The recovery of critical metals from low metal concentrations using impact electrochemistry

Oladeji, Abiola (2024). The recovery of critical metals from low metal concentrations using impact electrochemistry. University of Birmingham. Ph.D.

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Abstract

According to the definition provided by the European Commission, critical metals are materials that are commercially significant and have a high risk of supply disruption. The recapture of these critical metals from waste streams are essential for their sustainable use as they are often scarce and expensive. Traditional extraction techniques such as ion exchange, chemical precipitation, and adsorption/biosorption have often proven economically impractical for low concentrations of critical metals. These methods are limited by the environmental impact associated with the need for large volumes of reagent, and additional preconcentration and separation steps resulting in secondary waste generation. Electrochemical methods, including impact electrochemistry, would appear to be well-suited for the recovery metals, contingent upon the use of a suitable solvent and reduction potential. The key advantage of this technique is the high mass transport, operational feasibility, and potential for in-situ catalyst fabrication.

This thesis aims to investigate impact electrochemistry as a method to recover critical metals such as copper, palladium, and platinum from low concentration (0.5 mM) solutions. The study commences with the recovery of copper from 0.5 mM copper (II) sulphate, 1 mM sulphuric acid and 19 mM potassium sulphate to ensure a supported solution while minimising nanoparticle aggregation. Recovery would first be tested using metallic (silver and gold) nanoparticles where reductive transient peaks were observed indicating the deposition of copper onto the nanoparticles. After demonstrating this technique, the investigation was extended to study impact deposition onto fly-ash cenosphere particles which are generally considered as a waste material. The copper modified particles were characterised via scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDX) and inductively coupled plasma mass spectrometry (ICP-MS) methods.

Next, the recovery of palladium and platinum from 0.5 mM palladium (II) chloride and hexachloroplatinic acid solution respectively was investigated as they are highly valued platinum group metals. Impact electrochemistry was conducted with 50 nm carbon black nanoparticles as they offer an inexpensive core material with advantageous properties, such as good electrical conductivity and a high hydrogen overpotential. The fabricated Pd/CB NPs and the Pt/CB NPs were characterised via SEM-EDX, inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and thermogravimetric analysis of the modified particles. Additionally, the catalytic performance of the synthesised Pd/CB NPs and Pt/CB NPs was tested without any further modification in the Suzuki coupling reaction (Pd), hydrogen evolution reaction (Pd, Pt) and oxygen reduction reaction (Pt). Long term impact electrochemistry tests were also conducted to measure the extraction of palladium and platinum over time resulting in recoveries of 85% and 70% respectively in 26 h. It was noted that the use of nanoparticles optimised the recovery of both metals as the recovery rate increased by a factor of approximately 2 under the chosen experimental conditions.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):