Red Mud Surface Research Articles

The Impacts of Red Mud on Road Performance and Aging Resistance of Asphalt Mixture

Abstract Red mud as an asphalt modifier has been investigated in some studies, but few studies are further concerned about the effect of red mud on performance of asphalt mixture. In this study, the impact of red mud on road performance and aging endurance of asphalt mixtures was evaluated. Primarily, the optimal asphalt content was determined based on mechanical strength and volumetric properties. Then, the performance evaluations, including Marshall stability, low-temperature splitting, freeze-thaw splitting, indirect tensile fatigue, and thermal-oxidative aging, were executed. The outcomes demonstrate that in comparison with the base asphalt mixture, red mud asphalt mixture exhibits worse high-temperature stability and moisture resistance, and superior temperature shrinkage cracking resistance and fatigue performance. After the surface of red mud has been modified, the adhesion between asphalt mastics and aggregate is strengthened, and the distribution of red mud in asphalt mixture becomes more uniform, which intensifies the rigidity and road performance (except for low-temperature cracking resistance) of asphalt mixture. Furthermore, since red mud absorbs a portion of asphalt content, it can hinder the physical hardening and oxidation rate of asphalt mixture. The anti-aging ability of asphalt mixture is further reinforced by the incorporation of organic red mud.

Promoted ketonization of bagasse pyrolysis gas over red mud-based oxides

Ketonization of bagasse pyrolysis gas was performed over red mud-based oxides. The maximum yield of ketones in the catalytic conversion of bagasse pyrolysis gas over original red mud was 18.66% at 420 °C. To promote the oxidability of red mud and obtain a higher yield of ketones, the effect of metal oxides (CeO2, MnO2, TiO2, CaO, ZrO2) loading and loading amount of CeO2 on red mud on ketonization of bagasse pyrolysis gas were studied. The highest yield of ketones of 27.86% was obtained over red mud-based oxides with 40 wt% CeO2 loading. The oxidability of the catalyst was enhanced greatly by the high loading of CeO2, leading to the peroxidation of acetone as the side reaction. To control the oxidability and cut costs, bimetallic oxides were loaded on red mud. The yield of ketones reached 30.12% over the composite red mud catalyst with the loading of 20 wt% CeO2 and 20 wt% MnO2. The rough coating of MnO2 on the surface of red mud was beneficial to the loading of CeO2, resulting in smaller and more uniform grains. This study provides the efficient utilization of red mud and biomass as solid wastes for high-valued chemicals and fuels.

Mechanistic insight into the adsorption of mercury (II) on the surface of red mud supported nanoscale zero-valent iron composite

Recently, nanoscale zero-valent iron (nZVI) particles have been efficiently used in the remediation of many heavy metals, yet potential agglomeration and loss of nZVI remain a critical area of research. In this study, we used red mud as a stable supporting medium to develop red mud modified nZVI to form (RM-nZVI) composite. We assessed its sorptive/reductive removal of mercury (Hg2+) from aqueous solutions. The RM-nZVI was synthesized through the reduction of ferric iron by sodium borohydride (NaBH4) in the presence of red mud. Morphological characterization of RM-nZVI confirmed its diffusion state with lesser aggregation. The RM-nZVI has the BET surface area, pore diameter, and pore volume as 111.59 m2g−1, 3.82 nm, and 0.49 cm3g−1, respectively. Adsorption of mercury (Hg2+) by RM-nZVI exhibits pH-dependent behavior with increased removal of Hg2+ with the increase in pH up to 5, and the removal rate decreased gradually as the pH increased from 5 to 10. Extensive characterization of RM-nZVI corroborated the evidence that the removal of Hg2+ was initially by rapid physical adsorption, followed by a reduction of Hg2+ to Hg0. The adsorption data were best fitted with Langmuir isotherm with R2 (correlation coefficient) > 0.99 with high uptake capacity of 94.58 (mg g−1). The novel RM-nZVI composite with enhanced sorptive and reductive capacity is an ideal alternative for removing Hg2+ from contaminated water.

A comparison of anionic and cationic dye removal efficiency of industrial bauxite waste red-mud

Sorption characteristics of the acid-activated bauxite waste red-mud for Nylomine-Blue and Methylene-Blue were investigated to predict its potential removal ability for anionic-di-anthraquinone and cationic-thiazine-dyes, respectively. Surface characteristics of the red-mud were examined using atomic-force-microscopy, diffuse-reflectance-Fourier-transform, and X-ray-diffraction spectroscopy techniques. Kinetic data obtained at four different temperatures fit well to the pseudo-second-order and homogeneous-surface-diffusion models. The experimental Nylomine-Blue sorption capacity (0.020 mmol/g) is higher than that of Methylene-Blue (0.012 mmol/g) at 288 K but they change oppositely with the temperature and attain 0.013 and 0.043 mmol/g at 318 K, respectively. Experimental equilibrium data for Methylene-Blue and Nylomine-Blue are well predicted by the Freundlich, Langmuir, and Dubinin-Radushkevich isotherm equations. The mean-sorption-energies fall into the ion-exchange range for Methylene-Blue but electrostatic-attraction-forces play a more important role in Nylomine-Blue sorption. These mechanisms were correlated to the pH changes in the sorption process and the differences in the diffuse-reflectance-Fourier-transform spectra of dye-loaded sorbents. The atomic-force-microscopy topography and phase images revealed that the hematite and sodalite appear as hills on the red-mud surface but gibbsite and calcite minerals cover the valleys. The Methylene-Blue molecules are sorbed by ion-exchange in the positively-charged-valleys in dilute solutions but Nylomine-Blue is sorbed specifically on overall surface in whole concentration range.

Arsenic (III) Removal from a High-Concentration Arsenic (III) Solution by Forming Ferric Arsenite on Red Mud Surface

Arsenic (As) is considered one of the most serious inorganic pollutants, and the wastewater produced in some smelters contains a high concentration of arsenic. In this paper, we purified the high-concentration arsenic solution with red mud and Fe3+ synergistically. In this system, arsenite anions reacted with Fe(III) ions to form ferric arsenite, which attached on the surface of red mud particles. The generated red mud/Fe1−x(As)x(OH)3 showed a better sedimentation performance than the pure ferric arsenite, which is beneficial to the separation of arsenic from the solution. The red mud not only served as the carrier, but also as the alkaline agent and adsorbent for arsenic treatment. The effects of red mud dosage, dosing order, pH, and molar ratio of Fe/As on arsenic removal were investigated. The efficiency of arsenic removal increased from a pH of 2 to 6 and reached equilibrium at a pH of 7. At the Fe/As molar ratio of 3, the removal efficiency of arsenic ions with an initial concentration of 500 mg/L reached 98%. In addition, the crystal structure, chemical composition, and morphological properties of red mud and arsenic removal residues (red mud/Fe1−x(As)x(OH)3) were characterized by XRD, XPS, X-ray fluorescence (XRF), SEM-EDS, and Raman spectroscopy to study the mechanism of arsenic removal. The results indicated that most of the arsenic was removed from the solution by forming Fe1−x(As)x(OH)3 precipitates on the red mud surface, while the remaining arsenic was adsorbed by the red mud and ferric hydroxide.

Red Mud-activated Peroxymonosulfate for Ciprofloxacin Degradation: Efficiency and Mechanism

In this paper, the effects and mechanism of ciprofloxacin (CIP) degradation with peroxymonosulfate (PMS) catalyzed by solid waste red mud (RM) was firstly studied. The results indicated that RM has large specific surface area (10.96 m2·g-1) and complex pore structure, containing ferric, alumina and calcium oxide, which enhanced ciprofloxacin degradation by PMS effectively. Radical quenching experiments revealed that SO4-·and HO·were contributed to ciprofloxacin oxidation, and the reaction was mainly occurred on RM's surface. An increase in temperature could accelerate CIP degradation, and the corresponding reaction activation energy Ea was about 5.74 kJ·mol-1. Meanwhile, CIP degradation rate increased with PMS concentration and the optimal dosage of RM was 1.0 g·L-1. Eight degradation intermediates were identified using HPLC/MS/MS, and consequently, CIP was degraded mainly through two pathways; the piperazine groups were preferentially attacked by active free radicals. This study further indicated that RM is a cheap catalyst and can be potentially used in the treatment of antibiotic contaminated wastewater.

Multiscale Study on the Modification Mechanism of Red Mud Modified Asphalt

Red mud, a waste residue of aluminium industry, was used as modified asphalt material to prepare red mud modified asphalt and red mud modified asphalt under freeze‐thaw cycles. The matrix asphalt (MA), red mud modified asphalt (RMMA), and red mud modified asphalt under freeze‐thaw cycles (RMMAFC) were studied by scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FTIR), atomic force microscopy (AFM), and differential scanning calorimetry (DSC). Microscopic experiments were conducted to investigate the modification performance and mechanism. The modification mechanism of red mud modified asphalt was investigated using molecular dynamics simulation in this study. The results show that red mud can form a uniform and stable blending system with base asphalt after adding base asphalt. The structure of asphalt after adding red mud and adding red mud and freezing‐thawing cycles does not change. The bee‐structure decreases obviously with the addition of red mud by atomic force microscopy (AFM). Density decreases gradually, but bee‐structure height increases obviously; bee‐structure of red mud modified asphalt is destroyed after freeze‐thaw cycles. Through differential scanning calorimetry (DSC), after adding red mud, heat absorption decreases. Freeze‐thaw cycles greatly reduce heat absorption of red mud modified asphalt. Constructing molecular model of major components of red mud (Fe2O3, Al2O3) and asphaltene, simulation results show that the interfacial energy between asphaltene and red mud’s main components Fe2O3 and Al2O3 at −10°C, 25°C, and 170°C is stronger than that of Fe2O3. The results of calculating the interfacial energy of asphaltene on the chemical composition surface of red mud are negative. It can be seen that there are adsorption effects on the surface of asphaltene and red mud. Therefore, increasing the content of Al2O3 or decreasing the content of Fe2O3 in red mud is beneficial to the adsorption of asphaltene.

Enhancing Cd(II) sorption by red mud with heat treatment: Performance and mechanisms of sorption

Red mud is a waste generated from the aluminum industry in large quantities. The potential of red mud as a sorbent for beneficial reuse has been the focus of research efforts. However, the limited sorption capacity of red mud has hindered its applications in the removal of environmental pollutants. In this study, the feasibility of heat treatment in improving the sorption of toxic Cd(II) by red mud was investigated in the temperature range of 200–900 °C. Heat treatment at 500 °C resulted in the highest sorption capacity (42.64 mg g−1) and the fastest sorption rate. Further analyses revealed that heat treatment at 500 °C led to significant increases in specific surface area (32.77 m2 g−1), which likely contributed to the enhanced Cd(II) sorption performance. Notably, heat treatment at 500 °C nearly doubled Cd(II) sorption stability as compared with that of raw red mud, as demonstrated by leaching experiments with simulated rainwater. Sequential extraction and XPS analyses indicated that specific sorption was the predominant mechanism involved in Cd(II) removal by red mud heat-treated at 500 °C (RM500). The strength of specific sorption following heat treatment likely contributed to the increase in sorption stability due to the formation of inner-sphere complex (–OCdOH). Metal-metal ion exchange was identified as another sorption mechanism, which, however, likely had only a limited effect on Cd(II) sorption performance. As the final pH (6.57) of the sorption system was typically lower than the pHPZC (about 10.6) of RM500, positive charges would develop on the red mud surface and impede the retention of Cd(II) cations, resulting in weak electrostatic attraction between Cd(II) cations and red mud. In summary, heat treatment at 500 °C considerably enhanced the capacity, rate and stability of Cd(II) sorption by red mud, suggesting red mud could be optimized by heat treatment as a more effective sorbent for Cd(II) removal. These findings represent the first mechanistic characterization of Cd(II) sorption by heat-treated red mud, providing much needed insights into the potential strategies to enhance the effectiveness of red mud in the sorptive removal of toxic heavy metals.

Red mud based gold catalysts in the oxidation of benzyl alcohol with molecular oxygen

Red Mud (RM) based gold catalysts were prepared by supporting gold nanoparticles (AuNPs) on the RM residue reduced either with H2 or with ethanol – which promoted partial coating of the RM with carbon. The materials were characterized by X-ray diffraction, Mössbauer spectroscopy, elemental analysis CHN, transmission electron microscopy and EDS microanalysis. Their catalytic performance was evaluated in the liquid-phase oxidation of benzyl alcohol by molecular oxygen, for the first time, as far as we know. The results showed that AuNPs with diameters of around 10nm were successfully supported and distributed on the surface of red mud based materials. Furthermore, carbon coating allowed better incorporation of AuNPs on the material surface and better dispersion of the material into the reaction solutions. AuNPs supported on RM reduced in ethanol and, therefore, coated with carbon showed better catalytic performance than AuNPs supported on MR reduced in hydrogen.

Effect of experimental variables onto Co2+ and Sr2+ sorption behavior in red mud-water suspensions

ABSTRACTThe prospects of rinsed red mud (alumina production residue) utilization for liquid radioactive waste treatment have been investigated, with Co2+ and Sr2+ as model cations of radioactive elements. To evaluate the sorption effectiveness and corresponding binding mechanisms, the process was analyzed in batch conditions, by varying experimental conditions (pH, Co2+ and Sr2+ concentrations in single solutions and binary mixtures, contact time, and the concentration of competing cations and ligands common in liquid radioactive waste). Comparison of the Co2+ and Sr2+ sorption pH edges with the red mud isoelectric point has revealed that Co2+ removal took place at both positive and negative red mud surface, while Sr2+ sorption abruptly increased when the surface became negatively charged. The increase of initial cation content and pH resulted in increased equilibrium times and sorption capacity and decreased rate constants. From single metal solutions and various binary mixtures, Co2+ was sorbed more efficiently and selectively than Sr2+. While Sr2+ sorption was reduced by coexisting cations in the order Al3+ ≥ Ca2+ >Na+ ≥Cs+, removal of Co2+ was affected by Al3+ species and complexing agents (EDTA and citrate). Desorption of Co2+ was negligible in Ca2+ and Sr2+ containing media and in solutions with initial pH 4–7. Sr2+ desorption was generally more pronounced, especially at low pH and in the presence of Co2+. Collected macroscopic data signify that Co2+ sorption by red mud minerals occurred via strong chemical bonds, while Sr2+ was retained mainly by weaker ion-exchange or electrostatic interactions. Results indicate that the rinsed red mud represent an efficient, low-cost sorbent for Co2+ and Sr2+ immobilization.

Gold nanoparticles supported on modified red mud for biphasic oxidation of sulfur compounds: A synergistic effect

Gold nanoparticles were supported on the surface of three different matrixes based on red mud waste: (i) pure red mud, (ii) reduced red mud and (iii) partially carbon coated red mud, in order to produce different catalysts for desulfurization reactions. The catalysts were extensively characterized by X-ray diffraction, Mössbauer spectroscopy, thermogravimetric analyses, electron microscopies (SEM and TEM), energy dispersive spectroscopy (EDS) and BET surface area. Results showed that gold was successfully supported and distributed on the surface of red mud based materials as nanoparticles with diameters around 30nm. The catalyst prepared with carbon coated red mud has shown to be twice more efficient than others for biphasic desulfurization reactions. This result can be associated with its amphiphilicity, which allows the catalyst to be located on the interface of biphasic systems. In this position a synergistic effect occurs between gold nanoparticles that adsorb S containing molecules and red mud Fe sites that promote the formation of OH radicals. The same effect is not observed for catalyst with hydrophilic supports.

Effect of strong acids on red mud structural and fluoride adsorption properties

The removal of fluoride using red mud has been improved by acidifying red mud with hydrochloric, nitric and sulphuric acid. The acidification of red mud causes sodalite and cancrinite phases to dissociate, confirmed by the release of sodium and aluminium into solution as well as the disappearance of sodalite bands and peaks in infrared and X-ray diffraction data. The dissolution of these mineral phases increases the amount of available iron and aluminium oxide/hydroxide sites that are accessible for the adsorption of fluoride. However, concentrated acids have a negative effect on adsorption due to the dissolution of these iron and aluminium oxide/hydroxide sites. The removal of fluoride is dependent on the charge of iron and aluminium oxide/hydroxides on the surface of red mud. Acidifying red mud with hydrochloric, nitric and sulphuric acid resulted in surface sites of the form SOH2+ and SOH. Optimum removal is obtained when the majority of surface sites are in the form SOH2+ as the substitution of a fluoride ion does not cause a significant increase in pH. This investigation shows the importance of having a low and consistent pH for the removal of fluoride from aqueous solutions using red mud.

Research of the adsorptive regularities of anions on the red mud surface

The possibility of red mud (waste of aluminum production) use as an alternative sorbent of molybdate, phosphate and bichromate ions from water solutions was studied. The paper shows dependence of adsorption of these ions from pH and concentration of electrolyte. The way of activation of a red mud surface was developed.

Surface charge properties of red mud particles generated from Chinese diaspore bauxite

Acid/basic potentiometric titration can be used to quantify the red mud surface charge properties. The amount of surface active —OH groups and surface charge density on the red mud particles generated from Chinese diaspore bauxite were evaluated from the acid/basic potentiometric titration data in 0.1 mol/L or 0.5 mol/L NaCl solution. The results show that the adsorption of sodium polyacrylate(SPA) on the red mud surface causes the increase of the surface active —OH groups, which makes the point of zero charge(PZC) shift to a lower pH value. However, the adsorption of polyacrylamide(PAM) causes little change. As the concentration of NaCl solution increases, the surface charge becomes more positive in acidic solution and more negative in alkaline solution, which can be attributed to the presence of a porous surface gel coating on the red mud particles.

Removal of phenol from aqueous phase by using neutralized red mud

The objective of this study is to remove the phenol from aqueous solution by using the neutralized red mud in batch adsorption technique. The study was carried out as functions of contact time, pH, initial phenol concentration, red mud dosage and effect of salt addition. The experiments demonstrated that maximum phenol removal was obtained in a wide pH range of 1–9 and it takes 10 h to attain equilibrium. The adsorption data was analyzed using the Langmuir and the Freundlich isotherm models and it was found that the Freundlich isotherm model represented the measured sorption data well. The influence of addition of salt on phenol removal depends on the relative affinity of the anions for the red mud surface and the relative concentrations of the anions.

Improvement of red mud polymer-matrix nanocomposites by red mud surface treatment

The effects of chemical treatments on red mud (RM) were investigated in terms of thermal stabilities of PMMA/RM and PVC/RM nanocomposites. N 2/77 K adsorption behavior and contact angles were studied in the pore structures and surface energetics of RM, respectively. Thermal stabilities of the nanocomposites were investigated using a thermal mechanical analyzer (TMA) and thermogravimetric analysis (TGA). As a result, the acidically treated RM (ARM) had higher adsorption properties, including specific surface area, than untreated RM (VRM) or basically treated RM (BRM). A change in the structure of the ARM surface was due to hydrolysis or leaching a metal salt out of RM. Also, the electron acceptor ( γ S + , acid) of ARM and the electron donor ( γ S − , base) of BRM were increased in the development of acid and basic functional groups, respectively. PMMA/ARM nanocomposites had higher thermal stability and mechanical interfacial properties than PMMA/VRM or BRM nanocomposites. These results were due to the improvements of the dispersion properties and acid–base interfacial interactions of basic PMMA and ARM. In this work, although the dispersion properties of the BRM decreased, the thermal stabilities and mechanical interfacial properties of PVC/BRM nanocomposites increased, which could be attributed to improvement in the interfacial interactions between acidic PVC and BRM.

Surface treatment of red mud and its influence on the properties of particulate-filled polyester composites

The red mud surface was treated with organosilane, organotitanate and organozirconate coupling agents respectively. The change in the surface was determined by IR spectroscopy and SEM. The effect of coupling agents concentration on the tensile and flexural strength of red mud-filled polyester resin has been studied. The efficacy of these coupling agents was discussed in relation to dispersion of red mud in unsaturated polyester resin and also by measuring performance of finished castings under both dry and wet conditions. It was found that organotitanate treated red mud-filled polyester composite gives better physico-mechanical properties than the control and other coupling agents treated red mud. Fractography of failed samples was also discussed in terms of their mechanical properties.