Bauxite residue is the waste generated during alumina production by Bayer's process. The amount of bauxite residue (40-50 wt%) generated depends on the quality of bauxite ore used for the processing. High alkalinity and high caustic content in bauxite residue causes environmental risk for fertile soil and ground water contamination. The caustic (NaOH) content in bauxite residue leads to human health risks, like dermal problems and irritation to eyes. Moreover, disposal of bauxite residue requires a large area; such problems can only be minimised by utilising bauxite residue effectively. For two decades, bauxite residue has been used as a binder in cement industries and filler/reinforcement for composite materials in the automobile industry. Valuable metals and oxides, like alumina (AlO), titanium oxide (TiO) and iron oxide FeO, were extracted from bauxite residue to reduce waste. Bauxite residue was utilised in construction and structure industries to make geopolymers. It was also used in the making of glass-ceramics and a coating material. Recently bauxite residue has been utilised to extract rare earth elements like scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), neodymium (Nd) and dysprosium (Dy). In this review article, the mineralogical characteristics of bauxite residue are summarised and current progresses on utilisation of bauxite residue in different fields of science and engineering are presented in detail.
This experimental analysis aimed to fabricate low cost, lightweight metal matrix composite using Al 6061 as matrix material and alumina (Al2O3) and bagasse ash as reinforcing material through stir casting process. In this process one cast of single reinforced composite (Al 6061/5 wt% Al2O3) and three casts of hybrid reinforced composite (Al 6061/5 wt% Al2O3/ 4, 6, 8 wt% bagasse ash) were developed and processed as per ASTM standards followed by mechanical (micro-hardness, ductility, compression, tensile, and impact strength), physical (density and porosity), and microstructure (optical and SEM microscopy) characterization. The mechanical properties such as tensile strength, hardness, and compressive strength showed good improvements in the manufactured hybrid reinforced metal matrix composite (HRMMC) in comparison with the single reinforced metal matrix composite (SRMMC). The tensile strength and hardness of developed composite increased continuously with an increase in bagasse ash contents up to 6 wt% having maximum increment of 9.09% (tensile) and 16.5% (hardness) and thereafter both decreased for 8 wt% of bagasse ash, respectively. The results of impact strength and ductility of Al 6061/Al2O3/bagasse ash showed marginal reduction, as the wt% of reinforcements increased. It was found that the density of HRMMC was less than the SRMMC and it decreased with increasing wt% of reinforcements however, the composite contained some porosity percentage (max. value 2.26%), which increased as the wt% of reinforcement increased. The microstructure analysis showed fair distribution with good interface bonding up to 6 wt% bagasse ash.
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