Asphaltenes constitute high molecular weight constituents of crude oils that are insoluble in n-heptane and soluble in toluene. They contribute to the stabilization of the water-in-oil emulsions ...formed during crude oil recovery and hinder drop–drop coalescence. As a result, asphaltenes unfavorably impact water–oil separation processes and consequently oil production rates. In view of this there is a need to better understand the physicochemical effects of asphaltenes at water–oil interfaces. This study elucidates aspects of these effects based on new data on the interfacial tension in such systems from pendant drop experiments, supported by results from nuclear magnetic resonance (NMR) and dynamic light scattering (DLS) studies. The pendant drop experiments using different asphaltene concentrations (mass fractions) and solvent viscosities indicate that the interfacial tension reduction kinetics at short times are controlled by bulk diffusion of the fraction of asphaltenes present as monomer. At low mass fractions much of the asphaltenes appear to be present as monomers, but at mass fractions greater than about 80 ppm they appear to aggregate into larger structures, a finding consistent with the NMR and DLS results. At longer times interfacial tension reduction kinetics are slower and no longer diffusion controlled. To investigate the controlling mechanisms at this later stage the pendant drop experiment was made to function in a fashion similar to a Langmuir trough with interfacial tension being measured during expansion of a droplet aged in various conditions. The interfacial tension was observed to depend on surface coverage and not on time. All observations indicate the later stage transition is to an adsorption barrier-controlled regime rather than to a conformational relaxation regime.
Potassium copper hexacyanoferrate (KCuHCF) was immobilized in a cellulose-based hydrogel for the effective adsorption of cesium ions (HCF-gels). Cesium adsorption occurs both in KCuHCF particle and ...carboxylate of carboxymethyl cellulose (CMCNa) in the HCF-gels.
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•Potassium copper hexacyanoferrate immobilized in a cellulose hydrogel (HCF-gels) as a Cs+ adsorbent.•HCF-gels exhibited a superior Cs adsorption capacity (2.06–2.32mmolg−1).•Enhanced adsorption kinetics (90% removal in 1h) and high selectivity (Kd≈105) for Cs+ even in seawater conditions.
Potassium copper hexacyanoferrate (KCuHCF) was synthesized and immobilized in a cellulose-based hydrogel made of carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC) for the adsorption of cesium ions in aqueous solutions. The immobilization with the cellulose-based hydrogel facilitated the dispersion of nano-sized KCuHCF particles, showing the unprecedented adsorption capacity of the composite. In Cs+ removal experiments, KCuHCF-cellulose hydrogel composites (HCF-gels) exhibited exceptional Cs+ adsorption capacities (2.06–2.32mmolg−1) which was attributed to the presence of ion-exchangeable sites (COO−Na+) in the cellulose hydrogel. The HCF-gels also exhibited a rapid Cs+ removal (90.1% removal for 0.15mmolL−1 of Cs+ in 1h) with the uptake reaction kinetics expressed by a pseudo-second order kinetics model. Notably, the HCF-gels could adsorb Cs+ selectively (>90%) in seawater containing 0.11mmolL−1 Cs+. Such specificity with fast kinetics is due to the high ion accessibility from the inherent nature of hydrogels and the highly dispersed KCuHCF nanoparticles in the composites.
The demulsification mechanism of asphaltene-stabilized water-in-toluene emulsions by an ethylene-oxide–propylene oxide (EO–PO) based polymeric demulsifier was studied. Demulsification efficiency was ...determined by bottle tests and correlated to the physicochemical properties of asphaltene interfacial films after demulsifier addition. From bottle tests and droplet coalescence experiments, the demulsifier showed an optimal performance at 2.3 ppm (mass basis) in toluene. At high concentrations, the demulsification performance deteriorated due to the intrinsic stabilizing capacity of the demulsifier, which was attributed to steric repulsion between water droplets. Addition of demulsifier was shown to soften the asphaltene film (i.e., reduce the viscoelastic moduli of asphaltene films) under both shear and compressional interfacial deformations. Study of the macrostructures and the chemical composition of asphaltene film at the toluene–water interface after demulsifier addition demonstrated gradual penetration of the demulsifier into the asphaltene film. Demulsifier penetration in the asphaltene film changed the asphaltene interfacial mobility and morphology, as probed with Brewster angle and atomic force microscopy.
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•Waste pomelo peel converted into a novel adsorbent for use in CDI.•Removal of Pb and Cu ions strongly enhanced by functionalizing with pyrrolic-N.•Strong selectivity of Pb2+ from ...water containing multiple competing ions.•Easy regeneration of adsorbent on no loss in performance over 300 cycles.
Water is not only a valuable resource that is needed to sustain life, but also an essential ingredient in many engineering processes, which unavoidably leads to large volumes of water being contaminated. To achieve safe discharge and also recover valuable “pollutants”, better performing sorbents are needed to rapidly and efficiently decontaminate water while generating minimal secondary wastes. Bio-sorbents derived from pomelo peel were functionalized with pyrrolic-N (BNC-5 electrode) and pyridinic-N (BNC-6 electrode) to enhance electroadsorption and selectivity of Pb2+ and Cu2+. The interaction between soft acid ions (Pb2+) and soft base sites (pyrrolic-N) contributed to a strong chemisorption that elevated the electroadsorption capacity to 2.0 mmol g−1 for Pb2+ at an applied voltage of 1.2 V. With fast removal kinetics (0.077 g mg−1 min−1 of Pb2+), the BNC-5 sorbent performed comparably to other N-doped sorbents prepared using graphene. The large adsorption–desorption hysteresis of BNC-5 in responding to the applied electric voltage confirmed the nature of chemisorption. The results showed only 32.4% of the adsorbed ions being desorbed from the sorbent by reducing the applied voltage to 0 V, but reached almost complete desorption (98.5% of adsorbed ions) at –0.8 V. When operated in adsorption–desorption cycle mode, BNC-5 after ∼ 400 cycles maintained a capacity retention ≥ 80%. After 400 cycles, the electrode capacity was almost fully restored (98.7%) by only mild chemical washing (0.1 M HNO3) of the sorbent and the cycling performance maintained. The study demonstrated the robustness of the sorbent over 1200 cycles and hence the potential to successfully convert waste into high-performance materials for large-scale remediation strategies of contaminated wastewater using CDI.
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•The magnetic hydrogel (MHPVA) was prepared via a facile freeze/thaw method.•The MHPVA has a good Cs+ adsorption capacity of 82.8mg/g.•It exhibits very high removal efficiency of ...99.9% in 8.3ppm Cs+ solution.•It shows high Cs+ selectivity even in the presence of various competing cations.•It can be rapidly recovered from wastewater by a magnet without any turbidity.
Potassium copper hexacyanoferrate-immobilized magnetic hydrogel (MHPVA) has been synthesized via a facile freeze/thaw crosslinking method. The citric acid coated Fe3O4 is embedded into the hydrogel matrix to facilitate the dispersion of nano-sized KCuHCF particles for Cs+ removal, followed by the rapid recovery of the composite in a magnetic field. The Cs+ adsorption behavior of the MHPVA is fitted well with the Langmuir isotherm and the pseudo-second-order kinetic model. The MHPVA exhibits both high Cs+ adsorption capacity (82.8mg/g) and distribution coefficient (Kd) of 1.18×106mL/g (8.3ppm Cs+, V/m=1000mL/g). Sorption of above 90% Cs+ to the MHPVA is achieved in less than 3h of contact time. Moreover, the MHPVA reveals stable and high Cs+ removal efficiency across a wide pH range from 4 to 10. In terms of Cs+ selectivity, the MHPVA shows above 96% removal efficiency in the presence of 0.01M competing cations such as Mg2+, Ca2+, Na+, and K+ with 1ppm of Cs+. From a practical perspective, the MHPVA still exhibits stable and promising selective properties even in groundwater and seawater conditions and after 5days of contact time the used adsorbent is rapidly recovered leaving a turbidity-free aqueous environment.
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•Demonstration of flotation to separate cesium (Cs) contaminated clays.•EDAB surface decoration of CS-MMT modifying particle size and wettability.•Increased Cs contamination led to ...increased Cs-MMT recovery.•Selective separation of Cs-MMT when blended with pristine-MMT.
The ongoing boom of industrialization is conflicted by concerns regarding increased levels of environmental contamination, in particular the uncontrolled release of heavy metal ions and radionuclides into soils and groundwater systems. The extent of contamination can be substantial, hence ways to remediate and reduce the volume of waste for further treatment and ultimate disposal are highly desired. In the current study, flotation has been considered as an engineering solution to rapidly separate cesium contaminated clays from low-level contaminated and pristine clays. Cesium (Cs+) sorption by montmorillonite clay particles was considered over a range of ionic concentrations (0.01–500 mM), showing a multistage sorption isotherm that can be interpreted using a two-site model, which considers both interlayer ion-exchange and specific ion sorption on the clay basal planes at higher cesium concentrations. Assessment by X-ray photoelectron spectroscopy (XPS) and zeta potential confirmed the increased surface contamination with increasing Cs+ concentration, with the surface enrichment sufficiently altering the surface chemistry of the contaminated clays for them to favourably interact with the flotation collector, ethylhexadecyldimethyl-ammonium-bromide (EDAB). Within a critical concentration range of EDAB, the cesium contaminated clays were separated from pristine clays using flotation, with recovery efficiencies of ∼75% for the contaminated clays, compared to <25% for the pristine clays. When contaminated and pristine clays were blended, separation by flotation once again demonstrated excellent selectivity for the contaminated clays. The current study highlights the potential for flotation to rapidly treat contaminated clay rich soils and significantly reduce the volume of contaminated solids for further treatment or ultimate disposal.
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•KCuHCF-immobilized magnetic hydrogel was prepared via double crosslinking method.•HCF-Mbead showed a Cs+ adsorption capacity of 69.2mg/g with broad pH stability.•HCF-Mbead exhibited ...high selectivity for Cs+ even in highly competitive seawater.•HCF-Mbead was easily recovered by a magnet after Cs+ adsorption.
A potassium copper hexacyanoferrate (KCuHCF) embedded magnetic hydrogel bead (HCF-Mbead) was synthesized via a facile double crosslinking methods of Fe3+ ionic binding and freeze-thaw for effective Cs+ removal. The HCF-Mbead had a hierarchical porous structure facilitating fast access of Cs+ ions to embedded active sites. The adsorbent showed enhanced Cs+ removal properties in terms of capacity (69.2mg/g), selectivity (Kd=4×104mL/g, 1ppm Cs+ in seawater) and stability (>99.5% removal in pH 3∼11) with rapid magnetic separation. This study further opens the possibility to develop an efficient material that links the integration of adsorption and recovery.
Selective removal of 137Cs and 90Sr from aqueous environments is essential for the volume reduction and ultimate safe storage of nuclear waste. This study introduces a facile one-pot hydrothermal ...synthesis of Dual-cation form of TitanoSilicate (DTS, M3HTi4O4(SiO4)3, M = Na+ and K+) for the effective and simultaneous removal of Cs+ and Sr2+. DTS showed enhanced adsorption capacities (469 mg/g for Cs+ and 179 mg/g for Sr2+) and the adsorption kinetics were extremely fast with around 98% and >99% removal achieved within 1 min from a dilute Cs+ and Sr2+ solution, respectively. Moreover, DTS indicated the superior selectivity for both Cs+ and Sr2+ due to the dual-cation incorporation in the structure. In groundwater, the distribution coefficients (Kd at V/m = 1000 mL/g) for DTS were high for both Cs+ (1 ppm, 2.9 × 105 mL/g) and Sr2+ (1 ppm, 1.0 × 105 mL/g), and even in seawater DTS maintained a Cs+ (1 ppm) Kd value as high as 4.9 × 104 mL/g. Remarkably, DTS is synthesized as a membrane with graphene oxide for continuous removal of the radionuclides, which is extremely beneficial to purifying a large volume of contaminated water.
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•Dual-cation form of DTS was synthesized via a facile one-pot hydrothermal route.•DTS showed superior Cs+ and Sr2+ adsorption capacities with very fast kinetics.•Even in real-water systems, DTS exhibited high selectivity for Cs+ and Sr2+.•DTS was used as a membrane with GO for continuous separation of Cs+ and Sr2+.
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Natural clinoptilolite, of relatively low-grade, was investigated for its capability to remove cesium and strontium ions from water and simulated seawater. To improve its capacity, ...the material was pre-activated with concentrated NaCl and HCl solutions. Additionally, it was milled to a number of <300 μm size fractions, to expose exchange sites. Electron microscopy was used to characterise the naturally occurring impurities, where regions of high iron and potassium content was shown to correlate to lower levels of cesium adsorption. Adsorption kinetics for natural and activated resins with 5, 300 and 1500 ppm salt solutions were fitted with the Pseudo-Second Order (PSO) rate model. Activation led to clear increases in initial adsorption rate for both Cs+ and Sr2+, but only enhanced the overall rate constant for Cs+, due to the weaker interaction of the Sr2+. Equilibrium isotherms were compared with Langmuir and Freundlich monolayer models, where the adsorption capacity (Qc) for Cs+ was 67 mg/g which increased by over 100% with NaCl activation to 140 mg/g. Values for Sr2+ were significantly lower at 35 mg/g, with a considerably smaller enhancement with activation to 52 mg/g. Milling of the natural clinoptilolite was found to increase Cs+ uptake to similar levels as activation, in a linear correlation with specific surface area; although, improvements for Sr2+ were again lower, due to its weaker interaction with surface sites. In simulated seawater solutions, all materials gave considerably reduced performance due to K+ ion competition, with Sr2+ uptake decreased more extensively compared to Cs+. Overall, this work highlights that pre-activation and milling of clinoptilolite can be used to significantly enhance the grade of the ore for nuclear effluent treatment in low-salinity conditions.
The KCuHCF embedded PVA-Citric acid hydrogel adsorbent was synthesized through a facile two-step method for the selective and rapid Cs+ removal.
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•The HPC was synthesized by a noble ...solvent-assisted method.•The HPC showed superior Cs+ removal capacity of 667mg/g KCuHCF.•The HPC retained remarkable Cs+ removal efficiency of 99.5% in 30min.•In a wide pH range from 2 to 10, the HPC displayed stable Cs+ removal efficiency.
Potassium copper hexacyanoferrate-embedded poly(vinyl alcohol)-citric acid hydrogel film (HPC) was prepared via a two-step method of Cu immobilization, followed by the diffusion of potassium hexacyanoferrate accelerated by acetone evaporation. The diffusion-derived KCuHCF formation in the preformed hydrogel facilitated the preservation of the 3D-interconnected hydrogel structure and dispersion of the KCuHCF nanoparticles. Using acetone as a non-solvent, reverse diffusion of the incorporated Cu in the hydrogel matrix was hindered; hence a large amount of KCuHCF was loaded in the matrix. The HPC exhibited substantially enhanced Cs+ removal properties in terms of adsorption capacity, kinetics and selectivity. From the adsorption isotherm, the HPC showed a very high Cs+ uptake of 667mg/g KCuHCF. Moreover, the adsorbent revealed stable and high Cs+ removal efficiency of 99.9% across a wide pH range from 2 to 10. The kinetics of Cs+ removal was remarkably rapid with 99.5% removal achieved within 30min from a dilute Cs+ solution (9.18ppm). When using seawater, the HPC exhibited almost unaltered Cs+ removal efficiency above 99.5%, and high distribution coefficient Kd value of 7.7×105ml/g at an extremely low Cs+ concentration (0.67ppm,V/m=1000ml/g), which highlighted the tremendous affinity for Cs+.
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