Removal of soluble divalent manganese by superfine powdered activated carbon and free chlorine: Development and application of a simple kinetic model of mass transfer-catalytic surface oxidation

Catalytic oxidative removal of Mn2+ on activated-carbon surfaces by free chlorine was recently discovered and found to be potentially practicable for water treatment when using micrometer-sized activated carbon. Herein, we newly derived a kinetic model for trace-substance removal by catalytic reaction and applied it to the Mn2+ removal. External-film mass transfer, adsorption, and oxidation/desorption contributed similarly to the Mn2+ removal rate under actual practical conditions. The low removal rate in natural water was attributed to decreases in available adsorption sites: e.g., a 50% decrease in available sites in water with 0.26 mmol-Ca2+/L caused a 15% reduction in removal rate. Low temperature greatly reduced the removal rate by both enhancing the decrease in available sites and hindering mass transfer through increased viscosity. While adsorption sites differed 8-fold between different carbon particles, causing a 2.2-fold difference in removal rates, carbon particle size was more influential, with a > 10-fold difference between 2-and 30-mu m sizes.

Automated summary

Catalytic oxidative removal of Mn2+ on activated-carbon surfaces by free chlorine has been found to be potentially effective for water treatment using micrometer-sized activated carbon. In this study, a new kinetic model was developed to describe the removal of trace substances through catalytic reactions, and it was applied to the Mn2+ removal. External-film mass transfer, adsorption, and oxidation/desorption were found to contribute similarly to the Mn2+ removal rate under practical conditions.