Abstract
Background: Acid mine drainage (AMD) leads to contamination of surface and ground water by high levels of toxic metals including chromium. In many cases, these waters are sources of drinking water for communities, and treatment is therefore required before consumption to prevent negative health effects. Methods: Cationised hemp cellulose was prepared by etherification with two quaternary ammonium salts: 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTAC) and glycidyltrimethylammonium chloride (GTMAC) and examined for (i) the efficiency of Cr(VI) removal under acid mine-drainage (AMD) conditions, and (ii) antibacterial activity. Adsorbents were characterised by electron microscopy, Fourier transform infrared (FTIR), CP-MAS 13C nuclear magnetic resonance (NMR) spectroscopy, elemental composition and surface charge. Results: FTIR and solid state 13C NMR confirmed the introduction of quaternary ammonium moieties on cellulose. 13C NMR also showed that cationisation decreased the degree of crystallisation and lateral dimensions of cellulose fibrils. Nevertheless, 47 % - 72 % of Cr(VI) ions were removed from solutions at pH 4, by 0.1 g of CHPTAC and GTMAC-cationised cellulose, respectively. Adsorption kinetics followed the pseudo-second order model and isotherms were best described by the Freundlich and Dubinin-Radushkevich models. When GTMAC-modified cellulose was applied to AMD contaminated water (pH 2.7); however, Cr(VI) removal decreased to 22% likely due to competition from Al and Fe ions. Cationised materials displayed considerable antibacterial effects, reducing the viability of Escherichia coli by up to 45 % after just 3 hours of exposure. Conclusions: Together, these results suggest that cationised cellulose can be applied in the treatment of Cr(VI)-contaminated mine water particularly if pre-treatments to reduce Fe and Al concentrations are applied.
Highlights
Acid mine drainage represents a major source of water contamination in regions of previous mining activity (McCarthy, 2010; Naicker et al, 2003)
Materials All chemicals used were of analytical grade. 3-chloro-2-hydroxypropyl trimethylammonium chloride (CHPTAC; 60 wt% in H2O, Mw = 188.10), and glycidyltrimethylammonium chloride (GTMAC; > 90 wt % in H2O, Mw = 151.63), dipotassium chromate (K2CrO4), L-glutathione reduced (Mw = 307.32), 5,5′Dithiobis(2-nitrobenzoic acid) (Ellman’s reagent), Tris-HCl buffer, Na2HPO4.7H2O, NaH2PO4H2O, and NaCl were from Sigma Aldrich (South Africa)
Characterisation In this work cellulose fibres extracted from hemp plants were cationised using chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTAC) and GTMAC, and NaOH as a catalyst as shown in Scheme 1
Summary
Acid mine drainage represents a major source of water contamination in regions of previous mining activity (McCarthy, 2010; Naicker et al, 2003). Concentrations as high as 152 mg kg-1 of chromium have been reported in fly ash (Saha et al, 2011), which is thought to be responsible for the elevated chromium levels of soils around coal-fired power plants It exists as the relatively immobile Cr(III) under reducing conditions, oxidising conditions are characterized by highly mobile Cr(VI) which is classified as a carcinogen. Acid mine drainage (AMD) leads to contamination of surface and ground water by high levels of toxic metals including chromium. In many cases, these waters are sources of drinking water for communities, and treatment is required before consumption to prevent negative health effects. Cationised materials displayed considerable antibacterial effects, reducing the viability of Escherichia coli by up to Invited Reviewers version 1
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
