Stabilization/Solidification Additives - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 191

TABLE 8.1
Properties of Some Processing and Anti-Inhibition Aids

Physical
Property
Development

Control
Free Water
Content

Control of
Setting

Water
Reducers

Control
Viscosity Additive Retarders

Lime X X X

Soluble Silicates X X

Alumina X X

Surfactants X

Clays X

Polymers X

Flyash X X X X

Kiln Dust X X X

Silica Fume X

Diatomaceous Earth X

Vermiculite X

Rice Hull Ash X X X

Mineral Sorbents X

8.6.1 C ONTROL A GENTS

Cement-based systems, especially, are sensitive to many waste components dis-
cussed previously in their setting and strength development. Additives such as lime
and sodium silicate are often used to counter the inhibition effects of certain metals
and allow proper set and hardening to be achieved. 68 Research with soluble silicates
indicates that these materials are beneficial in reducing the interference from metal
ions in the waste solution. 69 Cement/lime and mixtures of cement, lime, and ferrous
sulfate have been used to produce solid, low-leaching products with lead, chromium,
and other heavy metal-containing wastes. Another additive commonly used along
with cement and lime is aluminum sulfate or alumina, which reportedly counters
the retarding effect of organic constituents in the waste. 70 Calcium chloride can be
used to accelerate setting in portland cement systems and overcome retardation by
organic compounds. 71 Clay, diatomaceous earth, flyash, and activated carbon can
remove interfering ions and organics.

8.6.2 R ETARDERS

Some waste components cause premature setting and require the use of set retarders
commonly used in making concrete. Control of setting is especially important for
in situ S/S.

8.6.3 W ATER -R EDUCING A GENTS

Water-reducing agents are usually surfactants that are used to lower the viscosity.
Flyash also reduces viscosity, but results in significant volume increase.