Removing Iron Compounds from Amakusa Pottery Stone by Combined Use of Hydrogen Reduction and Magnetic Separation

Abstract

The low grade pottery stone containing brown layer, of which color is due to the presence of high concentrated ferric ions, was reduced in H₂ atmosphere in order to obtain ferromagnetic materials. The results of Mössbauer spectrum, characteristics of magnetization vs. magnetic field, and X-ray diffraction patterns of brown layer before and after reduction treatment indicated that ferric ions are present in amorphous ferric hydroxide before the reduction treatment, and that ferromagnetic Fe₃O₄ or α-Fe is produced by the reduction treatment. The reduction treatment increased the magnetization of brown layer by a factor of 50. Thus, the brown layer was easily separated from the colorless part of pottery stone by applying the magnetic field to samples. When brown layer attracted to magnetic was immersed in dilute hydrochloric acid, ferromagnetic compounds were dissolved faster than that of raw pottery stone. This treatment lowered the Fe₂O₃ content in brown layer to 0.36%.