关键词: 天然锰钾矿, 八面体分子筛, 产出特征, 广西下雷锰矿

Abstract: In the supergene zones of Xialei manganese deposit in Guangxi, south China, there is abundant resource of natural cryptomelane, which is well known as a manganese oxide octahedral molecular sieve having a well-defined 2*2 tunnel structure (OMS-2) with K⁺ situated in tunnel positions. This study was focused on the occurrence characteristics of the cryptomelane-bearing ores and the mineralogical characteristics of natural cryptomelane. The morphology, chemical and structure features of natural cryptomelane were characterized by means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalyzer(EPMA), energy dispersive spectrometer (EDS) and X-ray fluorescence(XRF). The morphology of the natural cryptomelane crystals via SEM showed short prismatic, needle-like and fibrous shapes with the diameters varying from few nanometers to hundreds nanometres. The MnO₂ content was by and large over 90% and K₂O ranged from 2.52 to 4.37wt%. However, the composition resulted from EDS revealed a higher content of K, 3.37 - 4.17wt%. The XRD of the samples agreed with a monoclinic cryptomelane and the cell parameters were given as a = 9.956nm, b = 2.870nm, c = 9.706nm and β = 90.95°. The phase transformation temperature of the natural cryptomelane was about 635.5℃ examined by TGA and DTA and the cryptomelane was changed to bixbyite at a higher temperature. These studies reveal the significant features of cryptomelane for the potential application in the environmental materials science.

Key words: natural cryptomelane, manganese oxide octahedral molecular sieve, occurence, Xialei manganese deposit in Guangxi