An Introduction to Environmental Chemistry

The Chemistry of Continental Solids 127

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Pillared clay

Surfactant-modified clay

Toxicant

adsorption

Immobilized toxicant

Alumina-pillared clay

CO 2 + H 2 O + HX

Surfactant

Combustion

Fig. 2Scheme for recycling surfactant-modified pillared clay mineral adsorbents during thermal treatment
of toxicant. From Michot and Pinnavaia (1991), with kind permission from the Clay Minerals Society.

polar carboxylate group, for example sodium
octadecanoate (sodium stearate).

The polar carboxylate head dissolves in water,
while the long, non-polar hydrocarbon-chain
tail is hydrophobic (Box 4.14) but mixes well
with greasy (lipophilic, Box 4.14) substances,
effectively floating the grease into solution in
a sheath of COO-groups.

CH CH COO Na

non polar hydrocarbon tail carboxylate head

32 ( ) 16
( )( )

— -+

Surfactant-coated interlayer sites in

smectite have similar properties to

detergents. A hydrophobic molecule or

compound such as dioxin or other

chlorinated phenol is attracted to the

hydrophobic hydrocarbon tail projecting from

the interlayer surface and immobilized.

The modified smectite thus has good

affinity and selectivity for its target

contaminant and is thermally stable,

recyclable and economic to use (Fig. 2).