Improved remediation of fluoride contaminated water using titania-alumina sorbents

Abstract

Exposure to excessive fluoride levels in drinking water is a common problem to many communities. Activated alumina is the preferred commercial material for fluoride remediation. However, alumina is limited by a small operating pH range and issues with aluminium dissolution. The hypothesis was that if titania was incorporated into an alumina sorbent, the challenges with alumina use may be mitigated. Five synthesis methods were employed (pH swing, co-precipitation, hydrothermal, sol-gel, and sol-gel reflux). Solid products were found to either be crystalline or amorphous in character, with co-precipitation and sol-gel reflux materials possessing the highest surface areas (>250 m2/g). Kinetic studies indicated that the Al2O3/TiO2 materials were loaded within 4 to 6 h after initial contact with fluoride solutions (c.f. 8 h for commercial activated alumina). Equilibrium isotherms revealed that both favourable and unfavourable fluoride ion sorption occurred depending on the synthesis path. Maximum fluoride loading was 0.63 meq/g for co-precipitated Al2O3/TiO2 compared to 0.26 meq/g for commercial activated alumina. Significantly, both sol-gel reflux and co-precipitated oxide materials maintained superior fluoride capacity over the pH range of 4 to 9. However, only the co-precipitated Al2O3/TiO2 material minimized the dissolution of aluminium ions into the treated water. This study confirmed that Al2O3/TiO2 sorbents displayed greater fluoride uptake performance compared to commercial materials. The co-precipitation approach to make Al2O3/TiO2 is worthy of future investigation to not only optimize the synthesis procedure but also gain deeper insight into the nature of the sorption sites.