Study On Adsorption Of Fluoride Ion In Water By Stalks Of Two Aquatic Plants

Fluoride ion,which has a close relationship with our life,is widely distributed in water,soil and the atmosphere.Fluorine is an essential trace element for human being,plant and animal.But excessive amounts of fluorine will be harmful for organism.At present some methods of fluorine removing are still inadequate,so we need to find some more effective methods to remove the fluorine in water and it has a important scientific and practical significance.Two common aquatic plants,Polygonum orientale and Phragmites australis,were chosen as adsorption materials in the principle of economy and easy operation.Aqueous solutions of sodium fluoride were prepared as simulated fluoride waste water.The fluoride removal ability of two adsorbents was tested by static adsorption experiments.The effects of pH value,dosage,initial concentration,temperature,adsorption time,compatible anion and regeneration method on the adsorption efficiency were analyzed.Meanwhile,the adsorption kinetics and isotherm of adsorbents treated by different methods were studied.The fluoride removal abilities among three methods were compared and analyzed.The ultimate aim is to explore factors affecting adsorption.The results are showed as following:(1)According to experimental data,FT-IR and SEM analysis,P.orientale and P.australis the fluoride removal mechanism of adsorbent is mainly ion exchange.(2)Adsorption kinetics analysis showed that the adsorption data fit well to the pseudo-second-order kinetic model,which inferred that the adsorption process of fluoride ion is mainly chemical adsorption process.(3)Adsorption thermodynamics analysis showed that the adsorption of fluoride ion followed the Langmuir adsorption isotherm model,which inferred that adsorption is spontaneous and endothermic process.The increase of temperature is beneficial to the adsorption.(4)The optimal operating conditions were determine by experiments:initial concentration of sodium fluoride solution is lOmg/L;the optimum dosage of adsorbent is 0.5g/L without changing the original fluorine solution pH value;the fluoride ions concentration is satisfactory in meeting drinking water standards after treated by adsorbents;the adsorption equilibrium time is 210min,and it is irrelevant to concentration;adsorbent performed adsorption ability in the pH range of 2.0-9.0.Different concentrations of the coexistence anions have different effects on fluoride ion remove.In a specific concentration range,three kinds of anions(Cl-,SO42-,PO43-)have different effects on fluoride ion removal process.(5)Regeneration experiments showed that adsorption activity could be restored by alkali treatment when the adsorbent saturated.Adsorption capacity was reduced after regeneration,but still higher than the other adsorbents.This indicated that the adsorbent could be recycled.It reflects high application use value.There are a large number of P.orientale and P.australis abandoned in the past.According to our study,P.orientale and P.australis can be used as adsorbents after modified.They could be used to remove fluoride ions in water,which have a considerable practical significance in saving energy and chemical agents.Overall,two aquatic plants have good adsorption effects on the fluoride ion and can play an important role in drinking water fluorosis mitigation.Also this study aims to provide a theoretical basis for improving high fluoride water quality.