Current key options for management of industrial alkaline waste of alumina production (red mud)

Due to the ever-increasing demand of the world economy for aluminum, its alloys and compounds, the production of this metal is increasing annually throughout the world. This leads to an increase in the industrial production of alumina, which is obtained from bauxite ore in the Bayer process. After recovering the bulk of the aluminum from the bauxite ore, there remains a residue which is highly alkaline toxic waste, which is also called bauxite residues (tailings) or red mud (RM). About 140-150 million tons of RM are produced annually and almost 4 billion tons have already been accumulated. At the moment, the problem of RM recycling and the development of effective and cost-effective approaches to their reprocessing is extremely urgent. Reducing RM affects economic, environmental, social areas and is a prerequisite for the sustainable development of nature and society. Despite active scientific research and efforts to develop and optimize various methods for RM recycling and reprocessing, the problem of an annual increase in their volumes around the world remains unresolved. Recently, promising and efficient processes have been proposed that allows for the complex reprocessing of RM with the extraction of a number of valuable liquid products that may be in demand in various fields of industry. This allows to focus on large-scale disposal of RM and can be a solution to the problem of handling these industrial wastes. The article considers the main current trends in the field of management of various types of RM with a focus on complex reprocessing and zero waste concepts

Complex reprocessing of industrial alkaline waste of alumina production (red mud) for solving raw materials and environmental problems

Red mud are industrial large-scale toxic wastes of bauxite ore processing according to the Bayer method. They contain macrocomponents such as iron, aluminum, calcium, silicon, as well as a number of the most valuable and critical metals (microcomponents): scandium, gallium, germanium and rare earth elements (REEs), which are used in modern high-tech industry. Due to the relatively high content of scandium and REEs, red mud can be considered as a promising secondary source. Significant amounts of accumulated red mud and new flows of this waste entering the slime storage facilities need to be processed to obtaine the required valuable products. Development of complex reprocessing approach play an important role in addressing the problem of the elimination of red mud as toxic waste. Within the framework of this subject, the report considers the concept of complex reprocessing of Bogoslovsky Aluminum Plant (Russia) red mud, which includes the extraction of aluminum, scandium, REEs, zirconium and the production of iron-containing concentrate for ferrous metallurgy. The use of low-aggressive carbonate media and carbonation method using carbon dioxide gas characterizes this approach as more environmentally and technologically safe. The development of effective technology for utilization of red mud will not only provide a source of critical raw materials, but also solve the global environmental problem

Chemical Aspects of Scandium carbonate leaching from Red Muds

Red Muds (R.M.) – waste of bauxite reprocessing by the Bayer's method include many rare elements, such as Gallium, Titanium, Zirconium, Rare Earth Elements and Scandium, concentration of which in its reached 130 g/t. In the problem solving of Scandium extraction from R.M. get a two directions: immediate leaching of Scandium from R.M. and in passing Scandium recovery under complexing processing of R.M. The method of carbonate leaching of Scandium from R.M., which was work out in Institute of Solid State Chemistry Russian Academy of Sciences Urals Branch, include saturation by carbon dioxide of alkaline solutions, obtained after water process of R.M. and allow up to 20 % Scandium recovery in solutions. It is not effective for work out of technological scheme of R.M. processing. In recent paper, the chemical aspects of carbonate leaching of Scandium from R.M. in heterogeneous systems solid – liquid – gas carbon dioxide were investigated to determine of conditions for more Scandium recovery from R.M. It was shown, that Scandium leaching by aqueous sodium solutions without carbon dioxide gives small recovery yield and accompanied by alkaline hydrolysis under high pH in concentrated Na2CO3 solutions. Under saturation by carbon dioxide of carbonate R.M. pulp, the hydrolytic polymerization of hydroxocarbonates of Scandium and Aluminum in presence of carbonic acid proton take place. In the both process secondary precipitates are settle down and reduce of Scandium recovery yield. For increase of Scandium recovery from R.M. it is necessary to exclude the secondary precipitates under carbonate leaching with saturation by carbon dioxide

Simulation of active layer dynamics, Upper Kolyma, Russia, using the Hydrograph Hydrological Model

Freeze/thaw simulations were performed for seven permafrost sites at the Kolyma Water Balance Station (KWBS), northeast Russia, using the hydrological model Hydrograph equipped with a heat transfer analytical solution that accounts for soil profile phase changes. The study sites include slopes and plateaus with thaw depths of 0.5 to 1.8 m. Landscape conditions are characterised as rocky talus, mountain tundra with dwarf tree brush, moss-lichen cover and sparse-growth forest or larch forest. Soil horizons are distinguished as moss-lichen cover, peat layer, clay with a high stone content and weathered clayey shale. Schematisation of soil-vegetation profiles and model parameters were developed for each landscape. Parameterised model output was verified using time series of observed active layer thickness for the period of 1950 to 1990. The simulated values agree well with the observed values at the study sites. The results suggest that the soil profile schematisation and model parameters, along with the proposed algorithm of heat transfer, effectively simulate active layer dynamics under various landscape conditions at the KWBS and are suitable for hydrological modelling in the permafrost zone. The modelling efforts and results are highly relevant because the natural conditions at the KWBS are representative of large areas of northeastern Russia. Copyright © 2014 John Wiley & Sons, Ltd