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Sarkar B.,University of South Australia | Naidu R.,University of South Australia | Naidu R.,Crc Care Coop Research Center For Contamination Assessment And Remediation Of The Environment | Krishnamurti G.S.R.,University of South Australia | Megharaj M.,University of South Australia
Environmental Science and Technology | Year: 2013

Unlike lower valent iron (Fe), the potential role of lower valent manganese (Mn) in the reduction of hexavalent chromium (Cr(VI)) in soil is poorly documented. In this study, we report that citrate along with Mn(II) and clay minerals (montmorillonite and kaolinite) reduce Cr(VI) both in aqueous phase and in the presence of dissolved organic carbon (SDOC) extracted from a forest soil. The reduction was favorable at acidic pH (up to pH 5) and followed the pseudo-first-order kinetic model. The citrate (10 mM) + Mn(II) (182.02 μM) + clay minerals (3% w/v) system in SDOC accounted for complete reduction of Cr(VI) (192.32 μM) in about 72 h at pH 4.9. In this system, citrate was the reductant, Mn(II) was a catalyst, and the clay minerals acted as an accelerator for both the reductant and catalyst. The clay minerals also serve as a sink for Cr(III). This study reveals the underlying mechanism of the Mn(II)-induced reduction of Cr(VI) by organic ligand in the presence of clay minerals under certain environmental conditions. © 2013 American Chemical Society. Source

Rusmin R.,University of South Australia | Rusmin R.,University Technology of MARA | Sarkar B.,University of South Australia | Sarkar B.,Crc Care Coop Research Center For Contamination Assessment And Remediation Of The Environment | And 6 more authors.
Applied Surface Science | Year: 2015

This paper investigates the structural evolution of chitosan-palygorskite (CP) composites in relation to variable mass ratios of their individual components. The composite beads' performance in lead (Pb) adsorption from aqueous solution was also examined. The composite beads were prepared through direct dispersion of chitosan and palygorskite at 1:1, 1:2 and 2:1 mass ratios (CP1, CP2 and C2P, respectively). Analyses by Fourier transform Infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the dependence of the composites' structural characteristics on their composition mass ratio. The chitosan-palygorskite composite beads exhibited a better Pb adsorption performance than the pristine materials (201.5, 154.5, 147.1, 27.7 and 9.3 mg g-1 for CP1, C2P, CP2, chitosan and palygorskite, respectively). Adsorption of Pb by CP1 and CP2 followed Freundlich isothermal model, while C2P fitted to Langmuir model. Kinetic studies showed that adsorption by all the composites fitted to the pseudo-second order model with pore diffusion also acting as a major rate governing step. The surface properties and specific interaction between chitosan and palygorskite in the composites were the most critical factors that influenced their capabilities in removing toxic metals from water. © 2015 Elsevier B.V. All rights reserved. Source

Das P.,University of South Australia | Das P.,Crc Care Coop Research Center For Contamination Assessment And Remediation Of The Environment | Arias E. V.A.,University of South Australia | Arias E. V.A.,Crc Care Coop Research Center For Contamination Assessment And Remediation Of The Environment | And 6 more authors.
Water, Air, and Soil Pollution | Year: 2013

Perfluorooctane sulfonate (PFOS), which has numerous uses besides being an ingredient in the formulation of aqueous film-forming foams, is considered as an emerging pollutant of increasing public health and environmental concern due to recent reports of its worldwide distribution, environmental persistence and bioaccumulation potential. In an attempt to recommend a 'risk-based' remediation strategy, this study investigates the removal of PFOS from impacted waters and fixation of PFOS in impacted soils using a novel modified clay adsorbent (MatCARE™, patent number 2009905953). Batch adsorption tests demonstrated a much faster adsorption kinetics (only 60 min to reach equilibrium) and remarkably higher PFOS adsorption capacity (0.09 mmol g-1) of the MatCARE™ compared to a commercial activated carbon (0.07 mmol g -1). Treatability studies, performed by treating the PFOS-contaminated soils with the MatCARE™ (10 % w/w) and then incubating at 25 and 37 C temperatures maintaining 60 % of the maximum water holding capacity of the soils for a period of a year, demonstrated a negligible release (water extractable) of the contaminant (only 0.5 to 0.6 %). The fixation of PFOS in soils by the new adsorbent was exothermic in nature. Soils with higher clay and organic matter content, but lower pH values, retained PFOS to a much greater extent. A cost analyses confirmed that the MatCARETM could be an economically viable option for the 'risk-based' remediation of PFOS in contaminated waters and soils. © 2013 Springer Science+Business Media Dordrecht. Source

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