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The mining of layered soft bauxite under coal seams (BCS) will cause serious underground goaf disasters and surface Bayer process red mud (BRM) pollution. In order to realize the safe and efficient mining of BCS, the feasibility of recycling BRM as a backfilling aggregate was explored. A series of tests were conducted to prevent the pollution diversion of BRM from surface storage to underground goafs, and a numerical simulation analysis of the backfilling mining process was carried out based on FLAC3D to protect the overlying coal seam. The results show that: under the action of encapsulation, solidification and inhibiting precipitation from cementitious materials, the leaching concentration of harmful substances in red mud-based cemented backfill (RCB) can be reduced 70% more than fresh BRM. Mining disturbance redistributes the in-situ stress field of overlying strata; normal backfilling can not only reduce the pressure stress of pillars, but also release the tensile stress in the roof and floor from +0.4956 MPa to −0.1992 MPa, effectively preventing roof subsidence. Since the creep damage process of past backfill will absorb and dissipate lots of energy, the disturbance range caused by backfill mining is controlled within 3 m, which is only 10% of the open-stope method.

The effects of reduction temperature, particle size, pellet diameter, and the ratio on the reduction rate in red mud-coal composite pellets were studied. The iron phase change of the reduction under different temperatures was analyzed applying X-ray diffraction technique. The microstructure of reduction was investigated using scanning electron microscope. The conclusion of the study is that the reduction reaction rate increased rapidly with the increase of reduction temperature. The reduction of Fe2O3 forming Fe3O4 started under 700?. At 1100?, the red mud-coal composite pellets with carbon and oxygen mole ratio 1:1 obtained a good reduction result. The appearance of metal iron and the clear porous structure indicated that the reduction had developed to a high degree. nema

Red mud is the waste of bauxite refinement into alumina, the feedstock for aluminium production 1 . With about 180 million tonnes produced per year 1 , red mud has amassed to one of the largest environmentally hazardous waste products, with the staggering amount of 4 billion tonnes accumulated on a global scale 1 . Here we present how this red mud can be turned into valuable and sustainable feedstock for ironmaking using fossil-free hydrogen-plasma-based reduction, thus mitigating a part of the steel-related carbon dioxide emissions by making it available for the production of several hundred million tonnes of green steel. The process proceeds through rapid liquid-state reduction, chemical partitioning, as well as density-driven and viscosity-driven separation between metal and oxides. We show the underlying chemical reactions, pH-neutralization processes and phase transformations during this surprisingly simple and fast reduction method. The approach establishes a sustainable toxic-waste treatment from aluminium production through using red mud as feedstock to mitigate greenhouse gas emissions from steelmaking. Red mud is shown to yield green steel through fossil-free hydrogen-plasma-based reduction, a simple and fast method involving rapid liquid-state reduction, chemical partitioning, and density-driven and viscosity-driven separation.

The rare earth elements (REE) have attracted much attention in recent years, being viewed as critical metals because of China’s domination of their supply chain. This is despite the fact that REE enrichments are known to exist in a wide range of settings, and have been the subject of much recent exploration. Although the REE are often referred to as a single group, in practice each individual element has a specific set of end-uses, and so demand varies between them. Future demand growth to 2026 is likely to be mainly linked to the use of NdFeB magnets, particularly in hybrid and electric vehicles and wind turbines, and in erbium-doped glass fiber for communications. Supply of lanthanum and cerium is forecast to exceed demand. There are several different types of natural (primary) REE resources, including those formed by high-temperature geological processes (carbonatites, alkaline rocks, vein and skarn deposits) and those formed by low-temperature processes (placers, laterites, bauxites and ion-adsorption clays). In this paper, we consider the balance of the individual REE in each deposit type and how that matches demand, and look at some of the issues associated with developing these deposits. This assessment and overview indicate that while each type of REE deposit has different advantages and disadvantages, light rare earth-enriched ion adsorption types appear to have the best match to future REE needs. Production of REE as by-products from, for example, bauxite or phosphate, is potentially the most rapid way to produce additional REE. There are still significant technical and economic challenges to be overcome to create substantial REE supply chains outside China.

The research of the properties of the complex alumínate solutions obtained through Bayer process or sintering process, will enable to determine the optimal parameters for the process, to increase the efficiency of the production and will be instrumental in high quality alumina production. The key stages of the alumina production through Bayer process which define its efficiency are digestion and decomposition processes. The main properties of the obtained products and amount of losses of the commercial components are established on these stages.

Red mud (bauxite residue) is a highly alkaline solid waste of alumina production. The amount of red mud is huge while its alkalinity hinders the application in construction industries. Up to now, the most common treatment of red mud is disposed in man-made dams. However, the long-term storage of large-amount red mud pollutes environment and underground water, threats human life and leads to a huge waste of valuable metals resources. Recently, researchers have proposed various strategies to solve the red mud problems. In this review, the neutralization and recycling status of red mud have been systematically illustrated, their advantages and disadvantages are also discussed in detail in terms of environmental and economic benefits. Moreover, the recommendation of red mud treatment in the future is suggested, the application in road base material is highly valued because of the huge consumption.

Bauxite leachate, a byproduct of the alumina extraction process, is characterized by its high alkalinity (pH > 12) and elevated concentrations of heavy metal ions, such as Cr6+. It poses a serious threat to the surrounding environment and human health once leaked. In this study, polymer-modified bentonite geosynthetic clay liner (BPC GCL) was used as the impermeability material of bauxite leachate. The results showed that the combination of bentonite and polymer hydrogel could significantly reduce the permeability coefficient of bentonite. Additionally, the transport model of Cr6+ in BPC GCL found that the color of the transport map of Cr6+ at each interface of BPC GCL changed from dark to light within 10 years, indicating that the concentration of Cr6+ showed a attenuation trend and played a impermeability role. Further comparison of different polymer contents of BPC GCL shows that the concentration of Cr6+ at the same interface of BPC GCL CP6.5, CP7.5 and CP10.8 exhibits a decrease from high to low, indicating that the concentration of Cr6+ gradually decreases with the increase of polymer and the impermeability is progressively increased.

Rare earth elements (REEs) are increasingly critical to the high-technology and low-carbon economy. With a shift to sustainable socioeconomic development that aims to be less fossil fuel dependent, global demand for REEs continues to rise, despite their uncertain supply chain and high environmental impact of production. Here, we review recent research on REEs, including global reserve assessment, REE-based applications, major REE production pathways, environmental impacts, and the potential to leverage circular economies within the REE industry. The main objective of this review is to provide an overall socioeconomic and environmental perspective of the REE industry with a central focus on environmental impacts of various REE-related activities. The literature reveals significant interest in extracting REEs from secondary materials (e.g., tailings, bauxite residues, coal combustion ash) and electronic wastes. However, some of these REE recovery processes are not yet economically profitable and environmental-friendly. Continued technological advancements and increasing demands for REEs may entice countries with recently discovered REE reserves to break the current monopolistic REE supply chain. Furthermore, the sustainability of REE usage may also depend on consumer awareness of environmental and human health impacts associated with end-of-life electronics that contain REEs. On the other hand, REEs may show promise in sustainable agriculture and environmental applications. Nevertheless, further research on REE ecotoxicological impacts is required to establish environmental regulations that protect the environment and human health.

The objective of this work is to develop a vanadium recovery process from a liquor residue of Bayer process. Vanadium finds application in strategic industrial sectors such as steel production and energy storage. The recognized importance of vanadium has pushed academic and industrial research towards the development of technologies for its recovery from different types of secondary sources. The developed process refers to a sodium fluorovanadate sludge from a spent Bayer liquor. The resulting filter cake was characterized to determine its composition and a vanadium recovery process was studied and optimized. This starts with a solubilization of the filter cake by water, followed by a precipitation step of aluminum through pH adjustment with sulfuric acid till 9.2. Vanadium is then recovered as ammonium metavanadate by precipitation with ammonium sulfate using a ratio (NH4)2SO4/salt cake = 2.25 w/w, the precipitate was calcined at T = 500°C to obtain vanadium as V2O5. The results showed an overall vanadium recovery of about 95%, with a purity > 99.6%. The innovative contribution here addressed is represented by the feasibility of producing high-purity V2O5 from the Bayer liquor through a relatively simple precipitation route.

This paper addresses the global challenge of greenhouse gas emissions facing the aluminum industry. The demand, production and use of aluminum are increasing and so are the emissions. From bauxite mine to aluminum ingot, the total global average emissions vary somewhat in the literature, but most reported values are now between 12 and 17 metric tonnes of CO 2 -equivalents per tonne of aluminum, depending on the various estimates and assumptions made. Two-thirds of these gases are emitted because the electricity used for electrolysis is produced from fossil fuel sources, mainly coal but also natural gas. Reduction of these emissions is now the main environmental challenge for the aluminum industry. Globally, the best result is obtained by maximizing aluminum production using green electrical energy from renewable sources. Aluminum production is categorized as an activity at very high risk of carbon leakage, which occurs when there is an increase in carbon dioxide emissions by new production in one country as a result of ceased production with emissions reduction in a second country with a strict climate policy.