Fluoride Recovery in a Fluidized Bed: Crystallization of Calcium Fluoride on Silica Sand

The removal of fluoride in a fluidized bed reactor by crystallization on the surface of sand grains has been studied as an alternative to chemical precipitation, which generates huge amounts of a water rich sludge that is not possible to recover due to the high water content and the low quality of the sludge. Water recycling is required in order to decrease the fluoride concentration and prevent primary nucleation. However, water recycling may increase the secondary nucleation and, therefore, the efficiency of the process is lower due to the formation of fines, which cannot be recovered. The environmental benefits of the reuse of raw materials and the reduction of wastewater make it necessary to improve the efficiency of the process, reducing the formation of fines. The influence of supersaturation has been experimentally studied, leading to a quantitative model. The combination of a fluidized bed reactor and a sand filter bed in the process has been able to achieve a reduction in the formation of fines f...