STRUCTURAL EVOLUTION OF HEAT-TREATED COLLOIDAL PYRITE UNDER INERT ATMOSPHERE AND ITS APPLICATION FOR THE REMOVAL OF Cu(II) ION FROM WASTEWATER

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.