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Distribution, speciation, and extractability of cadmium in the sedimentary phosphorite of Hahotoé-Kpogamé (Southern Togo)
Gnandi, K.; Rezaie-Boroon, M.H.; Deheyn, D.D. (2009). Distribution, speciation, and extractability of cadmium in the sedimentary phosphorite of Hahotoé-Kpogamé (Southern Togo). Aquat. Geochem. 15(4): 485-495. http://dx.doi.org/10.1007/s10498-009-9062-7
In: Aquatic Geochemistry. Springer/Springer Science+Business Media: London; Dordrecht; Boston. ISSN 1380-6165; e-ISSN 1573-1421, meer
Peer reviewed article  

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Author keywords
    Phosphorites; Extractability; Cadmium speciation; Sequential extraction

Auteurs  Top 
  • Gnandi, K.
  • Rezaie-Boroon, M.H.
  • Deheyn, D.D.

Abstract
    The geochemistry and extractability of Cd in the phosphorite deposits of Hahotoé-Kpogamé (southern Togo) have been studied using various methodologies such as Cd distribution in profiles, grain-size dependence analysis of Cd content, Cd localization using scanning electron microscopy (SEM), sequential acid extraction, and a leaching experiment with artificial seawater. Results demonstrate that in the phosphorite deposits of Hahotoe-Kpogame, Cd is enriched by a factor of 157 compared to shale and by a factor of 3 compared to average world phosphorite composition. The main carrier of Cd appears to be apatite. This is evidenced by significant high positive correlations between the Cd content and P2O5 (in bulk sedimentr = 0.7 and in the 1–0.2 mm fraction r = 0.9). The grain-size dependence of Cd contents (concentrations decreasing with decreasing grain size) and SEM analysis supports these conclusions. Secondary Cd carriers include calcite, goethite, and various bone fragments. Sequential extraction tests with acetic acid and EDTA show an extraction rate reaching up to 40%. Leaching experiments with artificial seawater show evidence of Cd release in seawater. This leads to the conclusion that the processing of phosphorite by wet sieving using seawater and dumping of phosphorite tailings into the coastal waters of Togo can be a major source of marine pollution with Cd.

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