Breakthrough Volume Research Articles

Solid-phase extraction based on MIL-101 adsorbent followed by gas chromatography tandem mass spectrometry for the analysis of multiclass organic UV filters in water

A metal organic framework material MIL-101 was developed as an effective solid-phase extraction adsorbent for the extraction of eleven UV filters compounds. The MIL-101 adsorbent was packed into a polypropylene cartridge and connected at the outlet tip with the Visiprep™ vacuum manifolds allowing process up to 12-port SPE samples, simultaneously. The extracted UV filters were quantified by gas chromatography-tandem mass spectrometry. Several parameters affecting the extraction efficiency of the target analytes, i.e. desorption conditions, sample pH, the addition of salt and sample volume were optimized by ANOVA analysis followed by a multifactorial design. The sample breakthrough volume of the developed method was also evaluated. The SPE-GC–MS/MS method was validated in terms of linearity (R2 ≥ 0.9973), accuracy (with satisfactory recovery from 82% to 105%), precision (relative standard deviation of less than 10%) and limits of detection ranging from 1.0 to 11.7 ng L−1. The validated method was successfully applied for the extraction and quantification of the target UV filters in different types of water samples, including lake, river, seawater and swimming pool waters. The most often found UV filters were octocrylene, 4-methylbencylidene camphor and homosalate that also came out with the highest concentrations, up to 4000 ng L−1, particularly in swimming pool waters.

Novel MIPs-Parabens based SPE Stationary Phases Characterization and Application.

In this work, the synthesis, characterization, and application of novel parabens imprinted polymers as highly selective solid-phase extraction (SPE) sorbents have been reported. The imprinted polymers were created using sol–gel molecular imprinting process. All the seven parabens were considered herein in order to check the phase selectivity. By means of a validated HPLC-photodiode array detector (PDA) method all seven parabens were resolved in a single chromatographic run of 25 min. These SPE sorbents, in-house packed in SPE empty cartridges, were first characterized in terms of extraction capability, breakthrough volume, retention volume, hold-up volume, number of theoretical plates, and retention factor. Finally, the device was applied to a real urine sample to check the method feasibility on a very complex matrix. The new paraben imprinted SPE sorbents, not yet present in the literature, potentially encourage the development of novel molecularly imprinted polymers (MIPs) to enhance the extraction efficiency, and consequently the overall analytical performances, when the trace quantification is required.

The retrograde adsorption phenomenon at the onset of breakthrough and its quantitation: An experimental case study for gaseous toluene on activated carbon surface

The adsorption dynamics of common solid sorbents against various pollutant species are yet poorly understood with respect to the retrograde phenomenon in which the relationship between breakthrough vs. pulled volume is characterized by an early unusual trend (initial increase followed by a decrease to a minimum) and by a normal trend of finally increasing to 100% (or equilibrium). If such trend is expressed in terms of the partition coefficient (PC), a reversed trend of adsorption processes becomes more evident. Retrograde has been previously observed in the initial breakthrough (<10%) isotherms in continuous flow gas-phase adsorption processes. However, retrograde has been neglected/overlooked and not discussed at all in the main stream literature even when it is explicitly observed from isotherm datasets. To properly describe the various aspects of such process, a stop-flow technique was developed to measure the adsorption isotherm of a model volatile organic compound (i.e., toluene in this study) onto a commercial low-cost sorbent (activated carbon: AC). Accordingly, a 10% breakthrough volume of 762 L atm g−1 (corresponding adsorption capacity of 142 mg g−1) was determined (at an inlet stream 5 Pa of toluene in 1 atm of N2 and 5 mg of AC). This automated method was effective to generate a detailed breakthrough profile at high stream-flow rates (or high space velocities) to specifically detect the retrograde phenomenon at the breakthrough onset. This study offers a practical approach towards establishing an in-depth monitoring protocol for the rare retrograde phenomenon.

Application of Lecithin-templated Mesoporous Silica Microparticles for the Specific and Selective Removal of Phospholipids

Phospholipids are among the many components of algae bio oil, and they harbor the trans-esterification process by poisoning the catalyst, hence the need for they removal prior to this process is crucial. Mesoporous silica materials are feasible and viable candidates for the selective removal of phospholipids by tailoring their surface morphology using different surfactants (templates) for specific and selective adsorption. In this study, the adsorption of phospholipids using lecithin template mesoporous silica microparticles (Leci-MSM) was investigated. Comparative studies using cetyltriammoniumbromide mesoporous microparticles (CTAB-MSM) were also carried out. Both Leci-MSM and CTAB-MSM were synthesized via sol-gel process, packed into mini columns and used for column breakthrough adsorption studies. Scanning electron micrographs revealed a particle size of 5.0 µm for Leci-MSM and 2.95 µm for CTAB-MSM. Textural analysis by BET and BJH exhibited a surface area of 425 and 1210 m2/g for Leci-MSM and CTAB-MSM, respectively. A pore volume of 1.59 and 2.77 cc/g for Leci-MSM and CTAB-MSM, respectively, were also obtained. In addition, Leci-MSM revealed a column breakthrough volume of 28 mL at 41 min, while for the CTAB-MSM was 46 mL at 53 min. The actual adsorption capacity recorded by Leci-MSM was 11.34 mg/g and 8.71 mg/g for CTAB-MSM.

Room-temperature-ionic-liquid coated graphitized carbons for selective preconcentration of polar vapors

Most adsorbent materials used for preconcentrating and thermally desorbing volatile and semi-volatile organic compounds (S/VOCs) in portable or “micro” gas chromatographic (GC/µGC) instruments preferentially capture non-polar or moderately polar compounds relative to more polar compounds. Here, we explore the use of a known trigonal–tripyramidal room-temperature ionic liquid (RTIL) as a surface modifier for the graphitized carbons, Carbopack B (C-B) and Carbopack X (C-X), with the goal of enhancing their capacity and selectivity for polar S/VOCs. Breakthrough tests were performed by challenging tubes packed with ∼2.5 mg of C-B or RTIL-coated C-B (RTIL/C-B) with 13 individual S/VOCs, including several organophosphorus compounds and reference alkyl and aromatic hydrocarbons of comparable vapor pressures, at concentrations ranging from 14 to 130 mg/m3. The 10% breakthrough volume, Vb10, was used as the measure of capacity. For the RTIL/C-B, the Vb10 values of the five organophosphorus vapors tested were consistently ∼2.5 times larger than those for the untreated C-B, and Vb10 values of the four non-polar reference vapors were 11–26 times smaller for the RTIL/C-B than for the untreated C-B. For compounds of similar vapor pressure the capacity ratios for polar vs. non-polar compounds with the RTIL/C-B ranged from 1.8 to 34. Similar results were obtained with C-X and RTIL/C-X on a smaller set of compounds. Tests at 70% relative humidity or with a binary mixture of a polar and non-polar compound had no effect on the capacity of the RTIL/C-B, and there were no changes in Vb10 values after several months of testing that included cycling from 25 to 250 °C. Capacity was strongly correlated with vapor pressure. Attempts to reconcile the selectivity using models based on linear-solvation-energy relationships were only partially successful. Nonetheless, these results indicate that RTIL coating of carbon adsorbents affords a simple, reliable means of rendering them selective for polar S/VOCs.

Adsorption properties of advanced functional materials against gaseous formaldehyde

Intense efforts have been made to eliminate toxic volatile organic compounds (VOCs) in indoor environments, especially formaldehyde (FA). In this study, the removal performances of gaseous FA using two metal-organic frameworks, MOF-5 and UiO-66-NH2, and two covalent-organic polymers, CBAP-1 (EDA) and CBAP-1 (DETA), along with activated carbon as a conventional reference material, were evaluated. To assess the removal capacity of FA under near-ambient conditions, a series of adsorption experiments were conducted at its concentrations/partial pressures of both low (0.1–0.5 ppm/0.01–0.05 Pa) and high ranges (5–25 ppm/0.5–2.5 Pa). Among all tested materials at the high-pressure region ㅐ (e.g., at 2.5 ppm FA), a maximum adsorption capacity of 69.7 mg g−1 was recorded by UiO-66-NH2. Moreover, UiO-66-NH2 also displayed the best 10% breakthrough volume (BTV10) of 534 L g−1 (0.5 ppm FA) to 2963 L g−1 (0.1 ppm FA). In contrast, at the high concentration test (at 5, 10, and 25 ppm FA), the maximum BTV10 values were observed as: 137 (UiO-66-NH2), 144 (CBAP-1 (DETA)), and 36.8 L g−1 (CBAP-1 (EDA)), respectively. The Langmuir isotherm model was observed to be a better fit of the adsorption data than the Freundlich model under most of the tested conditions. The superiority of UiO-66-NH2 was attributed to the van der Waals interactions between the linkers (framework) and the hydrocarbon “tail” (FA) coupled with interactions between its open metal sites and the FA carbonyl groups. This study demonstrated the good potential of these advanced functional materials toward the practical removal of gaseous FA in indoor environments.

Synthesis and characterization of reduced graphene oxide-Fe3O4@polydopamine and application for adsorption of lead ions: Isotherm and kinetic studies

The functionalization of graphene causes many of its features to be altered, which can be used to better adsorption metal ions in aqueous solution. In this work, catecholamine, with a stable polymeric structure and as a safe material, was coated on graphene oxide by the self-polymerization and creates strong and toughness composite that exhibits high resistance to destruction due to stirring or sonication. Graphene oxide (GO) was reduced in the polymerization process and many functional groups including amine and hydroxyl groups are formed on the composite structure, which causes more interaction with Pb2+ ions. The surface area of the magnetic GO was increased after covering with polydopamine. The sorbent was characterized by Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, Vibrating-sample magnetometer and Energy-dispersive X-ray spectroscopy. To achieve the highest adsorption efficiency, various parameters including pH, sorbent amount, breakthrough volume, adsorption time, desorption time and volume and concentration of eluent solution were optimized. The sorbent capacity was achieved as about 35.2 mg g−1. The isotherm data fitted well with the Langmuir isotherm model. The experimental results proved that rGO/Fe3O4@PDA had higher stability than GO@Fe3O4 and can be reused many times after washing with eluent.

Study the effect of trypsin enzyme activity on the screening of applying frontal affinity chromatography

Frontal affinity chromatography (FAC) combined with enzyme has been widely used for drug screening. In this paper, the effect of target enzyme activity on screening of bioactive compounds was studied through applying FAC. Trypsin with different degree of inactivation were prepared as target enzyme by thermal denaturation. Their primary structure was identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and use Fourier transform infrared (FTIR) and ultraviolet-visible (UV–vis) spectroscopy to detect group structure. Ultimately, it was found that the main structure of enzyme with decreased activity remained unchanged. The oxymatrine and matrine which can interact with trypsin were selected to study their binding to trypsin with different activities in FAC. The results showed that oxymatrine and matrine had a significant difference in the breakthrough volume among seven kinds of columns prepared by trypsins with different activities, at the different concentration. It indicated that trypsins with different activities in FAC could combine with oxymatrine and matrine. The binding constant (Kd) variation between oxymatrine, matrine and trypsin with different activities are 5.520 ± 0.038 and 3.577 ± 0.071, within error range, which indicated that the activity of target enzyme with primary unchanged structure has no effect on screening of bioactive components by FAC.

Development of Membrane Hollow Fiber for Determination of Maleic Anhydride in Ambient Air as a Field Sampler.

This research develops a rapid method for sampling and analysis of maleic anhydride (MA) in air using a one-step hollow fiber (HF) membrane in the liquid phase followed by high-performance liquid chromatography. A sampling chamber was prepared for sampling of MA with HF-supported de-ionized water absorbency. Several important parameters, such as sampling flow rate, sampling time, and breakthrough volume (BTV), were optimized at different concentrations using a central composite design. The results showed that sampling could be performed at the maximum period of 4 h with a flow rate of 1 mL min-1 for different concentrations (in the range of 0.05-2 mg m-3). The BTV was 240 mL. The relative standard deviations for the repeatability of interday and intraday were 7-10%, 10%, respectively, and the pooled standard deviation was 0.088. The limit of detection and limit of quantitation values were 0.033 and 0.060 mg m-3, respectively. Moreover, our findings revealed that the samples could be stored in sealed HF flexible plastic tubes in a cover at refrigerator temperature (4°C) for up to 7 days. The HF method was compared with method number 3512 National Institute Occupational Safety and Health for determination of MA. There was a good correlation (R2 = 0.99) between the two methods at a concentration of 0.05 to 2 mg m-3 in the laboratory and the average concentration of MA for both methods was 0.11 mg m-3 in the ambient air at an adhesive manufacturer. Our findings indicated that the proposed HF can act as a reliable, rapid, and effective approach for sampling of MA in workplaces.

Evidence for superiority of conventional adsorbents in the sorptive removal of gaseous benzene under real-world conditions: Test of activated carbon against novel metal-organic frameworks

Recently, metal-organic frameworks (MOFs) have been used in air quality management, particularly adsorption of toxic gases/vapors (e.g., benzene). Nonetheless, the practicality of MOFs at near ambient conditions (e.g., sub-ppm levels of pollutants) is yet relatively unknown as their adsorption capacity data were commonly derived under unrealistically high-pressure conditions (e.g., >1000 Pa). In an effort to accurately assess their performance, the adsorption properties of some MOFs reported to have a significantly high capacity (e.g., MOF-199 [M199] and UiO-66 [U6]) were analyzed in reference to activated carbon (AC) across 0.01–5 Pa benzene. The maximum adsorption capacity of M199 (94.8 mg g−1) slightly exceeded that of AC (93.5 mg g−1) while that of U6 (27.1 mg g-1) was far lower than others. However, such dominance of M199 completely disappeared with decreases in the initial loading partial pressure, as reflected from the comparison of their 10% breakthrough volume (BTV10) or partition coefficient (PC) values. For instance, the BTV10 (L atm g−1) at 0.01 Pa benzene was far smaller in MOFs [e.g., M199 (1067) and U6 (330)] than in AC (14,410), as supported by the Kruskal-Wallis (K–W) rank test. The superiority of AC was also supported by isotherm modeling analysis as reflected by the existence of heterogeneous sorption sites (onto AC). The higher interaction affinity of AC for benzene was ascribed mainly to physisorption (4.66–1.86 kJ mol−1) via pi electrons relative to partitioning and/or pore-filling mechanisms of MOFs (4.56–1.27 kJ mol−1). The need for proper evaluation of performance is thus validated both experimentally and theoretically to help maximize the actual role of sorbent materials in treatment of a given gaseous pollutant.

Determination of Sevoflurane, Isoflurane and Enflurane in the air of workplace by gas chromatography

Objective: To establish a solvent desorption gas chromatographic method for determination of Sevoflurane, Isoflurane and Enflurane in the air of the Workplace. Methods: Sevoflurane, Isoflurane and Enflurane were collected with activated carbon tube and desorbed with dichloromethane, separated with DB-1 capillary columns, and then detected with flame ionization detector. Results: The linearity ranges were 1.9-304.8 μg/ml for Sevoflurane, 2.1-300.4 μg/ml for Isoflurane and 1.7-305.2 μg/ml for Enflurane, The correlation coefficient was both >0.999. Their limits of detection were 0.6 μg/ml, 0.6 μg/ml and 0.5 μg/ml, and Their limits of quatification were 1.9 μg/ml, 2.1 μg/ml and 1.7 μg/ml, and their minimum detectable concentrations were 0.1、0.2 and 0.1 mg/m(3) per 4.5 L of air. Their relative standard deviations (RSD) were 2.5%-3.0%, 2.3%-3.1% and 2.2%-3.0%. The average desorption efficiencies were 101.1%-103.3%, 100.7%-102.7% and 101.0%-102.9%. The sampling efficiency was both 100%. The breakthrough volume of 100 mg actived carbon was 3.7 mg, 3.4 mg and 3.4 mg. Sevoflurane, Isoflurane and Enflurane in activated carbon tube could be kept at least 10 days at room temperature without significant losses. Conclusion: The method shows lower detection limit, high accuracy and precision. It is feasible for determination of Sevoflurane, Isoflurane and Enflurane in the air of workplace.

Trace enrichment of phenylcarboxylic acids from a model biological fluid and serum of human blood.

The study was focused on the development of a solid-phase extraction protocol for seven phenylcarboxylic acids from albumin solutions by using unmodified hyper-cross-linked polystyrene restricted access materials with crosslinking degrees varying from 100 to 400% (four of the acids are known to be markers of sepsis). The breakthrough volume of the most hydrophilic 3,4-dihydroxybenzoic acid rises as the sorbent bridging extent grows. Inversely, the breakthrough volume of the most hydrophobic 3-phenylpropionic acid was found to decrease considerably when the degree of crosslinking exceeds 200%. This unusual pattern is because of the superposition of two opposite tendencies. Increasing substitution extent of phenyls facilitates their π-π-interactions with polar compounds whereas rising density of the network reduces the accessibility of sorption sites to all solutes. Mini-cartridges containing 30mg of an optimal sorbent take up the acids completely and reversibly, the recoveries being close to 100% even in the presence of high concentrations of albumin. By coupling the developed solid-phase extraction with high-performance liquid chromatography and diode array detection technique, we managed to determine quantitatively phenylcarboxylic acids in the serum of a healthy patient blood, and the recoveries varied from 93 to 100% while the limit of quantification was (4-9)×10-7 M.

Application of a needle trap device packed with XAD-2 polyaniline composite for sampling naphthalene and phenanthrene in air

The purpose of this study was to develop a new method for the sampling and analysis of naphthalene (Nap) and phenanthrene (Phe) in air. XAD-2 sorbent was prepared with polyaniline (PANI) to increase its adsorption area. Thus, 22-gauge needles were packed with XAD-2/PANI sorbent for the extraction of Nap and Phe, and sampling of the analytes of interest. The compounds were dynamically sampled from the headspace of the flask in laboratory and then analyzed using a gas chromatography (GC) device equipped with flame ionization detector (FID). The needle trap device (NTD) with the proposed sorbent was more sensitive and accurate than the NIOSH 5515 method. The results showed that the optimal temperature and time for the desorption of the analytes were 350 °C and 8 min, respectively. The analytical parameters such as carryover effect, breakthrough volume, and storage time were examined. The repeatability of the method was determined to be 9.4–13.5% for Nap and 7.1–15.7% for Phe. The limits of detection (LOD) for the analytes were in the range 0.002 - 0.09 ng L−1, and the limits of quantitation (LOQ) were in the range 0.01- 0.23 ng L−1. It was also found that the NTD packed with XAD-2/PANI sorbent was a sensitive and cost-effective method, and offered a high accuracy for the sampling and analysis of PAHs in air.

Sandwich membranes based on PVDF-g-4VP and surface modified graphene oxide for Cu(II) adsorption.

UV photo-preactivation/thermally-induced grafting was employed for grafting 4-vinylpyridine (4-VP) on polyvinylidene fluoride (PVDF), and graphene oxide (GO) was modified with 4'-carboxy-2,2':6',2"-terpyridine (CTPy). Then sandwich PVDF-g-4VP/GO-CTPy/polytetrafluoroethylene (PTFE) membrane was fabricated for adsorption of Cu (II) as a model. The membrane formation, static adsorption thermodynamics, kinetics and dynamic adsorption/desorption were studied. The results showed that, the addition of polyethylene glycol (PEG 4000) as porogen can significantly increase the porosity and adsorption capacity of the membranes. The adsorption could be well described by the Langmuir model and pseudo-second-order kinetic model. The breakthrough volume and saturated volume increased with rising GO-CTPy contents. The adsorption capacity of sandwich membranes was much higher than that of mixed matrix membranes. The sandwich membrane also exhibited excellent reusability in dynamic adsorption/desorption cycles, demonstrating great potential in adsorption of trace Cu (II).

Development of a needle trap device packed with zinc based metal-organic framework sorbent for the sampling and analysis of polycyclic aromatic hydrocarbons in the air

This study aimed to present a new method combined of needle trap devices (NTDs) packed with the Zn3(BTC)2 metal-organic framework (Zn-MOF) as a sorbent, for the sampling and analysis of polycylic aromatic hydrocarbons (PAHs) in the air for the first time. The electrochemical method was used to synthesize Zn-MOF sorbent packed inside 22 gauge needle trap. This method was investigated in the laboratory under different condition and applied in the field to determination of PAHs in air. In order to make different concentrations of PAHs in air, a glass chamber under temperature of 120 °C was used. The optimization of the desorption conditions and breakthrough volume was accomplished using the response surface method and Design-Expert software (version 7). According to the results, the best desorption temperature was obtained as 379 °C in 9 min, the limit of detection and limit of quantification for the analytes under investigation were within the ranges of 0.011–0.021 and 0.03–0.07 mg/m3, respectively. Moreover, repeatability and reproducibility of the method were estimated in the ranges of 3.6–9.9 and 5.3–24.1, respectively. By storing the needles at 4 °C, no significant reduction was observed in the amount of analytes after 60 days (P > 0.05). It could be concluded that NTD: Zn-MOF is a reliable and high collection efficiency method had a suitable performance in the sampling of PAHs, compared to the National Institute for Occupational Safety and Health (NIOSH)-5515 method.

Сорбционные характеристики сорбентов для твердофазной экстракции фенольных соединений из экстрактов лекарственных растений

В основе исследований настоящей работы находится твердофазное извлечение фенольных компонентов экстрактов лекарственного растительного сырья различными типами сорбционных материалов. В качестве сорбционных материалов использовали октадецилсиликагель (Strata C18-E), сополимер стирола и дивинилбензола, химически модифицированный N-винилпирролидоном,(Strata X), а также сополимер дивинилбензола и N-винилпирролидона (Oasis HLB). Для каждого из сорбентов получены сорбционные характеристики по отношению к целевым соединениям (объем до проскока, равновесный объем, объем удерживания и др.), а также десорбционные параметры (коэффициент концентрирования и степень извлечения). Показано, что сорбенты на основе октадецилсили-кагеля достаточно эффективны для извлечения группы флавоноидов и их гликозидов, а полимерные материалы - одновременно и флавоноидов, и фенольных кислот. Степени извлечения фенольных кислот и флавоноидов при коэффициенте концентрирования 5 на сорбенте Strata C18-E составили 27-40% и 79-105% соответственно. С применением сорбента Strata X также достигается концентрирова-ние в 5 раз при степенях извлечения 106-107% (для фенольных кислот) и 99-122% (для флавоноидов). На сорбенте Oasis HLB возможно концентрирование в 20 раз фенольных кислот при их степенях извлечения 74-96% и в 32 раза для флавоноидов при степенях извлечения в диапазоне 56-91%.

Studies on sorption of bifenthrin and diazinon insecticides on molecularly imprinted polymers

Synthesis and characterization of polymeric matrices for molecular recognition of pesticides are presented. For their preparation, methacrylic acid as a functional monomer and ethylene glycol dimethacrylate as a cross‐linking agent were used. As template molecules, diazinon and bifenthrin were applied. Syntheses were carried out in the presence of different porogens. Chemical structures were studied using FTIR‐ATR, elemental analysis, and alkacymetric titration, morphology by laser diffraction particle size analyzer and by particle size, and shape analyzer based on image analysis, whereas porous structure by nitrogen adsorption/desorption method. To study selectivity of the sorbent toward template molecule, breakthrough volumes and sorption kinetics for molecularly imprinted polymers and nonimprinted analogues were determined. Particle sizes of the studied sorbents (expressed as CE diameter) were in the range 40 to 44 μm (except sorbent obtained in the presence of hexane). The chemical composition of all obtained sorbents was close to theoretical one (60.13% C, 7.11% H, 32.77% O). The values of specific surface area of the sorbents were in the range 2 to 338 m2/g.

Breakthrough modeling of furfural sorption behavior in a bagasse fly ash packed bed

Adsorptive breakthrough modelling is essential for design of a sorption packed bed. In this work, breakthrough modelling of the furfural uptake in bagasse fly ash (BFA) packed bed has been performed. Effect of various parameters like bed height (Z = 15–60 cm), flow rate (Q = 0.02–0.04 L/min) and initial furfural concentration (Co = 50-200 mg/L) on the breakthrough curve of furfural sorption in a BFA packed bed have been studied. Enhanced breakthrough performance was observed for the higher value of Z, and lower values of Co and Q. For Co = 100 mg/L, packed bed operated at Q = 0.03 L/min and Z = 60 cm was found to have lowest adsorbent utilization rate of 5.61 g/L with highest breakthrough volume of 14.67 L. Bed depth service time and Thomas models well represented the experimental data points under all experimental conditions. It can be concluded that BFA can be utilized efficiently in continuous system for the removal of furfural. Overall, more than 99% of furfural was adsorbed in BFA packed bed at experimental conditions. Keywords: Bagasse fly ash, Breakthrough, Column study, Furfural removal, Sorption

The effects of interaction between vermiculite and manganese dioxide on the environmental geochemical process of thallium

The interaction among various soil minerals can significantly impact on the environmental geochemical process of contaminants. Therefore, this study investigated the effects of interaction between vermiculite (VER) and manganese dioxide (MnO2) on the migration and transformation of Tl(I). The VER exhibited typical layered structure and MnO2 possessed a flower-like structure with serious reunion phenomenon, while the production of interaction between vermiculite and manganese dioxide, labeled VER-MnO2, illustrated as fish scales evenly spread over a large sheet, suggesting that MnO2 could triumphantly be anchored on the VER and the aggregation of MnO2 was prevented. Compared with the pure MnO2, VER acted as template substrate contributed the higher specific surface area (298.18 m2·g−1) and the oxidation degree of Mn. VER-MnO2 showed the highest fixation capacity (144.29 mg·g−1) than other two materials in the order VER-MnO2 > MnO2 > VER, and there was no risk derived from Mn dissolution. The influence mechanism of VER-MnO2 on Tl(I) migration and transformation lied in immobilization, ion exchange and oxidization. Fixed-bed column immobilization experiments showed that VER-MnO2 could purify drinking water contaminated by Tl (20 μg·L−1) and the effective breakthrough volumes were 900 bed volumes until reaching the maximum limits allowed in drinking water (0.1 μg·L−1). VER-MnO2 excellently catches Tl to prevent groundwater pollution. This study provides a theoretical guidance for environmental fate and restoration of soil heavy metal pollution.

Streamline modeling of fluid transport in naturally fractured porous medium

Abstract To better understand the roles natural fractures play in porous media, an embedded discrete fracture model and streamline modeling method were combined to model natural fractures and compute the flow trajectory and time of fluid in matrix and fractures systems. The effects of fracture conductivity, number of fractures and fracture locations on fluid flow trajectory and time were examined through analyzing the differences in water breakthrough time and sweeping volume of reservoirs with different fracture networks. When other conditions are the same, compared with homogeneous reservoir without fractures, the fractured reservoir has water breakthrough time 30% sooner and swept volume 10% smaller. Although increase of single fracture can lead to faster water breakthrough and smaller swept volume, adding more fractures wouldn't necessarily reach the same effect. The effect of water flooding is also related to the strike and position of fractures. Fractures in different strikes and positions can result in 20% discrepancy in water breakthrough time and 9% gap in swept volume. The shorter the fracture, the less its effect on fluid flow trajectory and time will be. The position of fracture has a strong influence on sweeping efficiency, and the change of one fracture position could bring about 1% variation in swept volume.