Apparent Sorption Research Articles

Formation of cation bridges and its promoting mechanism for sorption of sulfamethoxazole by montmorillonite

The coexistence of metal cations is often accompanied by organic pollution and could affect the environmental fate of organics by mediating the formation of cation bridges. However, the environmental fate and risk of organics in cation co-existing environments are poorly understood due to the lack of accurate identification of cation bridge formation and stability. In this study, the sorption of sulfamethoxazole (SMX) on montmorillonite (MT) with the coexistence of three different valence metal cations (Na+, Ca2+, and Cr3+) was investigated. Ca2+ and Cr3+ can significantly promote the sorption of SMX on MT for about 5∼10 times promotion, respectively, while Na+ bridges displayed little effect on the sorption of SMX. The sorption binding energy of SMX with MT-Ca (−44.01 kcal/mol) and MT-Cr (−64.57 kcal/mol) bridges was significantly lower than that with MT-Na (−38.45 kcal/mol) and MT (−39.39 kcal/mol), indicating that the sorption affinity of SMX on Cr and Ca bridges was much stronger. The higher valence of the cations also resulted in a more stable adsorbed SMX with less desorption fluctuation. In addition, the relatively higher initial concentration of SMX and the valence of cations increased the bonding density of the cation bridges, thus promoting the apparent sorption of SMX on MT to a certain extent. This work reveals the formation and function of cation bridges in the sorption of SMX on MT. It lays a theoretical foundation for further understanding the environmental fate and risk of organics.

Mechanism insight of sorption of Er(III) and Nd(III) ions onto Aluminium barium tungstate synthesized via streamlined sol–gel technique: Time-transient study

Aluminium barium tungstate powder (ABT) was chemically synthesized via streamlined sol–gel technique and exploited as a sorbent material for sorption of erbium and neodymium ions from aqueous solutions under simulated conditions using batch technique. The pH influence, time and temperature factors have been studied. The sorption of neodymium ions was found to be marginally higher than that of erbium ions and the apparent sorption capacity has a progressive influence with temperature. Thermodynamic parameters such as Gibbs free energy change (ΔG◦), enthalpy change (ΔH◦) and entropy change (ΔS◦) were calculated. The negative ΔG◦ values declines with an increase in temperature value, demonstrating that the sorption reaction for both studied ions was spontaneous and more promising at greater temperature. The positive ΔH◦ values affirm that the nature of the sorption processes is endothermic. The comparison of different time transient models applied to the sorption data was assessed for the pseudo first-order (PFO), the pseudo second-order, (PSO) and homogeneous particle diffusion (HPD) models. The results revealed that both PSO and HPD models were found to best correlate the experimental sorption rate data and a monolayer model was adopted as the best suitable model to explore the sorption mechanism for both studied ions. The attained particle diffusion coefficients and rate constant values were acquired from the graphical illustration of the anticipated models. Activation energy change (Ea) and activation entropy change (ΔS±) were also calculated from the linearized Arrhenius model and indicated that the binding process between the sorbent and the studied ions occurred through chemisorption and the sorption of both ions onto synthetic sorbent took place through associative mechanism.

Novel carbohydrate derived nanocomposite materials for efficient arsenic and fluoride elimination

A bottom-up methodology synthesizes the carbohydrate-derived graphene oxide (CGO). Further, the CGO, triiron tetraoxide (TTO) and bentonite (B) synthesizes the carbohydrate- novel composite material (CGO/TTO/B@1:2). The BET surface area of 428.551, 238.645 and 195.814 m2/g, respectively, obtained for the CGO, CGO/TTO and CGO/TTO/B@1:2. The composite material are promising in eliminating of As(III), As(V), and F− under various parametric conditions. The CGO/TTO shows the apparent sorption capacities of 26.59 and 35.97 mg/g for As(III) and As(V), respectively, while the CGO/TTO/B@1:2 exhibits the removal capacity of 17.81 mg/g for F−. Applying an extended Sips equation further elucidated the sorption capacities of 31.88 and 6.57 mg/g for As(V) and F−, respectively, during their simultaneous removal using CGO/TTO. Furthermore, the nanocomposite demonstrated fair stability and exceptional performance in dynamic experiments, including regeneration, repeated operations, natural water, and column studies. The CGO/TTO-Beads show loading capacities of 1.55x102 and 1.15x102 mg/g for As(III) and As(V) removal under the fixed-bed column studies. In contrast, CGO/TTO/B@1:2-Beads shows 1.54 mg/g loading capacity for F− removal.

Sorption behavior of cesium ions to Mg-containing calcium silicate hydrate in a co-precipitation process

The sorption behavior of Cs to Mg-containing calcium silicate hydrate (C–S–H) was examined to consider C–S–H formation under the water-saturated conditions around a radioactive waste repository. The amount of Cs sorption was slightly lower for Mg-containing C–S–H than for C–S–H, because Mg leads to a decrease in sorption sites by facilitating the polymerization of silicate chains. However, the apparent sorption distribution coefficient Kd of Cs on C–S–H with a Ca/Si molar ratio of 0.8 and Mg contents up to 20% was estimated to be 3.4–6.1 mL/g. Furthermore, the amount of Cs sorption was not decreased by the presence of Ba. The apparent Kd obtained in this study was about 10 times higher than that conventionally estimated for host rocks in the plutonic repository, indicating that C–S–H retains the effect of Cs immobilization even when it contains Mg.Graphical abstract

Critical Role of Boundary Conditions in Sorption Kinetics Measurements.

In order to characterize the hygroscopic properties of cellulose-based materials, which can absorb large amounts of water from vapor in ambient air, or the adsorption capacity of pollutants or molecules in various porous materials, it is common to rely on sorption-desorption dynamic tests. This consists of observing the mass variation over time when the sample is placed in contact with a fluid containing the elements to be absorbed or adsorbed. Here, we focus on the case of a hygroscopic material in contact with air at a relative humidity (RH) differing from that at which it has been prepared. We show that the vapor mass flux going out of the sample follows from the solution of a vapor convection-diffusion problem along the surface and is proportional to the difference between the RH of the air flux and that along the surface with a multiplicative factor (δ) depending only on the characteristics of the air flux and the geometry of the system, including the surface roughness. This factor may be determined from independent measurements in which the RH along the surface is known while keeping all other variables constant. Then we show that the apparent sorption or desorption kinetics critically depend on the competition between boundary conditions and transport through the material. For sufficiently low air flux intensities or small sample thicknesses, the moisture distribution in the sample remains uniform and evolves toward the equilibrium with a kinetics depending on the value of δ and the material thickness. For sufficiently high air flux intensities or large sample thicknesses, the moisture distribution is highly inhomogeneous, and the kinetics reflect the ability of water transport by diffusion through the material. We illustrate and validate this theoretical description on the basis of magnetic resonance imaging experiments on drying cellulose fiber stacks.

Porous Core-membrane Microstructured Nanomaterial Composed of Deep Eutectic Solvents and MOF-808 for CO2 Capture.

A series of porous core-membrane microstructured nanomaterials, constructed of a deep eutectic solvent (DES) membrane and porous MOF-808 core via liquid surface tensions and electrostatic interactions, are introduced for carbon dioxide capture with the sorption mechanism coupling diffusion, physisorption, and chemisorption. MOF-808 as the porous core considerably improves the diffusion interactions for DES membranes, hence significantly enhancing the sorption performance of DESs. Although the DES consisted by monoethanolamine and tetrapropylammonium chloride (MEA-TPAC-7) has the highest sorption capacity among all DESs, it is only 4.39 mmol g-1 at 2.4 bar and further attenuates by fastidious diffusion interactions when increasing viscosity or dose. The sorption capacities of DES@MOF-120 are 5.18 mmol g-1 at 3.0 bar and 4.78 mmol g-1 at 2.4 bar without apparent sorption hysteresis in pressure swing sorption, which are substantially improved contrasted to MEA-TPAC-7. The sorption isotherms are reconstructed via Sips models considering surface heterogeneity with regression correlation coefficients over 0.9454 to forecast maximum sorption capacity over 6.33 mmol g-1 .

Degradation of the persistent organic pollutant-lindane in fixed-bed photoreactor packed with immobilized Zinc Oxide and Iron oxide-doped Zinc Oxide photocatalysts

The potential for the photocatalytic degradation of lindane, used as agricultural insecticide and pharmaceutical product, is investigated. Two types of photocatalysts, immobilized on 5 mm sodalime beads are synthesised using an easy and economical process: (1) Zinc Oxide (ZnO) nanoparticles and (2) Iron oxide-doped Zinc Oxide (Fe-ZnO). Tests of lindane degradation under continuous flow conditions are conducted on a stainless steel fixed bed photoreactor using a 6W UV-A lamp operating at 375 nm. The lindane sorption onto photocatalysts is examined with equilibrium and kinetic tests at batch mode. The experimental datasets are fitted with a 1-dimensional advection-dispersion-sorption-reaction numerical model to estimate the parameters controlling the lindane degradation rate: the apparent sorption capacity of the catalyst, and the surface reaction kinetic constant. Based on estimated parameter values, a comparative analysis of the performance of the two catalysts is done.

A two-sorbent system for fast uptake of arsenate from water: Batch and column studies

There is a critical need to use decentralized and/or point-of-use systems to address some challenging water quality issues in society. Sorption-based approaches are uniquely suitable for such applications because of their simplicity in operation; however, the sorbents must possess fast contaminant uptake kinetics to overcome short hydraulic contact times often encountered in small systems. Here we designed a two-sorbent system consisting of Fe2O3-coated mesoporous carbon (FeMC) and nano-Fe2O3-coated activated carbon (FeAC) and demonstrated its ability to remove arsenate with a < 1 min empty bed contact time (EBCT) by a capture-and-storage process. Batch experiments showed rapid capture of arsenate by FeMC, likely occurred on the rod-like structures protruding to the liquid film. The captured arsenate could subsequently be relocated to FeAC for storage, which had a higher apparent sorption capacity. Column studies, operated with a 10 h running time followed by a 14 h pump-off time, showed that with a 102 μg-As/L influent concentration and at 0.85 min EBCT, the column treated 20,022 bed volumes until the 10 μg-As/L breakthrough, corresponding to a sorption density of 2.36 mg-As/g. This capture-and-storage technique resulted in a rapid and high-capacity arsenate removal through a combined effect of facile access to sorption sites on one sorbent and dynamic equilibrium in the two-sorbent system possessing a large total sorption capacity.

Nickel removal by biogenic selenium nanoparticles (SeNPs): Characterization and simulation of non-symmetric breakthrough curves in continuous-flow packed-bed columns

Nanoparticles offer an alternative mean for heavy metals removal from aquatic environment. In this work we study the sequestering of nickel by biogenic selenium nanoparticles (SeNPs) both in native and in immobilized form in alginate matrix (alginate-SeNPs). The apparent sorption like process is attributed to the coordination chemistry of Ni with the functional groups of the extracellular polymeric substances (EPS) covering the SeNPs. The kinetics and the equilibrium of the process are presented, while the morphology and the properties of the adsorption beads are studied by SEM, FTIR and rheological analysis. Langmuir isotherm describes the adsorption equilibrium with maximum loading Q0 29.411 mg Ni/g SeNPs and 0.651 mg Ni/g alginate-SeNPs. The adsorption of nickel is fast and equilibrium is attained within one hour. Continuous flow experiments in packed beds reveal early elution patterns and non-symmetric sigmoidal profiles due to the reduced adsorption capacity of the immobilized SeNPs, the short depth of the beds and the apparent non-uniform flow pattern. The Bohart-Adams equation fits adequately the main sigmoidal part of the breakthrough curves, however fails to predict the early breakthrough data. By using the advection–dispersion-reaction equation (ADR) under two novel aspects: (a) the rapid equilibrium model with the introduction of an efficiency coefficient accounting for all the kinetic and sorption limitations and (b) the split flow model accounting for any non-uniform flow conditions in the column, the model accuracy is significantly improved. Repeated sorption–desorption experiments show that alginate-SeNPs retain 59% of the original adsorption capacity even after eight cycles.

Sorption Recovery of Platinum Metals from Production Solutions of Sulfate-Chloride Leaching of Chromite Wastes

This paper discusses the scientific rationale for methods of platinum metals sorption centralization from saturated solutions with a high content of macrocomponents. Methods of sorption centralization of platinum and iridium using local anionites such as AH-31, AB-17-8, Purolite S985 are described. The sorbents used were conditioned to remove organic and mineral impurities. The sorption isotherms of platinum group metals 1/EC=f(1/Cp) at a temperature of 20 °C and a duration of 24 h were plotted. The data on the sorption recovery of platinum and iridium from individual and combined sulfate-chloride solutions were determined. Isotherms of iridium sorption from sulfate-chloride solution are formed. Results of the apparent sorption equilibrium constant and values of standard Gibbs energy (ΔG, kJ/mol) of ion exchange for sorption of platinum and iridium from individual and combined sulfate-chloride solutions are presented. Linearized isotherms and kinetic curves of joint sorption of platinum and iridium from sulfate-chloride solution are described. Comparative sorption of the platinum-group metals (PGM) by anionites AB-17-8 and Purolite S985 from sulfate-chloride solutions is shown. The sorption diagram of platinum and iridium from sulfate-chloride product solutions is presented. It has been revealed that complete recovery is achieved using chelation ion-exchange resin Purolite S985, with recovery of Pt up to 95% and Ir more than 73%. The sorption process is accompanied by intradiffusion constraints that are confirmed by the analysis of kinetic curves using Schmukler and Boyd–Adams models.

Single and competitive sorption of sulfadiazine and chlortetracycline on loess soil from Northwest China☆

The fate of veterinary antibiotics (VAs) in soil environment is determined by the hydrophilic performance and solubility of VAs and the type of soil. In this study, sulfadiazine (SDZ) and chlortetracycline (CTC) were selected as target pollutants, and a batch sorption method was used to find out the single and sorption competitive behavior and mechanism of the target pollutants on loess soil. Kinetic studies showed the apparent sorption equilibrium was reached 0–6 h for CTC and 0–12 h for SDZ. The sorption kinetics of VAs on loess soil were fitted well with a pseudo-second order kinetic model. Sorption thermodynamic data indicated the isotherm sorption of both SDZ and CTC on loess soil was fitted well with Freundlich isothermal (R2, 0.960–0.975) and linear models (R2, 0.908–0.976). The sorption affinity of CTC (Kd, 290–1620 L/kg for CTC) was much greater than that of SDZ (Kd, 0.6–4.9 L/kg for SDZ). The results also suggest that SDZ may be easily mobilized or leached from loess soil at neutral and alkaline pH, while CTC may be easily mobilized or leached at neutral pH. The sorption of each single target pollutant on the outer layer complex decreased with increasing ionic strength. Higher initial concentrations resulted in greater sorption capacity of target pollutants on loess soil increased. The sorption capacities of CTC and SDZ in the mixed system were lower than the sorption capacity of each single system, showing a competitive sorption behavior of CTC and SDZ during the sorption process. Overall, CTC showed the highest sorption potential in loess soil, whereas SDZ showed a high leaching risk in loess soil. These findings contribute to understanding the fate of different VAs in loess in the natural environment.

Inverse modeling of laboratory experiment to assess parameter transferability of pesticide environmental fate into outdoor experiments under paddy test systems.

Extraction of environmental fate parameters for pesticides by inverse modeling in laboratory experiments has evolved to become a common practice in higher tier exposure modeling. This study focuses on flooded paddy soil conditions using a simple container test system. Four active ingredients of paddy herbicide were tested. The results were parameterized and transferred to analyze the effect of formulation types on the outdoor experimental data via inverse analyses of two structurally-compatible mathematical models, namely: pesticide concentration in paddy field for laboratory (PCPF-LR) and PCPF for outdoors (PCPF-1Rv1.1 ). After in-laboratory calibration, the PCPF-LR model revealed statistically acceptable or ideal simulations of pesticide concentrations in both the aqueous and soil phases (e.g. Nash-Sutcliffe efficiency > 0.7), in addition to determining the apparent sorption from the laboratory data. The extracted persistence indicators (degradation half-life, DegT50 ) in the aqueous phase were 1.4-38.7 times higher than those of the dissipation (DT50 ) due to the exclusion of partitioning and phase transfer processes (diffusion and sorption). In the outdoor experiment, 72% of the outdoor-calibrated simulations of the PCPF-1Rv1.1 model, showed statistically acceptable representations of the concentrations in paddy water. Furthermore, the DegT50 as 'bulk' degradation in paddy water was statistically insignificant between the formulation types; however, the DT50 demonstrated statistically different results. The laboratory/outdoor data interconnections using proposed modeling approach facilitate the data-specific model calibration and analysis. These can be useful in the exposure modeling of paddy pesticide by manipulating the parameter uncertainties associated with the experimental constraints. © 2020 Society of Chemical Industry.

Impact of percentage and particle size of sugarcane biochar on the sorption behavior of clomazone in Red Latosol.

Biochar is a carbonaceous material that has excellent potential as a fertilizer and soil conditioner. However, there is a lack of information concerning the effects of the amount and particle size of this pyrogenic material on the soil sorption capacity. In this work, evaluation was made of changes in clomazone (CMZ) sorption in a Red Latosol following soil conditioning using different percentages (0.25, 0.5, and 1% w/w) of sugarcane biochar in three particle sizes (<106, 106-508, and 508-610 µm). The conditioned soils presented apparent sorption coefficients (Kd) up to 1300 times higher than that of pure soil, besides changes in the behavior of CMZ sorption. The biochar particle size and percentage influenced sorption of the herbicide as well as its retention in the amended soil during desorption processes. Both sorption and desorption Freundlich constants were linearly correlated with the external surface area of the biochar present in the soil.

Persistence and availability of veterinary antibiotics in soil and soil-manure systems

The availability and persistence of various antibiotics in soil and soil amended with composted poultry manure were investigated through laboratory incubation assays. Six veterinary antibiotics (one fluoroquinolone, two tetracyclines, two sulfonamides and one lincosamide) and one active metabolite (ciprofloxacin) were studied. The incubation assays were conducted at a controlled temperature of 25 °C with different water regimes, such as constant moisture content (80% of water holding capacity) and drying-rewetting cycles. The studied antibiotics were determined in soil and soil aqueous phase samples by LC-MS/MS using internal standards. The results indicated that the highest levels found in the soil aqueous phase were for sulfamethoxazole, followed by sulfamethazine and lincomycin, being very low the levels of chlortetracycline, doxycycline, ciprofloxacin and enrofloxacin (≤1.8%). A positive correlation was observed between the antibiotic concentrations and the content of the dissolved organic carbon in soil aqueous phase with the incubation time. An increase in the apparent sorption coefficients of these antibiotics, except chlortetracycline and lincomycin, was observed when the soil was amended with composted manure. Except for fluoroquinolones, with remaining residues around 70% after 90 days of incubation, a fast dissipation of antibiotics was observed during the assay, with half-lives ranging from 8 to 27 days. These values increased between 6% and 53% in manure amended soil; nevertheless, half-lives remained short (9 days and 27 days for lincomycin and sulfamethazine, respectively). Similar results were obtained with soil under drying-rewetting cycles showing somewhat lower values in soil aqueous phase and slightly shorter half-lives in some cases. The results obtained pointed out that the route of entry of antibiotics into the soil, through recycled water or manure, may have an important effect on their behavior, particularly regarding their availability in soil.

Fate, uptake, and distribution of nanoencapsulated pesticides in soil-earthworm systems and implications for environmental risk assessment.

Nanopesticides are novel plant protection products offering numerous benefits. Because nanoparticles behave differently from dissolved chemicals, the environmental risks of these materials could differ from conventional pesticides. We used soil-earthworm systems to compare the fate and uptake of analytical-grade bifenthrin to that of bifenthrin in traditional and nanoencapsulated formulations. Apparent sorption coefficients for bifenthrin were up to 3.8 times lower in the nano treatments than in the non-nano treatments, whereas dissipation half-lives of the nano treatments were up to 2 times longer. Earthworms in the nano treatments accumulated approximately 50% more bifenthrin than those in the non-nano treatments. In the non-nano treatments, most of the accumulated material was found in the earthworm tissue, whereas in the nano treatments, the majority resided in the gut. Evaluation of toxicokinetic modeling approaches showed that models incorporating the release rate of bifenthrin from the nanocapsule and distribution within the earthworm provided the best estimations of uptake from the nano-formulations. Overall, our findings indicate that the risks of nanopesticides may be different from those of conventional formulations. The modeling presented provides a starting point for assessing risks of these materials but needs to be further developed to better consider the behavior of the nanoencapsulated pesticide within the gut system. Environ Toxicol Chem 2018;37:1420-1429. © 2018 SETAC.

Influence of selected cyclodextrins in sorption-desorption of chlorpyrifos, chlorothalonil, diazinon, and their main degradation products on different soils.

Cyclodextrins (CDs) can improve the apparent solubility and bioavailability of a variety of organic compounds through the formation of inclusion complexes; accordingly, they are suitable for application in innovative remediation technologies of contaminated soils. However, the different interactions in the tertiary system CD/contaminant/soil matrix can affect the bioavailability of the inclusion complex through the possible sorption of CD and CD complex in the soil matrix, as well as with the potential of the sorbed CD to form the complex, concurrent with the desorption processes. This work focuses in changes produced by three different CDs in soil sorption-desorption processes of chlorpyrifos (CPF), diazinon (DZN), and chlorothalonil (CTL), and their major degradation products, 3,5,6-trichloro-2-pyridinol (TCP), 2-isopropyl-6-methyl-4-pyrimidinol, and hydroxy-chlorothalonil (OH-CTL). Cyclodextrins used were β-cyclodextrin (β-CD), methyl-β-cyclodextrin (Mβ-CD), and 2-hydroxypropyl-β-cyclodextrin(HPβ-CD). The studied soils belong to the orders Andisol, Ultisol, and Mollisol with different organic matter contents, mineral composition, and pH. The apparent sorption constants were significantly lower for the three pesticides in the presence of all CDs. The highest displacement of sorption equilibria was produced by the influence of Mβ-CD, with the most pronounced effect for CPF, a pesticide strongly sorbed on soils. The same was obtained for TCP and OH-CTL, highlighting the need to assess the risk of generating higher levels of groundwater contamination with polar metabolites if degradation rates are not controlled. The highest desorption efficiency was obtained for the systems CPF-β-CD, DZN-Mβ-CD, and CTL-Mβ-CD. Since the degree of adsorption of the complex is relevant to obtain an increase in the bioavailability of the contaminant, a distribution coefficient for the complexed pesticide in all CD-soil-pesticide system was estimated by using the apparent sorption coefficients, the stability constant for each CD-pesticide complex, and the distribution coefficients of free pesticide.

Preparation and desulfurization kinetics of activated carbons from semi-coke of coal liquefaction residual

Microporous activated carbons were prepared from the semi-coke of coal liquefaction residual by KOH activation. The gas evolution during the activation process was analyzed by thermogravimetry–mass spectrometry. The SO2 adsorption equilibrium and desulfurization kinetics at low temperatures were also investigated. The results of this study indicate that three reactions are mainly responsible for the formation of pore structure in the activated carbons. The physical adsorption dominates the adsorption of SO2 (250–1250 ppm SO2, N2 as balance gas) at lower temperature for activated carbons. The Boltzmann model was found to be suitable for describing the desulfurization behavior of selected activated carbon at low temperatures under non-oxygen atmosphere instead of the linear driving force model. The apparent sorption rate constant of activated carbon ranges from 0.0027 to 0.0038 s−1. The temperature-programmed desorption study of the adsorption-saturated (393 K, 5% O2 + 1250 ppm SO2 + N2 balance) activated carbon suggests the presence of two types of adsorbed SO2 with the bond energy of 45.17 and 52.00 kJ mol−1, respectively.

Kinetic sorption of contaminants of emerging concern by a palygorskite-montmorillonite filter medium

Kinetic sorption of bisphenol A (BPA), carbamazepine (CMZ) and ciprofloxacin (CIP) by three palygorskite-montmorillonite (Pal-Mt) granule sizes was studied. For BPA, CMZ and CIP, apparent sorption equilibrium was reached within about 3, 5 and 16 h, respectively. The highest and the lowest sorption capacities were by the small and the large granule sizes, respectively. Experimental results were compared to various sorption kinetics models to gain insights regarding the sorption processes and achieve a predictive capacity. The pseudo-second order (PSO) and the Elovich models performed the best while the pseudo-first order (PFO) model was only adequate for CMZ. The intraparticle-diffusion (IPD) model showed a two-step linear plot of BPA, CMZ and CIP sorption versus square root of time that was indicative of surface-sorption followed by IPD as a rate-limiting process before equilibrium was reached. Using the pseudo-first order (PFO) and the pseudo-second order (PSO) rate constants combined with previously-established Langmuir equilibrium sorption models, the kinetic sorption (ka) and desorption (kd) Langmuir kinetic rate constants were theoretically calculated for BPA and CIP. Kinetic sorption was then simulated using these theoretically calculated ka and kd values, and the simulations were compared to the observed behavior. The simulations fit the observed sorbed concentrations better during the early part of the experiments; the observed sorption during later times occurred more slowly than expected, supporting the hypothesis that IPD becomes a rate-limiting process during the course of the experiment.

Impacts of water level fluctuations on the physicochemical properties of black carbon and its phenanthrene adsorption-desorption behaviors

The stability of black carbon (BC) as a slow cycling pool in the global C cycle is an important property and is likely governed by environmental conditions. Although the importance of role of the water regime in BC degradation was confirmed, direct impacts of water level fluctuations (WLF) on BC degradation were absent. This study investigated the changes in the physicochemical properties of BC and the behaviors of adsorption-desorption due to long-term WLF. The results showed that BC in the zone of WLF in soil contained higher amounts of carbon and lower amounts of oxygen, leading to contain few carboxylic functional groups and indicating that the WLF imposed on the reservoirs have altered BC decomposition, causing a decrease in mineralization. Furthermore, BC exhibited higher adsorption capacities and an apparent sorption–desorption hysteresis. Our results suggested that WLF has an advantageous role in preventing BC decomposition. Such protection has significance for the stability of BC in soils as well as for its effects on global C cycling and HOCs sorption. Understanding the decomposition mechanisms, dynamics and environmental influences should provide new insights into BC degradation and cycling.

The sorption of monovalent cations onto norway spruce: Model studies using wood flour and LiCl solution

The transport of chemicals in a porous material such as wood is very complex and involves several processes: the diffusion of chemicals in the cell pores (lumen and pit pores), through the cell walls at certain conditions, and sorption of wood tissue. In the present study, batch sorption experiments were performed to examine the sorption of Li+ ions from an aqueous LiCl solution onto Norway spruce wood flour samples. The experimental methodology employed is suitable for differentiating the amount of ions sorbed onto the wood tissue and dissolved in the solution in wood pores. The apparent equilibrium sorption data were analyzed using two widely applied isotherm models: Langmuir and Freundlich. The results suggest that the sorption was spontaneous, and for the experimental conditions studied, probably involved several interaction types between the different functional groups of the wood and the Li+/Cl− ions.