SELECTIVE LEACHING OF COPPER AND BARIUM FROM THE YBA2CU3O7-X SUPERCONDUCTOR BY CHELATING DIAMINES

Rapid selective leaching of Cu and Ba from the superconductor YBa2Cu3O7-x (1-2-3) is effected by exposure of the solid to aqueous and mixed H2O/MeOH solutions of ethylenediamine (en). Inductively coupled plasma emission spectroscopy revealed that virtually all of the Cu and most of the Ba are in the solution phase; almost all of the Y is in the solid residue resulting from the reaction. X-ray diffraction analysis and IR spectroscopy are consistent with the solid product being primarily amorphous Y(OH)3. The solid also contains small quantities of BaCO3 and Y2BaCuO5(2-1-1); the BaCO3 is formed by reaction of Ba2+ ions in the leaching solution with CO2, while the 2-1-1 was initially present as an impurity in the 1-2-3 samples employed and is comparatively unreactive toward the leachant. The leaching process was monitored spectrophotometrically through the formation of the purple trans-diaquobis(ethylenediamine)copper(II) complex. Kinetic studies reveal that the initial reaction rate is directly proportional to the 1-2-3 macroscopic apparent surface area. In mixed H2O/MeOH solutions the leaching rate follows a first-order rate law with the concentrations of water (2.5-30 M range in 2.0 M en) and ethylenediamine (0.12-2.5 M range in 30 M water). Concentrated en solutions gave corrosion rates of up to approximately 0.2-mu-m/min at room temperature, with rates increasing to approximately 1-mu-m/min at 65-degrees-C. The temperature dependence of the reaction rate yields an apparent activation energy of 55 +/- 5 kJ/mol between 25 and 65-degrees-C. Substitution of D2O for H2O in the leachant solution roughly halves the reaction rate at room temperature. Chelation appears to supply a significant driving force for the reaction: 1,2-diaminopropane, 1,3-diaminopropane, sym-dimethylenediamine, triethylenediamine, and 2,2'-bipyridine also serve as leachants. The leaching rate is negligible at room temperature with a variety of monoamines and nonchelating diamines.