Remediation methods for contaminated
sites (Red Mud Disaster)
By: Juho Kaasinen &
Luv Upadhyaya
Introduction
A site is considered contaminated when it exceeds the limits of concentration of any minerals or
compounds in a particular place. The main reason of contamination is that when some chemical plants or
nuclear plants fails then the chemicals those were stored within the chemical plants are introduced to the
environment by causing a negative impact on its surrounding, humans and all kind of live forms. These
sites should be cleaned up to minimize the risk potential of those chemicals on environment. So there are
different types of remediation methods that are in process. Remediation method should be more efficient
and effective as there is high risk of health hazard around the contaminated sites.
This essay will be focused on the Red mud disaster in Ajka Alumina Refinery, Hungary (October 4, 2010,
collapse of the Chamber 10 dam, about 1.3 million m3sloppy slurry escaped and spread over a territory of
some 10 km2), especially on the remediation methods that are used in those contaminated sites. Red mud
is the product of alumina process which is invented by Karl Bayer in 1887. In this process sodium hydroxide
is used to selectively dissolve the aluminium oxide to produce a sodium-aluminium solution and after few
steps the metal is recovered. Iron, titanium, sodium, silica and other impurities are all discarded. This waste
product forms its oxides and called red mud. The red colour is from oxide of iron. Two metric tons of mud
for one ton of alumina produced in Australia and the annual total produced in the world is 80 million metric
tons (Engineering & Mining Journal 2006).
Compounds and elements
Fe2O3
Al2O3
SiO2
Na2O
TiO2
CaO
K2 O
MgO
CO2
S
Mn
A.Z.
Table1 Composition of red mud.
Quantity (%)
35.04
20.20
13.50
9.40
4.00
5.30
0.39
0.33
3.19
0.06
0.02
8.44
The main aim of this essay is to provide the knowledge of remediation methods of contaminated sites and
the techniques developed by taking red mud remediation as an example. Throughout the essay we will
take the methods of removing of red mud from the environment and also about the risk assessments,
procedures and precautions. The role of authority, Acts and Decrees, and importance of social activity for
remediation of contaminated site will be discussed too.
Main part
An accident that has the potential to cause huge destruction is called disaster. They can never be predicted
as they are uncertain and unaccepted. Especially in the case of chemical plants and industries the
remediation methods should be pointed out so that if the plant fails and chemicals released, the methods
of remediation should apply as soon as possible. Here are the steps that are to be followed to remediate
the contaminants from the site of contamination.
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Character of contaminants. (in this case we know the contaminant is red mud)
Local climatic conditions. (Hungary)
Site hydrogeology. ( Groundwater, river channels near the sites, water quality)
Selection of site specific technologies
Selection of contaminant specific technologies(Physical, biological, chemical)
Continuous monitoring.
Local evacuation if necessary.
Costs of remediation methods
Fines according to the Act and Decree of the authority.
In the case of the Ajka disaster, there are very few immediate remedies, but the thin layer of mud left by
the initial wave will in time be neutralized by atmospheric oxygen and native vegetation. The greatest
threat posed by the burst is the contamination of groundwater, since in the aquifer neither the carbon
dioxide of air nor the acidic effects of vegetation can function. The immediate effect to the red mud’s
caustic alkalinity can be (and in the case of Ajka accident were) somewhat countered by treating the
contaminated soil and water with acids such as gypsum and acetic acid for immediate neutralization. This
has its own obvious problems, and its efficiency beyond immediate response is in question. (Reina 2010)
Red mud is stored in large, relatively shallow (five to six meters deep) beds. The alkalinity of the surface
layer is reduced first by reaction with atmospheric carbon, then by introducing vegetation to the mud bed.
Mixing organic waste with mud helps to encourage the plants to grow. The process of pH neutralization
begins at the top of the mud bed and slowly seeps down, reaching up to the depth of 1.2m in 35 years. The
vegetation only grows on the edges of the mud bed, since its topography (edges are higher than the centre)
causes the centre to occasionally form a pool of high pH water (due rain). On the edges, the drainage is
greater, the moisture content and the pH lower. The depth of neutralizing effect of the plants depends on
their root penetration, the scale on the root density (measured as grams of roots per gram of mud). The
roots of the plants generate organic acids, and the plants also generate cations (such as Ca2+ and Mg2+) and
H+ ions, important in the neutralization process. (Khaitan & Co 2010)
Pore water neutralization
Solid phase
Al(OH)4-(aq) + H+ = Al(OH)3 +H2O
NaOH(aq) + H+ = Na+ + H2O
NaCO3-(aq) + H+ = Na+ + HCO3-
Dissolution of tricalcium aluminate (“C3A”):
Ca3Al2O6(s) + 12H+ = 3Ca2+ + 2Al3+ + 6H2O
Precipitation of calcite:
Ca2+ + Co32- = CaCO3(s)
Two teams of Australia’s Commonwealth Scientific and Research Institution (CSIRO) are studying processes
by which the red mud could totally be recycled, by high temperature smelting. Warren Bruckard said of
handling red mud: “It’s very fine, difficult to settle and filter and is highly alkaline. however, it also contains
a range of valuable constituents, which we believe are worth attempting to recover.” (Engineering &
Mining Journal 2006)
In the smelting, pig-iron and alumina can be extracted from the red mud, and the remaining slag can be
progressed into a titania product suitable for cement kilns. Theoretically, this would result in waste-free
aluminium processing, but whether the process can be applied on industrial scale is still in question. Should
the research bear fruit, this promises an immense benefit both for the environment and the industry.
(Engineering & Mining Journal 2006)
Conclusion
Hereby in this essay we have concluded that depending upon the site of disaster, the remediation methods
are to be followed. In this case, the disaster could have been avoided if precautions were followed and the
warnings were heard by the authorities. However, as long as bauxite residue is stored in reservoirs and not
effectively remediated, the risk of such an accident will always be with us. The only final solution to the
environmental hazard the alumina industry and the red mud presents is a complete recycling of the
residue. Permanent storage can, at best, be a stop-gap measure.
The only remediation method currently in industrial use focuses on using atmospheric oxygen and alkalinetolerant vegetation to reduce red mud’s pH. Though this method can bring the pH down to neutral 7, the
resulting residue still goes to waste, and the process is extremely slow, taking decades to have an effect.
Perhaps in the future the technology will allow us to use the many useful compounds of red mud, but the
research on alternative methods has yet to produce anything applicable on industrial scale. In this,
however, the needs of the industry and the environment go as one.
Finally, during the remediation of contaminants we should consider the related hazards associated,
technologies, costs and the authority should be aware of the continuous monitoring of the site to be assure
that the remediation is effective.
Sources
Remediation Technologies for Soils and Groundwater, (Bhandari, Alok Surampalli, Rao Y. Champagne,
Pascale, ASCE; 02/2007)
Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization, (National Research
Council Staff, National Academies Press; 10/97)
Field Evaluation of Bauxite Residue Neutralization by Carbon Dioxide, Vegetation, and Organic
Amendments. (Khaitan, S. & Co, Journal of Environmental Engineering; Oct2010, Vol. 136 Issue 10, p10451053 9p.)
Clearing the Mud For the Alumina Industry. (Engineering & Mining Journal (00958948); Jul/Aug2006, Vol.
207 Issue 6, p66-68, 3p.)
Hungarian Tailings Dam Leak Kills 7, Contaminates Rivers. (Reina P., ENR: Engineering News-Record;
10/18/2010, Vol. 265 Issue 11, p16-16, 1p.)