Preparation Of Modified Natural Siderite And Its Characteristics Of Fluoride Removal

It is well known that fluoride is an indispensable element for human health, butexcessive fluoride intake can result in endemic fluorosis. Adsorption is believed to be agood technology for fluoride removal from water solution, which has been receivedmuch attention. Although many adsorbents had good fluoride adsorption capacities,most of them were commonly fine powders, leading to the limitation in practicalapplication. To overcome these limitations, this study has developed a novel granularadsorbent for defluoridation using natural siderite.Aluminum modified granular natural siderite (AMNS) was fabricated for fluorideremoval from drinking water. Effects of initial fluoride concentration, contact time,coexisting anions, and reaction temperature on F-adsorption on AMNS wereinvestigated. Adsorption capacity of AMNS was7.5times higher than pristine naturalsiderite. Adsorption closely followed the pseudo-second-order rate equation. Fluorideadsorption on AMNS was reasonably spontaneous and endothermic. Moreover, it wasobserved that the coexistence of HCO3-or PO43-negatively affected F-removal, whileCl-, SO42-, and NO3-had no significant effect on fluoride adsorption.The modified natural siderite was fabricated for F-removal by optimizing themixing ratio of natural siderite, Al2(SO4)3, and AlOOH, calcination temperatures andtime durations, and the optimaized adsorbent was obtained.(OMNS). Solution pH hadno significant effect on F-removal between3.5and10.0. Kinetic results showed thatadsorption followed the pseudo-second-order kinetic equation. Both the externaladsorption and the intra-particle diffusion contributed to adsorption processes.Thermodynamic data showed that fluoride adsorption was reasonably spontaneous andendothermic. Moreover, fluoride adsorption was obviously constrained by thecoexistence of HCO3-and PO43-. Column studies revealed that breakthrough time andadsorption capacity were lower at the higher F-concentration and/or higher flow rate.The XRD analysis indicated that the uptake of fluoride attributed to the coexistence ofhematite and γ-Al2O3in the modified material. In addition, aluminum, bentonite and soluble starch were used to modify naturalsiderite (ABS-NS) for fluoride removal from drinking water. Solution pH had nosignificant effect on F-removal between5and7. Adsorption closely followed thepseudo-second-order rate equation, which indicated that both external mass transferand intra-particle diffusion controlled F-adsorption. Thermodynamic data showed thatF-adsorption was reasonably spontaneous and endothermic. Effects of co-existinganions on fluoride adsorption followed: PO43-> HCO3-> SO42-> Cl-> NO3-. Thepresence of As(V), Ca2+and Mg2+promoted fluoride adsorption on ABS-NS.Pilot test was conducted at Changping Xiaotangshan nursery to remove F-fromhigh F-groundwater, using calcination-soaked modified natural siderite (CS-NS).Influence of solution pH was significant for fluoride removal. In single column withadjusted pH around6.5in influents, fluoride adsorption capacity is6.5times higherthan that pristine groundwater as influents (pH=7.79). In double-column series withadjusted pH around6.5in influents, fluoride adsorption capacity is6.7times higherthan that pristine groundwater as influents (pH=7.79). Adsorbent still showed highadsorption capacity after three regeneration cycles.