The Influence Factors Of Calcium Phosphate Defluorization Performance Research

Fluoride is a necessary trace element for human snince it plays a significant role in bone development along with bone and tooth strengthening. Excess adsorption will cause a kind of disease called "Fluorosis". Long term of over dose fluoride intake will lead to bone distortion, bone aching, muscle and tendon calcium, walking trouble and even paralysis for severe victims.Untill recently, great progress has been made in the study of fluoride removal with nanosized hydroxyapatite (nHAP), while fluoride removal with Nanosized fluorapaptite (nFAP), Amorphous Calcium Phosphates (ACP) are rarely reported, especially for ACP and the effect of LMWOAs on the defluoridation capacity of ACP. This study focus on the removal of fluoride aqueous solution onto nFAP,ACP and the effect of LMWOAs on the defluoridation capacity of ACP.This paper mainly includes four parts as follows:(1) Study of preparation of nFAP and ACP powders via precipitation method.XRD、IR、TEM were used to characterize nFAP and ACP. Results showed that the samples were pure nFAP and ACP and the particles are of homogeneous microstructure and formed a uniform nanomaterial.(2) Study on removal of fluoride aqueous solution onto nFAPThe influence factors on adsorption including adsorbent dose, initial fluoride concentration, pH, temperature, regeneration were studied for the purpose of investigating the defluoridation efficiency of three materials(nHAP, nFHAP, nFAP). A detailed analysis of the regression coefficients showed that Langmuir and Freundlich models adequately described the adsorption data, but the data were better fitted by the Langmuir isotherm. While the pseudo-second-order model was the best choice to describe the fluoride adsorption behavior, and thermodynamic studies revealed that the adsorption of flouride by nanosized fluorapatite was spontaneous and endothermic in nature. Nanosized fluorapatite exhibited a great defluoridation capacity up to7.45mg/g, which was similar to that of nanosized hydroxyapatite (7.75mg/g). In consideration of the lower cost and easier regeneration property of nanosized fluorapatite, it would provide an alternative for the adsorption and removal of fluoride from aqueous solution.(3) Study on removal of fluoride aqueous solution onto ACP In this study, the potential of ACP for fluoride removal from aqueous solution was evaluated. Several parameters including adsorbent dosage, contact time, initial fluoride concentration, and pH were investigated for their effects on the removal of fluoride. Results show that defluoridation efficiency of ACP performance better than nHAP when pH<5or T>328K. However, when the value of pH>5, it shows opposite results. Draw a conclusion that the smaller the particle size, the better the fluoride adsorption capacity, but when the particle size is small enough to amorphous state, the fluoride adsorption capacity depends on the adsorption factors.(4) The effect of LMWOAs on the defluoridation capacity of ACPIn this section, oxalic, citric and malic acids were selected as the representative of LMWOAs. Adsorption experiments were carried out to investigate the effects of contact time, initial fluoride concentration, solution pH, and LMWOAs on fluoride adsorption onto ACP. Results indicated the defluoridation capacity of ACP was enhanced by the addition of LMWOAs. The order of the ability of LMWOAs to enhance the defluoridation capacity of ACP was citric acid> oxalic acid> malic acid.