Empress Catherine II Saint Petersburg Mining University continues a series of laboratory experiments aimed at creating a fundamentally new technology for the production of aluminum. Now it is produced by electrolysis of alumina solution in molten cryolite, and this process takes place in apparatuses with horizontally arranged anode and cathode.
Such placement of electrodes allows to provide stable current distribution over their entire surface, which is a fundamental condition of the metal production process. However, the equipment designed according to this principle has a number of significant disadvantages. The most important of them is high power consumption. As a consequence of this state of affairs, the aluminum industry is highly dependent on electricity prices. If they rise too fast, the cost of production rises sharply, and smelters begin to work at a loss, as it happened last year in many European countries, where mass cases of bankruptcy or temporary shutdown of specialized enterprises were recorded.
Scientists have known how to cut this Gordian knot for quite a long time. One should simply use vertically arranged electrodes. This will not only reduce energy consumption, but will also dramatically increase specific productivity. After all, by reducing the size of electrolyzers it is possible to increase their number and get 5-6 times more metal on the same areas. That is, instead of 50-55 kilograms per meter of area per day to produce about 320. However, this is in theory, but it is not possible to put it into practice yet - the loss of stability of current distribution on the cathode surface prevents it.
"The management of the university set us the task to develop a technology to equalize macro- and micro-distribution of current density in aluminum electrolyzers over the entire surface of vertically arranged electrodes. In order to achieve this, we needed, first of all, to create a fundamentally new composite material and give it a shape that allows us to exclude uneven distribution of electric charge," said Evgeny Gorlanov, Deputy Director of the Scientific Center "Problems of Processing of Mineral and Technogenic Resources" of St. Petersburg Mining University.
Scientists have already managed to achieve significant successes on the way to the goal, which for many decades seemed unattainable. For example, they have obtained a composite electrode based on titanium and its compounds, which is best suited for the new generation of electrolyzers, and also revealed in the course of experiments that its best shape will be an oval. This will eliminate any current concentrators that make it difficult to distribute the current evenly across the cathode, such as sharp edges, corners or protrusions. In addition, an innovative way to smooth the surface of the product by forming a special coating to avoid roughness has been developed.
The technology has already passed the stage of laboratory tests. They confirmed the efficiency of elliptical composite electrodes and also showed that the anode dissolution rate in case of their use decreases three times in comparison with rectangular analogs. That is, among other things, their use allows to save significantly on consumable material.
The next stage of the experiments will be electrolysis using vertically arranged electrodes on a relatively small unit with a current of 100 amperes. If successful, the project will be scaled up to semi-industrial tests. It is these tests that will give the final answer to the question of whether mankind will really be able to create a much more cost-effective technology for the production of metal in the foreseeable future and reduce its production cost many times over.
"The laboratory studies we have conducted really allow us to count on this. In particular, we expect that the power consumption of production in case of vertical electrode arrangement in electrolyzers will be reduced from the current 13.5 kWh per kilogram of aluminum to 11.5, i.e. it will be reduced by about 15%. In addition, the specific capital cost of construction will be reduced by 5-6 times. No less important is a sharp reduction in carbon dioxide emissions, their level may drop by up to 90%," emphasized Evgeny Gorlanov.
He specified that the effect of CO2 emission reduction is achieved due to the use of composite materials in the production of cathodes. In case of using so-called inert, i.e. low-consumption analogs instead of classical carbon anodes, this indicator will go to zero.
Scientists all over the world are now trying to create such an innovation from ceramics or various alloys, because its appearance would sharply reduce the anthropogenic impact on the environment. However, so far all research in this direction leads to a decrease in the cost-effectiveness of the process, primarily due to even higher energy consumption. So the emergence of carbon-neutral aluminum smelters is probably a much more distant prospect than the commissioning of advanced plants where the electrolysis process takes place in apparatuses with vertically arranged electrodes.