Synthesized rare earth ion-adsorption clays (La, Ce, Nd, Dy and Y, ~ 400 ppm each) were prepared from kaolinite at various basic pH in open-air conditions. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICP-MS) were used to characterize the effect of pH on the adsorption mechanism of rare earth elements (REEs) on kaolinite. The crystal structure of kaolinite by XRD analysis is not altered after REE adsorption, suggesting that REEs are bound to the surface of kaolinite. Elemental analysis by XPS and ICP-MS show that the surface concentration of REEs on kaolinite is pH dependent, and a local maximum of the surface concentration is achieved at pH 10. Three characteristics of the La 3d_5/2 XPS photoemission feature were measured and compared to those of standard La compounds to probe the speciation of REEs, and electrostatically bound hydroxides such as REE(OH)₂⁺ are identified as the primary species on the surface of kaolinite. Compared to the typical ion-adsorption clays with intrinsic acidic pH, clays synthesized at basic pH exhibit similarly high rare earth ion-exchange efficiency with ammonium sulfate (AS), suggesting that rare earth ion-adsorption clays can exist in both acidic and basic environments.

在露天条件下，由高岭石在各种碱性pH下制备合成的稀土离子吸附粘土（La，Ce，Nd，Dy和Y，各约400 ppm）。X射线衍射（XRD），X射线光电子能谱（XPS）和电感耦合等离子体质谱（ICP-MS）用于表征pH对稀土元素（REE）在高岭石上的吸附机理的影响。REE吸附后，通过XRD分析得到的高岭石的晶体结构没有改变，这表明REE结合在高岭石的表面上。通过XPS和ICP-MS进行的元素分析表明，高岭石上REE的表面浓度与pH有关，并且在pH 10时达到了表面浓度的局部最大值。La 3d _5/2的三个特征测量XPS的光发射特征，并与标准La化合物的XPS光发射特征进行比较，以探测REE的形态，并确定静电结合的氢氧化物（例如REE（OH）₂ ^+）是高岭石表面的主要物种。与具有固有酸性pH值的典型离子吸附粘土相比，在碱性pH值下合成的粘土表现出与硫酸铵（AS）相似的稀土离子交换效率，这表明稀土离子吸附粘土可同时存在于酸性和碱性环境中。