Batch and column test analyses for hardness removal using natural and homoionic clinoptilolite: breakthrough experiments and modeling

摘要

Hard water causes many problems in domestic and industrial usage, which has to be removed using cost-effective technologies. To achieve this, the main goal of this study is to assess and optimize the factors controlling water softening applications. The research approach included a combined use of batch and column experiments performed in laboratory conditions through the ion exchange process, evaluating the effectiveness of natural and homoionic clinoptilolite on the removal characteristics of divalent cations. The equilibrium data could be fitted by both the Langmuir and the Freundlich models, even though it was fitted better by the Langmuir model with a maximum adsorption capacity of 10.5 mg g~(-1) for homoionic clinoptilolite (HC) and 9.68 mg g~(-1) for the natural clinoptilolite (NC). The adsorption kinetics can be successfully fitted to pseudo-second order kinetic model and the results of the intraparticle diffusion model suggest intraparticle diffusion was not the only rate-controlling step. It was also observed that the statistics indices of agreements from non-linear Thomas model were higher than that linear Thomas model. Nevertheless, the slope of the breakthrough curve for the linearized method decreased with increasing time as compared to non-linear method, thereby resulting in a slightly steeper slope for the nonlinear method and reducing the adsorption capacity. The study also concludes that the non-linear method is slightly more effective in predicting the performance of the selective removal efficiency of hardness ions. Results illustrate that clinoptilolite may be used as an alternative to more costly materials, due to its low cost and high abundance.