Phosphate removal from aqueous solutions using raw and activated red mud and fly ash

The effect of acidification and heat treatment of raw red mud (RM) and fly ash (FA) on the sorption of phosphate was studied in parallel experiments. The result shows that a higher efficiency of phosphate removal was acquired by the activated samples than by the raw ones. The sample prepared by using the RM stirred with 0.25 M HCl for 2h (RM0.25), as well as another sample prepared by heating the RM at 700 degrees C for 2h (RM700), registered the maximum removal of phosphate (99% removal of phosphate). This occurred when they were used in the phosphate sorption studies conducted at pH 7.0 and 25 degrees C with the initial PO(4)(3-) concentration of 155 mg P/l. The FA samples treated in the same way described above can achieve 7.0 and 8.2 mg P/l phosphate removal for FA0.25 and FA700 respectively, corresponding to 45.2% and 52.9% removal. The activated materials performed higher phosphate removal over broader pH range compared with the raw ones. The influences of various factors, such as initial pH and initial phosphate concentration on the sorption capacity were also studied in batch equilibration technique. Solution pH significantly influenced the sorption. Each sample achieved the maximal removal of phosphate at pH 7.0. The amount of phosphate removal increased with the solute concentration. The Freundlich and Langmuir models were used to simulate the sorption equilibrium. The results indicate that the Langmuir model has a better correlation with the experimental data than the Freundlich model.     

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.     

Phosphate removal from solution using steel slag through magnetic separation

Steel slag with magnetic separation was used to remove phosphate from aqueous solutions. The influence of adsorbent dose, pH, and temperature on phosphate removal was investigated in a series of batch experiments. Phosphate removal increased with the increasing temperature, adsorbent dose and decreased with increasing initial phosphate concentrations, while it was at its peak at pH of 5.5. The phosphate removal predominantly occurred through ion exchange. The specific surface area of the steel slag was 2.09m2/g. The adsorption of phosphate followed both Langmuir and Freundlich isotherms. The maximum adsorption capacity of the steel slag was 5.3mgP/g. The removal rates of total phosphorus (TP) and dissolved phosphorus (DP) from secondary effluents were 62-79% and 71-82%, respectively. Due to their low cost and high capability, it was concluded that the steel slag may be an efficient adsorbent to remove phosphate both from solution and wastewater.     

The color removal of dye wastewater by magnesium chloride/red mud (MRM) from aqueous solution

In this study, the MgCl₂/red mud system (MRM) was used to investigate the color removal efficiency of dye solutions. Parameters such as the effect of the dosage of red mud (RM) and MgCl₂ have been studied. The effect of pH on the conversion rate of Mg²⁺ has also been studied. The color removal efficiency of MRM was compared with that of PAC/RM and PAC/NaOH. Meanwhile, the color removal efficiency of RM was compared with that of NaOH. The results show that the MRM system can remove more than 98% of the coloring material at a dosage of 25 g RM/L dye solution and a volume of 1.5 mL MgCl₂/L dye solution in the decolorization process of reactive dye, acid dye and direct dye. The color removal efficiency was better than PAC/RM and PAC/NaOH system. The adsorption data have been analyzed using Langmuir and Freundlich isotherms. The results indicated that both models provide the best correlation of the experimental data. The decolorization mechanism of MRM was discussed, too. The MRM system was a viable alternative to some of the more conventional forms of chemical treatment of dye solutions and also provided another way to make use of industrial waste red mud.     

Characterisation and environmental application of an Australian natural zeolite for basic dye removal from aqueous solution

An Australian natural zeolite was collected, characterised and employed for basic dye adsorption in aqueous solution. The natural zeolite is mainly composed of clinoptiloite, quartz and mordenite and has cation-exchange capacity of 120 meq/100g. The natural zeolite presents higher adsorption capacity for methylene blue than rhodamine B with the maximal adsorption capacity of 2.8 x 10(-5) and 7.9 x 10(-5)mol/g at 50 degrees C for rhodamine B and methylene blue, respectively. Kinetic studies indicated that the adsorption followed the pseudo second-order kinetics and could be described as two-stage diffusion process. The adsorption isotherm could be fitted by the Langmuir and Freundlich models. Thermodynamic calculations showed that the adsorption is endothermic process with Delta H(0) at 2.0 and 8.7 kJ/mol for rhodamine B and methylene blue. It has also found that the regenerated zeolites by high-temperature calcination and Fenton oxidation showed similar adsorption capacity but lower than the fresh sample. Only 60% capacity could be recovered by the two regeneration techniques.     

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.     

Removal of fluoride from water by using granular red mud: Batch and column studies

This paper describes the removal of fluoride from water using granular red mud (GRM) according to batch and column adsorption techniques. For the batch technique, the experiments demonstrated that maximum fluoride removal was obtained at a pH of 4.7 and it took 6h to attain equilibrium and equilibrium time did not depend upon the initial fluoride concentration. Kinetics data were fitted with pseudo-second-order model. The Redlich-Peterson and Freundlich isotherm models better represented the adsorption data in comparison to the Langmuir model. Column experiments were carried out under a constant influent concentration and bed depth, and different flow rates. The capacities of the breakthrough and exhaustion points decreased with increase of the flow rate. Thomas model was applied to the experimental results. The modelled breakthrough curves were obtained, and they were in agreement with the corresponding experimental data. The column adsorption was reversal and the regeneration operation was accomplished by pumping 0.2M of NaOH through the loaded GRM-column.     

Equilibrium and kinetic studies on the removal of Acid Red 114 from aqueous solutions using activated carbons prepared from seed shells

The use of low-cost and ecofriendly adsorbents has been investigated as an ideal alternative to the current expensive methods of removing dyes from wastewater. This paper deals with the removal of Acid Red 114 (AR 114) from aqueous solutions using activated carbons prepared from agricultural waste materials such as gingelly (sesame) (Sp), cotton (Cp) and pongam (Pp) seed shells. Optimum conditions for AR 114 removal were found to be pH 3, adsorbent dosage=3g/L of solution and equilibrium time=4h. Higher removal percentages were observed at lower concentrations of AR 114. The adsorption isotherm data were fitted to Langmuir and Freundlich equation, and the adsorption capacity of the studied adsorbents was in the order Sp>Cp>Pp. Kinetic studies showed that the adsorption followed both pseudo-second-order and Elovich equation. The thermodynamics parameters such as DeltaG degrees, DeltaH degrees, DeltaS degrees were also evaluated. The activated carbons prepared were characterized by FT-IR, SEM and BET analysis.     

The potential application of red mud in the production of castings

The bauxite industry in Jamaica is the third largest producer of alumina in the world. Because of the technological method of processing the bauxite, there is a large amount of the world's red mud residue being disposed in Jamaica. The magnitude of the industry's production of alumina and the red mud disposal problem as a by-product is of the same order.

This research was conducted to investigate the feasibility of using a mixture of red mud and the traditional silica sand to produce quality-casting component.

The porosity of the aluminium specimens obtained from the red mud castings showed that porosity increased up to two-fold, depending on the ratio of sand and red mud. For applications where optimum casting strength is important, the use of 100% red mud may be unsatisfactory.

Although there are other variables that affect the quality of the mixture of silica sand and red mud mould in castings, the result is very significant given the possibility of applying portions of red mud in other casting techniques.     

Adsorptive removal of chlorophenols from aqueous solution by low cost adsorbent--Kinetics and isotherm analysis

Adsorptive removal of parachlorophenol (PCP) and 2,4,6-trichlorophenol (TCP) from aqueous solutions by activated carbon prepared from coconut shell was studied and compared with activated carbon of commercial grade (CAC). Various chemical agents in different concentrations were used (KOH, NaOH, CaCO(3), H(3)PO(4) and ZnCl(2)) for the preparation of coconut shell activated carbon. The coconut shell activated carbon (CSAC) prepared using KOH as chemical agent showed high surface area and best adsorption capacity and was chosen for further studies. Batch adsorption studies were conducted to evaluate the effect of various parameters such as pH, adsorbent dose, contact time and initial PCP and TCP concentration. Adsorption equilibrium reached earlier for CSAC than CAC for both PCP and TCP concentrations. Under optimized conditions the prepared activated carbon showed 99.9% and 99.8% removal efficiency for PCP and TCP, respectively, where as the commercially activated carbon had 97.7% and 95.5% removal for PCP and TCP, respectively, for a solution concentration of 50mg/L. Adsorption followed pseudo-second-order kinetics. The equilibrium adsorption data were analysed by Langmuir, Freundlich, Redlich-Peterson and Sips model using non-linear regression technique. Freundlich isotherms best fitted the data for adsorption equilibrium for both the compounds (PCP and TCP). Similarly, acidic pH was favorable for the adsorption of both PCP and TCP. Studies on pH effect and desorption revealed that chemisorption was involved in the adsorption process. The efficiency of the activated carbon prepared was also tested with real pulp and paper mill effluent. The removal efficiency using both the carbons were found highly satisfactory and was about 98.7% and 96.9% as phenol removal and 97.9% and 93.5% as AOX using CSAC and CAC, respectively.     

Radiological aspects of the usability of red mud as building material additive

Several researchers have examined and achieved favourable results in connection with the building industry's use of red mud extracted in large quantities from the processing of bauxite. These days more and more precedence is being given to limiting the radiological dose to the population. In this study carried out in Hungary, the use of red mud, bauxite, and clay additives recommended for the production of special cements, were examined from a radiological aspect.

²²⁶Ra and ²³²Th activity concentrations measured in Hungarian bauxite, red mud and clay samples were significantly similar with the levels for such raw materials mentioned in international literature.

Taking radiation protection aspects into consideration, none of these products can be directly used for building construction. Taking Hungarian and international values into consideration, a small amount of red mud, not exceeding 15% could be used for brick production, for example as a colouring material. However, beyond this amount the standards for building materials would not be met.

For the production of cements an even stricter limit needs to be determined when both bauxite and red mud are used.     

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.     

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.     

NaP1 zeolite synthesized via effective extraction of Si and Al from red mud for methylene blue adsorption

NaP1 zeolite, using red mud (RM) as raw material, was successfully prepared via alkali fusion and hydrothermal method. NaP1 zeolite, which was a mesoporous material, had specific surface area and pore diameter of 79.3 m²·g⁻¹ and 7.26 nm, respectively. NaP1 zeolite had excellent adsorption properties. Under the optimum adsorption conditions, methylene blue (MB) was adsorbed through NaP1 zeolite, the adsorption capacity was 48.7 mg·g⁻¹ and the removal efficiency was 97.1%. The adsorbent was regenerated with sodium chloride as eluent. The adsorption capacity of the adsorbent regenerated three times still was satisfactory 34.53 mg·g⁻¹, which showed the excellent stability performance from NaP1 zeolite. The adsorption conformed to the pseudo second order kinetic and Freundlich isotherm model. Moreover, MB molecules were adsorbed by diffusion on the outer surface, diffusion on the inner surface, and adsorption on the inner surface of NaP1 zeolite. And, during the external diffusion, electrostatic attraction and hydrogen bonding created. Al and Si were extracted from RM to prepare NaP1 zeolite with excellent adsorption properties. This result provides an important example for the development of the potential value of RM.     

Silica particles settling characteristics and removal performances of oxide chemical mechanical polishing wastewater treated by electrocoagulation technology

This study aimed at investigating the feasibility of using jackfruit peel (JFP), a solid waste, abundantly available in Malaysia, for the adsorption of methylene blue, a cationic dye. Batch adsorption studies were conducted to evaluate the effects of contact time, initial concentration (35-400mg/L), pH (2-11), and adsorbent dose (0.05-1.20g) on the removal of dye at temperature of 30 degrees C. The experimental data were analyzed by the four different types of linearized Langmuir isotherm, the Freundlich isotherm and the Temkin isotherm. The experimental data fitted well with the type 2 Langmuir model with a maximum adsorption capacity of 285.713mg/g. Pseudo-first and pseudo-second-order kinetics models were tested with the experimental data, and pseudo-second-order kinetics was the best for the adsorption of MB by JFP with coefficients of correlation R(2)> or =0.9967 for all initial MB concentrations studied. The results demonstrated that the JFP is very effective for the adsorption of methylene blue (MB) from aqueous solutions.     

Treatment of wastewater containing toxic chromium using new activated carbon developed from date palm seed

The use of a new activated carbon developed from date palm seed wastes, generated in the jam industry, for removing toxic chromium from aqueous solution has been investigated. The activated carbon has been achieved from date palm seed by dehydrating methods using concentrated sulfuric acid. The batch experiments were conducted to determine the adsorption capacity of the biomass. The effect of initial metal concentration (25-125mgl(-1)), pH, contact time, and concentration of date palm seed carbon have been studied at room temperature. A strong dependence of the adsorption capacity on pH was observed, the capacity increase as pH value decrease and the optimum pH value is pH 1.0. Kinetics and adsorption equilibrium were studied at different sorbent doses. The adsorption process was fast and the equilibrium was reached within 180min. The maximum removal was 100% for 75mgl(-1) of Cr(+ concentration on 4gl(-1) carbon concentration and the maximum adsorption capacity was 120.48mgg(-1). The kinetic data were analyzed using various kinetic models - pseudo-first order equation, pseudo-second order equation, Elovich equation and intraparticle diffusion equation - and the equilibrium data were tested using several isotherm models, Langmuir, Freundlich, Koble-Corrigan, Redlich-Peterson, Tempkin, Dubinin-Radushkevich and Generalized isotherm equations. The Elovich equation and pseudo-second order equation provide the greatest accuracy for the kinetic data and Koble-Corrigan and Langmuir models the closest fit for the equilibrium data. Activation energy of sorption has also been evaluated as 0.115 and 0.229kJmol(-1).     

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.     

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.     

Hydrocracking and hydrodesulfurization of diesel over zeolite beta-containing NiMo supported on activated red mud

NiMo nanocatalysts supported on activated red mud with different zeolite beta contents were successfully prepared by impregnation technique. Their hydrocracking and hydrodesulfurization activities were evaluated with two different kinds of diesel feed (iso diesel and heavy diesel) in a fixed bed reactor at ambient pressure and 500 °C. Physico-chemical properties of synthesized samples were characterized using the methods of XRF, XRD, FESEM, BET, FTIR and NH₃-TPD. The results indicated that zeolite incorporation resulted in a significant increase in specific surface area (BET result) and acidic strength (TPD result) of nanocatalysts. FESEM analysis confirmed that the particles size of zeolite-containing NiMo/ARM was less than 100 nm and the average size of particles was about 30 nm. Hydrocracking results illustrated that incorporation of zeolite beta improved cracking activity considerably. In addition, NiMo nanocatalyst containing 37.5 wt% of zeolite had the highest yields of desirable products (naphtha, kerosene and diesel) and the highest conversion. Moreover, the flash point and viscosity of the liquid product decreased notably the nanocatalysts with 37.5 wt% and 12.5 wt% of zeolite were able to remove approximately 96% and 72% of the sulfur content of iso diesel and heavy diesel, respectively.     

Enhancing phosphate removal from wastewater by using polyelectrolytes and clay injection

Aluminum sulfate, alum, is a common chemical coagulant used for coagulation. Recently, polymers have been utilized in coagulation/flocculation processes for water purification. In this study, the ability of two organic polymers, tannin (natural polyelectrolyte) and AN913 (synthetic anionic polyelectrolyte), and clay to act as coagulant aids was tested, in the removal of phosphate from synthetic wastewater. Contaminants in synthetic waters were coagulated using alum, alum+clay, alum+tannin, alum+AN913, alum+tannin+clay and alum+AN913+clay. Alum together with polymers as coagulant aids yielded a significant improvement in phosphate removal compared with alum alone, for initial phosphate concentrations of 5–15 mg/l PO₄³⁻. The use of clay and polyelectrolytes improved the efficiency of phosphate removal and lowered the required alum dose. Fourier transform infrared (FTIR) spectroscopy was used for the identification and characterization of the aluminum species formed during dephosphorization of the synthetic wastewater with and without tannin, AN913 and clay. Evidence from FTIR spectroscopy showed the formation of aluminum hydroxyphosphate, hydroxy-Al-tannate and aluminum complexes containing phosphorus, tannin and AN913.