Andrews, A. M.; Greenaway, Anthony M.; Dennis, P. F.; Barnes-Leslie, D. A.
Author Affiliation, Ana.
Department of Chemistry
Isotopic effects on inorganic carbon in a tropical river caused by caustic discharges from bauxite processing
Date of Publication
Stable C isotope compositions of dissolved inorganic C (DIC) and carbonate sediment in a Jamaican river (Rio Cobre), are used as natural tracers of accidental spillage of bauxite processing liquor and waste water. Bauxite processing produces highly caustic (OH super(-) and CO super(2) sub(3) super(-)) liquor and wash waters. These hydroxide-rich waters absorb atmospheric CO sub(2) that is isotopically fractionated resulting in very negative carbonate delta super(13)C and delta super(18)O values. Accidental spillage of these liquors into rivers causes rapid precipitation of CaCO sub(3) as a fine-grained suspension (`whiting') and subsequent deposition as calcite sediment. At the time of DIC sampling 'whiting' was not evident; however, delta super(13)C sub(DIC) values at sites with a history of contamination were about 2ppt more negative than ambient values. The history of bauxite processing spillages is recorded in the delta super(13)C values of carbonate riverbed sediments. At sites known to be impacted, particulate carbonate samples have delta super(13)C values between -11.2 and -14.2ppt; values that are between 1 and 4ppt more negative than the predicted ambient delta super(13)C value. Similarly, delta super(18)O values of carbonate sediments at impacted sites are on average 2ppt more negative than those from sites above and below them, supporting the interpretation that the `whiting events' form precipitates with isotopically negative values. Contamination is quite localized because carbonate sediments downstream of impacted sites show no evidence of anomalous isotope values. This suggests that the particulate carbonate is either flushed or re-dissolves, and is diluted downstream. The carbonate 'whitings' are thus highly visual but relatively benign, although the associated pH and dissolved Al super(3+) and Na super(+) flushes might have more serious impacts on the river environment.....
pollutant identification; water pollution; industrial wastes; carbonates; chemical precipitation; geochemistry; isotopic tracers; rivers; precipitation (chemical); streams (in natural channels); tropical environment; isotopes; carbon; industrial effluents; pollution effects; bauxite; rio cobre (jamaica);