Combing Seeding Crystallization with Flotation for Recovery of Fluorine from Wastewater: Experimental and Molecular Simulation Studies.

For effective removal and utilization of fluorine resources from industrial wastewater, stepwise removal and recovery of fluorine were accomplished by seeding crystallization and flotation. The effects of seedings on the growth and morphology of CaF2 crystals were investigated by comparing the processes of chemical precipitation and seeding crystallization. The morphologies of the precipitates were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM) measurements. The seed crystal, fluorite, helps improve the growth of perfect CaF2 crystals. The solution and interfacial behaviors of the ions were calculated by molecular simulations. The existing perfect surface of fluorite was proven to provide the active sites for ion adhesion and formed a more ordered attachment layer than the precipitation procedure. The precipitates were then floated to recover calcium fluoride. By stepwise seeding crystallization and flotation, the products with a CaF2 purity of 64.42% can be used to replace parts of metallurgical-grade fluorite. Both removal of fluorine from wastewater and the reutilization of the fluorine resource were realized.