Due to the feasibility of an electrically rechargeable zinc/air cell made of a zinc foil as active material, an aqueous choline acetate (ChAcO) mixture as an electrolyte and a spinel MnCo2O4 (MCO) and NiCo2O4 (NCO) as a bi-functional oxygen catalyst was investigated in this work. The 30 wt.% water-containing aqueous ChAcO solution showed high contact angles close to those of KOH favoring triple-phase boundary formation in the gas diffusion electrode. Conductivity and pH value of 30 wt.% H2O/ChAcO amounted to 5.9 mS cm−1 and 10.8, respectively. Best results in terms of reversible capacity and longevity of zinc/air cell were yielded during 100 h charge/discharge with the MnCo2O4 (MCO) air electrode polarization procedure at 100 µA cm−2 (2.8 mA g−1zinc). The corresponding reversible capacity amounted to 25.4 mAh (28% depth of discharge (DOD)) and the energy efficiency ranged from 29–54% during the first and seventh cycle within a 1500 h polarization period. Maximum active material utilization of zinc foil at 100 µA cm−2 was determined to 38.1 mAh (42% DOD) whereas a further charging step was not possible due to irreversible passivation of the zinc foil surface. A special side-by-side optical cell was used to identify reaction products of the zinc/air system during a single discharge step in aqueous ChAcO that were identified as Zn(OH)2 and ZnO by Raman analysis while no carbonate was detected.

ABSTRACT.A simple electrolytic cell was used for electrochemical recovery of silver from aqueous solutions containing 100 mg/L Ag(I). Two different sets of electrodes were applied to find the enhanced recovery of silver. Rocks and ores samples were processed through fire assay method and acid digestion. A set of electrodes comprised of stainless steel anode and aluminum cathode gave maximum recovery (96.5%) of silver. This simple, robust, environment friendly and highly sensitive method was effectively applied to various ores and rock samples. The developed method with slight modifications can also be applied for the recovery of other metals.