Investigation the Effects of Different Lead Compounds (PbO, PbCl2, PbCO3) on Electrochemical Deposition and Characterization, and Influence of Substrate Toward Lead Deposition
Authors: Hasdin Ornapsorn , Riley D. Jason 
Published: May 2020

Lead has commercially advantageous properties, since it is easy to extract, malleable, has low melting temperature, high density, durability and corrosive resistance. For these reasons lead and its compounds are used in many applications; an additive for gasoline and paintings, water piping, shielding, extruded products and lead acid batteries (LABs). Despite its usefulness, it is a highly poison material which can effect both humans and the environment. Lead can cause harm to humans by inhalation of dust, and ingestion from contaminated water and foods. This metal can enter the environment in several ways; lead airborne dispersion, solution leakage, etc. It also remains and accumulates in the food chain by the uptake of water by soil organisms.

The toxicity of this metal is a pollution issue that needs to be addressed. The demand for lead has decreased due to the banning of lead used in many products but not for LABs. Despite lead toxicity concerns, LABs continue to be employed owing to their ability to deliver high power, their robustness, how easy they are to produce and low maintenance cost. The use of LABs, which accounts for 80% of both primary and secondary forms of lead keeps increasing as a result of the expansion of the automotive sector.[1] As a consequence, the amount of waste lead acid batteries (WLABs) has undeniably increased. The significant number of WLABs have drawn attention and the challenge is how to treat the waste properly because improper disposal can lead to hazardous heavy metal spread to the environment.

Recycling is a sustainable and viable route to handle the spent LABs, due to the high degree of recycling that can be achieved.[2] Conventionally, recycling is based on pyrometallurgical and hydrometallurgical processes. The former one employs high temperature operation (smelting) to obtain metallic lead. It is a simple process with fast recovery rate and opportunity to perform at large scale, but without pollution control hazardous gases and particles can escape to the surroundings. The latter methodology employs wet processing to extract metal and electrodeposition to recover metal from scrap. However, hydrometallurgy also has issues with secondary pollution; as the low dissolution of some lead compounds means strong acids are required. This leads operational safety concerns.

A greener approach has been proposed recently by using deep eutectic solvents (DESs) which eliminate the high heat applied, toxic lead soot and concentrated acid. DESs exhibit environmentally friendly and excellent lead salt dissolution for the electrodeposition process. They also have high potential for reusability, are non-volatile and cost-effective. In this study, reline which is a composition of choline chloride (ChCl) and urea in 1:2 ratio was used. This liquid offered a wide electropotential window (EPW) and good lead salt dissolution, which made it suitable for lead recovery. Individual lead compounds were studied (PbO, PbCl2, PbCO3) to investigate the fundamental properties and characteristic behavior on glassy carbon working electrode at 60oC. The diffusion efficiency of Pb(II) from PbO is 3.09x10-7 cm2/s which shows a good agreement with a literature.[3] The nucleation mechanism of each lead compound showed the same pattern as increasing the applied voltage resulted in the growth modes shifting from instantaneous to progressive growth. The X-ray diffraction (XRD) and Energy dispersive X-ray (EDS) measurements also confirmed the reduction to metallic lead for all lead salts. The morphology obtained from scanning electron microscopy (SEM) of each compounds are compared and discussed. The effects of the deposition from PbO on different substrates (GC, Cu, Ni) were also considered. The electrochemical behavior, morphology and structure were investigated by CV scan, XRD and SEM. The final result revealed lead was electrodeposited successfully. The influence of material types to crystal preferential orientation and morphology are also described.

References:

[1] A. J. Davidson, S. P. Binks, and J. Gediga, “Lead industry life cycle studies: environmental impact and life cycle assessment of lead battery and architectural sheet production,” International Journal of Life Cycle Assessment, vol. 21, no. 11. pp. 1624–1636, 2016.

[2] M. Li, J. Liu, and W. Han, “Recycling and management of waste lead-acid batteries: A mini-review,” Waste Manag. Res., vol. 34, no. 4, pp. 298–306, 2016.

[3] H. Yang and R. G. Reddy, “Fundamental Studies on Electrochemical Deposition of Lead from Lead Oxide in 2:1 Urea/Choline Chloride Ionic Liquids,” Journal of The Electrochemical Society, vol. 161, no. 10. pp. D586–D592, 2014.