Removal of fluoride from spent pot liner leachate using ion exchange

Spent pot liner (SPL), a hazardous solid waste produced at cell houses of a luminum smelters, is a potential source of fluoride pollution. Leachates co llected from SPL disposal sites were found to contain fluoride at considera ble concentration levels (up to 575 mg/L). This paper reports a study of se lective fluoride removal following laboratory-prepared, ion-exchange treatm ent. Spent pot liner leachates were pretreated with lime to bring the fluor ide level down to approximately 10 mg/L for economic and effective working of the ion exchanger. The detailed ion-exchange treatment study for removal of fluoride was carried out on synthetic SPL leachates and the optimum tre atment thus developed was applied on natural SPL leachates. Bench-scale studies were carried out at various flow rates and pHs and in t he presence of other ions commonly available in the SPL leachates. The prep ared exchanger reduced the level of fluoride from approximately 10 mg/L to less than 1 mg/L. Results indicate that the extraction was 100% up to 6-mL/ min flow rate through the ion exchanger and it works efficiently in the pH range of 7 to 10. There is no effect of the other ions present in leachates on removal of fluoride. The exchanger has good capacity to exchange and ca n be recharged by eluting fluoride sorbed on the exchanger using two molar hydrochloric acid.