Experimental Study On Simultaneous Removal Of Fluorine/Calcium From Water By Chemical Crystallization Granulation Fluidized Bed

Fluorine is an important trace element to maintain health and plays an important role in chemical industry.The fluorine element mainly exists in the fluorine ore.As the groundwater scours and dissolves the fluorine ore for a long time,the fluorine element in the fluorine ore dissolves into the water,resulting in regional groundwater with high fluorine content,which has an impact on human health.The traditional fluoride removal process has the disadvantages of high energy consumption and low efficiency.It is urgent to research and develop the technology and equipment to remove fluorine and calcium hardness in water at the same time.Crystallization granulation fluidized bed is an efficient and environmental protection technology.In this paper,crystallization granulation fluidized bed induced crystallization technology was studied.This paper studies the high fluorine and high hardness groundwater and uses the method of fluorine calcium phosphate crystallization to achieve the purpose of fluoride removal.This paper focuses on the following aspects:（1）The influencing factors（pH,ion concentration,crystal seed type）and kinetic conditions（rising velocity,static bed thickness）that affect the effect of fluoride removal by induced crystallization.（2）The effect of pH on the simultaneous removal of fluorine/calcium from water by crystallization granulation induced by fluidized bed.（3）Mechanism of simultaneous removal of fluorine/calcium from water by dolomite seed induced crystallization.The main research conclusions are as follows:（1）The pH has the most obvious effect on the supersaturation index（SI）of apatite.The optimal pH of fluorapatite（FAP）crystallization is between 6.2 and 6.6.The best defluorination effect is achieved by dolomite seed induced crystallization,followed by dolomite and calcite mixed seed,and the defluorination effect is poor by apatite,hydroxyapatite（HAP）and calcite seed.（2）The simultaneous removal of fluorine/calcium can be achieved by controlling the pH of the water in the fluidized bed and the upward flow filter bed respectively.Adding Na OH to the upward flow filter bed can effectively reduce the concentration of residual phosphorus in the effluent and improve the removal rate of calcium.Under alkaline conditions,increasing the alkalinity of carbonate will reduce the effect of fluoride removal and is not conducive to reducing the concentration of residual phosphorus.（3）The pH regulation effect of dolomite makes it have good fluoride removal effect.The dissolution of dolomite surface is beneficial to the formation of FAP growth sites and the crystallization of FAP on the surface.Due to the action of ionic bond,its surface can adsorb F^-,PO₄^3-,HPO₄^2-and other polar ions or molecules.When the reaction force（FAP-SI）reaches a certain degree,FAP reverse crystallization on dolomite seed surface will be promoted.