Investigating the electrochemistry of critical metals on carbon black by Nano-impact techniques

Keal, Molly Emma ORCID: 0009-0004-6830-8826 (2025). Investigating the electrochemistry of critical metals on carbon black by Nano-impact techniques. University of Birmingham. Ph.D.

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Abstract

Our transition towards net zero emissions has necessitated the increased demand for critical metals such as manganese, nickel and ruthenium for use in batteries and other renewable technologies. The finite nature of these metals, coupled with the negative environmental and social impact of primary extraction methods, has led to the growing need for sustainable recovery techniques from secondary sources. Inefficiencies in primary extraction and metal recovery from secondary sources leads to the generation low-concentration metal waste streams. However, current recovery methods such as chemical precipitation, absorption and ion exchange are not suited to such low concentrations, often requiring costly pre-concentration steps. On the other hand, electrochemical methods, appear more well-suited due to their higher selectivity and energy efficiency. In particular, nano-impact electrochemistry has recently emerged as a promising recovery method for low-concentration solutions with the added advantage of higher rate of mass transport to the nanoparticles. This thesis explores the use of nano-impact electrochemistry as a potential method for recovering manganese, ruthenium and nickel from low-concentration solutions (0.5 – 1 mM) using inexpensive carbon black nanoparticle cores. Firstly, the electroreduction and electrooxidation of Mn(II) from 0.5 mM manganese sulfate and 20 mM potassium sulfate was investigated. Reductive impacts were observed in the presence of 5 pM carbon black and the deposition product was confirmed to be Mn(0) via scanning electron microscopy/ energy dispersive x-ray spectroscopy (SEM/EDX). Oxidative impacts were also observed in the presence in 5 pM carbon black and the deposition product was confirmed to be MnO2 and various other intermediate products via SEM/EDX and X-ray photoelectron spectroscopy (XPS).
Next, the electroreduction and electrooxidation of ruthenium from 1 mM ruthenium(III) chloride and 10 mM hydrochloric acid and 10 mM potassium chloride was studied. Impact electrochemistry was conducted and in the presence of 25 pM carbon black, reductive and oxidative impacts were recorded for the two respective processes. A long-term upscaled impact experiment for the reductive process yielded Ru-modified carbon black which were characterised via SEM/EDX, XPS and thermogravimetric analysis (TGA). Under partially-optimised conditions, >90% of ruthenium was recovered in ca. 8 hours. Finally, the electroreduction of nickel was studied from two electrolytes: 0.5 mM nickel(II) sulfate or nickel(II) chloride with the corresponding ammonium electrolyte. Reductive impacts were observed in the presence of 20 pM carbon black for both electrolytes. Upscaled long-term impact experiments were conducted and low-level nickel deposits were confirmed via SEM/EDX and inductively coupled plasmon/ mass spectrometry (ICP-MS).

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):