Value-Added\nLanthanum-Containing Products Recovered\nfrom Spent Cracking Catalyst

One of the wastes that can be considered as a promising\nsecondary\nraw material is a spent catalyst for cracking petroleum hydrocarbons,\ncontaining up to 4 wt % rare earth elements. The work analyzes in\ndetail three methods for recovering lanthanum from leaching solutions\nof spent catalytic cracking catalysts. Selective precipitation with\nammonia solution in the pH ranges of 3.2–6.8 and 6.8–8.2\nmade it possible to partially separate aluminum and obtain products\nwith a La<sub>2</sub>O<sub>3</sub> content of 50.9–51.7 wt\n%. The sediments contain basic lanthanum salts and their hydrates,\ncomplex lanthanum and aluminum salts, and lanthanum and aluminum hydroxides.\nThe La<sub>2</sub>O<sub>3</sub> content in the precipitation product\nwith a saturated solution of sodium bicarbonate in the pH range of\n4.5–4.7 was 17.6–18.3 wt %. The precipitate is a mixture\nof hydrated lanthanum carbonate and aluminum hydroxide. As an alternative\nmethod for recovering lanthanum compounds, evaporation of a nitric\nacid leaching solution was considered. Evaporation does not require\nadditional reagents and allows one to obtain a solution of nitric\nacid at a concentration of 10.8 M for reuse. The residue after evaporation\ncontains at least 80.0 wt % of the liquid phase and after cooling\nto 30–35 °C is a mixture of hydrated aluminum and lanthanum\nnitrates. The lanthanum content in the solid residue after evaporation\nand heat treatment reaches 19.6–20.2 wt %.