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 Mn 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 Mn adsorption capacities with ClO concentration and initial Mn⁺ 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 Mn⁺ adsorption. Jar tests demonstrate that 5% NaClO-modified activated carbon can completely remove 0.3 mg/L Mn or over 98% of 1 mg/L Mn⁺ in the presence of competing Fe⁺ 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).