Solidification/stabilization of chromium slag in red mud-based geopolymer

Red mud is the main by-product of the production of alumina according to the Bayer process. It is a highly alkaline, brick-red suspension. It is characterized by a diversity of chemical and mineralogical composition. The main elements in red mud are Fe, Al, Si, Ti, Na, Ca, and they account for about 90% of the mass of the mud. In addition to these, a large number of other components can be found in minor quantities. Most elements are present in the form of oxides and hydroxides in various minerals. The demand for aluminum is constantly growing, the amount of discharged red mud is continually increasing. The annual amount of red mud produced globally, is already estimated at 200 million tons, and further growth is expected. High production rates and only minimal and sporadic utilization of red mud have resulted in the accumulation of large quantities of disposed red mud, so that the global red mud stockpile is estimated at more than 5 billion tons. In addition to financial costs, the disposal of red mud also poses certain risks to the environment. For this reason, the safe disposal of red mud is one of the main concerns of all alumina producers. Reducing the amount of red mud that is disposed of, and consequently reducing the risks and costs, requires constant efforts to find procedures for its valorization. The possibilities of valorization of red mud are diverse. It has been shown that red mud can be successfully used in many areas, such as construction, metallurgy, chemical industry, environmental protection, agriculture, etc. Analyzing the patents related to the use of red mud, it can be observed that 12% of the patents refer to the wastewater and waste treatment. The heterogeneous composition of red mud indicates the possibility of its application as a composite sorbent. The application of red mud as a low-cost sorbent has been extensively investigated, and favorable results have been obtained in the sorption of metals and metalloids, radionuclides, phosphates, nitrates, fluorides, dyes and phenols, etc. In order to increase the sorption capacity of red mud and obtain a more environmentally friendly sorbent, various treatment techniques are applied. These treatment techniques can modify the physical and chemical properties, which can lead to a change in alkalinity, specific surface area and porosity, a change in the number of active sorption sites, and its surface charge can also be changed. Modifications of red mud to remove various types of pollutants have shown promising results. Many studies have shown that red mud can be used as an efficient and low-cost sorbent for removing heavy metal cations from solutions, such as Pb2+, Cu2+, Zn2+ , Cd2+, Ni2+, Co2+, Sr2+, Cs2+, as well as for the treatment of waste water and leachate from landfills and mines. During the removal of heavy metals from solutions using red mud, various mass transfer phenomena occur: physical and chemical adsorption, surface precipitation, co-precipitation, ion exchange, precipitation, complexation, hydration, dissolution, etc. Despite the numerous possibilities of application and the benefits that arise from it, we still do not have a significant utilization of red mud.

Enhanced and environment-friendly chemical looping gasification of crop straw using red mud as a sinter-resistant oxygen carrier

We face significant environmental pollution problems due to various industries, such as the aluminum industry, which generates large amounts of red mud (RM) waste, or agriculture, in which case the use of pesticides creates huge water pollution problems. In this context, the present study offers a better perspective to originally solve both environmental issues. Thus, the main target of the study referred to using RM waste as a filler for preparing composite copolymer beads. Thereafter, this can achieve significant removal of water pollutants due to their adsorption/oxidation characteristics. As evidenced by the changes in chemical structure and composition, thermal stability, morphology, and porosity, RM was homogenously incorporated in poly(acrylonitrile-co-acrylic acid) beads prepared by wet phase inversion. The final assessment for the removal of pesticides by adsorption and oxidation processes was proven successful. In this regard, 2,4-dichlorophenoxyacetic acid was chosen as a model pollutant, for which an adsorption capacity of 16.08 mg/g composite beads was achieved.

Red Mud is the solid residue generated from Alumina refinery during the process of bauxite ore processing through Bayer’s process. Typical generation of red mud is 1.5 tons of red mud per ton of alumina produced. The disposal and storage of red mud has been a concern for the alumina industry since its inception, more than a hundred years ago. With the increase in alumina production, the magnitude of the problem is getting multiplied. Its alkaline nature (Na2O ~ 3-7%) and fine size make red mud unsuitable for many applications; a limited utilization is reported in cement industries as one of the raw mix components for cement. The present work deals with the utilization of red mud in geopolymer based paving blocks. Alumina, silica and alkali are the essential items required for geopolymer preparation. Having all these in red mud, the current study attempted to use the same in geopolymer based products. The focus has been on bulk utilization of red mud; target strength of 20 MPa after 28 days of curing (M20 grade) has been the goal as this strength is sufficient for many applications. The study focused on optimizing the red mud content, alkali concentration, fly ash content, etc. The samples are tested for its compressive strength and leachability. The study reveals that significant amount of red mud incorporation is possible with products conforming to USEPA 1311 norms.

Red mud is a kind of solid waste in the production process of the aluminum industry. The long-term stockpiling of red mud not only occupies a large amount of land but also causes environmental pollution. In order to improve the strength, reduce the alkalinity and toxicity of red mud, and study its durability under freeze–thaw cycles, CGFPA binders, whose components were calcium carbide residue, ground granulated blast furnace slag, fly ash, phosphogypsum, and graphene, were adopted to solidify/stabilize red mud in this paper. The effects and the mechanism of freeze–thaw cycling on the unconfined compressive strength, pH value, and toxic leaching of the solidified/stabilized red mud was investigated. The micro-mechanism was analyzed by XRD, SEM-EDS, and FT-IR. The results of the study showed that the mass, unconfined compressive strength, and pH of the solidified/stabilized red mud decreased gradually with an increase in the number of freeze–thaw cycles, while the leaching concentration of pollutants increased gradually. The rate of loss of unconfined compressive strength satisfies an exponential function with the number of cycles, and the logarithm of pollutant concentration satisfies a linear relationship with the number of cycles. The cumulative loss of mass was 6.7%, 5.4%, 3.6%, and 3.3%, and the cumulative loss of unconfined compressive strength was 50.6%, 47.5%, 32.2%, and 25.3%, and the pH value was reduced to 9.42, 9.54, 9.80, and 9.92, respectively, after 10 freeze–thaw cycles at binder mixing ratios of 15%, 20%, 25%, and 30%, while the leaching concentrations of Cu, Zn, Cr, Ni, As, Pb, and Cd increased from 7.4 μg/L, 87.2 μg/L, 5.2 μg/L, 7.0 μg/L, 6.9 μg/L, 3.7 μg/L, and 0.7 μg/L to 17.5 μg/L, 123.5 μg/L, 10.2 μg/L, 15.7 μg/L, 11.4 μg/L, 5.6 μg/L, and 4.9 μg/L, respectively, under the condition of a 30% incorporation ratio. The gelling products generated by the hydration reaction of the binders were mainly C-S-H, C-A-S-H, C-A-H, AFm, etc. Under the action of freeze–thaw cycles, the lattice-like structure of the solidified/stabilized red mud was damaged, resulting in a decrease in its unconfined compressive strength and an increase in pollutant leaching concentration. The research results can provide a theoretical basis for the use of red mud in permafrost regions.

Red mud is a waste generated by the aluminium industry and its disposal is a major problem. Red mud waste from Eti Seydişehir aluminium plant of Turkey was considered as a hazardous waste for the environment and human health. The storage of the red mud is difficult due to its high amount of various metal oxides, elements and caustic content. In this study, the environmental compliance tests of the produced construction products of red mud were done and evaluated according to the >Regulation on Regularly Storage of Waste in Turkey<. According to the test results red mud, a hazardous waste alone, can be used in the construction products production. The construction products produced with red mud do not contain hazardous substances and thus, fit the requirements of the >Regulation on Regularly Storage of Waste in Turkey<.

Calcium sulphate dihydrate (CaSO4·2H2O) (gypsum) is often used as an amendment to improve soil structure. As this treatment eventually increases soil strength, thereby exacerbating conditions for root growth, reclamation of red mud tailings using this treatment can become counterproductive. Several years (7) after lithification by added gypsum, the effect of crushing, and added phyto-organics, on some physical properties of red mud wastes (RMW) was examined under laboratory conditions. It was hypothesized that mechanically breaking up the hardened masses would increase their permeability. However, on the contrary, crushing these rock-hard masses into 2-mm particles did not increase permeability. A phyto-organic treatment on the other hand greatly improved permeability of the crushed entities such that infiltration rates increased from 0 to 10 cm/h. After 24 weeks of incubation, the structure of the newly formed phyto-organically treated gypsum-hardened RMW aggregates was also substantially improved over that of the controls, as a 3-fold increase in resistance to disintegration during wet sieving was exhibited by the phyto-organically treated samples. The increase in water infiltration by combining crushing with phyto-organic infusions was ascribed to a decrease in particle dispersion, creating more stable clay clusters, which in turn stabilized micro channels and pores. This treatment increased the plant-growth-medium potential of the age-hardened gypsum-treated red muds, thereby justifying prior atmospheric carbonation and lithification of the red muds. Conversely, it was concluded that the singular crushing of CGR in the waste dumps to create a growth medium is potentially wasteful and ineffective. However, as CGR was seemingly of greater durability than soft limestone marl, it promises effectiveness as a stable road-bed material.

Preparation of Chromium-iron Metal Powder from Chromium Slag by Reduction Roasting and Magnetic Separation

Enhanced selective production of aldehydes and ketones by catalytic upgrading of pyrolysis vapor from holocellulose over red mud-based composite catalysts

Geopolymers have been studied as viable alternative to traditional Portland cement‐based products, given the use of industrial by‐products as raw materials. This work evaluated the mechanical and microstructural properties of geopolymeric mortars produced with sodium hydroxide solution, metakaolin, silica fume, and red mud. The mixtures were produced by means of dosages with different molar ratios and curing conditions. The raw materials were characterized by granulometry, chemical, mineralogical, and thermal analysis. The characterization of mortars was performed by scanning electron microscopy (SEM) and axial compressive strength tests. The precalcination at 850°C of the red mud was sufficient to make it more reactive and suitable for use in geopolymers. Noteworthy, the best mechanical strengths of metakaolin mortars for curing at 50°C, and with the lowest SiO 2 /Al 2 O 3 ratios. In the mortars with incorporated red mud, there was a decrease of strength at thermal curing conditions and with the increase of residue content, whose microstructure indicates the formation of more pores in the geopolymer matrix. The thermal curing promoted the formation of sodalite crystals, and the significant presence of Na particles on the surface suggests that part of the added NaOH did not react with the precursors.

Micro-chemomechanical properties of red mud binder and its effect on concrete

The issue of heavy metal pollution is a critical global concern that requires urgent solution. However, conventional heavy metal adsorbents are too costly to be applied in large-scale engineering. In this study, adsorption behavior and mechanism of sintering red mud (RM-A) and bayer red mud (RM-B) for heavy metals were investigated to address the disposal of red mud as industrial waste and remediation of heavy metal pollution. Batch adsorption experiments were conducted to explore the adsorption performances of RM-A and RM-B under various conditions. Characterization of RM-A and RM-B before and after adsorption by XRD, FTIR and SEM-EDX was applied to investigate the specific adsorption behavior and mechanism. Adsorption experiments of both RM-A and RM-B fitted pseudo-second-order kinetic model and Langmuir isotherm model, with estimated maximum adsorption capacity of 21.96 and 25.19 mg/g for Cd2+, 21.47 and 26.06 mg/g for Cu2+ and 55.47 and 59.65 mg/g for Pb2+, respectively. Precipitation transformation of calcite was the primary adsorption mechanism for RM-A, whereas ion exchange of cancrinite, surface coordination compounds of hematite and minor precipitation transformation of calcite accounted for the adsorption mechanism for RM-B. Overall, RM-A and RM-B exhibited best adsorption performance for Pb2+, with RM-B showing greater adsorption capacity attributed to its higher specific surface area. This study compared the adsorption properties of RM-A and RM-B for the first time and demonstrated that both red muds can be effectively applied to remove heavy metals, thereby contributing to the sustainable industrial waste management and resourceful reuse.

Preparation of glass-ceramics from chromite-containing tailings solidified with Red Mud

Re-use of waste red mud: Production of a functional iron oxide adsorbent for removal of phosphorous

Purpose The production of aluminum is based on obtaining alumina from bauxite, which is also known as the "Bayer Process." However, waste that is enough to endanger the environment is released at the end of this process applied to obtain aluminum. In Turkey, red mud waste is released from Seydişehir ETİ Aluminum production facilities into the pond located within the settlements. Red mud, which creates a potential environmental problem, should be systematically eliminated. In the literature, there are hundreds of studies on this subject. However, it is observed that these studies will not accelerate the waste consumption process. The consumption of the waste as soon as possible will be possible by using it as the main raw material. In this context, using both the literature and the doctorate study of the manuscript's author, the methods for using the waste as a building material were discussed for the systematic consumption of it. Design/Methodology/Approach Accordingly, in the study, the physical (specific gravity, plastic limit, differential thermal analysis, etc.) and chemical properties (XRF) of the waste red mud were discussed together with the waste generation process starting with the Bayer process. Furthermore, the physical (specific gravity, water absorption, water vapor permeability, initial water absorption velocity), mechanical (compressive strength) of the building materials that could be produced by using the waste were also included in the study. Findings It was concluded that it was possible to produce a quality building material by using the waste as a raw material. Research Limitations/Implications Type the research limitations/implications of the paper here. The study was limited to the mixing of red mud waste and pyroclastic rocks in certain proportions and their use as raw materials in the production of baked building materials by baking at different temperatures. Social/Practical Implications In this study, a solution method to a potential environmental problem was developed. Furthermore, a source of raw material was provided in sustainable building material production. Accordingly, a contribution can be made to the national economy with the building material that can be produced with local opportunities. Originality/Value With the materials and joining methods used in the study, a production was made on a unique subject.