Modern society rests on the availability of materials derived directly or indirectly from mineral resources in the earth's crust. Metals constitute a particularly important class of materials, not only as a construction material for things such as cars, planes, and buildings, but also ever more in sophisticated devices such as computers and smart phones. This has led to increased and shifting demands for metals such as nickel, zinc, copper and cobalt.
Most metals are not freely available in nature but must be extracted from the naturally occurring mineral. Nickel, cobalt, copper, and zinc are extracted in Norway by a process called electrolysis. Electrolysis requires large amounts of electrical energy. In Norway the production of copper, cobalt, nickel, and zinc corresponds to approximately 1 % of the total consumption of electrical energy.
In view of the pending climate challenges it becomes imperative to reduce this energy consumption as much as possible. In the LEAn project NTNU and SINTEF collaborate with Glencore Nikkelverk (copper, nickel, and cobalt), Boliden Odda (zinc) and Permascand (catalysts) to reduce the energy consumption in electrowinning through development of novel electrocatalysts.
So far, the project has designed and built special cells for the measurement of both catalyst performance and degradation rates, and performed a comprehensive set of measurements of degradation rates for industrial, iridium-containing anodes with these, including assessments of the so-called stability number; degradation is an important but often overlooked aspect of catalyst development. Furthermore, the project has discovered a significant effect of the electrolyte on the wetting properties of industrial anodes, which will have important consequences for how the electrodes behave during gas evolution and, in turn, impose constraints on the electrolyte baths. This type of characterization will be extended during the next project period. The project has also synthesized a number of novel catalysts that do not contain iridium and which are therefore possible candidates for a more (cost-) efficient operation. These catalysts are now being characterized with respect to performance and characterization, among other things.
Significant progress has been made in the development of stable and active catalysts. An antimony-based catalyst is currently under testing in a semi-industrial electrolysis cell, and is still stable after several hundred hours. Further work on improving the activity by resorting to other chemical compositions have resulted in a catalyst based on cobalt and manganese. This catalyst displays improved activity, but is apparently not as stable as the antimony-based catalyst. A significant amount of resources has also been spent on investigating the effect of pretreatment of the titanium substrates employed for the electrodes and the phenomenon of passivation, which may also shorten the lifetime of the electrodes.
The project was also jointly responsible with one of the project’s industry partners for the combined conference and webinar «The Electrochemistry Enabling the Green Transition» that took place in Ljungaverk, Sweden in June 2024. The conference gathered 70 participants in Ljungaverk in addition to the 50 participating digitally.
The project has published its results in a number of contexts, including on peer-reviewed publication so far. The project has its own web page.
Metal electrowinning is the process of extracting a metal from its ore by electrochemical processes. In aqueous electrowinning the ore from which the metal is to be extracted is dissolved into an electrolytic solution containing two electrodes. A voltage is applied between the two electrodes, and the metal is deposited at the negative electrode. Typically, oxygen is evolved at the positive electrode, i.e. at the anode. The annual energy consumption associated with this industry in Norway is on the scale of TWh.
The energy consumption associated with the process is substantial, particularly at the anode, but can be brought down by employing catalysts. Thus, if the lead anodes that currently dominate the industry are replaced by anodes containing iridium, the energy consumption may be reduced by 15 %. However, iridium is costly (115 € per gram) and scarce (annual global production < 10 ton); facing soaring iridium prices and an anode lifetime of only 5 years, it may pay off for companies to continue their use of the cheaper lead anodes and sustain the accompanying energy loss.
The LEAn project pursues alternative, energy efficient anodes with a catalytic activity that matches that of iridium-based anodes, but with a longer lifetime and that avoids the use of costly and scarce elements. Since only anode compositions that are at the outset expected to be stable under the rather harsh conditions of metal electrowinning, durability is built into the development work from the start. The challenges consist of finding compositions that are in addition both conductive, catalytically active, and have other necessary properties required for the application, including aspects of bath impurities and gas evolution. A range of sophisticated experimental and theoretical methods will be employed to achieve the goals. For risk mitigation, the project will include iridium in the composition space to be investigated, in this part of the project focusing on iridium thrift.
