Influence of potassium permanganate preoxidation on the interaction of humic acid with cadmium/arsenic

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.