Silver electrocrystallization from a nonpolluting aqueous leaching solution containing ammonia and chloride

Abstract

Silver electrocrystallization from aqueous solutions at pH 11, pC10 and pNH3 - 0.2, where Ag(NH3) + is the dominant Ag(i) species, has been studied. In spite of the complexities of this medium, the experimental results can be satisfactorily described in terms of multiple nucleation and diffusioncontrolled growth of hemispherical nuclei. Nucleation rates, A, and number densities of active sites on the electrode surface, No, were determined from potentiostatic current transients as a function of overpotential. Saturation number densities of silver nuclei on the electrode surface obtained from the A and No values were found to be in excellent agreement with those obtained from the direct, microscopic observation of the electrode surface. Spatial distributions of nuclei were also analysed for silver electrodeposited at different potentials. It was found that nuclei were uniformly distributed when electrodeposited at low overpotentiats, whereas inhibition of nucleation close to already established nuclei occurred at higher overpotentials. From the change of the true nucleation rate with overpotential, it was found that the critical nucleus is formed by a single atom within the - 100 to -300 mV overpotential range.