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[References: 22 tit.]

A spent cracking catalyst (SCC) containing 1 wt % of rare-earth-elements (REEs) oxides is proposed as an alternative raw material to obtain REEs. We have studied the process of removing silicon in the form of ammonium hexafluorosilicate (NH4)2SiF6 involving sintering samples of an fluid cracking catalyst with NH4F, followed by (NH4)2SiF6 sublimation, resulting in the formation of an aluminum-containing concentrate of REEs. The effect of three factors is studied using the central composite design (CCD) of the experiment: the temperature of sublimation (from 350 to 400°C), the sublimation duration (from 40 to 80 min), and the mass of the catalyst fluoride cake (from 5 to 10 g). The effect of these factors on the efficiency of (NH4)2SiF6 sublimation is explored. The results of the experiment are used to develop a second-order model consistent with experimental data. The dynamics of (NH4)2SiF6 recovery using sublimation is determined for a sublimation time of t = 10, 20, 40, and 80 min at processing temperatures of 350, 375, and 400°C. The degree of (NH4)2SiF6 recovery calculated using the second-order model for t = 44, 48, 52, 56, 60, 64, 68, 72, and 76 min is consistent with the experimental curves. The spectra of fluorinated catalyst samples are studied before and after sublimation using X-ray diffraction phase analysis (XRD) and IR spectroscopy. IR spectroscopy data does not contradict XRD data, indicating that the sinter containing SCC and NH4F also contains (NH4)2SiF6, (NH4)3AlF6, and unreacted NH4F. Only aluminum compounds NH4AlF4 and AlF3 remain after sublimation. The concentration of REEs is 15% due to the removal of silicon.