Physical, Static, and Kinetic Analysis of the Electrochemical Deposition Process for the Recovery of Heavy Metal from Industrial Wastewater

Abstract

Through the electrodeposition technique, toxic metals in wastewater can be removed and deposited on a chosen substrate with excellent selectivity. In this work, we use this technique to extract lead cations from simulated wastewater by using fluorine-doped tin oxide (FTO) substrate at various temperatures. In situ tracking of lead nucleation at advanced stages has been achieved by chronoamperometry. According to the experimental results, the theoretical models developed to study the kinetic growth of lead deposits in 2D and 3D are in good agreement. Nucleation rate and growth rate constants, for example, were found to be strongly influenced by temperature. Cottrell's equation is used to calculate the diffusion coefficient. X-ray diffraction, scanning electron microscopy, and energy-dispersiveX-ray techniques were used to investigate and characterize the lead deposits. The reported results could provide insight into the optimization of electrodeposition processes for heavy metal recovery from wastewater and electronic wastes.

Figure 1

Diagram of metal recovery from e-waste from industrial water. In terms of pretreatment, there are two types: manual processing, which involves sorting, separating, cleaning, emptying, dismantling, decontaminating, and segregating, and mechanical processing, which involves shredding, milling, grinding, and separating through eddy current or air stream classifiers.

Figure 2

Typical cyclic voltammograms measured for the FTO electrodes over the same voltage range and different temperatures in pure distilled water, and the curves are obtained from an aqueous solution of 0.1 M Pb(NO₃)₂ in 0.4 M NaNO₃.

Figure 3

Current density toward time recorded during the electrodeposition of Pb²⁺ on an FTO electrode. Black, blue, and green lines are the experimental results for T = 5, 20, and 35°C, respectively. The red line corresponds to their best fit.

Figure 4

Dependence of log(k₀), log(k′), and 3D on temperature for lead (II) on FTO.

Figure 5

SEM micrographs of Pb deposits on FTO substrate at different temperatures. (a) T = 5°C, (b) T = 20°C, and (c) T = 35°C.

Figure 6

Energy-dispersiveX-ray analysis (EDX) spectrum of a lead deposit on an FTO substrate at 20°C.

Figure 7

The XRD pattern of the lead deposited on an FTO substrate (with a potential pulse at −0.8 V at different temperatures). The patterns of Pb(NO₃)₂ and FTO are given for comparison.

Figure 8

Characteristic peak positions of FTO and lead in the 2θ range 36° − 41° of samples obtained at 5, 20, and 35°C.