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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. 相似文献
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The marine coastal sediments from Togo have been analysed for the trace elements Cd, Cr, Cu, Ni, Pb, Sr, V, Zn and Zr to
ascertain the geo-ecological impact of dumping of phosphorite tailings into the sea. Trace element concentrations ranged from
2–44 ppm for Cd, 22–184 ppm for Cu, 19–281 ppm for Ni, 22–176 ppm for Pb, 179–643 ppm for Sr, 38–329 ppm for V, 60–632 ppm
for Zn and 18–8928 ppm for Zr. Regional distribution of trace elements in the marine environment indicates that the concentrations
of Cr, Cu, Ni, Pb, V, Sr and Zn increase seawards and along the coastal line outwards of the tailing outfall, whereas Cd and
Zr showed reversed spatial patterns. Sorting and transport of phosphorite particles by coastal currents are the main factors
controlling the distribution of particle-bound trace metals in the coastal environment. The Cd, Sr and Zn concentrations decrease
with decreasing grain size in marine coastal sediments, whereas Cr, Cu, Ni and Zn concentrations increase with decreasing
grain size. Percolation and shaking experiments were carried out in laboratory using raw phosphate material and artificial
sea water. Enhanced mobilization of Cd from phosphorites by contact with the sea water was observed.
Received: 11 May 1998 · Accepted: 20 October 1998 相似文献
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