Resin Dosage Research Articles

Adsorption of Cu(II) ions from aqueous solutions using ion exchange resins with different functional groups

AbstractThe extraction of heavy metals from industrial effluents using efficient adsorbents is crucial for wastewater treatment and beneficial for metal recycling. In this study, the removal of Cu(II) from an acidic solution by commercial resins Dowex G‐26 and Puromet™ MTS9570 was investigated. The influences of contact time, solution concentration, pH, temperature, and a resin dosage on the adsorption process were studied with batch technique. The optimum adsorption conditions were obtained at a concentration of 1100 mg/L Cu, contact time of 30 min, pH 3.5, and resin dosage of 0.025 g/ml for the removal of 99.9% and 90% of copper ions by G‐26 and MTS9570, respectively. The experimental data of copper adsorption were analyzed using the Langmuir, Freundlich, and Temkin isotherm models. The highest metal uptakes of 41.67 and 37.70 mg/g were observed for Dowex G‐26 and MTS9570, respectively. It was found that both resins had higher adsorption capacities than the substances reported in the literature. The adsorption kinetic studies showed that the copper adsorption process could be better described by the pseudo‐second order model. Adsorption occurs spontaneously under endothermic conditions, which indicates the endothermic nature of the process.

Synthesis and characterization of novel polymeric-sepiolite composite resin for effective water softening: applications in batch and column adsorption

ABSTRACT A novel polymeric composite resin, based on sepiolite and polyacrylonitrile (Sep/PAN), was synthesised and characterized using Fourier transform infrared spectrometry (FTIR), X-ray diffraction spectrometry (XRD), thermogravimetric analysis (TGA), and scanning electron microscope-energy dispersive X-ray (SEM-EDX). The thermal, morphological, and surface properties of the composite were improved by the presence of Sep. Furthermore, the prepared composite was applied for the removal of water hardness using both batch and column techniques. The effects of parameters, such as Sep content ratio, contact time, composite dosage, and hardness concentration, were studied. The Sep/PAN composite increased the removal efficiency of water hardness by 26% when compared to the pure Sep. For synthetic water samples, the Sep/PAN showed 100% removal efficiency within 60 min, with an optimum composite resin dosage of 3 g per 1 L of hard water and a corresponding experimental adsorption capacity of 316 mg/g. The adsorption results were observed to fit a pseudo-second-order kinetic model and a Freundlich adsorption isotherm model. Correspondingly, the column breakthrough capacity of the prepared composite resin was studied under various operating conditions. The composite performance for hardness removal from natural water samples, with a total hardness of 237-680 mg CaCO3/L, was assessed. The results demonstrated an efficiency range of 81-100%. These results suggested potential applications of the Sep/PAN composite for water softening, circumventing some of the difficulties in using clay alone while providing higher levels of efficiency.

Recovery of Lead (II) Ions from Aqueous Solutions Using G-26 and MTS9570 Resins with Sulfonic/Phosphonic Functional Groups

This study presents Pb(II) recovery/removal from water solutions using two different commercial ion-exchange resins, i.e., Dowex G-26 with sulfonic functional group and Puromet™ MTS9570 with sulfonic and phosphonic functional groups. Overall, 100% Pb(II) recovery/removal by both resins was obtained at solution pH 3.5, resin dosage 25 g/L, adsorption time 30 min, room temperature, and initial Pb(II) concentration 1000 mg/L. Langmuir, Freundlich, and Temkin isotherms were used to model the experimental data. The mechanism of the adsorption process was investigated using kinetic and thermodynamic models. The experimental data fitted very well with the pseudo-second-order kinetic model, and thermodynamic analysis showed that the adsorption of Pb(II) from acidic solution onto both resins was a spontaneous and endothermic process in nature. Regeneration of the resins loaded with lead ions was tested for three cycles to evaluate the resin recyclability. Good stability of G-26 and performance degradation of MTS9570 resin was observed.

Synthesis, characterization of functionalized grafted cellulose and its environmental application in uptake of copper (II), manganese (II) and iron (III) ions

Acrylonitrile grafted cellulose was functionalized with hydrazine hydrate to form Cell-NH-NH2. IR, TGA, TEM, XRD, and elemental analyses were used to elucidate the obtained Cell-NH-NH2. It was applied as an effective adsorbent in elimination of various divalent metal ions from aqueous media, including copper (II), manganese (II), and iron (III). The batch technique was used to investigate many parameters, including pH, resin dosage, contact time, and the initial metal ions concentration. The maximum removal percent and uptake capacity were of 92, 93 and 93.8% and 5.9, 5.8 and 5.7 mgg−1 for Cu(II), Mn(II)) and Fe(III) ions, respectively. The results showed that with using 0.05 g of adsorbent, most of Cu(II) and Mn(II) were removed at pH value = 6 and at pH = 5 for Fe(III). Cell-NH-NH2 had fast kinetics; more than 50% of the adsorbed quantity was reached within the first 10 min (61.49, 56.02, and 54.26% for Cu(II), Mn(II), and Fe(III)), respectively. The capacity of adsorbent was reduced with raising the adsorbent dose and temperature. The maximum uptake yields and values of the isotherm parameters were calculated by applying the Langmuir, Dubinin-Radushkevich, and Freundlich isotherms. The low mean adsorption energy values (1.84–5.89 kJ/mol) displayed physisorption technique. The thermodynamic parameters were determined to be exothermic (negative ∆H°), spontaneous (negative ∆G°) and a high-ordered system (negative ∆S°). Acidified thiourea was used as an eluent for six cycles to regenerate the loaded adsorbent and make it suitable for further use. Elution efficiency was found to be 95–99%. Cell-NH-NH2 adsorption capability was examined using a sludge and water pump real samples with multi-metal ion concentrations.

The removal of toxic metals from liquid effluents by ion exchange resins. Part XVII: Arsenic(V)/H+/Dowex 1x8

The performance of anionic exchange resin Dowex 1x8 in the removal of arsenic(V) from aqueous solutions was investigated. Batch experimentation was carried out under different variables, including, the stirring speed applied on the system, the pH of the aqueous solution, resin dosage and temperature. Due to the characteristic speciation of arsenic(V) in aqueous phases, the removal of this element from the solution is negligible at highly acidic or alkaline pH values, but it is possible at the aqueous pH range of 4-9, thus, both HAsO42- and H2AsO4- species are loaded onto the resin. At the above pH range, arsenic(V) uptake is exothermic. Different models are fitted to the experimental values in order to gain knowledge about this ion exchange system: rate law, kinetics and solute loading onto the resin. This loading is compared against the yielded using non-functionalized multiwalled carbon nanotubes. The elution step is investigated using acidic solutions (HCl medium) as eluent, from the eluted solutions, arsenic(V) can be efficiently stabilized as ferric or calcium arsenates.

Kinetics and Adsorption Equilibrium Study of Free Fatty Acid (FFA) from Crude Palm Oil (CPO) on Anionic Resin

Crude Palm Oil (CPO) is obtained from palm fruit extraction. Free Fatty Acid (FFA) level is one of the most important parameters to determine the CPO quality. The standard FFA level in the industry is less than 5%. In the palm oil processing industry, FFA levels in CPO have been minimized through vacuum distillation processes. However, due to the emulsified water in oil and long departure waiting time in port, FFA levels in CPO raise to above 5% resulting in lower quality and selling price. This study has developed a novel approach to mitigate this problem by using anionic resin as an adsorbent to decrease the FFA level. We investigated the kinetics and equilibrium behavior of FFA adsorption in CPO on the anionic resin. The adsorption was conducted in several resin dose (17.5%; 25%; 33.33%; 43%). The kinetic study shows that the FFA adsorption kinetics on anionic resin follows the Pseudo-second-order rate model with the value of k2 vary between 2.1034×10-4 – 1.7375×10-3 and the qe value is in the range of 103.627 - 163.880 (mg/g). The equilibrium study shows that the Freundlich isotherm model is the fittest. The Kf values are obtained between 4.16-15.02, and the n values are in the range of 1.62-2.05. The thermodynamic observation was also involved in this study. The value of and are 28.59 kJ/mol and 91.25 J/mol/K respectively. The results show that the reaction is endothermic, spontaneous, and feasible.

Removing Calcium Ions from Remelt Syrup with Rosin-Based Macroporous Cationic Resin.

Mineral ions (mainly calcium ions) from sugarcane juice can be trapped inside the heating tubes of evaporators and vacuum boiling pans, and calcium ions are precipitated. Consequently, sugar productivity and yield are negatively affected. Calcium ions can be removed from sugarcane juice using adsorption. This paper described the experimental condition for the batch adsorption performance of rosin-based macroporous cationic resins (RMCRs) for calcium ions. The kinetics of adsorption was defined by the pseudo-first-order model, and the isotherms of calcium ions followed the Freundlich isotherm model. The maximal monolayer adsorption capacity of calcium ions was 37.05 mg·g−1 at a resin dosage of 4 g·L−1, pH of 7.0, temperature of 75 °C, and contact time of 10 h. It appeared that the adsorption was spontaneous and endothermic based on the thermodynamic parameters. The removal rate of calcium ions in remelt syrup by RMCRs was 90.71%. Calcium ions were effectively removed from loaded RMCRs by 0.1 mol·L−1 of HCl, and the RMCRs could be recycled. The dynamic saturated adsorption capacity of RMCRs for calcium ions in remelt syrup was 37.90 mg·g−1. These results suggest that RMCRs are inexpensive and efficient adsorbents and have potential applications for removing calcium ions in remelt syrup.

Adsorption and removal studies of cadmium ion onto sulphonic/phosphonic acid functionalization resins

AbstractCadmium is a persistent bio‐accumulative toxic metallic element, which causes hazardous impacts on living species, water, and the environment. This paper presents the study of cadmium ion removal from aqueous solutions in batch experiments using 22 ion exchange resins with different functional groups. It was found that Dowex G‐26 resin with a sulphonic functional group and Puromet™ MTS9570 resin with sulphonic and phosphonic functional groups had excellent performance for Cd (II) ion removal. The effects of resin dosage, adsorption time, initial concentration of cadmium, and initial pH of solution on cadmium removal were investigated systematically using Dowex G‐26 and Puromet™ MTS9570 resins. Maximum cadmium removal rates of 99.2% and 98.9% were achieved for G‐26 and MTS9570, respectively, at an initial cadmium concentration of 1000 mg/L, an initial solution pH of 5.0, an adsorption time of 30 min, and a 0.01 mg/L resin dosage for G‐26, and a 0.025 mg/L resin dosage for MTS9570. The ion‐exchange adsorption process was fast, and it reached equilibrium after 30 min of adsorption. The results obtained show that both resins performed well for the removal of Cd (II) ions from weakly acidic solutions. Langmuir, Freundlich, and Temkin isotherms models were employed to investigate and understand the adsorption characteristics. The results showed that the studied adsorption processes fitted well to the Langmuir adsorption isotherm. From the Langmuir adsorption isotherm, the maximum adsorption capacities of Cd (II) were found to be 78.125 and 51.020 mg/g for G‐26 and MTS9570, respectively. This research provides an efficient systemic approach for cadmium ion removal from aqueous solutions.

Viscosity, mechanical properties and phase-separated morphology of waterborne epoxy asphalt

This study aimed to investigate the viscosity, mechanical properties, and phase-separated morphology of waterborne epoxy asphalt (WEA). Adopting waterborne epoxy resin as the modifier, the rigid and flexible WEA with admixture amounts of 10 wt%, 20 wt% and 30 wt% were prepared by first emulsifying and then modifying. The Brookfield viscosity test and the tensile test were conducted to evaluate the viscosity, tensile strength, and ductility of WEAs. The phase-separated morphology of WEA were analyzed using the laser scanning confocal microscopy (LSCM) and image analysis software Image-Pro Plus. It was found that the viscosity of most WEAs increased with time. The best compaction time for WEA is 4–5 h after curing. With the addition of waterborne epoxy resin, WEA gradually changed from a continuous asphalt phase and a dispersed phase of cured epoxy resin to a three-dimensional network structure with the two-phase structure of asphalt and cured epoxy. This promoted a substantial increase in the viscosity and tensile strength of rigid WEA and a decrease in ductility. However, due to the rigidity of the cured products of flexible epoxy resin, the ductility of flexible WEA was significantly improved. Nevertheless, the increase in viscosity and tensile strength of flexible WEA was lower than that of rigid WEA. Different types of emulsifiers also had different effects on the viscosity, mechanical properties, and phase-separated morphology of WEA. The area ratio and average diameter of epoxy resin particles can be used as microscopic indicators to evaluate the influence of epoxy resin dosage on the viscosity, tensile strength, and ductility of WEA. Based on the macro and micro performance of WEA, the findings recommend A3T1 rigid WEA with 10–30 wt% waterborne epoxy resin and LBP1 rigid WEA with 30 wt% waterborne epoxy resin.

Separation of Lead and Copper Ions in Acidic Media Using an Ion-Exchange Resin with a Thiourea Functional Group

This research studied the selective separation of lead and copper ions in acidic solutions using Puromet MTS 9140 resin with a thiourea functional group. The effects of operation parameters, that is, resin dosage, solution pH, ion exchange time, metal concentration, and temperature, on metal ion exchange were investigated using batch-test protocols. Ion-exchange experimental data were analyzed with Langmuir, Freundlich, and Temkin models. The results demonstrate that the MTS 9140 resin has ion-exchange selectivity for copper ions over lead ions. The ion-exchange recovery of Cu exceeded 95%, while Pb coloading was under 19% with MTS 9140 resin dosage of 0.070 g/mL in the pH range of 2.5 to 4.5. The kinetic studies showed that the ion exchange process could be better described by the pseudo-second-order model for lead and copper ions. The temperature dependence indicates the endothermic nature of the ion-exchange process. The resin also showed potential application as an effective adsorbent for removing heavy metal ions in water or wastewater treatment.

Chromatographic separation and recovery of Zn(II) and Cu(II) from high-chlorine raffinate of germanium chlorination distillation

An anion-exchange-based chromatographic separation approach was developed to selectively recover zinc and copper from the high-chlorine raffinate generated in the process of germanium chlorination distillation using 717 resins based on the coordination difference between Zn2+/Cu2+ and Cl–. The theoretical calculation and spectroscopic analyses suggested that the coordination between Zn2+ and Cl– is much stronger than that between Cu2+ and Cl–, and the Cl– concentration significantly affects Zn(II) and Cu(II) species. The factors involving Cl– concentration, resin dosage, shaking speed, and temperature were investigated to determine the optimal condition, and the maximum separation factor of Zn/Cu reached as high as 479.2. The results of the adsorption isotherms, adsorption kinetics, SEM, FTIR, and XPS analyses indicated that the process followed the monolayer uniform chemisorption. Through the continuous adsorption experiments, Zn(II) and Cu(II) in the high-chlorine raffinate were separately recovered, allowing the reuse of residual waste acid and germanium.

Poly(vinylbenzyl Pyridinium Salts) as Novel Sorbents for Hazardous Metals Ions Removal.

Novel efficient complexing resins—poly(vinylbenzyl pyridinium salts) fabricated through poly(vinylbenzyl halogene-co-divinylbenzene) quaternization of N-decyloxy-1-(pyridin-3-yl)ethaneimine and N-decyloxy-1-(pyridin-4-yl)ethaneimine—were tested as adsorbents of Pb(II), Cd(II), Cu(II), Zn(II), and Ni(II) from aqueous solutions. The structure of these materials was established by 13C CP-MAS NMR, X-ray photoelectron spectroscopy, elemental analysis, and Fourier transform infrared spectroscopy, as well as thermogravimetric and differential thermal analyses. The textural properties were determined using scanning electron microscopy and low-temperature N2 sorption. Based on the conducted sorption studies, it was shown that the uptake behavior of the metal ions towards novel resins depended on the type of functionalities, contact time, pH, metal concentrations, and the resin dosage. The Langmuir model was investigated to be the best one for fitting isothermal adsorption equilibrium data, and the corresponding adsorption capacities were predicted to be 296.4, 201.8, 83.8, 38.1, and 39.3 mg/g for Pb(II), Zn(II), Cd(II), Cu(II), and Ni(II), respectively. These results confirmed that owing to the presence of the functional pyridinium groups, the resins demonstrated proficient metal ion removal capacities. Furthermore, VBBr-D4EI could be successfully used for the selective uptake of Pb(II) from wastewater. It was also shown that the novel resins can be regenerated without significant loss of their sorption capacity.

Fluoride ion removal using amine modified polymeric resin: Batch and column studies

The treatment of water containing pollutants by the solvent impregnated resin was found to be an effective method and caught the attention of the researchers. Here, the study was focused on the separation of fluoride ions from water using Aliquat-336 modified Amberlite XAD-4 resin in batch and continuous mode of operation. Batch studies were conducted to see the impact of resin dosage (2.5–27.5 g/L), pH (2–12), time (0–120 min), temperature (298–323 K), and initial fluoride concentration (1.8–13 mg/L) on the capability of the resin. Freundlich isotherm (R2 = 0.986) and pseudo-second-order model (R2 = 0.999) matched the equilibrium and kinetic data, respectively. Column experiments were designed using the two-level full factorial design considering inlet fluoride concentration (5–10 mg/L), volumetric flow rate (3–5 mL/min), and length of the bed (3–5 cm) as the design variables, and their effect was studied on the breakthrough time, saturation time, and effluent volume. Three regression models were obtained to predict the characteristics of the breakthrough curve with R2 close to one. The Thomas model (R2 = 0.952) best explained the trend of the breakthrough curve. The p-values (p less than 0.05) obtained using MINITAB software indicates that all the prime factors (coF,QandH) affect the breakthrough time.

Natural rubber-based cushion gum compound formulation at various type and dosage of rubber processing oil and tackifier resin

Cold retreading technique dominates retreaded tire manufacturing process. The technique applies rubber cushion gum compound as adhesion medium to bond new tread with a worn old tire. High-quality cushion gum compound mainly requires good adhesive strength. Tackiness of the rubber compound can be improved by addition of tackifier resin and rubber processing oil (RPO). The research was aimed to evaluate the performance of various types and dosages of tackifier resin and bio-based RPO to physic-mechanical properties of cushion gum. A method in the manufacture of natural rubber-based cushion gum compound was in accordance with ASTM D 3182. Cushion gum rubber compound formula was designed by using bio-based RPO such as pine tar oil at 5 and 12 phr and three types of tackifier resin such as rosin resin, phenolic resin, and hydrocarbon resin at 3 and 7 phr. Petroleum-based RPO and commercial cushion gum were selected as reference material. Curing characteristic and physic-mechanical properties test results were used as a reference to determine cushion gum quality. The observation during experiment indicated that natural rubber-based cushion gum compound formulated with addition of 5 phr rosin resin and 5 phr pine tar oil (code ZH4) has the closest curing characteristic and physic-mechanical properties to commercial cushion gum.

Effective removal of methyl orange dye using aliquat 336 impregnated Amberlite XAD-2 resin

Methyl orange (MO) dye was removed using Amberlite XAD-2 resin modified by wet impregnation method with Aliquat-336. The modified resin was characterized by FTIR, FE-SEM, SEM with EDX, and pH of zero charge. Experimental parameters such as time, initial dye concentration, pH, temperature, resin dose and presence of NaCl salt affecting the adsorption rate were studied. 2 g.L −1 of resin was found to be optimum for 20 mg.L −1 MO dye. A maximum of 40.93 mg dye was removed per gram of resin. Langmuir, Freundlich, and Temkin isotherms were used to predict the equilibrium points at four temperatures. Pseudo-second-order fitted the kinetic data ( R 2 = 0.982). The resin could be reused for five successive cycles effectively. Also, the prepared resin was used for the removal of a cationic dye, rhodamine-B and an industrial dye, Pink S8EB.

Removal of fluoride from coke wastewater by aluminum doped chelating ion-exchange resins: a tertiary treatment

Coke wastewater is one of the most problematic industrial wastewaters, due to its large volume and complex pollutant load. In this study, ion exchange technology was investigated with the objective of reducing the fluoride content of the effluent from a coke wastewater treatment plant (26.7 mg F-/L). Two Al-doped exchange resins with chelating aminomethyl-phosphonic acid and iminodiacetic groups were assessed: Al-doped TP260 and TP207 resins, respectively. The effect of resin dosage, varying from 5 to 25 g/L, was evaluated. F- removal was within the range 57.8–89.3% and 72.0–92.1% for Al-doped TP260 and TP207, respectively. A kinetic study based on a generalized integrated Langmuir kinetic equation fitted the experimental data (R2 > 0.98). The parameters of the said kinetics met the optimal conditions for the ion exchange process, which seemed to be more favorable with Al-doped TP260 resin than with Al-doped TP207 resin, using the same resin dosage. Furthermore, the experimental data were well described (R2 > 0.98) by Langmuir and Freundlich isotherm models, in agreement with the findings of the kinetic study: the maximum sorption capacity was obtained for the Al-doped TP260 resin.

Preparation of Slow-Release Insecticides from Biogas Slurry: Effectiveness of Ion Exchange Resin in the Adsorption and Release of Ammonia Nitrogen

The insecticidal ingredient in a biogas solution being fully utilized by cation exchange resin to produce slow-release insecticide is of great social value. In this work, the feasibility of ammonia nitrogen in a biogas slurry loaded on resin as a slow-release insecticide was evaluated by studying the effect of adsorption and the slow release of ammonia nitrogen by resin. The effects of the ammonia nitrogen concentration, resin dosage, adsorption time and pH value on the ammonia nitrogen adsorption by the resin were studied. The results showed that the ion exchange resin had a good adsorption effect on the ammonia nitrogen. With the increase of the resin dosage, time and ammonia nitrogen concentration, the adsorption capacity increased at first and then stabilized. The ammonia nitrogen adsorption capacity reached its maximum value (1.13 mg) when the pH value was 7. The adsorption process can be fitted well by the Langmuir isothermal adsorption equation and quasi-second-order kinetic model. Additionally, the release rate of the ammonia nitrogen increased with the increasing sodium chloride concentration. The adsorption capacity of ammonia nitrogen by the D113 (resin type) resin decreased by 15.8% compared with the ammonium chloride solution. The report shows that the ion exchange resin has a good adsorption effect on ammonia nitrogen, which is of guiding significance for expanding the raw materials for slow-release insecticides, improving the utilization rate of biogas slurry and cleaner production of slow-release insecticides from biogas slurry. Additionally, all variables showed statistical differences (p < 0.05).

Phosphate removal by Ion exchange in batch mode

AbstractWater with phosphate concentrations above 2 μM may adversely affect aquatic life and human health. In this study, the parameters affecting phosphate removal from aqueous solutions by ion exchange were investigated – contact time and temperature, initial pH, initial phosphate concentration and resin dosage, and the presence of other ions. The best phosphate removal (99%) from 100 mg-P/L initial solution was observed at pH 10 and 25 °C after 3 hours of contact time. No negative phosphate removal results were obtained from phosphate solutions containing sulfate, nitrate and ammonium ions; i.e., resembling real wastewater. Desorption (with NaOH or NaCl) and recovery (with CaO) studies of phosphate sorbed by resin were also carried out, as well as thermodynamic investigations. The proportional desorbability of phosphate from the resin with NaCl was 85.6%. The recovery efficiency of phosphate was 79.4%. The sorption process was spontaneous and endothermic. The ion exchange mechanism was determined using different internal and external diffusion models. The mechanism controlling the removal of phosphate from aqueous solution is both internal and external diffusion. Application of the Langmuir and Freundlich isotherm models showed that the experimental results fit well with the Freundlich model.

Synthesis of new functionalized Calix[4]arene modified silica resin for the adsorption of metal ions: Equilibrium, thermodynamic and kinetic modeling studies

In this study, a new efficient resin-based material has been synthesized through the surface modification of silica by functionalized calix[4]arene and applied for the adsorption of metal ions from aqueous media. The synthesis of functionalized calix[4]arene modified silica (FCMS) resin was characterized by FTIR, CHNS, BET surface area, SEM analyses. The FCMS resin has high thermal and chemical stabilities that were checked by the thermogravimetric analysis and various acidic/basic conditions. The efficiency of the FCMS resin was checked by performing a set of batch experiments under optimized parameters such as concentration of the metal solution, pH, resin dosage, time, temperature, and competitive adsorption in mixed solutions. The results showed that better adsorption has been achieved at pH 7, with 25 mg adsorbent dosage and 10 min contact time. The equilibrium kinetic study showed that the metal adsorption follows the pseudo 2nd order kinetic model with quite high coefficients of determination values (R2 > 0.99). The experimental data have been validated by applying three adsorption isotherm models and the results revealed that the Freundlich isotherm model (R2 > 0.99) was the best fit for the adsorption of Cu2+, Pb2+, and Cd2+ ions. However, the sorption energy calculated from the D-R isotherm model for Cu2+, Pb2+, and Cd2+ ions suggested that an ion-exchange mechanism is involved on the surface of the FCMS resin. The thermodynamic data demonstrated that the reaction is spontaneous and endothermic. The FCMS resin was also applied on real wastewater samples and the results demonstrated that the resin has a good ability to treat metal-contaminated wastewater.

La eliminación de metales tóxicos presentes en efluentes líquidos mediante resinas de cambio iónico. Parte XV: Iron(II)/H+/Lewatit TP208

Se ha investigado el uso de la resina de intercambio catiónico Lewatit TP208 en la eliminación de hierro(II) de disoluciones acuosas. En esta eliminación, se han considerado varias variables experimentales, incluyendo, la velocidad de agitación aplicada al sistema, la temperatura, el pH de la disolución acuosa y la dosificación de la resina. Para velocidades de agitación incluidas en el intervalo 300-1200 min-1, el proceso de intercambio catiónico responde al modelo de difusión en la disolución acuosa. El aumento de la temperatura, entre 20 y 60 ºC, va asociado a un aumento de la concentración de hierro(II) cargado en la resina, por lo que el sistema tiene un carácter endotérmico. La variación del pH del medio acuoso hacia pH ácidos (desde 5 a 1) da lugar a una disminución en la carga del metal en la resina. Asimismo, la dosificación de la resina Lewatit TP208 afecta a la eliminación del hierro(II) de la disolución acuosa, los resultados experimentales se ajustan a la isoterma de Freundlich. Los modelos cinéticos asociados a este sistema dependen también de la dosificación de la resina: usando la concentración de resina más alta (1 g·L-1) los datos experimentales se ajustan (r2= 0,999) al modelo de pseudo-segundo orden, mientras que con la concentración de resina más baja (0,13 g·L-1) el modelo cinético es el primer-orden (r2= 0,997). Los resultados experimentales obtenidos con la resina Lewatit TP208 se han comparado con los obtenidos con otras resinas de intercambio catiónico y con el uso de nanotubos de carbono de pared múltiple. El hierro(II), cargado en la resina, puede ser eluido mediante el uso de disoluciones ácidas.