The looming threat of environmental contamination, climate change, and a growing need for raw materials has given way to a new age in how the world views and manages waste.
As the population puts a strain on existing resources, never before has it been more important to see wastes in a new light – to reuse or recover materials from “wastes” – transforming them into raw materials that can be reused anew.
In an effort to highlight the ongoing research into sustainable reuse and recovery of waste materials, we will be highlighting new research around a specific topic each month. This month, we are showcasing research focused on utilizing red mud, an aluminum industry by-product, in construction materials.
Red Mud: The Risks
Red mud, also referred to as bauxite residue, is an industrial by-product of aluminum production.
The highly caustic nature of red mud, combined with the vast quantities in which it is produced make it a constant challenge to effectively and safely manage. Historically, the method of managing red mud has been to store it in containment ponds, but this approach is far from perfect; the waste is responsible for devastating a number of areas after containment pond failures. This method of waste management also takes up large sections of land and can pose a variety of additional environmental risks as well.
This, along with the increasing demand for aluminum (and subsequent increased production of red mud) has prompted a growing body of research around beneficial reuse and recovery applications for red mud – one of which, is the reuse of red mud in construction materials.
Red Mud in Construction Materials
The reuse of red mud in construction materials would be a multi-faceted advantage; not only would it mitigate the risks associated with storing red mud, but it would also reduce the construction industry’s dependence on mined raw materials. As mining is an energy-intensive endeavor, the benefits would be further compounded by the savings in energy.
The case for reusing red mud is not without challenge – the toxic nature of the mud has served as a barrier to reuse. And while more research is needed, recent studies have brought to light the promising potential for red mud to be reused in a variety of applications within the construction industry. In addition to providing an outlet for mass quantity utilization of red mud, studies have found that in many cases, red mud can even offer improvements to the end product.
Red mud has been explored for use in a number of applications within the construction industry. Below are some highlights from the most recent research:
General Construction Applications
A recent literature review conducted by Vijaya et al. looked at some of the more common reuse opportunities researchers have thus far examined. Among them:
- Cement Production (including clinkers, composite cements, and alkali-activated cements)
- Pigment in Concrete and Brick
- Road Base
- Embankment Material
- Backfill Material
Another literature review examined studies focusing on the use of red mud in ceramic products and summarized that researchers have discovered a number of benefits to this potential application, including the potential to decrease sintering temperatures and reduce energy requirements, and also to improve the resistance of ceramic materials.
Use in Porous Asphalt
A recent study looked at the replacement of limestone powder with red mud in porous asphalt. Porous asphalt is a special type of asphalt employed for the many benefits it can provide. And while the porosity offers many advantages, it can also make the structure more susceptible to wear.
The study, carried out by Zhang et al., found that when red mud was used as an alternative filler to limestone powder, the resulting porous asphalt exhibited improved resistance to wear such as rutting and raveling.
Use in Interlocking Blocks
Researchers in India, where there is a substantial aluminum industry, studied red mud for its use in interlocking blocks – an important material in Indian construction. Using 20-40% red mud as part of the brick’s makeup, researchers anticipate that bricks composed in part by red mud would reduce the weight of structures, ultimately reducing building and foundation costs. A number of other structure-related benefits are anticipated as well, including increased resistance to earthquakes, reduced energy use, improved acoustics, and more.
Coarse Bauxite Residue in Australia
The unique makeup of bauxite derived from Australia’s Darling Range presents an added challenge to red mud reuse. The high quartz content of the bauxite results in increased particle size of the waste material derived from alumina production – subsequently referred to as coarse bauxite residue.
The country, one of the world’s largest bauxite producers, has long struggled with management of the waste. A study aimed at using the coarse bauxite residue in road base material found that when modified with a specific pozzolanic-stabilized mixture (PSM) of fly ash and lime kiln dust, the material actually provided an improved road base over that of conventional materials.
In short, not only would this approach provide an outlet for the mass quantities of coarse bauxite residue the country produces, but it would also help to improve roadways and reduce construction costs. Additionally, the PSM formulated in the study would provide an outlet for other waste streams in the region (fly ash and lime kiln dust), further increasing the sustainability of the approach.
Challenges to Red Mud Utilization
The reuse of red mud presents a number of challenges that must be overcome while still allowing the intended process to be economic.
The composition of red mud can vary significantly and often contains trace heavy metals, but perhaps the most challenging aspect standing in the way of red mud reuse is its high alkalinity.
Depending on the application, this often requires that the material be neutralized first, by one of many methods. Unfortunately, a neutralization method that does not present additional environmental risks and is cost effective has largely eluded the industry. However, a recent study has found a potential alternative to previously employed neutralization techniques.
In their study, Characterization of red mud as a structural fill and embankment material using bioremediation, Panda et al. experimented with neutralizing red mud with other organic wastes such as cheese whey, sugar molasses, and rice water.
While the study was carried out in a lab setting using a single source of red mud, the results look promising; the use of organic wastes to neutralize red mud would provide a cost-effective neutralization approach, while also providing an additional outlet for other organic waste streams.
Conclusion
The increasing demand for aluminum, coupled with the significant environmental risks storage of red mud can pose has prompted a wave of research around beneficial reuse opportunities over the last several years. One area of focus has been the application of red mud in the construction industry.
Recent research has highlighted the potential for this promising opportunity. And although more research is needed, if the barriers to reuse can be overcome, the construction industry would provide a much-needed outlet for the utilization of red mud in significant quantities. This would help to mitigate issues surrounding the management of red mud and would also reduce the construction industry’s need to mine raw materials, even reducing costs and improving products in some cases.
FEECO offers a unique testing facility, The Innovation Center, where we can test hundreds of materials at batch and pilot scale. This includes advanced thermal testing of red mud for recovery and/or reuse applications, with a variety of test kilns and support equipment available. For more information, contact us today!