Clinoptilolite Supported Zn-Al Layered Double Hydroxides For The Adsorption Of Fluoride From Aqueous Solution

Fluorine is a trace element necessary for human body,appropriate amount of fluoride intake may promote the development of human teeth and bones,but beyond a certain range will cause harm to human health.Drinking water is the main source of fluoride consumption for human.The recently research on the drinking water quality in rural areas of Haidian District shows that the fluoride content of groundwater significantly exceed,which is a serious threat to the health of local residents.Zeolite and layered double hydroxides(LDHs) have excellent adsorptive performance,the purpose of this paper is to develop an efficient fluoride removal materials using low-cost natural zeolite of southwest Liaoning,Zn-A1 layered double hydroxides will be loaded on the surface of zeolite to improve its adsorption capacity.The X-ray diffraction,chemical analysis and electron microprobe analysis results indicate the main phases of natural zeolite are clinoptilolite and quartz.After loaded Zn-Al layered double hydroxides,the Zn-Al LDHs peaks can be found,and some white substance can be seen at the surface of zeolite through the scanning electron micrograph.For kinetics study,the experiments demonstrate that maximum fluoride removal was obtained at a pH between 4 and 6,and it took 8h to attain equilibrium,the optimized amount is 5g/L and the speed of oscillation is 180 r/min.Kinetics adsorption profiles offered excellent fit with pseudo-second-order model with a high R~2 value over 0.99.The intraparticle diffusion model indicates there are two-stage adsorption processes,in the first stage,the fluoride adsorption occurs at the surface,in the second stage the adsorption goes into the hole,the adsorption rate of the second stage is faster than the first stage.The shape of adsorption isotherm curve is S, Langrnuir model is not suitable to explain the experimental isotherm,Freundlich model demonstrate that the adsorption is unfavorable in the low fluoride concentration and is favorable in the high concentration.The calculated results of D-R model indicate that when the fluoride concentration is low,the adsorption is mainly physical;when the fluoride concentration is high,the adsorption is mainly chemical. The mechanism of fluoride removal for this material is ion exchange,the double hydroxide play a major role in the removal of fluoride.Compared with other methods(aluminum and ziconium),zeolite supported layered double hydroxide is better,the amount of adsorption is 14 times than natural zeolite,it has a good prospect for practical application on the removal of high fluoride concentration.