Study On Mechanisms Of Fluoride Removal From Groundwater Using Lanthanum-modified Bone Waste Composite

Fluoride contamination in groundwater water cause human diseases.Excessive intake of fluoride can lead to teeth and bone disease.A strict rule from WHO is adopted the maximum allowable fluoride concentration level for drinking water at 1.5mg/L.Adsorption has been considered a promising technique for fluoride removal because of its simplicity and selectivity.The current worldwide issue of fluoride contamination in groundwater has resulted in an increased demand for efficient adsorbents.Lanthanum is a widely used rare-earth metal that has a high fluoride adsorption.Meanwhile impertinent discard and landfill of bones waste led to environmental pollution.In order to achieve bones waste recycling and enhance the efficiency of fluoride removal,a lanthanum-modified bone waste?LBW?composite was synthesized and evaluated by batch experiments to remove fluoride from contaminated groundwater in this study.The main conclusions were as follows:?1?The LBW composite adsorbent was characterized by SEM,BET,XRD,FTIR and XPS.The SEM and BET revealed that the introduction of lanthanum could modify the porous structure of the adsorbent and enhance its specific surface area.The XRD patterns confirmed the presence of lanthanum oxide or hydroxide in LBW composite,and the micro amount of La doped contributed to significant defluorination.The FTIR spectra confirmed the presence of abundant-OH groups on the LBW composite,and the protonation of these-OH groups facilitated fluoride removal due to ion exchange.The high resolution XPS spectra of O 1s and La 3d showed that the content of hydroxyl groups?-OH?reduced and the peaks of La 3d shifted to the higher binding energy side after fluoride adsorption.?2?The LBW composite had a high pH_zpc of 11.4 and the fluoride adsorption was barely affected by the solution pH over a wide pH range of 2.5–10.0.The influence of common co-existing oxygen anions in the range of 0–100 mg/L was not significant.Possible defluoridation and regeneration were proposed.?3?The fluoride adsorption was a typical chemisorption process and followed PSO and F-L PSO equations.The FVER model provided a more accurate prediction of a larger surface coverage degree with respect to equilibrium at initial stage during adsorption of fluoride.Isotherm studies revealed that the reaction obeyed the Langmuir model,indicating that this process was monolayer adsorption.?4?The fluoride adsorption was mainly controlled by the processes of electrostatic attraction on the LBW surface with a positive charge and ion exchange between fluoride and hydroxide ions.In this study,the porous bone waste of animals with simple pretreatment in daily life is cheap and easy to obtain,which reduces the secondary pollution of biomass waste to the environment and realizes the reuse of resources.It also makes use of multivalent rare earth metals for the first time.The lanthanum-modified bone waste increases the adsorption of bone powder while maintaining a high surface activity of lanthanum.The composite material has a synergistic effect and is rich in hydroxyl,carbonyl,and other functional groups,so that the adsorption capacity of the modified bone powder is effectively improved.This research provides an alternative method for fluoride removal from contaminated groundwater in practical application.