Pseudo-second Order Kinetic Model Research Articles

Synthesis of a novel chitosan-TiO2 nanocomposite as an efficient adsorbent for the removal of methylene blue cationic dye from wastewater

This study investigates the efficacy of chitosan-TiO2 nanocomposites (CS-TiO2) as an efficient adsorbent for removing Methylene blue (MB) cationic dye from wastewater. The synthesis of chitosan-TiO2 nanocomposites (CS-TiO2) involved the co-polymerization and crosslinking of Chitosan biopolymer (CS) with titanium dioxide (TiO2). The CS-TiO2 nanocomposites involved their structure, morphology, and characteristics through the utilization of several analytical methods such as FTIR, XRD, SEM, TEM, TGA, UV-visible, DLS, and XPS. The removal of MB dye examined in different concentrations of chitosan exhibits an increase as the pH of the solution increases; the maximum value was attained at pH 6 and 120 minutes of contact time. The optimal dosage of CS-TiO2 nanocomposites for adsorbing methylene blue (MB) was found to be between 0.10 mg/L and 0.20 mg/L. The experimental data was evaluated using the thermodynamic process, Dubinin-Radushkevich, Langmuir, and Freundlich isotherm models. The data were examined using various kinetic models and found to be consistent with pseudo-first order, pseudo-second order, and Intraparticle diffusion kinetics models. Desorption and reuse after adsorption of MB onto CS-TiO2 nanocomposite was investigated using different desorbing agents like NH4OH/NH4Cl or NaOH. These results indicate that CS-TiO2 nanocomposite is a highly effective and cost-effective adsorbent for removing MB dyes from contaminated water.

Acid Mine Drainage Precipitates from Mining Effluents as Adsorbents of Organic Pollutants for Water Treatment.

Acid mine drainage (AMD) is one of the main environmental problems associated with mining activity, whether the mine is operational or abandoned. In this work, several precipitates from this mine drainage generated by the oxidation of sulfide minerals, when exposed to weathering, were used as adsorbents. Such AMD precipitates from abandoned Portuguese mines (AGO, AGO-1, CF, and V9) were compared with two raw materials from Morocco (ClayMA and pyrophyllite) in terms of their efficiency in wastewater treatment. Different analytical techniques, such as XRD diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), N2 adsorption isotherms, and Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) were used to characterize these natural materials. The adsorption properties were studied by optimizing different experimental factors, such as type of adsorbent, adsorbent mass, and dye concentration by the Box-Behnken Design model, using methylene blue (MB) and crystal violet (CV) compounds as organic pollutants. The obtained kinetic data were examined using the pseudo-first and pseudo-second order equations, and the equilibrium adsorption data were studied using the Freundlich and Langmuir models. The adsorption behavior of the different adsorbents was perfectly fitted by the pseudo-second order kinetic model and the Langmuir isotherm. The most efficient adsorbent for both dyes was AGO-1 due to the presence of the cellulose molecules, with qm equal to 40.5 and 16.0 mg/g for CV and MB, respectively. This study confirms the possibility of employing AMD precipitates to adsorb organic pollutants in water, providing valuable information for developing future affordable solutions to reduce the wastes associated with mining activity.

Study on improving the fluorine removal performance of Chitosan-Al2(SO4)3 modified bauxite

To improve the fluoride removal performance of the bauxite, chitosan (CTS)-Al2(SO4)3 modified bauxite was prepared to remove F− from water. The fluoride removal rates of chitosan and unmodified bauxite were 16.36 % and 48.69 % respectively, and that of CTS-Al2(SO4)3 modified bauxite could reach 98.28 %. The effects of addition amount of Al2(SO4)3 and chitosan, bauxite calcination temperature, reaction time, adsorbent dose, initial F− concentration and co-existing anions were investigated. SEM, FTIR, 77K N2 adsorption-desorption isotherm and XRD were used to analyze the bauxite before and after modification. The results showed that chitosan successfully combined with bauxite, and the morphological changes before and after modification were relatively small. The pseudo second-order kinetic model was more suitable for F− adsorption process of on CTS-Al2(SO4)3 modified bauxite.

Efficient CO2 capture using a novel Zn-doped activated carbon developed from agricultural liquid biomass: Adsorption study, mechanism and transition state

A Zn-doped carbon was prepared and used as an effective CO2 adsorbent. This carbonaceous material was developed from olive mill wastewater (OMWW) by an innovative process using thermal shock flash pyrolysis followed by zinc chloride impregnation at ambient temperature. The developed Zn-doped carbon is highly porous (1406.56 m2.g−1), thermally stable and rich in active sites. The Temkin isotherm and the pseudo-second order kinetic model best describe the adsorption of CO2 on the developed material, and the storage capacity is of 370.41 mg g−1 (293 K). Thermodynamic parameters showed favorable, exothermic, and orderly adsorption. Two new isotherms, based on the number of layers formed at the surface, developed by advanced statistical modelling, were adapted and used to understand the mechanism in depth. The analysis of the results showed that CO2 adsorption occurs through the appearance of double layers on the adsorbent surface. Adapted models showed: only one molecule was adsorbed per surface active site, a very low degree of aggregation of CO2 molecules before adsorption and the molecules were adsorbed in a parallel orientation. The activation parameters showed a rapid and physical adsorption with a drop in entropy at the transition state. The mechanisms involved were governed by thermodynamic control with the possibility of easy desorption at high temperature. Zn-doped carbon is an ecological approach to reduce CO2 emissions on the globe.

Adsorption of a Multicomponent Pharmaceutical Wastewater on Charcoal-Based Activated Carbon: Equilibrium and Kinetics

The treatment of pharmaceutical wastewater is a critical environmental challenge, necessitating efficient removal methods. This study investigates the adsorption of a synthetic multicomponent pharmaceutical wastewater (SPWW) containing methanol, benzene, methylene chloride, 4-aminophenol, aniline, and sulfanilic acid onto charcoal-based activated carbon (AC). Batch experiments were conducted to study the effects of pH, contact time, and initial concentrations of the adsorbates. The results show that longer contact time and higher initial concentrations increase the adsorption capacity, whereas pH shows no significant effect on the adsorption capacity at a value of less than 10, eliminating the need for pH adjustment and reducing process costs. The pseudo-second order (PSO) kinetic model best describes the adsorption process, with intraparticle diffusion playing a key role, as confirmed by the Weber and Morris (W-M) model. Six models describing the adsorption at equilibrium are applied to experimental data, and their parameters are estimated with a nonlinear regression model. Among isotherm models, the Langmuir-Freundlich model provides the best fit, suggesting multilayer adsorption on a heterogeneous granular activated carbon (GAC) surface. The maximum adsorption capacity is estimated to be 522.3 mgC/gAC. Experimental results confirm that GAC could effectively treat highly concentrated pharmaceutical wastewater, achieving up to 52% removal efficiency.

Gellan Gum grafted poly acrylic acid hydrogels: Synthesis and adsorption studies

Gellan Gum (GG) grafted poly-acrylic acid (GG-g-pAAc) hydrogels of different composition were synthesized by changing the concentration of GG through free radical polymerization. The hydrogels were characterized through SEM, TGA, and FTIR. The FTIR spectra confirmed the grafting of GG into the network of polyacrylic acid and evidenced the GG-g-pAAc formation. The rough surface nature of the hydrogels was elaborated through SEM analysis provided the information about the materials to be utilized for removal purpose. The thermal stability was confirmed by TGA analysis and the hydrogels were found stable upto a high temperature range. With an efficiency of 96%, Basic Orange-2 dye (BO-2) was successfully removed from wastewater using synthesized hydrogels as an adsorbent. The adsorption parameters were calculated using a number of different kinetic models. According to the findings, the pseudo-second order kinetics model best suited to the kinetics data, while the Langmuir isotherm provided the most comprehensive explanation of the process of adsorption. BO-2 was removed to the greatest extent (257.5 mg/g). Additionally, the results showed that the adsorption process on synthesized hydrogels was exothermic with values of ΔH = −13.2, −219.4 and −12.9 kJ/mol for pAAc, 10%GG-g-pAAc, and 20%GG-g-pAAc respectively. The adsorption process is spontaneous, with negative values of ΔG = −8.2, −214.4 and −7.947 kJ/mol for pAAc, 10%GG-g-pAAc and 20%GG-g-pAAc at 293K, respectively. The adsorption process on synthesized hydrogels showed no dis-orderness with negative values of ΔS = −17.2, −461.16 and −16.42 kJ/mol for pAAc, 10%GG-g-pAAc and 20%GG-g-pAAc, respectively.

Synthetic Zeolite from Blast Furnace Slag (BFS) as an effective sorbent for simultaneous removal of Cadmium and Copper ions

The main challenge for remediation of metals contaminated water is the application of a proper, effective, low-cost material for decontamination of hazardous metal. In this study, low-cost zeolite derived from blast furnace slag (Z-BFS) by a facile hydrothermal method was investigated for adsorption of copper (Cu2+) and cadmium (Cd2+) ions from aqueous solutions. Furthermore, the characteristics of the prepared Z-BFS were evaluated via different techniques (FT-IR, XRF, XRD, SEM and EDX). The results showed the complete removal of Cd2+ and Cu2+ ions. Notably, the maximum adsorption capacity of metals had the trend Cu2+ (103 mg/g) > Cd2+ (80 mg/g) within 20 min at pH 5.5 and 2 g Z-BFS/l. The experimental data fit well with the pseudo-second order kinetic model elucidating that chemisorption is the rate determining step. The isotherms of adsorption were satisfactorily described by the Langmuir isotherm model indicating the monolayer adsorption process. The thermodynamic study demonstrated that adsorption process is endothermic. The obtained results from this study show that Z-BFS proves to be a proper candidate adsorbent for the removal of Cd2+ and Cu2+ ions from contaminated water.

RGO-MoO3 Nanocomposite for superior methylene blue removal by adsorption and photocatalysis

Efficient MoO3 and rGO (0.5,1,2 wt.%)-MoO3 nanosorbent was prepared by facile hydrothermal method. X-ray diffraction (XRD) and Raman spectroscopy techniques confirms the orthorhombic phase. Remarkably in 10 ppm MB dye, complete removal was observed for 1:3, 1:5, 1:3.3, 1:3 (mass of catalyst: volume of dye solution) ratio for pure, 0.5 wt.%, 1 wt.%, 2 wt.% rGO-MoO3 nanocomposite, by merely stirring for one hour without any light exposure. The adsorption mechanism was examined in detail using different models including Langmuir isotherm and Pseudo second-order kinetic model. The composite sample, rGO (0.5 wt.%)-MoO3 is the most efficient nanosorbent whereas rGO (2 wt.%)-MoO3 showed the least adsorption. rGO (2 wt.%)-MoO3 was further used for time dependent study in the presence of UV and in the dark. The presence of UV enhances removal due to the combined effect of adsorption and photocatalysis. Scavenger studies were performed to analyze the mechanism of photocatalysis.

Removal of methylene blue from aqueous solutions by adsorption onto Carpobrotus edulis biomass

The aim of this work is to investigate the influence of an alkaline pretreatment of the Mediterranean plant Carpobrotus edulis on the adsorption capacity toward the dye methylene blue and to estimate the content of soluble organic matter that can be released into the aqueous solution by this biomaterial. The biomaterial used was characterized by SEM-EDX, SS, FT-IR, pHZ, COD and BOD5. Removal of methylene blue (MB) dye by this biomaterial was carried out and the effects of physicochemical factors such as initial pollutant concentration, adsorbent dose, contact time, pH and temperature were investigated. After adsorbent treatment, the soluble organic matter was reduced by 97%, 96%, and 96% for biological oxygen demand, chemical oxygen demand, and organic matter, respectively. Kinetics and equilibrium studies of MB adsorption on the bioadsorbents were fitted with a pseudo-second order kinetic model and a Langmuir model, respectively. The maximum adsorption amount of the modified C. edulis plant was 153.9 mg/g at 298°K. The thermodynamic parameters show that the adsorption process was possible and spontaneous in nature. The adsorption mechanism of MB on the surface of biomaterials was attributed to the electrostatic interaction and H-bonding. The prepared biomaterial (0.016 U$ per gram) was easily regenerated with aqueous HNO3 solution, with a slight decrease in adsorption capacity up to five cycles. The results of Taguchi experimental design and analysis of variance showed that contact time, adsorbent mass and initial concentration are the most important factors affecting the removal efficiency with a contribution of 43.91%, 32.68%, and 22.95%, respectively. The maximum removal capacity of MB dye in optimal operating conditions was 99.39%, which was obtained at the optimum conditions of m = 1 g, pH 4, T = 35 °C, Ci = 1000 mg/L, tc = 5 min. These results confirm previous results obtained with the batch system and show that this absorbent is also promising for the removal of cationic dyes from wastewater.

Artificial neural networks (ANN)-genetic algorithm (GA) optimization on thermosonicated achocha juice: kinetic and thermodynamic perspectives of retained phytocompounds

The extraction of phytocompounds from Achocha (Cyclanthera pedata) vegetable juice using traditional methods often results in suboptimal yields and efficiency. This study aimed to enhance the extraction process through the application of thermosonication (TS). To achieve this, an artificial neural network (ANN) and a genetic algorithm (GA) were utilized to simulate and optimize the process parameters. The study investigated the influence of ultrasonic amplitude (30%–50%), temperature (30 °C–50 °C), and sonication duration (15–60 min) on total polyphenolic content (TPC), total flavonoid content (TFC), antioxidant activity (AOA), and ascorbic acid content (AA). Remarkably, the ANN-GA optimization resulted in optimal TS conditions: an ultrasonic amplitude of 40%, a temperature of 40 °C, and a sonication duration of 30 min. Subsequent analysis of extraction kinetics and thermodynamics across various temperatures (30 °C–50 °C) and extraction times (0–30 min) demonstrated R 2 (0.98821) and χ2 (1.74773) for TPC with activation energy (Ea) 26.0456, R 2 (0.99906) and χ2 (0.07215) for TFC with Ea 26.2336, R 2 (0.99867) and χ2 (0.03003) for AOA with Ea 26.0987, R 2 (0.99731) and χ2 (0.13719) for AA with Ea 26.0984, validating the pseudo second-order kinetic model. These findings indicate that increased temperature enhances the saturation concentration and rate constant of phytochemical extraction.

Surfactant-Modified Bolivian Natural Zeolite for the Adsorption of Cr (VI) from Water

The present study reports the surfactant modification of Bolivian natural zeolite with hexadecyltrimethylammonium bromide (HTDMA-Br) for the adsorption of hexavalent chromium Cr (VI) anions from water. The surfactant-modified natural zeolite was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption/desorption isotherms, and Fourier-transform infrared spectroscopy (FTIR) to analyze the effect of its modification with HTDMA-Br and to verify its charge on the zeolite surface. We report a maximum adsorption capacity of 17 mg/g of Cr (VI) anions, surpassing the findings of some of the previous investigations on surfactant-modified natural zeolites of different geological origins. The analysis of the equilibrium data described the Cr (VI) anions adsorption by Langmuir isotherm and the pseudo second-order kinetic model. In addition, thermodynamics revealed an exothermic adsorption. Furthermore, anion exchange, electrostatic attraction, and chemical reduction were indicated to be dominating sorption mechanisms by X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) characterization techniques.

Development of a sustainable adsorption system based on alginate-encapsulated clay for pharmaceutical pollutant capture in aqueous solution using Box–Behnken methodology

Our study focused on the removal of metformin in aqueous solution. Metformin, an antidiabetic drug, is increasingly detected in wastewater. This study explored the feasibility of using bentonite encapsulated in sodium alginate as a sustainable and efficient sorbent for metformin removal. The adsorbent was characterized by RAMAN, Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), electron-dispersive spectrometer (EDS), and point of zero charge (pHzc). The adsorbent contains various functional groups including hydroxyl (-OH) groups from both bentonite and sodium alginate, carboxyl (-COOH) groups from sodium alginate, and silanol (-Si-OH) groups from bentonite. Batch kinetic studies were carried out as a function of pH, metformin concentration, sorbent amount, and solution temperature. The Freundlich and Langmuir models were used to describe the isotherm data. The maximum monolayer adsorption capacity of the sorbent material was 19,19 mgg−1. The pseudo-second order kinetic model adequately describes the kinetic data. The negative ΔH (−35,253 kJmol−1) confirms an exothermic process, which is further supported by the negative Gibbs energy values (−0,489 to −3,668 kJmol−1), indicating spontaneity and reversibility. Moreover, ΔS° = −0.105 kJ/mol−1.K−1. Response surface methodology was employed to identify the optimal parameters for metformin removal. These parameters were found to be: pH of 6.34, metformin concentration of 5.4 mgL−1, and adsorbent dosage of 3 g L−1 resulted in a remarkable efficiency of 94%. Additionally, bentonite beads (BBs) maintained a significant adsorption capacity for up to three cycles, demonstrating promising reusability. This study highlights that the encapsulation of clay in sodium alginate is a sustainable and effective approach for removing metformin during water treatment.

Engineering of dual recognition functional aptamer-molecularly imprinted polymeric solid-phase microextraction for detecting of 17β-estradiol in meat samples

In this study, an enhanced selective recognition strategy was employed to construct a novel solid-phase microextraction fiber coating for the detection of 17β-estradiol, characterized by the combination of aptamer biorecognition and molecularly imprinted polymer recognition. Benefiting from the combination of molecularly imprinted and aptamer, aptamer-molecularly imprinted (Apt-MIP) fiber coating had synergistic recognition effect. The effects of pH, ion concentration, extraction time, desorption time and desorption solvent on the adsorption capacity of Apt-MIP were investigated. The adsorption of 17β-estradiol on Apt-MIP followed pseudo-second order kinetic model, and the Freundlich isotherm. The process was exothermic and thermodynamically spontaneous. Compared with polymers that only rely on imprinted recognition, non-imprinted recognition or aptamer affinity, Apt-MIP had the best recognition performance, which was 1.30–2.20 times that of these three materials. Furthermore, the adsorption capacity of Apt-MIP for 17β-estradiol was 885.36–1487.52 times than that of polyacrylate and polydimethylsiloxane/divinylbenzone commercial fiber coatings. Apt-MIP fiber coating had good stability and could be reused for more than 15 times. Apt-MIP solid-phase microextraction coupled with high-performance liquid chromatography was successfully applied to the determination of 17β-estradiol in pork, chicken, fish and shrimp samples, with satisfactory recoveries of 79.61 %–105.70 % and low limits of detection (0.03 μg/kg). This work provides new perspectives and strategies for sample pretreatment techniques based on molecular imprinting technology and improves analytical performance.

Efficient removal of cationic dyes using lemon peel-chitosan hydrogel composite: RSM-CCD optimization and adsorption studies

The most prominent and easily identifiable factor of water purity is its colour, which may be both physically undesirable, and act as an alert towards potential environmental contamination. The current study describes the optimum synthesis technique for Lemon Peel-Chitosan hydrogel using the Response Surface Methodology integrated Central composite Design (RSM-CCD). This adsorbent is both environmentally friendly and cost-effective. The hydrogel exhibited a maximal dye removal capacity of 24.984, 24.788, 24.862, 23.483, 24.409, and 24.726 mg g−1, for 10 mg L−1 aqueous medium of Safranin O, Methylene blue, Basic fuchsin, Toluidine blue, Brilliant green and Crystal violet, respectively. The adsorption kinetics and isotherm data suggest that the Pseudo second-order kinetic and Freundlich adsorption isotherm models precisely represent the respective behaviour of all the dyes. The thermodynamic viability of the process is determined by the values of ΔG, ΔH, and ΔS. The probable mechanism of adsorption was the electrostatic interaction between the dye molecules and the hydrogel. The regenerated hydrogel had removal efficiencies of over 80 % even after enduring six cycles. Hence, the exceptional recyclability and utility of the adsorbent show their sustainability for wastewater treatment in textile factories.

Adsorption behavior of Methylene Blue and Rhodamine B on microplastics before and after ultraviolet irradiation

The accumulation of microplastics (MPs) and dyes has attracted extensive attention because of their environmental effects, which will be exacerbated especially after the aging of MPs. This study aimed at investigating the significance of Methylene Blue (MB) and Rhodamine B (RhB) adsorption behavior by PLA (polylactic acid) and PA66 (Polyamide 66) MPs after UV aging. After aging, there was an observed increase in the hydrophilicity, specific surface area, and oxygen content of MPs. The results indicate that aging enhances the adsorption capacity of both PLA and PA66. Furthermore, it is noteworthy that PLA undergoes more significant changes in its physicochemical properties compared to PA66 following aging. The adsorption process conformed the pseudo-second order (PSO) kinetic model and Langmuir isotherm well, and the adsorption capacity followed the sequence of aged-PLA > aged-PA66 > pristine-PA66 > pristine-PLA. Besides, the adsorption of dyes onto the MPs was studied across four variables (pH, salinity, surfactants, and dissolved organic matter). The aforementioned findings collectively demonstrate that the aged MPs still exhibit a higher adsorption capacity than the pristine MPs. In desorption experiments, the desorption efficiency of MB (PLA) was reduced from 35.29 % (P-PLA) to 32.76 % (A-PLA), and the similar trend was observed on other aged MPs. These findings suggest that aged MPs could have a more pronounced ability for dye transportation. These results would contribute to a deeper understanding of the adsorption and desorption behavior of dyes on MPs and their potential health risks.

Adsorption Characteristics of Antibiotic Oxytetracycline on CoFe2O4@Au nanocomposite

Oxytetracycline (OTC) is a widely used broad-spectrum antibiotic for treating bacterial infections in humans and animals. Gold nanoparticles (AuNPs) and cobalt iron oxide (CFO) were combined to create composite magnetic materials designed for the selective adsorption of OTC. The strong affinity of AuNPs for the amine group in the OTC molecule allows for the preferential adsorption of OTC. Simultaneously, the high magnetism of CFO enables the efficient retrieval of materials from the sample solution. The CFO@Au nanomaterials showed an enhanced adsorption capacity of 23.75 mg/g at optimum conditions of pH 7.0; an adsorption time of 90 min, and an adsorbent mass of 0.05g. The adsorption isotherm was in accordance with a Langmuir monolayer model while the kinetic adsorption follows pseudo–second-order kinetic model.. This study provides a simple method for the effective adsorption of OTC as well as a suggestion for the adsorption of other amine-containing substances.

Evaluation of characterization and adsorption kinetics of natural organic matter onto nitric acid modified activated carbon

Natural organic substances (NOM) found in drinking water are a major contributor to disinfectant by-product formation and are potentially toxic to humans. Traditional water treatment techniques may not always effectively treat NOMs. Therefore, an advanced treatment method such as adsorption can be inexpensive, simple and efficient. The selected adsorbent's and the NOMs properties both affect the removal effectiveness of the adsorption method. Activated carbon (AC), which is widely used in real-scale water treatment plants, has been modified and used in recent years In order to oxidize the porous carbon surface, raise its acidic qualities, eliminate mineral components, and enhance the surface's hydrophilic qualities. In this research, AC was modified with nitric acid (M-PAC) and NOM removal was investigated. In addition, it is discussed how the modification with nitric acid changes the adsorbent structure and chemistry. A morphology with smooth and irregular voids was observed as a result of nitric acid modification of the original AC by SEM analysis. The particle size increased from 387.65 nm to 502.07 nm for the M-PAC adsorbent. The FTIR spectrum indicates that structures connected to aromatic rings get formed in the M-PAC adsorbent as a result of the modification. The highest NOM removal for the original powdered activated carbon (PAC), 47%, was observed at 36 hours of contact time. On the other hand, M-PAC adsorbent achieved 40% NOM removal at contact times of 72 hours and above. It was concluded that the pseudo-second order kinetic model better represented NOM adsorption for both adsorbents.

Ionic liquids functionalized chitosan: An effective, rapid and green adsorbent for gold recovery

Thiosulfate has been considered as a more environmentally-friendly alternative to cyanide salts for the extraction of gold from gold ores and the development of affordable, green and efficient adsorbents for the isolation of gold-thiosulfate complex (Au(S2O3)23−) from the leaching solution remains a significant challenge. To address this issue, chitosan, a natural macromolecule, was selected as a carrier and chemically modified with ionic liquids. The ionic liquids modified chitosan showed greater adsorption capacity towards Au(S2O3)23− compared with pristine chitosan. The adsorption of Au(S2O3)23− on ionic liquid modified chitosan followed Freundlich isotherm and pseudo-second order kinetic models, involving an anion-exchange mechanism with liquid film diffusion as the rate-limiting step. The chitosan modified with butylimidazolium-based ionic liquid had an adsorption capacity of 5.0 mg g−1 for gold (10 mg L−1 of gold, pH 6, 2 g L−1 of adsorbent dosage), outperforming other reported adsorbents. The ionic liquid modified chitosan showed a high adsorption efficiency of up to 96.7 % for Au(S2O3)23− in an actual thiosulfate leaching solution with a desorption efficiency of 98.4 %, suggesting that the ionic liquid modified chitosan has the potential to be a eco-friendly, biocompatible and effective adsorbent for the recovery of Au(S2O3)23−.

Recovering ammonium from real treated wastewater by zeolite packed columns: The effect of flow rate and particle diameter

Nitrogen (N) recovery from wastewater is a desirable way to create a (N) neutral society in view of a circular economy approach. Nitrogen recovery from wastewater by employing adsorption columns filled with zeolite can be a very attractive solution. This study assessed the effect of influent flow rates (namely, 1.6 and 2.3 L h−1) and particle diameters (namely, 0.5–1.0 and 2.0–5.0 mm) of zeolite packed in columns on recovering NH4+ from real domestic treated wastewater (RDTWW). Findings revealed that maximum NH4+ recovery can be achieved by using zeolite with the smallest particle diameter (0.5–1.0 mm) and the highest influent flow rate (2.3 L h-1). The maximum NH4+ adsorption rate was 1.2, 21 and 9.8 mg NH4+ kg-1 h-1 after 205, 32 and 35 h of operation. NH4+ adsorption data were analysed by fitting them to both pseudo-first and pseudo-second order kinetic models. The former model best approximated NH4+ adsorption data. Such a result suggested that the amount of NH4+ adsorbed depended solely on the amount of NH4+ in contact with the zeolite surface. Results successfully established the application of zeolite-packed columns in removing NH4+ from real domestic treated wastewater and the effects of process parameters.

Kinetics of Nitrite Adsorption onto a Styrene Divinylbenzene Macroporous Strong Base Polymer

A suitable adsorbent for the treatment of nitrite in wastewater was investigated using a macroporous styrene divinylbenzene strong base polymer for 10−3 M to 6 x 10−3M NaNO2 at room temperature using a batch protocol. The supernatant concentrations were determined rapidly and inexpensively by an electrochemical method. To investigate the sorption mechanism and the rate-determining step, four kinetic models were investigated. The pseudo-second order kinetic model best fit the nitrite adsorption onto the polymer. The highest correlation coefficient (0.9999) and chi square (7.59 x 10−4) values were obtained for 0.046 to 0.276 g L−1 NO2 - which is characteristic of chemosorption. The results demonstrate that the investigated polymer is suitable at room temperature for removing nitrites for water to the legally allowed values for 10−3 M to 1.5 x 10−3 M NaNO2 but dilution is required for higher concentrations.