Removal of fluoride from drinking water using a modified fly ash adsorbent

摘要

Fly ash from a coal-fired power station was chemically modified and utilized for the removal of fluoride from drinking water. Two types of beds were used. Bed Ⅰ was prepared by treatment with 12M HC1 followed by neutralization with 5M NaOH solution. The reaction mass was filtered, washed, dried, and crushed to fine powder. Bed Ⅰ material was mixed with alum and MgCl_2 solutions and treated with 0.9M Na_2CO_3 until pH reached to 4.5. Mass was again filtered, washed, dried at 120℃ for 4 h and crushed to fine powder. This bed material is Bed Ⅱ, which was used for defluoridation. Bed Ⅰ was used to maintain pH (7.5-8.5) of the final effluent. Fluoride (100 ppm) present in both synthetic mixtures and drinking water samples was allowed to pass through Bed Ⅱ (15 g) absorbent and effluents were found to contain no fluoride but pH of the effluent was 5.4-5.5. To maintain WHO guidelines for drinking water on pH, this effluent was again passed through Bed Ⅰ. The effectiveness of the modified fly ash bed was satisfactory.