Pathways of birnessite formation in alkali medium
Birnessite is a common weathering and oxidation product of manganese-bearing rocks. An O2 oxidation procedure of Mn(OH)2 in the alkali medium has been used to synthesize birnessite. Fast and powder X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction (ED), energy dispersed X-ray analysis (EDAX), infrared spectroscopy (IR) techniques and chemical composition analysis, Eh-pH equilibrium diagram approaches were employed to investigate the reaction process and pathways of birnessite formation. Results showed that the process of the birnessite formation could be divided into four stages: (1) formation stage for hausmannite and feitknechtite, (2) stage of transformation of hausmannite and feitknechtite to buserite, (3) buserite crystal growing stage, and (4) stage of conversion of buserite into birnessite. Mn(OH)2 was mainly present as amorphous state only for a short initial time of oxidation reaction. In the oxidation process, buserite formed following two pathways by recrystallization after dissolution of the intermediates, and the transformations of the minerals depended on the Eh determined by the dissolved O2 concentration on their surfaces. The results are fundamental in further exploration on the mechanism of birnessite formation in the alkali medium. A great practical significance would also be expected with respect to the areas of material sciences.
作 者： FENG Xionghan TAN Wenfeng LIU Fan HUANG Qiaoyun LIU Xiangwen 作者单位： FENG Xionghan,TAN Wenfeng,LIU Fan,HUANG Qiaoyun(College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China)LIU Xiangwen(Testing Center, China University of Geosciences, Wuhan 430074, China)
刊 名： 中国科学D辑(英文版) SCI 英文刊名： SCIENCE IN CHINA (EARTH SCIENCES) 年，卷(期)： 2005 48(9) 分类号： P3 关键词： birnessite pathway of formation reaction process Eh-pH diagram hausmannite feitknechtite