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Desilication products (DSPs) are one of the main components of bauxite residue, which is currently discharged without further usage. The present study reports on the use of DSPs as adsorbents for basic fuchsine dye. Using artificial spent liquor, we synthesized not only neat DSP but also solids in the presence of various organics, to account for their likely occurrence during the Bayer process. The physico-chemical properties of all DSPs are similar, except for the specific surface area (SSA), which decreases as the organic content in the final product increases. Further, we compared the adsorption characteristics of DSP to those of Y-type faujasite (FAUY). Strikingly, both time-dependent adsorption measurements and adsorption isotherms showed that DSP, despite its 28-fold smaller SSA, binds 4–5 times more dye molecules. Computational modelling for sodalite (as a model for DSP) and FAUY indicates not only more favourable adsorbent-adsorbate interactions, but also more available free Si-OH sites for binding of fuchsine in the case of sodalite. Finally, we find that organic impurities present in the Bayer liquor do not alter the adsorption capacity of neat DSP to any significant degree; therefore, this adsorbent tolerates numerous organic contaminants without decreasing its affinity to the binding of fuchsine. [Display omitted] • Desilication products (DSPs) were synthesized in the presence of various organics. • The characeristics of the solids are only slighty altered by these templating agents. • As for the adsorption of fuchsine, the adsorption capacity is fully decoupled from the surface area. • DSPs form stronger interactions with fuchsine and have more binding sites than Y-type faujasite. • The binding of fuchsine by DSPs are not significantly altered by organics used for their synthesis. [ABSTRACT FROM AUTHOR]

Microbially-driven soil formation process is an emerging technology for the ecological rehabilitation of alkaline tailings. However, the dominant microorganisms and their specific roles in soil formation processes remain unknown. Herein, a 1-year field-scale experiment was applied to demonstrate the effect of nitrogen input on the structure and function of the microbiome in alkaline bauxite residue. Results showed that the contents of nutrient components were increased with Penicillium oxalicum (P. oxalicum) incorporation, as indicated by the increasing of carbon and nitrogen mineralization and enzyme metabolic efficiency. Specifically, the increasing enzyme metabolic efficiency was associated with nitrogen input, which shaped the microbial nutrient acquisition strategy. Subsequently, we evidenced that P. oxalicum played a significant role in shaping the assemblages of core bacterial taxa and influencing ecological functioning through intra- and cross-kingdom network analysis. Furthermore, a recruitment experiment indicated that nitrogen enhanced the enrichment of core microbiota (Nitrosomonas , Bacillus , Pseudomonas , and Saccharomyces) and may provide benefits to fungal community bio-diversity and microbial network stability. Collectively, these results demonstrated nitrogen-based coexistence patterns among P. oxalicum and microbiome and revealed P. oxalicum -mediated nutrient dynamics and ecophysiological adaptations in alkaline microhabitats. It will aid in promoting soil formation and ecological rehabilitation of bauxite residue. Bauxite residue is a highly alkaline solid waste generated during the Bayer process for producing alumina. Attempting to transform bauxite residue into a stable soil-like substrate using low-cost microbial resources is a highly promising engineering. However, the dominant microorganisms and their specific roles in soil formation processes remain unknown. In this study, we evidenced the nitrogen-based coexistence patterns among Penicillium oxalicum and microbiome and revealed Penicillium oxalicum -mediated nutrient dynamics and ecophysiological adaptations in alkaline microhabitats. This study can improve the understanding of core microbes' assemblies that affect the microbiome physiological traits in soil formation processes. [Display omitted] • The contents of nutrient are increased with Penicillium oxalicum (P. oxalicum) incorporation. • Nitrogen input alters microbial nutrient acquisition strategy between nitrogen and phosphorus. • Nitrogen enhances P. oxalicum -mediated core microbiota assemblages. • Nitrogen-based coexistence patterns may provide benefits to microbial network stability. • First demonstration of P. oxalicum -mediated microbial life strategies in bauxite residue. [ABSTRACT FROM AUTHOR]

Red mud, the Bayer process residue, is generated from alumina industry and causes environmental problem. In this paper, a novel calcification–carbonation method that utilized a large amount of the Bayer process residue is proposed. Using this method, the red mud was calcified with lime to transform the silicon phase into hydrogarnet, and the alkali in red mud was recovered. Then, the resulting hydrogarnet was decomposed by CO 2 carbonation, affording calcium silicate, calcium carbonate, and aluminum hydroxide. Alumina was recovered using an alkaline solution at a low temperature. The effects of the new process were analyzed by thermodynamics analysis and experiments. The extraction efficiency of the alumina and soda obtained from the red mud reached 49.4% and 96.8%, respectively. The new red mud with <0.3% alkali can be used in cement production. Using a combination of this method and cement production, the Bayer process red mud can be completely utilized. [ABSTRACT FROM AUTHOR]

Abstract: Arsenic was detected in a red mud (RM) produced during alumina production from bauxite known as the Bayer process. The transporting RM was a mixture of RM solid phase (RMsf) and RM liquid phase (RMlf). The mass content of RMsf in RM is about 30–40%. The alkalinities concentrations in the RMlf were in a range of 37.2×103 mg/l to 51.5×103 mg/l. Acidification by CO2 or waste acid (WA) combined with ferrous (Fe2+) treatment was evaluated for arsenic immobilization in the RM. The aqueous arsenic concentration in the RMlf decreased from 6.1mg/l to 0.5mg/l and 0.06mg/l with the addition of CO2 and WA, respectively. Ferrous was then added to decrease the aqueous arsenic concentration to be lower than 0.05mg/l. The cost-effective dosages of CO2 or WA were 80.1g/l or 26.7g/l, and the corresponding dosages of ferrous were both 6g/l. A 23 full factorial design was employed to evaluate the importance of chemical components of the RM in the cost of arsenic immobilization. High concentrations of arsenic and alkalinities in the RM will increase the cost while the effects of alumina contents varied during the different acidifications. Dissolvable arsenic in the RMsf was 8.2% and 9.5% after the CO2 and WA combined ferrous treatments, respectively. [Copyright &y& Elsevier]

Abstract: Unameliorated residue mud from the Bayer process generates highly alkaline leachates (pH ca. 13) after deposition in storage areas. Pre-deposition treatment of bauxite residue mud (BRM) with CO2 gas (carbonation) lowers leachate pH to ca. 10.5. Laboratory scale leaching columns were used to investigate the potential for in situ pH reduction in existing uncarbonated BRM deposits through exposure to carbonated mud leachate. Leachates from uncarbonated and carbonated residues in single and dual-layer column configurations were analysed for pH, electrical conductivity, carbonate and bicarbonate content, and element concentrations. Air-dried solids were analysed by X-ray diffraction before and after leaching. Cross layer leaching lowers leachate pH from uncarbonated BRM. Leachate pH was significantly lower in dual layer and carbonated residue than in uncarbonated residue between one and 400 pore volumes leached. Carbonated residue porewater as well as dawsonite and calcite dissolution were identified as sources of (bi-)carbonate. Leachate concentrations of As, Cr, Cu, Ga and La were immediately reduced in dual layer treatments compared with uncarbonated residue. No element analysed exhibited a significantly higher leachate concentration in dual layer treatments than the highest observed concentration in single layer treatments. The implementation of dual layer leaching in the field therefore presents an opportunity to improve leachate quality from existing uncarbonated residue deposits and justifies further testing at field scale. [Copyright &y& Elsevier]

Abstract: Electrofilter powders, a by-product of the Bayer process for the production of alumina from bauxite, were leached with sulphuric acid to dissolve gibbsite and transition aluminas, thus obtaining a commercial aluminium sulphate solution and a solid residue. This residue is treated again under more drastic conditions with sulphuric acidic in a furnace at a higher temperature, is then leached with water and filtered, a small amount of solid remaining (α-alumina). The liquid is a highly acidic aluminium sulphate solution which does not fulfil commercial grade specifications; the liquor is accordingly treated with potassium hydroxide or ammonium hydroxide to obtain potassium or ammonium alum. Experimental tests were conducted to investigate the synthesis of alum by crystallization. The effects on alum formation of various operating conditions, including the amount of potassium or ammonium hydroxide, temperature and seed alum dosage, were examined. The crystallization process was found to be quite effective in obtaining alum. [Copyright &y& Elsevier]

Red mud can be derived from the processing of bauxite using different methods. The chemical and mineralogical composition of the combined Bayer Process and bauxite calcination red mud (BPBCRM) differs markedly from those of the pure Bayer Process red mud (PBPRM). In this study, red mud derived from a combined Bayer Process and bauxite calcination method was characterized. The results show that pH of the red mud decreased with increasing duration of storage time. Na dominated among the soluble cations, but the concentration of soluble Na decreased with increasing duration of storage time as a result of leaching. Cation exchange capacity also decreased with increasing duration of storage time, probably due to a decrease in pH causing a reduction in negatively charged sites on the red mud particles. Ca was the predominant exchangeable cation in the fresh red mud but the concentration of exchangeable Ca markedly decreased in the old red mud, which was dominated by exchangeable Na. The degree of crystallization and thermal stability of the red mud increased with increasing duration of storage. The acid neutralizing capacity of red mud obtained from this study was about 10molkg−1, which is much greater than the reported values for the pure Bayer Process red mud. Column filtering experiment indicates that the red mud also had a very strong capacity to remove Cu, Zn and Cd from the filtering solution. It is conservatively estimated that the simultaneous removal rates of Cd, Zn and Cu by red mud are over 22,250mgkg−1, 22,500mgkg−1 and 25,000mgkg−1, respectively. The affinity of these metals to the red mud was in the following decreasing order: Cu>Zn>Cd. In general, the fresh red mud retained more heavy metals than the old red mud did. [Copyright &y& Elsevier]

• The alkalinity formation and release processes of BR are introduced in detail. • The typical dealkalization methods are discussed and evaluated comprehensively. • Characteristics of BR and regional resources determine the appropriate process. • Financial efficiency should be well considered in the dealkalization process. Bauxite residue is a kind of strong alkaline waste produced in the production of alumina. Its long-term storage poses a potential threat to the environment. With the tightening of environment policies in various countries, the strong alkalinity of bauxite residue has become a bottleneck restricting the sustainable development of aluminum industry all over the world. This review covers the composition characteristics of bauxite residue, and describes the Bayer process in detail, where emphasis is put on the formation of alkaline substances in bauxite residue and its release process in long-term storage. This review focuses on several typical processes for the management of bauxite residue alkalinity in recent decades around the world. The phase transformation mechanisms, merits and limitations, as well as application status are discussed. The potential application values of these typical methods are evaluated based on process characteristics. The large amount and varied characteristics of bauxite residue determine that it is unrealistic to solve the dealkalization problem of all bauxite residue with one method. It is recommended that the appropriate dealkalization process of bauxite residue should be selected according to the characteristics of bauxite residue and regional resources, as well as the planning of subsequent application. [ABSTRACT FROM AUTHOR]

A new way out of the bauxite residue, synthesizing a micro-electrolysis composite material (MECM) by carbothermal reduction of the bauxite residue towards the catalytic degradation of high-concentration organic wastewater for the sustainable development of resources and environment. • Bauxite residue was used to treat organic waste water. • MECM was prepared using bauxite residue by carbothermal reduction. • ZVI and carbon in MECM form many micro-electrolysis systems. • MECM provides Fe(Ⅱ) and solid active sites for Fenton process. • Fenton synergized with micro-electrolysis can efficiently degrade organic pollutants. Over 150 million tons of high-alkaline bauxite residue was produced during the Bayer process of Bauxite smelting in the world annually, causing massive encroachment and irreversible pollution of soil. In this work, we proposed a new way out of bauxite residue, synthesizing a micro-electrolysis composite material (MECM) by carbothermal reduction of the bauxite residue towards the degradation of high-concentration organic wastewater. Batch experiments of organic compounds degradation were conducted to evaluate the performance of MECM with or without synergistic Fenton process. XRD and SEM-EDS analysis results indicated that a proper calcination temperature (1000℃) could facilitate the generation and growth of zero-valent iron (ZVI), thereby forming a large number of galvanic cells with carbon, which could efficiently break the azo bonds. Additionally, the micro-electrolysis reaction of MECM could provide lots of Fe(Ⅱ), which constituted the Fenton system with the additional H 2 O 2. In Fenton system, the aromatic rings and alkyl chains were further degraded and mineralized, which reduced the chemical oxygen demand (COD) of methyl orange (MO) from 450 to 54 mg/L. Therefore, the combination of the micro-electrolysis and Fenton process provides a clean and efficient method for the treatment of organic wastewater, which is a promising way out for bauxite residue. [ABSTRACT FROM AUTHOR]

• Origin of organic compounds in Bayer liquor is discussed. • Considerable damages posed by organics on production of aluminum hydroxide. • A combination of electrooxidation and wet oxygen oxidation represents a promising method for organics removal from Bayer liquor. • Future research needs on organics removal from Bayer liquor are discussed. Alumina is a valuable raw material for the production of adsorbents, abrasives, polishing agents, refractory materials, and aluminum. It is generally produced from bauxites through the Bayer process. Several organic compounds such as humic matters and oxalates are introduced into the Bayer liquor during the digestion process, resulting in significant hazards to precipitation of aluminum hydroxide. Therefore, it is crucial to remove these organic compounds from Bayer liquor to enhance the production of alumina. It is difficult to remove these organic compounds. Various approaches for organics removal from Bayer liquors have been developed in the past few decades, including thermal treatment, chemical precipitation, membrane technology, photocatalytic degradation, biodegradation, and wet oxidation. This paper reviews the technologies for organics removal from Bayer liquor and the relative mechanisms proposed in the literature to identify its essential parameters. Chemicals dosage, temperature, pH value, reaction time, and solution concentration are essential factors in the process. Removal efficiency, green principle, and economic viability of various methods are discussed, and potential technologies are suggested. Wet oxidation appears to be a promising method for removing organic matters in Bayer liquors. Moreover, the combination of wet oxidation and electrooxidation shows excellent potential in organics removal. Various approaches for removing organic compounds and perspectives for further investigation are proposed. [ABSTRACT FROM AUTHOR]

• The influence of red mud on mechanical and durability properties of SCC were studied. • High superplasticiser dosages required for red mud concrete to meet the SCC requirements. • Mechanical strengths of SCC particularly at early age increased with increasing red mud content. • Corrosion potential of reinforced SCC samples decreased with increasing red mud content. • Presence of red mud in SCC did not make negative influence on the leaching of metals. Red mud is a hazardous waste material produced during alkaline leaching of bauxite in the Bayer process. This study proposed the use of red mud to replace fly ash in self-compacting concrete (SCC) and the influences of red mud on fresh and hardened properties, and durability performances of SCC were studied. The fresh concrete results show that red mud had a slight negative impact on the fresh properties of SCC. The hardened concrete results show that the mechanical strength of concrete increased with increasing of red mud content. The half-cell potential test results indicated that red mud had a significant effect on restraining the corrosion process in SCC. Compared to the control sample, the red mud samples suffered less corrosion. Cracks associated with corrosion of reinforcement were observed in RMC0 and RMC100 samples after 28 day accelerated corrosion test. The ICP-MS results showed that there's no significant difference in metal elements among the solutions regardless the red mud content in concrete.The relative corrosion rate test results suggested that red mud can suppress the corrosion current. The SCC samples consisting 75% red mud performed the best resistance to corrosion according to the results of half-cell potentials and mass loss of rebar. [ABSTRACT FROM AUTHOR]