Characteristics and model studies for fluoride and arsenic adsorption on goethite.

Fluoride and arsenic are major anionic elements of concern in drinking water treatment. The effects of contact time, pH, surface loading and ionic strength on adsorption of fluoride and As(V) were investigated using batch methods. Adsorption of fluoride and As(V) onto goethite obeyed a pseudo second-order rate law. Through experimental data and adsorption kinetic analysis, the affinity of As(V) onto goethite was stronger than fluoride. Fluoride and As(V) uptake by goethite all decreased with pH increasing at the same surface loading; however, ionic strength had slight influence on their adsorption. A surface sites-species model was used to quantify the adsorption of fluoride and As(V) onto goethite as function of pH and surface loading. This model can satisfactorily predict their adsorption characteristics with several adsorption constants.