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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 HAsO and HAsO 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., To the CSIC (Spain) for support. To Mr, J.M. Medina, Mrs. E. Moroño and Mrs. M. López (CENIM) for assistance in the experimental and analytical work.

Iron(II) was removed from aqueous solutions by the use of the cationic ion exchange resin Lewatit TP208 (Na+ form). The influence of different experimental variables was investigated on the ion exchange process: stirring speed, temperature, pH of the solution and resin dosage. At stirring speeds included in the 300-1200 min-1, iron(II) uptake onto the resin fitted well to the film-diffusion model, whereas the increase of the temperature, from 20 to 60 C, was accompanied by an increase in the metal loaded onto the resin, thus, resulting in an endothermic ion exchange process. This ion exchange process was influenced by the variation of the pH of the solution: There was a decrease in metal uptake when the pH of the solution was shifted towards more acidic values. Also the ion exchange process was sensitive towards the variation of Lewatit TP208 resin dosage, being the process associated to the Freundlich isotherm model. This variation in the resin dosage had also an influence in the fitting of the experimental data, at various resin dosages, with the kinetics model associated to them. At the highest resin dosage (1 gL-1) the exchange process fitted well (r2= 0.999) to the pseudo-second order model, however, at the lowest resin dosage (0.13 gL-1), the process fitted (r2= 0.997) the first-order model. Metal uptake was compared with that yielded with other cation-exchange resins and also against the use of multiwalled carbon nanotubes. Iron(II) loaded onto the resin was eluted using acidic solutions., CSIC

Mercury(II) was eliminated, from acidic aqueous solutions, by the cationic ion exchange resin Lewatit SP112. Various experimental conditions were tested in the investigation, such as, stirring speed (275-1000 min), temperature (20-60 °C), pH of the aqueous solution (0-4) and resin dosage (0.05-0.4 g·L). Mercury(II) uptake onto the resin decreased with the increase of the temperature (exothermic reaction) in a spontaneous process, whereas the moving boundary model represented the metal uptake in the 20-60 °C temperatures range. Moreover, the experimental data fitted to the second order kinetic model (275 min) or the pseudo-second order kinetic model (500-1000 min), though maximum metal uptake was not dependent on the stirring speed applied to the system. The experimental results responded well to the Langmuir type-2 isotherm. The Hg(II)-loading ability of Lewatit SP112 was compared against that of other resins and non-functionalized multiwalled carbon nanotubes. Mercury(II) loaded onto the resin can be eluted by means of various eluants, furher, zero valent mercury was yielded from the eluates., To the CSIC (Spain) for support. To Mrs. E. Moroño (CENIM) for assistant in the analytical work, and to Prof. Dr. P. Adeva (CENIM) to obtain the images of Fig. 4.

Zinc(II) was removed, from aqueous solutions, by the ion exchange resin Lewatit OC-1026 (having di-2-ethylhexyl phosphoric acid as adsorbed functional group). Different experimental variables influencing metal uptake, such as, stirring speed (400–1200 min−1), temperature (20–60 °C), pH of the aqueous solution (1–4) and resin dosage (0.05–1 g·L−1) were investigated. The concentration of zinc(II) loaded onto the resin decreased with the increase of the temperature (exothermic reaction) in a spontaneous process, whereas equi-librium was achieved at shorter times as the temperature was increased. The experimental values fitted to the second order kinetic model (60 °C) or the pseudo-second order kinetic model (20 °C).The ion exchange process was pH-dependent, decreasing the percentage of zinc(II) loading onto the resin from pH 4 to pH 1. At pH 4, the rate law was best fitted to the particle diffusion model, and to the Langmuir type-2 isotherm. Zinc(II) removal from the aqueous solution using this resin is by far better than when oxidized or non-oxidized multiwalled carbon nanotubes were used as adsorbents for zinc(II). This element can be eluted from zinc-loaded resin using acidic solutions., To the CSIC (Spain) for support

The removal of cobalt(II) from aqueous solutions by ion exchange with Lewatit TP260 resin was investigated. The experimental variables investigated in the present work were: stirring speed (300-1400 min-1), temperature (20-60 ºC), pH of the aqueous solution (1-5), resin dosage (0.07-0.5 g·L-1) and the aqueous ionic strength. Cobalt(II) was loaded onto the resin by a cation exchange reaction in an endothermic and spontaneous process. Metal uptake was defined by the aqueous diffusion rate law and the pseudo-first order kinetic model (20 ºC) and the pseudo-second order kinetic model (60 ºC), whereas the experimental results responded well to the Langmuir isotherm. Several resins as well as non-oxidized and oxidized multiwalled carbon nanotubes were tested in order to compare the uptake results with that of Lewatit TP260, whereas the selectivity of the Co(II)-Lewatit TP 260 system was compared against the presence of other cations (Co-metal binary solutions) in the aqueous phase. Cobalt(II) can be recovered from metal-loaded resin by the use of acidic solutions (HCl or H2SO4).

The present work investigates the removal of Sb(III) from acidic aqueous solution by the ion exchange resin Ionac SR7. Several experimental parameters were considered in the study: stirring speed of the system (280-1000 min), temperature (20-60 °C), aqueous acidity (0.1-2 M HCl), resin dosage (2.5-20 g·L) and the source of the aqueous ionic strength. The load of Sb(III) onto the resin is attributable to an anion exchange reaction, being this process exothermic and spontaneous. Based in the experimental data, several modes were tested to explain loading kinetics, loading mechanism and loading isotherm, which respectively are the pseudo-second order kinetic model, the particle-diffusion controlled model and the Freundlich isotherm. The performance of the resin with respect to antimony load was compared against other anion exchanger resins and multiwalled.carbon nanotubes. It was found that water is an effective medium to remove antimony(III) from the metal-loaded resin., To the CSIC (Spain) for support.

The removal of cobalt(II) from aqueous solutions by ion exchange with Lewatit TP260 resin was investigated. The experimental variables investigated in the present work were: stirring speed (300-1400 min-1), temperature (20-60 ºC), pH of the aqueous solution (1-5), resin dosage (0.07-0.5 g·L-1) and the aqueous ionic strength. Cobalt(II) was loaded onto the resin by a cation exchange reaction in an endothermic and spontaneous process. Metal uptake was defined by the aqueous diffusion rate law and the pseudo-first order kinetic model (20 ºC) and the pseudo-second order kinetic model (60 ºC), whereas the experimental results responded well to the Langmuir isotherm. Several resins as well as non-oxidized and oxidized multiwalled carbon nanotubes were tested in order to compare the uptake results with that of Lewatit TP260, whereas the selectivity of the Co(II)-Lewatit TP 260 system was compared against the presence of other cations (Co-metal binary solutions) in the aqueous phase. Cobalt(II) can be recovered from metal-loaded resin by the use of acidic solutions (HCl or H2SO4). Este trabajo investiga sobre la eliminación de cobalto(II) presente en medios acuosos mediante la resina de cambio iónico Lewatit TP260. El sistema se estudia bajo distintas condiciones experimentales: velocidad de agitación (300-1400 min-1), temperatura (20-60 ºC), pH del medio acuoso (1-5), dosificacion de la resina (0.07-0.5 g·L-1) y fuerza iónica de la disolución acuosa. El metal se carga en la resina mediante una reacción de intercambio catiónica en un proceso endotérmico y espontáneo. Esta reacción de intercambio se define por un proceso de difusión en la disolución acuosa y el modelo cinético de pseudo-primer orden (20 ºC) y el modelo cinético de pseudo-segundo orden (60 ºC), asimismo los resultados experimentales se ajustan bien a la isoterma de Langmuir. Los resultados experimentales del sistema se han comparado con los obtenidos con otras resinas de intercambio cationico y también con nanotubos de carbono de pared multiple oxidados y sin oxidar. Se estudia la selectividad del sistema Co(II)-Lewatit TP260 con respecto a la presencia de otros cationes (disoluciones binarias Co-metal) en el medio acuoso). El cobalto(II) cargado en la resina se puede fluir con disoluciones ácidas (HCl o H2SO4).

The anionic exchange resin Amberlite 958 was used to remove manganese(VII), as permanganate ion, from aqueous solutions of different pH values. Besides the aqueous pH, other variables involved in the exchange process were investigated, including, stirring speed of the system, temperature, ionic strength and resin concentrations. The non-lineal fit of the experimental points, indicated that the equilibrium isotherm is best explained by the Langmuir equation, whereas the anion exchange equilibrium is endothermic and non-spontaneous. The Mn(VII) loading performance of Amberlite 958 resin was compared with that of other anion exchangers and multiwalled carbon nanotubes. The elution of the Mn(VII) loaded onto Amberlite 958 was investigated using hydrazine sulphate solutions, which render manganese to the eluate as the somewhat less hazardous form of Mn(II)., To the CSIC (Spain) for support. To Mr. J.M. Medina for assistance in part of the experimental work.

In this sixth part of the series, Manganese(II) was removed from aqueous solutions by the cationic exchange resin Lewatit K2621. The investigation was performed under various experimental conditions such as the stirring speed associated with the system, aqueous pH, temperature, resin dosage and the ionic strength of the solution. The performance of the resin against the loading of metals from metal-binary solutions as well as the removal of Manganese(II) from the solutions using multiwalled carbon nanotubes and functionalized (carboxylic groups) multiwalled carbon nanotubes, were also investigated. Experimental results fit well with the pseudo-first kinetic order model, whereas fit of the data show that at 20 °C the process responded well to the diffusion controlled model, and that at 60 °C, the system is controlled by the moving boundary model. Adsorption data is better related to the Freundlich isotherm. Elution of the Manganese(II) loaded onto the resin was investigated using acidic (HSO or HCl) solutions., To the CSIC (Spain) for support. To Mr. J.M. Medina for assistance in part of the experimental work.

The removal of the toxic arsenic(III) from aqueous solutions is investigated using the ion exchange technology and the Dowex 1x8 resin. Different experimental variables which may influence the uptake equilib-rium are considered: Stirring speed of the system, temperature, NaOH concentration in the solution, and resin dosage. The anion exchange equilibrium is endothermic and non-spontaneous, in the 20 °C - 60 °C range of temperatures the metal uptake onto the resin responded to the pseudo-second order kinetic model, however, the loading mechanism is temperature dependent in the 20 °C - 40 °C range. The linear fit of the experimental data showed that the loading isotherm is best explained by the Freundlich model. The results of arsenic(III) uptake in the present system are compared against the metal uptake which one can obtain with other resins and multi-walled carbon nanotubes. Arsenic(III) loaded onto the resin is eluted by the use of 1M HCl solution., To the CSIC (Spain) for support. Also to Mrs. J. Fernandez and Mrs. E. Moroño for assistance in the analytical work.

The cationic exchange resin Dowex C400 was used to remove nickel(II) from aqueous solutions of different pH values and under various experimental conditions: stirring speed of the aqueous solution/resin system, temperature, resin dosage and aqueous ionic strength. The selectivity of the resin was investigated against the presence of various metals in the aqueous solution, and the removal of nickel(II) from aqueous solutions was also compared with results obtained using multiwalled carbon nanotubes or functionalized (carboxylic groups) multiwalled carbon nanotubes as adsorbents. According to batch experimental data, best fit of the results is obtained with the Freundlich model, whereas the ion exchange process is best explained by the pseudofirst order model. Experimental data fit well to the moving boundary controlled model. Elution of the nickel(II) loaded onto Dowex C400 resin is fully possible using acidic solutions.