Preparation And Defluoridation Properties Of Hydroxyapatite Modified Composites

Excessive fluorine in drinking water has been recongnized as one of the serious problems around the world. In China, there are several ten millions of people suffer from endemic disease caused by extra intake of fluoride from drinking water. The removal of fluoride contained in drinking water has become an urgent need.In this study, a series of available defluoridation adsorbents were prepared by modified hydroxyapatite. The preparation conditions, physicochemical characteristics, defluoridation properties and mechanism were discussed and the drawing conclusions as follows:（1） Hydroxyapatite was synthesized by co-precipitation method was used to remove fluoride ions from aqueous solutionVThe defluorination effect of various parameters were investigated. The research results show that the reaction temperature was 40<, Ca/P was 1.5:1, reaction time was 60 mins, ageing time was 48 h, ageing temperature was 25<, calcination time was 2h, calcination temperature was 200<. The relevant sample was confirmed by using scanning electron microscope（SEM）, Transmission Electron Microscopy（TEM）, X-ray diffraction（XRD）, Fourier transform infrared spectroscopy（FT-IR） techniques.The pH was 5.0, initial fluoride concentration was 10mg/L, adsorbent dose was 0.05g/50 mL, the maximum adsorbent capacity was 9.68mg/g. Ascending fluoride adsorption capacity increases with the increasing amount of chloride, nitrate and sulfate ions. Opposite effect for carbonate ions was happened in fluoride uptake on HAP. As for phosphate ions, it kept constant on the fluoride sorption on HAP different previous ions mentioned. The experimental data showed that the adsorption process follows the Langmuir equation models. The kinetic adsorption data showed that the adsorption process follows the pseudo-second order kinetic. The results of adsorption and reuse experiments indicated that the HAP adsorbent could be employed as a promising adsorbent for fluoride adsorption from drinking water.（2） In order to improve the defluoridation capacity, defluoridation adsorbent of Al-OH-HAP was prepared by hydroxy-aluminium modified HAP. The relevant sample was confirmed by using SEM, XRD, FT-IR, surface area measurement（BET） techniques. The defluoridation properties were discussed. It was clearly to see that the defluoridation capacity was influenced greatly by the parameters of pH, adsorbent dosage, coexisting anions and fluoride initial concentration. The experiment data were fitted well by Langmuir istherm equation, and the maximum adsorption capacity was 36.15 mg/g. The defluoridation capacity was increased obviously when the reactive temperature was improved. Adsorption kinetics was mainly controlled by two steps of particle internal diffusion and chemical reaction. After four regeneration and reuse cycles, the Al-OH-HAP adsorbent still showed high adsorption capacity.（3） A bioinorganic composite namely hydroxyapatite/chitosan（HAP/CS） composite which could be employed for the in-situ co-precipitation method was prepared and studied for its defluoridation efficiency. The absorbents were characterized with SEM, XRD, FT-IR and BET studies. The pH has a significant effect on the adsorption and the optimum equilibrium pH value is about 6.0. Both models of Langmuir and the Freundlich could predict the experimental data conducted; however, Langmuir model had the better correlation coefficient than Freundlich model did at different temperatures. The kinetic adsorption data showed that the adsorption process follows the pseudo-second order kinetic. The thermodynamic and kinetics parameters were obtained. The mechanism of fluoride adsorbed on HAP/CS was also discussed. The negative G0 and H0 at different temperatures indicates respectively spontaneous nature and exothermic natureu however, positive S0 represents increasing process for entropy. The E value（7.639 kJ/mol） ranged from 1 to 8 kJ/mo L demonstrates that the adsorption is dominated by physical process. But the Ea value was positive and S* approximates to zero indicate that the adsorption is chemical process. Adsorption process was mainly controlled by combined action of physical and chemical reaction.（4） Fe₃O₄/HAP composites materials（magnetic HAP） were fabricated by the in-situ co-precipitation method in the preparation of HAP mixed with Fe₃O₄. The adsorption of F- ions by magnetic HAP was investigated. Compared with HAP adsorbent, HAP mixed with Fe₃O₄ has magnetic properties, and can separate and recycle by the ordinary magnets. The effects of parameters, such as reaction time, reaction temperature, aging temperature, aging time and Fe₃O₄ dosages, et al. on absorption property were investigated. The results show that the optimal experimental conditions were obtained as follows: reaction temperature 60 oC, reaction time 1h, aging temperature 25 oC, aging time 12 h and Fe₃O₄ dosages 0.08 g. The adsorption capacity reach maximum of 7.82 mg/g. The adsorption data could be fitted by both models of Langmuir and the Freundlich. Especially, Langmuir model had the better correlation than Freundlich model. The maximum absorption capacity was 21.76 mg/g by calculation of Freundlich model. Based on the thermodynamic parameters, including G0, H0, S0 calculated, indicated the adsorption of fluoride ion on the magnetic HAP was belonging to the spontaneous reaction. The kinetics result shows that F- absorption follows Pseudo second-order kinetics.（5） In order to improve fluoride adsorption capacity and bacteriostatic effect, fluoride adsorbents of Ag-HAP was prepared by silver modified HAP. The absorbents of before and after adsorption were characterized by FT-IR. The mechanism of fluoride adsorbed on Ag-HAP was also discussed by adsorption thermodynamics and adsorption kinetics. The adsorption process was spontaneous nature, exothermic and increasing process for entropy. bacteriostatic effect shows that Ag-HAP can inhibit bacteria in domestic water up to 30 days. Compatible water purifying devices had continuous filtration water, the water quality indicators measured are eligible. The concentration of fluoride was less than 1.0 mg/L.（6） In this experimentuactivated carbon（AC） was blended with hydroxyapatite, The HAP/AC composite particles was prepared with heating. The influence of the HAP/AC, concentration of PVA, columnar, roasting time and roasting temperature on adsorption the effect was studied. Then applied the composite particles to study the adsorption of the simulate F- waste water. The composite particles were tested for its ability to remove F- from aqueous solution by batch static adsorption and dynamic column adsorption, and the mechanism of the adsorption process was determined. Field studies were carried out with the fluoride containing water sample collected from a fluoride-endemic area in order to test the suitability of the absorbents at field conditions.