Phosphate removal from wastewater using red mud

Red mud, a waste residue of alumina refinery, has been used to develop effective adsorbents to remove phosphate from aqueous solution. Acid and acid-thermal treatments were employed to treat the raw red mud. The effects of different treatment methods, pH of solution and operating temperature on adsorption have been examined in batch experiments. It was found that all activated red mud samples show higher surface area and total pore volume as well as higher adsorption capacity for phosphate removal. The red mud with HCl treatment shows the highest adsorption capacity among all the red mud samples, giving adsorption capacity of 0.58 mg P/g at pH 5.5 and 40 degrees C. The adsorption capacity of the red mud adsorbents decreases with increase of pH. At pH 2, the red mud with HCl treatment exhibits adsorption of 0.8 mg P/g while the adsorption can be lowered to 0.05 mg P/g at pH 10. However, the adsorption is improved at higher temperature by increasing 25% from 30 to 40 degrees C. The kinetic studies of phosphate adsorption onto red mud indicate that the adsorption mainly follows the parallel first-order kinetics due to the presence of two acidic phosphorus species, H(2)PO(4)(-) and HPO(4)(2-). An analysis of the adsorption data indicates that the Freundlich isotherm provides a better fitting than the Langmuir model.     

Reuse of a treated red mud bauxite waste: studies on environmental compatibility

Red mud is the major solid waste produced in the process of alumina extraction from bauxite (Bayer process). Environmental "compatibility" of a treated red mud was studied in order to evaluate its possible recycling in environmental compartments. The leaching test requested by the Italian law on treated solid waste to be "re-introduced in the environment" was performed on this material. Moreover, in order to better evaluate the environmental compatibility, three different types of eco-toxicological tests were applied (Microtox test, ASTM microalgae toxicity test and sea urchin embryo toxicity test). These "chemical" and eco-toxicological tests gave encouraging results. The possibility to use this material for treating contaminated waters and soils was evaluated, again with particular attention to the Italian regulatory system, through experiments on the treated red mud metal trapping ability and on the subsequent release of trapped metals, at low pH conditions. The treated red mud showed a general high metal trapping capacity and the release at low pH was generally low.     

Leaching of metals from fresh and sintered red mud

The disposal of red mud, a solid waste generated during the extraction of alumina from bauxite, is one of the major problems faced by the aluminum industry. Proper disposal followed by its utilization, for example as bricks, can provide a satisfactory solution to this problem. Pollution potential of red mud and its finished product, due to metals leaching out from them under certain environmental conditions, need to be studied. Sintering of red mud was performed in a resistance type vertical tube furnace to simulate the brick-making conditions in lab-scale. Leachability of metals in red mud and the sintered product was evaluated by performing sequential extraction experiments on both. The metals studied were the 'macro metals' iron and aluminum and the 'trace metals' copper and chromium. The total extractabilities of all the metals estimated by the microwave digestion of red mud samples decreased due to sintering. The leachability in sequential extraction of the macro metals iron and aluminum, on the other hand, increased due to sintering in all phases of sequential extraction. However, the effect of sintering on the leachability of the trace metals by sequential extraction was different for copper and chromium in different fractions of sequential extraction.     

Lime-stabilized red mud bricks

Red mud is a waste material obtained from the aluminium extraction industry and consists mainly of the oxides of aluminium, iron and titianium. The present red mud production in the country is above two million tons every year, which is not being put to any worthwhile use except as a filler to a small extent in the preparation of roads. Efforts have been made at CBRI to produce burnt clay bricks by partially replacing the clay with red mud and fly-ash. In this process, the red mud is expected to find a major use shortly. Efforts have also been made to incorporate in the red mud a small percentage of lime and compress the mix at optimum moisture content in the form of bricks with a purpose of examining their strength and stability to the erosive action of water. A maximum wet compressive strength of 3.75 MN m^?2 with 5% lime and 4.22 MN m^?2 with 8% lime has been obtained after 28 days of casting and humid curing in the month of August. The red mud sample studied was obtained from the Indian Aluminium Company. The brick samples were studied for accelerated weathering and found suitable for use as a walling material for low-cost shelters. Modifications in the red mud mix, especially from the viewpoint of particle size distribution, have also been examined simultaneously by its part replacement with coarse-grained soil and fly-ash. The results indicate that the basis of the beneficial action of lime on red mud is predominantly chemical.     

Erosion of geopolymers made from industrial waste

Solid-particle erosion studies were conducted on geopolymers derived from various combinations of granulated blast-furnace slag, flyash, sand, clay, and rock. The erodent particles were 390-μm angular Al₂O₃, which impacted at 30, 60, or 90° at a velocity of 50, 70, or 100 m/s. Steady-state erosion rates were obtained as weight of target lost per weight of impacting particles. Material-loss mechanisms were studied by scanning electron microscopy (SEM). All of the geopolymers responded to normal impact as conventional brittle solids, but impact at 30° led to anomalously rapid erosion, probably because of presence of microcracks and consequent enhanced removal of aggregates within the geopolymers. Erosion rates at 90° impact were proportional to erodent velocity to the 2.3–2.7 power. The geopolymers exhibited crushing strengths of approximately 32–57 MPa. Erosion rate correlated with density and strength for geopolymers of similar composition. All of the geopolymers that contained flyash were more resistant to erosion than was the geopolymer without flyash.     

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.     

粉磨工艺对赤泥胶结充填料性能的影响

为提高胶结充填材料的强度性能,试验研究了分别粉磨和梯级粉磨工艺对赤泥全尾砂胶结充填材料强度性能、粉体粒径以及水化过程的影响.结果表明：梯级粉磨工艺下试块的1、3、28 d最大抗压强比分别粉磨工艺下试块1、3、28 d最大抗压强度分别高出21%、16.6%、3.7%;梯级粉磨工艺使物料粉体的比表面积均高于分别粉磨工艺的粉...     

Removal of congo red from aqueous solution by adsorption onto acid activated red mud

The objective of this study is to remove the congo red (CR) anionic dye, from water by using the acid activated red mud in batch adsorption experiments. The effects of contact time, pH, adsorbent dosage and initial dye concentration on the adsorption were investigated. The pH of the dye solution strongly affected the chemistry of both the dye molecules and activated red mud in an aqueous solution. The effective pH was 7.0 for adsorption on activated red mud. It was found that the sufficient time to attain equilibrium was 90 min. The adsorption isotherms were analyzed using the Langmuir, the Freundlich, and the three parameter Redlich-Peterson isotherms. The Langmuir isotherm was the best-fit adsorption isotherm model for the experimental data obtained from the non-linear chi-square statistic test.     

Preparation and properties of glass-ceramic materials obtained by recycling goethite industrial waste

The recycling of toxic goethite waste, originated in the hydrometallurgy of zinc ores, in glass-ceramic matrices has been studied. Oxide compositions suitable to form glasses were prepared by mixing the goethite waste with granite scraps and glass cullet, yielding the following oxide composition (wt%): SiO₂, 44.6; Al₂O₃, 3.3; Fe₂O₃, 25.5; MgO, 1.6; CaO, 4.5; Na₂O, 5.9; PbO, 3.1; ZnO, 6.5; K₂O, 1.0; TiO₂, 2.0; other 2.0. By proper addition of carbon powder, the initial Fe³⁺/Fe²⁺ ratio (12) of glasses melted in air at 1450 °C was approximated to the stoichiometric value of magnetite (2) to obtain high nucleation and crystallization rates. The heat treatment of iron supersaturated goethite glasses above 630 °C led to the formation of magnetite nuclei with a high tendency to grow and coalesce with time. The crystallization of pyroxene, occurring on the magnetite crystals above 800 °C, was found to be influenced by the nucleation period, so that the highest crystalline volume fraction, V _f (0.80–0.85), was obtained for 90–120 min nucleation time at 670 °C and 120 min crystallization at 860 °C. This revised version was published online in November 2006 with corrections to the Cover Date.     

Silica materials recovered from photonic industrial waste powder: its extraction, modification, characterization and application

This study explored the possibility of recovering waste powder from photonic industry into two useful resources, sodium fluoride (NaF) and the silica precursor solution. An alkali fusion process was utilized to effectively separate silicate supernatant and the sediment. The obtained sediment contains purified NaF (>90%), which provides further reuse possibility since NaF is widely applied in chemical industry. The supernatant is a valuable silicate source for synthesizing mesoporous silica material such as MCM-41. The MCM-41 produced from the photonic waste powder (PWP), namely MCM-41(PWP), possessed high specific surface areas (1082 m²/g), narrow pore size distributions (2.95 nm) and large pore volumes (0.99 cm³/g). The amine-modified MCM-41(PWP) was further applied as an adsorbent for the capture of CO₂ greenhouse gas. Breakthrough experiments demonstrated that the tetraethylenepentamine (TEPA) functionalized MCM-41(PWP) exhibited an adsorption capacity (82 mg CO₂/g adsorbent) of only slightly less than that of the TEPA/MCM-41 manufactured from pure chemical (97 mg CO₂/g adsorbent), and its capacity is higher than that of TEPA/ZSM-5 zeolite (43 mg CO₂/g adsorbent). The results revealed both the high potential of resource recovery from the photonic solid waste and the cost-effective application of waste-derived mesoporous adsorbent for environmental protection.     

Removal of boron from aqueous solution by using neutralized red mud

The adsorptive removal of boron from aqueous solution by using the neutralized red mud was studied in batch equilibration technique. The effects of pH, adsorbent dosage, initial boron concentration and contact time on the adsorption were investigated. The experiments demonstrated that boron removal was of a little fluctuation in pH range of 2-7 and it takes 20 min 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.     

Catalytic hydrodechlorination of tetrachloroethylene over red mud

Hydrodechlorination of tetrachloroethylene was investigated using red mud (RM, a by-product in the production of alumina by the Bayer process) as the catalyst. Use of RM as a hydrodechlorination catalyst is of interest from an industrial point of view because its cost is much lower than that of commercial catalysts. Hydrodechlorination reactions were carried out in a continuous fixed bed reactor. The influence of catalyst sulfiding, temperature (50-350 degrees C), pressure (2-10MPa), hydrogen flow rate and the presence of solvents (hexane, heptane, benzene and toluene) on the reaction was studied. Sulfided red mud is active as a hydrodechlorination catalyst, conversion of tetrachloroethylene increases as the pressure and temperature increase. The solvents did not influence the conversion, nor were side reactions involving the solvent observed.The kinetics of the reaction was studied at 350 degrees C and 10MPa, conditions for which mass transfer limitations were negligible. A good fit of a Langmuir-Hinselwood model to the experimental data was obtained.     

Titanium leaching from red mud by diluted sulfuric acid at atmospheric pressure

Laboratory-scale research has focused on the recovery of titanium from red mud, which is obtained from bauxite during the Bayer process for alumina production. The leaching process is based on the extraction of this element with diluted sulfuric acid from red mud under atmospheric conditions and without using any preliminary treatment. Statistical design and analysis of experiments were used, in order to determine the main effects and interactions of the leaching process factors, which were: acid normality, temperature and solid to liquid ratio. The titanium recovery efficiency on the basis of red mud weight reached 64.5%. The characterization of the initial red mud, as well as this of the leached residues was carried out by X-ray diffraction, TG-DTA and scanning electron microscopy.     

Evaluation of blends bauxite-calcination-method red mud with other industrial wastes as a cementitious material: properties and hydration characteristics

Red mud is generated from alumina production, and its disposal is currently a worldwide problem. In China, large quantities of red mud derived from bauxite calcination method are being discharged annually, and its utilization has been an urgent topic. This experimental research was to evaluate the feasibility of blends red mud derived from bauxite calcination method with other industrial wastes for use as a cementitious material. The developed cementitious material containing 30% of the bauxite-calcination-method red mud possessed compressive strength properties at a level similar to normal Portland cement, in the range of 45.3-49.5 MPa. Best compressive strength values were demonstrated by the specimen RSFC2 containing 30% bauxite-calcination-method red mud, 21% blast-furnace slag, 10% fly ash, 30% clinker, 8% gypsum and 1% compound agent. The mechanical and physical properties confirm the usefulness of RSFC2. The hydration characteristics of RSFC2 were characterized by XRD, FTIR, (27)Al MAS-NMR and SEM. As predominant hydration products, ettringite and amorphous C-S-H gel are principally responsible for the strength development of RSFC2. Comparing with the traditional production for ordinary Portland cement, this green technology is easier to be implemented and energy saving. This paper provides a key solution to effectively utilize bauxite-calcination-method red mud.     

Metallurgical recovery of metals from electronic waste: a review

Waste electric and electronic equipment, or electronic waste, has been taken into consideration not only by the government but also by the public due to their hazardous material contents. In the detailed literature survey, value distributions for different electronic waste samples were calculated. It is showed that the major economic driver for recycling of electronic waste is from the recovery of precious metals. The state of the art in recovery of precious metals from electronic waste by pyrometallurgical processing, hydrometallurgical processing, and biometallurgical processing are highlighted in the paper. Pyrometallurgical processing has been a traditional technology for recovery of precious metals from waste electronic equipment. However, state-of-the-art smelters are highly depended on investments. Recent research on recovery of energy from PC waste gives an example for using plastics in this waste stream. It indicates that thermal processing provides a feasible approach for recovery of energy from electronic waste if a comprehensive emission control system is installed. In the last decade, attentions have been removed from pyrometallurgical process to hydrometallurgical process for recovery of metals from electronic waste. In the paper, hydrometallurgical processing techniques including cyanide leaching, halide leaching, thiourea leaching, and thiosulfate leaching of precious metals are detailed. In order to develop an environmentally friendly technique for recovery of precious metals from electronic scrap, a critical comparison of main leaching methods is analyzed for both economic feasibility and environmental impact. It is believed that biotechnology has been one of the most promising technologies in metallurgical processing. Bioleaching has been used for recovery of precious metals and copper from ores for many years. However, limited research was carried out on the bioleaching of metals from electronic waste. In the review, initial researches on the topic are presented. In addition, mechanisms and models of biosorption of precious metal ions from solutions are discussed.     

Incorporation of waste materials into portland cement clinker synthesized from natural raw materials

For every ton of portland cement that is manufactured, approximately half a ton of carbon dioxide is released from calcining limestone. One method of reducing the carbon dioxide from portland cement production is to reduce or eliminate the use of limestone through replacement with calcium oxide-bearing waste materials. In this study, portland cement clinker was synthesized using minimal limestone content and maximal waste material content, specifically fly ash and blast furnace slag. The synthetic cements were characterized using X-ray diffraction, scanning electron microscopy, and isothermal calorimetry. Results show that portland cement clinker can be successfully synthesized from a maximam of 27.5% fly ash and 35% slag. The synthetic cements possessed early-age hydration behavior similar to a commercial Type I/II portland cement. However, the presence of sulfur impurities contained in waste materials significantly affected phase formation in portland cement clinker.

---