The global primary Aluminium industry has been constantly reeling under pressure with accusations of environmental pollution and carbon emission. At every stage of aluminum production, starting from open cast Bauxite mining to caustic soda leach Bayer’s Alumina refining process to the fluoride fused salt electrolytic process of aluminium smelting; there are a large number of environmental degradation issues involved. However, global aluminium industry has been since long making serious attempts to improve its status in this regard.
A major problem of pollution from Aluminium industry begins with the Bayer process of refining of Bauxite to produce Alumina. The slurry insoluble waste produced during the Bayer process is referred as Red Mud. It is a mixture of non- alumina compounds originally present in the parent mineral, bauxite, and of compounds formed or introduced during the Bayer process cycle. It is disposed as a slurry having a solid concentration in the range of 25- 55 % ( high caustic containing water content), pH in the range of 13 and high ionic strength. Red Mud also contains insoluble chemicals like silica, alumina, iron, calcium, titanium oxides, as well as many other minor and rare earth compounds.
The disposal of red mud remains an environmental concern all around in the alumina- aluminium producing countries. With other process residues (Caustic soda, lime etc.) and impurities added up, the amount of red mud getting generated continuously is around 2-2.5 Tons per ton of alumina and twice that amount for every ton of aluminium metal produced. Thus, a 3 million TPA alumina refinery would generate 6-7 million tons of red mud per annum and over its average life span of 50 years, produce around 300-350 million tons of this environment unfriendly material.
The most common process of red mud disposal is dumping it into secured large inland artificial ponds, which is known as Closed Cycle Disposal system. If red mud with its highly alkaline content is disposed as it is, on land or its leach water overflows from its disposal ponds due to leakage or landslide on the banks, or due to heavy tropical rains, severe damage could be caused to water bodies, grass lands and vegetation. The problem can be minimized by washing and filtering the red mud repeatedly, evaporating the liquid and putting back the thickened slurry in the same pond after using clay beds of up to 300-400 mm thickness at the bottom and , and most of the modern day alumina refineries have adopted this process. Still red mud ponds turn out to be a threat during heavy monsoon when the sludge can overflow and damage the nearby areas with toxic substances.
Another major and limiting issue of Alumina refinery has been the availability of land to build large red mud disposal plant. An old ‘thumb rule’ stated that in the operation of a 1 million TPA plant for 5 years, 1 square Km. of land is lost forever. This problem may have been contained to some extent using thickened slurry disposal system in the modern plants but it does continue to be a serious issue in designing alumina plants in high population density and inland alumina refineries.
Recent studies have shown that the caustic soda content of the red mud reacts with the clay over decades and finally zeolites form through a complex reaction mechanism which could ultimately destroy the embankments of the abandoned red mud ponds and the aqua system around. This has raised serious alarm for the older alumina refinery works where abandoned red mud ponds have existed since over 50 years.
Another process of red mud disposal is Direct Disposal into the Sea under which process, the sea water dilutes neutralizes the causticity of the red mud and the iron oxide released into sea water helps the marine life algae, corals and other crawling life system grow at a faster rate. Many of the shore based alumina refineries in the world are continuing with this form of red mud disposal system despite occasional agitations by the environmentalists. Interestingly, the best supporters of this form of disposal system are the fishermen of the region.
The 3rd and improved solution is the Dry Disposal Method in which the wet slurry undergoes several stages of filtration and water is separated from it. After that, the dry mud is disposed of as pyramids or dumped at the pond side. The dry mud is covered by cotton soil and requires regular water sprinkling to prevent the metallic dust from polluting the air, live stock and crops around.
Attempts are also on to use the red mud in bulk for producing ferretic cements and also for iron extraction, which expect to utilize the waste in a more productive manner.
As such, the potential danger to human health and environment from red mud is limited. The red mud is considered toxic primarily due to its high alkaline content and presence of heavy metals. As red mud is generated by chemical extraction of alumina from bauxite it has typically twice the concentration of natural radio-nuclides found in bauxite. Therefore, Red Mud may contain Technologically Enhanced Naturally Occurring Radioactive Material (TENORM). However, the count depends on the quality of bauxite ore from which alumina is extracted and the process of disposal.
Except for the Red Mud issue, alumina refineries are now being designed and operated as zero effluent plants, near total recycling of water and efficient dust collection systems. Dust collection from calcification process and mechanical losses during handling is also a major issue since Alumina powder has the characteristics of flowing like ‘water’ or flying like ‘gas’!
Red Mud disposal still remains a major environmental issue in alumina production and the world wide aluminium industry has been constantly trying to find a viable and permanent solution to dispose and reuse the red mud produced enormously during alumina extraction.
Reference:
“The Realities and Myths of Industrial pollution – The case of Aluminium Industry”–By: B.S.Pani
Unfortunate that nobody speaks about red mud remediation by the Canadian company Orbite Aluminae.
http://www.orbitealuminae.com/en/news/press-releases/canadian-company-offers-first-treatment-neutralize-red-mud/
Your post, Red Mud Disposal: The Ecological Concern of Alumina Refining | Aluminium Circlel, is really well written and insightful. Glad I found your website, warm regards!
This is a good article, well comprehended and summarized. Still the concern remains relating to disposal of red mud from alumina refineries. I have heard about experiments going on to check that whether it is possible to carry out some plantation activities at the red mud pond. If this happens to be successful then much of the problem definition would get addressed.
Hi Ms. Beethika Biswas,
We appreciate your efforts in publishing structured article on Red mud.The Red mud generation data indicated in the 3rd para of your article as 2.0 to 2.5 tonnes per tonne of alumina is totally incorrect. It generally varies from 1.15 to 1.25 tonnes per tonne of alumina. The refinery generating 2.0 to 2.5 tonnes of Red mud per tonne of alumina can be termed as Red Mud Plant in place of Alumina Plant. We never expect incorrect data from a Content Editor like you. Request to check and cross check the data / information from competent people before publishing any technical article as it may hurt the sentiments of Alumina Experts.
Thanks and best regards.
Kunwar Rajendra
Thank you for taking interest and offering your valuable comments on the mentioned blog. We apologize if any information that we gave has gone against the recorded data. However, we would like to add that the information was based on data received from our sources from Bauxite- Alumina industry professionals.
We have re-checked our figures which we had received from Bauxite- Alumina industry professionals.
We are told that:
The recoverable alumina from a 42% +/- 2 % – 90% gibbsitic alumina is around 35-36% of the overall weight of Bauxite (Dry basis). Therefore 65-66% of bauxite goes off as red mud. Which works out to 1.95 T per ton of Alumina produced. To this gets added caustic and lime contamination. Therefore, we are told that the thumb rule in the industry is of considering 2-2.5 tons as the weight of ‘Red Mud’ generation per ton of Alumina produced from +90% gibbsitic – 38-40-42% Al2O3 bauxite through atmospheric pressure low temperature digestion route. Obviously, with richer alumina and higher pressure & temp digestion, the alumina recovery rate would be higher and the red mud generation rate too would be consequentially lower.
We have also referred to http://www.redmud.org/Files/banvolgyi040110.pdf for red mud related data in this blog.
However – should you have further views on this stoichiometric balance that we followed, we would be more than happy to publish it on our blog section.
Please, keep posting your valuable feedback on our other blogs too.
Hi madam, Iam persuing MTech at NIT Bhopal and i want to do project on redmud. please suggest me in which area i can do a better research work which helps me to continue even for PhD.
thanking you
I need this Paper “The Realities and Myths of Industrial pollution – The case of Aluminium Industry”–By: B.S.Pani, can anyone help me.
We have successfully completed tests on tyre pyrolisis waste and are opening a pilot plant in the UK. The first of its type in the world. Tests have been completed and not limited to. Compression. Tensile. Acoustic. Fire and leaching have been done on the products made with this industrial waste.
Our core products are made in the majority with Cement or on occasions with Alkali Activated Material or Geopolymer. With either 8 to 13 Ph Red Mud or Neutralised Red Mud.
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Samples available. 50 to 100 Kilo of Red Mud required shipped to UK.
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