Efficient removal of manganese ions from waters using hypochlorite-modified granular activated carbon

Conventional drinking waterworks generally disregard the manganese removal efficiencies. For the first time, this study demonstrates the potential of ClO^--modified activated carbon for efficient Mn removal from raw water. The 10% NaClO-modified granular activated carbon increases the Mn²⁺ adsorption capacity from 4.28 mg/g to 28.1 mg/g at an initial Mn concentration of 50 mg/L at pH 7 and 25 °C. Conversely, applying strong acids, bases, oxidants, or microwave treatments adversely impacts the adsorption capacity of the modified activated carbon. The kinetic adsorption tests and equilibrium measurements reveal increased Mn²⁺ adsorption capacities with ClO^- concentration and initial Mn²⁺ concentration, peaking at 35 °C. The mechanistic studies show that the chemical complexation with the C=C bonds on the carbon's surface from ClO^--modification principally contributes to the enhanced Mn²⁺ adsorption. Jar tests demonstrate that 5% NaClO-modified activated carbon can completely remove 0.3 mg/L Mn²⁺ or over 98% of 1 mg/L Mn²⁺ in the presence of competing Fe²⁺ ions. The ClO-modified granular activated carbon has excellent potential for practical drinking water production since all materials used are certified by the National Sanitation Foundation (NSF).