Caracterização da rocha fosfática de Angico dos Dias (Bahia) e identificação dos minerais portadores de terras raras

The Angico dos Dias carbonate phosphate rock deposit has been exploited and treated in a dry processing plant that includes classification and low, medium and high intensity magnetic concentration. The non-magnetic fraction is used in the production of fertilizers and the fines and magnetic fractions are discarded as tailings. Previous studies indicate the relevant presence of light rare-earth elements and low concentrations of thorium and uranium in the ore. The objective of this work was to characterize the ore, the concentrate and the magnetic tailings of the plant. The results of chemical and mineralogical analyzes indicate that the ore, the product and the tailings are rich in calcium, phosphorus, iron, silicon, aluminum and magnesium. The total content of rare earths is greater than 9 g/kg in the ore and 6 g/kg in the magnetic tailings. The main constituents of the ore are: fluorapatite, hydrobiotite and vermiculite. More detailed analyzes show that cerium, lanthanum, neodymium and samarium are present in the structure of apatite and in monazite particles. Cerium is also found in another mineral without association with other rare earth elements. The results also indicate that the fertilizer production process, with acid attack, promotes the leaching of a significant portion of light rare earth elements contained in apatite and cerianite, which may allow their recovery without significant additional costs.