Composite Anode Materials Pulse Electrodeposition Preparation And Electrochemical Properties Of Aluminum Inertia

In modern hydrometallurgy, the anode materials play a critical role in improving product quality and reducing energy consumption. The lead-based alloys known as cheap, easy to shape and self-healing are used as anode materials in zinc electrowinning. However, there are some inherent defects of lead-based alloys, including high energy consumption, low mechanical strength, poor corrosion resistance and catalytic activity, short service life and low level of cathode product. In the study, aluminum-based inert composite anode materials Al/Pb-WC-CeO2and Al/Pb-WC-CeO2/β-PbO2-WC-CeO2are prepared by pulse composite electrodeposition technology. The relationship between electrode microstructure and electrochemical properties like oxygen evolution overpotential, electrocatalytic activity and corrosion resistance are studied. The nature of electrode in reducing cell voltage, increasing current efficiency and improving cathode product quality are explored when the electrode was used in zinc electrowinning at laboratory level. Besides, the mechanism of composite electrodeposition and its influence factors are discussed.1. Pre-treatment of aluminum substrateIn order to enhance the bonding force of aluminum substrate and intermediate layer(Pb-WC-CeO2), some pre-treatment are applied in the surface of aluminum substrate by following processes:sandblastâ†'two-step dip zinc(the key point)â†'nickelage. In two-step dip zinc process, Zn-Fe alloy formed by adding Fe3+which can refine grains and improve the bonding force of coating. The light beige nickelage layer with smooth, dense and uniform surface combined with the substrate well, which can meet the requirements of subsequent plating process.2. The study of Al/Pb-WC-CeO2electrode preparation(1) The optimum conditions for preparing Al/Pb-WC-CeO2electrode by double-pulse electrodeposition were:Pb(CH3COO)2200-250g·L-1, HBF4160-200g·L-1, H3BO310-20g·L-1, C102H151O39N311-3g·L-1, cationic surfactant0.5-1g·L-1, pH=0.5, WC40g·L-1,CeO240g·L-1, positive duty cycle30%, negative duty cycle10%, forward current density120mA·cm-2, forward working time200ms, temperature40℃. The composite electrode was irreversible electrode when it was used as anode in zinc electrowinning, which can prevent the solution infiltrating into coating effectively and improve the corrosion resistance significantly. (2) CeO2particles can refine grains, level off coating surface and restrain W content in the coating. Proper pulse parameters were favorable to forming dense crystal nucleus and increasing specific surface area of coating. It was conducive to co-deposition of Pb, WC and CeO2by increasing temperature and forward working time, but excess temperature will reduce the adsorption of solid particles on cathode surface.(3) Compared with DC technology, the electrodeposition rate of pulse technology increased about200%. The surface of composite coating was more uniform, lower porosity and decreased oxygen evolution overpotential significantly, which can reduce the cell voltage effectively.3. The study of Al/Pb-WC-CeO2/PbO2-WC-CeO2electrode preparation(1) The optimum conditions for preparing Al/Pb-WC-CeO2/PbO2-WC-CeO2composite electrode by single-pulse anodic oxidation method were:Pb(NO3)2190g·L-1, Cu(NO3)2·3H2O15g·L-1,NaF0.5g·L-1, CeO230g·L-1, WC40g·L-1, temperature60℃, forward average current density75mA·cm-2, positive duty cycle30%.(2) Micron WC increased coating grains, nanometer CeO2with interstitial lattice and grain refinement effect can reduce the porosity, lessen coating defects and played a key role in tissue and structure of PbO2crystallizing, forming lead-cerium-oxygen nitrocarburizing compound. For the synergistic effect of WC and CeO2, the PbO2grains produced preferred orientation, which resulted in the surface morphology of electrode turning into diamond structure from flat octagonal shape. But the main phase of electrode was still β-PbO2.(3) Compared with DC technology, the composite electrodes prepared by pulse technology had significant advantages in surface morphology, corrosion resistance, energy conservation.4. The comparison of electrode properties in zinc electrowinning(1) For the synergistic effect of CeO2and WC, the electrode surface was more uniform, compact and smooth, the average Faradic current was higher, current spikes of local area was uniform distribution and electrocatalytic activity was stable.(2) The Al/Pb-WC-CeO2/PbO2-WC-CeO2electrode with lowest cell voltage had better comprehensive properties in corrosion resistance, current efficiency, service life and lead contend of cathode zinc; the main reasons for failure were sedimentary shedded gradually and the electrode surface cracked inevitably, which leading to corrosion medium permeated into substrate. (3) The corrosion behavior of lead-based alloys were influenced by the electrode potential and the surface coverage(θ) of the porous corrosion production. That of Al/Pb-WC-CeO2/PbO2and Al/Pb-WC-CeO2/Pb02-Ce02electrodes were mainly controlled by charge transfer resistance, while the Al/Pb-WC-CeO2/PbO2-WC and Al/Pb-WC-CeO2/PbO2-CeO2-WC electrodes were mainly controlled by diffusion.5. The study of composite electroplating mechanism(1) During the pulse electroplating of Al/Pb-WC-CeO2electrode, the alternate effect of pulse current changed the adsorption, diffusion and double electrical layer of electrode surface; reaction of adsorption and desorption of solid particles on cathode surface affected the deposition and diffusion process.(2) During the anodic oxidation deposition of Al/Pb-WC-CeO2/PbO2-WC-CeO2electrode, adding F" replaced hydroxide radical of PbO2crystal lattice, which promoted the growth of (101)(200)(301) crystal plane of PbO2, decreased diffraction peak of (110)(200)(301)(310) crystal plane and produced preferred orientation in PbO2crystal. After doping CeO2and WC particles, the deposition of PbO2was changed into one step process:Pb(â…¡) ion was oxidated to Pb(â…£) directly.