Especiação de mercurio em solos contaminados por analise de termodessorção acoplada a absorção atomica

AUTOR(ES)
DATA DE PUBLICAÇÃO

1996

RESUMO

An equipment based on thermal release of mercury in solid samples was built and optimised. lt consists basically of an oven (a quartz rube wrapped in a Ni-Cr coil), coupled to an atomic absorption spectrophotometer (AAS). The output of the coupled system is a thermogram, i. e., absorbance readings as a function of temperature. The thermal release analysis was performed using the system TDAAS with the following mercury standards: Hg, Hg2Cl2, HgCI2, HgO and HgS, which were added to two diferent soil matrices. These standards showed different temperarure ranges of thermal release, and the thermograms were very similar in both matrices, indicating the possibility of application of the method to mercury speciation in soils. Contaminated soil samples of two different sources, one from the gold mines of Poconé, Mato Grosso, Brasil (BRA samples), and the other from a chlor-alkali industry at the Halle region, Germany (GER samples), were analysed by the TDAAS. It was shown that the Hg, mainly contaminant in both cases, was oxidised. This oxidation occurs more intensively in the samples from the chlor-alkali process, which contain high concentration of chloride ion. These ions favours the oxidation because of its high complexation capacity. The BRA samples showed the presence of mercury species more frequently in lower oxidation state, i. e. Hg2 in combination with Hg and small amounts of Hg. One sample showed the presence of Hg only. The GER samples showed, in general, the presence of Hg, probably bound to humic substances, in the case of samples with high contends of carbon, or as HgCl2. Only the highly contaminated ones (>33000 mg/kg of mercury) showed the presence of Hg as the predominant species. The mercury oxidation/reduction process was studied in both matrices, BRA and GER, by the addition of Hg, Hg2 and Hg followed by the obtaintion of thermograms periodically. It was confirmed the higher tendency of mercury oxidation in the GER matrix compared to the BRA matrix (100 and 54% respectivelly, when Hg was added to both matrices). In contrast a tendency of mercury reduction was observed in the BRA matrix, the Hg added to it was partially reduced to Hg2 (40%). The TDAAS method showed to be very suitable to mercury quantitative analysis in soil, with an absolut detection limit of 75 ng of mercury. Soil samples from Tanque dos Padres, Poconé (MT), with mercury coments between 12 and 100 mg/kg were analysed by TDAAS and CVAAS. Both methods showed a comparable accuracy, by the Paired t-Test and the Regression and Correlation tests.

ASSUNTO(S)

mercurio quimica analitica quantitativa espectroscopia de absorção atomica solos

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