Kinetics of fluoride adsorption onto native and Mg(OH)2-amended limestone

Abstract

The adsorption kinetics of fluoride onto limestone (LS) and Mg(OH)2-amended LS were investigated using batch adsorption technique. Data were best fitted to second-order and Elovich models. The Mg(OH)2-ameded LS showed substantial increases in F− adsorption relative to native LS. Similarity of ionic radii and charge of both F− and OH− were hypothesized to be the major cause of such increases. The OH− functional group of the surface Mg(OH)2 could be exchanged by aqueous F− through surface complexation (ligand exchange). No background effect of naturally occurring anions in F−-rich groundwater on adsorption capacity of Mg(OH)2-amended LS. The results reveal that the Mg(OH)2-amended LS can be environmentally safe and economical for F− removal.