Budapest University of Technology and Economics, Department of Applied Biotechnology and Food Science, Environmental Microbiology and Biotechnology Group
- 01 WASTE RESULTING FROM EXPLORATION, MINING, QUARRYING, AND PHYSICAL AND CHEMICAL TREATMENT OF MINERALS
- 01 03 wastes from physical and chemical processing of metalliferous minerals
- 01 03 09 red mud from alumina production other than the wastes mentioned in 01 03 07
The Ajka red mud resulted from the Bayer process. The Bayer process extracts alumina by caustic digestion of crushed bauxite at high temperature and pressure in an autoclave, followed by clarification, precipitation, washing and finally calcination to produce pure anhydrous alumina. Alumina, a white powder, is the final product of the Bayer Process, ready for shipment to aluminium smelters or the chemical industry. Alumina is used for the production of aluminium metal, through the Hall–Héroult electrochemical smelting process.
The major steps in alumina refining are as follows:
• Wet grinding of the bauxite ore in rod mills, ball mills, or semiautogenous grinding mills to produce fine slurry.
• Digestion of the slurry by caustic soda (NaOH) at strengths exceeding 170 g/L in vessels under pressure at temperatures ranging from 145 to 265°C depending on the type of bauxite being processed.
• Separation and washing of insoluble residues (termed “sand and mud”) from the process solution (termed “green liquor”). Residues are stored in residue drying areas.
• Crystallization (precipitation) of aluminum trihydrate from the sodium aluminate (NaAlO2) of green liquor, leaving “spent liquor” containing primarily caustic soda to be returned to digestion.
• Calcination of the aluminum trihydrate crystals at approximately 1000°C, driving off water molecules and leaving the final product of anhydrous alumina.
The red mud is the insoluble, wet, solid residue after separation by fitration of the process solution. Due to a novel technology the high water content of this residue is reduced from 80% to 30 % by hight pressure filtration resulting a muddy, solid material.
The composition of the red mud resulted from the Bayer process varies according to the composition of the processed bauxite ore. In general the alkalinity of red mud may also vary. In case of the Ajka red mud we have to distinguish the red mud from the wet technology (used before the Ajka dam failure up to the end of 2011) from the red mud resulted from the dry technology introduced at the end of 2011. This datasheet provides a description of the very alkaline bauxite residue resulted from the wet technology
- Fémek, félfémek és vegyületeik
- vas
- Fémek, félfémek és vegyületeik
- alumínium
- Egyéb szervetlen vegyi anyagok
- szilícium
- Egyéb szervetlen vegyi anyagok
- kálcium
- Egyéb szervetlen vegyi anyagok
- nátrium
- Fémek, félfémek és vegyületeik
- ón
- Fémek, félfémek és vegyületeik
- vanádium
- Egyéb szervetlen vegyi anyagok
- magnézium
- Egyéb szervetlen vegyi anyagok
- szén
- Egyéb szervetlen vegyi anyagok
- foszfor-pentoxid (P2O5)
- Egyéb szervetlen vegyi anyagok
- fluor/fluorid
Main components: iron-, aluminium-, silica-, titanium-, sodium- and calcium-oxides, and heavy- and light metals: Na, K, Cr, V, Ni, Ba, Cu, Mn, Pb, Zn, etc, radioactive daughter elements . Its composition depends on the bauxite it originates from and on the processing technology.
It is a paste-like, wet, red-coloured material made up of colloid particles stronly retaining water, having speciel rheological properties. After drying it becomes powder and mixed with water it will not regain its plasticity. Originally the rud mud is watertight, but saturated with water, its watertightness is lost. Its volume is changing depending on the temperture and rain conditions.
90% of the red mud grains are below 75 µm, the average grainsize is below 10 µm.
Red mud is thixotropic during compression and shear stress. At the same time it has low hydraulic conductivity, and high cation exchange capacity. The plasticity index of red mud may range from 4 to 27. The smaller values are related to the coarser, while larger values to the finer samples. Small changes in water content may result in higher changes in consistency. The volume of red mud may be influenced also by temperature and rain conditions. The radioactivity of this Ajka red mud is low, it is 10-20 fold of the characteristic value for Hungarian soils.
The Ajka red mud is only experimentally utilized, however re-mud from other countries are largely utilized in various fields:
Construction, chemical industry: construction materials, adsorbents, catalyst; ceramics, glass, plastics, paints.
Environment and agriculture: water treatment, waste treatment, gas scrubbing, agriculture (adsorbent, trace element source).
Metallurgy: recovery of its main components (Fe, Al);
Steel production, slag additive;
Extraction of other elments (Ti, V, REE) (Szépvölgyi 2011)
(1) http://www.tankonyvtar.hu/konyvek/kornyezettechnika/kornyezettechnika-5-...
(2) Sushil, S., Batra, V.S.: Catalitic applications of red mud, an aluminium industry waste: A review, Applied Catalysis B: Environmental, Volume 81, 64-77, 2008
(3) Sglavo, V. M., Maurina, S., Conci, A., Salviati, A., Carturan, G., Cocco, G.: Bauxize ’red mud’ int he ceramic industry. Part 2: production of day-based ceramics, Journal of the European Ceramic Society, Volume 20, 245-252, 2000
(4) Yadav, V. S., Prasad, M., Khan, J., Amritphale, S.S., Singh, M., Raju, C.: Sequestration of carbon dioxide (CO2) using ’red mud’, Journal of Hazardous Materials, Volume 176, 1044-1050, 2010
(5) http://enfo.agt.bme.hu/drupal/node/7687
(6) http://enfo.agt.bme.hu/drupal/sites/default/files/Review%20of%20Bauxite%...
BME's Environmental Microbiology and Biotechnology research group has conducted biological and ecotoxicity tests on various Ajka red-mud samples at various pH. The test included: determination of the aerobic heterotrophic cell counts, Sinapis alba germination inhibition test, Collembola (Folsomia candida) lethality test.
The red mud sample from the vicinity of the broken wall (pH > 12) did not contain any living cell. The red mud samples of pH >11 were very toxic to the plant (Sinapis alba), germination inhibition was > 90% . The red mud at pH: 12.4 showed the highest lethality (95%) to Folsomia candida. Only one organism survived. The three tests showed that the high alkalinity is toxic to all three test organisms. Other characteristics of red mud ( moisture, texture, etc) have considerable influence on its effects. On the other hand red mud mixed at 20-30% into soil did not indicate high toxicity.
Hazardousness of red mud may be associated with its: high toxic metal content , radioactivity, pH, Na-ion content (salinization) and grainsize influencing soil microbiological activity. Due to its grainsize it is prone to dusting, for which reason it should be stored wet or under a covers layer. The alkaline dust is irritative and corrosive to the eyes and the skin, Its inhalation may irritate and corrode the respiratory truct and the lungs.