Effect of mechanical activation on the leaching of rare earth elements from Esfordi phosphate concentrate

The Esfordi phosphate concentrate with total assay of REE equal to 1.2 percent is one of the richest source of rare earth elements in Iran. It contains Ce(5608 ppm), La(1959ppm) and Nd(2227ppm). In this research, the effect of mechanical activation on the leaching of rare earth elements by nitric acid from Esfordi phosphate concentrate was investigated. For the investigation of mechanical activation effect on leaching of REE, a planetary ball mill was used with steel balls of diameter about 20 mm, ball to powder ratio of 15 and 2 and with a retention time of 90 minuts in dry situation and air atmosphere. Because of high and low leachability of fluorapatite and REE minerals by nitric acid, respectively, tow stage leaching methode was used. The first leaching stage residue, that contained about 99 % of REEs in initial phosphate concentrate, was activated mechanically at ball to powder ratio of 12 and then leached. Results showed that the mechanical activation had important influence on leaching of REE by nitric acid from phosphate concentrate and improved the leaching of Ce, La and Nd from about 1% (without mechanical activation) to 35.79, 42.61 and 30.34% , respectively. The amorphization degree increased to 1.2 and 57% after 90 min intensive milling with ball to powder ratio of 2 and 15 to 1, respectively. Also, the crystallite size and microstrain of Fluorapatite differed from 225 nm and 0.08 % for initial sample to 225 nm and 0.09 % and 81.8 nm and 0.63 % for mechanically activated samples with ball to powder ratio of 2 and 15 to 1 respectively.