Adsorption Step Research Articles

Low-cost Ca/Mg co-modified biochar for effective phosphorus recovery: Adsorption mechanisms, resourceful utilization, and life cycle assessment

Effective recovery of phosphorus from wastewater and reutilization are important for controlling water eutrophication and achieving resourceful utilization of pollutants. In this study, a low-cost, eco-friendly, and highly efficient Ca/Mg co-modified coffee grounds biochar (CMBC) was synthesized in one step for phosphorus adsorption, and the potential application of the phosphorus absorbed CMBC (CMBC-P) as a fertilizer was also explored. The results showed that the surface of CMBC was covered by granular calcium/magnesium oxides with a rougher layered stacking structure. The adsorption capacity of CMBC for phosphorus has been significantly improved compared with that Ca or Mg modification, with the maximum adsorption capacity reached 144.31 mg/g. The mechanisms primarily involve surface precipitation, complexation, ligand exchange, and electrostatic attraction. Density functional theory calculation revealed that the Ca-based active sites were the main binding sites (−6.58 and −6.41 Kcal/mol) for phosphorus compared with that of the Mg (−0.89 Kcal/mol). Natural aging experiment showed that approximately 74.87 % of the adsorbed phosphorus can be released to soil within 60 days and the soil available phosphorus also increased significantly. The CMBC-P also significantly enhanced the germination and growth of plants. Moreover, life cycle assessment revealed that the production of CMBC emitted only 8.38 kg CO2 eq, and a more environmentally friendly approach was also proposed. Cost benefit analysis confirmed the exceptional cost-effectiveness (15.15 g P/$) of CMBC among various adsorbents. Overall, CMBC demonstrated excellent potential for removal phosphorus from water and further use as a phosphorus fertilizer.

Cupin-1.1 Adsorption Layers at the Surface of 8 M Urea Solutions.

The adsorption layers of cupin-1.1, one of the two evolutionary conserved β-barrel domains of vicilin─the garden pea storage globulin─at the liquid-gas interface were studied by a few methods of the surface chemistry. The kinetic dependencies of the surface pressure of cupin-1.1 solutions in 8 M urea overlap in a single master curve if the surface pressure is plotted as a function of the normalized time. The analysis of the master curve allows separation of a few adsorption steps including the induction period, the regions of the diffusion-controlled and barrier-controlled adsorption kinetics, and a plateau region of slow adsorption. Another master curve can be constructed from the dependencies of the dynamic surface elasticity on surface pressure. This curve has some similarities with the corresponding results for recently studied cupin-1.1 spread layers on the surface of urea solutions and gliadin adsorption layers. There are also important distinctions with the master curve for adsorption layers of cupin-1.1 in the system without denaturants. This difference can be connected with the formation of larger and more rigid aggregates in pure water than the aggregates in urea solutions.

Enhanced photocatalytic synthesis of urea from co‐reduction of N2 and CO2 on Z‐schematic SrTiO3‐FeS‐CoWO4 heterostructure

The photocatalytic co‐reduction of CO2 and N2 is a sustainable method for urea synthesis under mild conditions. However, high‐yield synthesis of urea is a challenge due to the sluggish kinetics of the C‐N coupling reaction. Herein, we have successfully engineered a Z‐scheme photocatalyst, SrTiO3‐FeS‐CoWO4, for boosting photocatalytic urea synthesis via enhancing the initial CO2 and N2 adsorption step and reducing the energy barrier for the C‐N coupling reaction. A high urea yield of 8054.2 μg·gcat−1·h‐1 was achieved on SrTiO3‐FeS‐CoWO4, which was significantly higher than the state‐of‐the‐art. The SrTiO3‐FeS‐CoWO4 Z‐scheme photocatalyst, with accelerated charge transfer by FeS, not only had dual active sites for the chemical adsorption and activation of CO2 and N2, but also retained the high conduction band (‐1.50 eV) and accelerated supply of electrons and protons, which are responsible for its good photoreduction activity and significantly reduced energy barrier for the rate‐determining step of C‐N coupling reaction.

Enhanced Photocatalytic Synthesis of Urea from co-Reduction of N2 and CO2 on Z-Schematic SrTiO3-FeS-CoWO4 Heterostructure.

The photocatalytic co-reduction of CO2 and N2 is a sustainable method for urea synthesis under mild conditions. However, high-yield synthesis of urea is a challenge due to the sluggish kinetics of the C-N coupling reaction. Herein, we have successfully engineered a Z-scheme photocatalyst, SrTiO3-FeS-CoWO4, for boosting photocatalytic urea synthesis via enhancing the initial CO2 and N2 adsorption step and reducing the energy barrier for the C-N coupling reaction. A high urea yield of 8054.2 μg ⋅ gcat -1 ⋅ h-1 was achieved on SrTiO3-FeS-CoWO4, which was significantly higher than the state-of-the-art. The SrTiO3-FeS-CoWO4 Z-scheme photocatalyst, with accelerated charge transfer by FeS, not only had dual active sites for the chemical adsorption and activation of CO2 and N2, but also retained the high conduction band (-1.50 eV) and accelerated supply of electrons and protons, which are responsible for its good photoreduction activity and significantly reduced energy barrier for the rate-determining step of C-N coupling reaction.

Process swing adsorption with selective purge gas recirculation (PSA-SPUR): Adsorption process technology optimised for separation of heavy component from a gas mixture and its design for CO2 capture through Equilibrium Theory analysis

PSA-SPUR (Pressure Swing Adsorption with Selective Purge Gas Recirculation) has been developed aimed at separating the most strongly adsorbing component from a gas mixture at high product purity and recovery. The innovative strategy for designing a Pressure Swing Adsorption system features recycling its purge gas stream exiting the column and mixing it back into the feed. This operation enriches the mixed feed with an elevated fraction of the heavy component during the adsorption step, thus enhancing the PSA’s performance greatly. Reusing the purge gas helps significantly increase the product recovery compared to conventional methods where purge gas is simply discarded or taken as a low-quality product. For theoretical analysis of a PSA-SPUR system, a bespoke Equilibrium Theory model was developed and solved successfully, providing valuable insights into the performance of the PSA-SPUR system designed for capturing CO2 from a flue gas. The study revealed that there exists an optimum extent of purging that maximises the heavy component mole fraction in the mixed feed, leading to the best possible feed throughput of the adsorption system. Furthermore, the effects of the desorption pressure and feed composition on the PSA-SPUR system’s performance were investigated. The results indicate that the CO2 capture PSA-SPUR system using commercial zeolite 13X has excellent potential to achieve very high product purity and recovery, being allowed to operate at moderate vacuum pressures without having to compress the flue gas feed, even when the gas feed contains less than 10 mol% CO2.

Upgrading of kraft lignin pyrolysis products: Managing sulfur impurities

Pyrolysis stands as a powerful method for the valorization of biomass like kraft lignin, an aromatic-rich and sulfur-containing polymeric by-product from the pulping industry. Sulfur in the raw matrix is released during thermal processes and is redistributed in pyrolysis products. However, the presence of sulfur lowers the quality of products due to its corrosive and toxic character. In this work, commercial activated carbons have been used as adsorbents to remove the main sulfur compounds from the gas phase (i.e., CH3SH, COS, H2S). The analysis of sulfur content in biochar has been performed through SEM-EDXS, while the sulfur content in oils has been obtained by GC–MS analysis. The adsorption of sulfur on the activated carbon bed results in an enhancement of the release of sulfur in the gas phase from 34 % without activated carbon to 44 %. Up to 88 % of H2S removal is achieved after the adsorption step, together with a reduction of the overall sulfur content in the bio-oil rich in intermediates such as guaiacols and alkylated phenols. The residual sulfur contained in the liquid product is lowered to 3 % of the total sulfur in the system, thus improving the quality of the liquid pyrolysis product. This process limits the amount of sulfur in the gas and improves its quality and market value. At the same time, this results in a redistribution of sulfur in pyrolysis products such as bio-oil, improving its range of application as a source of chemical intermediates from kraft lignin.

Enhancing carbon dioxide adsorption in a hybrid fixed bed via structuring and thermal management: a numerical study

Systems based on physical sorption are an attractive solution for CO2 capture from flue gases, biogas upgrading or gas storage. Besides the sorbent choice, one of the most important factors related to the design of such systems is proper heat management. Commonly used sorbents typically have low thermal conductivity. Nevertheless, catalyst particles characterized by high conductivity are inherently present in adsorptive (hybrid) reactors. Thus, appropriate structuring of hybrid beds can be used for controlling temperature profiles and improving the bed performance. In this study, the behaviour of a nonadiabatic adsorptive reactor described by a two-dimensional model was analysed for the adsorption step. The effect on the CO2 adsorption performance of different spatial distributions of functionalities in the bed was investigated. The optimality problem for nonuniform radial distribution of sorbent and catalyst in the bed was solved, indicating that such a configuration is a potentially important direction for structuring hybrid beds. Results demonstrate that the optimal configuration of radially distributed functionalities significantly increases the amount of CO2 absorbed under identical boundary and initial conditions for the bed. It appears that precise control of the heat generated and removed from the bed is achievable. Such control could be advantageous for the regeneration phase.

In-situ growth of Fe-MOF on magnetic materials by self-template method to enhance practicality and removal of tetracycline antibiotics from aqueous solution

In this work, core–shell structured Fe3O4@PCN-333 (Fe) composite was constructed using a self-template method, in which Fe3O4 microspheres not only serve as magnetic centers but also provide Fe (III) for the preparation of PCN-333 (Fe). PCN-333 (Fe) uniformly grew as a shell on the surfaces of the microspheres, and the shell thickness was approximately 38 nm. The composite exhibited high adsorption performance, with maximum adsorption capacities of 471.7, 303.3 and 314.5 mg/g for chlortetracycline, tetracycline and oxytetracycline, respectively. The adsorption of tetracycline antibiotics (TCs) was based on the Langmuir and pseudo-second-order model, and external diffusion and pore diffusion were the rate-limiting steps in adsorption. The strong adsorption capacity was attributed to the mechanism of π–π interaction, coordination bonds, electrostatic interaction, hydrogen bonding, and van der Waals force. Fe3O4@PCN-333 (Fe) composite displayed good stability in the aqueous solution, strong TCs adsorption capacity, high selectivity, anti-interference performance for adsorbing TCs, fast recovery with external magnetic field, reusability, thus effectively reducing the cost for removing water pollutants. These features make the composite a potential material for removing TCs in the environment.

Leveraging Soft Acid-Base Interactions Alters the Pathway for Electrochemical Nitrogen Oxidation to Nitrate with High Faradaic Efficiency.

Electrocatalytic nitrogen oxidation reaction (N2OR) offers a sustainable alternative to the conventional methods such as the Haber-Bosch and Ostwald oxidation processes for converting nitrogen (N2) into high-value-added nitrate (NO3 -) under mild conditions. However, the concurrent oxygen evolution reaction (OER) and inefficient N2 absorption/activation led to slow N2OR kinetics, resulting in low Faradaic efficiencies and NO3 - yield rates. This study explored oxygen-vacancy induced tin oxide (SnO2-Ov) as an efficient N2OR electrocatalyst, achieving an impressive Faradaic efficiency (FE) of 54.2% and a notable NO3 - yield rate (22.05µg h-1 mgcat -1) at 1.7V versus reversible hydrogen electrode (RHE) in 0.1m Na2SO4. Experimental results indicate that SnO2-Ov possesses substantially more oxygen vacancies than SnO2, correlating with enhanced N2OR performance. Computational findings suggest that the superior performance of SnO2-Ov at a relatively low overpotential is due to reduced thermodynamic barrier for the oxidation of *N2 to *N2OH during the rate-determining step, making this step energetically favorable than the oxygen adsorption step for OER. This work demonstrates the feasibility of ambient nitrate synthesis on the soft acidic Sn active site and introduces a new approach for rational catalyst design.

Screening of Subnanoscale Metal Hydride Formation for Late Transition Metals Using Dimer Cations─Group IX Element.

The energetically stable structures of M2Hm+ (M = Co, Rh, Ir; m = 2, 4, 6, ...) were investigated using density functional theory calculations, and possible reaction pathways for the sequential adsorption of H2 molecules on M2+ were proposed. Based on the most stable structures, adsorption energies of H2 were calculated for each adsorption step, and the maximum numbers of adsorbed H atoms on Co2+, Rh2+, and Ir2+ were estimated to be 14, 16, and 16, respectively. Compared to group XI elements (M = Cu, Ag, and Au), which are conceivably inert to H2, more H atoms were bound to Co2+, Rh2+, and Ir2+. The adsorption of H2 on M2+ (M = Co, Rh, Ir, or Cu) in the gas phase was investigated experimentally at 300 K using mass spectrometry. Although Rh2+ and Ir2+ stored numerous H2 molecules as predicted by calculations, Co2+ was found to adsorb no H atoms. It was probably due to the insufficient adsorption energy of Co2+ and the kinetic effect in the H2 adsorption process. Thus, computational calculations can overestimate the number of adsorbed H atoms.

Cyclic Atomic Layer Etching of PdSe2

AbstractThe unique characteristic of 2D transition‐metal dichalcogenide (TMD) semiconductor materials such as PdSe2 is the ability of the bandgap to vary on the basis of the number of layers present. This variation results in a broad bandgap range spanning from semi‐metallic to semiconducting materials, underscoring the significance of precisely controlling the material thickness. In this study, the thicknesses of chemical vapor deposited PdSe2 films are precisely controlled layer‐by‐layer via cyclic atomic layer etching (ALE), which comprised a radical adsorption step generated by oxygen and chlorine plasmas, followed by a desorption step with an organic solvent vapor such as formic acid. Cyclic etching with one monolayer of PdSe2/cycle is achieved using both types of adsorption gases while maintaining the ratio of Se/Pd underlying PdSe2 at ≈2. This cyclic ALE method is also applicable for smoothing TMD material surfaces by isotropically removing individual rough surface layers. Because this etching method only utilizes chemical reactions with radicals generated by plasmas and organic vapors, it is not only unaffected by the physical damage caused by the irradiation of energetic particles such as ions in plasmas, but also is applicable to 3D structure processing.

Recovery of carboxylic acids from actual effluent by using sequential cationic-anionic adsorption steps at semi pilot scale

This work presents for the first time an exhaustive experimental assessment at semi-pilot scale for the sequential use of cationic-anionic adsorption columns for recovering carboxylic acids (CAs) from a real fermentation broth. The consecutive steps were dedicated to i) remove cations limiting the CAs interaction with the functional group of the anionic resin, and ii) adsorb CAs onto the anionic resin, respectively. The experimental broth was obtained from anaerobic co-fermentation of urban biowaste (UBW-broth). Breakthrough (BT) tests were firstly performed with the cationic column containing the strong-acid resin Lewatit® S2568H. This allowed both to assess the single process and to prepare 60 L of decationised UBW-broth to be used in the BT-tests with the anionic column (containing the weak-basic resin Lewatit® A365). Both columns were assessed (at 25°C) under packed and expanded bed modes, by feeding at different rates the actual UBW-broth or synthetic solutions. Main study innovative outputs were: 1) 100 % of the CAs occurring in UBW-broth were recovered with the proposed system; 2) best performances were obtained under expanded bed mode of operation, allowing to use 100 % of the installed capacity; 3) the affinity of other organic matter else than CAs resulted weaker than Na+/NH4+ and CAs/PO4x-/Cl- in both cationic and anionic columns, respectively (i.e. low adsorption performances generally reported are due to inorganic cations/anions presence); 4) a very preliminary economic analysis carried out on the basis of the obtained data indicates overall costs ranging 0.58–1.49 EUR/kg of CAs (depending on the process configuration).

Isoreticular Metal-Organic Frameworks with Aromatic Pores and Dimethylammonium Cations Enable Separation of Light Hydrocarbons and Xenon/Krypton.

The separation of C2-C3 hydrocarbons from methane in natural gas and xenon/krypton purification are crucial yet challenging industrial processes. Herein, we report two isoreticular metal-organic frameworks, ZJU-89 and ZJU-90, featuring aromatic pore environments and dimethylammonium cations, that synergistically enhance the separation of these industrially relevant gas mixtures. ZJU-90 exhibits an exceptional separation performance, achieving C3H8/CH4 and C2H6/CH4 ideal adsorbed solution theory (IAST) selectivities of 1065 and 48, respectively, at ambient conditions, outperforming most reported adsorbent materials. Remarkably, ZJU-90 enables the recovery of >99.95% purity methane from a C3H8/C2H6/CH4 mixture in a single adsorption step. The material also demonstrates the efficient separation of xenon from krypton, even at low concentrations. The superior performance stems from the aromatic rings decorating the pore walls and the free dimethylammonium cations in the channels, which provide an ideal chemical environment for the selective binding of C2H6, C3H8, and Xe through multiple C-H···π interactions and van der Waals forces, as elucidated by theoretical calculations. This work highlights the power of reticular chemistry in designing materials with synergistic pore environments for efficient separations.

Exploring enhanced CO2 separation from blast furnace gas: A multicolumn vacuum swing adsorption approach with process design and experimental assessment

Excessive emissions of carbon dioxide (CO2) are a major driver of global warming. Blast furnace gas (BFG) represents a major source of CO2 emissions in the steel industry, accounting for approximately 30 % CO2 emissions among the industry sectors. Hence, effective CO2 capture from BFG is imperative. This study presents an approach utilizing the vacuum swing adsorption (VSA) technology to capture CO2 from BFG. A 6-column VSA rig was designed and constructed to separate CO2 from a simulated BFG (CO2/N2 = 20 %/80 %) using zeolite 13X as adsorbents. The VSA process involved steps of adsorption, desorption, heavy product purge, light product re-pressurization, and pressure equalization. Five different process modes, i.e., 1-column and 3-step, 2-column and 6-step, 2-column and 8-step, 3-column and 9-step, and 4-column and 16-step configurations, were implemented to evaluate the influence of various process design factors on the separation performance. Additionally, a 6-column and 36-step process was devised to conduct a parametric study of VSA cycles by varying the adsorption duration and desorption pressure. Results revealed the pivotal role of heavy product purge and pressure equalization on the separation performance. The six-column process achieved a CO2 purity and recovery of 94 % and 82 %, respectively, with a energy consumption of 0.76 GJ/tonCO2 when employing a desorption step duration of 240 s and pressure of 8 kPa. In addition, a method of process optimization based on the bed capacity ratio, C, was introduced in this study, which provides a dimensionless quantity of the utilization of the adsorption column. Moreover, capturing CO2 from BFG through the VSA cycle not only enhances its heating value but also yields substantial advantages in terms of mitigating CO2 emissions.

FACILE SYNTHESIS OF ACTIVATED CARBON/ALGINATE/CHITOSAN COMPOSITE BEADS AS RHEMAZOLE BRILLIANT BLUE R ADSORBENT

Developing composite beads composed of chitosan, alginate, and activated carbon for dye removal is essential due to their improved adsorption capabilities and environmental benefits. By utilizing natural resources efficiently for an effective dye removal process, this study developed an activated carbon/alginate/chitosan composite bead as Rhemazole Brilliant Blue R (RBBR) adsorbent. The surface shape of composites exhibits more protrusions, grooves, and asymmetric pores than activated carbon, which could improve dye adsorption capability. FTIR analysis verified that functional groups such as OH, NH, protonated amine, and carboxylate from the constituent polymers were enriched in the activated carbon/alginate/chitosan composite. These groups also function as active sites for adsorbents. It was aligned with the composite beads' Freundlich isotherm model, which shows that heterogeneous or many active sites contribute to adsorption and provide multilayer adsorption. The kinetic model of pseudo-second order fits well with the adsorption process, indicating that chemisorption is the rate-limiting step in RBBR adsorption. The optimum adsorption conditions were at pH 1, with an adsorbent dose of 0.08 g, RBBR dye concentration of 125 mg/L, and a contact time of 60 min. The composite beads also exhibit stability in acidic and basic solutions, with the effectiveness of being reused up to four times, providing a reusable adsorbent with versatility in various water treatment conditions. Hence, synthesizing activated carbon/alginate/chitosan composite beads presents a promising solution for sustainable wastewater treatment based on biodegradable and eco-friendly composite.

Coadsorption mechanisms of copper and sulfamethoxazole by functionalized cellulose: A kinetic and DFT study

In order to address the issue of compound pollution from heavy metals and antibiotics in aquatic environments, multibranched functionalized cellulose materials (DACS) with abundant adsorption affinity groups (such as amino, carboxyl and imine groups) were prepared by oxidation, etherification and grafting. The maximum adsorption capacities of DACS for copper (Cu) and sulfamethoxazole (SMZ) were 42.27 and 117.92 mg/g, respectively. In addition, its excellent pH buffering capacity, resistance to coexisting interfering substances and great regeneration performance of up to 91 % after 5 cycles. In the coadsorption experiment, the multibranched structure strengthened the bridge effect during the coadsorption process, and weakened the inhibition of SMZ adsorption caused by competition. Kinetic models and error functions analysis showed that PNO model and F&S model were the most consistent with the adsorption process, and the limiting step of adsorption was the external diffusion of Cu and SMZ around the surface of DACS. Moreover, the density functional theory (DFT) was used to quantitatively calculate the adsorption binding energy of multiple sites on DACS, and clarified the adsorption tendency of DACS as electron donors for Cu and as acceptor for SMZ. In addition, the binding energy of sequential adsorption was greater than that of single and binary adsorption, and the binding stability of SMZ was significantly increased in sequential adsorption for the increasing of binding energy. The electron exchange process in the adsorption showed that SMZ played a bridging role in the binary adsorption, while Cu was the main reaction part of the complex adsorption.

Pressure swing adsorption process modeling using physics-informed machine learning with transfer learning and labeled data

Pressure swing adsorption (PSA) modeling remains a challenging task since it exhibits strong dynamic and cyclic behavior. This study presents a systematic physics-informed machine learning method that integrates transfer learning and labeled data to construct a spatiotemporal model of the PSA process. To approximate the latent solutions of partial differential equations (PDEs) in the specific steps of pressurization, adsorption, heavy reflux, counter-current depressurization, and light reflux, the system's network representation is decomposed into five lightweight sub-networks. On this basis, we propose a parameter-based transfer learning (TL) combined with domain decomposition to address the long-term integration of periodic PDEs and expedite the network training process. Moreover, to tackle challenges related to sharp adsorption fronts, our method allows for the inclusion of a specified amount of labeled data at the boundaries and/or within the system in the loss function. The results show that the proposed method closely matches the outcomes achieved through the conventional numerical method, effectively simulating all steps and cyclic behavior within the PSA processes.

Effects of Ellagic Acid on Vaginal Innate Immune Mediators and HPV16 Infection In Vitro.

Ellagic acid (EA) is a phenolic phytochemical found in many plants and their fruits. Vaginal epithelial cells are the first line of defense against pathogen invasion in the female reproductive tract and express antimicrobial peptides, including hBD2 and SLPI. This study investigated the in vitro effects of EA (1) on vaginal innate immunity using human vaginal epithelial cells, and (2) on HPV16 pseudovirus infection. Vaginal cells were cultured in the presence or absence of EA, and the expression of hBD2 and SLPI was determined at both transcriptional and translational levels. In addition, secretion of various cytokines and chemokines was measured. Cytotoxicity of EA was determined by CellTiter-blue and MTT assays. To investigate the ability of EA to inhibit HPV16 infection, EA was used to treat HEK-293FT cells in pre-attachment and adsorption steps. We found significant increases in both hBD2 mRNA (mean 2.9-fold at 12.5 µM EA, p < 0.001) and protein (mean 7.1-fold at 12.5 µM EA, p = 0.002) in response to EA. SLPI mRNA also increased significantly (mean 1.4-fold at 25 µM EA, p = 0.01), but SLPI protein did not. Secretion of IL-2 but not of other cytokines/chemokines was induced by EA in a dose-dependent manner. EA was not cytotoxic. At the pre-attachment step, EA at CC20 and CC50 showed a slight trend towards inhibiting HPV16 pseudovirus, but this was not significant. In summary, vaginal epithelial cells can respond to EA by producing innate immune factors, and at tested concentrations, EA is not cytotoxic. Thus, plant-derived EA could be useful as an immunomodulatory agent to improve vaginal health.

Removal of two cationic dyes by adsorption on F400 commercial activated carbon

In this investigation, we studied the removal of two cationic dyes, methyl green MG and malachite green Mc G, by a commercial adsorbent. This adsorbent is a F400 activated carbon with a specific surface area of 1203 m2. g-1, which is expected to be high compared with ordinary adsorbents. Adsorption tests were carried out on both dyes in batch mode. The results show that both kinetics are fast, with equilibrium reached after 20 minutes and 30 minutes respectively for Methyl Green and Malachite Green. The kinetics of both dyes are well adapted to pseudo-second order, and for the intraparticle diffusion model, two lines can be distinguished for each dye, proving the existence of two adsorption steps. The isotherm for this system reveals an L-type shape for both dyes, in line with the classification of Giles &amp; al. so there is little competition for sorption sites between solvent and adsorbate. The adsorption isotherms for methyl green by PAC obeyed the Langmuir, Freundlich and Temkin models, while that for malachite green followed only the Langmuir isotherm, with a much higher maximum amount.

Modelling the Fate of Linear Alkylbenzene Sulfonate in Agricultural Soil Columns during Inflow of Surfactant Pulses from Domestic Wastewaters

Linear alkylbenzene sulfonate (LAS), a widely used anionic surfactant, is present in wastewater and can be discharged, causing environmental damage. When biodegradation is negligible, adsorption and desorption reactions play an important role, depending on the media characteristics (organic matter and clays) and hydrodynamic parameters. Previously published laboratory column data are modelled with PHREEQC (version 2.18) in three scenarios of LAS input: spill (LAS pulse), continuous discharge (LAS adsorption step) and remediation (LAS desorption step). The distribution coefficients (0.1–4.9 × 10−3 L/g) in the sand columns are lower than those determined in this paper from batch tests and in columns of 25% and 50% agricultural soil mixtures (1–70 × 10−3 L/g). Considering the Freundlich constant parameters from the modelling, the results are similar to the distribution coefficients, but the linear isotherms are more consistent throughout. The mass transfer coefficient from the sand columns is lower than the agricultural soil columns (20–40 h−1), indicating longer elution times for the heavier homologues and a higher percentage of agricultural soil. For lighter homologues, fast migration could cause contamination of aquifers. The great persistence of LAS in the environment necessitates the development of mitigation strategies using reactive transport models, which predict longer times for the remediation of LAS homologues.