SORPTION AND DESORPTION ISOTHERMS FOR SILICATE ON GIBBSITE

Sorption and desorption of silicate on gibbsite were investigated. The sorption isotherm was complex, and consisted of Langmuir behavior at low silicate concentrations and Freundlich behavior at high silicate concentrations. The transition region was characterized by interaction between adsorbed silicate ions and multilayer adsorption or cluster formation; this corresponds to the onset of formation of a sodium aluminum silicate phase. The equilibrium sorption isotherm data reported here corroborate the scheme proposed to explain the sorption kinetics results reported elsewhere. The desorption data conformed to a Freundlich isotherm. In addition, desorption of silicate decreased with increasing silicate concentration in the solution, and reached a constant value at a solution concentration of 80 μgSiO2/cm3 and beyond. Desorption was larger at lower temperatures. © 1991 Academic Press, Inc. All rights reserved.