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

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). 13 C 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. Electronic supplementary material The online version of this article (10.1007/s11356-018-3902-1) contains supplementary material, which is available to authorized users.

An Assessment of the Phytoremediation Potential of Planted and Spontaneously Colonized Woody Plant Species on Chronosequence Fly Ash Disposal Sites in Serbia—Case Study

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Transformation and Mobility of Cu, Zn, and Cr in Sewage Sludge during Anaerobic Digestion with Pre- or Interstage Hydrothermal Treatment

“…To better represent Cr speciation in the bulk sample, we averaged the LCF results of μ-XANES from multiple hot spots (Figure ). A large library of reference compounds based on previous studies − was employed for the LCF analysis, including a Cr­(III)-humic complex, Cr­(III) (oxy)­hydroxides, mixed Cr­(III)-Fe­(III) (oxy)­hydroxides, Cr­(III)-bearing silicate minerals, CaCrO 4 , K 2 CrO 4 , etc. (Table S1 and Figure S1).…”

Surface Coverage Simulation and 3D Plotting of Main Process Parameters for Molybdenum and Vanadium Adsorption onto Ferrihydrite

“…For this, wastewater treatments protocols, including adsorption based ones, are designed. Furthermore, for adsorption-based technologies, the depollution efficiency is a function of the amount of the adsorbent dosed in the wastewater treatment reactor/plant [ 61 ]. Thus, from a process engineer`s point of view, the maximum uptake capacity of any adsorbent used for specific pollutants is important and should be known, as well as its optimal working conditions.…”