Mercury reduction and chemisorption on the surface of synthetic zeolite silver nanocomposites : equilibrium studies and mechanisms

Tauanov, Z. and Lee, J. and Inglezakis, V. J. (2020) Mercury reduction and chemisorption on the surface of synthetic zeolite silver nanocomposites : equilibrium studies and mechanisms. Journal of Molecular Liquids, 305. 112825. ISSN 0167-7322

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    Abstract

    This work presents the utilization of a coal power plants waste, namely coal fly ash for the synthesis of zeolites and zeolite silver nanocomposites for the removal of Hg2+ from water. Equilibrium data are derived for all materials for mercury concentration range of 10–500 mg/L and models are applied. The removal mechanisms are discussed in detail and complemented by XRD, XRF, SEM-EDS, and TEM characterizations and water phase mercury speciation modeling. According to findings, the adsorption capacity of zeolites is about 4 mg/g and increased by almost 5 times after the modification with silver nanoparticles to 20.5–22.3 mg/g. Langmuir equilibrium model fits well the experimental data of the nanocomposites indicating monolayer adsorption process. The mechanism is complex, involving Hg2+ reduction to Hg+ and possibly Hg0 followed by formation of calomel and amalgams on the surface of the nanocomposites. The mercury reduction is accompanied by Ag0 oxidation to Ag+ and subsequent formation of silver chloride.