Study of the content of rare earth elements in the composition of phosphate rocks of the Aznek deposit and development of methods for their recovery

This article presents the results of a study of phosphate rocks from the Aznek deposit (Central Kyzylkum, Uzbekistan) aimed to establish the content of rare earth elements (REE) in their composition in order to identify whether the REE may be recovered to yield standard products for further processing. REE are not typically recovered separately in the manufacture of phosphate fertilizers. The presence and contents of these elements, however, affect the commercial properties of mineral fertilizers. Moreover, phosphate rocks are extensively processed for large-scale production of phosphate fertilizers. Closer attention is therefore paid to the associated recovery of REE, with their mass fraction amounting to 0.8–0.9 %, and sometimes reaching up to 5 %. Chemical, neutron activation, and spectrometric analyses were conducted in order to establish the REE content in the phosphate rocks of the Aznek deposit and select a suitable recovery method. The analysis results provide data on the content of 16 REEs. The highest values were found for Nd (neodymium), La (lanthanum), and Ce (cerium) that are available in the phosphate rocks of the Aznek deposit in the amounts of 30, 48 and 65 g/t, respectively. Among the proposed phosphate rock processing methods, the most effective method for REE recovery is decomposition with nitric acid, which renders both valuable REE concentrates and phosphorus and nitrogen fertilizers. Phosphate rock decomposition experiments have been carried out using 55 % nitric acid. In order to improve REE recovery, NaNO3 or Na2CO3 was introduced into the solution as it enables precipitation of fluorine ions (60–70 %). A preliminary process has been proposed for the phosphate rocks of the Aznek deposit, which may also be utilized for rare earth element recovery.

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