A semiempirical kinetic model for removal of iron (Fe3+) from saturated boric acid solution by ion exchange using amberlite IR-120 resin

Abstract

The removal of iron (Fe3+), originating in raw colemanite, from saturated boric acid solution is important in the production of pure boric acid. In this study, the kinetics of iron ion removal from saturated boric acid solution was studied by ion exchange technology using Amberlite IR-120, a strong acidic resin. The experiments were carried out as a function of solution pH, reaction temperature, resin-to-solution ratio, and resin contact time. Optimum conditions were determined as solution pH = 1.3, reaction temperature 313 K, resin-to-solution ratio 4.9625 g/250 mL, and 20 min contact time. Under these conditions, maximum iron removal was about 99%. Also, data calculated from a mass balance equation were employed for pseudo-first-order and pseudo-second-order kinetic equations. The pseudo-second-order kinetic equation was the equation which best fit the data. Furthermore the sorption mechanism was also investigated using diffusion models such as film diffusion, pore diffusion, and moving boundary process. It was found that rate limiting steps in the ion exchange reaction were both film and pore diffusion. Activation energy of the ion exchange reaction was calculated as 23.64 kJ/mol and this indicated a diffusion controlled process. Based on adsorption capacity approach, an empirical kinetic model was developed to predict operational conditions of the batch process as follows: t/q(t) = 132971.89 x [H+](0.5887) x exp(-23.64/RT) x (S/L)(1.1578) x [Co](0.6151) x t(0.8944)