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Recycling alum flocs may promote the removal of NOM during the coagulation process. The performance of alum-humic-floc (AHF), poly aluminum chloride (PACl) and AHF and PACl mixtures (AHF+PACl) in the removal of humic acid (HA) were comparatively evaluated in regards to their coagulation behaviors and floc structure characteristics. Jar tests were conducted at neutral pH and in a dosage range from 6.11 to 26.49 mg Al/L. The dual coagulant, AHF with additional PACl, could significantly improve the removal efficiency of organic matter and residual turbidity, which probably depended on the physical adsorption and the charge neutralization mechanism. The experimental data using AHF fit with BET and Freundlich models, which indicated that the adsorption of HA onto AHF was a multilayer adsorption. Floc characterization was also performed to investigate the relationship between floc structure and organic matter removal. The highest removal efficiency of organic matter and residual turbidity occurred when using the combination of AHF with additional PACl as the coagulant, which suggested that fractal dimension of the flocs was the most significant factor in determining the removal of pollutants from the water solution. HA was released again into solution during floc breakage. The combination of AHF and PACl demonstrated a lower release of organic matter after breakage and the stronger dissolved organic carbon (DOC) removal capacity during re-growth process. The functional group on the AHF was the main factor in site-specific hydrogen bonding, which is the main mechanism for removal of HA. [ABSTRACT FROM AUTHOR]

Novel high capacity hybrid sorbents for CO 2 capture have been developed based on zinc-functionalized ionic liquid (IL) impregnated into mesoporous silica beads derived from calcium alginate template beads. Pore modification and development of a surface-confined layer of IL synergistically enhanced the uptake capacity (up to 8.7 wt%) and kinetics of these materials. Spectroscopic and thermophysical signatures of the IL impregnated materials confirm the existence of a highly confined IL layer at low IL:SiO 2 ratio, and multilayer-mimicking bulk phase at higher IL loading. Our results clearly demonstrate that developing a thin layer of zinc-functionalized IL onto porous silica beads effectively enhances the uptake kinetics by exposing interaction sites across a large surface area, and facilitating diffusion through the pore network of the support. [ABSTRACT FROM AUTHOR]

Calcium alginate cohered beads of copper hexacyanoferrate (CuHCF), and iron hexacyanoferrate (FeHCF), were prepared and studied for their competence in the environmental Cs decontamination. The influence of temperature and solution pH, parameters which are crucial for effective decontamination are studied in detail. Kinetic study performed at varying temperatures showed that adsorption of Cs onto CuHCF is faster than on FeHCF, the difference observed mainly due to the difference in the adsorption capacities of the materials. Additionally, an important environmental issue, which is often omitted, the possibility of release of the ferrocyanide ion into the effluent solution, is discussed in detail. The concentration of total cyanide in the effluent solution passed through FeHCF is comparatively very high beyond pH 4. In contrary, it is lower than in CuHCF passed solution at pH below 4. Based on these results, FeHCF is a good option in highly acidic solutions, and for weakly acidic to slightly alkaline pH, CuHCF is effective. [ABSTRACT FROM AUTHOR]

A continuous-flow adsorption/desorption process for the recovery of phenolic compounds (PCs) from olive mill wastewaters (OMWs) was developed in a 0.53 m packed column, using a previously selected resin (Amberlite XAD16) and an actual OMW. The main goals of the study were (i) to evaluate the PC adsorption/desorption performances of XAD16 by means of adsorption isotherms and adsorption/desorption breakthrough tests, and (ii) to develop a reliable model of the process. A combination of centrifugation and microfiltration resulted necessary to attain a high suspended solid removal (98.5%) and thus avoid clogging of the packed bed. The quality of two packing procedures was evaluated by means of frontal analysis tests. XAD16 performed well in terms of both adsorption yield at 20% breakthrough (87–88%) and PC/COD selectivity (PC/COD adsorption constant = 7–9). The desorption solvent (acidified ethanol) was effectively regenerated by vacuum distillation. The adsorption breakthrough curves were successfully simulated with a 1-D convection/dispersion model with mass-transfer ( R 2 = 0.95–0.99; k L a = 0.8–2.5 · 10 −3 1/s), whereas an equilibrium adsorption model with dispersion failed to predict the experimental data. In the perspective of a process scale-up, the simulation of the best-performing operational condition was used to evaluate the process performances for different column lengths (0.5–10 m). A precise and automated HPLC method for total PC measurement was developed and compared to the traditional Folin–Ciocalteu methodology. Further research is needed to optimize the desorption step, to scale up the process and to evaluate the long-term resin performances. [ABSTRACT FROM AUTHOR]

Adsorption of ibuprofen and tetracycline onto a commercial granular activated carbon, multi-walled carbon nanotubes, and two low-cost activated carbons synthesized in the laboratory, has been investigated. The kinetic experimental data obtained at 30 °C and 250 r.p.m. were fitted to pseudo-first, pseudo-second and Elovich models, obtaining a high accuracy between the experimental data and the pseudo-second order equation. Therefore, the equilibrium adsorption data were analyzed by using Langmuir, Freundlich, Sips, Guggenheim–Anderson–de Boer, and Tempkin models. The highest ibuprofen adsorption capacity was obtained for AC-RH activated carbon, 239.8 mg g −1 , and in the case of tetracycline removal was of 845.9 mg g −1 onto the peach stones activated carbon. These results are linked to the textural and chemical surface properties of the adsorbents. Fixed-bed experiments allowed obtaining good removal efficiencies at breakthrough time, 97.2% for ibuprofen and 96.1% for tetracycline onto activated carbon from rice husk. Desorption efficiencies were moderate in all systems, being higher by using NaOH solution at high concentration as elution agent. Finally, the important role of the acidic functionalities in the adsorption process was demonstrated by the accomplishment of FTIR studies of the adsorbents before and after the adsorption of both pharmaceutical compounds. [ABSTRACT FROM AUTHOR]

The adsorption of dioxin–modeling compounds on activated carbon has been investigated in this manuscript. A series of benzene compounds with different numbers and types of substituent groups were chosen as the dioxin–modeling compounds, and the gas adsorption behaviors were evaluated using a fixed-bed reactor. The adsorption results showed that the methyl, chlorine and phenolic substituent groups on a benzene ring can greatly promote gas adsorption, especially the phenolic group, the addition of which increased the adsorption capacity to more than 1.5 times that of benzene. The adsorbed AC samples were detected by TPD-MS with the combines between adsorbate and adsorbent analyzed, the methyl and chlorine groups enhanced the attraction between the gaseous compounds and AC, while the phenolic group reduced the combine force due to its oxidation on AC. The effect of an increasing number of chlorine substituents on the adsorption of gases and the combine forces were investigated. On average, the capacity of gas adsorption doubled and the desorption temperature increased by 20 K with one chlorine substituent on a benzene ring. The attachment of chlorine substituent groups to the AC lactone and quinone groups has been verified again, and the increasing chloric substituent groups consumed more oxygen groups. According to the linear relationships between gas properties and adsorption behaviors, the actual dioxin adsorption capacity has been inferred to be 600 mg/g or greater, showing that dioxin is much more easily adsorbed on AC than the conventional organic gases. [ABSTRACT FROM AUTHOR]

CPL- n porous coordination polymers (PCPs) in general exhibit concomitant structural expansion during adsorption without a sudden gate-opening feature, but implications on the practical aspects of gas separation or storage are yet to be understood. In an attempt to gain further knowledge, we have gathered CO 2 and CH 4 adsorption/desorption and fractional uptake data using Cu 2 (pzdc) 2 L ( pzdc : pyrazine-2,3-dicarboxylate) variants CPL-2 ( L : 4,4′-bipyridine) and CPL-5 ( L : 1,2-Di (4-pyridyl) ethylene). Both exhibited good affinity toward CO 2 probably because of interactions with the adsorbate permanent quadrupole moment. Adsorption and desorption of CO 2 also features hysteresis that increases in size upon an increase in the maximum pressure registered during a complete adsorption/desorption cycle. Furthermore, the size of the hysteresis increases with an increase in equilibration time interval ( t e ), suggesting that the structural expansion proceeds at a slower rate compared to the adsorption one. CO 2 heats of adsorption (max. −27 kJ mol −1 ) and desorption (max. 36 kJ mol −1 ) also reflect the aforementioned framework expansion, particularly in the case of CPL-2. Diffusion time constants calculated using a phenomenological model show hysteresis up to gas pressures of ca. 0.4 atm. The structural changes seem beneficial for the equilibrium separation of bulk quantities of CO 2 from CH 4 as evidenced by selectivity values based on the Ideal Adsorbed Solution Theory ( S IAST ∼ 6.7 avg.), which are larger than those of MOFs with similar pore dimensions. Although kinetic selectivity values are similar to that of other metal organic frameworks (MOFs), these are smaller than those of small pore zeolites. [ABSTRACT FROM AUTHOR]

A new approach is proposed for pre-concentrating emerging pollutants, taking nalidixic acid as representative. The approach consists of performing successive adsorption–desorption cycles in order to remove the pollutant from the main stream, generating a new stream with higher pollutant concentration during the adsorbent regeneration. For accomplishing these scopes (efficient removal and capability for pre-concentrate), adsorbents presenting both high adsorption capacity and regeneration easiness are needed. In this work, the performance of three different adsorbents is studied: activated carbon (GF-40), multi-walled carbon nanotubes (MWCNTs) and high surface area graphite (HSAG-500). Adsorption experiments were performed at 25 °C, whereas two different desorption temperatures (35 and 40 °C) were chosen in order to evaluate the ability of the materials for concentrating the NAL. The adsorption breakthrough curves were modeled considering different models: Bed Depth Service Time (BDST), Thomas and Yoon-Nelson. Although activated carbon largely presents the highest adsorption capacity, it is difficult to regenerate needing long regeneration times, leading to very dilute regeneration solutions. By contrast, MWCNTs present lower adsorption capacity, but they are more easily regenerated leading to higher NAL concentrations. [ABSTRACT FROM AUTHOR]

Organo-montmorillonites (OMts) modified by cationic surfactant (hexadecyltrimethylammonium bromide, C16) and zwitterionic surfactant (hexadecyldimethyl (3-sulphonatopropyl) ammonium, Z16) were used to remove phenol and Cu(II) from aqueous solution. The OMts were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), Fourier-transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), and C, H, and N elemental analyses. Besides the independent adsorption of single contaminants, simultaneous and sequential adsorption of phenol and Cu(II) onto OMts were also investigated. The organic carbon contents of the two OMts were similar but the basal spacing of Z16 modified montmorillonite (Z16-Mt) was larger than that of C16 modified montmorillonite (C16-Mt) indicating a higher packing density of surfactant and hydrophobicity in C16-Mt with a slight higher adsorption capacity toward phenol. On the other hand, C16-Mt showed much lower capacity in adsorbing Cu(II) as compared with raw montmorillonite. On the contrary, the adsorption capacity of Z16-Mt toward Cu(II) was comparable with that of raw montmorillonite. The equilibrium data of phenol and Cu(II) were fitted satisfactorily with Linear and Langmuir models, respectively. In the sequential adsorption system, the adsorption of one contaminant was not affected by the other pre-adsorbed one; desorption of pre-adsorbed contaminant was also investigated. For both two contaminants, one did not affect the adsorption of the other one onto Z16-Mt and C16-Mt in the simultaneous system. Z16-Mt could rapidly and efficiently remove both phenol and Cu(II) simultaneously. The adsorption kinetics followed the Pseudo-second order model. The results of this work might provide novel information for developing new effective adsorbents toward organic contaminants and heavy metals. [ABSTRACT FROM AUTHOR]