Investigation of fluorapatite crystallization in a fluidized bed reactor for the removal of fluoride from groundwater

Abstract

BACKGROUND This work further investigates fluoride removal from groundwater by induced crystallization in batch experiments and in a fluidized bed reactor (FBR). Phosphate rock (PR), which is an abundant ore and represents the basic raw material for the phosphatic fertilizer industry, was used as seed crystal in the induced crystallization process. RESULTS Induced crystallization in FBR reduced the concentration of F− in synthetic groundwater from 9.5 mg L‐1 to <1.0 mg L‐1. Phases with the potential for precipitation were calculated through thermodynamic equilibrium modeling. The formed precipitates were identified by powder x‐ray diffraction (XRD) and scanning electron microscopy, coupled with energy dispersive spectroscopy (SEM–EDS). Finally, fluorapatite crystallization mechanisms were confirmed by the induced crystallization of Ca5(PO4)3F on the surface of PR. CONCLUSION The fluorapatite crystallization process in FBR removed F− from groundwater, and the used seed crystal PR was rich in phosphorus and that could be recovered as raw material for the phosphatic fertilizer industry. © 2018 Society of Chemical Industry

Synthesis and characterization of aluminum-based adsorbent and application in fluoride removal from aqueous solution

“…Due to these impacts on human health and environment, a number of international regulators have issued regulations to control the fluoride levels in water 33,34 . Different processes have been studied to remove excessive fluoride from water namely, biological processes (plants or microorganisms) 35,36 and physicochemical processes such as fluidized bed precipitation 37 , electrocoagulation-flotation 38,39 , ion-exchange 40,41 , electrochemical methods 42 and membrane processes (reverse osmosis 43,44 , electrodialysis 45,46 , Donnan dialysis 47 , nanofiltration 48 , etc.). However, each of these methods presents its drawbacks, such as a long disposal time, the use of dangerous and expensive reagents 49 .…”

Impact of Ca2+ and Mg2+ on the Removal of F− by Magnesium Potassium Phosphate

“…Electrocoagulation is utilized for the removal of F − because it involves relatively compact and trouble‐free operation in which no extra chemical reagents are needed; however, it also has high operation costs . Induced crystallization is a novel method to remove F − from drinking water by forming Ca 5 (PO 4 ) 3 F on fluorapatite/calcite or phosphate rocks . Adsorption has been widely used to remove F − due to its relatively low cost as well as its simplicity of design and operation …”

“…The concentration of Ca 2+ should be <152.7 mg L −1 when only Ca 2+ causes the hardness of water; the concentration of Mg 2+ should be <109.3 mg L −1 when only Mg 2+ causes the hardness of water. F − can be removed by electrocoagulation, [13,14] induced crystallization, [15,16] adsorption, [17][18][19] etc. Electrocoagulation is utilized for the removal of F − because it involves relatively compact and trouble-free operation in which no extra chemical reagents are needed; however, it also has high operation costs.…”

“…[14] Induced crystallization is a novel method to remove F − from drinking water by forming Ca 5 (PO 4 ) 3 F on fluorapatite/calcite or phosphate rocks. [15,16] Adsorption has been widely used to remove F − due to its relatively low cost as well as its simplicity of design and operation. [18,19] Magnesium potassium phosphate (MPP) has been employed as a material for dental implants [20] as well as in the rapid repair of concrete.…”

“…F − can be removed by electrocoagulation, induced crystallization, adsorption, etc. Electrocoagulation is utilized for the removal of F − because it involves relatively compact and trouble‐free operation in which no extra chemical reagents are needed; however, it also has high operation costs .…”