Determination and evaluation of hexavalent chromium in power plant coal combustion by-products and cost-effective environmental remediation solutions using acid mine drainage

Abstract

The chromium species leaching from a coal combustion fly ash landfill has been characterized as well as a novel approach to treat leachates rich in hexavalent chromium, Cr(VI), by using another natural waste by-product, acid mine drainage (AMD), has been investigated during this study. It is observed that as much as 8% (approximately 10 microg g(-1) in fly ash) of total chromium is converted to the Cr(VI) species during oxidative combustion of coal and remains in the resulting ash as a stable species, however, it is significantly mobile in water based leaching. Approximately 1.23 +/- 0.01 microg g(-1) of Cr(VI) was found in the landfill leachate from permanent deposits of aged fly ash. This study also confirmed the use of AMD, which often is in close proximity to coal combustion by-product landfills, is an extremely effective and economical remediation option for the elimination of hexavalent chromium in fly ash generated leachate. Speciated isotope dilution mass spectrometry (SIDMS), as described in EPA Method 6800, was used to analytically evaluate and validate the field application of the ferrous iron and chromate chemistry in the remediation of Cr(VI) runoff.

Validation of a European standard for the determination of hexavalent chromium in solid material

“…The closed vessel method has been reported for determination of Cr(VI) in fly ash samples and is assumed to prevent Cr(III) from oxidizing to Cr(VI) to a larger degree compared to the hotplate method where the extraction solution is exposed to ambient air. 10 The reported results from one laboratory were in good agreement with the methods using hotplate and heating block equipment (soil 1: 1.48 mg kg À1 ; soil 2: 2100 mg kg À1 ; waste 1: 10 970 mg kg À1 ). The Cr(VI) results reported from the other laboratory were only in agreement for waste 1 (10 180 mg kg À1 ) and in moderate agreement for soil 2 (1620 mg kg À1 ); for soil 1 a four fold higher Cr(VI) content was recovered (6.8 mg kg À1 ).…”

“…[1][2][3][4][5] To limit the release of Cr(VI) into the environment, the European Commission has set up restrictions in several directives. These European directives have triggered studies and new analytical protocols for Cr(VI) determination and Cr speciation in solid matrices: packaging material, 6 cement, 7 materials in the automotive industry, 8 steelmaking solid waste, 9 fly ash, 10 paint samples 11 and airborne Cr(VI) compounds. 12,13 Within the framework of the Landfill Directive (2003/33/ EC) knowledge of the composition of the waste is the first step in the acceptance procedure for a safe disposal.…”

Microbial Reduction of Chromate in the Presence of Nitrate by Three Nitrate Respiring Organisms

“…For selected samples, media were amended with 100 μM Cr(VI) and aliquots (60 μL) were collected in 0, 24, 48, 72, 96, and 120 h. The samples were spiked with 50 Cr(III) and 53 Cr(VI) isotopes using isotope dilution mass spectrometry (MS) with EPA method 6800 on a Shimadzu ICP-MS (Kingston et al, 1998, 2005). Cr(VI) and Cr(III) concentrations were determined using Chromium Speciated Analysis Calculation Software (Applied Isotope Technologies, Inc.).…”

The influence that different urban development models has on PM2.5 elemental and bioaccessible profiles

“…Combustion processes would normally oxidize a fraction of Cr (III) to the hexavalent form. It is therefore interesting that the soluble Cr fraction in Curitiba was lower than what was expected, especially due to the close proximity of atmospheric Cr emitters: a cement plant and thermal power generation 37,38,57–59 . However, we should consider the trivalent Cr atmospheric budget in Curitiba 58 for example from the road dust and 18,000 motor vehicles per day on the highway BR277 (40–45% of trucks) 60 .…”