Use of mining waste as a novel low-cost material for fluoride removal from groundwater in CKDu endemic areas of Sri Lanka

Abstract

A cost-effective fluoride removal process from groundwater using locally sourced waste materials was postulated for use in remote areas such as northern Sri Lanka. The process is relatively simple to operate, reduces fluoride levels to meet WHO guidelines and uses locally available waste from lime extraction. The “Natural Red Earth” (NRE) waste was a mixture of clays (12.43 wt%) and iron oxides (8.13 wt%) deposited on quartz (64.04 wt%). The smallest mesh size (<63 μm) of NRE was preferred to remove fluoride due to enrichment with aluminium and iron materials. Fluoride exchange kinetics were relatively fast (ca. 5 min) for NRE which was ascribed to sorption sites present in an active coating. Equilibrium studies revealed a low fluoride loading (0.009 meq/g). Thermal modification of the NRE at 350 °C increased the maximum fluoride uptake to 0.014 meq/g. Exposure of NRE to 1 M hydrochloric acid solution was preferred as the fluoride sorption capacity was promoted to 0.02 meq/g. Protonated surface sites on NRE were considered responsible for the enhanced fluoride sorption capacity. Acid activated NRE successfully batch treated simulated groundwater contaminated with fluoride ions to meet WHO guidelines. Practically, NRE may be used in addition to a sand filter and charcoal bed if required to remove organic matter. The economics for constructing and using a new NRE based treatment system is suitable for rural farming communities in Sri Lanka.