6533b832fe1ef96bd129a364

RESEARCH PRODUCT

Speciation of Cr in Leachates of a MSWI Bottom Ash Landfill

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Cr concentrations and speciation were determined in leachate from a municipal solid waste incinerator bottom ash landfill both experimentally and by thermodynamic model calculations. Total dissolved Cr concentrations of 0.2 mmol L-1 were determined by GFAAS. Two orders of magnitude lower values were determined upon preconcentration by an in-situ solid-phase extraction technique based on the 8-HQ cation exchanger that is specific for Cr(III) but unspecific for Cr(VI). This suggests that chromate dominates the dissolved Cr concentrations in the leachates but was up to 5 orders of magnitude undersaturated with respect to the solubility of CaCrO4 or BaCrO4. Chromate adsorption by oxyhydroxides is less efficient in the highly alkaline environment, but coprecipitation and solid-solution formation with BaSO4 can explain the low chromate concentrations in the leachates. This model assumption was verified by EPMA/WDX measurement of Cr in secondary barite precipitates found in aged bottom ash. Scavenging by this se...