Fluidized bed reactor for fluoride removal

The common methods for fluoride removal from industrial wastewater involve chemical precipitation. This process generates large amounts of a water rich sludge requiring disposal with increasing costs. Due to the high water content and the low quality of the sludge, reuse of fluoride is not an economical option. The crystallization in a fluidized bed reactor offers an alternative to the conventional precipitation. The influence of the supersaturation and recycling conditions in order to control the efficiency of the process was studied. A high supersaturation level decreases the fluoride removal efficiency due to the formation of small particles (fines). The main mechanism concerning the precipitation of calcium fluoride in a fluidized bed was established. Fines were produced by nucleation in liquid phase (homogeneous and secondary nucleation) in the reactor and the dilute fluoride tank, in order to decrease the amount of fines it is very important the control of the supersaturation.