Adsorption Tests of Humic Substances on Raw Clay from Bikougou (Gabon)

Abstract

The presence of organic material of natural origin is characteristic of surface waters. Humic substances (HS) are generally the largest category in these waters. The objective of this work was to evaluate the adsorption performance of raw clay from Bikougou (Gabon) for the removal of humic substances.

During the experimental study, the batch equilibration technique was used to follow the kinetics of adsorption of humic substances on clay. The influence of reaction parameters such as the initial concentration, the pH of the solution and the presence of inorganic salts (calcium or magnesium ions) was also observed. Optimum removal is obtained for low values of initial concentrations. pH variation showed that acidic medium (pH 4) can achieve good yields retention of humic substances. The presence or absence of mineral salts in the medium appears as one of the most critical parameters. Indeed, the impact of water mineralization has resulted in a significant improvement in removal efficiency of humic substances, taking as reference the results obtained in demineralized water. The promoting effect of cations such as calcium and magnesium may be the cause of this improvement. This let suggest a mechanism based on adsorption bridging clay-cation-SH. The kinetic study also showed that the adsorption equilibrium is reached after more than ten hours of reaction, whatever the dilution medium humic substances.

Keywords: Clay, adsorption, humic substances