Content area
Abstract
Sedimentary phosphorites are being exploited in southern Togo. The ore is processed to high-grade purified commercial phosphorite by wet sieving, using water pumped directly from the sea. The resultant muddy tailings are dumped directly into the sea without any pretreatment. 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 bioavailability of various metals. The results show that the purification 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 purified 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. [PUBLICATION ABSTRACT]