The pretreatment of granular activated carbon using sodium persulfate and hydrogen peroxide under basic conditions: Properties, metal impregnation, and As(V) adsorption

Abstract

The effect of sodium persulfate (PS) and hydrogen peroxide (HP) pretreatment on granular activated carbon (GAC) was investigated with regard to surface properties, metal impregnation, and application to As(V) adsorption. PS pretreatment at pH 12 and 50 °C destroyed the GAC pore structures but increased the number of oxygen-containing functional groups (OFGs), especially carboxyl. HP pretreatment at pH 12 only slightly increased the amount of carboxyl groups on the surface. Both pretreatments increased the point of zero charge from 8.5 to 10.3. The involvement of hydroperoxide anion in changing the proportions of OFGs is discussed. There is a correlation between OFGs, especially carboxyl groups, and the impregnation and dissolution of metals, especially Fe. PS pretreatment significantly enhanced metal impregnation on GAC surface and reduced Fe dissolution into the solution. The increasing surface area by the single metal impregnation on PS pre-treated GAC (GACP) is observed. Preliminary tests on various modified GACs indicate that As(V) adsorption is effective with GACs impregnated with both Fe and Mn, particularly those with Fe as an outside layer. PS-pretreated GAC impregnated with Mn followed by Fe (GACPMF) demonstrated the greatest As(V) adsorption and the least metal dissolution. Our results suggest that the impregnated Mn is completely coated by Fe in GACPMF. The Langmuir and pseudo-second order kinetic models are good fits for modeling As(V) adsorption on GACPMF. The adsorption capacity (b) of GACPMF is 9.52 mg g−1. Therefore, the advantages of GACPMF include a large adsorption capacity with good hydraulic properties.