A novel cement-based technology for the treatment of fluoride ions

Abstract

Previous studies have confirmed the effective removal of fluoride by cured cement paste powder from wastewaters originating from semiconductor and fertilizer industries. However, the mineralogical changes taking place in cement paste during fluoride removal were not reported. There is need to understand the significance of cement hydration products and performance of different types of cements in fluoride removal. The present study shows the fluoride removal efficiency using different types of cement, such as cement containing calcium sulfate dihydrate, cement containing calcium sulfate anhydrate, clinker and Ordinary Portland Cement (OPC). OPC gave the best result with 61.1% of fluoride removal efficiency within 5 h of reaction time, and reduction the followed pseudo-first-order kinetics. Further, the column studies were carried out using granules of OPC run under two different conditions, by passing the solution containing only fluoride ions and another condition in which the mixture of fluoride and nitrate was passed to see the reduction efficiencies of OPC granules. The results showed a 91% reduction in fluoride ions on fourth day of cement hydration in former condition; however, the reduction was less when mixture was passed. Further, to understand the mineralogical and morphological changes in cement during anionic removal reactions, analytical tools such as X-ray diffraction (XRD) and scanning electron microscope (SEM) were used.