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Mine Water Environ (2009) 28:6573 DOI 10.1007/s10230-008-0058-0
TECHNICAL ARTICLE
The Geochemical Characterization of Mine Efuents from the Phosphorite Processing Plant of Kpm (Southern Togo)
K. Gnandi M. H. Rezaie Boroon P. Edorh
Received: 17 April 2008 / Accepted: 22 November 2008 / Published online: 12 December 2008 Springer-Verlag 2008
Abstract Sedimentary phosphorites are being exploited in southern Togo. The ore is processed to high-grade puried commercial phosphorite by wet sieving, using water pumped directly from the sea. The resultant muddy tailings are dumped directly into the sea without any pre-treatment. We have separated the solid and liquid phases of the muddy tailings and characterized their metal contents. Leaching tests were conducted with weak acid and saline water to evaluate the solubility and the potential bioavail-ability of various metals. The results show that the purication process leads to the enrichment of certain metals (Cr, Cu, Ni, V, Zn, Ba, Sr, Fe, and Al) in the tailings due to their association with the clay minerals, whereas Cd, Th, and U are enriched in the puried apatite-rich phase. The leaching tests showed that the solubility of metals generally increases when salinity increases or when pH decreases. Thus, the processing of phosphorites with sea water and the dumping of phosphorite tailings into the sea represent a serious potential risk for the marine ecosystem and for human health through the food chain.
Keywords Phosphorite mine tailings Trace metals
Toxicity Salinity Coastal pollution Togo
Introduction
The worldwide increase in demand for metals in industrial societies has intensied ore exploitation. Most of these ore deposits are low grade, so large quantities of mine waste material are generated (Allan 1995; Garcia-Meza et al. 2006). Phosphorites have been exploited since 1959 in the areas of Hahoto and Kpogam (southern Togo). These marine sedimentary phosphate deposits, like those elsewhere in the world, are highly enriched with numerous heavy metals, such as Cd, Cr, Cu, Ni, V, Zn, Pb, U, Th, Mo, Ag, F, Y, and rare earths (Altschuler 1980; Johnson 1987; Kunkel 1990; Piper 1994). The main phosphorite mineral in Togo phosphorite is a carbonate uorapatite (francolite; Johnson 1987; Kunkel 1990). The chemical composition of francolite is very variable because its crystal structure allows a variety of substitutions (McArthur 1990; McClellan 1980; McClellan and Van...