TREATMENT OF AQUEOUS EFFLUENT FOR FLUORIDE REMOVAL

Fluoride forms a common aqueous effluent in many chemical industries. Excess of fluoride in the effluent can cause a health hazard. So, effluent containing fluoride needs treatment to reduce its concentration to a disposable value before discharge into public sewage. By conventional methods, the fluoride concentration in the industrial effluent can not be reduced to less than 10-15 mg l-1 without the help of dilution with fresh water. A method of chemical treatment is discussed here which has been very effective to remove the fluoride ion from effluent to a concentration of 1.5 mg l-1 or less (which is disposable) by precipitation technique followed by complexation. In this method, precipitation reduces the fluoride ion to a concentration of about 15 mg l-1 and the balance (1.5 mg l-1) is complexed to a stable form which being already totally dissociated at that low concentration does not break on further dilution. This improved method has made it possible to save a huge quantity of fresh water which otherwise is needed to dilute the fluoride effluent after conventional treatment in order to meet the statutory requirement.