Chromium Speciation in Solid Waste Material and Eluates by X-Ray Absorption Spectroscopy and Ion Chromatography

Abstract

The tremendous generation of solid waste material is a worldwide problem. Apart from avoidance of waste materials, their reuse is a main goal of modern waste management. Reuse of waste materials demands adequate risk assessment and reliable quantification methods considering the release potential of harmful compounds. In this context, due to its cancerogenity, hexavalent chromium (Cr(VI)) is of high ecotoxicological, human toxicological and environmental relevance. In this contribution, we focus on the speciation of chromium in two representative solid waste materials (demolition waste material, DWM; municipal waste incineration product, MWIP) and eluates obtained after leaching. For chromium speciation, X-ray absorption spectroscopy (XAS) and ion chromatography coupled with inductively coupled plasma optical emission spectrometry (IC/ICP-OES) were applied. It could be observed that in spite of relatively low contents of Cr(VI) in both solid materials (DWM: 16 ± 1 mg/kg, MWIP: 67 ± 5; aqua regia digestion), environmentally relevant concentrations of Cr(VI) were released from the materials as revealed by batch and column leaching experiments. In particular, threshold values for Cr(VI) of the German Federal Soil Protection and Contaminated Sites Ordinance were significantly exceeded. Application of XAS allowed both the determination of mobilizable Cr(VI) directly in the solid materials and in the alkaline eluates, even at concentrations below 500 µg/L. The results obtained were in agreement with data of leaching tests and with IC/ICP-OES measurements. IC/ICP-OES enabled a rapid, well-reproducible and sensitive quantification of Cr(VI) in the eluates in the lower µg/L range. The presented combination of independent analytical methods and mutual validation is highly powerful and is a valuable contribution for risk assessment of waste material. The principle of the approach can be used for the investigation of other solid materials and elements and their assessment.