Spectroscopic characterization of the reduction and removal of chromium (VI) by tropical peat and humin |
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| Authors: | S da CA Cerqueira LPC Romão SCO Lucas LE Fraga ML Simões P Hammer JR Lead AP Mangoni AS Mangrich |
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| Affiliation: | 1. Department of Chemistry, Federal University of Sergipe (UFS), 49100-000 São Cristovão, SE, Brazil;2. Department of Analytical Chemistry, Institute of Chemistry, São Paulo State University (UNESP), 14800-900 Araraquara, SP, Brazil;3. Embrapa Instrumentação Agropecuária, 13560-970 São Carlos, SP, Brazil;4. Department of Physical Chemistry, Institute of Chemistry, São Paulo State University (UNESP), 14800-900 Araraquara, SP, Brazil;5. Division of Environmental Health and Risk Management, School of Geography, Earth and Environmental Sciences, University of Birmingham, B15 2TT Birmingham, United Kingdom;6. Department of Chemistry, Federal University of Parana (UFPR), 80060-000 Curitiba, PR, Brazil;7. National Institute of Science and Technology: Energy and Environment, 40170-290 Salvador, BA, Brazil |
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| Abstract: | The reduction of Cr(VI) to Cr(III) in aqueous solution, and the subsequent removal of Cr(III) using in natura peat or its humin fraction, was characterized by electron paramagnetic resonance (EPR), ultraviolet–visible (UV–Vis) spectroscopy and X-ray photoelectron (XPS) spectroscopy. EPR spectroscopy g-factors ranging from 2.0029 to 2.0030 indicated the presence of organic free radicals (OFR) associated with carbon atoms. The spin densities of the samples increased with pH in the range pH 2.0–pH 6.0. An XPS spectroscopy peak at 579.0 eV was attributed to Cr(VI), and peaks at 576.8 eV and 677.3 eV to two different chemical forms of Cr(III). Removal of chromium increased with the reduction of Cr(VI) to Cr(III), and removal rates after 50 h were 13% (peat) and 15% (humin) at pH 6.0, and 70% (peat) and 80% (humin) at pH 2.0. The greater efficiency of the humin fraction in the reduction/removal process is discussed in terms of the chemical structures of these materials. |
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