Oxidative removal of soluble divalent manganese ion by chlorine in the presence of superfine powdered activated carbon

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

“…Adsorptive Mn 2+ removal by SPAC alone is not significant ( Saito et al., 2020 ). Even after SPAC was pre-oxidized by free chlorine, Mn 2+ removal was not evident when free chlorine was absent at the time of the reaction (Fig.…”

“…In such a situation, in a membrane filtration pilot experiment, we discovered that Mn 2+ was removed to below the quantification limit by superfine powdered activated carbon (SPAC; particle size of less than a few micrometers) in the presence of free chlorine ( Saito et al., 2020 ). A little earlier, Li et al.…”

“…Moreover, traditional drinking-water treatment approaches would avoid any direct interaction between activated carbon and free chlorine because of the reductive tendencies of the carbon to the free chlorine. However, the use of small particles (SPAC) would compensate for the weak catalytic activity and provide sufficient Mn 2+ removal performance even with a short reaction time, and this approach has been demonstrated to be practicable as a drinking-water treatment method ( Saito et al., 2020 ).…”

“…The removal of Mn 2+ by activated carbon and free chlorine follows first-order reaction kinetics ( Eq. (1) ) ( Li et al., 2019a ; Saito et al., 2020 ). However, the theoretical basis for this apparent kinetics remains uncertain, and to date there is no analysis of the removal kinetics or mechanism.…”

“…The Markle model is superior to the Nakanishi model in that it is capable of describing the change in the Mn 2+ removal rate with fluid conditions. In this model, it is necessary to assume that either the mass transfer or the oxidation reaction is the rate-limiting step to derive the pseudo-first-order reaction rate characteristics that are observed with activated carbon as a catalyst ( Li et al., 2019a ; Saito et al., 2020 ). On the other hand, the rate coefficient of Mn 2+ removal by activated carbon is little affected by differences in free chlorine concentration, especially in the high concentration range ( Saito et al., 2020 ), but it is affected by the presence of co-existing substances (explained in Section 4.1 ) and the mixing intensity of the reactor (explained in Section 4.2 ).…”