Interaction between copper(II) oxide and aqueous ammonia in the presence of ethylenediaminetetraacetic acid

The interaction of copper(II) oxide with aqueous ammonia containing ethylenediaminetetraacetic acid (H 4L) is analyzed in terms of formal heterogeneous kinetics and the fractal dimension of the dissolving space. It is shown experimentally that, in the presence of H 4L, the dissolution rate of CuO grows with increasing ammonia concentration. At a fixed ammonia concentration, the dissolution rate of CuO passes through a maximum at an H 4L concentration of 8 × 10 -3mol/l. Two mechanisms of dissolution are suggested, namely, an adsorption and a redox mechanism. The adsorption mechanism involves four intermediate species and implies that the dissolution rate is a fractional rational function of the EDTA concentration. The redox mechanism takes into account the oxide/electrolyte interfacial potential. The role of the CuOHL 3-ion is elucidated, and the kinetic parameters of dissolution are derived.