Batch experiments to investigate the effect of colloidal silica on benzene adsorption

Abstract

Benzene is one of the most harmful compounds in groundwater. In the groundwater environment, adsorption plays a major role in benzene attenuation. In this study, laboratory experiments were conducted using jars to systematically investigate the effect of benzene adsorption under static conditions. Experiments were conducted using colloidal silica, which is representative of colloids in groundwater. In the single benzene system, more benzene was adsorbed at high than low pH because of the reduction in available H+ to compete with benzene for adsorption with increased pH. In addition, more benzene was adsorbed at high than low ionic strengths (ISs), because the presence of metal cations neutralized more negative charges and weakened the electrostatic interaction between benzene and the media. In the benzene-colloidal silica system, the presence of colloidal silica accelerated benzene adsorption, because colloidal silica can attach to the surface of the porous media and act as additional sites for adsorption while also enhancing the adsorption capacity of the C–H bonds. As the pH increased, the particle size of the colloidal silica also increased, which increased the colloidal silica adsorption capacity of benzene. As ISs increased, the colloidal silica became more unstable, and colloidal silica could easily attach to the surface of the porous media, enabling more benzene to be adsorbed. However, in the presence of colloidal silica, the effects of pH and ISs on benzene adsorption are not obvious and colloidal silica plays a leading role in benzene adsorption. Colloidal silica promotes benzene adsorption, primarily because it provides sites for adsorption and has a higher affinity for benzene than the surfaces of the porous media. This allows the porous media to rapidly adsorb benzene until reaching the saturation point, which has a much stronger effect on benzene adsorption than hydro-chemical conditions.