Value-Added Lanthanum-Containing Products Recovered from Spent Cracking Catalyst

One of the wastes that can be considered as a promising secondary raw material is a spent catalyst for cracking petroleum hydrocarbons, containing up to 4 wt % rare earth elements. The work analyzes in detail three methods for recovering lanthanum from leaching solutions of spent catalytic cracking catalysts. Selective precipitation with ammonia solution in the pH ranges of 3.2–6.8 and 6.8–8.2 made it possible to partially separate aluminum and obtain products with a La2O3 content of 50.9–51.7 wt %. The sediments contain basic lanthanum salts and their hydrates, complex lanthanum and aluminum salts, and lanthanum and aluminum hydroxides. The La2O3 content in the precipitation product with a saturated solution of sodium bicarbonate in the pH range of 4.5–4.7 was 17.6–18.3 wt %. The precipitate is a mixture of hydrated lanthanum carbonate and aluminum hydroxide. As an alternative method for recovering lanthanum compounds, evaporation of a nitric acid leaching solution was considered. Evaporation does not require additional reagents and allows one to obtain a solution of nitric acid at a concentration of 10.8 M for reuse. The residue after evaporation contains at least 80.0 wt % of the liquid phase and after cooling to 30–35 °C is a mixture of hydrated aluminum and lanthanum nitrates. The lanthanum content in the solid residue after evaporation and heat treatment reaches 19.6–20.2 wt %.