EBSD-XPS法分析磷石膏中杂质物相

Phosphogypsum (PG) is a solid by product generated from the wet phosphoric acid process. A broad spectrum of compositions, including phosphorus, fluorine, silicon, and other hazardous impurities in the PG matrix significantly affect the PG's quality as the end-products, let alone its persistent ecological and environmental impacts caused by the huge quantity of storage and disposal. Therefore, identification of its impurity phases of PG becomes pivotal. Not only it provides the theoretical guidance for the separation processing but it also sheds insightful lightonits value-added utilization. Different spectral characterization techniques were deployed to unveil its impurity phases in the PG. The X-ray fluorescence spectroscopy (XRF) results show that the elements including P, Si, F and Al remain at a relatively higher level, while the elements such as Ba, Fe and Mg are present at the trace level. The X-ray diffraction spectroscopy (XRD) spectrum presents the dominant crystallite gypsum, whilethe crystal spectrum of other impurities is hardly observed. The electron backscatter diffraction (EBSD) by scanning electron microscope (SEM) results indicate the impurities in the form of silicon dioxide, sodium fluorosilicate, potassium fluorosilicate, calcium fluorophosphate, calcium fluoride, barium sulfate, iron sulfide, and aluminum oxide, etc. These compositions exist as the singular metallic oxides and present in the binary, ternary and multiple metallic oxides complex, making the impurities as a series ofthe composites in the crystallite PG framework. In order to investigate the surface binding energy of the prepared PG, X-ray photoelectron spectroscopy (XPS) was also employed. The results indicate the complexities of the impurities as in the form of calcium silicate, aluminum fluoride, magnesium fluoride, aluminum sulfate, aluminum phosphate, calcium phosphate, calcium hydrogen phosphate and calcium dihydrogen phosphate. In addition, the XPS result also shows the close featured positions, which underpins the characteristic peaks of calcium phosphate, calcium hydrogen phosphate, calcium dihydrogen phosphate and calcium fluorophosphates, indicating their relative similar surface bonding energy. To the best of the author's knowledge, thecombined characterization techniques using both EBSD and XPS, have been rarely applied in the elucidation of complex phase of the impurities of PG generated from the phosphoric acid process. The inherent advantages of using this proposed hybrid spectrum technique withan accurate establishment of the structure-activity relationship between the impurity phases and calcium sulfate crystal, the comprehensive constructing impurity phases, will pave a new way for the impurity phase characterization, value-added conversion, and integrated utilization of PG.