磷酸三钙去除U(Ⅵ)的性能与机理研究

    Performance and Mechanism of U(Ⅵ) Removal by Tricalcium Phosphate

    • 摘要: 为了探究磷酸三钙对U(Ⅵ)的吸附性能与机理,以碳酸钙和磷酸氢二铵为原料,采用固相法合成磷酸三钙粉末,并利用X射线衍射仪(XRD)、傅里叶转换红外光谱仪(FTIR)、扫描电子显微镜(SEM)和比表面积分析仪(BET)对其理化特性进行表征。研究pH、固液比、吸附时间、U(Ⅵ)初始浓度、吸附温度等因素对磷酸三钙去除U(Ⅵ)性能的影响。采用动力学吸附、等温吸附、热力学吸附等模型及XRD、FTIR、X射线光电子能谱(XPS)、SEM、能谱仪(EDS)、电感耦合等离子体发射光谱仪(ICP-OES)等表征手段揭示磷酸三钙去除U(Ⅵ)的机理。结果表明:在pH=3.0、固液比0.1 g/L、吸附时间60 min、U(Ⅵ)初始质量浓度120 mg/L、吸附温度308 K的条件下,磷酸三钙对U(Ⅵ)的平衡吸附容量达到999.25 mg/g。该吸附过程符合准二级动力学模型(化学吸附)和Langmuir模型(单层吸附),且为自发吸热过程。磷酸三钙对U(Ⅵ)的去除机理为溶解和沉淀过程:在酸性水溶液中,磷酸三钙溶解出的Ca2+和PO3-4与UO2+2发生沉淀反应,在磷酸三钙表面生成准钙铀云母(Ca(UO2)2(PO4)2·6H2O)。以上结果表明:磷酸三钙可作为一种有应用前景的用于处理含U(Ⅵ)废水的吸附材料。

       

      Abstract: In order to explore the adsorption performance and mechanism of tricalcium phosphate for removing the U(Ⅵ), the tricalcium phosphate powder was synthesized by the solid phase method using calcium carbonate and diammonium hydrogen phosphate as the raw materials. And then, the physical and chemical properties of tricalcium phosphate powder were characterized by X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM) and specific surface area analyzer(Brunauer-Emmett-Teller, BET). The effects of pH, solid-liquid ratio, adsorption time, initial U(Ⅵ) concentration, adsorption temperature on the U(Ⅵ) adsorption performance of tricalcium phosphate were also investigated. The kinetic adsorption, isothermal adsorption, thermodynamic adsorption models, as well as XRD, FTIR, X-ray photoelectron spectroscopy(XPS), SEM, energy dispersive spectroscopy(EDS), inductively coupled plasma optical emission spectrometer(ICP-OES) were used to reveal the U(Ⅵ) adsorption mechanism of tricalcium phosphate. The results show that the adsorption capacity of U(Ⅵ) by tricalcium phosphate is up to 999.25 mg/g, when the adsorption conditions are as follows: pH of 3.0, solid-liquid ratio of 0.1 g/L, adsorption time of 60 min, initial U(Ⅵ) mass concentration of 120 mg/L and adsorption temperature of 308 K. The adsorption process conforms to the pseudo-second-order kinetic model(chemical adsorption) and Langmuir model(monolayer adsorption), which is a spontaneous endothermic process. The U(Ⅵ) adsorption mechanism of tricalcium phosphate is the dissolution and precipitation process. In acidic aqueous solution, Ca2+ and PO3-4 dissolved from tricalcium phosphate can combine with UO2+2 to form meta-autunite (Ca(UO2)2-(PO4)2·6H2O) on the surface of tricalcium phosphate. The aforementioned results suggest that tricalcium phosphate can be utilized as a kind of promising adsorption materials for U(Ⅵ) containing wastewater treatment.

       

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