Green steel might be produced from aluminum mining waste
The metals that support contemporary civilization also give rise to a host of issues. The process of separating the desired metals from other minerals is frequently energy-intensive and can produce significant amounts of hazardous waste. Purifying them frequently necessitates a second, significant energy input, increasing the corresponding carbon emissions.
Now, a German research team has developed solutions for some of these issues with regard to a particular kind of mining waste generated during the manufacture of aluminum. Their process removes iron and maybe other metals from the waste and depends on hydrogen and electricity, both of which can be obtained from renewable energy sources. The residue that remains might still be hazardous, but it won’t harm the ecosystem as much.
From the muck
Separating aluminum oxide from the other components of the ore is the first stage in the manufacturing of aluminum. This results in the production of red mud, of which an estimated 200 million tons are produced annually. Iron oxides give it its red color, but it also contains a variety of other substances, some of which may be hazardous. Furthermore, the substance has an extremely basic pH when the aluminum oxide is isolated.
Because of all these characteristics, red mud usually cannot be returned to the environment, or at least shouldn’t. It is often stored in containment ponds, which are thought to hold 4 billion tonnes of red mud worldwide. Over time, many of the containment pods have ruptured.
In certain places, the iron oxides can make up more than half the weight of red mud, suggesting that it could be a valuable supply of iron. Carbon dioxide has been released during the processing of iron ores using traditional methods. However, attempts have been made to produce “green steel” production, where water is the main byproduct and a reaction with hydrogen takes the place of this stage. This has the potential to reduce a significant portion of the carbon emissions related to the manufacturing of iron as hydrogen may be produced from water using renewable electricity.
The German team made the decision to test a green steel production technology on red mud. In an electric arc furnace, they heated a portion of the material in an environment primarily composed of argon (which is non-reactive) and hydrogen (10% of the mixture).
The response came quite quickly. Metallic iron nodules began to form in the mixture in a matter of minutes. By ten minutes or so, the iron was almost completely produced. With iron making up roughly 98% of the nodules’ weight, the iron was unusually pure.
Due to the method, a 15-gram sample of red dirt was reduced to 8.8 grams since a large amount of the material’s oxygen was released as water. (It’s important to remember that this water might be recycled to produce hydrogen again, completing the cycle on this part of the process.) Approximately 2.6 (30%) of those 8.8 grams were iron.
The investigation revealed that some tiny fragments of comparatively pure titanium have also developed in the mixture. Thus, there’s a chance that this can be used to produce other metals, however optimizing the process would likely be necessary to increase the yield of any metal other than iron.
The good news is that following this, red mud becomes considerably less of a concern. Certain portions of this might include comparatively high concentrations of valuable materials, like rare earth minerals, depending on where the original aluminum-containing ore came from. The drawback is that the concentration of any hazardous elements in the original ore will be much higher.
Additionally, the procedure balances the pH of the leftover residue, which is a little benefit. That means you have one less thing to worry about, at least.
The drawback is that the procedure uses a lot of energy, both to power the arc furnace and produce the necessary hydrogen. Things become difficult financially because of the cost of that electricity. The lower processing costs are partially countered by the fact that the ore has already been collected and is reasonably pure.
However, the incredibly low carbon emissions are the salient element of this. The majority of countries do not now charge for those, which makes the economics of this procedure much more challenging.