Cation Exchange Interaction Research Articles

Geochemical Characteristics and Driving Factors of High-Iodine Groundwater in Rapidly Urbanized Delta Areas: A Case Study of the Pearl River Delta

The source of iodine in the groundwater of coastal urbanization areas is complex, and high-iodine groundwater is a potential threat to the safety of drinking water. Based on this, this study took the Pearl River Delta, which is developing rapidly in urbanization, as the research area. Additionally, the occurrence characteristics and driving factors of iodide in shallow groundwater of different aquifers and different urbanization levels in the Pearl River Delta were studied using mathematical statistics, principal component analysis, and other methods. The results showed that the concentration of iodide in the shallow groundwater was 2.34 mg·L-1 and undetected in the form of I-. Among 1567 groundwater samples in the study area, there were 120 groups of groundwater with high iodine content greater than 0.1 mg·L-1, accounting for 7.7%. Among them, 84 and 36 groups were detected in shallow porous and shallow fissure high-iodine groundwater, respectively, whereas no high-iodine groundwater was detected in the karst aquifer. The proportion of high-iodine groundwater was 8.0% in the shallow porous aquifer and 7.5% in the shallow fissure aquifer. Both the porous aquifer and the fissured aquifer with high iodine content were mainly distributed in the urbanized areas, the proportion of which was more than three times that of the non-urbanized areas. The chemical types of the high-iodine groundwater were mainly HCO3·Cl-Ca·Na and Cl-Na type water, which have the characteristics of high pH and low redox potential. The reduction and dissolution of iodine-containing Fe/Mn (oxygen) hydroxides and the decomposition of iodine-rich organics in sediments may be the main sources of high-iodine groundwater in the shallow porous aquifers of the Pearl River Delta Plain. The degradation and urbanization of organic matter in carbonate-rich rocks is accompanied by the leakage of reducing sewage, which may be the main source of high-iodine groundwater in shallow fissured aquifers. The neutral to weakly alkaline reduction environment with rich organic matter was the main cause of high-iodine groundwater in the Delta Plain area. Weathering, leaching, cation exchange, and sea-land interactions are the main hydrogeochemical processes in the evolution of high-iodine groundwater in the Pearl River Delta.

Study on the physicochemical properties changes of field aging biochar and its effects on the immobilization mechanism for Cd2+ and Pb2+

It has been widely reported that biochar can be used as a cost-effective amendment to immobilize of heavy metal contaminants in soil. While less research has been conducted on effect of biochar long-term field aging on its properties and the adsorption capability. In this study, the characteristics of aged biochar were investigated by comprehensive characterization to elucidate its mechanism transformation for heavy metal immobilization. Our results showed that, compared to fresh biochar, the relative content of C of aged biochar was reduced by 34.12%, while O was increased by 8.79%. Additionally, the specific surface area, pore volume, pore size and oxygen-containing functional groups of aged biochar were significantly increased compared to the fresh biochar. Batch adsorption experiment indicated that the maximum adsorption for Cd2+ (Qm = 32.157 mg/g) and Pb2+ (Qm = 39.216 mg/g) on aged biochar surface was much larger than that of Cd2+ (Qm = 7.573 mg/g) and Pb2+ (Qm = 8.134 mg/g) on fresh biochar. The underlying adsorption mechanisms for Cd2+ and Pb2+ on fresh biochar were dominated by coprecipitation, cation exchange and cation-π interaction, whereas surface complexation and cation exchange appeared to be more vital for aged biochar, as more active adsorption sites and Oxygen-containing functional groups were formed on its surface during aging, which was well explained by BET, XPS, FTIR and Elemental Analysis. Our study found that the physicochemical properties of biochar changed significantly during field aging. Although these changes increased the adsorption of heavy metals by biochar, the reduced stability of biochar to passivated heavy metal ions.

The sorption and short-term immobilization of lead and cadmium by nano-hydroxyapatite/biochar in aqueous solution and soil

In this study, the composite materials using different ratios of biochar (BC) to nano-hydroxyapatite (nHAP) were prepared for the remediation of lead (Pb) and cadmium (Cd) contaminated water and soil. The sorption and the immobilization experiments indicated a higher sorption capacity and immobilization efficiency of Pb compared to those of Cd. The characteristics of XRD, FTIR, SEM, and XPS manifested that dissolution-precipitation, cation exchange, complexation, and cation-π interaction were the main four mechanisms for the sorption of Pb2+ and Cd2+ using composite material PC1 (nHAP/BC = 1/1). From semi-quantitative analysis, the mineral effect accounted for the majority of the immobilization of Pb and Cd. Due to obvious Pb-precipitates in the sorbed material, dissolution-precipitation primarily affected the sorption of Pb using PC1, while the immobilization of Cd was mainly attributable to cation exchange. Such results corresponded to the stable Pb-precipitates and unstable Cd-compounds in soil, among which the latter was prone to be released into the environment. The sorption capacity in aqueous solutions and the immobilization efficiencies in the soil for both Pb and Cd increased with the addition of nHAP, which were linearly correlated to the nHAP proportion in the composite materials. In future practical applications, the percentages of composite materials can be designed according to the specific pollutant concentration. This study sheds light on the explicit immobilization mechanisms for Pb and Cd in aqueous solutions to better understand their behaviors in the soil remediated by relevant materials.

Co-pyrolysis of corn stover with industrial coal ash for in situ efficient remediation of heavy metals in multi-polluted soil

Coal ash incorporated biochar (CA/BC) composite was prepared by co-pyrolysis of agricultural residue and industrial coal ash and applied for remediation of soils polluted by lead (Pb) and cadmium (Cd). The results showed that immobilization efficiency of CA/BC for heavy metals (HMs) was significantly enhanced by 77.1 % (Pb) and 42.7 % (Cd) compared to pristine biochar (BC), and this was mainly due to the increased pH value, surface functionality and surface negative charge. By the introduction of 5 % CA/BC, the polluted soils showed the highest reduction of leaching toxicity by 67.9 % (Pb) and 49.7 % (Cd), respectively. The chemical speciation of Pb and Cd in soils was changed remarkably and the reduced bioavailable Pb and Cd were mainly transformed from acid-soluble fraction into the most stable form of residual fraction. The mechanism study showed that surface precipitation, complexation, cation exchange and cation-π interaction of CA/BC mainly contributed to heavy metals (HMs) immobilization. The pot experiments further confirmed that incorporation of 5 % CA/BC effectively reduced plant Pb and Cd accumulation by 81 % and 62.5 % respectively, and significantly promoted the plant growth of paddy rice by 3.1, 2.2 and 2.0 times in terms of root, stem length and dry mass parameters. The present study offered a cost-effective and green method to prepare soil amendment with great potential for remediation of soils polluted by HMs and realized the value-added utilization of waste agricultural residue and industrial coal ash.

Analysis on the removal of emerging contaminant from aqueous solution using biochar derived from soap nut seeds

For clearing pollutants and emerging contaminants like ciprofloxacin-500mg from wastewaters generated from pharmaceutical industries, soapnut seeds biochar was synthesized and used as an adsorbent for the effective removal process. Tubular furnace operated under nitrogen gas environment was used to synthesize biochar. The batch analysis were carried out successfully to study the removal mechanism and the removal efficiency of the chosen pollutant. The soapnut seeds biochar showed excellent adsorption of ciprofloxacin at pH 6 and temperature 303 K when the dosage was 0.07 g. The Langmuir removal capacity of 33.44 mg/g was received and the Freundlich model provided the best-fits. The ciprofloxacin-500mg adsorption process correlated well with the pseudo-second-order kinetics equation, and the intraparticle diffusion mechanism mainly controlled the process. The characterization of biochar concluded that O–H groups, CO groups, COO−groups and C–F groups, and π-π interactions, pore-filling effect, and cation exchange interactions played a role in the adsorption process. Therefore, the findings of the present work revealed that soapnut seeds biochar would be an excellent low-cost adsorbent for the removal of ciprofloxacin-500mg from wastewater.

Evaluating a new mixed-mode resin Diamond MMC Mustang using Capto MMC ImpRes as a benchmark

Diamond MMC Mustang is a relatively new mixed-mode resin, which mediates both cation exchange and hydrophobic interactions. In this work, we evaluated this resin using Cytiva's Capto MMC ImpRes, a well-established mixed-mode resin with similar properties, as a benchmark. The data suggest that in comparison with Capto MMC ImpRes, Diamond MMC Mustang exhibits comparable binding capacity and resolution. In addition, the resin under evaluation shows good lot-to-lot consistency. The information provided in this study allows users to have additional options when selecting mixed-mode resin for intermediate purification or final polishing, which is favourable especially at the present time when the supply chains of many manufacturers are negatively impacted by the coronavirus pandemic.

Sorption of four s-triazine herbicides on natural zeolite and clay mineral materials with microporosity

Sorption is an important process that controls the fate and transport of herbicides in the soil and aquifer environment. However, sorption of these pollutants on natural microporous mineral materials has received little attention. This study investigated the sorption of four model s-triazine herbicides, namely, atrazine, metribuzin, ametryn, and prometryn, on two common natural zeolites (i.e., clinoptilite and Fe-mordenite) and two common clays (i.e., kaolin and attapulgite) with microporosity in batch experiments. The results showed that the sorption of s-triazines on the natural zeolites increased in the order of metribuzin < atrazine < ametryn < prometryn, which corresponded approximately to the order of increasing sorbate hydrophobicity and indicated the significant contribution of the hydrophobic effect. In contrast, the sorption of s-triazines on the natural clays increased in the order of metribuzin < atrazine < prometryn < ametryn, which corresponded to the order of increasing sorbate basicity and indicated the significant contribution of cation exchange and electrostatic interactions. The sorption of these s-triazines on the mineral materials was strongly pH-dependent, resulting from the pH dependence of the mineral surface charge and protonation/deprotonation of the s-triazines. Common alkali and alkaline earth cations at low concentrations had no significant impact on the sorption of s-triazines on the natural microporous mineral materials. Meanwhile, the presence of Fe3+ (at 0.05 mmol/L) significantly enhanced the sorption of atrazine, ametryn, and prometryn by increasing the protonation of s-triazine molecules in the interfacial region between the mineral surface and bulk solution (due to hydrolysis of Fe3+). Co-sorption of s-triazines on the natural microporous mineral materials exhibited significant competitive effects when these herbicides are sorbed through similar mechanisms. The findings of this study provide insights on the interactions of s-triazine herbicides with natural microporous mineral materials, which help better understand and predict their occurrence and behavior in the subsurface.

Biochemical Characterization of Two Polygalacturonases Purified from the Digestive Juice of the Snail Limicolaria flammea

Polygalacturonases constitute the major part of pectinase preparations for many bioprocess purposes. Investigation on the digestive juice of snail Limicolaria flammea led to purification of two polygalacturonases named PG1 and PG2. Properties of these enzymes were examined to explore their potential in biotechnology applications. A three steps procedure including size exclusion, anion and cation exchange and hydrophobic interaction chromatography were used for purification. The enzymes PG1 and PG2 had native molecular weights of approximately 46 and 86 kDa, respectively and functioned both as monomeric structures. The purified polygalacturonases PG1 and PG2 showed optimum hydrolysis activities at 50°C in sodium acetate buffer pH 5.6. The common inhibitor of the two purified polygalacturonases activity were Mn2+, Ca2+, Zn2+, EDTA, SDS and L-cystein. NH3+ stimulate the polygalacturonase PG1 while Ba2+ was an activator for polygalacturonase PG2. Substrate specificity indicated that these enzymes hydrolyse a broad range of pectin from different sources. The highest activity of PG1 was observed with apple pectin and lemon pectin while PG2 showed its highest activity with orange pectin. The catalytic efficiency of PG1 was highest for lemon pectin (0.125 µmol/min/mL) and orange pectin (0.124 µmol/min/mL). PG2 displayed highest catalytic efficiency (0.325 µmol/min/mL) towards orange pectin. These results suggest that orange and lemon pectin would be the potential physiological substrates of the two purified enzymes.

Multiferroic properties of Mn-substituted BiFeO3

To study the multiferroic behavior of BiFeO3 at low concentrations of Mn as dopant, BiFe1−xMnxO3 (BFMO) at x = 0.01, 0.02, and 0.03 has been successfully synthesized via chemical combustion method. X-ray diffraction reveals distorted rhombohedral structure for BiFeO3 and respective variation in lattice parameters. The particle size is studied with FESEM images. Wide-range frequencies are used to carry out dielectric constant and tan δ (loss factor) measurements. The typical behavior of BFMO samples is attributed via charge-carrier hopping mechanisms due to structural inhomogeneity and formation of vacancies. The hysteresis loop measurements are used to study the ferroelectric and magnetic response. The canting of spin moments and cation–anion–cation exchange interactions leads to observed room-temperature ferromagnetism, while ferroelectric performance enhances with increasing Mn doping in BiFeO3. The altered ferroelectric and magnetic properties along with possible magnetoelectric coupling would make BFMO as suitable candidate for magnetoelectric devices. The maximum value obtained for $${\alpha }_{\text{ME}}$$ is 29.03 mV cm−1Oe−1 at Hdc = 1.4 kOe and could be attributed due to strong antiferromagnetic character of BFO with Mn doping.

Substituting the Thiol Ester of Human A2M or C3 with a Disulfide Produces Native Proteins with Altered Proteolysis-Induced Conformational Changes.

Most proteins in the α-macroglobulin (αM) superfamily contain reactive thiol esters that are required for their biological function. Here, we have characterized the human α2-macroglobulin (A2M) and complement component C3 mutants A2M Q975C and C3 Q1013C, which replace the CGEQ thiol ester motifs of the original proteins with the disulfide-forming sequence CGEC. Mass spectrometry showed that the intended disulfide was formed in both proteins. The correct folding and native conformation of A2M Q975C were shown by its assembly to a tetramer, an initially slow electrophoretic mobility with a demonstrable conformational collapse induced by proteolysis, functional protease trapping, and conformation-dependent interactions with low-density lipoprotein receptor-related protein 1. However, A2M Q975C had a decreased capacity to inhibit trypsin and was more susceptible to cleavage by trypsin or thermolysin when compared to wild-type A2M. C3 Q1013C also folded correctly and was initially in a native conformation, as demonstrated by its cation exchange elution profile, electrophoretic mobility, and interaction with complement factor B, although it assumed a conformation that was distinct from native C3, C3b, or C3(H2O) when cleaved by trypsin. These results demonstrate that disulfides can substitute thiol esters and maintain the native conformations of A2M and C3. Additionally, they indicate that proteolysis is not the sole factor in the conformational changes of A2M and C3 and that thiol ester lysis also plays a role.

Interactions between Active Ingredient Ranitidine and Clay Mineral Excipients in Pharmaceutical Formulations.

Excipients play an important role in pharmaceutical formulations. Many clay minerals, because of their large specific surface area and inert behaviour in reactions with active ingredients, are commonly used as excipients. In this study, the uptake of ranitidine (RT), the active ingredient of Zantac, on and released from palygorskite (Pal), kaolinite (Kao), and talc was evaluated under different physicochemical conditions. The results showed that the uptake of RT on these minerals was limited to the external surface areas only. Cation exchange and electrostatic interactions were responsible for the RT uptake on Pal and Kao, resulting in a monolayer sorption. In contrast, multilayer RT uptake was found on the talc surfaces. Under different desorbing conditions, significant amounts of sorbed RT remained on the solid surface after 5 h of desorption. The results suggest that the sorptive interactions between the active ingredients and the excipients may not be neglected in pharmaceutical formulations, should these minerals be used as additives and/or excipients.

Adsorption of Cu(II) and Ni(II) ions from wastewater onto bentonite and bentonite/GO composite.

Two superior adsorbents, namely bentonite and graphene oxide (GO), were hybridised to study the removal of copper and nickel ions from synthetic and industrial wastewater. The as-synthesised GO, bentonite/GO and bentonite were characterised by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and N2 adsorption-desorption analysis. The factors influencing the adsorption behaviours including contact time, initial solution pH, ionic strength, initial concentration of metal ions, temperature and adsorbent dosage were systematically investigated by batch equilibrium method. The adsorption equilibrium for copper and nickel onto bentonite was attained in 90 min while equilibrium was reached in 60 min on bentonite/GO. The adsorption of copper and nickel was pH-dependent in the range from pH 2 to pH 7 and from pH 2 to pH 8. Pseudo-first-order kinetic model excellently described the adsorption of copper and nickel onto bentonite and bentonite/GO. The equilibrium adsorption data was well described by the Langmuir isotherm model and the maximum adsorption capacity was 248.9 mg/g, 558.4 mg/g, 215.8 mg/g and 402.5 mg/g for bentonite-copper, bentonite/GO-copper, bentonite-nickel and bentonite/GO-nickel adsorption systems, respectively. The bentonite/GO composite exhibited a higher adsorption capacity of both cations from synthetic wastewater than pure bentonite owning to the synergistic effect between bentonite and GO. In all adsorption studies, copper was more efficiently removed than nickel due to its higher tendency to form bond with adsorbent surfaces. The adsorption of copper and nickel on bentonite/GO was mainly due to cation exchange, intermolecular and electrostatic interactions and physisorption dominated the adsorption processes. The practical application of bentonite/GO on adsorption of copper was investigated using real wastewater and its removal efficiency was beyond 98%. The excellent adsorption performances of composites for the copper and nickel removal from wastewater demonstrated its significant potential for pollution mitigations.

Batch Adsorption and Column Leaching Studies of Aniline in Chinese Loess Under Different Hydrochemical Conditions

Through batch adsorption and column leaching experiments, this study aimed to investigate the adsorption and transport behavior of aniline in loess and related mechanism under different hydrochemical conditions. Batch experiments results indicated that aniline adsorption reached equilibrium after about 120min, and the adsorption fitted the pseudo-second-order kinetic and Freundlich models well. The adsorption was spontaneous and exothermic process, indicating the aniline adsorbed by inherent colloidal particles (ICPs) tended to transport. Low pH value, ionic strength and temperature benefitted the adsorption. Column experiments results under different ionic strengths (100, 10 and 1mM) confirmed the potential transport of aniline. The FT-IR spectra have further suggested that aniline was adsorbed by the ICPs through hydrogen-bond, hydrophobic effect and cation exchange interactions. Low ionic strength was advantageous for the adsorption of aniline in loess and the stabilities of ICPs in solution, but enhanced the co-transport probability of ICPs with aniline in loess.

Preparation and evaluation of a molybdenum disulfide quantum dots embedded C18 mixed-mode chromatographic stationary phase.

Molybdenum disulfide quantum dots (MoS2 QDs) were chosen as a functional two-dimensional material to improve the separation performance of a traditional C18 column. In this work, MoS2 QDs were synthesized by the combination of sonication and solvothermal treatment of bulk MoS2. The prepared MoS2 QDs were characterized by transmission electron microscope (TEM), Zeta potential measurement, UV-visible absorption and fluorescence spectroscopy. Then, a novel MoS2 QDs embedded C18 (Sil-MoS2-C18) stationary phase was prepared for performing mixed-mode liquid chromatography. The results of elemental analysis (EA), thermogravimetric analysis (TGA), Fourier transform infrared spectrometry (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET) measurements indicated the stationary phase was prepared successfully. Five types of compounds including alkylbenzenes, polycyclic aromatic hydrocarbons (PAHs), nucleosides and nucleobases, anilines and flavonoids were utilized to evaluate reversed phase, weak cation exchange and hydrophilic interaction of the new column. To a certain extent, the column could achieve separation for different properties of samples on one column, with less organic solvent and shorter time than conventional alkyl and amino columns. Furthermore, the mechanism for separation was studied by investigating effects of mobile phase composition and pH on retentions. In summary, the Sil-MoS2-C18 stationary phase was deemed able to serve the performance of various types of phases, which revealed the prepared mixed-mode column could be potentially applied for the analysis of complex samples. Graphical abstract.

Evaluation of sulfonic acid functionalized covalent triazine framework as a hydrophilic-lipophilic balance/cation-exchange mixed-mode sorbent for extraction of benzimidazole fungicides in vegetables, fruits and juices

The functionalization of covalent organic frameworks (COFs) enhances chemical properties and expands future applications. Herein, a facile strategy for sulfoacid-functionalized COF is presented through post-modification of covalent triazine frameworks (CTFs) platform. The magnetic solid phase extraction (MSPE) material is obtained by anchoring in situ Ni particles on CTF support (Ni/CTF-SO3H) possessing a dual retention mechanism combining hydrophilic-lipophilic-balance (HLB) and cation-exchange interaction. We established the (Ni/CTF-SO3H)-MSPE method for selectively enriching carbendazim (CBZ) and thiabendazole (TBZ) from food samples and reducing matrix effect simultaneously. The method detection limit is 1.23–7.05 µg kg−1 for CBZ and TBZ in vegetable, fruit and juice samples, determined by high-performance liquid chromatography-ultraviolet detector. The recoveries of spiked CBZ and TBZ in the samples are 80.2–115.1% and RSDs 6.0–11.4%, depending on both analytes and samples. Our work provides a unique perspective in the development of functionalized COFs as a versatile HLB/cation-exchange mixed-mode SPE sorbent for extraction of basic analytes in complex matrix.

Extraction enhancement and mechanism of light rare-earth elements (III) in chloride medium through adding complexing agent and synergistic effect

ABSTRACT A binary mixture of two acidic organophosphorus extractants, such as 2-ethylhexylphosphonic mono-2-ethylhexyl ester (HEHEHP) and di-2-ethylhexyl phosphoric acid (D2EHPA), is widely employed for the extraction and separation of light rare earths (LRE) from chloride medium, which displayed pronounced synergistic effect. The water-soluble complexing agent lactic acid (HLac) was added to the aqueous phase to optimize the extraction process. The interactions of LRE with water, HLac and extractants in each phase have been deeply studied to elucidate the extraction behavior. Based on the experiment results, the chemical reactions that occur during extraction are studied in detail, the cation exchange (P-OH bands) and coordination interaction (P = O bands) contribute to LRE extraction were verified.

Refolding and purification of cGMP-grade recombinant human neurturin from Escherichia coli inclusion bodies

Neurturin is a potent neurotrophic factor that has been investigated as a potential therapeutic agent for the treatment of neurodegenerative diseases, including Parkinson's disease, and, more recently, for the treatment of type II diabetes. However, purification of neurturin for clinical applications has been hampered by its low solubility in aqueous solutions. Here we describe the development of a scalable manufacturing process for recombinant neurturin from E. coli. inclusion bodies. Neurturin was refolded from solubilized inclusion bodies by fed-batch dilution refolding with a titer of 90 mg per liter refold and a refold yield of 89%. A two-step purification process using cation exchange and hydrophobic interaction chromatography, followed by formulation using tangential flow filtration resulted in an overall process yield of about 56 mg purified neurturin per liter refold. Solubility of neurturin during the purification process was maintained by the addition of 15% (w/v) glycerol to all buffers. For clinical applications and parenteral administration glycerol was replaced by 15% (w/v) sulfobutyl ether-beta-cyclodextrin (i.e. Captisol) in the drug substance formulation buffer. The final purified product had low or undetectable levels of product-related impurities and concentrations of process-related contaminants such as host cell proteins, host cell DNA, endotoxins and Triton X-100 were reduced more than 10,000-fold or below the limit of detection. Bioactivity of purified recombinant neurturin was demonstrated in a cell-based assay by activation of the MAPK signaling pathway.

DFT and 2D-CA methods unravelling the mechanism of interfacial interaction between amino acids and Ca-montmorillonite

We explored the effect of contact time on the interfacial interaction mechanism of amino acids (AAs) connected to the aluminol group (AlOH) and interlayer Ca ions of Ca-montmorillonite (CaMt) in an aqueous solution using density functional theory (DFT) and two-dimensional correlation analysis (2D-CA) technology. The results showed that these interactions include electrostatic (or van-der-Waals) interaction, cation exchange and hydrophilic interaction. In particular, the electrostatic (or van-der-Waals) interaction between the –COO−(H) (and –NH3+) groups of the AAs and surface negative O atoms of CaMt were found to be the main interaction leading to the adsorption behaviour of AAs onto CaMt. With increasing contact time, the Ca-d0 orbital splitting (dx2+y2 → dx2+y2 + dZ2) not only changes the orbital coupling between the Ca-d0 and O-2p4 orbitals (Ca-dx2+y2-O-2p4 → Ca-dx2+y2 + dZ2-O-2p4) but also enhances the formation of Ca+–COO−(H) p-p σ (neutral: glycine and serine) and Ca+-NH3+ p-p π (charged: glutamate and arginine) hybrid orbitals, as well as the cation exchange (AlOH-Ca + AAs) that mainly contributes to the short-range van-der-Waals interaction. Furthermore, the H-1 s (H2O) orbital is degenerate, which in turn enhances the orbital overlap of H-1 s (H2O) with O-2p4 (-HOCO) and N-2p3 (-NH3), leading to the formation of hydrated clusters: -NH3·(H2O)+ and –HOCO·(H2O)−. The hydrophilic interaction (AlOH-H2O + AAs) mainly contributes to the long-range electrostatic interaction. The results of the study provide a new perspective to understand the adsorption process of AAs onto clay mineral surfaces.

Synthesis of di-carboxylic acid functionalized zeolites from coal fly ash for Cd (II) removal from acid mine drainage using column studies approach

Di-carboxylic acid functionalized zeolites were synthesized from coal fly ash (CFA). The materials were then evaluated for adsorption of Cd (II) from spiked aqueous solutions and acid mine drainage (AMD) in column cartridges. Characterization of CFA using SEM showed a mixture of rough edged and spherical particles of an average size of 2.387 μm. The EDS spectra indicated the presence of ions such as Na+, Ca2+ and Mg2+. These elements were vital for cation exchange applications, due to their mobility which facilitated adsorption of Cd (II) onto the zeolite surface. The optimized concentration of the activating agent was 3 M NaOH aged for 24 h at a solid/ liquid ratio of 0.125 g mL−1. The effects of H2O/SiO2 ratio, crystallization time and crystallization temperature were studied where 0.53, 140 °C and 24 h were the optimum conditions. The types of interaction between the adsorbent and Cd (II) was cation exchange and electrostatic interaction for the zeolite and the carboxylate end of the functionalized zeolite, respectively. The adsorption performance of these materials was evaluated with respect to bed-height, influent concentration and flow rate, where the optimized conditions were 6.0 cm, 8.0 mg L−1 and 1.0 mL min−1, respectively. Application of the optimized parameters were then applied for the adsorption of Cd (II) in AMD. Generally, the shorter chained oxalic acid@zeolite was observed to have a better removal efficiency in comparison to longer alkyl chain coated zeolites such as succinic acid@zeolite and adipic acid@zeolite.

Transport of a PAH-degrading bacterium in saturated limestone media under various physicochemical conditions: Common and unexpected retention and remobilization behaviors.

Laboratory saturated columns packed with granular limestone grains were used to explore the retention and remobilization of functional bacteria FA1 under various physicochemical conditions. The unique surface properties of limestone and FA1 caused some unexpected phenomena. Solution IS, cation type, temperature and surface biological property all affected FA1 retention in the columns. The IS effect was temperature dependent and initial solution pH showed little influence due to the strong buffering ability of limestone. Perturbations of solution IS caused slight release of previously retained bacteria in some columns with NaCl as the background electrolyte, while increase in flow rate caused no release at all. When CaCl2 was the background, bacterial remobilization only occurred following both cation exchange and IS reduction. DLVO forces incorporating with surface roughness calculation were determined to assist with interpretation of interaction mechanisms. All the experimental evidences suggest the importance of cation bridging, cation exchange, surface roughness, and hydrophobic interaction in controlling bacterium transport in saturated limestone porous media.