Effects of additives on zinc electrodeposition from alkaline zincate solution

The effects of additives on the surface and cross-sectional morphologies of zinc deposits on iron substrate from alkalinezincate solution were characterized by scanning electron microscope(SEM).The cathodic reaction mechanisms under variousconcentrations of additives were investigated using cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS)techniques.It is found that with increasing the additive A content in the bath solution,the nucleation overpotential(NOP)value isobviously increased and the inhibition effect is strengthened.This may be mainly due to the adsorption of additive A on the cathodicelectrode surface,which can cover the active sites and block the discharge reduction.The results of EIS analysis indicate that therate-determining step of zinc electrodeposition process is changed from mixed control step into electrochemical reduction step in thepresence of additive A.However,any quantity of additive B has little effect on the NOP value and the inhibition effect is not obvious.Furthermore,addition of additive A and additive B at the same time displays the strongest inhibition effect and shows a strongsynergism because of their co-adsorption on the cathodic electrode surface.

Phase separation in solvent extraction of cobalt from acidic sulfate solution using synergistic mixture containing dinonylnaphthalene sulfonic acid and 2-ethylhexyl 4-pyridinecarboxylate ester

Phase separation rate is a critical character in determining the usefulness of a solvent extraction system in hydrometallurgy. A survey of the synergistic mixture containing dinonylnaphthalene sulfonic acid (HDNNS) and 2-ethylhexly 4-pyridinecarboxylate ester (4PC) for the extraction of cobalt from acidic single metal sulfate solution was carried out to suggest how the physicochemical properties and the morphology of the reverse micelles in the loaded organic phase affect the phase separation. The results show that effective parameters affecting the phase separation are the viscosity and the excess water uptake of the loaded organic phase. It is obvious that the specific settling rate (SSR) decreases with the apparent increase of these two parameters. The measurement of small angle X-ray scattering (SAXS) proves that the morphology of the reversed micelles in the loaded organic phase changes evidently with the change of the specific settling rate (SSR).

Cathodic process of nickel electrodeposition from ammonia-ammonium chloride solutions

Mechanism of cathodic process on nickel electrodeposition from ammonia-ammonium chloride solutions was studied by Tafel polarization curves,linear sweep voltammetry(LSV),cyclic voltammograms(CV)and chronopotentiometry(CE)technologies.In the electrolyte with 1.0 mol·L^(-1) NiCl_(2)·6H_(2)O,4.0 mol·L^(-1) NH_(3)·H_(2)O and2.5 mol·L^(-1) NH4Cl,nickel ion mainly complexed with ammonia and almost no free nickel ion could be found.It is confirmed that the dominant form of nickel ammonia complex ion in the system is Ni(NH_(3))_(4)^(2+)by measuring the equilibrium potential of the electrode at various concentrations of ammonia.The species of Ni(NH_(3))42+turns into Ni(NH_(3))_(2)^(2+)during pre-chemical reaction step before discharging reduction reaction.Then,Ni(NH_(3))_(2)^(2+)discharges at the cathodic interface to form metal nickel deposit directly.Nucleation process is involved during nickel electrodeposition according to CV results.The reduction reaction of Ni(NH_(3))_(2)^(2+)is irreversible which is controlled by diffusion step.Other processes are also accompanied during the electrodeposition process,except for the diffusioncontrolled process.