Continuous fixed-bed column studies of arsenite removal via oxidation and adsorption coprocesses

Arsenite (As(III)) was removed via oxidation and adsorption coprocesses in fixed-bed columns. A manganese oxide octahedral molecular sieve (K-OMS2) and iron(III) trimesate (Fe-BTC) were applied as oxidizer and adsorbent, respectively. Before use in the column, K-OMS2 and Fe-BTC powders were coated on ceramic balls, with K-OMS2 and Fe-BTC to ceramic ball ratios of 1 to 50. The As(III) and arsenate (As(V)) removal efficiencies for single fixed-bed columns of K-OMS2 and Fe-BTC, respectively, as well as for the two columns combined, were determined. From the single-column run results, K-OMS2 maintained notable efficiency in oxidizing As(III) to As(V) during a three-round-use cycle, with leached Mn and K concentrations below the groundwater standard. The average As(III) oxidation percentages in K-OMS2 column for 600 min in the 1st, 2nd, and 3rd rounds were 95, 92, and 93%, respectively. In the Fe-BTC single-column run, the Yoon-Nelson model was found to represent the adsorption kinetics model of the run, with a maximum As(V) adsorption capacity of 52.60 mg/g, and more than 75% of As(V) was removed for 600 min. Maximum Fe leaching from Fe-BTC column was 0.23 mg/L, which was lower than Fe concentration range found in natural freshwater. The adsorption behavior can be explained by the fact that the adsorption rate decreased depending on the As(V) breakthrough and Fe-BTC proportion. In the case of two columns combined, more than 62% of the total As was removed over 2200 min of operation time under optimal experimental conditions.