# The Effect of Calcium and Iron (III) Oxides on Lead Spent Plates: Spectroscopic, Voltametric, and EIS Investigations

## TL;DR

This study investigates how adding calcium and iron oxides affects the structure and properties of lead spent battery plates using various analytical techniques.

## Contribution

The study reveals how varying CaO concentrations alter the structural and electronic properties of lead-based materials through spectroscopic and electrochemical methods.

## Key findings

- X-ray diffraction showed structural changes in the lead network with increasing CaO content.
- EPR spectra indicated Fe3+→Fe2+ interconversion and Fe3O4 formation in samples with 5 ≤ x ≤ 12.
- Higher CaO levels increased the radius of curvature in EIS plots and decreased conductivity.

## Abstract

In this study, xCaO‧5Fe2O3‧(95−x)Pb glasses and vitroceramics containing various concentrations of calcium ions (from 0 to 50 mol% CaO) were prepared using the spent anodic plate of a car battery. X-ray diffraction analysis revealed changes in the network structure as a function of CaO content. The intensities of the IR bands due to the sulfate and sulfite units were lowered, indicating a decrease in the sulfurization degree within the lead network. In the UV–vis spectra, the presence of electronic transitions of the Fe3+, Pb2+, and Fe2+ ions were identified. The EPR spectra were characterized by resonance signals centered at about g ~ 2 and 4.3, corresponding to the trivalent iron ions. For the samples with 5 ≤ x ≤ 12, the signals decreased abruptly, suggesting a Fe3+→Fe2+ interconversion and the formation of the Fe3O4 crystalline phase. A considerable increase in the intensity of the signal centered around g ~ 2 was observed as the CaO concentration increased to 30% in the host matrix. Our results confirm that the higher CaO levels of 3 mol% are responsible for the increase in the radius of curvature of the semicircle arcs in the EIS plots and the decrease in their conductivity.