Development of methods for concentration and dissolution of Rh and Ru from copper slime

In copper (Cu) smelters, precious metals in recycled materials are distributed into electrolytic Cu slime. During the precious metal refining process, rhodium (Rh) and ruthenium (Ru) are concentrated from the slime into residues containing selenium (Se) and tellurium (Te). In this study, new methods were developed for refining Rh and Ru by obtaining aqueous solutions of Rh and Ru and separating Se and Te using a hydrometallurgical process followed by a pyrometallurgical process. In the hydrometallurgical process, Se and Te are dissolved by air oxidation in a sodium hydroxide (NaOH) solution, and Cu is dissolved using diluted sulfuric acid (H₂SO₄). Se and Te are removed by dissolution and separated from the undissolved Rh and Ru. In the pyrometallurgical process, the residual Se and Te in the Rh and Ru concentrates obtained from the hydrometallurgical process are chlorinated and separated by volatilization. Rh, Ru, Se, and Te are chlorinated by heating to 1000–1100 K in chlorine (Cl₂) gas. Volatilization was used for separation of Se and Te from Rh and Ru because the vapor pressures of Se and Te chlorides are higher than those of Rh and Ru chlorides. Because the chlorides of Rh and Ru have poor solubility, they are mixed with sodium chloride (NaCl), heated, and converted to soluble complex salts containing Rh and Ru, which are later dissolved in water to obtain an aqueous solution containing concentrated Rh and Ru.