Enhanced Defluoridation from Aqueous Solutions using Zirconium – coated Pumice in Fixed-bed Column Systems

Millions of people across the globe suffer from health issues related to excessive fluoride levels in drinking water. The objective of this study was to test natural and modified rock materials as adsorbents for the cleanup of fluoride-laden waters. Fluoride uptake onto natural pumice and zirconium–coated pumice (Zr – Pu) packed fixed-bed adsorption column was investigated. The extent of surface modification with enhanced porosity of Zr – Pu was evident from recorded SEM micrographs. A FTIR study of pumice and Zr – Pu before and after adsorption did not reveal any significant structural changes. The pH drift method demonstrated that pumice and Zr – Pu possesses positive charges at pH_PZC lower than 7.3 and 6.5, respectively. The highest removal capacity of 225 mg/kg and 110 mg/kg were gained for Zr – Pu and pumice, respectively at pH = 2 and Q_O = 1.25 mL/min. Breakthrough time increases with decreasing pH and flow rate. The experimental adsorption data was well-matched by the Thomas and Adams-Bohart models with correlation coefficients (R²), of ≥ 0.980 (Zr – Pu) and ≥ 0.897 (natural pumice), confirming that the models are appropriate tools to design fixed-bed column systems using volcanic rock materials. Overall, coating of pumice with zirconium improved the defluoridation capacity of pumice, hence, Zr – Pu packed fixed-bed could be applied for the defluoridation of excess fluoride from groundwater. However, additional investigations on, for instance, competitive ions effects are advisable to draw definite conclusions.