Kinetics and mechanism of ion exchange sorption of some detergents on zinc ferrocyanide

Abstract

Studies have been made on the kinetics and mechanism of exchange sorption of detergents on zinc ferrocyanide using a modified limited bath technique. The effects of concentration, particle size of the sorbent material, and temperature on the sorption rate have been investigated. In the case of cationic detergents (cetyl pyridinium bromide and cetyl trimethylammonium bromide), equilibrium is attained in a period of 2–3 h while 12–16 h are required for anionic detergents, viz., sodium dodecyl sulphate and sodium dodecyl benzene sulphonate. The slowest step governing the sorption rate is found to be the diffusion within the exchanger particles at higher concentrations. The effective diffusion coefficients have been evaluated at four different temperatures and found to be comprised of mainly two components. The energy barriers against the diffusion of exchanging ions have been assessed from the Arrhenius equation. Entropies of activation for various sorption systems have also been calculated. The results are discussed in terms of the size and geometry of the detergents, pore-widths in the sorbent material, and the electric potential gradient along the diffusion path. No change in the internal structure of zinc ferrocyanide is inferred due to the sorption of detergent ions.