Solidification/Stabilization of Chromium in Red Mud-based Geopolymer

Up to 1.5wt%of Cr(Ⅲ)salts(CrCl_(3),and Cr_(2)O_(3))and Cr(Ⅵ)salts(Na_(2)CrO_(4),and CaCr_(2)O_(7))were incorporated into red mud-based geopolymers,respectively.The solidification/stabilization,compressive strength,and durability of the Cr-containing geopolymers were investigated.The experimental results indicate that the red mud-based geopolymer could effectively solidify/stabilize different types of Cr salts with solidification/stabilization rates of above 99.61%.Geopolymers are environmentally safe when the dosage of CaCr_(2)O_(7)is≤1.0wt%,or the dosage of CrCl_(3),Cr_(2)O_(3),and Na_(2)CrO_(4)is≤1.5wt%,respectively.The effects of Cr salts on the compressive strength varies with the type and content of Cr salts.The freeze-thaw cycle is more destructive to geopolymer properties than sulfate attack or acid rain erosion.The solidification/stabilization of Cr is mainly attributed to the following reasons:a)The chemical binding of Cr is related to the formation of Cr-containing hydrates(eg,magnesiochromite((Mg,Fe)(Cr,Al)_(2)O_(4)))and doping into N-A-S-H gel and C-A-S-H gel framework;b)The physical effect is related to the encapsulation by the hydration products(e g,N-A-S-H gel and C-A-S-H gel).This study provides a reference for the treatment of hazardous Cr-containing wastes by solid waste-based geopolymers.

Analysis of Calcined Red Mud Properties and Related Mortar Performances

Red mud(RM)is a low-activity industrial solid waste,and its utilization as a resource is currently a hot topic.In this study,the micro characteristics of red mud at different calcination temperatures were analyzed using X-ray diffraction and scanning electron microscopy.The performance of calcined red mud was determined through mortar strength tests.Results indicate that high-temperature calcination can change the mineral composition and microstructure of red mud,and increase the surface roughness and specific surface area.At the optimal temperature of 700°C,the addition of calcined red mud still leads to a decrease in mortar strength,but its activity index and flexural coefficient increase by 16.2%and 11.9%with respect to uncalcined red mud,reaching values of 0.826 and 0.974,respectively.Compared with the control group,the synergistic activation of calcined red mud with slag can increase the compressive and flexural strength of the mortar by 12.9%and 1.5%,reaching 8.7 and 62.4 MPa,respectively.Correspondingly,the activity index and flexural coefficient of the calcined RM and GGBS(Ground Granulated Blast furnace Slag)mixtures also increase to 1.015 and 1.130,respectively.

Influence of Bayer Red Mud on the Operational and Mechanical Characteristics of Composite Cement Mortar

The aim of this study is to enhance the value and utilization of red mud generated in the Bayer process by preparing composite cement mortars.The effects of two different types of Bayer red mud with varying physical and chemical characteristics on the fluidity,mechanical strength,mineral composition,and microstructure of the composite cement mortar were systematically evaluated.The results showed that the optimal addition of red mud A was 10 wt%,while it was 20 wt% for red mud B.The mechanical properties of the composite cement mortar met the standards for P·O42.5 cement.Furthermore,the composite mortar with the addition of red mud B showed higher flexural and compressive strengths compared to the composite mortar with red mud A.This improvement is attributed to the smaller particle size of red mud B,which filled the micro-pores and increased the compactness of the cement stone,as well as its higher content of Na_(2)O,K_(2)O,and other free alkalis,which resulted in more obvious alkali activation,accelerating the hydration of the active minerals in the slurry.

Research Progress on Green Utilization of Red Mud

Based on the research at home and abroad in recent years,this paper summarizes the recycling of metals in red mud,the preparation of cement and concrete with red mud,and the preparation of cementitious materials with red mud,so as to achieve the purpose of efficient utilization of waste and turning waste into wealth,make positive contribution to environmental protection,and ensure the green and sustainable development of various industries.

Adsorption removal of phosphate from aqueous solution by active red mud

Red mud is the waste of alumina industry and has high TiO2 and Fe2O3 content which are active components for the adsorption of anion pollutants. In this study, the uptake of phosphate by red mud activated by heat treatment and acid-heat treatment was investigated. The factors influencing the adsorption were also investigated. The result showed that the red mud sample treated using acid-heat method at 80℃ with 0.25 mol/L HCl for 2 h achieved the highest phosphate removal. For the heat-activated red mud, the sample heated at 700℃ for 2 h preformed better than the other heat treatment. Phosphate removal by the activated red mud was significantly pH dependent, and pH 7 was the optimal pH for phosphate removal. The adsorption fits Langmuir isotherm model well and the maximum adsorption capacities of the acid-heat activated red mud and the heat activated samples were 202.9 mgP/g and 155.2 mgP/g, respectively.

Production of pig iron from red mud waste fines using thermal plasma technology

Red mud, an insoluble residue produced during alkali leaching of bauxite, is considered as a low-grade iron ore containing 30% to 50% iron. The present paper deals with the use of thermal plasma technology for producing pig iron from red mud waste fines. The smelting reduction of red mud was carried out in a 35 kW DC extended arc thermal plasma reactor. Red mud was properly mixed with fluxes and graphite （fixed carbon, 99%） as a reductant as per stoichiometric requirement. The effect of various process parameters like a reductant, fluxes and smelting time on iron recovery was studied and optimized. An optimum condition for the maximum recovery of iron was obtained. A new thermal plasma process applicable to direct iron making from red mud waste fines that would achieve significant utilization of red mud was proposed.

Extraction of scandium from red mud by modified activated carbon and kinetics study

Activated carbon （AC） was modified by tri-butyl phosphate （TBP） for selectively extracting scandium from red mud and characterized by BET （Brunauer-Emmett-Teller） surface area. The modified AC had a preferential adsorption to scandium. The influences of adsorbent dos- age, adsorption temperature, and time on adsorption capacity and selectivity to scandium were examined. An optimum adsorbent dosage （-6.25 g/L）, adsorption temperature （308 K）, and adsorption time （40 min） were figured out. A pseudo-second-order kinetics model was employed for describing the adsorption process of scandium.

Investigation of the medium calcium based non-burnt brick made by red mud and fly ash: durability and hydration characteristics

Red mud is a type of highly alkaline waste residue produced in the process of alumina smelting by the Bayer process.Based on the idea of medium calcium content,solid wastes such as red mud and fly ash were used to prepare non-burnt bricks;and the mass ratio of CaO/SiO2 was selected in the range of 0.88–1.42.Mechanical properties and durability were investigated with a compressive strength test.X-ray diffractometry(XRD),scanning electron microscope(SEM),and Fourier transform infrared spectroscopy(FTIR)techniques were used to characterize the hydration characteristic.The environmental performance was analyzed by Inductively Coupled Plasma Mass Spectrometry(ICP).The results indicated that the mechanical properties and the durability were optimal when the mass ratio of CaO/SiO2 was 1.23.The hydration products were mostly C–S–H gel,ettringite,Na4Ca(Si10All6)O32·12H2O and Ca3Al2(SiO4)(OH)8.They were responsible for the strength development,and the CaO/SiO2 mass ratio of 1.23 had the best polymerized structure.The results of an environmental performance test showed that the heavy metals in the raw materials were well-solidified in the brick.Therefore,this paper provides an effective solution for use of solid wastes in building material.

Recovery of alkali and alumina from Bayer red mud by the calcification–carbonation method

Red mud produced in the Bayer process is a hazardous solid waste because of its high alkalinity; however, it is rich in valuable components such as titanium, iron, and aluminum. In this study, a novel calcification-carbonation method was developed to recover alkali and alumina from Bayer red mud under mild reaction conditions. Batch experiments were performed to evaluate the potential effects of im- portant parameters such as temperature, amount of CaO added, and CO2 partial pressure on the recovery of alkali and alumina. The results showed that 95.2% alkali and 75.0% alumina were recovered from red mud with decreases in the mass ratios of Na2O to Fe2O3 and of Al2O3 to Fe2O3 from 0.42 and 0.89 to 0.02 and 0.22, respectively. The processed red mud with less than 0.5wt% Na2O can potentially be used as a construction material.

Complementation in the composition of steel slag and red mud for preparation of novel ceramics

A method for preparing novel ceramics was developed in this study. Different ratios red muds were added to steel slags to optimize the preparation of novel ceramics by a traditional ceramic preparation process. The sintering mechanism, microstructure, and performance were studied by X-ray diffraction techniques, scanning electron microscopy, and combined experiments of linear shrinkage, water absorption, and flexural strength. The results confirmed that red mud can reduce the volumetric instabilities through the complementarity of red mud and ferroalloy slag. The crystal phases in the ceramics are all pyroxene group minerals, including diopside ferrian, augite, and diopside. The flexural strength of the ceramic that contains 40 wt% red mud and was prepared at the optimal sintering temperature(1140°C) is greater than 93 MPa; its corresponding water absorption is less than 0.05%.

Durability and microstructure analysis of the road base material prepared from red mud and flue gas desulfurization fly ash

The present study aimed to investigate the durability and microstructure evolution of road base materials(RBM)prepared from red mud and flue gas desulfurization fly ash.The durability testing showed that the strength of RBM with the blast furnace slag addition of 1wt%,3wt%and 5wt%reached 3.81,4.87,and 5.84 MPa after 5 freezing–thawing(F–T)cycles and reached 5.21,5.75,and 6.98 MPa after 20 weting–drying(W–D)cycles,respectively.The results also indicated that hydration products were continuously formed even during W–D and F–T exposures,resulting in an increase of the strength and durability of RBM.The observed increase of macropores(>1μm)after F–T and W–D exposures suggested that the mechanism of RBM deterioration is pore enlargement due to cracks that develop inside their matrix.Moreover,the F–T exposure showed a greater negative effect on the durability of RBM compared to the W–D exposure.The leaching tests showed that sodium and heavy metals were solidified below the minimum requirement,which indicates that these wastes are suitable for use as a natural material replacement in road base construction.

Strength Development and Microstructure of Hardened Cement Paste Blended with Red Mud

Red mud was activated to be a mineral admixture for Portland cement by means of heating at different elevated temperatures from 400 ℃ to 700 ℃ . Results show that heating was ef-fective, among which thermal activation of red mud at 600 ℃ was most effective. Chemical analysis suggested that cement added with 600 ℃ thermally activated red mud yielded more calcium ion dur-ing the early stage of hydration and less at later stage in liquid phase of cement water suspension sys-tem, more combined water and less calcium hydroxide in its hardened cement paste. MIP measure-ment and SEM observation proved that the hardened cement paste had a similar total porosity and a less portion of large size pores hence a denser microstructure compared with that added with original red mud.

Feasibility of co-reduction roasting of a saprolitic laterite ore and waste red mud

Large scale utilization is still an urgent problem for waste red mud with a high content of alkaline metal component in the future.Laterite ores especially the saprolitic laterite ore are one refractory nickel resource,the nickel and iron of which can be effectively recovered by direct reduction and magnetic separation.Alkaline metal salts were usually added to enhance reduction of laterite ores.The feasibility of co-reduction roasting of a saprolitic laterite ore and red mud was investigated.Results show that the red mud addition promoted the reduction of the saprolitic laterite ore and the iron ores in the red mud were co-reduced and recovered.By adding 35wt%red mud,the nickel grade and recovery were 4.90wt%and 95.25wt%,and the corresponding iron grade and total recovery were 71.00wt%and 93.77wt%,respectively.The X-ray diffraction（XRD）,scanning electron microscopy,and energy dispersive spectroscopy（SEM-EDS）analysis results revealed that red mud addition was helpful to increase the liquid phase and ferronickel grain growth.The chemical compositions＂Ca O and Na_2O＂in the red mud replaced Fe O to react with Si O_2 and Mg Si O_3 to form augite.

Investigation on the fabrication of lightweight aggregate with acid-leaching tailings of vanadium-bearing stone coal minerals and red mud

Proper treatment of acidleaching tailings(ALTs)of vanadiumbearing stone coal minerals is of great urgency.One approach is adding it into the raw materials during the preparation of lightweight aggregate(LWA).But clay is always needed.In this paper,another solid waste,red mud,was mixed with ALTs as a source of flux components instead of clay.Evaluation of the physical characteristics,morphological structures,as well as crystal phases during the sintering process were investigated.When their mixtures with a proper ratio were sintered at 1080℃,a glassy phase with certain viscosity was formed,and the gases generated simultaneously were encapsulated by the melt.Finally,LWA with a onehour water absorption as low as 1.46%,a bulk density as low as 728.76 kgm 3 and a compressive strength as high as 10.77 MPa was fabricated.

INFLUENCE OF ADDITIVES ON SLAG－IRON SEPARATION DURING DIRECT REDUCTION OF COAL－BASE HIGH－IRON－CONTENTREDMUD

ＩＮＦＬＵＥＮＣＥＯＦＡＤＤＩＴＩＶＥＳＯＮＳＬＡＧ－ＩＲＯＮＳＥＰＡＲＡＴＩＯＮＤＵＲＩＮＧＤＩＲＥＣＴＲＥＤＵＣＴＩＯＮＯＦＣＯＡＬ－ＢＡＳＥＨＩＧＨ－ＩＲＯＮ－ＣＯＮＴＥＮＴＲＥＤＭＵＤＱｉｕＧｕａｎｚｈｏｕ；ＬｉｕＹｏｎｇｋａｎｇ；Ｊｉａｎｇ...

Preparation of Porous Ceramisite for Waste Water Treatment Made from Red Mud

The porous ceramisites for wastewater treatment were made from red mud, which is the industrial waste discharged from the production of Al2O3. The sintering process and the degreasing experiments with porous ceramisites have been finished. The results show that the sintering temperature control is dominant for the preparation of the porous ceramisites. The optimal sintering temperature is between 1 110-1120℃, a narrow range. The surface of ceramists is distributed with a lot of coarse holes with diameters of about 1-10μm. Moreover, the sintering temperatures have a great influence on the efficiency of degreasing, and the curve between the sintering temperature and the efficiency ofdegreasing is like a parabola.

Statistical Modeling Studies of Iron Recovery from Red Mud Using Thermal Plasma

Optimization studies of plasma smelting of red mud were carried out. Reduction of the dried red mud fines was done in an extended arc plasma reactor to recover the pig iron. Lime grit and low ash metallurgical （LAM） coke were used as the flux and reductant, respectively. 2level factorial design was used to study the influence of all parameters on the responses. Response surface modeling was done with the data obtained from statistically designed experiments. Metal recovery at optimum parameters was found to be 79.52%.

Hydration kinetics of cementitious materials composed of red mud and coal gangue

To elucidate the intrinsic reaction mechanism of cementitious materials composed of red mud and coal gangue（RGC）, the hydration kinetics of these cementitious materials at 20°C was investigated on the basis of the Krstulovi？-Dabi？ model. An isothermal calorimeter was used to characterize the hydration heat evolution. The results show that the hydration of RGC is controlled by the processes of nucleation and crystal growth（NG）, interaction at phase boundaries（I）, and diffusion（D） in order, and the pozzolanic reactions of slag and compound-activated red mud-coal gangue are mainly controlled by the I process. Slag accelerates the clinker hydration during NG process, whereas the compound-activated red mud-coal gangue retards the hydration of RGC and the time required for I process increases with increasing dosage of red mud-coal gangue in RGC.

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 techqicalparameters were proposed with 700 ℃roasting for 20 min,as 50wt% carbon and 4wt% additive were added.The experimentalresults indicated that the iron recovery and the grade of totaliron were 91% and 60%,respectively.A novelprocess is applicable to recover ferric oxide from the red mud waste fines.

Utilization of Bayer Red Mud Derived from Bauxite for Belite-Ferroaluminate Cement Production

Bayer red mud(BRM)is a kind of industrial solid waste characterized by huge volume and high alkalinity.Its disposal generates serious environmental pollution and occupies a large number of farmland.The utilization and recycling of BRM is currently a crucial issue and needs to be addressed as soon as possible.The chemical composition of BRM is similar to cement clinker.In this study,the feasibility of preparing Belite-ferroaluminate clinker(BFAC)with different BRM was explored.The physical properties,mechanics performance,radioactivity levels and trace harmful metals leaching were measured.XRD,BEI and EDS were used to characterize the mineral formation,and SEM is used to reveal the solidified mechanism of trace harmful metal.The results show that the preparation of BFAC using a certain amount of BRM was feasible.The formed phases in clinkers mainly included C_(4)A_(3)Š,C_(2)S and C_(4)AF.The flexural strength and compressive strength of BFAC at 3 days increased whereas 28 and 90 days decreased with the increase of BRM due to the formation of higher C_(4)AF and lower C_(2)S.The formation of large amounts of Al_(2)O_(3)·3H_(2)O gel and Fe_(2)O_(3)·3H_(2)O gel in hydration products enhanced the adsorption capability to heavy metals and other ions.The trace harmful metal concentration in the leaching solution was much less than the upper limits.The radioactivity level of leaching solution was close to natural radioactive background.BRM is safe as raw material of BFAC.