Bauxite Residue

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Recovery of Rare Earths and Major Metals from Bauxite Residue (Red Mud) by Alkali Roasting, Smelting, and Leaching

Bauxite residue (red mud) with a high alumina content requires large amounts of fluxes during smelting, which increases the overall process cost, the energy consumption during smelting, and the acid consumption during slag leaching and decreases the throughput of bauxite residue in the smelting phase. Therefore, alumina was removed (or recovered) from bauxite residue by alkali roasting prior to smelting. The sample after alumina removal could be smelted at 1500°C without the need of adding any flux to obtain a clear slag-metal separation. After smelting, the slag was leached with acids (HCl, H 2 SO 4 , or HNO 3). The recovery yields of the rare-earth elements (REEs), except scandium, drastically decreased in the low-alumina slags, compared to the original bauxite residue. These poorer recovery yields are due to the formation of a perovskite (CaTiO 3) phase, which binds REEs except scandium. CaTiO 3 is a stable phase and does not dissolve in acids under normal conditions. Therefore, slag was quenched to suppress the CaTiO 3 formation. The REEs and titanium could also be dissolved in acidic solutions at 25°C by quenching the molten slag. Removal of alumina from bauxite residue by alkali roasting with sodium carbonate requires high temperatures ([900°C). Therefore, sodium carbonate was replaced with sodium hydroxide to decrease the energy consumption by decreasing the roasting temperature (\500°C).

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- by Yiannis Pontikes
- •
- 7
  Chemistry, Smelting, Waste Processing, Red Mud

Feasibility Study for an investment of an industrial plant evaluating Red Mud by an innovating method. A case study

An innovating purely chemical method allows the evaluation of the bauxite residue. The proposed method is economic, energy saving, industrially feasible and not noxious for the environment. Red mud is considered a secondary ore of valuable constituents. All the contained metal oxides are almost totally recovered. The metal oxides (CaO, TiO 2 , Fe 2 O 3, Al 2 O 3 , SiO 2) delivered by this method, are of high purity (85-99%) and can be sold as they are, with very satisfactory prices, or be transformed in high added value products. Eg. Fe 2 O 3 is converted in Ferrite Fe 3 O 4 and is widely demanded in international market. Furthermore, during the process leading to the final products significant amounts of thermal energy are gained. The cost of the investment is reasonable and the feasibility study of the case study, for an industrial plant evaluating 32tn/day, is proved viable and sustainable. For the feasibility study all the costs have been computed (construction cost, staff cost, raw material cost, energy cost, equipment cost, reagent cost, maintenance cost, loan cost) as well as the revenues of the products sale and the gained energy. Furthermore, the investment placed next to or near the primary aluminum production plant, contributes potentially to economic development and chemical sustainability, while at the same time vanishes the environmental and ecological impact of the aluminum industry.

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Characterization of Settled Particles of the Red Mud Waste Exposed to Different Aqueous Environmental Conditions

Red mud waste is generally transferred to the storage area in a slurry form with solids content varying from 15 to 40%. Due to arise of a variety of environmental and climatic conditions in the due course of time, settling behaviour of particles as well as properties of settled particles changes. Thus, understanding of the settling behaviour of waste particles becomes essential after disposing the waste into the pond. In addition, studies related to the settling behaviour of particles become important during the extraction of alumina from bauxite ore (i.e. in settlers). In the present study, efforts are made to investigate the settling behaviour of red mud waste particles when exposed to different aqueous environmental conditions. For testing purpose, a series of differential free swell tests were conducted considering aqueous environmental conditions such as tap water, distilled water, kerosene, NaCl solutions of 1.71 and 3.42 M, and HCl solutions with a pH range from 1 to 4, respectively. In addition, efforts are also devoted to characterizing the post-exposed sediment samples to ascertain possible changes in the mineralogical, morphological , and elemental compositions of the particles. Results reveal that aqueous environment has a considerable effect on the settling behaviour of particles, while the effect of pH found to be trivial. The analyses of characterization studies disclose a marginal to considerable changes in elemental, phase compositions and morphological characteristics of the post exposed particles.

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- by Narala Gangadhara Reddy and +1
  Hanumantha Rao B
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- 6
  Solid Waste Management, Mineralogical Identification, Red Mud, Slurry

Sustained Bauxite Residue Rehabilitation with Gypsum and Organic Matter 16 years after Initial Treatment

Bauxite residue is a high volume byproduct of alumina manufacture which is commonly disposed of in purpose-built bauxite residue disposal areas (BRDAs). Natural waters interacting with bauxite residue are characteristically highly alkaline, and have elevated concentrations of Na, Al, and other trace metals. Rehabilitation of BRDAs is therefore often costly and resource/infrastructure intensive. Data is presented from three neighboring plots of bauxite residue that was deposited 20 years ago. One plot was amended 16 years ago with process sand, organic matter, gypsum, and seeded (fully treated), another plot was amended 16 years ago with process sand, organic matter, and seeded (partially treated), and a third plot was left untreated. These surface treatments lower alkalinity and salinity, and thus produce a substrate more suitable for biological colonisation from seeding. The reduction of pH leads to much lower Al, V, and As mobility in the actively treated residue and the beneficial effects of treatment extend passively 20−30 cm below the depth of the original amendment. These positive rehabilitation effects are maintained after 2 decades due to the presence of an active and resilient biological community. This treatment may provide a lower cost solution to BRDA end of use closure plans and orphaned BRDA rehabilitation.

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- by William Mayes
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- 3
  Red Mud, Industrial wastes, Bauxite Residue

Article Environmental Sustainability of the Alumina Industry in Western Europe

The implementation of European policies on environmental protection is enforcing some substantial modifications in the processing methods and technologies traditionally adopted in the alumina industry and, in particular, in the management of the alumina residue produced. The article analyses the evolution of the alumina production and the residue disposal practices in Western Europe. Some critical aspects regarding the legal implementation of the EU Directive on the landfill of waste are highlighted and discussed. With reference to the requirements established for the landfill of non-hazardous waste, a key point is represented by the possibility of reducing the deposit protection measures if the collection and treatment of leachate is not necessary. The flexibility introduced by the Directive is not incorporated into the Italian law; this fact may represent a major issue in the prospect of disposal conversion from wet to dry methods for companies operating in Italy, as it may endanger the economic sustainability of the plants' upgrade, as well as the opportunity to attract outside investments.

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- by Giorgio Massacci
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- 3
  European Policies, Sustainability, Bauxite Residue

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