Leading Research Institute of Chemical Technology JSC, Moscow, Russia:

V. Yu. Koltsov, Director for Research, Candidate of Technical Sciences, e-mail: basilik2@yandex.ru
А. А. Zakharov, Engineer
T. V. Vlasova, Lead Engineer
N. S. Velichkina, Senior Researcher, Candidate of Technical Sciences, e-mail: natalia.velichkina@gmail.com

There has recently worsened the situation related to the environmental impact produced by mining and metallurgical companies – in particular, due to the growing amount of stored industrial waste, such as overburden, country rock, dumps, and tailings. Phosphogypsum is one of such waste materials resulting from sulphuric acid processing of apatite and phosphate concentrates that entraps most of the rare earth metals (REM) contained in the concentrates. The average concentration of REMs in phosphogypsum is 0.4–0.6%. There exists a great number of processing techniques applicable to dumped phosphogypsum material, and heap leaching of pre-sulphated material (using sour solutions) would be the one that offers the best performance and cost effectiveness. The Leading Research Institute of Chemical Technology has developed a process to prepare phosphogypsum for heap leaching. The process involves phosphogypsum granulation with sulphuric acid, leaching of the obtained granules, sorption of a combination of REMs from the pregnant solution, their desorption from resin and deposition of the concentrate. The laboratory testing involved leaching in a percolation column with the barren solution returning to the leaching stage. A KU-2-8 type of cationite was used to achieve sorption of a combination of REMs from the pregnant leach solution. The obtained results are indicative of the prevailing sorption of a combination of REMs, the recovery of which was 97%, whereas the recovery of impurities was only 18%. Recirculation of the barren solution and the pregnant solution does not affect the process of REM leaching from phosphogypsum granules. Thus, high REM recovery was observed (94%) after 8 cycles of leaching/sorption. The proposed processing technique will ensure a continuous automatic heap leaching process resulting in better performance, higher efficiency and lower processing costs.

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