Selective Nitric Acid Leaching of Rare-Earth Elements from Calcium and Phosphate in Fluorapatite Concentrate

Esfordi phosphate concentrate (Yazd Province, Iran) contains 13.1% P, 34.6% Ca, and 1.09% rare-earth elements (REEs), being one of the most important sources of REEs in Iran. REEs can be extracted from phosphate concentrates as a by-product of phosphoric acid production processes. In this work, nitric acid was used for leaching of REEs and phosphate from Esfordi phosphate concentrate, and the effects of the acid concentration (35-65 wt.%), leaching time (30-90 min) and temperature (24-90 degrees C) were investigated. Due to the difficulty of calcium separation from REEs in nitrate-phosphate solutions, the possibility of selective leaching of calcium and phosphate from REEs was examined. At acid concentration of 35%, temperature of 60 degrees C, and leaching time of 70 min, most of the calcium, more than 80% of the phosphate, and less than 10% of the REEs were dissolved. Accordingly, 90.7% of the REEs remained in the residue and their grade was increased from 1% to 4% in the nitric acid leaching residue. This concentrated residue of REEs could be an appropriate feed for subsequent processes, including acid baking.