In this study, the use of a common clay mineral, montmorillonite and its
modified derivatives for adsorptive removal of toxic heavy metals from aqueous system
has been reviewed. The modification of clay was primarily done by pillaring with
various polyoxy cations of Zr4+, Al3+, Si4+, Ti4+, Fe4+, Cr3+ or Ga3+, etc. Some quaternary
ammonium cations, viz, tetramethylammonium-, tetramethylphosphonium-, trimethylphenylammonium-,
etc. are also used for pillaring purposes. Moreover the acidactivation
of montmorillonite is also reported. The adsorption of toxic metals, namely,
Cd, Cr, Co, Cu, Fe, Pb, Ni, Zn, etc. have been studied predominantly. Various
experimental parameters, like, pH of metal solution, amount of montmorillonite, initial
metal ion concentration, interaction time, temperature, etc. are considered for adsorption
process. Application of models as given by the Freundlich, Langmuir etc. has been
shown by many authors and these have also been reviewed. The review aims to give a
comprehensive picture on the studies of isotherm of adsorption for metal removal on
montmorillonites during the last few years.
Keywords: Clay mineral, Colloid, Isomorphic substitution, Montmorillonite,
Acid-activation, Intercalation, Pillaring, Cation exchange capacity, Surface area,
Swelling, Surface acidity, Metal ion, Adsorption, Adsorption capacity, Isotherm
model, Freundlich adsorption capacity, Langmuir adsorption capacity, Ion
exchange, Kinetics, Mean free energy.
