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Current work is exploring the feasibility of using potassium manganate (K2MnO4) in drinking water treatment. The manganate species (MnO42-) can act as both an oxidant and a coagulant/adsorbent arising from the formation of insoluble manganese dioxide from the chemical reduction of Mn(VI) to Mn(IV). Extensive tests have been undertaken to investigate the treatability of humic acids by manganate, with and without the co-addition of ferrous sulphate. In these tests solutions of commercial humic acid (HA) have been reacted at varying concentrations of K2MnO4 and FeSO4 and pH. A high degree of HA removal has been demonstrated, particularly at low pH (pH 5), as expected from conventional theories of charge interaction and solid phase adsorption. In attempting to understand the mechanisms of HA reaction and separation by manganate, given the heterogeneous nature of HA, laboratory tests have been undertaken also with resorcinol as a model compound of HA. Since manganate disproportionates during its aqueous reaction to permanganate and MnO2, the comparative reactivity and separation of resorcinol by manganate (Mn(VI)) and permanganate (Mn(VII)) have been considered. During the chemical reduction of potassium manganate and potassium permanganate insoluble manganese dioxide (Mn(IV)) is produced which can adsorb un-reacted resorcinol and reaction products. The adsorption of resorcinol by MnO2 was studied by pre-forming MnO2 by the reaction of the Mn(VI) and Mn(VII) with sodium thiosulphate, prior to the addition of the resorcinol. The influences of adsorption time and MnO2 dose have been investigated. The combined effects of chemical oxidation by manganate or permanganate and MnO2 adsorption, on resorcinol have been studied in detail. In particular, the influence of the ratio of oxidants to resorcinol, oxidation time and adsorption time on resorcinol removal have been evaluated. The tests were undertaken at pH 5, which is a preferred treatment pH for low turbidity, high humic waters in practice, and also allowed comparison with the results from experiments involving HA. The changes in resorcinol concentration were measured in both absolute terms by HPLC, and indirectly as NPDOC. The results have shown that resorcinol can be removed to a moderate degree by MnO2 adsorption where the adsorbent was formed in solution from the two Mn oxidants immediately prior to interaction with resorcinol. The adsorption/contact time had only a minor effect on compound removal with a greater removal at a longer contact time. In reaction with both Mn oxidants, the ratio of oxidant to resorcinol had a significant effect on compound removal, with the removal increasing substantially at higher ratios of oxidant to resorcinol. During the chemical oxidation and MnO2 adsorption experiments with the two Mn oxidants, varying the respective periods of oxidation and adsorption had only a moderate effect on the compound removal efficiency; in the former case compound removal increased with the period length. Comparatively, the treatment performance of potassium manganate was superior to that of potassium permanganate.
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PROGRESS IN ENVIRONMENTAL SCIENCE AND TECHNOLOGY, VOL III: PROCEEDINGS OF THE 2011 INTERNATIONAL SYMPOSIUM ON ENVIRONMENTAL SCIENCE AND TECHNOLOGY
年份: 2011
页码: 602-612
语种: 英文