Study of interaction of polymeric aluminium hydroxide with fluoride

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Abstract
The interaction between polymeric aluminium hydroxide, Alp, and fluoride has been investigated to optimize the conditions for removal of fluoride from waste waters of aluminium manufacturing plants using Alp. The results of these studies have shown that the nature of products formed between Alp and fluoride depends on the molar concentration ratio of fluoride to aluminium (rF), pH, and initial fluoride concentration. In the absence of interfering ions, fluoride can be effectively precipitated as Al13(OH)29F10 with Alp, using rF .simeq. 0.7 and 4 < pH .ltoreq. 7. At rF > 1, Alp dissociates and fluoride is precipitated as cryolite, and the residual fluoride concentration is controlled by its high solubility.