Abstract
Coal fly ash-derived zeolites have attracted considerable interest in the last decade due to their use in several environmental applications such as the removal of dyes and heavy metals from aqueous solutions. In this work, coal fly ash-derived zeolites and silver nanoparticles-impregnated zeolites (nanocomposites) were synthesized and characterized by TEM/EDX, SEM/EDX, XRD, XRF, porosimetry (BET), particle size analysis (PSA) and zeta potential measurements. The synthesized materials were used for the removal of Hg2+ from aqueous solutions. The results demonstrated that nanocomposites can remove 99% of Hg2+, up to 10% and 90% higher than the removal achieved by the zeolite and the parent fly ash, respectively. Leaching studies further demonstrated the superiority of the nanocomposite over the parent materials. The Hg2+ removal mechanism is complex, involving adsorption, surface precipitation and amalgamation.
| Original language | English |
|---|---|
| Pages (from-to) | 164-171 |
| Number of pages | 8 |
| Journal | Journal of Environmental Management |
| Volume | 224 |
| Early online date | 21 Jul 2018 |
| DOIs | |
| Publication status | Published - 15 Oct 2018 |
Funding
The novel fly ash-derived nanocomposite with Ag NPs in the range of 5 and 40 nm (Ag-ZFA), its parent synthetic zeolite (K-ZFA) and the raw fly ash (K-CFA) were successfully applied for Hg 2+ removal from water. The adsorption kinetics of Hg 2+ on K-ZFA, Ag-ZFA and respective reduced material R-ZFA has shown that the nanocomposite demonstrate a strong (<99%) and fast adsorption (<24 h) compared with parent K-ZFA and K-CFA. The characterization by use of XRD, TEM/EDX and mapping of the post-adsorption materials has shown that the dominating mechanisms of mercury uptake in zeolites is physical adsorption, whereas in nanocomposites a combination of adsorption, redox reaction producing Hg° and finally amalgamation take place. The hypothesis of amalgamation reaction explains the superiority of the nanocomposite and is supported by the leaching experiments as well. This preliminary study demonstrated the ability of the fly ash derived nanocomposite to remove Hg 2+ from water at relatively low loading of Ag NPs. The removal is much faster and leachability much less than this of the parent zeolite justifying the use of silver in the nanocomposite. Nevertheless, further experiments are needed in order to better understand the mechanism of Hg 2+ uptake and evaluate the costs and benefits of using Ag NPs in CFA-derived nanocomposite materials. The authors would like to acknowledge the Ministry of Education and Science of Kazakhstan and Nazarbayev University Research Council for funding the project entitled “ Hyperstoichiometry Activity in Metal Nanoparticle Interaction ” (HyperActiv, SOE 2015 009 ), and the Royal Academy of Engineering (UK) for their financial and research support of the project IAPP/1516/13 . We thank Oskemen city power plant for generously providing coal fly ash samples to carry out this research work.
Keywords
- coal fly ash
- mercury removal
- nanocomposites
- silver nanoparticles
- synthetic zeolite
- water treatment