CATION EXCHANGE SELECTIVITY AND HYDROTHEMAL REACTIONS OF K-DEPLETED MICAS

Open Access
Author:
Cho, Yunchul
Graduate Program:
Soil Science
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
October 04, 2007
Committee Members:
  • Sridhar Komarneni, Committee Chair
  • Richard Charles Stehouwer, Committee Member
  • Carmen E Martinez, Committee Member
  • Jerzy Dec, Committee Member
  • Rustum Roy, Committee Member
Keywords:
  • Mica
  • Ion exchange
  • Transformation
  • Radioactive species
  • Heavy metals
Abstract:
The main goal of this thesis research was to study selective cation exchange properties of K-depleted micas and transformation/alteration of micas under hydrothermal conditions. Cation exchange equilibria of Cs+ and Sr2+ and heavy metal cations such as Co2+ and Ni2+ with K-depleted phlogopite, K-depleted biotite, and K-depleted muscovite were conducted to evaluate their selective cation exchange properties. Na+¡æ Cs+ exchange equilibria revealed that all K-depleted micas have high selectivity for Cs+ ion at low equivalent fractions of Cs+ in solid. The order of cation exchange for Cs+ ion was K-depleted phlogopite > K-depleted biotite &#8776; K-depleted muscovite. For 2 Na+¡æ Sr2+ equilibria, K-depleted biotite had a high selectivity for Sr2+ ion. Studies of heavy metal cation exchange with K-depleted phlogopite and K-depleted biotite revealed that both the K-depleted micas have high selectivity for Co2+ and Ni2+ ions at low concentrations of these metal cations. Both K-depleted phlogopite and K-depleted biotite were found to show higher selectivity for Ni2+ ion than Co2+ ion. The d(001)-spacing of both Co-exchanged and Ni-exchanged micas increased to ~ 14 &Aring; at higher equivalent fractions of these metal ions in solid. In addition, cation exchange mechanism and rate of Cs+ exchange was investigated using two different particle size (< 2 ¥ìm and 20-2 ¥ìm) fractions of K-depleted phlogopite. Kinetic results revealed that the 20-2 ¥ìm particle size fraction of the K-depleted phlogopite took up more Cs+ ions than the <2 ¥ìm particle size fraction. Elovich model described the kinetic data of the <2 ¥ìm particle size fraction well, while the modified first-order model or parabolic diffusion model described those of the 20-2 ¥ìm particle size fraction well. Topotactic cation exchange under hydrothermal conditions (at 200 oC) was explored as another alternate method to immobilize or fix radionuclides such as Cs+ and Sr2+ in the K-depleted biotite or K-depleted muscovite by forming mica-like hydroxylated phases. The K-depleted biotite treated with alkali cations produced anhydrous hydroxylated phases by topotactic exchange. The alkaline earth cations, however, produced hydrous hydroxylated phases with both K-depleted biotite and muscovite. Also, weathering of K-depleted phlogopite, K-depleted biotite, and natural biotite under acidic hydrothermal conditions (3 N AlCl3 at 200 oC) was investigated to understand weathering mechanism and predict final weathering products of the micas. Studies of weathering showed that the order of transformation rate was K-depleted phlogopite > K-depleted biotite > natural biotite. The alteration pathway of K-depleted micas is as follows: K-depleted biotite ¡æ hydroxy-Al interlayered vermiculite ¡æ kaolinite. Results from all the above studies of K-depleted micas indicate that they could be used as excellent ion exchangers for separation and immobilization of radioactive species such as Cs+, Sr2+, and Co2+ as well as heavy metal cations such as Ni2+ and Co2+.