Influence of potassium permanganate pre-oxidation on the interaction of humic acid with cadmium/arsenic

Abstract

Permanganate pre-oxidation could enhance coagulation in water treatment of surface water in the presence of humic acid (HA). The pre-oxidation process affects the characteristics of HA and the species of Cd/As, thereby influencing the diverse associations of HA with trace elements. In the present study, KMnO₄ pre-oxidation was found to enhance the coagulation of arsenic in HA aqueous solution by iron chloride, but the opposite result was observed for cadmium removal. This finding may be attributed to the fact that KMnO₄ could oxidise the organics, thereby allowing them to be easily adsorbed by the hydrolysis products of the coagulant. KMnO₄ may also have influenced the removal of arsenic and cadmium in the process of coagulation. Another reason may be that the manganese dioxide (MnO₂) formed in situ could adsorb arsenic and cadmium successively. KMnO₄ pre-oxidation was employed in this paper and the changes between the unoxidised and potassium permanganate pre-oxidised systems were investigated. These changes included the interactions of HA with Cd/As ions, the zeta potential value and the spectral analysis, such as specific binding sites on HA and quantifying binding parameters.