This study demonstrates a three-step process consisting of primary prefiltration followed by ultrafiltration (UF) and adsorption with thiol-functionalized microfiltration membranes (thiol membranes) to effectively remove mercury sulfide nanoparticles (HgS NPs) and dissolved mercury (Hg2+) from wastewater. Thiol membranes were synthesized by incorporating either cysteine (Cys) or cysteamine (CysM) precursors onto polyacrylic acid (PAA)-functionalized polyvinylidene fluoride membranes. Carbodiimide chemistry was used to cross-link thiol (−SH) groups on membranes for metal adsorption. The thiol membranes and intermediates of the synthesis were tested for permeability and long-term mercury removal using synthetic waters and industrial wastewater spiked with HgS NPs and a Hg2+ salt. Results show that treatment of the spiked wastewater with a UF membrane removed HgS NPs to below the method detection level (<2 ppb) for up to 12.5 h of operation. Flux reductions that occurred during the experiment were reversible by washing with water, suggesting negligible permanent fouling. Dissolved Hg2+ species were removed to non-detection levels by passing the UF-treated wastewater through a CysM thiol membrane. The adsorption efficiency in this long-term study (>20 h) was approximately 97%. Addition of Ca2+ cations reduced the adsorption efficiencies to 82% for the CysM membrane and to 40% for the Cys membrane. The inferior performance of Cys membranes may be explained by the presence of a carboxyl (−COOH) functional group in Cys, which may interfere in the adsorption process in the presence of multiple cations because of multication absorption. CysM membranes may therefore be more effective for treatment of wastewater than Cys membranes. Focused ion beam characterization of a CysM membrane cross section demonstrates that the adsorption of heavy metals is not limited to the membrane surface but takes place across the entire pore length. Experimental results for adsorptions of selected heavy metals on thiol membranes over a wide range of operating conditions could be predicted with modeling. These results show promising potential industrial applications of thiol-functionalized membranes.
|Number of pages||13|
|State||Published - Sep 8 2020|
Bibliographical noteFunding Information:
This work is supported by Chevron Energy Technology Co., Richmond, CA, and by the National Institute of Environmental Health Sciences (NIH-NIEHS-SRC) (grant P42ES007380) and by NSF-EPSCoR (Grant 1355438). We thank Dr. Gregory V. Lowry, Carnegie Mellon University, Pittsburgh, PA for providing the suspension of HgS nanoparticles. We thank Michael J. Detisch (graduate student) of the Department of Chemical and Materials Engineering, University of Kentucky (UK) for his support during XPS and EDS analysis. We also thank Dr. Nicolas Briot of Electron Microscopy Center (EMC), UK for his support to prepare samples for the FIB instrument as well as to analyze FIB samples. We also express our gratitude to Hongyi Wan (graduate student) of the Department of Chemical and Materials Engineering, UK for supporting us to explain FIB characterization data. We thank Md Ariful Hoque (graduate student) of Professor Marcelo Guzman’s research group, Department of Chemistry, UK to support us to conduct (ATR-FTIR) experiments. We also express our sincere gratitude to Namal Wanninayake and Nadeesha Lakmali Kothalwala (graduate students) of Professor Doo Young Kim’s research group, Department of Chemistry, UK for helping us to conduct (ATR-FTIR) experiments. Finally, we also acknowledge the support of Megan Combs of Environmental Research Training Laboratory (ERTL), UK for ICP-OES analytical assistance.
© 2020 American Chemical Society
ASJC Scopus subject areas
- Chemistry (all)
- Chemical Engineering (all)