钾位铈掺杂黄钾铁矾的磷吸附特性及机理研究

K+-Site Ce-Doped Jarosite for Phosphate Adsorption:a Mechanism Study

黄钾铁矾是一种自然界常见的含铁矿物,它对砷酸根有一定吸附作用,但几乎不吸附同样构型的磷酸根.为了改善黄钾铁矾的磷吸附性质,本研究制备了铈掺杂的黄钾铁矾,并采用X射线衍射(XRD)、电感耦合等离子发射光谱(ICP-OES)等表征手段,构建了铈离子占据钾离子位的结构模型.磷吸附实验结果表明,少量铈的掺杂可将黄钾铁矾的磷吸附容量(pH=7,24 h)从1.69 mg/g显著提升至29.33 mg/g.同时,初始p H和共存阴离子对其除磷效果影响较小,说明含铈黄钾铁矾对磷酸盐的吸附具备高选择性.进一步分析表明,该吸附过程符合准二级动力学模型,吸附等温线符合Freundlich等温吸附模型,分析结果表明吸附过程可能是易进行的化学吸附.利用XRD及阴离子交换色谱,证实了相比于纯黄钾铁矾,铈的掺杂提高了黄钾铁矾的反应活性,大幅提升了吸附过程中磷酸根与硫酸根的置换.通过X射线光电子能谱与红外光谱表征,推测吸附过程形成稳定的Ce—O—P化学键,实现特异性化学吸附.这些研究结果为含磷废水的吸附治理提供了一种新的吸附材料,并有望为黄钾铁矾的改性和资源化利用提供参考.

Jarosite is a common iron-containing mineral.Researchers have studied its application for removing aqueous pollutants,such as Cr(VI)and As(V).Surprisingly,it shows adsorption for arsenates,but little for the structurally similar phosphate ions.In this study,we prepare cerium doped jarosite and prove the successful doping of cerium at the K^(+)site by X-ray diffraction(XRD),inductively coupled plasma-optical emission spectrometry(ICP-OES),energy dispersive spectroscopy(EDS),and X-ray photoelectron spectroscopy(XPS).Phosphorus adsorption experiments show that the small amount of cerium doping(Ce content:8.75×10^(-5)mol/g)significantly improves the phosphate adsorption of jarosite,from 1.69 mg/g to29.33 mg/g(pH=7,24 h).The phosphate adsorption of Ce-doped jarosite exhibits good p H stability(from pH=3 to pH=11)and excellent selectivity,which is capable of maintaining more than 91%of its adsorption capacity in the presence of various competing anions,such as HCO_(3)^(–),CO_(3)^(2–),humic acid anion,SO_(4)^(2–),NO_(3)^(–),and Si O_(3)^(2–).Further analysis reveals that the adsorption process obeys the pseudo-second order kinetic model while the adsorption isotherms represent the Freundlich isotherm.The analysis indicates that the adsorption may be a chemical adsorption process that is easy to proceed.To explore the mechanism of adsorption enhancement,we first characterize the Zeta-potential of the pure jarosite and Ce-doped jarosite.The result indicates similarity of the surface potential between the two samples,which rules out the electrostatic adsorption mechanism.Next,based on the result of anion exchange chromatography,we confirm that the cerium doping greatly increases the exchange between the sulfate groups in jarosite and the phosphate groups in solution,from 2.85 mg/g to 24.90 mg/g.Finally,XPS high-resolution spectroscopy reveals that the chemical environment of Ce changes after the phosphate adsorption,likely indicating the formation of Ce—O—P chemical bonds to achieve specific chemisorption.These results may provide insights for the modification and application of jarosite,as a new adsorbent material for treating phosphorus rich wastewater.