Red Mud Samples Research Articles

Hematite (α-Fe2O3) – A potential Ce4 + carrier in red mud

Cerium is the most abundant rare earth element (REE) within the waste product of alumina production (red mud), but its speciation in this complex material is still barely understood. Previous studies showed evidence for a correlation between Ce and the main constituent of red mud, iron oxides, which led us to investigate the most abundant iron oxide in red mud, hematite, as possible carrier phase for Ce.Synthetic hematite can incorporate up to 1.70±0.01wt% Ce, which leads to a systematical increase of all unit cell parameters. Investigations by extended X-ray absorption fine structure spectroscopy suggest an incorporation of Ce4+O6 into the hematite structure by a novel atomic arrangement, fundamentally different from the close-range order around Fe3+ in hematite.Samples of red mud were taken in Lauta (Saxony), Germany and analyzed by powder X-ray diffraction, inductively coupled plasma mass and optical emission spectrometry, electron microprobe analysis and X-ray absorption near-edge structure spectroscopy. Red mud samples consist of hematite (Fe2O3) (34–58wt%), sodalite (Na8Al6Si6O24Cl2) (4–30wt%), gibbsite (Al(OH)3) (0–25wt%), goethite (FeOOH) (10–23wt%), böhmite (AlOOH) (0–11wt%), rutile (TiO2) (4–8wt%), cancrinite (Na6Ca2Al6Si6O24(CO3)2) (0–5wt%), nordstrandite (Al(OH)3) (0–5wt%) and quartz (SiO2) (0–4wt%). While the main elemental composition is Fe>Al>Na>Ti>Ca (Si not included), the average concentration of REE is 1109±6mg/kg with an average Ce concentration of 464±3mg/kg. The main carrier of Ce was located in the Fe-rich fine-grained fraction of red mud (0.10wt% Ce2O3), while other potential Ce carriers like monazite, lead oxides, secondary Ce-minerals and particles of potentially anthropogenic origin are of subordinated relevance. Cerium in red mud occurs predominantly as Ce4+, which further excludes Ce3+ minerals as relevant sources.

Radon Exhalation from Industrial Residues as Suitable Additives for Building Materials

Radon exhalation from phosphogypsum (PG) and red mud (RM) samples are of environmental concern. The study is oriented to evaluate by different nuclear techniques, industrial materials cumulated in sites at Moron (PG) and Puerto Ordaz (RM) in Venezuela. RM samples and industrial by products are assessed for its potential use as additives in building materials regarding its radiological health risk. Radioactive matter concentration in RM is up to 11.6 kBq.kg-1. Radon concentration range for RM dry powder is between DL and 2.5 kBq.m-³ and for PG is between 105-340 Bq.m-³. Results indicate that industrial by product before it can be used as additive; require remedial actions to lower the environmental impact. Experimental values are compared with locally available cement, bricks and gypsum building materials.

Awaso bauxite red mud-cement based composites: Characterisation for pavement applications

This paper presents the development of Bauxite residue (red mud) based cement composite mortar blocks for applications in pavement construction. The experimental techniques considered include the structural, thermal, morphological and microscopy analysis of the raw bauxite and red mud samples calcined at 800°C. Composite mortar blocks of different batch formulations were produced and their physicochemical properties were investigated. The results show that the compressive strength of the as-prepared composite mortar blocks increased by ∼40% compared to the type M mortar strength of ∼2500N/mm2. The load bearing applications of the composites are discussed to influence the adoption of the calcined red mud as supplement in the production of low-cost Portland cement based composite mortar blocks for the construction industry.

Studies on extraction of gallium (III) from chloride solution using Cyphos IL 104 and its removal from photodiodes and red mud

An efficient solvent extraction process was developed for extraction of gallium (III) from acidic chloride medium using the ionic liquid Cyphos IL 104 diluted with toluene. The kinetics of gallium extraction was very fast. The extraction percent of gallium was found to increase with increase in hydrochloric acid concentration in the feed and 99.8% extraction of gallium was achieved with 3M HCl. The stoichiometry of the formation of gallium-Cyphos IL 104 complex was found to be 1:1 and the corresponding extracted species was proposed as [R3R′PGaCl4]. Presence of sodium chloride increased the percentage extraction of gallium. The thermodynamic parameters calculated from the temperature variation study suggested the process was spontaneous and endothermic. Loading capacity of the ionic liquid was executed and the stripping study of the loaded organic phase was investigated using four stripping agents namely HCl, H2SO4, NH3 and HNO3 each having concentrations of 0.5mol/L. It was found that HCl performance was poor and the rest three could recover >90% gallium from the loaded organic phase. Binary separation studies were carried out using commonly associated metal ions with gallium (Al (III)/Zn (II)/Fe (III)/Cu (II)/Ni (II)) and the process was extended to study the recovery of gallium from leach liquors of photodiodes and red mud sample.

Controlled reduction of red mud by H2 followed by magnetic separation

The current study presents a novel processing approach for the separation of the iron oxide from Red Mud (RM), based on the gentle reduction by hydrogen in static conditions followed by wet magnetic separation. The conversion degree of hematite, initially contained in RM, to magnetite was investigated in relation to reduction time, temperature, and the H2 supply. The maximum achieved conversion reached 87% at 480°C. The phase transformations during the thermal reduction were investigated via X-ray diffractometry, Mössbauer spectroscopy, electron microscopy, and magnetic measurements. After reduction at the optimal conditions, the reduced RM sample was subjected to magnetic separation and a magnetic fraction with over 54wt% magnetite concentration was obtained. Such magnetic fractions could be used as a feed in the pig iron industry, while the non-magnetic fraction could be further treated in order to recover the rare earths or to be used as a raw material for building materials.

Physicochemical, mineralogical and radiological properties of red mud samples as secondary raw materials

The main goal of the presented research was the preliminary investigation of possibility of red mud - Hungarian dump sites Almasfuzito (sample A) and Ajka (sample B) - application as a pigment or as a raw material for use in the construction materials industry. Also, the aim of this work was the characterization of red mud as industrial waste generated by the Bayer process in the aluminum industry - which may cause environmental problems if appropriate treatment is not carried out. The main mineral phases of both red mud are hematite (Fe2O3), calcite (CaCO3), gibbsite (Al(OH)3) and they consists of particles of median particle size 2.1 mm (sample A) and 2.5 mm (sample B) and have a characteristic red color, which was the reason for its testing for use in the industry of building materials as a pigment for standard concrete mixtures. The radionuclides content in the samples was determined by gamma spectrometry, and the radiological hazards originating from 238U, 232Th, 40K in the samples, were assessed through the radium equivalent activity, and the external radiation hazard index. The absorbed dose rate and the annual effective dose were calculated in accordance with the UNSCEAR 2010 report and the results are presented in this paper.

Modification of ash fusion behavior of coal with high ash fusion temperature by red mud addition

The influences of two red mud (RM) samples (ZZ and ZM) on fusion behaviors of three high ash fusion temperature (AFT) coals (FZ, JC and JZ) were investigated. It was evaluated by determining AFTs of coals, RMs, and the mixtures of coal ash with RM, as well as their compositions of ashes and mineral. The results showed that the contents of CaO, Fe2O3, and Na2O in RMs were higher than those in coal ashes, which caused RMs’ AFTs lower than those of coals. The formation of high melting-point mullite might be the main factor causing coal AFTs higher. With the increase in RM mass ratio, the increasing amount of low-melting eutectic (anorthite (CaAl2Si2O8), fayalite (Fe2SiO4), and anorthite (Na-rich) (Ca,Na)(Si,Al)4O8)) and amorphous matter made AFTs lower. ZZ reduced AFTs obviously than ZM because the content of Na2O in ZZ was higher than that in ZM. Owing to lower ion potential of Na+ than those of Ca2+ and Fe2+, Na+ is easier to enter into the lattice of mullite and results in the reduction of AFTs.

Removal of Phosphate Using Red Mud: An Environmentally Hazardous Waste By-Product of Alumina Industry

The industrial waste, bauxite residue generated in the Bayer chemical process of alumina production, commonly known as red mud (RM) has been used as the adsorbent for selective removal of phosphate in aqueous solutions. RM collected from the storage area of alumina industry was characterized by chemical analysis and physical methods such as BET surface area, Scanning Electron Microscopy (SEM), particle size analysis, and X-ray diffraction (XRD) methods. Among the various red mud samples (0.2–200 μ) studied, the samples treated with 1 M HCl for 2 h were found better for the selective adsorption of phosphate in comparison with untreated and heat treated RM samples. The presence of phosphate in the aqueous samples collected after adsorption studies with red mud was determined by standard spectrophotometric procedure using ammonium molybdate and ascorbic acid in nitrate medium at λmax 880 nm. The studies reported significant adsorption of phosphate on acid treated red mud in comparison with adsorption of phosphate on untreated and heat treated red mud, respectively. The adsorption of phosphate on raw red mud and activated red mud was further investigated with respect to stirring time, pH of the solution, dose of adsorbent, and varying phosphate concentration. Acid treated RM is observed as an efficient and cost-effective adsorbent for selective removal of phosphate in aqueous solutions.

Hydrocarbon Cracking Over Red Mud and Modified Red Mud Samples

The aluminum industry generates large quantities of red mud during the beneficiation of bauxite ore. The red mud is disposed of as a waste in dry or wet form. Given the issues with its disposal due to the large volume and high alkalinity, many research groups and industries have examined the use of red mud for different applications. The use of red mud as a pre-catalyst for the cracking of hydrocarbon leads to hydrogen formation and carbon deposition. Our earlier studies have shown its activity for reaction with methane and the formation of magnetic materials containing iron, iron carbide, and nanocarbon species. In this study, two aspects were studied: one was methane cracking over red mud, modified red mud, and waste from a nailwork factory site and the other was the application of different hydrocarbons, including nitrogen-containing precursors over red mud. Preliminary characterization of the resulting carbon deposits was performed. The activity for methane cracking increased when the red mud was activated and reduced before the reaction. Nitrogen-containing reactants led to the formation of nitrogen-doped carbon nanotubes. The nitrogen amount and morphology varied with the precursor used and the reaction temperature. This is an attractive application with potential for further modification of the carbon deposits for other catalytic and electrochemical applications.

Recovery of ferric oxide from bayer red mud by reduction roasting-magnetic separation process

A great amount of red mud generated from alumina production by Bayer process was considered as a low-grade iron ore with a grade of 5wt% to 30wt% iron. We adopted the reduction roastingmagnetic separation process to recover ferric oxide from red mud. The red mud samples were processed by reduction roasting, grinding and magnetic separating respectively. The effects of different parameters on the recovery rate of iron were studied in detail. The optimum techqical parameters were proposed with 700 °C roasting for 20 min, as 50wt% carbon and 4wt% additive were added. The experimental results indicated that the iron recovery and the grade of total iron were 91% and 60%, respectively. A novel process is applicable to recover ferric oxide from the red mud waste fines.

Effects of thermal treatments on the characterisation and utilisation of red mud with sawdust additive.

Extremely large amounts of red mud (bauxite residue) are generated globally every year from alumina refining industries, which are being disposed of on engineered landfills. The objective of this study is to investigate the effects of thermal treatments on red mud for development of utilisation strategies. Thermal treatments of red mud samples and their characterisations were investigated under inert (N2) and oxidative (air) conditions with and without sawdust addition at 200-600°C. After calcination, the resulting samples were analysed using thermogravimetric-infrared spectroscopy (TG-IR) for functional group transformations, thermogravimetric analysis (TGA) for thermal loss profiles and X-ray diffraction (XRD) for mineral transformations. The characterisation results showed that in N2 environment, boehmite in red mud was transferred to transition alumina at around 400°C while losing water from structural components. The addition of sawdust for incubation and calcination of red mud in air increased the surface area, whereas that in nitrogen atmosphere lead to reduction of hematite to magnetite at around 500°C. The incorporated carbon materials played a major role in increasing the surface area especially for pore size less than 2.5 nm. This treated red mud with altered mineral composition and improved properties for binding contaminants can be used for environmental remediation and in the process of metal recovery such as iron.

Sulfur Fixation by Chemically Modified Red Mud Samples Containing Inorganic Additives: A Parametric Study

Sulfur retention ability of Bayer red mud from alumina plant was investigated. Bayer red mud modified by fusel salt and waste mother liquor of sodium ferrocyanide as the main sulfur fixation agent and the calcium based natural mineral materials as servicing additives; the experimental results showed the following: (1) Through 10 wt% waste mother liquor of sodium ferrocyanide modifying Bayer red mud, sulfur fixation rate can increase by 13 wt%. (2) Magnesium oxide can obviously improve the sulfur fixation performance of Bayer red mud and up to a maximum sulfur fixation rate of 47 wt% at adding 1 wt% magnesium oxide. (3) Dolomite enhanced the sulfur fixation performances with the sulfur fixation rate of 68 wt% in optimized condition. (4) Vermiculite dust reduced sulfur dioxide during the fixed-sulfur process of modified Bayer red mud, and the desulphurization ration could reach up to a maximum 76 wt% at 950°C. (5) An advanced three-component sulfur fixation agent was investigated, in which the optimized mass ratio of modified Bayer red mud, dolomite, and vermiculite dust was 70 : 28 : 2 in order, and its sulfur fixation efficiency has reached to a maximum 87 wt% under its 20 wt% dosage in the coal.

The carbon deposits formed by reaction of a series of red mud samples with methanol

Magnetic carbon materials were prepared by the catalytic growth of graphitic carbon and carbon nanofibers using methanol as carbon source with a series of red mud wastes from different sources.

Potential leaching of Cr(VI) from laterite mines and residues of metallurgical products (red mud and slag): An integrated approach

We here report the chemical composition of (a) Fe–Ni laterite ores from central and northern Greece and bauxite ores from Parnassos-Ghiona deposit, (b) the corresponding high volume residues (slag and red mud) produced during the metallurgical processing of ferronickel and alumina, (c) experimentally produced water (natural and/or seawater) leachates of these ores and metallurgical leachates and (d) chromium isotope composition (expressed as δ53Cr values) of the leachates, seawater and of Cr (VI) contaminated natural water, in an attempt to assess the role of industrial mining processes on the Cr(VI) contamination of groundwater in ultramafic rock-dominated terrain.The five week lasting laboratory leaching experiments, performed under atmospheric conditions, showed that only small amounts of Cr(VI) (<~2μg·L−1) from Fe–Ni laterites of Lokris (Central Greece) were mobilized into the aqueous phase. In contrast, Cr(VI) concentrations in leachates from Fe–Ni laterites of Kastoria reached values as high as 1300μg·L−1. In addition, unexpectedly high Cr(VI) concentrations were measured in water leachates from red mud samples (2100μg·L−1). The leachates from red mud are also characterized by relatively high V (6200μg·L−1) and Ga (90μg·L−1) concentrations. In contrast to leachates from red mud, the Cr(VI) concentrations in leachates from slag remained below ~2μg·L−1.The δ53Cr values measured in natural water leachates of Fe–Ni-laterite from Kastoria range between +0.03±0.06‰ and −0.21±0.08‰ and differ from the more positively fractionated value of +1.01±0.05 ‰ obtained for the laterite from Lokris. The δ53Cr values in natural water and seawater leachates from red mud returned δ53Cr values of +0.83±0.05‰ and +0.73±0.08‰, respectively, and thus are statistically indistinguishable. Although there is no clear-cut relationship between Cr(VI) concentrations and δ53Cr values in the diverse leachates, there is an indication that the laterite leachates from Kastoria with high Cr(VI) concentrations yielded less positively fractionated δ53Cr values, compared to the laterite leachates from Lokris.The agreement between chromium isotope compositions of artificial leachates of red mud and that of contaminated seawater from the Assopos river extrusion (estuary) forming a heavily Cr(VI) contaminated point source, suggests that the release of Cr(VI) from the red mud rather than from the primary bauxite ore is a major source of toxic Cr(VI), and that insignificant back-fractionation (reduction) of this mobile and toxic chromium along its pathway to the sea takes place.

Quantitative X-ray Diffraction (QXRD) analysis for revealing thermal transformations of red mud

Red mud is a worldwide environmental problem, and many authorities are trying to find an economic solution for its beneficial application or/and safe disposal. Ceramic production is one of the potential waste-to-resource strategies for using red mud as a raw material. Before implementing such a strategy, an unambiguous understanding of the reaction behavior of red mud under thermal conditions is essential. In this study, the phase compositions and transformation processes were revealed for the Pingguo red mud (PRM) heat-treated at different sintering temperatures. Hematite, perovskite, andradite, cancrinite, kaolinite, diaspore, gibbsite and calcite phases were observed in the samples. However, unlike those red mud samples from the other regions, no TiO2 (rutile or anatase) or quartz were observed. Titanium was found to exist mainly in perovskite and andradite while the iron mainly existed in hematite and andradite. A new silico-ferrite of calcium and aluminum (SFCA) phase was found in samples treated at temperatures above 1100°C, and two possible formation pathways for SFCA were suggested. This is the first SFCA phase to be reported in thermally treated red mud, and this finding may turn PRM waste into a material resource for the iron-making industry. Titanium was found to be enriched in the perovskite phase after 1200°C thermal treatment, and this observation indicated a potential strategy for the recovery of titanium from PRM. In addition to noting these various resource recovery opportunities, this is also the first study to quantitatively summarize the reaction details of PRM phase transformations at various temperatures.

Usability of clay mixed red mud in Hungarian building material production industry

The naturally occurring radionuclide (226Ra, 232Th and 40K) content of building Materials (NORM) contributes to the total radiation dose experienced by humans. In this survey 27 clay and 68 red mud samples were surveyed with gamma spectrometry and screened according to European Basic Safety Standards (BSS) I-index. It was found that average I-index of clays was 0.6 (0.4–0.8) less than the I-index of 1, which makes them suitable for building material production. The average I-index of red mud 2.3 (1.3–3.0). The maximal mixing ratio of red mud was calculated, varied between 12 and 39 %, with 23 % average.

Thermogravimetric study of the dehydration and reduction of red mud

The processes of drying and reduction of red mud in the pure state and with coal additions in vacuum or in gaseous media (helium, hydrogen) have been experimentally studied by thermogravimetry using a Setaram TAG24 thermogravimetric analyzer. The minimum total weight loss (∼20%) is observed for red mud samples without additives in forevacuum, and the maximum loss (∼38%) is detected in samples with coal. It is demonstrated that, for this type of red mud with iron oxide Fe2O3, water molecules are bonded in the form of iron hydroxide Fe2O3 · 3H2O rather than goethite FeOOH. The peak of magnetite formation is observed in differential thermogravimetry (DTG) curve in the range 270–400°C. The simulation of the magnetite dehydration and formation rates under experimental conditions in the relevant temperature ranges agrees with the experimental data. A peak of wustite formation in hydrogen above ∼600°C is recorded in a DTG curve, and the removal of one-third of sodium oxide, which is likely not to be fixed into strong sodium alumosilicate, is observed in the range 800–1000°C. The peak detected in the DTG curve of the mud with charcoal in helium in the range 350–450°C is similar to the peak of hematite reduction in magnetite in a hydrogen atmosphere. The most probable source of hydrogen-containing gases in this temperature range consists of the residual hydrocarbons of charcoal. The reduction reactions of disperse iron oxides with coal proceed only at temperatures above 600°C. These processes occur in the same temperature range (600–900°C) both in forevacuum and in a helium atmosphere. It is experimentally demonstrated that sintering process occurs in the mud in the temperature range 450–850°C.

Monitoring the Acid Neutralisation Capacity and Options for Leaching Iron from Waste Mud from the Production of Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;

Red and brown mud is created in the processing of bauxite into Al2O3. The chemical composition of red and brown mud depends upon the method of processing bauxite on a mud landfill, and the time and availability of mud leaching by rain. Samples of red mud from landfill in Žiarska Kotlina had pH values of 9.46 ± 0.11 and brown mud had 10.2 ± 0.15. We studied the development of changes in pH and concentrations of Fe (spectrometrically with AAS) in eluates during the leaching of red and brown mud samples. Results show that there is no release of Fe during brown mud elution. When using 0.025 and 0.05 M H2SO4 for elution, the pH decreased slightly from 10.2 ± 0.15 to 2.4 ± 0.05. Elution of 0.1 M H2SO4 shows that pH decreased to a value of 2.2 ± 0.05 by the 40th fraction and then it fell to a value of 1.77 ± 0.04 in the 100th fraction. The greatest amount of iron was released in the 8th and 55th fraction at a pH of 2 – 4 which could be observed by the change in colour of eluates. The progress of the release of iron was similar for both kinds of mud. Then we determined the neutralisation capacities of various fractions of mud in H2SO4, NaOH and H2O leachates by titration. It was discovered that the reaction of the alkaline proportions of red mud with the agent is greatest with fine granularity but for red mud, it does not change depending upon the size of the grain. The release of acid proportions depended upon time not upon texture. When leaching with water, the leached alkaline compounds from brown mud are mainly from the finest particles, and in the case of red mud, it was the opposite, from the largest particle fraction.

Need for database extension for reliable identification of bacteria from extreme environments using MALDI TOF mass spectrometry

AbstractThe ability of MALDI TOF MS (matrix-assisted laser desorption ionisation time-of-flight mass spectrometry) to identify cultivable microflora from two waste disposal sites from non-ferrous metal industry was analysed. Despite the harsh conditions (extreme pH values and heavy metal content in red mud disposal site from aluminium production or high heavy metal content in nickel sludge), relatively high numbers of bacteria were recovered. In both environments, the bacterial community was dominated by Gram-positive bacteria, especially by actinobacteria. High-quality MALDI TOF mass spectra were obtained but most of the bacteria isolates could be not identified using MALDI Biotyper software. The overall identification rate was lower than 20 %; in two of the environments tested identification rates were lower than 10 %. As a dominant bacterial species, Microbacterium spp. in drainage water from an aluminium red mud disposal site near Žiar nad Hronom, Bacillus spp. in red mud samples from the same site, and Arthrobacter spp. from nickel smelter sludge near Sereï were identified by a combination of the Biolog system and 16S rRNA sequence analysis. As the primary focus of the MALDI TOF MS-based methodology is directed towards medically important bacteria, reference database spectra expansion and refinement are needed to improve the ability of MALDI TOF MS to identify environmental bacteria, especially those from extreme environments.

Selected applications of Rietveld-XRD analysis for raw materials of the aluminum industry

In the last few decades, X-ray diffraction (XRD) systems have been paramount and irreplaceable in controlling bauxite exploration, as well as Bayer and reduction processes. XRD quantitative phase analysis in the aluminum industry witnessed a steady deployment of the Rietveld method, which at present progressively replaces existing methodologies in research and plant laboratories. Rietveld analysis not only helped to surpass traditional XRD calibration methods, it also opened the door for new applications previously not possible. The use of the Rietveld method to characterize selected materials unique to the aluminum industry, such as bauxite, red mud, and alumina is demonstrated and discussed. This paper also presents how synchrotron-based diffractograms obtained for bauxite and red mud samples allowed a much better understanding of mineralogical representation, and made it possible to leverage their Rietveld quantification. Despite clear advantages, the Rietveld method also has limitations that are revealed. For alumina phase quantification, a dedicated Rietveld analytical program was built with structure data for eight alumina mineralogical phases: alpha, beta (β-Al2O3 = Na2O•11Al2O3), delta, gamma (2), kappa, sigma, and theta. The paper gives unique examples of phase quantification in aluminas of various origins and phase composition.