Regeneration Properties And Adsorption Properties Of The Hydrotalcite-like Compound Defluorinating Agent

According to the intake of fluoride，fluorine can be beneficial or harmful to the healthof the human. The World Health Organization states that the concentration of fluorine ionsin drinking water shall not exceed1.5mg/L，while China provides the concentration of F-in drinking water shall not exceed1.0mg/L. Worldwide, especially in semi-arid areas, thehazards of fluoride in groundwater to human is a concern.This article expanded the research which have been done by our research group abouthydrotalcite-like compound defluorination agent. The influence of various regenerationmeans: calcination, soaking in alkali liquor or acid liquor, being calcined after soaking inalkali liquor or in acid liquor or in CaCl2solution, the results showed that the meanswithout calcination had no significant regeneration effect, the defluorination rate of theagent that had been calcined was high, especially the agent that soaked in alkali liquor, thedefluorination rate reached up to90%. Calcined temperature300,350,400,450,500,550,600°C were studied, the results showed that400°C was themost suitable calcination temperature; calcined the saturated adsorbent in400°Crespectively for0.5,1,1.5,2,2.5,3,3.5,4h the results showed that2h is preferably calcinedtime; soaked in the NaOH solution （respectively pH=8,9,10,11,12,13,14）1.5h, afterbeing washed, calcined under conditions of400°C for2h, the results showed that pH=9was the best condition.Fixed-bed reactor filled with the composite adsorbent was prepared to study thedynamic adsorption performance and then analysed the breakthrough curves （effluentconcentration of F-1.0mg/L for breakout point）, and the breakthrough curves weresimulated respectively by Thomas model,"shortcut" model and Boltzmann model. Fixedbed reactor’s diameter was4cm, length20cm. The general parameters set as that thequality of the bed was4g, flow velocity was12mL/min, the initial concentration of F-was10mg/L,the temperature was30°C, initial pH=7. In the case of other conditionsremain unchanged, designed single factors experiment: the quality of the bed were3,4,5g; flow velocity were10,12,14mL/min; initial concentration of F-were5,10,15, mg/L; temperature were20,30,40°C; initial pH were3,7,10; anions were Cl^-, SO₄^2-, NO_<sup>3-,HCO₃^-. Breakthrough curves showed that the volume of water treated before the breakoutpoint increased with increases of the quality of the bed, decreases of the flow rate,decreases of the concentration of F^-, increases of the temperature. Worse adsorption performance was showed under alkaline conditions, anions’ competitive adsorption degreeordered as HCO₃^-> SO₄^2-> NO_<sup>3-> Cl^-. Boltzmann model could simulated the breakthroughcurves best.