title: Effects of fluoride on the removal of cadmium and phosphate by aluminum coagulation.
abstract: This study focuses on the effects of pH and fluoride at different molar ratios of fluoride to Al (RF:Al) on the removal of cadmium (Cd2+) and phosphate by Al coagulation. Fluoride at RF:Al≥3:1 inhibits the removal of Cd over wide Al dose ranges from 5 to 10 mg/L as Al. The removal of phosphate decreases significantly at high RF:Al of 10:1 whereas at lowered RF:Al (i.e., ≤6:1), an adverse effect is observed only at insufficient Al doses below 2 mg/L. Fluoride shows inhibitive effects towards the removal of Cd at pH7 and 8 and that of phosphate at pH6. Fluoride decreases the ζ-potential in both systems, and the decreasing extent is positively correlated to the elevated RF:Al. The Al fluoride interactions include the formation of Al-F complexes and the adsorption of fluoride onto Al(OH)3 precipitates, i.e., the formation of Al(OH)nFm. Al-F complex formation inhibits Al hydrolysis and increases residual Al levels, and a more significant increase was observed at lower pH. Al-F complexes at high RF:Al complicate the coagulation behavior of Al towards both negative and positive ionic species. Moreover, fluoride at low RF:Al shows little effect on Al coagulation behavior towards Cd2+ and phosphate, and the spent defluoridation adsorbent, i.e., aluminum (Al) hydro(oxide) with adsorbed fluoride at RF:Al of below 0.1:1, may be reclaimed as a coagulant after being dissolved.
authors.affiliation: Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Ruiping
authors.initials: R
authors.lastname: Liu
authors.affiliation: Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100039, China.
authors.forename: Bao
authors.initials: B
authors.lastname: Liu
authors.affiliation: Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Lijun
authors.initials: L
authors.lastname: Zhu
authors.affiliation: Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100039, China.
authors.forename: Zan
authors.initials: Z
authors.lastname: He
authors.affiliation: Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Jiawei
authors.initials: J
authors.lastname: Ju
authors.affiliation: Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Electronic address: hclan@rcees.ac.cn.
authors.forename: Huachun
authors.initials: H
authors.lastname: Lan
authors.affiliation: Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Huijuan
authors.initials: H
authors.lastname: Liu
mesh_terms: D000536:Aluminum Hydroxide / Q000737:chemistry*; D002104:Cadmium / Q000302:isolation & purification*; D005459:Fluorides / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D010710:Phosphates / Q000302:isolation & purification*; D062065:Wastewater / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*
chemical_list: D000536:Aluminum Hydroxide; D002104:Cadmium; D005459:Fluorides; D010710:Phosphates; D062065:Wastewater; D014874:Water Pollutants, Chemical
keywords: Adsorbent reclamation; Aluminum coagulation; Al–F complexes; Fluoride; ζ-Potential