Experimental Equilibrium Data Research Articles

Chromium adsorption using Sargassum filipendula algae waste from alginate extraction: Batch and fixed-bed column studies

Chromium is a toxic metal widely used in several industrial activities, being frequently found in industrial effluents. The presence of chromium in its soluble ionic form Cr(III) is related to health risks, damage to living beings and to the environment. In this work, the capture of Cr(III) using alginate extraction residue (RES) from the Sargassum filipendula algae was evaluated to investigate the adsorption properties of this waste material. The study steps included batch and continuous adsorption assays, characterizations, and desorption evaluation. The adsorbent residue was not submitted to pre-treatment steps. The investigation of chromium adsorption and the fluid dynamic study are presented in this work. The equilibrium and thermodynamic studies indicated that the uptake of Cr(III) by the RES occurred spontaneously, endothermic, and energetically favorable on a heterogeneous surface with energetically distinct sites, mainly by chemisorption. The Freundlich and Dubinin-Radushkevich, and pseudo-second order models showed better fit to the equilibrium and kinetic experimental data, respectively. In the continuous fixed-bed system, the breakthrough curves showed a smaller mass transfer zone under flow rate and Cr(III) inlet concentration conditions of 0.5 mL/min and 1.0 mmol/L, respectively. The low desorption percentages corroborate the chemical nature of the bonds involved in adsorption. The best result of 67.5% was obtained with the combined eluent of HCl and CaCl2, both at 1 mol/L. SEM and EDX analyzes showed that ion exchange is involved in the adsorptive process with a reduction in the amount of light ions (Na, Ca, Mg, and K) on the RES surface. The characterization analyzes indicated that hydroxyls are the main group involved in the adsorption of metal that occurred on the surface of the RES.

Adsorption of Zn (II) ions from refinery wastewater by sulfuric acid-modified bentonite: Kinetic and isotherm studies

A local bentonite clay from Maghnia (Algeria) was activated with chemical method characterized and tested for its ability to adsorb Zinc (II) from refinery wastewater. Batch experiments were conducted to study the effects of the main parameters such as contact time, initial metal concentration and agitation speed on the adsorption of Zn (II) by local bentonite clay. Experiences have led to the following results: an adsorption rate of the order of 98 % with operating conditions of pH = 4.5, agitation speed of 400 rpm and temperature of 25 ºC. Pseudo-first-order, pseudo-second-order and intraparticle diffusion models were used to analyze the kinetic data obtained at different concentrations. The pseudo-second-order kinetic model agrees very well with the experimental results. In order to determine the best-fit isotherm, in the studied concentration range of Zn(II) at 25 ºC, the experimental equilibrium data were analyzed using tow adsorption isotherm models: Langmuir and Freundlich models, these two models give a good fit.

Thiabendazole Fungicide Adsorption Onto Four Agricultural Soils Collected from the Loukkos Area of Northwestern Morocco

Abstract A serious environmental problem can arise from the presence of pesticides in soils and waters. Hence, in this study we have carried out the adsorption of the Thiabendazole fungicide onto four soils collected from several areas in Morocco as Larache, Laouamra, Ksar kebir and Tlata drissana. Physicochemical properties, elemental analysis, X-ray diffraction (XRD) were investigated to characterise the four selected soils. The experimental equilibrium data were analysed using Langmuir, Freundlich models. The equilibrium data were best described by a Langmuir model for all adsorbents. The maximum estimated adsorption capacity was 0.747 mg∙g−1, 0.751 mg∙g−1, 0.473 mg∙g−1 and 1.083 mg∙g−1, for Larache, Laouamra, Ksar kebir and Tlata drissana soils, respectively.

Adaptive intermolecular interaction parameters for accurate Mixture Density Functional Theory calculations

The description of fluid mixtures molecular behavior is significant for various industry fields due to the complex composition of fluid found in nature. Statistical mechanics approaches use intermolecular interaction potential to predict fluids behavior on the molecular scale. The paper provides a comparative analysis of mixing rules applications for obtaining intermolecular interaction parameters of mixture components. These parameters are involved in the density functional theory equation of state for mixtures (Mixture DFT EoS) and characterize thermodynamic mixture properties in the bulk. The paper demonstrates that Mixture DFT EoS with proper intermolecular parameters agrees well with experimental mixtures isotherms in bulk: Ar+Ne,CO2+CH4,CO2+C2H6 and CH4+C2H6. However, predictions of vapor–liquid equilibrium (VLE) experimental data for CO2+C4H10 are not successful. Halgren HHG, Waldman – Hagler, and adaptive mixing rules that adjust on the experimental data from the literature are used for the first time to obtain intermolecular interaction parameters for the mixture DFT model. The results obtained provide a base for understanding how to validate the DFT fluid mixture model for calculating thermodynamic properties of fluid mixtures on a micro and macro scale.

Applicability of new sustainable and efficient alginate-based composites for critical raw materials recovery: General composites fabrication optimization and adsorption performance evaluation

Based on the 2020 list of raw materials for the EU, there are 30 critical minerals on the critical raw materials list, among which the rare earth elements group is placed. This study demonstrates a viable approach to the increasing possibility of the critical materials recovery through biosorption. The environmentally friendly biosorbents were prepared modifying calcium alginate with biochar and clinoptilolite. Firstly, the optimization procedure was applied for obtaining new biocomposites. After that the adsorption studies of La(III), Ce(III), Pr(III), and Nd(III) ions as a function of solution pH, biosorbent mass, interaction time, initial metal concentration, temperature, and competing ions presence were carried out using the batch mode. The kinetic studies were analyzed using the pseudo-first order, pseudo-second order, Weber and Morris intraparticle diffusion, Boyd as well as Dumwald-Wagner kinetic models. The experimental equilibrium data were fitted using the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. The thermodynamic functions, i.e. ΔG°, ΔH°, and ΔS° were also determined. Importantly, the biocomposite beads were readily regenerated using diluted mineral acids (exemplary 0.1 mol/dm3 HNO3) and moreover, the adsorption effectiveness was very satisfactory even after six adsorption–desorption cycles (97%). New biocomposites as potential sorbents were characterized with ATR/FT-IR and XPS spectroscopy, SEM, EDX, OM and AFM microscopy, nitrogen adsorption, TG/DTG, CHNS, XRD as well as the sieve analysis and pHpzc measurements. After the interactions of the alginate composites with La(III) ions, a possible sorption mechanism was analyzed by ATR/FT-IR, XPS, and EDX spectroscopy.

Biosorption of Cu(II) ions as a method for the effective use of activated carbon from grape stalk waste: RMS optimization and kinetic studies

ABSTRACT This study was undertaken to examine the effect of such biosorption factors as initial Cu(II) concentration, biosorbent dosage, reaction temperature, contact time and mixing speed on the efficiency of removal Cu(II) ions from wastewater using activated carbon from grape stalk waste. In this case, Response Surface Methodology (RSM) was used in conjunction with a Box–Behnken design of experiments to predict the final Cu(II) concentration (CFin ), while considering the previously mentioned biosorption factors. In an attempt to obtain the maximum removal of final Cu(II) concentration, while minimizing energy consumption, the Multi-Response Surface Methodology (MRS) was used. Three possible optimizations were proposed for the maximum elimination of final Cu(II) in this case. The maximum (100 mg/L), minimum (2 mg/L) and intermediate (51 mg/L) values of the study were used for the initial Cu(II) concentration. The optimal values that were reached were 92.21% when the initial copper concentration was 51 mg/L and the activated carbon dose, temperature, mixing speed and reaction time, were, respectively, 0.895 g/L, 20.036°C, 105.313 rpm and 30.181 s. Also, in regard to thermodynamic studies, the experimental equilibrium data provided a good fit using the Freundlich model, whereas the kinetic data were efficiently by the pseudo-second order. These results support the use of grape stalk waste in the production of activated carbon for the removal of Cu(II) ions from water. This could help to improve the economics of treating wastewater.

Adsorption of brilliant green dye onto activated carbon prepared from cashew nut shell by KOH activation: Studies on equilibrium isotherm

Activated carbon from cashew nut shell via a potassium hydroxide (KOH) at 600 °C in an N2 atmosphere and their characteristics using FT-IR, XRD, SEM with EDS, and BET analysis was investigated. The cashew nut shell activated carbon obtained by KOH activation with a CNS/KOH ratio of 1:1 at 600 °C (N2 atmosphere) for 2 h had the highest surface area (407.80 m2/g) as compared to other ratio samples. Amongst, CNS/KOH ratios of 1:1 sample are used for the adsorbent, they are effects of contact time, pH, adsorbent dose, and initial dye concentration on brilliant green (BG) removal efficiency were studied. Moreover, the Langmuir and Freundlich adsorption models consisted utilized to affirm the adsorption isotherms. They are, best fitting for BG experimental equilibrium data was achieved with the Langmuir isotherm, giving a maximum BG adsorption capacity of 243.90 mg/g.

Scavenging of hexavalent chromium from aqueous solution by Macadamia nutshell biomass modified with diethylenetriamine and maleic anhydride

Based on the premise that aqueous anions of hexavalent chromium (Cr(VI)) are capable of electrostatic interaction with cationic and polar active sites, acid-washed Madacamia nutshell biomass was sequentially treated with diethylenetriamine (DETA) and maleic anhydride (MA) to graft poly(diethylenetriamine–co–maleic anhydride). By displaying a new peak at 1685 cm−1 ascribed to amide CO stretching vibrations, Fourier transform infrared spectroscopy highlighted the formation of amide groups through reaction of DETA with carboxyl groups on the biomass surface. Scanning electron microscopic images of the MA-modified biomass displayed polymeric growths attributed to copolymerization of DETA with MA. The polar and ionizable amide and amine groups of the grafted copolymer endowed the adsorbent with Cr(VI) removal capabilities over a wide pH range demonstrated by removal efficiencies between 70.9% and 81.7% in the pH 1.6 to pH 10.0 range for the treatment of 20 mL solutions containing 100 mg L−1 Cr(VI) with 200 mg of adsorbent. Conformity of the adsorption isotherm data to the Freundlich model revealed the heterogeneous nature of the adsorbent surface, which comprised a variety of functional groups capable of interaction with Cr(VI) species in solution. The Sips isotherm model provided the best fit to the equilibrium experimental data, and the adsorption capacity was 779.1 mg g−1 at pH 1.6, room temperature and an adsorbent dosage of 5.0 g L−1. The findings indicate that Cr(VI) adsorption onto diethylenetriamine and maleic anhydride modified Madacamia nutshell biomass is a promising option for Cr(VI) removal from aqueous solutions.

Comparative Evaluation of the Adsorption Performance of Citric Acid-Treated Peels of Trapa natans and Citrullus lanatus for Cationic Dyes Degradation from Water

Various chemicals were explored in chemical combinations with two selected agrowastes in order to optimize, enhance, and improve their biosorption potential for the optimal and effective eradication of noxious, carcinogenic, and malignant cationic and basic dyes from wastewater. In this project, environmentally safe, economic, inexpensive, and widely available peels of Trapa natans (TP) and Citrullus lanatus (CP) were collected, dried, and pretreated with citric acid, revealing promising results. FT-IR and SEM characterizations of chemically changed biosorbents (C-TP and C-CP) have evidenced the presence of more secondary adsorption sites on their surfaces. These acid-modified biosorbents were employed to eliminate the hazardous and toxic basic dyes such as Rhodamine B (RAD) and Brilliant Green Dye (BLG) in batch mode processing. The Langmuir model was best fitted to equilibrium experimental data as compared to Freundlich and Temkin isothermal mathematical models with Qmax of 15.63 and 27.55 mg/g for RAD using C-TP and C-CP, respectively, whereas, for BLG on C-TP and C-CP, it was 128 and 189 mg/g, respectively. Therefore, the mechanism is related to chelation and ion exchange modes between adsorbate molecules and adsorbent surfaces, leading to homogeneous and monolayer adsorption and following pseudo-2nd-order kinetics in the best way. Thermodynamic parameters such as ΔG0, ΔS0, ΔH0, and ΔE0 are determined statistically for the adsorption performance of both novel chemically mutant biosorbents, which reflect that biosorption mechanisms are exothermic as well as spontaneous.

Removal of Cylindrospermopsin by Adsorption on Granular Activated Carbon, Selection of Carbons and Estimated Fixed-Bed Breakthrough

Climate change and the increase in the availability of nutrients in aquatic environments have increased the occurrence of cyanobacterial blooms which can produce cyanotoxins such as cylindrospermopsin (CYN). Activated carbon adsorption have been proved to be efficient for CYN removal. In the present study, a carbon with high CYN adsorption capacity was identified between two granular activated carbons. For this carbon was estimated the operating time of a full-scale granular activated carbon column under different empty bed contact times (EBCT). The fixed-bed breakthrough was estimated using the Homogeneous Surface Diffusion Model (HSDM). Wood carbon showed greater capacity to remove CYN. The experimental equilibrium data best fitted Langmuir isotherm model, in which wood carbon had a maximum adsorption capacity of 3.67 μg/mg and Langmuir adsorption constant of 0.2791 L/μg. The methodology produced satisfactory results where the HSDM simulated the fixed-bed breakthrough with a coefficient of determination of 0.89, to the film diffusion coefficient (Kf) of 9 × 10−6 m/s and surface diffusion coefficient (Ds) of 3 × 10−16 m2/s. It was observed that the increase in EBCT promotes a reduction in the carbon use rate. The best carbon use rate found was 0.43 kg/m3 for a EBCT of 10 min and breakthrough time of 183.6 h.

Novel metal based nanocomposite for rapid and efficient removal of lead from contaminated wastewater sorption kinetics, thermodynamics and mechanisms

A sol–gel method was utilized to prepare a novel nanocomposite adsorbent (nMgO/bentonite) and was tested for Pb(II) removal from aqueous solutions. The produced nanocomposite was investigated using, SEM–EDX, XRD, and FTIR analyses before and after Pb adsorption. Adsorption equilibrium and kinetic experiments were run in batch system under different conditions of pH, adsorbent dose, competitive cations, contact time and temperature. The results exhibited rapid Pb(II) adsorption by the nanocomposite in the first five min. Experimental lead adsorption equilibrium and kinetics data fitted well to Langmuir and power function models, respectively as indicated from the lowest standard error (SE) values. The calculated Langmuir maximum adsorption capacity (qmax) value of nanocomposite (75 mg g−1) was 4.5 times higher than that of bentonite (16.66 mg g−1). Moreover, the highest quantity of Pb(II) uptake was achieved at temperature of 307 K and pH 9. The Langmuir sorption capacity of the nanocomposite for Pb(II) increased from 75 to 145 mg g−1 with increasing temperature from 287 to 307 K. The thermodynamic parameters of Pb(II) adsorption by the nanocomposite affirm the spontaneous and endothermic nature of the adsorption process. Lead adsorption mechanisms by the nanocomposite were proposed and discussed.

Physicochemical, structural, and adsorption properties of chemically and thermally modified activated carbons

In this work, granular activated carbon (GAC1240W Norit N.V.) was chemically and thermally modified to diverse its acid-base character. The main aim of this work was to assess the efficiency of surface modifications of activated carbons (ACs) concerning studying the differentiation of their affinity towards aromatic organic compounds of various properties. For this purpose, the comprehensive characteristics of oxidized activated carbon (AC-OX) and oxidized thermally modified carbons at 180, 280, 380, 480, 640, and 800 °C (AC-OX, AC-OX-180, 280, 380, 480, 640, and 800) were analyzed using several analytical techniques:low-temperature nitrogen sorption (porosity characteristics), potentiometric titration of suspension (SPT) (acid-base properties), X-ray photoelectron spectroscopy (XPS) (quality and quantity analysis of elements), thermal analysis (TA) coupled with mass spectrometry (MS) (materials thermal stability, identification of gaseous products emitted during thermal decomposition). To verify the applicability of adsorbents for removing selected organic compounds, the equilibrium and kinetic experimental data were measured and analyzed by applying various equations and models.

Doxycycline Adsorptive Interaction with Mesoporous MCM-41: Kinetic and Isotherm Modelling with Thermodynamics

Antibiotics are bio-accumulating and persistent. its inappropriate disposal can affect human health and aquatic fauna. Development of antimicrobial resistance has been announced as one of the top ten threats to global health in 2019. In this study, Doxycycline adsorption on to MCM-41 (not reported earlier) was studied. Adsorbent dose (m), Doxycycline solution pH, adsorption time (t) and temperature (T) were considered as process parameters, and %Doxycycline removal and adsorption capacity were measured as responses of the adsorption. Parameters (m, pH and t) interaction, modelling and optimization for %Doxycycline removal and adsorption capacity was performed using Box Behnken Design. Based on this, a suitable model equation and adsorption mechanism was suggested. At optimized parameters, kinetics and adsorption rate controlling mechanism was studied. Further, various isotherm models (Freundlich, Langmuir and Redlich-Peterson) were studied to represent the adsorption equilibrium experimental data. the optimum process parameters were found to be pH = 7.3, m = 0.02 g/L and t = 20 min. At optimized parameters, very high %Doxycycline removal of 99% with 2425 mg/g adsorption capacity was observed (max 835.5 mg/g adsorption capacity for Doxycycline is reported in literature). Thermodynamics study revealed enthalpy (ΔH°) = 23.02 kJ/mol confirming DCL physisorption on MCM-41.

Application of biorefinery by-product of Nigella sativa L. herb for green treatment of synthetic dye impurity in aquatic environment: a circular economy based approach to water purification

In this work, the performance of residual biomass of Nigella sativa L. plant from the process of bio-oil production toward the green removal of synthetic dye pollution from aquatic medium was systematically studied for the first time based on the circular economy strategy. The characterization of material was performed using Electron Microscope of Scanning and Infrared Spectrometer of Fourier Transform. The main process variables like pH, biosorbent amount, synthetic dye loading, and contact duration were optimized by the batch biosorption experiments to achieve the maximum remediation yield. The analyses of kinetics, equilibrium, and thermodynamics were conducted to understand the possible mechanism of purification. The experimental dynamics and equilibrium data were in better agreement with the pseudo-second-order and Langmuir models. For the targeted model synthetic dye compound (C. I. Basic Red 46), the biosorption capacity was obtained as 136.2 mg g−1 at the optimized conditions of pH of 8, biosorbent amount of 10 mg (100 mg L−1), synthetic dye loading of 30 mg L−1, and duration of 360 min. The treatment process was favorable, spontaneous, and physical. The characterization operation showed that the dye molecules were restrained on the rough surface of biosorbent. This study reveals that the reuse of herbal oil refinery residue as a biosorbent can present an economic, efficient, and eco-friendly option for the remediation of synthetic dye pollution in aqueous medium.

Equilibrium Biosorption of Zn2+ and Ni2+ Ions from Monometallic and Bimetallic Solutions by Crab Shell Biomass

This work explored the technical feasibility of using crab shell (CS) as a promising, low-cost biosorbent to individually and simultaneously remove Zn2+ and Ni2+ from aqueous solutions. It was found that in both monometallic and bimetallic systems, Zn2+ and Ni2+ biosorption by CS was strongly dependent on the solution pH, with the optimum biosorption occurring at a pH of 6.0 for both heavy metals. The obtained isotherms for Zn2+ and Ni2+ biosorption onto CS in monometallic and bimetallic systems demonstrated that CS has a higher affinity for Zn2+ than for Ni2+. The experimental equilibrium data for the bimetallic system revealed that when one heavy metal is present in the system, there is a decrease in the equilibrium biosorption capacity for the other heavy metal; therefore, the combined action of Zn2+ and Ni2+ was antagonistic. The Sips and Redlich–Peterson isotherm models best fitted the equilibrium biosorption data for Zn2+ and Ni2+ in the monometallic systems, while the modified Sips model best fitted the binary biosorption equilibrium data. DRIFTS analyses indicated that carbonate ion, chitin, and proteins are mainly involved in the biosorption of Zn2+ and Ni2+ by CS from aqueous solutions, as confirmed using a range of analytical techniques.

Simultaneous adsorption of three anionic dyes at neutral pH from their individual and multi-component systems on a CTAB modified Pennisetum glaucum based carbon nanotube green composite: Adsorption mechanism and process optimization by Box-Behnken design model

In this study, an efficient, cost-effective, and environmentally friendly cetyltrimethylammonium bromide (CTAB) surfactant modified Pennisetum glaucum (RM) based composite containing 0.5% functionalized carbon nanotube (CNT) has been developed. The main aim of this study was to assess and optimize the synthesized adsorbent used for the removal of Reactive Red 35 (RR), Coomassie Brilliant Blue R-250 (BB), and Eriochrome Black-T (EBT) dyes in their single, binary, and ternary solutions by employing the Box Behnken Design (BBD) under Response Surface Methodology (RSM). According to the analysis of variance (ANOVA), the proposed quadratic model was significant, with a good correlation between the experimental and predicted data of the desired response, and it can be used to navigate the design space. Furthermore, the batch adsorption experiments of anionic dyes were conducted to discuss the bio-sorption kinetics, thermodynamics, isotherms, and possible adsorption mechanisms involved in single and multi-component systems were accordingly proposed.The equilibrium experimental data was best fitted to the monolayer Langmuir adsorption isotherm model, giving a maximum adsorption capacity of 210.97, 259.07, and 289.85 mgg−1 for RR, BB, and EBT dyes, respectively, in individual component systems, at neutral pH conditions, and a pseudo-2nd-order kinetic model best followed the kinetic data. The modified Langmuir model was used to study the interactions among the dye molecules in multi-component systems, and the observed results indicate the synergistic and competitive behaviour of dyes. A regeneration study of the exhausted bio-composite evaluated the renewal efficiency. This requires simple processing methods and little expense than other adsorbents fabricated from costly materials. Ultimately, the CTAB treated Pennisetum glaucum based CNT composite could be adopted as an efficient, cost-effective, and environmentally benign green biosorbent.

Effective Carbon/TiO2 Gel for Enhanced Adsorption and Demonstrable Visible Light Driven Photocatalytic Performance.

A new strategy to synthesise carbon/TiO2 gel by a sol–gel method is proposed. Textural, morphological, and chemical properties were characterised in detail and the synthesised material was proven to be an active adsorbent, as well as a visible light photocatalyst. Homogenously distributed TiO2 is mesoporous with high surface area and, hence, exhibited a high adsorption capacity. The adsorption equilibrium experimental data were well explained by the Sips isotherm model. Kinetic experiments demonstrated that experimental data fitted a pseudo second order model. The modification in electronic structure of TiO2 resulted in a reduced bandgap compared to commercial P25. The absorption edge studied through UV-Vis shifted to the visible region, hence, daylight photocatalytic activity was efficient against degradation of MB dye, as an example pollutant molecule. The material was easily removed post treatment, demonstrating potential for employment in industrial water treatment processes.

Facile synthesis, characterization and application of magnetic Fe3O4-coir pith composites for the removal of methyl violet from aqueous solution: Kinetics, isotherm, thermodynamics and parametric optimization

Dyes are commonly used in coloring clothes; in fertilizers, as anti-freezers, as detergents and so on. The use of such dyes has carcinogenic and genotoxic effects. These dyes require proper removal from the environment. Subsequently, a green and low-cost approach promises to adhere to sustainability of the environment while maximum removal of these toxic dyes. The present study describes removal of methyl violet (MV) dye by adsorption process magnetically separable Fe3O4-coir pith composites. The study was evaluated in batch system taking the optimum conditions as: pH: 7, contact time: 12 h, stirring speed: 200 rpm, concentration of dye: 100 mg/L, adsorbent weight: 3 g/L, temp.: 308 K. The central composite design approach of response surface methodology in design-expert software showed maximum removal efficiency (>98%) for optimal parameters. The experimental equilibrium data fitted reasonably well to Langmuir isotherm model. ANOVA analysis along with Fisher's statistical test was also performed to validate the model. The predicted model was at par with the experimental values with adjusted R2 of 0.9914. A thorough investigation of kinetic (RPseudo second order2 = 0.99; RPseudo second order2=0.97;Rintra−particle diffusion2=0.98), thermodynamic, adsorption isotherm (RLangmuir isotherm2=0.997RFreundlich isotherm2=0.99 and eco-toxicological characteristics were performed for proper evaluations of the properties as well as sustainability of the adsorbent material. The whole research indicated encouraging potential of the developed material for adsorption, reusability and sustainability in applications for industrial scale wastewater treatment.

Experimental and computational investigation of two-component mixtures for the alkyl (ethyl, propyl and butyl) oleate in supercritical carbon dioxide

The main aim of the current study is to understand of solubility curve in solvents at supercritical conditions and including thermodynamics modeling, as well as van der Waals-type models. A thermodynamic approach was commissioned to predict the solubility of a model alkyl oleate monomers in supercritical carbon dioxide (Sc-CO2). Furthermore, the experimental data of phase equilibrium were employed here which are based on measuring the solubility of alkyl oleate monomers in CO2 at supercritical conditions, and the experiments were performed using common synthetic-type method. The thermodynamic equilibrium properties for the two-component mixture of ethyl oleate, propyl oleate and butyl oleate in Sc-CO2 were reported. Bubble (dew)-point data determinations were performed through the synthetic method from various temperatures T= (313.2 to 393.2) K and pressures p = (3.07 to 31.71) MPa. The obtained results indicated that the phase equilibria of Sc-CO2 were found to increase monotonically with the augmented of system temperatures and mole fraction of (ethyl oleate, propyl oleate and butyl oleate) in binary (solute + solvent) mixtures. The solubility curve of ethyl oleate, propyl oleate, and butyl oleate in the ethyl oleate + Sc-CO2, propyl oleate + Sc-CO2, and butyl oleate + Sc-CO2 models rises as the temperature raises at a persistent pressure. The ethyl oleate + Sc-CO2, propyl oleate + Sc-CO2, and butyl oleate + Sc-CO2 models show type-I phase behavior. Moreover, laboratory investigated results of these systems were adequately compared with the P-R EOS. RMSD for the ethyl oleate + Sc-CO2 [κij = 0.060, ηij=-0.030], propyl oleate + Sc-CO2 [κij = 0.062, ηij=-0.030], and butyl oleate + Sc-CO2 [κij = 0.061, ηij=-0.030] models using 2 factors determined at 353.2 K were 4.06 %, 7.43 %, and 5.06 % correspondingly. Also, RMSD of ethyl oleate + Sc-CO2, propyl oleate + Sc-CO2, and butyl oleate + Sc-CO2 systems predicted by adjusted factors at each temperature was 8.46 %, 9.43 %, and 6.29 %, respectively.

Removal of ivermectin from aqueous media using commercial, bentonite-based organophilic clay as an adsorbent

AbstractThe worldwide use of pharmaceuticals is of concern to those researchers who develop new techniques for the removal of these compounds from the aquatic medium. The objective of the present work was to characterize and evaluate the performance of a commercial, bentonite-based organophilic clay in removing ivermectin from aqueous solution. The adsorbent was characterized by nitrogen physisorption, thermogravimetric-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). Batch-scale adsorption experiments were performed to evaluate the kinetics, isotherms, thermodynamics and effect of pH on removal of this drug and reuse of the clay. The bentonite has a small specific surface area with an irregular surface. The Elovich kinetic model fits the experimental data better than other models, indicating that chemisorption contributes to drug removal in this case. The Langmuir and Sips isothermal models best fit the experimental equilibrium data. The process was shown to be favorable (ΔG°ads<0), endothermic (ΔH°ads>0), with an increase in the degrees of freedom at the solid–liquid interface (ΔS°ads>0), and with characteristics of a physical-chemical adsorption process (Ea = 11.065 kJ mol–1) under the study conditions. Adsorption was favored at the natural pH of the solution and the organophilic clay could be regenerated with water and reused in consecutive adsorption cycles. The amount of ivermectin adsorbed on the organophilic clay ranged from 1.78 to 3.88 mg g–1. The organophilic clay was shown to be a cost-effective potential adsorbent for ivermectin-contaminated water-treatment applications.