Red mud

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(Redirected from
Bauxite tailings
)
For the tannin used in drilling mud, see Quebracho tree.
Red mud near Stade (Germany)
iron oxides
that make up the main part of the red mud.

Red mud, now more frequently termed bauxite residue, is an industrial waste generated during the processing of bauxite into alumina using the Bayer process. It is composed of various oxide compounds, including the iron oxides which give its red colour. Over 95% of the alumina produced globally is through the Bayer process; for every tonne of alumina produced, approximately 1 to 1.5 tonnes of red mud are also produced. Annual production of alumina in 2020 was over 133 million tonnes resulting in the generation of over 175 million tonnes of red mud.[1]

Due to this high level of production and the material's high alkalinity, if not stored properly, it can pose a significant environmental hazard. As a result, significant effort is being invested in finding better methods for safe storage and dealing with it such as waste valorization in order to create useful materials for cement and concrete.[2]

Less commonly, this material is also known as bauxite tailings, red sludge, or alumina refinery residues.

Production

Red mud is a side-product of the Bayer process, the principal means of refining bauxite en route to alumina. The resulting alumina is the raw material for producing aluminium by the Hall–Héroult process.[3] A typical bauxite plant produces one to two times as much red mud as alumina. This ratio is dependent on the type of bauxite used in the refining process and the extraction conditions.[4]

More than 60 manufacturing operations across the world use the

calcined
(heated) at over 1000 °C in rotary kilns or fluid flash calciners to produce aluminium oxide (alumina).

The alumina content of the bauxite used is normally between 42 and 50%, but ores with a wide range of alumina contents can be used. The aluminium compound may be present as gibbsite (Al(OH)3), boehmite (γ-AlO(OH)) or diaspore (α-AlO(OH)). The residue invariably has a high concentration of iron oxide which gives the product a characteristic red colour. A small residual amount of the sodium hydroxide used in the process remains with the residue, causing the material to have a high pH/alkalinity, normally >12. Various stages of solid/liquid separation processes recycle as much sodium hydroxide as possible from the residue back into the Bayer Process, in order to reduce production costs and make the process as efficient as possible. This also lowers the final alkalinity of the residue, making it easier and safer to handle and store.

Composition

Red mud is composed of a mixture of solid and

silica, unleached residual aluminium compounds, and titanium oxide.[6]

The main constituents of the residue after the extraction of the aluminium component are insoluble metallic oxides. The percentage of these oxides produced by a particular alumina refinery will depend on the quality and nature of the bauxite ore and the extraction conditions. The table below shows the composition ranges for common chemical constituents, but the values vary widely:

Chemical Percentage composition
Fe2O3 5–60%
Al2O3 5–30%
TiO2 0–15%
CaO 2–14%
SiO2 3–50%
Na2O 1–10%

Mineralogically expressed the components present are:

Chemical name Chemical formula Percentage composition
Sodalite 3Na2O⋅3Al2O3⋅6SiO2⋅Na2SO4 4–40%
Cancrinite Na3⋅CaAl3⋅Si3⋅O12CO3 0–20%
Aluminous-goethite (aluminous iron oxide) α-(Fe,Al)OOH 10–30%
Hematite (iron oxide) Fe2O3 10–30%
Silica
(crystalline & amorphous)		 SiO2 5–20%
Tricalcium aluminate 3CaO⋅Al2O3⋅6H2O 2–20%
Boehmite AlO(OH) 0–20%
Titanium dioxide TiO2 0–10%
Perovskite CaTiO3 0–15%
Muscovite K2O⋅3Al2O3⋅6SiO2⋅2H2O 0–15%
Calcium carbonate CaCO3 2–10%
Gibbsite Al(OH)3 0–5%
Kaolinite Al2O3⋅2SiO2⋅2H2O 0–5%

In general, the composition of the residue reflects that of the non-aluminium components, with the exception of part of the silicon component: crystalline silica (quartz) will not react but some of the silica present, often termed, reactive silica, will react under the extraction conditions and form sodium aluminium silicate as well as other related compounds.

Environmental hazards

Discharge of red mud can be hazardous environmentally because of its alkalinity and species components.

Until 1972, Italian company Montedison was discharging red mud off the coast of Corsica.[7] The case is important in international law governing the Mediterranean sea.[8]

In October 2010, approximately one million cubic meters of red mud slurry from an

alumina plant near Kolontár in Hungary was accidentally released into the surrounding countryside in the Ajka alumina plant accident, killing ten people and contaminating a large area.[9] All life in the Marcal river was said to have been "extinguished" by the red mud, and within days the mud had reached the Danube.[10] The long-term environmental effects of the spill have been minor after a €127 million remediation effort by the Hungarian government.[11]

Residue storage areas

Residue storage methods have changed substantially since the original plants were built. The practice in early years was to pump the slurry, at a concentration of about 20% solids, into lagoons or ponds sometimes created in former bauxite mines or depleted quarries. In other cases, impoundments were constructed with dams or levees, while for some operations valleys were dammed and the residue deposited in these holding areas.[12]

It was once common practice for the red mud to be discharged into rivers, estuaries, or the sea via pipelines or barges; in other instances the residue was shipped out to sea and disposed of in deep ocean trenches many kilometres offshore. From 2016, all disposal into the sea, estuaries and rivers was stopped.[13]

As residue storage space ran out and concern increased over wet storage, since the mid-1980s dry stacking has been increasingly adopted.[14][15][16][17] In this method, residues are thickened to a high density slurry (48–55% solids or higher), and then deposited in a way that it consolidates and dries.[18]

An increasingly popular treatment process is filtration whereby a

amphirols
to dewater the material once deposited and then 'conditioned' using farming equipment such as harrows to accelerate carbonation and thereby reduce the alkalinity. Bauxite residue produced after press filtration and 'conditioning as described above are classified as non-hazardous under the EU Waste Framework Directive.

In 2013

Vedanta Aluminium, Ltd. commissioned a red mud powder-producing unit at its Lanjigarh refinery in Odisha, India, describing it as the first of its kind in the alumina industry, tackling major environmental hazards.[20]

Use

Since the

soil acidity, landfill capping and carbon sequestration.[25][26]

Reviews describing the current use of bauxite residue in Portland cement clinker, supplementary cementious materials/blended cements and special calcium aluminate cements (CAC) and calcium sulfo-aluminate (CSA) cements have been extensively researched and documented.[27]

  • Cement manufacture, use in concrete as a supplementary cementitious material. From 500,000 to 1,500,000 tonnes.[28][29]
  • Raw material recovery of specific components present in the residue: iron, titanium, steel and REE (rare-earth elements) production. From 400,000 to 1,500,000 tonnes;
  • Landfill capping/roads/soil amelioration – 200,000 to 500,000 tonnes;[23]
  • Use as a component in building or construction materials (bricks, tiles, ceramics etc.) – 100,000 to 300,000 tonnes;
  • Other (refractory, adsorbent, acid mine drainage (Virotec), catalyst etc.) – 100,000 tonnes.[30]
  • Use in building panels, bricks, foamed insulating bricks, tiles, gravel/railway ballast, calcium and silicon fertilizer, refuse tip capping/site restoration,
    desulfurisation of flue gas, arsenic removal, chromium removal.[31]

In 2015, a major initiative was launched in Europe with funds from the European Union to address the valorization of red mud. Some 15 Ph.D. students were recruited as part the European Training Network (ETN) for Zero-Waste Valorisation of Bauxite Residue.[32] The key focus will be the recovery of iron, aluminium, titanium and rare-earth elements (including scandium) while valorising the residue into building materials. A European Innovation Partnership has been formed to explore options for using by-products from the aluminium industry, BRAVO (Bauxite Residue and Aluminium Valorisation Operations). This sought to bring together industry with researchers and stakeholders to explore the best available technologies to recover critical raw materials but has not proceeded. Additionally, EU funding of approximately Euro 11.5 million has been allocated to a four-year programme starting in May 2018 looking at uses of bauxite residue with other wastes, RemovAL. A particular focus of this project is the installation of pilot plants to evaluate some of the interesting technologies from previous laboratory studies. As part of the H2020 project RemovAl, it is planned to erect a house in the Aspra Spitia area of Greece that will be made entirely out of materials from bauxite residue.

Other EU funded projects that have involved bauxite residue and waste recovery have been ENEXAL (ENergy-EXergy of ALuminium industry) [2010–2014], EURARE (European Rare earth resources) [2013–2017] and three more recent projects are ENSUREAL (ENsuring SUstainable ALumina production) [2017–2021], SIDEREWIN (Sustainable Electro-winning of Iron) [2017–2022] and SCALE (SCandium – ALuminium in Europe) [2016–2020] a 7 million Euro project to look at the recovery of scandium from bauxite residue.

In 2020, the International Aluminium Institute, launched a roadmap for maximising the use of bauxite residue in cement and concrete.[33][34]

In November 2020, The ReActiv: Industrial Residue Activation for Sustainable Cement Production research project was launched, this is being funded by the EU. One of the world's largest cement companies, Holcim, in cooperation with 20 partners across 12 European countries, launched the ambitious 4 year ReActiv project (reactivproject.eu). The ReActiv project will create a novel sustainable symbiotic value chain, linking the by-product of the alumina production industry and the cement production industry. In ReActiv modification will be made to both the alumina production and the cement production side of the chain, in order to link them through the new ReActiv technologies. The latter will modify the properties of the industrial residue, transforming it into a reactive material (with pozzolanic or hydraulic activity) suitable for new, low CO2 footprint, cement products. In this manner ReActiv proposes a win-win scenario for both industrial sectors (reducing wastes and CO2 emissions respectively).

Fluorchemie GmbH have developed a new flame-retardant additive from bauxite residue, the product is termed MKRS (modified re-carbonised red mud) with the trademark ALFERROCK(R) and has potential applicability in a wide range of polymers (PCT WO2014/000014). One of its particular benefits is the ability to operate over a much broader temperature range, 220 – 350 °C, that alternative zero halogen inorganic flame retardants such as aluminium hydroxide, boehmite or magnesium hydroxide. In addition to polymer systems where aluminium hydroxide or magnesium hydroxide can be used, it has also found to be effective in foamed polymers such as EPS and PUR foams at loadings up to 60%.

In a suitable compact solid form, with a

thermal capacity in the range of 0.6 – 0.8 kJ/(kg·K) at 20 °C and 0.9 – 1.3 kJ/(kg·K) at 726 °C; this enables the material to work effectively in energy storage device to maximise the benefits of solar power, wind turbines and hydro-electric systems. High strength geopolymers have been developed from red mud.[35]

Sustainable Approach to Low-Grade Bauxite Processing

The IB2 process is a French technology developed to enhance the extraction of alumina from bauxite, especially low-grade bauxite. This method aims to boost alumina production efficiency while decreasing the environmental impacts typically linked with this process, notably the generation of red mud and carbon dioxide emissions.

The IB2 technology, patented in 2019 [1], is the outcome of a decade of research and development efforts by Yves Occello, a former Pechiney chemist. This process provides an alternative to the Bayer process, which has been utilized for more than a century to extract alumina from bauxite. It presents a significant decrease in caustic soda consumption and a notable reduction in red mud output, thereby minimizing hazardous waste and environmental risks.

In addition to reducing red mud production, the IB2 process aids in lowering CO2 emissions, primarily through the optimized treatment of low-grade bauxite. By limiting the necessity to import high-grade bauxite, this process reduces the carbon footprint associated with ore transportation. Furthermore, the process yields a byproduct that can be utilized in the production of eco-friendly cements, promoting the concept of a circular economy.[36]

See also

References

  1. ^ Annual statistics collected and published by World Aluminium.
  2. doi:10.1007/s40831-016-00060-x
    .
  3. ^
    ISBN 978-3-8027-2936-2
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  4. ^
    ISBN 978-0-8155-1393-3
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  5. ^
    ISBN 978-0-87335-233-8.{{cite book}}: CS1 maint: numeric names: authors list (link
    )
  6. doi:10.1557/mrs2001.119
  7. ^ Crozier, Jean (17 February 2013). "Le long combat contre la pollution de la Méditerranée par la Montedison". France 3 Corse ViaStella (in French). Retrieved 4 January 2019.
  8. ^ Huglo, Christian. "Le recours au juge est la garantie de conservation de l'intégralité de la règle environnementale". Actu-Environnement (in French). Retrieved 4 January 2019.
  9. ^ Gura, David (5 October 2010). "Toxic Red Sludge Spill From Hungarian Aluminum Plant 'An Ecological Disaster'". NPR.org. National Public Radio. Retrieved 5 January 2019.
  10. ^ "Hungarian chemical sludge spill reaches Danube". BBC News. 7 October 2010. Retrieved 3 February 2021.
  11. ^ "Hungarian red mud spill did little long-term damage". Retrieved 14 December 2018.
  12. ISBN 9781118359259
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  13. doi:10.1016/j.hydromet.2011.02.006
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  14. ^ B. G. Purnell, “Mud Disposal at the Burntisland Alumina Plant”. Light Metals, 157–159. (1986).
  15. ^ H. H. Pohland and A. J. Tielens, “Design and Operation on Non-decanted Red Mud Ponds in Ludwigshafen”, Proc. Int. Conf. Bauxite Tailings, Kingston, Jamaica (1986).
  16. ^ E. I. Robinsky, “Current Status of the Sloped Thickened Tailings Disposal System”, Proc. Int. Conf. Bauxite Tailings, Kingston, Jamaica (1986).
  17. ^ J. L. Chandler, “The Stacking and Solar Drying Process for disposal of bauxite tailings in Jamaica”, Proc. Int. Conf. Bauxite Tailings, Kingston, Jamaica (1986).
  18. ^ "Bauxite Residue Management: Best Practice" (PDF). World Aluminum. Retrieved 5 January 2019.
  19. ^ K. S. Sutherland, "Solid/Liquid Separation Equipment", Wiley-VCH, Weinheim (2005).
  20. ^ "Vedanta commissions red mud powder plant in Odisha". Business Line. 19 November 2013.
  21. doi:10.1016/j.resconrec.2006.03.003
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  22. ^ Y. Pontikes and G. N. Angelopoulos "Bauxite residue in Cement and cementious materials", Resourc. Conserv. Recyl. 73, 53-63 (2013).
  23. ^ a b W.K.Biswas and D. J. Cooling, "Sustainability Assessment of Red Sand as a substitute for Virgin Sand and Crushed Limestone", J. of Ind. Ecology, 17(5) 756-762 (2013).
  24. doi:10.1016/j.minpro.2009.08.005
  25. ^ "Bauxite Residue Management". bauxite.world-aluminium.org. The International Aluminium Institute. Retrieved 9 August 2016.
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  27. ^ "Mining and Refining – Bauxite Residue Utilisation". bauxite.world-aluminium.org. Retrieved 2019-10-04.
  28. ^ Y. Pontikes and G. N. Angelopoulos "Bauxite residue in Cement and cementious materials", Resourc. Conserv. Recyl. 73, 53–63 (2013).
  29. ^ Y. Pontikes, G. N. Angelopoulos, B. Blanpain, "Radioactive elements in Bayer’s process bauxite residue and their impact in valorization options", Transportation of NORM, NORM Measurements and Strategies, Building Materials, Advances in Sci. and Tech, 45, 2176–2181 (2006).
  30. ^ H. Genc¸-Fuhrman, J. C. Tjell, D. McConchie, "Adsorption of arsenic from water using activated neutralized red mud", Environ. Sci. Technol. 38 (2004) 2428–2434.
  31. ^ B. K. Parekh and W. M. Goldberger, "An assessment of technology for the possible utilisation of Bayer process muds", published by the U. S. Environmental Protection Agency, EPA 600/2-76-301.
  32. ^ "Project | European Training Network for Zero-Waste Valorisation of Bauxite Residue (Red Mud)".
  33. ^ "Technology Roadmap - Maximizing the use of Bauxite Residue in Cement". International Aluminium Institute. 2021-06-22. Retrieved 2023-05-25.
  34. ^ "Mining and Refining – Bauxite Residue Utilisation". bauxite.world-aluminium.org. Retrieved 2019-10-04.
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  36. ^ "IB2 Secures 8 Million Euro Investment from Otium Capital to Further Green Industrial Technology". Yahoo Finance. 2024-02-16. Retrieved 2024-02-27.

Sources

External links
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