engleski

Decontamination of soil burdened with Cr(VI)

Demonstrated in the experimental investigations (chapter 3.1 and 3.2) conversion of Cr(VI) contaminated soil to C.M500™ and Xbase™ provides the possibility to reduce the ecological risk of Cr(VI). Other toxicologically relevant heavy metals (i.e. lead, Nickel, Copper, Zinc, …) are immobilized by emplacement within the ceramic matrix of the Xbase™ material. Nevertheless too few experiments could be performed (due to a lack of soil material) to determine suffcient data for the defnition of an ecologically and economically satisfying decontamination process of soil material highly burdened with hexavalent Chromium. In the first experiment (chapter 3.1) about 73.4 kg of C.M500™ have been formed by use of 5.7 kg of Cr(VI) contaminated soil material. This huge increase of mass is much too high to be acceptable. Therefore, subsequent experiments are to be performed to decrease this increase in mass. During processing of the Cr(VI) contaminated materials MPI and MPII (chapter 3.2) to form the corresponding Xbase derivatives more than 97% of the originally present Cr(VI) were chemically reduced. Comparing the masses of Xbase materials and the corresponding input materials shows that the mass of Xbase is about 3 times higher than the mass of Cr(VI) contaminated soil material (m(Xbase-MPI)/ m(MPI) ≈ 3 ; m(Xbase-MPII)/m(MPII) ≈ 3.4)). Despite quite well reduction yields of > 97%, chemical reaction of MPI and MPII to Xbase materials is not yet satisfying. This has to be derived from the analytical results of the aqueous eluates. Concentrations of 1.1 mg/l and 0.8 mg/l for Cr(VI) (s. Table 9) are much too high to be acceptable. In the landfll classifcation of Germany there is an upper Cr(VI) concentration threshold of 0.05 mg/l. Chemical reduction of Cr(VI) was obviously not quantitative on fring of CM500 to Xbase at 1000°C. Due to low TOC and high pH values (s. Table 8 and Table 9) this result is not very surprising. Low TOC values indicate that there was no more reductive (i.e. Carbon) present in the material at the end of the fring process. In combination of low TOC values, alkaline conditions and excess of i.e. oxygen there is a high probability for oxidizing trivalent Chromium to hexavalent Chromium (s. Chapter 1.2) at temperatures of about 1000°C. It is worth mentioning once more, that the low amounts of CM500-MPI and CM500-MPII were not suffcient to achieve steadystate operational conditions during the fring process. Therefore, it was not possible to determine the optimum air injection rate for the combustion of the organic compounds.

contaminated soil; hexavalent Chromium; two step process for a mineral oil binder; from contaminated soil to product; ecocycling; cost effective decontamination; ecological and economical handling of contaminated soil

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