Mechanism of fluoride removal by AlCl3 and Al13: The role of aluminum speciation

Mechanism of fluoride removal by AlCl3 and Al13: The role of aluminum speciation

Publication Year:
Wang, Xi; Xu, Hui; Wang, Dongsheng
Affiliated Orgs.:
Research Center for Eco-Environmental Sciences
Resource Type:
Journal Article
Coagulation is vital for defluorination, but conventional methods leave excess residual aluminum. This study used AlCl3 and the molecule Al13 to treat fluoride-rich water. Different pH levels showed varied defluorination efficiencies. Analyzing floc compositions and aluminum residues revealed defluorination mechanisms, with coprecipitation playing a significant role. This research offers fresh perspectives on coagulation and defluorination processes.
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Resource Information


Coagulation is an important defluorination process. However, because of the poor sedimentation properties, conventional coagulants often result in limited defluorination performance and excessive residual aluminum. In this study, AlCl3 and the highly-positively-charged molecule [AlO4Al12(OH)24(H2O)12]7+ (Al13) was utilized to treat fluoride-containing water. By comparison, the role of aluminum speciation in fluoride removal was elucidated. Under initial pH of 6.0, 7.0 and 8.0, the highest defluorination efficiencies of high-fluoride water ([F−]0 = 8.0 mg/L) were 78.2%, 71.6% and 83.2% at Al13 dosage of 20 mg/L, 40 mg/L and 50 mg/L. Combined with detailed investigations of the chemical compositions of flocs, along with electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) analysis of residual aluminum, the defluorination mechanisms of both coagulants were discussed. In acidic conditions, both coagulants hydrolyzed and formed various Al clusters, among which transient Al (Alts) was the intermediate of the other clusters. The coprecipitation of high-polymerized Al and F− contributed most of the defluorination rate. While under neutral and alkaline conditions, hydrogen bonding and ion exchange together with coprecipitation were the main roles for Al13. The effects of AlCl3 were merely physical actions, and were affected by the decreased pH. This work provides new insights into the coagulation and defluorination process.

Resource Type

Journal Article

Publication Year



Wang, Xi; Xu, Hui; Wang, Dongsheng



Organizational Affiliation

Research Center for Eco-Environmental Sciences

Specific Contaminants

Other Chemicals, Fluoride

University Affiliation

University of the Chinese Academy of Sciences

Business Connect Takeaways

Aluminum coagulants can be effective for removing fluoride from water through coagulation processes
The defluorination efficiency of aluminum coagulants is influenced by various factors, such as the initial pH of the water, the concentration of the coagulant, and the raw water quality.
Understanding the chemical speciation of aluminum coagulants and their interactions with fluoride ions can help optimize the defluorination performance and reduce the amount of sludge generated during the coagulation process.

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