contaminant may have different interference effects on different