Environmental Applications of Acid-Leached Residue Obtained during Lanthanum Recovery from Spent Cracking Catalyst

Lanthanum is widely used as a structural and textural promoter in zeolite-containing FCC catalysts. This work investigates the structural, textural, and sorption properties of the solid residue formed after acid leaching of lanthanum from spent petroleum hydrocarbon cracking catalyst. It is shown that nitric and sulfuric acids treatment aimed at extracting the rare earth element leads to significant changes in the chemical composition and surface characteristics of the residual material, while the crystalline Y-type zeolite framework is preserved. The aluminum content in the solid residue decreases from 26.8 to 14.0−15.3 wt %, while the relative proportion of silicon increases to 30.4−33.7 wt.%, indicating preferential dealumination of the amorphous matrix. The specific surface area of the material increases from 89 to 107−112 m2/g when treated with nitric acid and to 118–120 m2/g when using sulfuric acid, and the total pore volume increases by 21–60%. The formation of additional mesoporosity in the range of 1.5−5 nm contributes to improved sorption characteristics. The practical sorption capacity for Fe(III), Cu(II), Zn(II), and NH4+ ions increases by 1.5−1.8 times compared to the initial catalyst. The results show that the solid residue after lanthanum extraction is not an inert waste, but a functional sorption material comparable in characteristics to low-cost mineral sorbents and promising for environmental applications.