A study of iron mineral transformation to reduce red mud tailings

Cleaning Disposal of High-Iron Bauxite Residue Using Hydrothermal Hydrogen Reduction

The hydrothermal hydrogen reduction process for treating high-iron bauxite residue (red mud) was investigated, and the optimum conditions of alumina extraction as well as the enrichment of iron minerals were verified by experiments. Results show that the surface magnetization of Al-goethite under the function of hydrogen reduction accelerates its conversion to hematite and/or magnetite. This conversion releases the substituted Al in goethite as well as the undigested gibbsite/boehmite and further enriches the iron content in residue. After hydrothermal hydrogen reduction with H₂/Red mud ratio of 0.085 mol/20 g at 270°C for 60 min, the alumina relative recovery ratio reaches 95.40% and the grade of iron (total iron in the form of iron element) in the residue can be enriched to 55.85%. Further, co-processing of the obtained iron-rich residue in the steel industry can achieve a significant reduction of red mud discharge.

Study on Reductive Smelting of High-Iron Red Mud for Iron Recovery

In this paper, the characteristics and current problems associated with red mud and the progress of research on iron extraction from high-iron red mud are briefly described. By adding conditioning materials to red mud and quenching and tempering, the iron tailings extracted from red mud were reconstructed by heating to form molten tailings in the laboratory. A thermodynamic analysis of the iron reduction reaction during tailings reconstruction was performed, and the best conditions for iron extraction by calcified slag reduction were verified. The contents of CaO, Al2O3 and Na2O in the reduced tailings were 37.07, 37.67 and 0.48%, respectively. According to X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses, the main crystalline phases in the calcified extracted iron tailings were C2AS and CT, which aggregated and met the expected composition standard for calcified extracted iron tailings.

Low-temperature thermal conversion of Al-substituted goethite in gibbsitic bauxite for maximum alumina extraction

Low-temperature roasting can improve the conversion of Al-goethite in gibbsitic bauxite to porous Al-hematite, and favor increasing the alumina extraction during Bayer digestion and enrichment of iron minerals in red mud.

Iron Recovery from Bauxite Tailings Red Mud by Thermal Reduction with Blast Furnace Sludge

More than 100 million tons of red mud were produced annually in the world over the short time range from 2011 to 2018. Red mud represents one of the metallurgical by-products more difficult to dispose of due to the high alkalinity (pH 10–13) and storage techniques issues. Up to now, economically viable commercial processes for the recovery and the reuse of these waste were not available. Due to the high content of iron oxide (30–60% wt.) red mud ranks as a potential raw material for the production of iron through a direct route. In this work, a novel process at the laboratory scale to produce iron sponge (≤ 1300 °C) or cast iron (> 1300 °C) using blast furnace sludge as a reducing agent is presented. Red mud-reducing agent mixes were reduced in a muffle furnace at 1200, 1300, and 1500 °C for 15 min. Pure graphite and blast furnace sludges were used as reducing agents with different equivalent carbon concentrations. The results confirmed the blast furnace sludge as a suitable reducing agent to recover the iron fraction contained in the red mud. For all the conditions tested, the metallization degree was higher than 70%, and the best condition to reduce red mud through blast furnace sludge was identified at 1:1 red mud/blast furnace (B.F.) sludges equal to 0.85 C/Fe2O3.

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 9.20 μm, 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.

Enabling safe dry cake disposal of bauxite residue by deliquoring and washing with a membrane filter press

Dry cake disposal is the preferred technique for the disposal of bauxite residue, when considering environmental issues together with possible future utilisation of the solids. In order to perform dry cake disposal in an economical way, the deliquoring of the residue must be carried out efficiently, and it is also important to wash the obtained solids well to minimise the amount of soluble soda within the solids. The study presented in this article aims at detecting the most important variables influencing the deliquoring and washing of bauxite residue, performed with a horizontal membrane filter press and by determining the optimal washing conditions. The results obtained from pilot-scale experiments are evaluated by considering the properties of the solids, for instance, the residual alkali and aluminium content, as well as the consumption of wash liquid. Two different cake washing techniques, namely classic washing and channel washing, are also used and their performances compared. The results show that cake washing can be performed successfully in a horizontal membrane filter press, and significant improvements in the recovery of alkali and aluminium can be achieved compared with pressure filtration carried out without washing, or especially compared with the more traditionally used vacuum filtration.

Recovery of iron from cyanide tailings with reduction roasting-water leaching followed by magnetic separation

Cyanide tailing is a kind of solid waste produced in the process of gold extraction from gold ore. In this paper, recovery of iron from cyanide tailings was studied with reduction roasting-water leaching process followed by magnetic separation. After analysis of chemical composition and crystalline phase, the effects of different parameters on recovery of iron were chiefly introduced. Systematic studies indicate that the high recovery rate and grade of magnetic concentrate of iron can be achieved under the following conditions: weight ratios of cyanide tailings/activated carbon/sodium carbonate/sodium sulfate, 100:10:3:10; temperature, 50 °C; time, 60 min at the reduction roasting stage; the liquid to solid ratio is 15:1 (ml/g), leaching at 60 °C for 5 min and stirring speed at 20 r/min at water-leaching; exciting current is 2A at magnetic separation. The iron grade of magnetic concentrate was 59.11% and the recovery ratio was 75.12%. The mineralography of cyanide tailings, roasted product, water-leached sample, magnetic concentrate and magnetic tailings were studied by X-ray powder diffraction (XRD) technique. The microstructures of above products except magnetic tailings were also analyzed by scanning electron microscope (SEM) and energy disperse spectroscopy (EDS) to help understand the mechanism.

Recovery of iron from vanadium tailings with coal-based direct reduction followed by magnetic separation

A technique with coal-based direct reduction followed by magnetic separation is presented in this study for recovering and reusing iron otherwise wasted in vanadium tailings. Process parameters such as usage of additives, tailings/reductant/additives ratio, reduction temperature and time, as well as particle size were experimentally determined. The optimum process parameters were proposed as follows: using lime as the additive, lignite as the reductant, weight ratios of vanadium tailings/lignite/lime at 100:30:10, reduction roasting at 1200 °C for 60 min, and particle size of 98% less than 30 μm in the final roasted product feeding to magnetic separation. Under these conditions, a magnetic concentrate containing 90.31% total iron and 89.76% metallization iron with a total iron recovery rate of 83.88% was obtained. In addition, mineralography of vanadium tailings, coal-based reduction product and magnetic concentrate were studied by X-ray powder diffraction technique (XRD). The microstructures of above products were analyzed by scanning electron microscope (SEM) to help understand the mechanism.

Extraction of alumina and sodium oxide from red mud by a mild hydro-chemical process

A mild hydro-chemical process to extract Al(2)O(3) in red mud to produce sodium aluminate hydrate was investigated, and the optimum conditions of Al(2)O(3) extraction were verified by experiments as leaching in 45% NaOH solution with CaO-to-red mud mass ratio of 0.25 and liquid-to-solid ratio of 0.9, under 0.8 MPa at 200 degrees C for 3.5h. Subsequent process of extracting Na(2)O from the residue of Al(2)O(3) extraction was carried out in 7% NaOH solution with liquid-to-solid ratio of 3.8 under 0.9 MPa at 170 degrees C for 2h. Overall, 87.8% of Al(2)O(3) and 96.4% of Na(2)O were extracted from red mud. The final residues with less than 1% Na(2)O could be utilized as feedstock in construction materials. The chemical reactions taking place in both Al(2)O(3) and Na(2)O extractions from red mud are proposed.

Application of Bayer red mud for iron recovery and building material production from alumosilicate residues

Red mud is a solid waste produced in the process of alumina extraction from bauxite. In this paper, recovery iron from Bayer red mud was studied with direct reduction roasting process followed by magnetic separation, and then building materials were prepared from alumosilicate residues. After analysis of chemical composition and crystalline phase, the effects of different parameters on recovery efficiency of iron were carried out. The optimum reaction parameters were proposed as the following: ratio of carbon powder: red mud at 18:100, ratio of additives: red mud at 6:100, roasting at 1300 degrees C for 110min. With these optimum parameters, total content of iron in concentrated materials was 88.77%, metallization ratio of 97.69% and recovery ratio of 81.40%. Then brick specimens were prepared with alumosilicate residues and hydrated lime. Mean compressive strength of specimens was 24.10MPa. It was indicated that main mineral phase transformed from nepheline (NaAlSiO4) in alumosilicate residues to gehlenite (Ca2Al2SiO7) in brick specimens through X-ray diffraction (XRD) technology. The feasibility of this transformation under the experimental conditions was proved by thermodynamics calculation analysis. Combined the recovery of iron with the reuse of alumosilicate residues, it can realize zero-discharge of red mud from Bayer process.

The exploration of making acidproof fracturing proppants using red mud

In this study, the exploration of making acidproof fracturing proppants using red mud was carried out. The main raw materials are red mud and the refractory waste. During the exploration, three methods were explored to enhance the acid resistance of the samples of the fracturing proppants. Eventually, fracturing proppants with good acid resistance were produced using red mud, the refractory waste, barium carbonate and plasticizer. The acid solubility of the samples of the acidproof fracturing proppants was less than 4.5% which reached the demands of The Petroleum and Gas Industrial Standards of China (SY/T5108-2006). The results show that adding barium carbonate to the raw materials can decrease the acid solubility of the samples effectively. The main reason is the monoclinic celsian-BaAl2Si2O8 formed in sintering process which can protect the other compositions of the acidproof fracturing proppants to prevent them from erosion by acid. The exploration shows that it is probable to produce fracturing proppants with good acid resistance using red mud.

Arsenate removal from aqueous solutions using modified red mud

Red mud (RM), a waste tailing from alumina production, was modified with FeCl(3) for the removal of arsenate from water. The RM and modified red mud (MRM) were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) microanalysis. Adsorption of arsenate on modified red mud (MRM) was studied as a function of time, pH, and coexisting ions. Equilibrium time for arsenate removal was 24h. Solution pH significantly affected the adsorption, and the adsorption capacity increased with the decrease in pH. Langmuir and Freundlich isotherms equation were used to fit the adsorption isotherms. The Langmuir isotherm was the best-fit adsorption isotherm model for the experimental data. Adsorption capacity of MRM was found to be 68.5mg/g, 50.6 mg/g and 23.2mg/g at pH 6, 7 and 9, respectively. NO(3)(-) had little effect on the adsorption. Ca(2+) enhanced the adsorption, while HCO(3)(-) decreased the adsorption. MRM could be regenerated with NaOH, and the regeneration efficiency reached 92.1% when the concentration of NaOH was 0.2 mol/L.

Revegetation strategies for bauxite refinery residue: a case study of Alcan Gove in Northern Territory, Australia

Alumina extraction from bauxite ore with strong alkali produces waste bauxite refinery residue consisting of residue sand and red mud. The amount and composition of refinery residue depend on the purity of the bauxite ore and extraction conditions, and differs between refineries. The refinery residue is usually stored in engineered disposal areas that eventually have to be revegetated. This is challenging because of the alkaline and sodic nature of the residue. At Alcan Gove's bauxite refinery in Gove, Northern Territory, Australia, research into revegetation of bauxite residue has been conducted since the mid-1970s. In this review, we discuss approaches taken by Alcan Gove to achieve revegetation outcomes (soil capping of refinery residue) on wet-slurry disposal areas. Problems encountered in the past include poor drainage and water logging during the wet season, and salt scalding and capillary rise during the dry season. The amount of available water in the soil capping is the most important determinant of vegetation survival in the seasonally dry climate. Vegetation cover was found to prevent deterioration of the soil cover by minimising capillary rise of alkalinity from the refinery residue. The sodicity and alkalinity of the residue in old impoundments has diminished slightly over the 25 years since it was deposited. However, development of a blocky structure in red mud, presumably due to desiccation, allows root penetration, thereby supplying additional water to salt and alkali-tolerant plant species. This has led to the establishment of an ecosystem that approaches a native woodland.