Recovery of Ru from Ru/C and Ru/MgO spent catalysts: Ru/C and Ru/MgO catalysts, with their high catalytic activity and ability to reduce the working pressure and temperature of ammonia synthesis, are widely used in the ammonia synthesis industry. The process for treating Ru/C spent catalysts containing Ba and K is as follows: First, soak the catalyst in HCl solution for 12 hours to dissolve Ba and K. Add H₂SO₄ to the filtrate to precipitate BaSO₄ (recovery rate >87%). The barium precipitation mother liquor is directly concentrated and crystallized to obtain KCl (recovery rate >77%). The HCl leaching residue is incinerated at 800℃ for 10 hours. The ash is then mixed with an equal amount of KOH + KNO₃ (mass ratio 1:1) and heated to 650℃ for 1 hour to melt. After cooling, the excess potassium salt is leached out with cold water. The filter residue was dissolved in 80℃ hot water to obtain a K2RuO4 solution. A small amount of NaClO was added, and the solution was heated to 60℃ for 0.5 h for oxidation. Concentrated H2SO4 was slowly added dropwise, and the solution was distilled under reduced pressure to obtain golden-yellow RuO4. This RuO4 was absorbed with 37% HCl solution, and the absorbent was slowly concentrated to obtain RuCl3·nH2O product, with a recovery rate of 94.6%. Alternatively, it can be absorbed with HNO3 solution to obtain Ru(NO3)3 product.
For Ru/MgO waste catalysts containing Ba and Cs as catalysts, Ba and Cs were first dissolved in 1 mol/L ammonia solution (solubility >97%), while Ru/MgO remained insoluble. Then, MgO was selectively dissolved in 1 mol/L HNO3 heated to 70℃ to obtain a pure Mg(NO3)2 solution, which can be converted to MgO using carbonates for reuse. The nitric acid-insoluble residue is crude metallic Ru, with a recovery rate >94%.
Direct production of RuCl3 from waste catalysts: This is common in chemical catalysis, electronics, and electroplating industries, where ruthenium trichloride is often directly used. Therefore, directly producing this product from ruthenium-containing waste catalysts can simplify the process, reduce reagent consumption, and improve the recovery rate. A process for producing tertiary ruthenium chloride from ruthenium-containing waste was studied. For example, waste containing 67.9% Ru, with the remainder mainly consisting of Pt, Ag, and Pb, was placed in a distillation reactor. A 30% NaOH solution, prepared at approximately five times the amount of waste, was added to the distillation reactor in three portions, while chlorine gas was simultaneously introduced to oxidize the distillation process (the reaction is Ru + NaOH + 4Cl = RuO4 + 8NaCl + 4H2O). The first stage used water absorbent to isolate any salt-containing solution that might splash from the distillation reactor. Then, a seven-stage 6mol/L HCl + 0.5% C2H5OH solution was connected in series to absorb the volatilized RuO4 (the reaction is 2RuO4 + 20HCl = 2H2RuCl5 + 8H2O + 5Cl2). After filtering the second-stage absorbent, the solution is slowly concentrated to a syrupy consistency, then slowly dried using infrared light to obtain the RuCl3 product, which is then sealed (to prevent moisture absorption). The residue from the first distillation is added to an alcohol reducing agent and allowed to stand for 12 hours until the solution is colorless, then filtered. The distillation residue is used to separate Ag and Pb using nitric acid solution. The residue containing approximately 19% Ru is mixed with mNaOH:nNaClO3:mresidue = 3:1:1 and melted at 700℃ for 1 hour. The melt is poured into cold water for a second oxidation distillation to produce ruthenium trichloride. The residue from the second distillation contains very little Ru. After two distillations, ruthenium trichloride is obtained, with a Ru recovery rate of 98%.
