PHOSPHATE MINERALS IN CLAY-RICH MINE TAILINGS FROM A CLOSED PHOSPHATE MINE NEAR BARTOW, FLORIDA

Phosphate minerals in clay-rich mine tailings from a closed phosphate mine near Bartow, Florida were investigated for long term environmental management practices. X-ray fluorescence investigation on bulk samples indicates that P2O5 content varies from 0.52 to 21.79 wt%. In the <2 micrometer size fraction phosphate minerals comprised approximately 10 to 25% of the clay fraction. Apatite, wavellite and an unidentified Ca-Al-Fe phosphate mineral occur. Apatite is the most common phosphate mineral composing approximately 80 to 90 percent of the phosphate bearing minerals. Yellow colored sediment is dominated by abundant wavellite. The unidentified Ca-Al-Fe phosphate composed 1 to 5% of the phosphate bearing minerals. Two populations of apatite were observed, one that was Fe and Si- bearing and another that was only Si-bearing. Fe-bearing apatite had Fe2O3 contents that varied from 0.38 to 5.32 wt% and SiO2 contents that varied from 0.90 to 3.32 wt%. The other apatite population had a wider range of SiO2 contents that varied from 0.77 to 8.80 wt%. TEM imaging shows that apatite grains are dominantly single crystals with lesser amounts of aggregates. Wavellite commonly occurs as individual or clusters of lath-like crystals and the chemical composition differed from the pure aluminium phosphate end member with average concentrations of components being that of CaO (1.57 wt%), Fe2O3 (1.98 wt%), SiO2 (5.94 wt%). In the all phosphate minerals investigated no fluorine was found above detection limit (approximately 0.15 wt%), nor was any uranium, radium, heavy metal, or REE element detected. If technological and engineering issues can be resolved the phosphate in this particular tailing deposit may be suitable for reprocessing / recycling as fluorine, heavy metals, and uranium were not detected. The size distribution of the phosphate minerals suggests that mechanical separation at high speeds may not feasible owing to broad particle size overlap with other minerals, however sequential leaching may be feasible if economic considerations can be met.