Recovery of valuable elements from spent YBa2Cu3O7-x/Ag composite superconductor bulks

Silver as a highly conductive metal is usually doped in YBa₂Cu₃O_7–x superconductor bulks to improve critical current density of YBa₂Cu₃O_7–x superconductor. The valuable metal elements silver, yttrium, barium and copper in waste YBa₂Cu₃O_7–x/Ag composite superconductor bulks were recovered, respectively. Silver was recovered with process at first, the waste was dissolved by nitric acid and silver chloride was precipitated by adding chloride acid, then silver pig was obtained by melting silver chloride together with sodium carbonate at 1 000 °C. The effective factors on recovery ratio and purity of silver were studied. The chemical analysis proves that the purity of silver ingot is 95.86%. The recovery ratio of silver is calculated to be 92.56%. The loss of silver may be due to the loss of silver chloride during filtering and the volatilization of silver when silver chloride and sodium carbonate are smelted at high temperature. For other three metal elements, Y³⁺, Ba²⁺ and Cu²⁺, in the surplus waste liquid after recovering silver, they were separated with the sequence of barium, copper and then yttrium step by step. First, sulfate acid was used to precipitate barium sulfate. Then, sodium sulfide was added to the surplus solution so that copper could be separated as copper sulfide. During this separation procedure, it was important to control the pH value to be 1–2. After that, oxalic acid was added into the surplus solution to obtain yttrium oxalate. Finally, yttrium oxide was formed by burning yttrium oxalate. The XRD results indicate that the final products are all single-phase compounds as BaSO₄, CuS and Y₂O₃, respectively.