Electrochemical Nucleation and Growth of Mn and Mn-Zn Alloy from Leached Liquors of Spent Alkaline Batteries Using a Deep Eutectic Solvent

Abstract

In this work, the leaching of the active material electrodes of spent alkaline batteries was carried out using a deep eutectic solvent formed by acetylcholine chloride-urea as leaching medium. From the leaching liquors of the cathode or the cathode/anode mix, the electrochemical formation of Mn or Mn-Zn alloy, onto a glassy carbon electrode, was respectively performed by means of cyclic voltammetry and chronoamperometry techniques. The analysis of the potentiostatic current density transients was done using of models that involve the three-dimensional nucleation and diffusion controlled growth of a) bimetallic phases [Díaz-Morales et al. J. Solid. State Electrochem. 17 (2013) 345–351], in the case of the Mn-Zn alloy and b) metallic nuclei, for Mn electrodeposition [Scharifker and Mostany, J. Electroanal. Chem., 177 (1984) 13–23]. From scanning electron microscopy and EDX, it was verified that the nuclei formed were composed of Mn, or the Mn-Zn alloy depending on the leaching liquors used.

Analysis of the electrodeposition process of Fe–Mn films from sulfate electrolytes

“…Multi-step mechanisms are expected in codeposition of non-monovalent metal ions in aqueous solutions, as the cases of FeNi, NiCo, FeCo and MnZn alloys [2][3][4]23]. The proposed mechanisms usually include a first step of reduction of the divalent ions in solution to a monovalent adsorbed ion, followed by the reduction of the adsorbed ion to solid neutral metal, as indicated by the partial reactions (4)- (7) bellow.…”

“…The more detailed three-dimensional approach has not a simple analytical solution and has been recently reviewed [10,11]. A common approach is based on the growth of planar diffusion zones [18][19][20][21][22][23][29][30][31], and is called standard model or Scharifker-Hills model [8,10,11,20]. This last model has the advantage to present a single analytical expression for the time (t) dependence of the current density, represented in equation (10) (current density 'i' in modulus).…”

“…In equation (10), A represents the nucleation frequency (nucleation rate, assumed constant), N o represents the initial number of electroactive sites per area of the electrode surface, the product z·F is the molar charge transferred, ρ is the density of the deposit, and M its molar mass. A modification of equation (4) has been also proposed to deal with the deposition of alloys where the parameters are weighted averages of the parameters of each metal [5,23]. However, both the Scharifker-Hills model (SH) as its modified version for alloys, as well as the three-dimensional approaches involve many parameters which are hard to determine experimentally.…”

“…In order to investigate these aspects, we have compared our experimental results with the models from Isaev et al [9][10][11] and Scharifker et al [18][19][20] for current transients during the deposition. Both these models have been used recently in the analysis of single metal electrodeposition [21,22], as well as for alloys deposition [23]. The model for current transients of alloys is, in fact, an extended approach for diffusion controlled electrodeposition introducing the concept of 'apparent' parameters which take into account bimetallic phases [5].…”

The importance of using hydrogen evolution inhibitor during the Zn and Zn-Mn electrodeposition from ethaline

“…5 A literature search evidenced that only a few research groups have tackled the possibility of Zn-Mn electrodeposition from choline-based deep eutectic solvents: reline with boric acid as an additive was used for electrodepositing Zn-Mn on copper, 6,7 while acetylcholine chloride-urea eutectic mixture was employed for Zn-Mn electroplating from the leached liquors of spent alkaline batteries. 8 Besides reline, the second most successfully characterized and the most often cited DES in the last two decades is ethaline (a eutectic mixture of choline chloride and ethylene glycol). Yet, to the best of our knowledge, ethaline has hitherto not been applied in Zn-Mn electrodeposition, although it was reported as an electrolyte for electroplating of other Zn alloys, two examples of which are Zn-Sn, 9 and Zn-Ni alloy.…”