The process of separating metals from other minerals and obtaining them in a pure form can be energy-intensive and lead to the creation of large volumes of toxic waste. However, a team of researchers from Germany has developed a method to address these issues for a specific class of mining waste generated during aluminum production. This method utilizes hydrogen and electricity, both of which can be obtained from renewable sources, to extract iron and potentially other metals from the waste. The resulting waste is less environmentally damaging, despite still being toxic.
After the isolation of aluminum oxide from the ore during aluminum production, a waste material known as red mud is left behind. This material contains iron oxides and other toxic materials, and due to its basic pH and toxic nature, it cannot be returned to the environment. The red mud is typically stored in containment ponds, which globally hold an estimated 4 billion tonnes of red mud. The high content of iron oxides in some locations makes red mud a potentially valuable source of iron.
The team from Germany conducted a test of green steel production on red mud by heating the material in an electric arc furnace under an atmosphere consisting mostly of argon and 10 percent hydrogen. This resulted in the rapid formation of metallic iron nodules, with the iron being remarkably pure at about 98 percent by weight. Additionally, small bits of relatively pure titanium were also formed in the mix.
The process significantly reduced the amount of red mud, and depending on the source of the original aluminum-containing ore, the remaining residue may contain relatively high concentrations of valuable materials such as rare earth minerals. However, the concentration of any toxic materials in the original ore would also be higher. The process also neutralized the pH of the remaining residue.
While the process is energy-intensive and economically challenging due to the cost of energy, it offers low carbon emissions, making it environmentally friendly. This aspect of the process is particularly valuable, despite the current lack of economic incentives related to low carbon emissions in most countries.
