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Abiotic reduction of Cr(VI) by humic acids derived from peat and lignite: kinetics and removal mechanism

DOI: 10.1007/s11356-018-3902-1 DOI Help

Authors: Suha T. Aldmour (University of Leeds) , Ian T. Burke (University of Leeds) , Andrew W. Bray (University of Leeds) , Daniel L. Baker (University of Leeds,) , Andrew B. Ross (University of Leeds) , Fiona L. Gill (University of Leeds) , Giannantonio Cibin (Diamond Light Source) , Michael E. Ries (University of Leeds) , Douglas I. Stewart (University of Leeds)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Environmental Science And Pollution Research , VOL 29

State: Published (Approved)
Published: December 2018
Diamond Proposal Number(s): 12696 , 15711

Open Access Open Access

Abstract: Hexavalent chromium contamination of groundwater is a worldwide problem caused by anthropogenic and natural processes. We report the rate of Cr(VI) removal by two humic acids (extracted from Miocene age lignite and younger peat soil) in aqueous suspensions across a pH range likely to be encountered in terrestrial environments. Cr(VI) was reduced to Cr(III) in a first-order reaction with respect Cr(VI) concentration, but exhibited a partial order (~ 0.5) with respect to [H+]. This reaction was more rapid with the peat humic acid, where Cr(VI) reduction was observed at all pH values investigated (3.7 ≤ pH ≤ 10.5). 13C NMR and pyrolysis GC-MS spectroscopy indicate that the reaction results in loss of substituted phenolic moieties and hydroxyl groups from the humic acids. X-ray absorption spectroscopy indicated that at all pH values the resulting Cr(III) was associated with the partially degraded humic acid in an inner-sphere adsorption complex. The reaction mechanism is likely to be controlled by ester formation between Cr(VI) and phenolic/hydroxyl moieties, as this initial step is rapid in acidic systems but far less favourable in alkaline conditions. Our findings highlight the potential of humic acid to reduce and remove Cr(VI) from solution in a range of environmental conditions.

Journal Keywords: Humic substances; Humic acids; Chromium; Contaminated land; Groundwater

Subject Areas: Environment, Chemistry

Instruments: B18-Core EXAFS , I18-Microfocus Spectroscopy