Equilibrium and kinetic studies of adsorption of silica onto activated alumina

Among the treatment processes appropriate for the removal of silica, it seems that activated alumina presents more advantages than membrane separation and chemical processes. Silica removal from aqueous solution was investigated using activated alumina. The nature of silica in a solution has a significant influence on its removal. Optimization of pH for adsorption of silica was done by studying the uptake of silica over activated alumina as a function of pH. Studies were conducted to delineate the effect of adsorbent dose and temperature. The adsorption equilibrium data followed both Langmuir and Freundlich isotherms. The effect of foreign ions on adsorption such as sulfate, fluoride, nitrate and hydrogenocarbonate did not significantly decrease the amount of silica removed. Silica concentrations were obtained by absorbance measurement of the of yellow or blue-colored silicomolybdic acid. Anion species concentrations were determined by ionic chromatography.