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| Fig. 1: Red Mud - the primary byproduct of alumina extraction from bauxite. (Source: Wikimedia Commons) |
Red mud, also known as bauxite residue, is an insoluble byproduct generated from the extraction of alumina from bauxite during the Bayer process (Fig. 1), a crucial step in the manufacturing of aluminum. Highly alkaline and difficult to deal with, red mud presents a significant environmental hazard, especially when spilled out of the clay-lined impounds designed to contain it, as in the 2010 case of Ajka in Hungary. [1] Neutralization techniques such as the application of mineral acids, coating with coal dust, and sintering with silicate material have been used to mitigate some of the other negative effects of red mud in the environment. [2] One aspect of the risk of Red mud which has been ignored, however, is its radiation.
Through the use of thermal and epithermal neutron activation analysis - advanced techniques used to determine the radiation properties of a given material - scientists have studied the nuclear properties of red mud. In addition to the more traditional environmental risks listed above, nuclear radiation dosing could present another disastrous property of red mud which further dictates how carefully it should be stored. [3] While the average person is exposed to approximately 50 mSv per year, a worker consistently exposed to red mud would receive an additional dosage of several mSv per year. However, this additional exposure (Fig. 2) would likely not pose significant health risks, according to researchers. [3]
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| Fig. 2: Radiation Warning - although red mud does contain several radioactive isotopes, it is not a significant environmental concern when compared with the other dangerous characteristics of the material. (Source: Wikimedia Commons) |
As opposed to significant nuclear disasters, such as that at the Chernobyl nuclear plant in 1986, red mud is a relatively low risk in terms of environmental radiation. [4] In fact, the radiation exposure for those simply living in Eastern Europe during the time of the Chernobyl Power Plant accident were approximately 50 times higher than that which a worker would receive with 2000 hours of exposure annually to a red mud field. Despite this, the radiation levels from red mud - which includes U-238 and Th-232 each with radiation in the hundreds of Becquerels per kilogram (Bq/kg) - are still not acceptable in many countries, including the United States. [5] While red mud or similar materials may be included in building materials in developing countries, efforts are being undergone to reduce the radiation levels of red mud to acceptable levels in developed countries. [6]
The occurrence of alpha decay, beta decay, and isomeric gamma transitions result in somewhat high radioactivity in red mud, which can accumulate and contaminate the environment, including water sources. [6] By forming glass network structure to reduce the velocity of radiation particles - in other words, to absorb some of the high-energy from these particles - researchers were able to significantly reduce the risk that red mud radiation poses to humans and the environment.
While the radiation from red mud may pale in comparison to that of a significant nuclear disaster like Chernobyl, the radioactivity levels cannot simply be ignored. While the average radioactivity of ocean water, for example, is 14 Bq/kg, red mud is more than two orders of magnitude more potent, including the more dangerous variety of radiation, gamma radiation. [7,8]
© Wyatt Pontius. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] W. M. Mayes et al., "Advances in Understanding Environmental Risks of Red Mud After the Ajka Spill, Hungary," J. Sustain. Metall. 2, 332 (2016).
[2] S. Rai, K.L. Wasewar, and A. Agnihotri, "Treatment of Alumina Refinery Waste (Red Mud) Through Neutralization Techniques: A Review," Waste Manage. Res. 35, 563 (2017).
[3] S. Landsberger et al., "Characterization of Bauxite Residue (Red Mud) for U-235, U-238, Th-232 and K-40 Using Neutron Activation Analysis and the Radiation Dose Levels as Modeled by MCNP," J. Environ. Radioactiv. 173, 97 (2017).
[4] "Radiation Levels: WHO Reports on Chernoby,l" IAEA Bull. 28, No. 3, 27 (Autumn 1986).
[5] M. O. Miller and D. A. Miller, "The Technological Enhancement of Normally Occurring Radioactive Materials in Red Mud due to the Production of Alumina," Int. J. Spectroscopy 2016, 4589460 (2016).
[6] S. Qin and B. Wu, "Reducing the Radiation Dose of Red Mud to Environmentally Acceptable Levels as an Example of Novel Ceramic Materials," Green Chem. 13, 2423 (2011).
[7] J. Chen, "Evaluation of Radioactivity Concentrations From the Fukushima Nuclear Accident in Fish Products and Associated Risk to Fish Consumers," Radiat. Prot. Dosim. 157, 1 (2013).
[8] B. H. O'Connor et al., "Radiological Assessment for Bauxite Mining and Alumina Refining," Ann. Occup. Hyg. 57, 63 (2013).
