Adsorptive Removal of Fluoride from Water by Heat-Treatment Waterworks Alum Sludge

Alum sludge( AS) is a world-wide by-product generated in the drinking water treatment process when aluminum salts are used as coagulant. Its high Al content makes it a potential adsorbent for flouride removal from water. A high performance adsorbent was fabricated via heat treatment of AS and batch adsorption experiments were carried out to investigate its flouride adosroption performance. The results indicated that AS treated at 300℃( AS300) for 1 h had the highest adsorption capacity for fluoride( 52. 9% fluoride removal). The adsorption of fluoride by AS300fitted better the Langmuir isotherm model than the Freundlich model. The maximum fluoride adsorption capacity of AS300increased from 4. 0 to 9. 3 mg /g sludge when reaction temperature increased from 15 to 35 ℃. Thermodynamic parameters showed that the adsorption of fluoride by AS was spontaneous and endothermic.Hence higher temperature was favorable for fluoride adsorption.The adsorption process followed the pseudo-second-order equation.In addition,the fluoride adsorption on AS300 decreased from 4. 3 to2. 5 mg /g sludge when the solution initial pH increased from 4. 0 to9. 0,which meant that adsorption capacity was greatly dependent upon the initial pH of the solution. The results provide new insight into the resource utilization of AS for fluoride removal.