ION-EXCHANGE SEPARATION OF RARE EARTH ELEMENTS AND ALUMINIUM DURING RECYCLING THE SPENT FLUID CRACKING CATALYSTS

The possibility of selective ion-exchange separation of rare earth elements (REE), in particular La3+, from weakly acidic solutions containing an excess of Al3+ and Fe3+ ions has been demonstrated. The sorption of REEs and Al3+ was conducted under static and dynamic conditions using the chelating ampholytic resin Purolite S-930 in the Na-form. Selective REE desorption was performed by washing the column with the aqueous solution of EDTA, while Al3+ ions were retained in the column. The conditions for La3+ ion extraction were optimized, and the mechanism of their sorption was investigated. Experiments confirmed effective lanthanum extraction at the optimal pH 4.0 and a temperature of 25 °C. An increase in temperature to 65 °C reduces the sorption equilibrium time from 5 to 3 hours at an initial lanthanum concentration of 2.4 mg/L. The effective activation energy of the process was calculated to be 36.9 kJ/mol, and the maximum sorption capacity was determined as 322 mg/g. The influence of EDTA concentration on the efficiency of La3+ ion desorption in the presence of Al3+ was demonstrated. The developed methodology was applied for the sorption purification of REE-containing technological solution obtained during complex fluoride processing of the spent oil-cracking catalysts. Laboratory-scale sorption purification of this solution yielded a sufficiently pure concentrate (with the total REE oxide content at 85 wt%). Selective desorption from the iminodiacetate ampholyte allows a 30-fold REE concentrating from the technological solution, with losses not higher than 20 %.