Red Mud Samples Research Articles

The Use of Waste Materials Red Mud and Fly Ash as Road Embankment Fill

This study provides a comprehensive evaluation of red mud as a sustainable material for road base construction, particularly in combination with bottom ash. Red mud, a by-product of the Bayer process used in alumina extraction, is known for its high alkalinity and heavy metal content. For this reason, this waste material causes environmental challenges. Red mud sourced from the Eti Aluminum Factory in Seydişehir, Konya (Turkey), was stabilized with bottom ash. Then, these waste materials were tested through a number of experiments, such as in relation to their Atterberg limits, compaction characteristics, unconfined compressive strength (UCS), California bearing ratio (CBR), and microstructure through a scanning electron microscopy (SEM) analysis. The results highlight that the UCS of stabilized red mud samples significantly improved with the addition of bottom ash and longer curing periods. Specifically, the UCS values increased from 0.5 MPa to 2.5 MPa after 28 days of curing. Moreover, RM specimens stabilized with 25% bottom ash achieved a CBR value of 146.64% after 28 days, far exceeding Turkey’s road fill material requirement, which mandates a minimum unsoaked CBR value of 15%. These findings indicate that red mud stabilized with bottom ash not only meets but exceeds the structural requirements for road base materials. This approach provides a sustainable solution for the environmental management of red mud while contributing to infrastructure development. Through the recycling of these industrial by-products, this study presents a viable method to reduce waste and support economic and environmental sustainability in road construction projects.

Environment Assessment of Modified Red Mud Utilized in Roadbed

Utilization of red mud in road projects is an effective way to consume large amounts of red mud on a large scale. In order to meet the requirements for road performance, a modified material, Heinchem, has been developed on the basis of extensive experiments, and the long-term environmental risks of red mud modified by this material have been investigated. By collecting and modifying original red mud samples, a series of continuous leaching tank experiments are carried out based on the exposure scenario analysis. According to the leaching content of pollution in the original and modified red mud, the characteristic pollutants are identified. The release mechanism of these characteristic pollutants in the modified red mud is revealed, and the long-term release amount is predicted. Furthermore, in light of the actual road use scenario of the modified red mud, a risk assessment model is established and used to simulate the release, migration, and transformation of characteristic pollutants during the use of modified red mud as roadbed material. The groundwater environmental risk is then assessed. Finally, an acute toxicity test of earthworms and a seed germination test are conducted to investigate the impact of the modified red mud on the farmlands. The results showed that the proposed red mud modified materials have obvious curing effects on V, As, Se, Mo, and F. When the leaching contents of V, Cr6+, Cr3+, As3+, Se4+, Se6+, Mo, and F in the modified red mud were lower than 0.15 mg/L, 0.1 mg/L, 0.2 mg/L, 0.012 mg/L, 0.012 mg/L, 0.012 mg/L, 0.075 mg/L, and 1.2 mg/L, respectively, the environmental risk of modified red mud during long-term road use is acceptable. This study provides a new way for the resource utilization of red mud.

Waste Management of Red Mud and Fly Ash to Utilize in Road Subgrade Material

Red mud (RM) is a waste material obtained during the production of aluminum from bauxite minerals. RM causes environmental pollution due to its high alkaline properties. Therefore, RM materials are stored in waste reservoirs. As production continues, the number of required waste reservoirs increases day by day. This study aims to utilize RM waste material in construction structures to contribute to the economy. The research investigates the potential use of RM waste material as road fill material. RM was improved using another waste material of fly ash (FA) since RM has low strength. Atterberg limit tests, compaction tests, unconfined compression tests, CBR tests, and SEM analyses were conducted on stabilized RM samples. In the physical properties of stabilized RM, Atterberg limits and optimum moisture content increase and density decreases since FA content increases. In the mechanical properties of stabilized RM, unconfined compressive strength, initial and secant modulus of elasticity, and California bearing ratio increase and maximum peak strain decreases since FA content and curing period increase. SEM images prove the increase in mechanical properties due to the cementation products (CSH and CAH gels) formed in the microstructure of stabilized RM. The results showed that RM waste stabilized with FA can be used as road subgrade material.

Experimental investigation of multiple industrial wastes for carbon dioxide removal strategies

Industrial solid waste by-products are being increasingly employed for geochemical carbon dioxide removal (CDR) strategies due to their fine grain size, accessibility, and large annual production tonnages. Here, a range of such by-products has been tested experimentally for their reactivities with CO2 and water. Sample solutions were monitored for 100 h for changes in chemistry, and solid samples were characterised pre- and post-experiment. Samples rich in Ca- and Mg-bearing minerals, such as dunite, kimberlite, and ilmenite mine tailings, as well as marble quarry cuttings, were key cation sources. Ni sulphide, fluorite and borax tailings, coal-fired power plant fly ashes, and red mud samples showed high dissolution rates. The highest reaction rates were often observed during the initial few hours, and compared well to rates determined for rocks typically targeted for CDR purposes, such as basalt and gabbro. Several samples also showed secondary carbonate precipitation, suggesting opportunities for the development of single-step CDR technologies. Overall, the results of this study indicate that several industrial by-products can provide sufficient cations at favourable dissolution rates for geochemical CDR purposes. Any on-site or near-site conditions for reaction acceleration such as heat, concentrated CO2 or microbes, could further increase favourability for geochemical CDR opportunities.

Suppressive effects of geotextiles on soil water evaporation

Geotextiles find wide applications in the field for filtration and drainage. When applied on the soil surface they influence soil evaporation. The objective of this work is twofold: (a) to assess the effectiveness of four different geotextiles as cover materials on soil evaporation, (b) to study the combined effect of geotextile and perforated mechanical barriers on soil evaporation. The first set of experimental programs consisted of three soil samples i.e. kaolin, dredged mud from the port of Brisbane and a locally obtained red mud sample from Queensland, Australia tested with four types of non-woven geotextiles under four controlled climatic conditions. All the 4 geotextiles had suppression effects on soil evaporation to degrees that varied with the type of soil, ratio of pore size to thickness of geotextiles (M*), product of pore size to thickness of the geotextiles (N*) and climatic conditions. Geotextiles with a higher pore size (O95) and M* allowed water vapor to move through relatively easily leading to higher evaporation rates. Geotextile with a higher thickness and N* value provided a higher suppression effect on soil evaporation. In a recently introduced dewatering method involving perforated ventilated well method, evaporation from soil take place through geotextiles and the perforated well. Mimicking this, impacts on soil evaporation with geotextiles sandwiched between soil sample and perforated sections were also studied. Maintaining similar number and arrangement of the perforations, soil evaporation was noted to be higher with rectangular shaped perforation compared to circular shaped perforations.

Study on hydration mechanism and environmental safety of thermal activated red mud-based cementitious materials

Red mud (RM) cementitious materials were prepared with the thermally, thermoalkali- or thermocalcium-activated RM, steel slag (SS), and other additives. The effects of different thermal RM activation methods on the cementitious material hydration mechanisms, mechanical properties, and environmental risks were discussed and analyzed. The results showed that the hydration products of different thermally activated RM samples were similar with the main products being C-S–H, tobermorite, and Ca(OH)2. Ca(OH)2 was mainly present in thermally activated RM samples, and the tobermorite was mainly produced by samples prepared with thermoalkali- and the thermocalcium-activated RM. The mechanical properties of the samples prepared by thermally and thermocalcium-activated RM had early-strength properties, while the thermoalkali-activated RM samples were similar to the late-strength type of cement properties. The average flexural strength of thermally and the thermocalcium-activated RM samples at 14 days were 3.75 MPa and 3.87 MPa respectively, whereas, the 1000 °C thermoalkali-activated RM samples only at 28 days was 3.26 MPa; the above data could reach the single flexural strength (3.0 MPa) of the first-grade pavement blocks of the building materials industry standard of the People’s Republic of China-concrete pavement blocks (JC/T446-2000). The optimal preactivated temperature for different thermally activated RM was different; the optimal preactivated temperature for both thermally and thermocalcium-activated RM was 900 °C, and the flexural strength was 4.46 MPa and 4.35 MPa, respectively. However, the optimal preactivated temperature of thermoalkali activated RM at 1000 °C. The 900 °C thermally activated RM samples had better solidified effects for heavy metal elements and alkali substances. 600~800℃ thermoalkali activated RM samples had better solidified effects for heavy metal elements. Different temperatures of thermocalcium-activated RM samples showed different solidified effects on different heavy metal elements, which may be due to the influence of thermocalcium activation temperature on the structural changes of the hydration products of the cementitious samples. In this study, three thermal RM activation methods were proposed, and the co-hydration mechanism and environmental risk study of different thermally activated RM and SS were further elucidated. This not only provides an effective method for the pretreatment and safe utilization of RM, but also facilitates the synergistic resource treatment of solid waste and further promotes the research process of replacing part of traditional cement with solid waste.

The remediation efficiency of heavy metal pollutants in water by industrial red mud particle waste

This study aims to treat heavy metal pollutants in water by applying red mud particle waste. An experiment on the static adsorption of heavy metal ions Pb 2 + (or Cd 2 + and Cu 2 + ) by red mud particles was carried out, and the influences of the type of heavy metal ion, ion concentration, pH value, red mud dosage, reaction time, and temperature on adsorption performance were explored. The competitive adsorption mechanisms of various coexisting heavy metal ions by red mud particles were compared. The red mud samples loaded and not loaded with heavy metal ions were detected by zeta potential measurement, scanning electron microscopy, and Fourier transform infrared spectrometry. The adsorption strength of red mud particles for heavy metal ions was ranked in the sequence of Pb 2 + , Cd 2 + , and Cu 2 + , while increasing temperature enhanced their adsorption. When the initial pH values were 4.3, 5.0, and 3.6 for Pb 2 + , Cd 2 + , and Cu 2 + solutions, the removal peaks were 94.5%, 92.8%, and 78.1%, respectively. The preferred order of adsorption for red mud was Pb 2 + , Cd 2 + and then Cu 2 + under the competitive mechanism of binary/ternary systems due to the discrepancy in the functional groups of red mud particles loaded with different heavy metal ions. • A concept for purifying heavy metal pollutants in water using red mud is proposed. • The competitive adsorption mechanism of various heavy metal ions is revealed. • The influence of temperature on the interaction of heavy metal ions and red mud is emphasized. • An adsorption–desorption model with hysteresis is verified by experimental results.

Evaluation of Main Factors for Improvement of the Scandium Leaching Process from Russian Bauxite Residue (Red Mud) in Carbonate Media.

The carbonate leaching of scandium from the landfilled bauxite residue (red mud) of the Bogoslovsky Aluminum Plant (Russia) and samples of red mud (RM) after alkaline pretreatment has been investigated. The results of kinetic studies allowing to compare and evaluate the effectiveness of different conditions and intensification factors in the process of scandium leaching from RM in carbonate/bicarbonate media are presented. It was determined that for 2.0 mol L–1 Na2CO3 leaching solution ultrasonic treatment under gas (CO2) carbonation conditions in the pH range of 9.5–10.0 allows reducing the scandium leaching time by two times and reaching 40–45% scandium extraction. Leaching of RM in carbonate/bicarbonate media is accompanied by secondary processes (adsorption, hydrolysis, and coprecipitation) leading to a decrease in scandium extraction. The obtained results allow improving understanding of scandium chemical behavior in complex aqueous carbonate/bicarbonate systems and can be used for the optimization of the alternative carbonate process for scandium extraction from RM.

Uranium stabilization in red mud by sintering: Mechanism and leachability

Uranium(VI)-bearing waste is inevitably produced in the process of aqueous U(VI) abatement by red mud (RM). Such U(VI)-bearing waste has been considered to be highly hazardous to the environment and human because of their easy mobility, high toxicity, and radioactive. The stabilization of uranium constitutes an urgent challenge that must be solved through an economic and feasible waste management strategy. Herein, a low thermal stabilization process was well-designed for stabilizing U(VI) in red mud into particular phase(s) such as geopolymer-like microstructures. Characterization and leaching experiments were further performed for U(VI)-bearing RM samples thermally stabilized at various temperatures, and the stabilization mechanism of uranium in the RM was explored. X-ray diffraction (XRD) results revealed that a geopolymer-like phase whose main components were Al, Si and O was formed when the U(VI)-bearing RM was treated at 600 °C; thus, uranium was successfully stabilized. When treated at higher temperature (i.e., 900 °C), the U(VI)-bearing RM formed feldspar minerals from the oxides of Si and Al, which originated from the broken geopolymers (a stable three-dimensional network), thus exposing uranium to the surface. The constant-pH leaching test evidenced that the sintering temperatures of 600–800 °C could facilitate the fixation of uranium by RM. The findings of this study offer us a promising strategy on the utilization of RM to eliminate and stabilize U(VI) from waste streams.

Use of red mud activated at different temperatures as a low cost adsorbent of reactive dye

ABSTRACT Red mud, a waste product generated during alumina extraction from bauxite, could be used as a low-cost adsorbent. Here, the effect of thermal treatment on the adsorption of Reactive Blue 19 (RB19) dye by red mud was compared with the adsorption capacity of untreated red mud. Thermal treatment of red mud at 500°C results in an increase in adsorption capacity from 357 mg g-1 (untreated red mud) to 416 mg g-1, under acidic conditions. Red mud samples thermally treated at 600°C and 800°C show a reduction in adsorption capacity, however, falling to 337 mg g-1, in acid medium. The change in the maximum adsorption capacity of red mud to RB19 following thermal treatment is associated with specific surface area. Red mud subjected to 500°C can be used for the treatment of water and wastewaters with a higher efficiency than untreated red mud, thus finding possible application in the textile industry.

Extraction of Rare Earths from Red Mud Iron Nugget Slags with Oxalic Acid Precipitation

ABSTRACT Red mud contains large amounts of rare and valuable minerals. Specifically, rare earth elements are present at a concentrated amount in many red mud samples around the world. There is currently only one ore source in the United States that can produce rare earth elements. Pursuing avenues to extract rare earths from red mud is highly advantageous to reduce the amount of red mud being stockpiled, give value to red mud as a waste, and utilize a source for producing rare earths. The iron nugget process effectively increases the concentration of rare earth elements by removing iron. Slag from the iron nugget process upgraded the concentration of rare earth elements by 100%, which makes this a desirable feed for processing. Hydrochloric acid was used to dissolve the rare earth oxides present in the nugget slags, rare earths were then precipitated as a solid using oxalic acid. HCl leach can recover 170 grams of rare earths per ton of red mud nugget slag and oxalic acid precipitation can recover 45 grams per ton.

Preparation of a mixed Al/Sc nano-oxide derived from the bauxite residue (red mud) via the sulfuric acid roasting–leaching–precipitation process

In this study, three methods were used and compared for the selectable extraction of aluminum/ scandium with the least amount of iron in red mud (RM) samples from the Iran alumina plant in Jajarm as follows: 1) RM direct acid leaching with H2SO4, 2) RM washing with hydrochloric acid and oxalic acid before leaching with H2SO4, and 3) RM sulfuric acid roasting-leaching-precipitation. The aim was to extract the highest amount of scandium while preventing the leaching of other metals, especially iron. Due to any discriminative features, the selective separation of Al/Sc with methods 1 and 2 was impossible practically. While, method 3 resulted in 73.7% of extracted scandium under optimal conditions with only 0.6% of iron found in the final product. The characterization of the final oxide product was done via inductively coupled plasma mass spectrometry (ICP-MS) and energy-dispersive X-ray analysis (EDX). The morphology of the oxide product was examined by field emission scanning electron microscopy (FE-SEM). This mixture oxide had a nanosize spherical shape and was distributed uniformly. The pH of the remaining red mud after the acid roasting-leaching-precipitation method was 8, which was far more environmentally desirable than the primary red mud with a pH = 12.

Hydrothermal Resource-saving Processes in Complex Processing of Bauxite and Red Mud


 
 
 The Bayer bauxite residue (red mud, RM) is environmentally hostile and hazardous to human health. Red mud can be viewed as an important and promising source of scandium, yttrium, zirconium and other elements rather than a solid waste. Due to a high content of iron in bauxites and especially in RM, the conversion of hematite into magnetite in Bayer liquor plays a key role in the exploration of a cleaner technology of alumina production. Thus, RM and raw bauxite were used for hydrothermal digestion in an original one-stage method of magnetite production during co-recovery of alumina. The yield of alumina reaches 80% from RM and more from bauxites during digestion with addition of lime and Fe(II) or Fe . The saturation magnetization of a bulk sample of magnetized bauxite is 40.5 emu/g, two orders of magnitude higher than that of a raw red mud sample. Moreover, magnetite containing a residue has a high crystallinity, which contributes to better deposition and magnetic separation in the development of an overall flowsheet for RM utilization.
 
 
 
 Keywords: Red mud, bauxite, hydrothermal treatment; enrichment, extraction, magnetization, hematite, magnetite, rare elements
 
 
 
 
 

Influence of Sodium Sulfate Addition on Iron Grain Growth during Carbothermic Roasting of Red Mud Samples with Different Basicity

Red mud is an iron-containing waste of alumina production with high alkalinity. A promising approach for its recycling is solid-phase carbothermic roasting in the presence of special additives followed by magnetic separation. The crucial factor of the separation of the obtained iron metallic particles from gangue is sufficiently large iron grains. This study focuses on the influence of Na2SO4 addition on iron grain growth during carbothermic roasting of two red mud samples with different (CaO + MgO)/(SiO2 + Al2O3) ratio of 0.46 and 1.21, respectively. Iron phase distribution in the red mud and roasted samples were investigated in detail by Mössbauer spectroscopy method. Based on thermodynamic calculations and results of multifactorial experiments, the optimal conditions for the roasting of the red mud samples with (CaO + MgO)/(SiO2 + Al2O3) ratio of 0.46 and 1.21 were duration of 180 min with the addition of 13.65% Na2SO4 at 1150 °C and 1350 °C followed by magnetic separation that led to 97% and 83.91% of iron recovery, as well as 51.6% and 83.7% of iron grade, respectively. The mechanism of sodium sulfate effect on iron grain growth was proposed. The results pointed out that Na2SO4 addition is unfavorable for the red mud carbothermic roasting compared with other alkaline sulfur-free additives.

Improvement of Oxygen Mobility with the Formation of Defects in the Crystal Structure of Red Mud as an Oxygen Carrier for Chemical Looping Combustion.

Fe₂O₃ is the major component of red mud, which is a by-produced after eluting aluminum from bauxite in the Bayer process, and can be used as an oxygen carrier. On the other hand, red mud is unsuitable for using oxygen in the crystal lattice because of its low surface area. In this study the red-mud sample was sulfidated at high temperatures to improve the lattice oxygen mobility by forming lattice defects in the iron oxide crystals. To form crystal defects on red mud, iron oxide was converted to iron sulfide with hydrogen sulfide, and then re-oxidized by air to remove the sulfur components. In these processes, it was possible to generate defects could be generated in the crystal structure. Crystal defects are formed by the difference in the molar volume of oxygen and sulfur bound to the metal in the oxidation-sulfidation process. The surface area of the defective red mud increased from approximately 25.9 m₂/g to 122.1 m₂/g, and the pore volume increased from 0.1714cc/g to 0.2803 cc/g. In addition, the formation of crystal defects increased the oxygen transfer capacity of red mud from 1.75% to 2.25% at 15 vol.% hydrogen. This means that the amount of oxygen transported during the reduction process could be enhanced approximately 1.29 fold.

Evaluation of microwave acid baking on Indian red mud sample

The present study validates the application of microwave heating for acid baking of red mud and the dissolution of metallic values during water leaching. The effect of microwave power and exposure time is evaluated on the sulfation and decomposition mechanism of the constituent phases present in the red mud. It is inferred that the processing time can be significantly reduced to less than 3 min for the enrichment of Fe (~41%) and Ti (~15%) in the residue by employing microwaves as a heating source. The low solution pH value (<2) for baking experiments with less than 90 s synergized to improve metal dissolution during the leaching stage. The metallic values in the solution were precipitated and calcined to produce a product containing refractory phases such as mullite, alumina, and hematite, which can be segregated using a conventional magnetic separation process. The dissolved titanium values interact with iron values and occur in ilmenite and pseudobrookite phases in the calcined precipitate. The microwave-assisted acid baking process is a potential first step process for the complete utilization of red mud and separation of iron and titanium values.

Radiological assessment of the bauxite mining in Turkey and estimation of radiation dose contribution of the red mud as a concrete agent of the model room by using RESRAD-BUILD computer code

Red mud resulting from bauxite mining and processing is a cause of considerable concern because of the large amount of production and potential risks of long-lived natural radionuclides. In this study, samples taken from ore to end-products including waste in facilities were measured by gamma-ray spectrometry and radiological assessment indexes were calculated. For assessment of the usage of red mud as an additive in concrete, exposures of the occupant were calculated by using RESRAD-BUILD computer code for a model room. The radiological risk did not found for the use of red mud samples in the determined ratios in concrete.

A regiocentric economic sensitivity analysis for scandium recovery from red mud

Abstract Red mud is the industrial waste generated from bauxite processing and is a highly alkaline and hazardous material that has been stockpiled over decades near aluminum mining sites all over the world. The chemical composition of stockpiles depends on the region and is rich in transition metal oxides and metal ions along with rare earth metals. Remediation of red mud is of utmost importance due to the ecological danger they present and also due to the huge quantities produced every day. Even though red mud contains valuable metals, remediation with their extraction is not economically attractive. Recently the authors have developed a process for the recovery of scandium from red mud and optimized it for economic viability using cost evaluation studies. But the amount of Sc depends on the place of generation. Various red mud samples from Jamaica, Alcoa (US), Canada, Korea and India were collected and analyzed using TXRF, XRD, SEM, EDX. A preliminary comparative probabilistic economic assessment of the earlier developed process is done using Monte Carlo simulation Techniques with the red mud samples of various origins.

Red-mud based porous nanocatalysts for valorisation of municipal solid waste

Red mud samples were used to catalyse in-situ co-pyrolysis of pinewood and low-density polyethylene for the production of high-quality bio-oil. The sodium cation in the crude red-mud was exchanged with barium and calcium cations and further tested to explore their role in oil upgrading. The relationship between red-mud catalytic activity and its constituents was explored using synthetic sodalite. The red-mud catalysts exhibited a considerable aromatisation capacity compared to the thermal co-pyrolysis, as the selectivity towards monocyclic aromatic hydrocarbons increased from 12.7 to 19.6%, respectively. Long-chain molecules cracking was more significant in synthetic sodalite associated with their acidic active sites. The addition of barium and calcium cations to the red-mud largely improved oxygen elimination as a result of the enhanced catalyst basicity. In contrast, the aromatisation ability of red-mud significantly impeded by the large cation size (Ba2+ and Ca2+) due to the limited diffusion of pyrolysis vapours to the active sites. Ba-exchanged red-mud catalysts reduced the content of carboxylic acids in the bio-oil to 1.8 % while maintained a high yield of the organic fraction (34 %). Ca-exchanged red-mud catalysts produced the lowest fraction of oxygenated compounds (35.1 %); however, the organic phase yield was as low as 23.6 %. The modified red-mud catalysts reduced the fraction of oxygenated compounds from 69.9–35.1% during the biomass-plastic co-pyrolysis.

Production of electrolytic iron from red mud in alkaline media

In this study, the feasibility of producing electrolytic iron from red muds in a strongly alkaline medium at 110 °C was studied. The red mud samples from a French industry were characterized by various techniques (ICP-AES, SEM, XRD) to determine their chemical and mineralogical compositions. The main phase in the red mud investigated was hematite (α-Fe2O3). Iron electrodeposition tests from red mud suspended in a 12.5 mol/L NaOH electrolyte were conducted at constant current in a stirred electrochemical cell. The solid:liquid ratio and amounts of impurities contained in red mud were varied to optimize the faradaic yield and the production rate of electrolytic iron. Whereas hematite can be reduced to iron with a current efficiency over 80% for a current density (cd) up to 1000 A/m2, the current efficiency with red muds was highest for a cd below 50 A/m2 and then decreased regularly to 20% at 1000 A/m2. In all cases, the deposit produced contained more than 97% metal iron. The moderate performance of the process investigated with red mud was attributed to a troublesome adsorption of red mud particles on the cathode, making the reduction far less efficient than that with hematite.