Synthesis of a novel Fe-Mn binary oxide-modified lava adsorbent and its effect on ammonium removal from aqueous solutions.

Abstract

Ammonium is strongly related to eutrophication and a key control of eutrophication in aquatic systems, especially in agricultural runoff. In this study, a novel Fe-Mn binary oxide-modified lava (FMML) granular adsorbent was synthesized for ammonium removal from aqueous solutions by co-precipitation method. The kinetic data were described by pseudo-second-order kinetic model well and intraparticle diffusion had effects on ammonium adsorption. For pH between 4.0 and 10.0, the adsorption efficiency was >80%, and its optimum was recorded at pH 7.0. FMML exhibited strong ammonium adsorption selectivity under the single presence of cations like Na+ , K+ , Ca2+ , and Mg2+ . The optimum adsorbent dose and particle size were 4g/L and 3-5mm, respectively, for an aqueous solution containing 10mg/L of ammonium under normal conditions (298K and pH 7.0). Furthermore, the adsorption process was endothermic, following both the Langmuir (R2 >0.98) and Freundlich (R2 >0.96) models. Compared with other adsorbents, the FMML can be prepared following a simpler protocol. After 30 times of adsorption-regeneration cycle, the FMML also had a relatively high ammonium adsorption capacity; hence, we see it as a prospective adsorbent for ammonium adsorption from aqueous solutions. PRACTITIONER POINTS: Fe-Mn binary oxide-modified lava with Fe/Mn ratio 3:1 was prepared using co-precipitation method. Adsorption maximum of modified lava was 20.8mg/g (298K and pH 7.0). Adsorption was sensitive to changes in adsorbent dose, particle size, and pH. Inorganic cations decreased ammonium adsorption in order of Na+ >K+ >Ca2+ >Mg2+ . Mechanisms for ammonium removal by FMML include diffusion, electrostatic attraction, oxidation, and complexation reaction.