Resumo

GARCIA MURCIA, JULIÁN ANDRÉS  e  AHRENS, MICHAEL J.. Quantification of Coal on Colombian Caribbean Beaches (Department of Magdalena). Acta biol.Colomb. [online]. 2014, vol.19, n.1, pp.101-112. ISSN 0120-548X.  https://doi.org/10.15446/abc.v19n1.38085.

To quantify the percentage of unburnt coal in beach sediments from the department of Magdalena (Colombia) a simple procedure was devised to separate the sediment mineral phases according to their density. Sediments were collected from six beaches, at two tidal heights, in November 2012 and February 2013, before and after a spill from a coal barge that occurred on 12 January 2013. Sediments were dried, suspended in an aqueous solution of sodium polytungstate (density: 2.0 g*cm-3) and centrifuged. Because coal has a lower density (1.2-1.9 g*cm-3) than other inorganic minerals and rocks, any coal particle present in a sample concentrated in the suspended fraction, whereas more dense particles settled. To remove organic matter not corresponding to coal, the light fraction was subsequently subjected to a weak oxidation with hydrogen peroxide. To estimate an upper limit for any coal present, weight loss on ignition at 550 °C was determined for whole sediments. For the six beaches examined, the maximum weight loss on ignition was 2.4 % and the weight percentage of the light fraction (with a density < 2 g*cm-3) and resistant to oxidation by H2O2 was 0.07 % in November 2012 and 0.02 % in February 2013. No significant differences in coal content were found between the two sampling events, suggesting that the coal spill that occurred in January 2013 did not result in an increase in coal accumulation on the beaches, probably due to coal's characteristic low density. We conclude that the weight percentage of carbon in the six beaches investigated is less than 0.1 % and that sediments owe their black appearance to inorganic minerals, poorly-combustible at 550 °C, with a density > 3 g*cm-3, which comprise between 10-70 % of the total sediment dry weight.

Palavras-chave : coal; contamination; density; Department of Magdalena; sediments.

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