Transformation of Birnessite to Buserite, Todorokite, and Manganite under Mild Hydrothermal Treatment

D. C. Golden, C. C. Chen and J. B. Dixon
Department of Soil & Crop Sciences, Texas A&M University College Station, Texas 77843

Abstract: Investigations were conducted to determine the hydrothermal transformations of synthetic birnessite exchanged with different metal ions. Autoclaving in a Teflon-lined stainless steel pressure vessel at 155°C for 24 hr of Mg-, Ca-, La-, and Co-saturated birnessite yielded manganese minerals having 10-Å X-ray powder diffraction (XRD) spacings. The autoclaved Mg-birnessite yielded a mineral identical to natural todorokite in its infrared (IR) spectrum and XRD patterns. High-resolution transmission electron microscopy (HRTEM) provided images having 10-, 12.5-, 15-, and 20Å wide fringes indicating heterogeneous channel widths in the crystallographic a direction, and IR spectroscopy produced bands at 757, 635, 552, 515, 460, and 435 cm−1, confirming the product obtained by autoclaving Mg-birnessite to be todorokite. Prolonged autoclaving of Mg-birnessite yielded manganite (γ-MnOOH) as a by-product; manganite did not form when the autoclaving time was shortened to 8 hr. Also, when Ca-saturated samples were autoclaved, the product gave d-values of 10 Å, but the XRD lines were broad and heterogeneity of the channel sizes was evident from HRTEM observations. The Ca-derivative had an IR spectrum similar to that of natural todorokite. Images showing 10-Å lattice fringes were observed by HRTEM for the Ni-saturated sample, which also produced an XRD pattern similar to that of the Mg-saturated sample. Co- and La-saturated samples did not form todorokite, although HRTEM of La-saturated samples indicated some 10-Å lattice fringes that were unstable in the electron beam. Birnessite saturated with Na, K, NH4, Cs, Ba, or Mn(II) gave products having 7-Å spacings upon autoclaving.

Key Words: Birnessite • Buserite • High-resolution transmission electron microscopy • Hydrothermal • Manganite • Todorokite

Clays and Clay Minerals; August 1987 v. 35; no. 4; p. 271-280; DOI: 10.1346/CCMN.1987.0350404
© 1987, The Clay Minerals Society
Clay Minerals Society (www.clays.org)