Showing papers on "Activated alumina published in 2021"

Fluoride removal by thermally treated egg shells with high adsorption capacity, low cost, and easy acquisition

Abstract: In this study, the use of eggshells was suggested as an adsorbent for fluoride removal, and their mechanism of fluoride removal was investigated. The eggshells underwent thermal treatment to improve their adsorption capacity; 800 °C was found to be the optimal temperature for treatment. Eggshells thermally treated at 800 °C (ES-800) were mainly composed of Ca (82.4%) and C (15.9%), and the peaks of ES-800 obtained from X-ray diffraction (XRD) corresponded to calcite, portlandite, and lime. Fluorine adsorption by ES-800 reached 70% of the equilibrium adsorption amount within 15 min and gradually increased until 24 h. The maximum adsorption capacity of ES-800 at pH 7 and 25 °C was 258.28 mg/g, which is 18 times larger than that of activated alumina; this is classified as the best available technology by the United States Environmental Protection Agency. Both enthalpy and entropy increased in the process of fluoride adsorption onto ES-800. Fluoride adsorption of ES-800 decreased from 59.16 to 11.85 mg/g with an increase in pH from 3 to 11. Fluoride adsorption decreased in the presence of anions, whose impact follows the order: HPO43- > HCO3- >> SO42- > Cl-. XRD, and X-ray photoelectron spectroscopy analysis revealed that fluoride removal was achieved by the formation of calcium fluorite (CaF2). Thus, it can be concluded that eggshells can function as highly efficient adsorbents for fluoride removal, replacing bone char and activated alumina; further, their adsorption capacity can be improved by thermal treatment.

Enhanced Fluoride Uptake by Layered Double Hydroxides under Alkaline Conditions: Solid-State NMR Evidence of the Role of Surface >MgOH Sites.

Abstract: Layered double hydroxides (LDHs) are potential low-cost filter materials for use in fluoride removal from drinking water, but molecular-scale defluoridation mechanisms are lacking. In this research, we employed 19F solid-state NMR spectroscopy to identify fluoride sorption products on 2:1 MgAl LDH and to reveal the relationship between fluoride sorption and the LDH structure. A set of six 19F NMR peaks centered at -140, -148, -156, -163, -176, and -183 ppm was resolved. Combining quantum chemical calculations based on density function theory (DFT) and 19F{27Al} transfer of populations in double resonance (TRAPDOR) analysis, we could assign the peaks at -140, -148, -156, and -163 ppm to Al-F (F coordinated to surface Al) and those at -176 and -183 ppm to Mg-F (F coordinated to surface Mg only). Interestingly, the spectroscopic data reveal that the formation of Al-F is the predominant mode of F- sorption at low pH, whereas the formation of Mg-F is predominant at high pH (or a higher Mg/Al ratio). This finding supports the fact that the F- uptake of 2:1 MgAl LDH was nearly six times that of activated alumina at pH 9. Overall, we explicitly revealed the different roles of the surface >MgOH and >AlOH sites of LDHs in defluoridation, which explained why the use of classic activated alumina for defluoridation is limited at high pH. The findings from this research may also provide new insights into material screening for potential filters for F- removal under alkaline conditions.

Electrocoagulation for Arsenic Removal: Field Trials in Rural West Bengal

Abstract: Arsenic contamination in drinking water is a great concern in different regions of the world as well as in India. Several technologies have been investigated to remove arsenic from water, such as coagulation and co-precipitation, ion exchange, adsorption, and reverse osmosis. In the present research, electrocoagulation with iron electrodes has been assessed as a treatment technology for arsenic removal from groundwater to reach concentrations below 0.01 mg/L (WHO limit) and which is technically effective, affordable for the local area, and easy to operate and maintain. Electrochemically generated iron is converted to hydrated ferric oxide within the contaminated water, which takes up the arsenic from water. A downstream filtration unit (sand or activated alumina) is applied to remove ferric hydroxide flocs produced during the process. The laboratory experiments were conducted in a batch reactor using iron plates as electrodes with monopolar configuration to study the effects of initial pH and electro-charge loading (ECL) on arsenic removal. The optimum operating condition was observed for an electro-charge loading of 25–30 Coulombs/L at pH 7.0 and an initial arsenic concentration of 0.2 mg/L. Two field trials were implemented in West Bengal after suitably designing the electrocoagulation system. Arsenic removal was significant (75–80%) delivering safe water with arsenic below 0.01 mg/L (acceptable limit). Passivation of the electrodes occurred during the operation and calcium-based (including iron) deposition was observed on the cathodes. Passivation is avoidable after running regular polarity reversal of the electrodes.

The preparation of δ-FeOOH/γ-Al2O3 under mild conditions as an efficient heterogeneous Fenton catalyst for organic pollutants degradation

Abstract: The δ-FeOOH/γ-Al2O3 composite were prepared under mild conditions by the activated alumina absorption of Fe2+ followed by rapid oxidation by H2O2. The δ-FeOOH growing on γ-Al2O3 was composed of nanoneedles, forming a 3D flower-like morphology with a diameter of ~10 nm to provide a large number of active sites. The effects of Fenton reaction conditions, such as catalyst dosage, H2O2 concentration, phenol concentration, initial pH value and temperature, on the catalytic activity of δ-FeOOH/γ-Al2O3 were investigated. Under the optimal conditions, about 97.4% of phenol and 81.6% of total organic carbon (TOC) were removed in 5 min and 2 h, respectively. In addition, with γ-Al2O3 as macroscopic size carrier (the diameter of 1-2 mm), the catalyst could be easily reused 10 runs with no significant reduction in catalytic activity. The possible mechanism was discussed, and it revealed that OH· was the main active species for degradation of phenol into intermediates and further into CO2 and H2O. The δ-FeOOH/γ-Al2O3 also showed high catalytic activity and reusability in the treatment of real industrial wastewater, making it a promising catalyst for industrial application.

Effective fluoride removal using granular bauxite filter media as an affordable and sustainable alternative to activated alumina

Abstract: Despite centuries of advancements in water treatment, hundreds of millions of people worldwide continue to suffer detrimental health impacts from drinking water with unsafe fluoride levels. Our study compares the performance of low-cost mildly heated bauxite ores and commercial activated alumina (AA) in treating a synthetic groundwater matrix representative of global, fluoride-contaminated aquifers. Batch kinetics studies of fluoride adsorption onto global bauxite ores and AA follow a pseudo-second order rate law, with adsorption increasing exponentially in the first few hours. Fluoride removal efficiencies increase from 73.5% to 85.5% as media particle sizes decrease from 0.6–1.2 mm to <0.1 mm. Column studies demonstrate that increasing the ratio of reactive media in filters from 1 to 100 weight percent increases the volume of treated water from 0.2–56.1 L for Guinea bauxite (GB) and from 0.5–58.3 L for AA. We predict the performance of large-scale columns by modifying the bed depth service time (BDST) model to scale breakthrough time with adsorbent mass rather than with column height. Our modified BDST model predicts that large-scale columns using 1039 kg AA and 1436 kg GB can treat 405 444 L and 338 859 L of potable water in 1.4 and 1.1 months. We also demonstrate application of the rapid small scale column test (RSSCT) model to design smaller lab-scale columns with lower resource, cost, and time inputs by scaling down known field systems parameters including column height, pump flow rate, empty bed contact time, and approach velocity.

Fabrication of Manganese-Supported Activated Alumina Adsorbent for Defluoridation of Water: A Kinetics and Thermodynamics Study

Abstract: Fluoride pollution frequently occurs in many underground drinking water sources due to discrepancies in the geological environment. To address this problem, a manganese-supported activated alumina (MnOOH-supported AA) adsorbent was proposed in the present study. The adsorbent was prepared with an impregnation method, then the morphology and microstructure were systematically characterized. Further, the adsorption kinetics and thermodynamics were systematically explored through static experiments to confirm the adsorption mechanism. The results showed that MnOOH was successfully loaded on the activated alumina (AA), and irregular and convex spinous structures were formed on the surface of particles. Compared with the AA, MnOOH-supported AA exhibited a significantly higher defluoridation rate, which has been doubled. The kinetic behavior of fluoride adsorption on MnOOH-supported AA was governed by the quasi-second-order kinetics model with regression coefficients of 0.9862, 0.9978 and 0.9956, respectively. The adsorption rate was mainly ascribed to the intra-particle diffusion. Additionally, the Freundlich isotherm equation fitted the adsorption thermodynamic process reasonably well compared with the Langmuir adsorption model. Specifically, the correlation coefficients were 0.9614, 0.9383 and 0.9852 at 25 °C, 35 °C and 45 °C, respectively. The adsorption–desorption isotherm plot was similar to the Type V isotherm. The whole fluoride adsorption was a spontaneous endothermic reaction, and controlled by chemical adsorption. These results demonstrated that MnOOH-supported AA as an alternative to the conventional AA showed promising potential for defluoridation in drinking water treatment.

Kinetics and thermodynamics of organo-sulfur-compound desorption from saturated neutral activated alumina

Abstract: Desulfurization of liquid fuels mitigates the amount of noxious sulfur oxides and particulates released during fuel combustion. Existing literature on oxidative-adsorptive desulfurization technologies focus on sulfur-in-fuel removal by various materials, but very little information is presented about their desorption kinetics and thermodynamics. Herein, we report for the first time, the mechanism of sulfur desorption from neutral activated alumina saturated with dibenzothiophene sulfone. Batch experiments were conducted to examine the effects of agitation rate, desorption temperature, sulfur content, and eluent type on sulfur desorption efficiencies. Results show enhanced desorption capacities at higher agitation rate, desorption temperature, and initial sulfur content. Desorption efficiency and capacity of acetone were found to be remarkably superior to ethanol, acetone:ethanol (1:1), and acetone:isopropanol (1:1). Desorption kinetics reveal excellent fit of the nonlinear pseudo-second-order equation on desorption data, indicating chemisorption as the rate-determining step. Results of the thermodynamics study show the spontaneous (ΔG° ≤ -2.08 kJ mol-1) and endothermic (ΔH° = 32.35 kJ mol-1) nature of sulfur desorption using acetone as eluent. Maximum regeneration efficiency was attained at 93% after washing the spent adsorbent with acetone followed by oven-drying. Scanning electron microscopy, Fourier transform infrared, and X-ray diffraction spectroscopy analyses reveal the intact and undamaged structure of neutral activated alumina even after adsorbent regeneration. Overall, the present work demonstrates the viability of neutral activated alumina as an efficient and reusable adsorbent for the removal of sulfur compounds from liquid fossil fuels.

Integrated ZnO-Al2O3 nano particles as absorbent for heavy metal ions and organic impurities

Abstract: Nanotechnology is an emerging interdisciplinary technology that has been booming in many areas during recent decade. The objective of this work was to verify Activated Alumina for removal of heavy metal arsenic with designed filtration unit. Alumina and Zinc oxide nanoparticles were successfully synthesized using both sol-gel and chemical techniques. This study is mainly focused on the synthesis method of Al2O3-NPs using two different type of acids namely sulphuric acid and hydrochloric acid with the base NaOH and KOH. The water treatment filtration unit designed using AutoCAD software. The alumina is prepared to remove heavy metals, especially arsenic from drinking water in order to obtain clean water. Chemical synthesis method of ZnO-NPs was carried out using prepared sodium hydroxide and zinc nitrate heptahydrate zinc acetate. The samples were characterized by different techniques such as Fourier transform infrared spectra (FTIR) and UV-vis. The average crystallite size of synthesized alumina range from 7.1 to 28 nm.

Electrothermal Desiccant Regeneration Technique for Air Dehumidification

Abstract: Adsorption dehumidification and drying equipment is essential general equipment for domestic and industrial use. The most commonly used type in industry is the compressed air adsorption dryer. The analysis results show that the heat loss of the traditional heat air regeneration system of the compressor dryer is 39.4%, and the exhaust waste heat is 32.4%. The actual use of heat energy for desiccant regeneration is only 28.2%. Therefore, this study uses an innovative electrothermal adsorbent unit (ETAU) to regenerate the desiccant. By directly heating the adsorbent, heat loss can be effectively improved. On the other hand, the composite arrangement of zeolite and activated alumina is used. The inlet compressed air is firstly treated by the activated alumina, which has a high adsorption capacity in the high relative humidity condition, then a zeolite is used as a second part to make the dew point reach –40 °C. In the regeneration step, the airflow direction is reversed, whereby the zeolite is regenerated by the ETAU, and the waste heat of the exhaust air is used to regenerate the activated alumina, which reduces the temperature of the exhaust air. Compared with the traditional heat air compressed air system, the two technologies can save about 27% energy in total.

Sol-Gel Method on the Preparation of Boron-doped Activated Alumina

Abstract: In this paper, the crystal phase, pore structure, and surface properties of boron doping γ-alumina were investigated systematically, by the sol-gel method. The influence of the chemical environment and the modification mechanism of aluminium was explored in boron doping alumina. The samples were characterized by using XRD, N2 adsorption at low temperature, NH3-TPD, TEM, and NMR. The X-ray diffraction peaks of boria-alumina have no obvious change with the increasing content of boron, which still gives priority to the characteristic diffraction peaks of γ-Al2O3. Both the specific surface area of boria-alumina and pore volume diameter increase. The result of NMR indicates that boron alters the chemical environment of aluminium, then causes the difference in physical and chemical properties on the surface.

Modelling and simulation of water vapor adsorption in silica gel bidisperse beds

Abstract: Desiccant cooling systems are widely recognized as an alternative technology to vapor compression cooling. Desiccant systems are attractive for air conditioning applications due to the possible use of low-grade heat and green refrigerants in their operation. In such systems, air dehumidification is achieved using bed compacted with desiccant materials such as silica gel, activated alumina, and zeolite. Desiccant systems, on the other hand, present a low coefficient of performance due to the poor heat and mass transfer in the adsorbent bed. A way to enhance the heat and mass transfer in desiccant systems can be accomplished by optimizing the adsorbent packing in the bed. This paper presents a numerical investigation of the dynamics of water vapor adsorption in silica gel bidisperse bed. The adsorbent bed is compacted with particles of two different sizes to reduce the voids between the adsorbent particles and hence increase the amount of desiccant and the adsorbed water mass in the bed. The effect of bidisperse packing in the air dehumidification capacity and adsorbed water mass is studied. The influence of the pressure drop applied on the adsorbent column and the inlet air conditions in the dehumidification process is also investigated. The numerical results showed that bidisperse packing increases the dehumidification capacity (improvement of 22.9%) and the amount of water adsorbed (improvement of 25%) in the bed compared to the case where monodisperse packing is applied to the system, contributing to the improvement in the performance of desiccant beds in air conditioning applications.

Bleaching with the Mixed Adsorbents of Activated Earth and Activated Alumina to Reduce Color and Oxidation Products of Anchovy Oil

Abstract: Fish oil is a rich source of polyunsaturated fatty acids, and its refinement has drawn attention for years. An appropriate adsorbent can effectively remove the pigment impurities in the fish oil. This study evaluated the impact of different absorbents on the reduction of oxidation products and color of anchovy oil during the decolorization under high vacuum. Using the single factor design, four process parameters including adsorbents type, adsorbent amount, temperature and time were tested to determine the optimum decolorization parameter. The results showed the optimum decolorization conditions were that the fish oil was treated with 8% activated alumina at 80 °C for 40 min. In the central group experiment, the addition amounts of mixed absorbents (activated earth and activated alumina), including the mass ratio of adsorbent in oil (5%–11%, w/w) and the mass ratio of activated earth in total absorbent (20%–80%, w/w) were optimized to remove the oxidation products. Under the optimum condition at 10.18% of adsorbent and 70% of activated earth, the total oxidation value (TOTOX value) showed the minimum with the 44.4% of removal rate. Eight metal elements were analyzed in decolorized oil using inductively coupled plasma mass spectrometry (ICP-MS). The removal rates of Zn and Pb were 94.12% and 55.35%, respectively. The decolorization process using mixed absorbents under appropriate condition can significantly reduce the oxidation products and pigments in fish oil, which will benefit the industrial production of fish oil.

Effect of phase type in the alumina precursor on the flash calcination synthesis

Abstract: Economical alumina precursors, derived from bauxite or nepheline ores, were calcined through a very short time process. Results showed that phases of the precursor are a key parameter on the flash calcination process. The number of structural water molecules is the dominant phenomenon. A porous and fine structure of activated alumina was developed as the hydroxyl groups are explosively driven off and establish a hydrothermal condition. The presence of gibbsite phase with larger particle size and most structural water molecules has better product properties in comparison of other alumina precursors phase with small particle size because water vapor pressure achieves a critical value for splitting particles and developing nucleation desirable phases. The changes rate of properties reaches to its maximum value for gibbsite phase at lower calcination temperature. FESEM images showed the precursor phase forms different morphologies of products like, nanodimensional, a coral-like co-continuous or loose particles surrounded with macropores.

Porous Desiccant Wheel Produced Using Inductively Coupled Plasma Technique

Abstract: In this study, the adsorption material is fabricated from the aluminum residues using inductively coupled plasma (ICP) technique and applied as a raw material to manufacture porous solid desiccant wheel. An ICP system is developed to refine aluminum hydroxide extracted from aluminum residues into activated alumina by utilizing its high energy densities. A six-turn induction coil is suitable for our match box to produce alternating electromagnetic field, to sustain space discharge, and to have well reaction zone. The ICP generator power is set at 800 W, and the batch of aluminum residues is purified to generate activated alumina with a BET surface area of 122 m2/g. The porous desiccant wheel is manufactured using activated alumina with a 3-D random porous structure and applied to adsorb moisture from the air. The equilibrium time for the solid desiccant wheel and humidity are determined by observed kinetics in the adsorption experiment. The adsorption equilibrium time of the desiccant wheel (60 pores per inch) with 15-cm diameter and 5-cm thickness is 12 minutes. The maximum adsorption capacity is 51.4 g (at 12 min) and per gram of the desiccant wheel can adsorb 0.184-g water.