Treatment Of Red Mud Research Articles

Selective Removal of Iron from Acid Leachate of Red Mud by Aliquat 336

Extraction of valuable rare-earth elements (REEs) from red mud is important for both resource recovery and waste treatment of red mud. However, the Fe present in red mud makes the extraction of REEs unsatisfactory, because Fe(III) is co-extracted and is difficult to remove. In this study, the feasibility and mechanism of selective removal of Fe from the acid leachate of red mud using Aliquat 336 were investigated. According to the theoretical calculation, Fe(III) mainly existed as FeCl3 species in a wide range of chloride concentrations, and the concentration of FeCl4− species significantly increased with chloride concentration. The extraction studies show that the chloride concentration strongly affects the extraction of Fe. The Fe removal efficiency is > 98% when the chloride concentration is 2.65 mol L−1, while the loss of REEs is 90% under the optimal conditions.

Effective Utilization of Waste Red Mud for High Performance Supercapacitor Electrodes.

In recent years, metal oxide‐based, inexpensive, stable electrodes are being explored as a potent source of high performance, sustainable supercapacitors. Here, the employment of industrial waste red mud as a pseudocapacitive electrode material is reported. Mechanical milling is used to produce uniform red mud nanoparticles, which are rich in hematite (Fe2O3), and lower amounts of other metal oxides. A comprehensive supercapacitive study of the electrode is presented as a function of ball‐milling time up to 15 h. Ten‐hour ball‐milled samples exhibit the highest pseudocapacitive behavior with a specific capacitance value of ≈317 F g−1, at a scan rate of 10 mV s−1 in 6 m aqueous potassium hydroxide electrolyte solution. The modified electrode shows an extraordinary retention of ≈97% after 5000 cycles. A detailed quantitative electrochemical analysis is carried out to understand the charge storage mechanism at the electrode–electrolyte interface. The formation of uniform nanoparticles and increased electrode stability are correlated with the high performance. This work presents two significant benefits for the environment; in energy storage, it shows the production of a stable and efficient supercapacitor electrode, and in waste management with new applications for the treatment of red mud.

The modified red mud reduction smelting

The article presents the results of investigations of complex processing of red mud obtained from high-alumina bauxites of alumina production by the smelting reduction method. Red mud is a production waste that contains useful components and can used as a complex raw material for the production of pig iron, rare earth element (REE) concentrates and titanium dioxide. Known methods of red mud processing by the smelting reduction method have not found application because of the impossibility of obtaining slag with low iron content. The urgency of the problem solved by the research is in the need of ways for red mud recycling. As a result, a method for processing the modified red mud by the smelting reduction was developed to produce cast iron and an oxide-free slag containing rare earth elements and titanium dioxide. The method consists in the preliminary treatment of red mud in a high-modulus alkaline solution at a temperature of 240-260 ° C with the addition of calcium oxide to the pulp from the calculation for obtaining a modified red mud – a hydrogarnete slurry those main compound is the ferrous garnet-3CaO ∙ Fe2O3 ∙ 2SiO2 ∙ 2H2O. Reducing melting of the hydrogarnete slurry has made it possible to produce cast iron, and after magnetic separation – a nonmagnetic slag fraction containing 0.22 % of iron, which determines the possibility of obtaining high-quality REE concentrates and titanium dioxide in hydrometallurgical processing. The extraction of iron into cast iron is 88.0 %, into the magnetic fraction – 11.9 %, into the non-magnetic fraction – 0.1 %. The extraction of titanium into the magnetic fraction was 34.3 %, and in the nonmagnetic fraction was 65.7 %. The recovery of REE into the nonmagnetic fraction was 65.7 %.

Effect of metal oxide redox state in red mud catalysts on ketonization of fast pyrolysis oil derived oxygenates

Iron oxide catalysts derived from red mud were reduced at different temperatures and alkali metals extracted to determine the effect of iron redox state and mixed alkali doping on ketonization of key oxygenates (acetic acid, acetol, formic acid, and levoglucosan) found in fast pyrolysis oil aqueous phase. Hydrogen reduction at 300 °C, compared to 400 and 500 °C, generated the highest level of magnetite and weak and strong acid sites (NH3-TPD), while maintaining base sites (CO2-TPD) in the catalytic material, resulting in the highest acetone and 2-butanone yields from the oxygenate mixture with limited coking. Acid treatment of red mud and subsequent reduction generated higher surface area, yet significantly lower ketonization activity and higher coking activity. This was attributed to the lack of alkali metals, and subsequent base sites generated upon calcination and H2 reduction, when in the presence of levoglucosan. Similarly, poor results were obtained with iron oxides supported on SiO2/Al2O3 without alkali metals when upgrading the oxygenate mixture. The results indicate the need for a multifunctional catalyst (acid and base sites with oxygen vacancies) when upgrading complex oxygenate mixtures in fast pyrolysis oil.

Ispitivanje uticaja tretmana i mineraloškog sastava na tačku nultog naelektrisanja crvenog mulja

Red mud represents tailings which remains after the processing of bauxite into alumina by Bayer's proceedings. All the elements are present in the red mud are found in the form of different minerals. These minerals do not exist as individual particles, but are associated with other minerals in aggregates which represent particles of red mud. Surface charge is an important property of the red mud, which affects a number of its characteristics. Surface charge can be considered through the zero charge point. In this paper, the point of zero charge of the original red mud and certain treated samples is determined. Incomplete washing, thermal and acid treatment were used as treatments. The applied treatments had a different effect on the movement of the PZC and buffer region. The red mud sample was distinguished by a high value of pHPZC (9.7 ± 0.2). Incomplete washing did not affect the change in PZC, while thoroughly rinsing caused a significant movement of PZC to a lower pH. This suggests to a large amount of residual base from the leaching process. Thermal treatment of red mud did not significantly affect the change in the final pH at which plateau was observed (pHPZC 9.4-9.9), while acid treatment had a more pronounced effect (pHPZC 6.2-7.9). PZC values for acid-treated samples obtained in an inert electrolyte were lower than those obtained in distilled water, at least for one pH unit. All the analysed samples had a pronounced buffer region in which the final pH values were independent of the initial ones. Partial rinsing and thermal treatment did not significantly affect the change in buffer region, while acid treatment caused the narrowing of the buffer region with increasing acid concentration, but the samples continued to retain significant neutralization capacity. For the move of the PZC treated muds, major responsibility have phase changes that occur in the treatment, neutralization of the residual base and the anions in the solution, and changing the crystallinity and the solubility of minerals in the mud. Applying the appropriate treatment can affect the change in the mineral composition and, consequently, the changes in the charge of the surface.

Electro-Membrane Technology for Extraction of Valuable Compounds and Rare Earth Elements from the Red Mud

The paper is devoted to the developed technology of treatment of red mud, a dangerous waste formed in the process of production of aluminum from bauxite ores by the Bayer process. The technology was examined on the samples of red mud from Russia and Iran aluminum plants. Detailed description of the process is presented. The chemical analysis data before and after the treatment are presented. It is shown that the new technology based on the use of electro-membrane apparatuses makes possible to neutralize the hazardous red mud with separate production of valuable compounds including rare earth metals. Several schemes of the process are presented.

Treatment of Red Mud with Distilled Water to Improve Its Efficiency to Remove Methylene Blue from Aqueous Solution

Treatment of Red Mud with Distilled Water to Improve Its Efficiency to Remove Methylene Blue from Aqueous Solution

Combined treatment of red mud and coal fly ash by a hydro-chemical process

Red mud (RM) is a solid waste produced in the process of alumina extraction from bauxite and causes serious environmental problem. The recycle of alumina and alkali from RM by hydro-chemical process is believed to be an effective method for the utilization of RM. However, this industrial application has been limited for its difficulty in the solid-liquid separation of leached slurry and the low alumina extraction efficiency. In this paper, a novel process for the combined treatment of RM and coal fly ash (CFA) was proposed, and the effect of the mass ratio of CFA to RM, the Fe2O3 content and A/S (mass ratio of Al2O3 to SiO2) of the CFA on the extraction alumina efficiency and the filtration rate of leached slurry were investigated. When the CFA with A/S of 1.35 was used and the mass ratio CFA to RM was 1:1, the alumina extraction efficiency can be elevated from 72.14% to 91.70%. Especially, the filtration rate of leached slurry increased from 0.308m3/(m2·h) to 1.264m3/(m2·h). In addition, by decreasing the Fe2O3 content and increasing the A/S of CFA, the filtration rate of leached slurry could be enhanced obviously and the alumina in the mixture of RM and CFA could be extracted effectively. The results of phases and morphology of the residues showed that the increase of alumina extraction efficiency is attributed to two chemical processes, one is the complete transformation from Na8(Al6Si6O24)(OH)2.04(H2O)2.66 to NaCaHSiO4, and the other is the reduction of the generation of Ca3(Fe0.87Al0.13)2(SiO4)1.65(OH)5.4 with the increase of mass ratio CFA to RM. Furthermore, the growing number and length-diameter ratio of the rod-like structure of NaCaHSiO4 particles resulted in the increase in the filtration rate of leached slurry.

A Mineralogical Assessment on Residues after Acidic Leaching of Bauxite Residue (Red Mud) for Titanium Recovery

Due to its alkalinity, red mud produced by the Bayer process may affect both the environment and human health. For this reason, its further utilization instead of disposal is of great importance. Numerous methods have already been studied for hydrometallurgical treatment of red mud, especially for the recovery of various metallic components such as iron, aluminum, titanium or rare earth elements. This study focuses on the extraction of titanium from red mud and in particular the mineralogical changes, induced by leaching. Sulfuric acid, hydrochloric acid and their combination have been utilized as leaching agents with the same leaching parameters. It has been determined that sulfuric acid is the best candidate for the red mud treatment in terms of titanium leaching efficiency at the end of 2 h with a value of 67.3%. Moreover, samples from intermediate times of reaction revealed that leaching of Ti exhibit various reaction rates at different times of reaction depending on acid type. In order to explain differences, X-ray Diffraction (XRD), scanning electron microscope (SEM) and QEMSCAN techniques were utilized. Beside titanium oxide (TiO2) with available free surface area, a certain amount of the TiO2 was detected as entrapped in Fe dominating oxide. These associations between Ti and Fe phases were used to explain different leaching reaction rates and a reaction mechanism was proposed to open a process window.

Improvement of Strength and Radiation Protection Properties of Biodegradable Jute Fiber Reinforced Material

Over past few years, polymer composites with natural fiber reinforcement, called eco-composites, have achieved a worldwide compliance due to their strong potentiality to save the environment from pollution as a result of their ultimate disposability, as compared to glass-filled composites. Since natural fibers combine a low cost and low density with high toughness, biodegradability, renewability, reduced tool wear, and higher energy recovery. They are carbon dioxide neutral when burned and are present in abundance, which make composites made from them also sustainable and economical. We report a facile method for the improvement of strength and radiation protection properties of biodegradable jute fiber reinforced material by ceramic treatment of red mud. The developed powder was further blended with polyester resin to form thick, viscous radiation protection organic gel-based material. The developed protection gel material was then cured for making advanced non-toxic, biodegradable radiation protection panels using jute as natural fiber reinforcement. The developed radiation protection panels were analyzed by X-ray method with different energies of X-ray photons and were found to possess highly competent properties. Their various mechanical properties, like tensile, flexural, and impact strength values and morphological features were evaluated. The developed non-toxic, biodegradable, jute fiber reinforced, X-ray radiation protection panels combine good shielding and mechanical properties, which ensures their broad application spectrum ranging from diagnostic X-ray and CT scanner room installations to nuclear power plant and other strategic radiation shielding tasks.

Treatment of alumina refinery waste (red mud) through neutralization techniques: A review.

In the Bayer process of extraction of alumina from bauxite, the insoluble product generated after bauxite digestion with sodium hydroxide at elevated temperature and pressure is known as 'red mud' or 'bauxite residue'. This alumina refinery waste is highly alkaline in nature with a pH of 10.5-12.5 and is conventionally disposed of in mostly clay-lined land-based impoundments. The alkaline constituents in the red mud impose severe and alarming environmental problems, such as soil and air pollution. Keeping in view sustainable re-vegetation and residue management, neutralization/treatment of red mud using different techniques is the only alternative to make the bauxite residue environmentally benign. Hence, neutralization techniques, such as using mineral acids, acidic waste (pickling liquor waste), coal dust, superphosphate and gypsum as amenders, CO2, sintering with silicate material and seawater for treatment of red mud have been studied in detail. This paper is based upon and emphasizes the experimental work carried out for all the neutralization techniques along with a comprehensive review of each of the processes. The scope, applicability, limitations and feasibility of these processes have been compared exhaustively. Merits and demerits have been discussed using flow diagrams. All the techniques described are technically feasible, wherein findings obtained with seawater neutralization can be set as a benchmark for future work. Further studies should be focused on exploring the economical viability of these processes for better waste management and disposal of red mud.

Development of Functional Material for Simultaneous Shielding X-ray and EMI Radiations Using Inorganic–Organic Hybrid Gel

We report an unique method for the development of functional, non-toxic, flexible and moldable, simultaneous X-ray and EMI radiation shielding material, capable of simultaneous X-ray and EMI radiations shielding by exploring the multi elemental, multi componental phases present in red mud. The ceramic treatment of red mud leads to the formation of tailored radiation shielding powder having multilayered and multi shielding phases. Further, the shielding powder was treated with rheological and chemical compatible silicone polymer i.e. Polydimethylsiloxane (PDMS) to make inorganic–organic hybrid gel, which was further used to develop functional radiation shielding material of varying desire dimensions. The process basically involves sorption of PDMS on to the surface of particles of tailored radiation shielding powder via functional groups at interface which helps in achieving excellent dispersibility in the developed functional shielding material. The developed functional shielding material was evaluated for its diagnostic X-ray attenuation as well as electromagnetic shielding effectiveness (EMSE) characteristics and found to posses highly effective properties. X-ray attenuation was studied using Nomex Multimeter from PTW for energies of 80 kVp and 100 kVp X-ray photons. Evaluation of EMSE of the developed shielding material was done using vector analyzer in the frequency range of 8.2 GHz to 12.4 according to ASTM D4935. Also, the developed material was characterized by using various complementary techniques like FTIR, TGA, DSC, FESEM, XRD and EDXA for studying the chemical compatibility of PDMS with shielding powder. The developed functional material can be used in broad application spectrum ranging from diagnostic X-ray and CT scanner room to other strategic radiation shielding installation and other electronic devices simultaneously.

Study on dealkalization and settling performance of red mud.

At present, the dealkalization and comprehensive utilization of red mud is a worldwide problem. Studies on the settling performance and phase transformation of red mud by HCl, CaO, and H2O leaching are limited. In this study, the characteristics of red mud were systematically analyzed. The average sizes of graded and initial red mud were 4.11 and 9.20μm, respectively. X-ray diffraction (XRD), X-ray fluorescence spectra (XRF), and thermogravimetry-differential scanning calorimetry (TG-DSC) results indicated the different mineralogical phases, composition, and thermal behavior. The addition of HCl could neutralize the alkalization in the red mud slurry, and CaO could replace the Na and K. Notably, the pH of the red mud slurry had no obvious change with the increase in water washing times in a certain pH. Interestingly, soluble Al and Fe were not detected in the HCl-red mud and CaO-red mud. In addition, the settling ratio was used to express the settling performance of the red mud slurry. Their interaction mechanisms were proposed, which may include phase transformation and the changing of the size and surface area. The research provided a better understanding of the phase transformation and settling performance in the treatment of red mud by HCl, CaO, and H2O leaching.

Gallium and vanadium extraction from red mud of Turkish alumina refinery plant: Hydrogarnet process

In this paper the treatment of red mud by autoclave leaching for its conversion into ferrous hydrogarnet product and extraction of valuable components (i.e. Na2O, Al2O3, Ga and V2O5) was investigated. Leaching of red mud using high modulus alkaline solution (Na2O 240g/L; αк=30) in the presence of lime at 240–260°C was found to allow the recovery of the contained values (98.5% Na2O, 65.3% AI2O3, 55.5% Ga and 65.8% V2O5) and the fixing silica in the form of hydrogarnet mud (3СаО·Fe2O3·2SiO2·2Н2О) with a low alkali content (0.35% Na2O). An effective treatment scheme for the leach solution based on precipitation and two-stage carbonization processes was developed and demonstrated. This allowed the generation of alkaline solutions suitable for recycling back to leaching stage and recovery of a concentrate (30% AI2O3) that is rich in Ga (0.32%) and V2O5 (3.7%). The chemical and phase composition of the solid products obtained from each stage of processing were determined by XRF and XRD analyses. This study has demonstrated that Bayer–hydrogarnet process can be suitably exploited for processing of red mud.

Experimental and simulative study on phase transformation in Bayer red mud soda-lime roasting system and recovery of Al, Na and Fe

Red mud, or bauxite residue, is the largest environmental concern of alumina refineries, mainly because of the size of this waste stream and its caustic characteristics. This paper reports part of a research effort aimed at developing an economically feasible zero waste process for the treatment of red mud. Soda-lime roasting was carried out on fine red mud, which was separated from raw red mud physically with particle size below 75μm, under reductive atmosphere prior to leaching and magnetic separation. The aim was to recover valuable components such as Al, Na and Fe from the fine red mud. This study found that, the recovery of Al and Na after the water leaching was about 75.7% and 80.7%, respectively. The recovery of iron depended on the type of reduction products. Under the roasting conditions applied in this study, spinel, sodium aluminosilicate, and larnite are dominant mineral phases in the roasted samples, with calcium aluminoferrite, melilite and wustite being minor phases. The effect of Ca content and of reaction atmosphere on the equilibrium phases was studied by experiments and thermodynamic modeling, and the dependence of the recovery of Al and Na on these factors was demonstrated.

Stockpiling and Comprehensive Utilization of Red Mud Research Progress

With increasing production of red mud, the environmental problems caused by it are increasingly serious, and thus the integrated treatment of red mud is imminent. This article provides an overview of the composition and the basic characteristics of red mud. The research progress of safe stockpiling and comprehensive utilization of red mud is summarized. The safe stockpiling of red mud can be divided into two aspects: the design and safe operation of the stocking yard. The comprehensive utilization of red mud can be further divided into three aspects: the effective recycling of components, resource utilization and application in the field of environmental protection. This paper points out that the main focus of previous studies on red mud stockpiling is cost reproduction and land tenure. The recovery of resources from red mud has a high value-added, but low level industrialization. The use of red mud as a building material and filler material is the most effective way to reduce the stockpiling of red mud. Red mud used for environmental remediation materials is a new hotspot and worth promoting for its simple processing and low cost.

Environmental and economic life cycle assessment of aluminum-silicon alloys production: a case study in China

A coupled life cycle costing and life cycle assessment was carried out to estimate the economic and environmental impact of silicon-aluminum alloy production. The results showed that the aluminum alloy made from secondary aluminum accounted for 70%–95% of the environmental benefits in most categories, except in the land occupation and economic categories, compared with the aluminum alloy made from primary aluminum. These findings could be attributed to the decrease in energy and raw material consumption (i.e., electricity, sodium hydroxide, petroleum coke, and charcoal consumption) and the relatively high cost of secondary aluminum scrap. Optimizing raw material and electricity consumption efficiency, decreasing the transport distance from raw material (e.g., bauxite and old aluminum scrap) buyers to suppliers, and changing the end-life treatment of red mud from landfill to road building material production are key factors in reducing the overall environmental and economic impact.

Bioremediation of acid mine water utilising red mud and Desulfotomaculum nigrificans

The efficiency of red mud as an adsorbent for the removal of metal ions and sulphate from synthetic acid mine water was assessed. Almost complete removal of Fe–z (98%), Fe3+ (99%) and Cu2+ (97%) and a significant removal of Zn2+ (84%) was achieved from acid mine water at pH 2·3. However, only about 27% of sulphate reduction could be attained. A noteworthy feature was the concomitant increase in pH from 2·3 to 7·6 with the increase in red mud loading under appropriate conditions. The adsorption isotherms adhered to Freundlich and Langmuir relationships and were endothermic in nature. The free energy of the adsorption process was found to be negative attesting to the feasibility of the reaction. The adsorption kinetics followed the first order Lagergren rate equation. The filtrate obtained after treatment of red mud with synthetic acid mine water supplemented with carbon and nitrogen sources served as a successful growth medium for the sulphate reducing bacteria, namely Desulfotomaculum nigrificans (Dsm. nigrificans). Bacterial growth studies indicated that about 22, 41 and 52% of sulphate reduction could be achieved at initial pH values of 5, 6·1 and 7·2 respectively. The pretreatment of the acid mine water with red mud followed by bioremoval using Dsm. nigrificans resulted in about 27, 47 and 62% of sulphate removal at initial pH values of 5, 6·1 and 7·2 respectively, cumulatively by adsorption and bioreduction. The mechanisms of metal ion removal utilising red mud and sulphate reduction using Dsm. nigrificans are discussed.

Alumina recovery from spent Bayer liquor by methanol

Decomposition of sodium aluminate solution is the key step for alumina production; however, approximately only 55% alumina yield is obtained by seeded precipitation. So, it is difficult to obtain sodium aluminate solution with high caustic ratio. In this study, a method was explored to recover alumina from spent Bayer liquor by deep decomposition with methanol. A variety of conditions, including reaction temperature, reaction time, methanol amount and seed coefficient were elaborately investigated. The results showed that the appropriate conditions were 1:1 in volume ratio of methanol to spent Bayer liquor, more than 1.0 seed coefficient and in a 40 °C water bath for 24 h. By characterizing through XRD, the crystal products were found to be Al(OH) 3. With this method, the molar ratio of Na 2O to Al 2O 3 of the spent liquor can be increased from about 3.0 to 10.0 due to the recovery of alumina, which is beneficial for the treatment of red mud.

Effect of Acidic Surface Treatment of Red Mud on Mechanical Interfacial Properties of Epoxy/Red Mud Nanocomposites

In this work, red mud (RM) was chemically modified by 0.1, 1, and 5 M H3PO4 solution to prepare epoxy/RM nanocomposites. The effect of chemical treatment on a RM surface was studied in terms of pH, acid–base values, N2/77 K gas adsorption, equilibrium spreading pressure (πe), and surface free energy. The mechanical interfacial properties of epoxy/RM nanocomposites was measured in the context of critical stress intensity factor (KIC) and critical strain energy release rate (GIC) measurements. From the experimental results, the acidic surface treatment led to a modification of the RM surface properties, such as the surface acid values, porosity, specific surface area, πe, and London dispersive component (γSL) of surface free energy of the treated RM as an increase of the treatment concentration. In the fracture toughness (KIC and GIC) measurements, the mechanical interfacial properties of epoxy/treated RM nanocomposites were intimately correlated with the improvement of interfacial adhesion between the RM surface and a matrix and the increase of γSL of surface free energy of the RM due to the development of SBET or porosity of RM surfaces.