Highly Efficient Removal of Fluorine from Groundwater by Membrane Capacitive Deionization

Abstract

The fluorine content of groundwater exceeds the standard in most areas of China. In this study, the self-made mesoporous carbon electrode combined with the ion exchange membrane was used to form a membrane capacitive deionization (MCDI) device. In this article, a single factor test was conducted with the removal efficiency of the configured simulated fluorine-containing water as the evaluation index. The results showed that, under the conditions of 3.6 mg/L of influent water and 18 mL/min of flow rate, the optimal process conditions were voltage 1.2 V and the spacing was 1 mm. The adsorption of the electrode was saturated by a cycle test, and the maximum removal rate of fluoride ions reached 77.3%. Using F⁻ excess groundwater as raw water, the application test showed that the fluorine content dropped sharply within 2 min, and the instantaneous removal rate was 95.8%. By monitoring the adsorption-desorption process of the electrode, the fluorine removal rate was 85.1% and the water production was 79.2%. The fluorine content in the effluent reaches lower than the drinking water standard. Different kinetic and equilibrium models were applied to the experimental data of F⁻ electrosorption. The first-order dynamics model and Freundlich adsorption isotherm model showed better fitness to the experimental data. The adsorption process of F⁻ by mesoporous carbon electrode belongs to multilayer physical adsorption. The results of this study can be used to develop a new type of MCDI groundwater removal F⁻ electrode material.