Highly selective removal of fluorine from wastewater containing phosphorus and fluorine in a microreaction system

Selective removal of fluorine from wastewater containing phosphorus and fluorine is significant to wastewater purification and resource recycling. However, serious problems including long handling time and poor selectivity exist in batch processes due to limited mass transfer rate at large flow rate ratio (R) and high solid content. In this work, we develop an active microreaction system based on the miniaturized magnetic reactor to intensify the selective fluorine removal process by chemical precipitation with Ca(OH)2 which is easy to scale-up for industrial applications. The effects of various process parameters and operational conditions are systematically investigated. The mixing process at complex operating conditions can be intensified by increasing the rotational speed, and the reaction time can be adjusted by setting the stirred units in series. The reaction performance in the microreaction system is not sensitive to the flow rate and R. High fluorine removal rate (87.4 %) and high selectivity (14.4) are obtained at rotational speed of 1500 r center dot min- 1 and residence time of 1.6 min with low energy consumption (10- 3 - 10- 2 W center dot kg- 1) in the microreaction system. Moreover, mathematical models are established for predicting the selective fluorine removal performance.