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This article in JEQ

  1. Vol. 15 No. 2, p. 129-133
     
    Received: July 29, 1985
    Published: Apr, 1986


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doi:10.2134/jeq1986.00472425001500020008x

Solubility Relationships and Mineral Transformations Associated with Recarbonation of Retorted Shales1

  1. K. J. Reddy,
  2. W. L. Lindsay,
  3. F. W. Boyle and
  4. E. F. Redente2

Abstract

Abstract

Oil shales are heated at high temperatures to obtain oil. During this process carbonate minerals are destroyed by driving off CO2(g) and large amounts of waste materials (retorted shale) are produced. The pH of such retorted shales often approaches 12.0. With time, the pH of these materials will drop by attaining equilibrium with calcite (CaCO3) and atmospheric carbon dioxide (recarbonation). The objective of this paper was to examine solubility relationships and mineral transformations associated with recarbonation of retorted shales. Carbon dioxide gas (CO2[g]) was bubbled through two shale samples, one retorted by Los Alamos National Laboratory (LANL) and another retorted by Lurgi Ruhrgas (Lurgi) to lower their pH. X-ray diffraction analysis was used to identify different mineral phases of retorted and recarbonated shales. The results show that recarbonation caused silicate minerals to dissolve, CaCO3 to precipitate, and lowered pH from approximately 12.0 to 8.0. Solubility measurements showed that upon recarbonation Ca2+ activity for both shales approached equilibrium with CaCO3 and measured CO2(g). Initially Mg2+ activity appeared to be in equilibrium with either diopside (CaMg[SiO3]2) or antigorite (Mg2.825Si2O5(OH)3.65) and measured silica, but not with dolomite (CaMg[CO3]2) nor magnesite (MgCO3). After 20 d of recarbonation for LANL, Mg2+ solubility decreased from 10−2.78 M to 10−3.15 M. The experimental findings in this study further suggest that bubbling CO2(g) through retorted shales can reduce the concentrations of F and, in some cases Mo, in leachates.

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