Red mud, also commonly called bauxite residue, is a waste product left over from the Bayer process, in which alumina is extracted from bauxite ore. Produced in mass quantities (estimates hover around 1-2 tons of red mud per ton of alumina produced), red mud has become an increasingly debated topic as of late, both for the problems it presents and for the problems it could potentially solve; concern over the environmental risks the caustic waste presents has been growing, but so has the body of research around the potential to recover metals from the red mud.
The ability to recover valuable metals from this industrial waste would be an environmental and economic win, helping to resolve a number of problems at once.
Factors Pushing the Recovery of Metals from Red Mud
There are many reasons why red mud is being examined as a potential source of metals:
An Increasing Demand for Metals
Efforts to reach a low-carbon economy have experts predicting a surge in demand for some metals. In a time when high ore grades are becoming extinct, this leaves many wondering, where will we get all of these materials.
This has prompted many in the industry to look for alternative sources of the metals, and in particular, where materials might currently be going to waste. This has increasingly resulted in an industry-wide trend of examining wastes that could serve as a secondary resource, thereby creating a more sustainable approach overall.
As a process by-product rich in some metals, many experts are wondering if red mud could be a part of the solution to the growing demand for metals.
Red Mud: An Industry Challenge
Red mud has long presented challenges to the aluminum industry; its caustic nature and the mass volumes in which it is produced make safe and economic management of the waste a constant challenge.
Current methods of disposal are far from ideal, taking up huge amounts of land, incurring significant disposal costs, and presenting long-term liabilities.
Furthermore, among the metals predicted to see increased consumption is aluminum. A recent World Bank report found that demand for aluminum could see as much as a near-1,200% spike in the energy storage market alone in the pursuit of a low-carbon economy.¹ This would likely mean an increase in production of red mud as well, making more sustainable management methods a growing priority.
Red Mud: An Environmental Risk
Part of the reason why red mud is so difficult to manage, is its caustic nature; red mud has a very high pH and contains a number of components that can pose a risk to the environment if not properly managed.
This is evident in the many catastrophes brought on by the failure of red mud containment ponds that have taken lives and devastated surrounding areas, perhaps the most famous of which, is the Ajka spill in western Hungary that occurred in 2010.
The ability to recover much-needed metals from red mud could play a part in alleviating all of the aforementioned issues.
Valuable Metals/Elements in Red Mud
While red mud is a major problem, it also contains a variety of metals that could be extracted. Some estimates say that red mud can contain as much as 64% Iron oxide (Fe2O3), 43% aluminum oxide (Al2O3), and 24% titanium dioxide (TiO2),² though it’s important to note that the composition of red mud varies significantly across sources.
Among the most dominant metals typically found in red mud that are being researched for recovery applications are:
Iron
Red mud is rich in iron (in the form of oxides and hydroxides), hence its infamous red color.
As a critical raw material, the recovery of iron from red mud has attracted a fair amount of attention, with several potential reuse opportunities available, including reuse in the sintering process of alumina production, use as pig iron, use in pigment applications, and more.
Aluminum
Despite having been processed via the Bayer process, there still remains a significant amount of aluminum components in red mud. As a material continuing to grow in importance, the ability to extract the remaining aluminum from red mud is a highly attractive endeavor.
Titanium
Titanium in the form of titanium dioxide (TiO2) may also be recovered from red mud. TiO2 is a diverse material widely used throughout a number of products as a pigment, even offering protection from UV rays, which has lent it to use in cosmetics and sunscreen products. It may also be used in more industrial applications as a pigment.
Rare Earths
Rare earth elements (REEs) are used in a wide array of applications, most notably in electronics, with consumption on the rise as technologies continue to advance; the unique properties of REEs make them irreplaceable in many applications.
Additionally, REEs (except for scandium), are defined as “critical” in relation to their economic importance and risk of supply by the European Commission. The challenges associated with economically obtaining rare earths, combined with their increasing demand, has many looking at all potential retrieval avenues.
Additional Materials
In addition to the major metals listed above, red mud also contains a number of more minor components that could offer potential value as well:3
- Silicon Dioxide (SiO2)
- Calcium Oxide (CaO)
- Sodium Oxide (Na2O)
- Potassium Oxide (K2O)
- Lithium Oxide (Li2O)
- Vanadium Pentoxide (V2O5)
- Zirconium Dioxide (ZrO2)
Extraction of scandium is also frequently examined.
An Industry in Progress
The recovery of metals from red mud is still very much in its infancy. While much research has been done, there is still a long way to go, and currently, very little of the available red mud is utilized in recovery/reuse applications.
Many approaches are being examined for recovering the various metals and components from bauxite residue, with methods typically being either hydrometallurgical, pyrometallurgical, or perhaps most commonly, a combination of the two.
In the recovery of iron, for example, a commonly investigated approach involves reduction roasting followed by magnetic separation.
Red mud samples shown at various stages of reduction during thermal testing in the FEECO Innovation Center
Depending on the source material and the intended process, a drying step is required prior to additional processing in many settings.
While most research has focused on targeting the removal of a specific component, many are beginning to look at a more integrated approach that provides a complete utilization of the valuable materials within red mud, which would provide the most economic value, assuming the economics of the process would remain manageable.
In addition to recovering metals and other materials from red mud, researchers are also focusing on the potential use of red mud as a pigment, an adsorbent in water treatment, and for use in construction and building materials.
Red Mud Testing Services
Amid all the R&D work, testing facilities that can accommodate red mud are getting to be in high demand. Bauxite sources and subsequent red mud can vary significantly, further emphasizing the need for comprehensive testing. This is evident in the FEECO Innovation Center, where inquiries around the material have increased, according to FEECO Process Sales Engineer, Alex Ebben.
“There is a huge push to find a better solution for red mud and producers are looking for facilities that can simulate the entire pyro-processing flowsheet and provide extensive data collection. People are excited when they hear that we can offer the testing capabilities they’re looking for.”
The Innovation Center is a testing facility that boasts a number of direct- and indirect-fired rotary kilns for batch/feasibility testing, as well as continuous pilot scale testing of red mud and other bauxite and alumina products.
Indirect-fired continuous kiln used for testing of red mud in the Innovation Center
Conclusion
Increasing demand for metals paired with the economic challenges and environmental risks presented by red mud are a growing concern in the path to a more sustainable future. However, the ability to recover metals from the caustic byproduct of the Bayer process could help to alleviate many of these issues. While there is still much work to be done, research and development around recovering metals (and other applications) from bauxite residue continue to grow, with testing facilities in high demand.
FEECO offers comprehensive thermal treatment testing options in the Innovation Center for bauxite, alumina, and red mud, whether you are looking to recover metals, find an alternative use for the material, or otherwise. Our thermal testing capabilities are complemented by our extensive agglomeration testing capabilities, data gathering and reporting system, as well as our experienced process design engineers and custom equipment designers.
Interested in testing your bauxite, alumina, or red mud in the Innovation Center? Contact us today!
Sources:
- The Growing Role of Minerals and Metals for a Low Carbon Future. Rep. Washington, DC: The World Bank Group, 2017. PDF.