Simultaneous Removal of Molybdenum, Antimony and Selenium Oxyanions from Wastewater by Adsorption on Supported Magnetite

Abstract

Mo, Sb and Se form oxyanions in solution, and are therefore difficult to remove by traditional wastewater treatment methods (e.g. alkaline precipitation). In this paper, a method for the simultaneous removal of these three elements from wastewater by adsorption, zeolite-supported magnetite is developed. The adsorbent consists of finely divided magnetite particles on a zeolite substrate as carrier material. Basic adsorption parameters such as ideal pH, maximum adsorption capacity and equilibration time, are determined for the oxyanions separately. Much attention is paid to the study of interferences that can limit adsorption. Anions like sulphate and chloride, which often occur in large amounts in wastewaters, do not really compete for adsorption places on magnetite, but oxyanions largely interfere with each other. The reason for this competition is a similar adsorption mechanism (inner-sphere complex formation) for all studied oxyanions, except for selenate, that forms outer-sphere complexes, as was confirmed by geochemical modeling. The adsorption of Mo, Sb and Se oxyanions from an aqueous solution containing the most important detected interferences and from a real wastewater containing also cations is compared, showing that the most important interferences are identified. The order of adsorption is Mo(VI) > Sb(V) > Se(VI). As a case study, Mo, Sb and Se oxyanions are removed by adsorption from an industrial wastewater, the flue gas cleaning effluent of a waste incinerator. For an adsorbent concentration of 20 g/l, removal efficiencies of 99, 97 and 77 % are obtained for Mo, Sb and Se.