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 N-2 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 N-2 atomosphere did not change the crystal structure, arsenic content and magnetic susceptibility at lower temperatures (<350 degrees C). A small amount of magnetite and monoclinicpyrrhotite were formed at 400 degrees C. Monoclinic pyrrhotite was the major product at 500 degrees C. Hexagonal pyrrhotite appeared and magnetite transformed to pyrrhotite at 600 degrees C. Hexagonal pyrrhotite further transformed to troilite (FeS). At 900 degrees C, troilite (FeS) was the only final product. The magnetic susceptibility shows a sharp increase by increasing the temperature from 400 degrees C to 450 degrees 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 heat-treated at 500 degrees C.