Preparation of hydroxyapatite with high specific surface and its application in defluoridation of ferric phosphate wastewater
In order to improve the adsorption efficiency of hydroxyapatite(HAP)for fluoride ion,HAP with high specific surface area was synthesized by chemical precipitation method through optimizing the preparation conditions such as reaction temperature,Ca/P molar ratio and aging time.The obtained HAP was characterized by FTIR,XRD,XPS,SEM and BET,and its adsorption performance of F-in simulated wastewater was evaluated.The results showed that the optimal preparation parameters of HAP were as follows:the reaction temperature of 20 ℃,Ca/P molar ratio of 1.6 and aging time of 24 h.The specific surface area of the HAP synthesized under the optimal conditions was up to 108.0 m2/g.The adsorption process of F-by HAP was a spontaneous and endothermic process and conformed to the Langmuir model.The maximum absorption capacity of F-by HAP at 303 K was up to 13.53 mg/g and the adsorption process conformed to the pseudo-second-order reaction kinetic model.The fluoride removal by HAP under acidic conditions was mainly through ion exchange.Continuous adsorption experiment of the prepared HAP in processing ferric phosphate wastewater demonstrated that the effluent F-concentration could be kept less than 1.0 mg/L for 32 h,showing good defluorination efficiency.The research results can provide some guidance for the preparation of high-efficiency fluoride removal adsorbents and the deep fluoride removal of iron phosphate wastewater.