Abstract
In this paper, we report a study on structural evolution, magnetic susceptibility and arsenic content of colloidal pyrite from
Xinqiao deposits in Tongling, Anhui Province, China. The pyrite was treated under N2 atmosphere and charaterized with X-ray
powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), magnetic susceptibility analysis, and atomic
fluorescence spectroscopy (AFS). We observed that heating of colloidal pyrite in N2 atomosphere did not change the crystal
structure, arsenic content and magnetic susceptibility at lower temperatures (<350 °C). A small amount of magnetite and
monoclinicpyrrhotite were formed at 400°C. Monoclinic pyrrhotite was the major product at 500°C. Hexagonal pyrrhotite
appeared and magnetite transformed to pyrrhotite at 600°C. Hexagonal pyrrhotite further transformed to troilite (FeS). At 900°C,
troilite (FeS) was the only final product. The magnetic susceptibility shows a sharp increase by increasing the temperature from
400°C to 450°C due to formation of magnetite and monoclinic pyrrhotite. We also compared the removal of Cu(II) ion from
wastewater with colloidal pyrite and its heat-treated products. Removal of Cu(II) ion was most efficient with the products heattreated
at 500°C.