La3+-Assisted coagulation approach for fluoride removal from water
Fluoride ions in water were effectively removed by adding soluble lanthanum salt to form La-F colloid and then using ferric chloride-calcium oxide-polyacrylamide(PAM)coagulation system.Under a cer-tain reaction conditions,e.g.,La3+∶F-(molar ratio)=2∶3,pH =5,PAM∶F-(mass ratio)=5∶1,F--con-taining wastewater with initial concentration of 20～200 mg/L could be well controlled to F-<1 mg/L.Due to the strong affinity between La3+ and F-,they could form colloidal particles in the form of LaFx(OH)3-x in water,and the subsequent addition of ferric chloride and calcium oxide destroyed the stable colloidal system.Through the coagulation effect brought by Fe3+ and PAM,fluoride ions in water were eventually removed.The as-formed precipitate by-product could be adopted as adsorbent for organic dye removal from water,which showed an adsorption capacity of 337.8 mg/g for model dye of Congo red.And most of the effective adsorption occurred in the first reaction stage of 3 min.
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