Desorption Tests Research Articles

Valorization of Date Pits as an Effective Biosorbent for Remazol Brilliant Blue Adsorption from Aqueous Solution

In this work, the adsorption of Remazol Brilliant Blue (RBB) over raw date pits (RDPs) as an inexpensive adsorbent has been examined. In addition, all parameters such as the adsorbent mass, solution pH, RDP particle size, RBB initial concentration, and temperature on the adsorption of RBB influencing the adsorption procedure were studied to provide fundamental information of the adsorption equilibrium. The characterization of RDP material is investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR). Based on the calculation, the kinetic rate of the adsorption was well modeled by pseudo-second-order and Langmuir isotherm. Surface functional groups of RDP have substantially been influenced by the adsorption characteristics of RBB. The capacity of the adsorption has achieved 105 mg/g and a removal efficiency of 90.4% at 1.5 g/L RDP mass, 40 mg/L initial dye concentration, pH 2, temperature of 328 K, 40 µm particle size, and contact time of 50 min. The capacity of the adsorption could reach 198 mg/g by increasing the ionic strength of RBB solution. Desorption tests showed that RDP adsorbent has the disadvantage of losing efficiency while reusing for many cycles. However, it still abundant and inexpensive. Therefore, RDP can be used as a potential low-cost bioabsorbent for the elimination of RBB from wastewater.

Isolation and Purification of Kudinosides from Kuding Tea by Semi-Preparative HPLC Combined with MCI-GEL Resin

Background: Kuding tea, a Traditional Chinese drink, has a history of thousands of years in China. Triterpenoid saponins in Kuding tea are regarded as one of the major functional ingredients. Objective: The aim of this paper was to establish separation progress for the isolation and purification of five triterpenoid saponins (kudinoside A, C, D, F, G) from Kuding tea. Methods: Nine types of resins, including seven macroporous resins and two MCI-GEL resins, were firstly used for purifying triterpenoid saponins by the adsorption and desorption tests. Further dynamic adsorption/desorption experiments were carried out to obtain the optimal parameters for the five targeted saponins. Then the purification of five triterpenoid saponins (kudinoside A, C, D, F, G) was completed by semi-preparative high-performance liquid chromatography (semi-pHPLC). Results: As of optimized results, the HP20SS MCI-GEL was selected as the optimal one. The data also showed that 65.24 mg of refined extract including 7.04 mg kudinoside A, 3.52 mg kudinoside C, 4.04 mg kudinoside D, 4.13 mg kudinoside F, and 34.45 mg kudinoside G, could be isolated and purified from 645.90 mg of crude extract in which the content of five saponins was 81.51% and the average recovery reached 69.76%. The final contents of five saponins increased 6.91-fold as compared to the crude extract. Conclusion: The established separation progress was highly efficient, making it a potential approach for the large-scale production in the laboratory and providing several markers of triterpenoid saponins for quality control of Kuding tea or its processing products.

Preparation of Chitosan-Graphene Oxide Composite Aerogel by Hydrothermal Method and Its Adsorption Property of Methyl Orange.

Graphene based aerogel has become one of the most likely functional adsorption materials that is applicable to purify various contaminated water sources, such as dye wastewater, because of its high porosity, structural stability, large specific surface area, and high adsorption capacity. In this study, chitosan and graphene oxide were first selected as the matrix to prepare the composite hydrogel through the hydrothermal method, which was further frozen and dried to obtain the target aerogel. The microscopic structures and adsorption capacity of the composite aerogel were then characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and N2 (nitrogen) physical adsorption and desorption tests. The results show that the specific surface area of the composite aerogel was reached at 297.431 m2/g, which is higher than that of graphene oxide aerogel and chitosan aerogel. The aperture was reduced to about 3 nm. The adsorption rate of the composite aerogel for the methyl orange solution was as high as 97.2% at pH = 1, and the adsorption capacity was 48.6 mg/g. The adsorption process of the composite aerogel satisfies the Langmuir equation and can be described by the second-order adsorption kinetics. In addition, it is worth noting that this composite aerogel can provide a striking adsorption characteristic on methyl orange due to the combining effects from massive amino groups on chitosan and the structural conjugation of graphene oxide.

Geological controls on gas content distribution of coal seams in the Kınık coalfield, Soma Basin, Turkey

The Miocene Soma Coal Basin may be one of the most promising areas for low-rank coalbed methane in Turkey. So far, the coalbed methane potential of the coal seams in the Kınık Coalfield, Soma Basin has not been adequately studied. A systematic investigation was performed on the gas content distribution of the kP1 and kM2 coal seams and its geological controls, which has been based on the geological data and the experimental results of 84 coal samples taken from 37 coal exploration wells in the Kınık coalfield, Soma Basin. Samples were analyzed in terms of coal properties and gas content. The gas content was measured by the direct method based on the canister desorption test. The gas content of the kP1 and kM2 coal seams range from 0.90 to 2.61 m3/t and 0.51 to 3.86 m3/t respectively, on as-received basis, with increasing trend from west to east areas in both seams. Diffusivity values of the kP1 and kM2 coal seams vary from 2.84 × 10−5 min−1 to 56.4 × 10−5 min−1, and from 0.64 × 10−5 min−1 to 54.3 × 10−5 min−1, respectively. The gas content of the kP1 seam has not been correlated with the coal properties, whereas the gas content of the kM2 seam has positive correlation with fixed carbon content and gross calorific value, and negative correlation with moisture and ash content. Normal faults are well developed in the study area play an important role at gas migration, causing gas dissipation and reduced gas content of each coal seam. In the northern part, the low gas content may result from the combined effects of the geological structure, thickness of overlying unit, burial depth and coal thickness. In the southern part, the gas content of coal seams is controlled by the combined effects of relatively favorable factors including fewer normal faults, thicker overlying unit, high burial depth and thick coal seam. The variation of the gas content for the coal seams is a comprehensive reflection of geological factors with each coal seam has its own pattern of gas distribution and this should be considered for the future coalbed methane exploration and development studies in Soma Basin.

Inorganic–organic hybrids based on sepiolite as efficient adsorbents of caffeine and glyphosate pollutants

Sepiolite clay mineral was functionalized with (3-chloropropyl)triethoxysilane (ClPTES) or 3-[tri(ethoxy/methoxy)silyl] propylurea (TEMSPU) alkoxides and tested as adsorbent for herbicide glyphosate and also of caffeine, two pollutants with very different chemical composition. The materials obtained were characterized by X-ray diffractometry, infrared spectroscopy, thermal analysis, scanning electron microscopy and nitrogen adsorption at −196 °C, and submitted to toxicity and desorption tests. Silane functional groups blocked sepiolite active positions, and adsorption occurred within the zeolitic channels and on the surface of the functionalized solids. Caffeine and glyphosate effectively interacted with urea groups from grafted alkoxide, which could lower the mobility of the adsorbed contaminants. Glyphosate adsorbed on functionalized sepiolite derivatives showed low toxicity.

CO2 Desorption Performance from Imidazolium Ionic Liquids by Membrane Vacuum Regeneration Technology.

In this work, the membrane vacuum regeneration (MVR) process was considered as a promising technology for solvent regeneration in post-combustion CO2 capture and utilization (CCU) since high purity CO2 is needed for a technical valorization approach. First, a desorption test by MVR using polypropylene hollow fiber membrane contactor (PP-HFMC) was carried out in order to evaluate the behavior of physical and physico-chemical absorbents in terms of CO2 solubility and regeneration efficiency. The ionic liquid 1-ethyl-3-methylimidazolium acetate, [emim][Ac], was presented as a suitable alternative to conventional amine-based absorbents. Then, a rigorous two-dimensional mathematical model of the MVR process in a HFMC was developed based on a pseudo-steady-state to understand the influence of the solvent regeneration process in the absorption–desorption process. CO2 absorption–desorption experiments in PP-HFMC at different operating conditions for desorption, varying vacuum pressure and temperature, were used for model validation. Results showed that MVR efficiency increased from 3% at room temperature and 500 mbar to 95% at 310 K and 40 mbar vacuum. Moreover, model deviation studies were carried out using sensitivity analysis of Henry’s constant and pre-exponential factor of chemical interaction, thus as to contribute to the knowledge in further works.

Si3N4 nanofelts/paraffin composites as novel thermal energy storage architecture

The environmental problems associated with global warming are urging the development of novel systems to manage and reduce the energy consumption. An attractive route to improve the energy efficiency of civil buildings is to store the thermal energy thanks, during heating, to the phase transition of a phase-change material (as paraffin) from the solid to the liquid state and vice versa. The stored energy can be then released under cooling. Herein, we developed a novel material (nanofelt) constituted by Si3N4 nanobelts able to absorb huge amounts of liquid paraffin in the molten state and to act as an efficient shape stabilizer. The nanofelt manufacturing technology is very simple and easy to be scaled-up. The effect of the Si3N4 nanofelts density and microstructure on the paraffin sorption and leakage and on the thermal properties of the resulting composite structures is investigated. It is shown that the produced Si3N4/paraffin composites are able to retain enormous fractions of paraffin (up to 70 wt%) after 44 day of desorption test on absorbent paper towel. The thermal energy storage efficiency measured through calorimetric tests is as high as 77.4% in heating and 80.1% in cooling.

Developing an adsorption-based gas cleaning system for a dual fluidized bed gasification process

Biomass has the potential to make a major contribution to a renewable future economy. If biomass is gasified, a wide variety of products (e.g., bulk chemicals, hydrogen, methane, alcohols, diesel) can be produced. In each of these processes, gas cleaning is crucial. Impurities in the gas can cause catalyst poisoning, pipe plugging, unstable or poisoned end products, or harm the environment. Aromatic compounds (e.g., benzene, naphthalene, pyrene), in particular, have a huge impact on stable operation of syngas processes. The removal of these compounds can be accomplished by wet, dry, or hot gas cleaning methods. Wet gas cleaning methods tend to produce huge amounts of wastewater, which needs to be treated separately. Hot gas cleaning methods provide a clean gas but are often cost intensive due to the high operating temperatures and catalysts used in the system. Another approach is dry or semi-dry gas cleaning methods, including absorption and adsorption on solid matter. In this work, special focus was laid on adsorption-based gas cleaning for syngas applications. Adsorption and desorption test runs were carried out under laboratory conditions using a model gas with aromatic impurities. Adsorption isotherms, as well as dynamics, were measured with a multi-compound model gas. Based on these results, a temperature swing adsorption process was designed and tested under laboratory conditions, showing the possibility of replacing conventional wet gas cleaning with a semi-dry gas cleaning approach.

The 3D networked MnCO3-C composite as anode materials for lithium ion batteries

Abstract The Bayberry-like MnCO3 is prepared by hydrothermal method with sodium citrate as shape regulator. The crystalline structure, chemical component, micromorphology and pore size distribution of the as-synthesized sample are characterized by XRD, FE-SEM, HR-TEM, Raman spectra, TGA and Nitrogen desorption test (BET); The electrochemical performances are investigated by galvanostatic charge-discharge, which shown the discharge capacity of 407.2 mAh g−1 at the current density of 100 mA g−1 after 70 cycles. In order to improve the electrochemical properties of material, the nanostructured MnCO3 is successfully grown on porous sponge-like carbon to form the three-dimensional (3D) networked MnCO3-C composite via the in-situ hydrothermal method. Specifically, 3D networked MnCO3-C composite electrode delivers a high discharge capacity of 952.9 mAh g−1 at 100 mA g−1 over 70 cycles. The excellent electrochemical performance can be ascribed to the unique 3D structure of porous sponge-like carbon whose structure serves as an electron conductor, inhibits agglomeration of MnCO3 particles, and acts as an effective buffer against volume change of MnCO3 during cycling.

Producing gasoline-like hydrocarbons by cracking crude soybean oil: tuning the NaZSM-5 zeolite’s acidity for increasing the catalyst lifetime

This work investigates the effect of NaZSM-5 zeolite’s acid properties on the catalytic cracking of crude soybean to produce gasoline-like hydrocarbons. We modified both the acid concentration and the acid strength of the NaZSM-5(60) zeolite (where 60 denotes the SiO2/Al2O3 molar ratio) either by varying the SiO2/Al2O3 ratio (i.e., 30, and 90) or by exchanging the compensation cation (i.e., from Na+ to H+). Given the ammonia temperature-programmed desorption and temperature-programmed oxidation tests, we observed that the acid strength of the catalyst is associated not only with the distribution of the cracking products, but also with the nature of the carbonaceous deposits formed during the reaction. Weak, medium, and strong acidity were associated with the formation of heavy hydrocarbon species, soft, and hard coke, respectively. The NaZSM-5 zeolites exhibited weak and medium acidity, while the HZSM-5(60) zeolite exhibited weak and strong acidity. Although both NaZSM-5(30) and HZSM-5(60) zeolites delivered higher gasoline yield than the NaZSM-5(60) zeolite due to its higher acid concentration, the HZSM-5(60) zeolite formed carbonaceous deposits with lower reactivity (i.e., hard coke). Therefore, low values of SiO2/Al2O3 ratio in the NaZSM-5 zeolite drive the reaction products towards gasoline-like hydrocarbons and favor the catalyst reactivation through the formation of more reactive carbonaceous deposits.

Deriving probabilistic soil distribution coefficients (Kd). Part 1: General approach to decreasing and describing variability and example using uranium Kd values

A general approach is presented to derive probabilistic radionuclide distribution coefficients (Kd) in soils from a Kd dataset. The main aim was to derive informed estimates with a low inherent uncertainty by restricting the Kd value data to subsets based on key soil factors and the experimental approach used to calculate the Kd value (e.g., sorption and desorption tests). As an example, the general approach was applied to uranium (U) Kd values that are part of a critically reviewed dataset containing more than 5000 soil Kd entries for 83 elements and an additional 2000 entries of Kd data for 75 elements gathered from a selection of other, non-soil, geological materials. The overall soil U Kd dataset included 196 values spanning a range of four orders of magnitude (1–67,000 L kg−1), with additional 50 entries for other geological materials. Whereas the effect of the experimental approach could be disregarded, major factors in decreasing U Kd variability were pH and organic matter content (OM). Limitation in the number of entries made it difficult to use texture information (sand, silt, clay) to further decrease U Kd variability. The integrated combination of pH + OM permitted some soil groups to have U Kd confidence intervals as narrow as two orders of magnitude. Specifically for U Kd, data in the Mineral (< 20% OM) and Organic (≥ 20% OM) partial datasets were significantly different. Analogue data from geological materials other than soils, such as subsoil, till and gyttja (a lacustrine mud having elevated organic matter (OM) contents), were also statistically evaluated to determine whether they could be used to fill U Kd data gaps. It was shown that U Kd from subsoils and tills, but not gyttjas, could be used to enhance soil U Kd datasets. Selection of probabilistic Kd values for risk modelling can be made more reliably and with less uncertainty by using appropriate geochemical data representative of the study site to narrow the wide range of potential Kd values.

Tritium release and retention in beryllium and titanium beryllide after neutron irradiation up to damage doses of 23-38 dpa

• For the first time, beryllium and titanium beryllide as massive pellets were irradiated in a nuclear reactor at temperatures of 710−1040 K up to production of 430–653 appm tritium and 4144–5992 appm helium, respectively. • The tritium retention in irradiated Be-7at.%Ti pellets is much lower than that in Be pellets, for example, 1 and 0.5 % to 48 and 34 % at 940 and 1040 K, respectively. • Open channels along grain and sub-grain boundaries are formed under neutron irradiation in beryllium, essentially contributing to the enhanced tritium release. Titanium beryllide is considered as an advanced neutron multiplier in the Helium Cooled Pebble Bed (HCPB) blanket of DEMO. Neutron irradiation of titanium beryllide together with beryllium as a reference material in material testing nuclear reactors can give essential data for the DEMO blanket design. Be-7at.%Ti (Be-7Ti) as well as Be were irradiated in the HFR, Petten, the Netherlands, at four temperatures of 710, 800, 940, 1040 K up to 23, 31, 36, 38 dpa, respectively. The post-irradiation examination (PIE) included thermal-programmed desorption (TPD) and Vickers hardness tests as well as microstructure study by optical metallography. Be and Be-7Ti pellets maintained their integrity after irradiation. Microstructure of Be-7Ti contains two phases, mainly, TiBe 12 , and also small amount of Be. Under irradiation, gas bubbles were formed in Be samples as well as in Be-phase in Be-7Ti samples. These bubbles contain helium and tritium produced in Be under irradiation. TPD tests showed a much lower tritium retention in Be-7Ti than in Be for all four irradiation temperatures. Vickers hardness of TiBe 12 phase is much higher than that of Be-phase. According to the obtained data, Be-7Ti could be considered more preferred than Be as a neutron multiplier material in future fusion reactors due to the enhanced radiation damage resistance.

Effect of initial hydrogen distribution on the parameter extraction of the thermal desorption spectra: A finite element study

The main objective of this study was to clarify whether the commonly encountered inhomogeneous hydrogen distribution in thermal desorption tests, resulting from unsaturated hydrogen charging and hydrogen release during specimen transfer, could affect the desorption curves and parameter determination. The transient hydrogen distributions in the specimen, both in normal lattice sites and trap sites, during absorption, air exposure, and thermal aging were simulated using finite element method based on the Oriani's local equilibrium theory. Results indicated the significant effect of initial inhomogeneous hydrogen distribution on the transient hydrogen distribution and the desorption spectra. This effect could result in both the shift of peak temperature and the artifact in desorption curves, depending on the trap binding energy. The effect of testing parameters and trap parameters on the validity of Kissinger's theory was also discussed.

Understanding hydrogen retention in damaged tungsten using experimentally-guided models of complex multispecies evolution

Fuel retention in plasma facing tungsten components is a critical phenomenon affecting the mechanical integrity and radiological safety of fusion reactors. It is known that hydrogen can become trapped in small defect clusters, internal surfaces, dislocations, and/or impurities, and so it is common practice to seed W subsurfaces with irradiation defects in an attempt to precondition the system to absorb hydrogen. The amount of H can later be tallied by performing careful thermal desorption tests where released temperature peaks are mapped to specific binding energies of hydrogen to defect clusters and/or microstructural features of the material. While this provides useful information about the potential trapping processes, modeling can play an important role in elucidating the detailed microscopic mechanisms that lead to hydrogen retention in damaged tungsten. In this paper, we develop a detailed kinetic model of hydrogen penetration and trapping inspired by recent experiments combining ion irradiation, hydrogen plasma exposure, and thermal desorption. We use the stochastic cluster dynamics method to solve the system of coupled partial differential equations representing the mean field description of the multispecies system. The model resolves the spatial distribution of defects and hydrogen clusters during the three processes carried out experimentally and is parameterized with information from atomistic calculations. We find that the calculated thermal desorption spectra are broadly characterized by three H emission regions: (i) a low temperature one where dislocations are the main contributors to the release peaks; (ii) an intermediate one governed by hydrogen release from small overpressurized clusters with multiple overlapping peaks, and (iii) a high temperature one defined by clean isolated emission peaks from large underpressurized bubbles. These three temperature intervals are seen to largely correlate with the depth at which the clusters are found. The relevance of the ‘super abundant’ vacancy mechanism is assessed, finding that its main role is to transfer more clusters from the intermediate to the high temperature regions as its relevance increases. We find this picture to be in very good agreement with the experiments, adding confidence to the predictive potential of the models and their useto understand irradiation damage and plasma exposure effects in plasma facing components.

Development of a powerful zeolitic imidazolate framework (ZIF-8)/carbon fiber nanocomposite for separation of hydrocarbons and crude oil from wastewater

Abstract Pollution from crude oil spills is a global concern owing to its destructive effect on the environment; in particular, the aquatic life. In this work, a facile synthesis method is applied to produce a novel highly hydrophobic zeolitic imidazolate framework (ZIF-8) coated onto carbon fiber (CF) fabric as a substrate without pre-modification. The product ZIF-8/CF was characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and surface area estimation as well as sorption and desorption tests. The porous structure of ZIF-8/CF consisted of fixed layers of carbon fabric and nanocrystalline ZIF-8. The ZIF-8 crystals increased the water contact angle of the carbon fabric to 150°, whereas the oil contact angle was nearly 0°, creating a shield toward water penetration. ZIF-8/CF displayed high porosity, strong hydrophobicity, low density and high sorption capacity of the hydrocarbons; up to 24 times its weight. Recycling of the sorbed hydrocarbons and crude oil was achieved by squeezing the organic out of the ZIF-8-CF, followed by simple heating to 80 °C and two-stage washing of the sorbent using toluene and acetone, respectively. The ZIF-8/CF exhibited excellent reusability and recyclability (up to 20 cycles), without losing its efficiency, proving its high potency for cleaning up oil spills.

Preparation and kinetic study of organic amine‐loaded ion‐exchange resin as CO2 adsorbents

AbstractOrganic amine adsorbents prepared by template method using ion exchange resin (D001) as support and polyethyleneimine (PEI) as a modifier, and the preparation process was optimized by orthogonal experiment plan. The results showed that adsorbents prepared under conditions (the copper ion concentration was 0.2 mol/L, the ultrasonic time was 3 hr, and the PEI loadings were 30%) had an excellent CO2 adsorption properties. The effects of temperature and gas influent velocity on CO2 adsorption properties were investigated in a fixed bed reactor. When PEI loadings were 30%, the adsorption temperature was 65°C and the gas influent velocity was 40 ml/min, organic amine adsorbents performed a better PEI dispersion, stability, and CO2 adsorption capacity. Maximum CO2 adsorption capacity was 4.00 mmol/g. Besides, the CO2 adsorption capacity decreased by only 10% after 10 cycles of adsorption–desorption tests, attribute to a small amount of PEI was volatilize during the regeneration process. The external diffusion was eliminated by increasing the gas influent velocity, and the adsorption data were well fitted the Weber‐Morris particle diffusion model, indicating that CO2 adsorption was controlled by internal diffusion.

Nano-assembly Pd anchoring in the non-stoichiometric spongy zinc ferrite to catalyze the electro-oxidation of C1 organic compounds

In the polymeric fuel cell, improving the efficiency of the electrodes is one of the challenges to commercialize this technology. The utilization of spongy support is an efficient and novel approach for uniform dispersion of nano-metallic electrocatalyst and increasing the active surface area. In this work, the non-stoichiometric spongy zinc ferrite (NSZF) has been synthesized by the solution combustion technique. The scanning electron microscopy, X-ray diffraction, and N2 ad-/de-sorption test have proven the production of pure cubic spinel ZnFe1.6O4 phase with a spongy morphology and average grains size 11.9 nm. Nano-assembled palladium (NAPd) has been anchored on NSZF as a ceramic support via wet processing, and used in the anodic oxidation of single-carbon organic compounds, such as methanol, formaldehyde, and formic acid. The stability and CO-tolerance ability of NAPd-NSZF have been represented by comparing with NAPd as non-supported palladium. The NSZF as a transition metal oxide has effective property in the dispersion of NAPd in its porous structure. The NSZF promotes NAPd ability for the elimination of carbonaceous intermediates blocking of the catalyst active site through the surface oxygens, and creation of the cycling redox between the high and low valences of iron. The chronoamperometry study has been displayed the higher catalytic activity of NAPd-NSZF in comparison with NAPd for the electrooxidation of single-carbon organic compounds.

Modified Activated Carbon Using NiO for Natural Gas Storage

The technology of natural gas adsorbed can be called Adsorbed Natural Gas (ANG) technology use porous adsorbents to adsorb natural gas. The material is activated carbon (AC), which has a large specific surface area. Activated carbon made from cassava peel waste because of abundance as agricultural waste in Indonesia. Cassava peel has a high cellulose and lignin content. Cassava peel through the carbonization process with furnace temperature 500 ° C in vacuum condition for 1.5 hours. Then, chemical activation with a different activator agent KOH and NaOH by mass ration (3:1). After that, physic activation with N2 and CO2 gas of 150 mL/minute using temperature muffle furnace 750 ° C. Product of physic activation modified using (Ni (NO3)2). Characterization of activated carbon performed with iodine test, SEM, EDX, adsorption, and desorption testers. The best of activated carbon is activated carbon impregnated KOH and with physic activation at 750 ° C, which has 612 mg / g of iodine number. Then, after activated carbon modified using (Ni (NO3)2) has the best performance with 1% NiO, has 662 mg / g of iodine number, and 657 m2 / g of SBET. Then, activated carbon through adsorption and desorption test by ANG technology has 0.02928 kg/kg of adsorption capacity and 39.17% of desorption percent.

Preparation of activated red mud and its application for removal of hydrogen sulfide in air

Red mud is a highly alkaline solid waste from the Bayer process for aluminum production. Red mud reservoirs are usually considered as a potential environmental risk. The treatment of red mud is costly due to the lack of an effective and economical treatment technology. On the other hand, the main components of red mud are Fe2O3, Al2O3, SiO2, and Na2O, which could be employed as a promising precursor for the preparation of various nanomaterials. In this study, we prepared activated red mud by thermal and acid treatment method and applied it for adsorption of H2S in air. The red mud was activated under different temperatures (i.e., 200, 400, 600, and 800 oC for 4 h), types of acid (i.e., H2SO4 and HCl), and acid concentrations (i.e., 0.5, 1.5, and 2.5 M). The produced materials were then applied for H2S removal in air with concentration of 90 – 110 mg/m3 using a fix-bed adsorption column test. Results showed that red mud activated at 800 oC and with 1.5 M H2SO4 solution had the highest adsorption capacity of 29.38 mg/g with an average removal efficiency of 80.2%. The effects of gas flow rate and initial H2S concentration were also investigated, and the highest removal capacity was achieved at an inlet concentration of 100 mg/m3 and flow rate of 1 L/min. Both Langmuir and Freundlich adsorption isotherms were employed for modelling the H2S adsorption by this material and the experimental result was more fitted with the Langmuir isotherm. The thermal desorption and recyclability test were also conducted for evaluating the practical application of activated red mud material and 200 oC was the suggested desorption temperature with 81.7% adsorption capacity recovery.

Enhanced biosorption of Cr(VI) from synthetic wastewater using algal-bacterial aerobic granular sludge: Batch experiments, kinetics and mechanisms

Biosorption is considered as a cost-effective and environmentally friendly Cr(VI) removal process from wastewater. This study is the first report on algal-bacterial aerobic granular sludge (AGS) being used as biosorbent for Cr(VI) removal in comparison to conventional bacterial AGS with respect to biosorption performance. Batch tests revealed that Cr(VI) biosorption onto algal-bacterial AGS was highly pH dependent and the maximum Cr(VI) biosorption capacity of 51.0 mg g−1 occurred at pH 2. The Cr(VI) removal by algal-bacterial AGS was found to be accomplished by both biosorption and bioreduction reactions, in which four mechanisms, namely electrostatic interactions, ion exchange, surface complexation and bioreduction were involved. In addition, desorption tests showed that 64–73% of the adsorbed Cr onto the algal-bacterial AGS could be recovered by NaHCO3, and most of the adsorbed Cr was in the form of Cr(III). Compared to the conventional bacterial AGS, algal-bacterial AGS demonstrated higher biosorption capacity and better granular stability, implying that algal-bacterial AGS can be more potentially utilized as a Cr(VI) removal and recovery biomaterial for the treatment of Cr(VI)-containing wastewater.