Study On The Chemical Composition Of Functional Components Of The Filtration Aterial Used In Contact Precipitation Defluoridation

Contact precipitation can be used not only for small-scale and decentralized drinking water treatment but also in the centralized drinking water supply. The filtration material selection is one of the key issues to remove fluoride from water by contact precipitation process successfully. Researching on the chemical composition of functional components of filtration materials is the fundamental work for the development of new filtration materials.Running conditions were performed and precipitation was investigated by contact precipitation filtration experiment using fluoride Saturated Hydroxyapatite (SHap). The chemical composition of functional components of SHap and fluoride Saturated Bone Char (SBS) was studied by materials characterizing. The result were concluded through comparing the difference of the filtration materials before and after used in contact precipitation filtration experiment.Water containing fluoride was mixed with calcium chloride and sodium dihydrogen phosphate at dosage level corresponding to Ca/P/F molar ratio of5/3/1, and flowed through columns which were filled with SHap granules while the filtration velocity and EBCT were0.30m/h and0.5h respectively. The fluoride concentration of the treated water was below lmg/L while the fluoride concentration of the raw water was4.37mg/L. The production of treated water was at least600bed volumes.When the water pH was7.2, fluoride removal efficiency was higher in contact precipitation experiment for defluoridation. Due to the combination of calcium chloride and sodium dihydrogen phosphate could reduce the pH, contact precipitation for fluoride removal only has the better removal efficiency for high alkaline or alkaline raw water. The greater dosage of Ca/P/F or the longer empty bed contact time in a certain range can get a better defluoridation effect.The functional components of SBC granules which before and after used as contact precipitation filtration materials was fluorapatite-type composition. The general chemical formulas were Ca(4.895-5)(P04)(2.995～3.03)F(0.75～1)(OH)(0～0.35)Cl(0～0.23)//Ca54)3F//Ca(5.061～5.164)(P(2.87～2.892)O(11.46～11.532)) F(0.89～0.959). The functional components of SHap granules which before and after used as contact precipitation filtration materials was also the fluorapatite-type composition. The general formulas were Ca(4.895～5)(PO4)(2.995～3.o3)F(0.75～1)(OH)(0～0.35)Cl(0～0.23)//Ca5(PO4)3F//Ca(5.061～5.164)(P(2.87～2.892)O(11.46～11.532)) F (0.89～0.959).The chemical composition of functional components of the SBC and the SHap was the same or nearly the same as that of precipitation. The validity of the contact precipitation filtration materials was renewable while the mechanical regeneration could get the satisfactory results. The chemical regeneration was absolutely not necessary.