A Study Of Fluoride Removal From Groundwater By Modified Natural Zeolite

Fluorine is an essential trace element for humans body’s normal growth, amountof fluoride is beneficial to humans, but excess and deficiencies of fluorine will causeharm to humans. According to investigation, about7700million people are drinkinggroundwater that the fluoride concentration is more than1.0mg/L,2297.78millionpeople have fluorosis because the poor natural water quality. Drinking high fluoridewater is seriously endanger human health and safety. Therefore, for groundwaterquality conditions, the local socio-economic conditions, it is particularly urgent andimportant that research an efficient and economical material processing of highfluoride groundwater.In this paper, natural zeolite as based material, respectively using ferric chloride,aluminum sulfate, magnesium chloride and chitosan modified it. Optimalmodification conditions of four modifide method have determined. Parameters of pH,stirring rate, adsorption time, initial zeolite dosage and standing time on theadsorbent effect of fluoride removal have been researched. The four kinds of mainanions in groundwater—C1^-, HCO₃^-, SO42-, PO₄^3-on fluoride removal effect of themodified zeolite also have been studied. And the adsorption sequence of these fouranions in a variety of modified zeolite have been determined. The structure andcomposition of the zeolite before and after modification have been determined bySEM+EDS, and the adsorption mechanism of the modified zeolites werepreliminary studied.The results show that the effect of fluoride removal of natural zeolite modifiedby iron salts, aluminum salts, magnesium salts and chitosan has improvedsignificantly. The natural zeolite modified by10%ferric chloride solution and2%aluminum sulfate solution can to treatment the water with fluoride concentration of2mg/L standards when the amount of0.5g/250mL. After immersion for3h with10%magnesium chloride solution, the modified natual zeolite can to treatment the flurinecontaining water standard within1.5h. Switch to the concentration of chitosan for0.05mg/L modified zeolite, when raw water pH is6.0, zeolite dosage is0.1g/250mL, reactiong time is50min, the high fluoride water could treatment standard.The SEM results show: after modified, the zeolite pore structure have beenadjusted and the surface area increase, thus the effective absorption of iron,aluminum, magnesium, chitosan and its hydrolysis product, it became a good carrierof inorganic salts and organic matter. Anion experimental results show that: C1^-,HCO₃^-have little impact on effect of fluoride removal of a variety of modifiednatural zeolite, but SO42-, PO₄^3-have greater impact. The anion adsorption sequenceof natural zeolite modified by iron salts and aluminum salts isPO₄^3->SO42->HCO₃^->C1^-; The anion adsorption sequence of natural zeolite modifiedby magnesium salts and chitosan is SO42->PO₄^3->HCO₃^->C1^-.Using the Langmuir and Freundlich isotherm models fit the adsorption behaviorof the four modified zeolite, zeolite modified by ferric chloride, aluminum sulfateand magnesium chloride are in line with the Langmuir and Freundlich isothermadsorption model. The maximum adsorption capacity obtained by the Langmuirisotherm adsorption model deduced respectively2.91mg/g,1.985mg/g and0.52mg/g.Zeolite modified by chitosan is in line with the Langmuir isotherm adsorption model.The maximum adsorption capacity is10.63mg/L.