Removing fluoride from water - by pptn. with calcium then adsorption on aluminium hydroxide

摘要

Fluoride is removed from water by first adding a Ca salt to prod. a finely-divided ppte. of CaF2, and then adding an Al salt so that the ppte. is adsorbed onto the Al(OH)3 flocs formed. These flocs are then removed from the soln. by flotation of filtration. Pref. additives are CaCl2 or Ca(HCO3)2. esp. to provide as Ca 2-4 wt. times the concn. of F ions, and polymeric Al chloride. Esp. the treated soln. is satd. with air under excess pressure, then the pressure released so that the flocs of Al(OH)3 are carried to the surface as a thin layer by air bubbles. Reduced requirement for chemicals is obtd. c.f. use of Al sulphate only. The flocs can be sepd. by flotation as well as sedimentation.