No abstract

Most of the analytical procedures used in organotin (OT) speciation from sediment involves the Grignard derivatization reaction followed by a cleanup step and a desulfuration reaction since sulfur and/or sulfur species interfere with OT determination by GC/MS or GC-FPD. However, alkyl sulfides are generated from the coextracted elemental sulfur, and they are not removed by conventional desulfurization procedures. We propose here a method based on the oxidation of all the sulfur species with dimethyldioxirane (DMD) to sulfones or sulfur oxides. While sulfones are easily eliminated by alumina adsorption chromatography because they have higher polarity than OTs, the sulfur oxides are spontaneously evaporated. The DMD chemoselectivity favors the oxidation of sulfur compounds to sulfones in a few minutes, whereas OTs remain unreacted. In addition, the excess DMD is easily removed by evaporation under a nitrogen stream before the Al(2)O(3) cleanup step. The effectiveness of the desulfurization reaction combined with the cleanup step is demonstrated for a variety of sediment samples containing up to 3.1% of elemental sulfur, which is completely removed by adding 0.6 molar equiv of DMD. No statistical differences in the OT distribution pattern throughout the DMD intermediate oxidation steps were observed.

A process is proposed for the decontamination of fly ash from an urban solid‐waste incineration facility (USWI), where the target contaminants are polychlorodibenzodioxins (PCDDs) and dibenzofurans (PCDFs), a class of highly toxic tricyclo‐polychlorinated organics. In general, the ash waste requires inertization and disposal into a controlled landfill. Here, we propose an inertization process based on the reduction of the PCDDs and PCDFs content before dumping. Inertization is brought about by extraction with a solvent consisting of supercritical carbon dioxide modified with a co‐solvent (10% toluene). The plant would run in semibatch mode, with continuous flow of fluid through a packed bed of fly ash. Then, carbon dioxide and the co‐solvent would be separated and recycled. Favorable extraction conditions were found in the laboratory at 300 bar and 60°C. Under these conditions, the removal efficiency of native PCDDs and PCDFs is around 50% refereed to the extraction of the same sample using the EPA method 1613 (Soxhlet extraction with toluene). A techno‐economic appraisal of a treatment facility is presented for a medium sized incineration plant (50,000 ton urban waste yearly) producing 1,500 ton of fly ash/y. The ash production would be inertised in a specially designed supercritical fluid (SCF) extraction unit, located on‐site at the incineration facility.