Spectral Analysis of Trace Fluorine Phase in Phosphogypsum

Abstract

Phosphogypsum, which contains more than 90% of the calcium sulfate dehydrate (CaSO4 · 2H2O), is a kind of important renewable gypsum resources. Unlike the natural gypsum, however, phosphorus, fluorine, organic matter and other harmful impurities in phosphogypsum limit its practical use. To ascertain the existence form, content and phase distribution of trace fluoride in phosphogypsum has important theoretical values in removing trace fluoride effectively. In this present paper, the main existence form and phase distribution of trace fluoride in phosphogypsum was investigated by the combination of X-ray photoelectron spectroscopy (XPS) and Electron microprobe analysis (EMPA). The results show that trace fluoride phase mainly includes NaF, KF, CaF2, K2SiF6, Na2SiF6, Na3AlF6, K3AlF6, AlF3 · 3H2O, AlF2.3(OH)0.7 · H2O, Ca5(PO4)3F, Ca10(PO4)6F2. Among them, 4.83% of fluorine exists in the form of fluoride (NaF, KF, CaF2); Accordingly, 8.43% in the form of fluoride phosphate (Ca5(PO4)3F, Ca10(PO4)6F2); 12.21% in the form of fluorine aluminate (Na3AlF6, K3AlF6); 41.52% in the form of fluorosilicate (K2SiF6, Na2SiF6); 33.02% in the form of aluminum fluoride with crystal water (AlF3 · 3H2O, AlF2.3(OH)0.7 · H2O). In the analysis of phase constitution for trace elements in solid samples, the method of combining XPS and EMPA has more advantages. This study also provides theoretical basis for the removal of trace fluorine impurity and the effective recovery of fluorine resources.