Adsorption of some Weak Organic Electrolytes from Aqueous Solutions on Silica

The adsorption of organic electrolytes from aqueous solutions on various adsorbents has been frequently investigated because of its importance in water purification. Phenol and substituted phenols are very common contaminants of water. In this paper, the adsorption results of some weak organic electrolytes (hydrochinon, phloroglucin and acidum gallicum) from aqueous solutions on silica are presented. The adsorption of the organics was investigated by the batch method. Effects of solution pHs (in the 2-10 range) and concentrations of these compounds on the adsorption were investigated. In the case of acidum gallicum, adsorption isotherms (in the 2-6 pH range) were determined. The obtained results indicate that the amount of adsorbed acidum gallicum increases with its increasing concentration. The maximum adsorption was recorded at pH=2-3 (pH equal to pHpzc of SiO2) with acidum gallicum molecule being undissociated (pKa= 4.41). The experimental data were fitted with different adsorption isotherms models. The maximum amount of acidum gallicum adsorbed as well as the Freundlich constants of adsorption were calculated. The adsorption of hydrochinon and phloroglucin from aqueous solutions (in the investigated pH range) on silica was negligible.