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Solubility Relationships and Mineral Transformations Associated with Recarbonation of Retorted Shales
Author(s) -
Reddy K. J.,
Lindsay W. L.,
Boyle F. W.,
Redente E. F.
Publication year - 1986
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq1986.00472425001500020008x
Subject(s) - solubility , chemistry , magnesite , oil shale , dolomite , carbon dioxide , mineral , calcite , mineralogy , carbonate , silicate , environmental chemistry , geology , magnesium , organic chemistry , paleontology
Oil shales are heated at high temperatures to obtain oil. During this process carbonate minerals are destroyed by driving off CO 2 (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 (CaCO 3 ) 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 (CO 2 [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, CaCO 3 to precipitate, and lowered pH from approximately 12.0 to 8.0. Solubility measurements showed that upon recarbonation Ca 2+ activity for both shales approached equilibrium with CaCO 3 and measured CO 2 (g). Initially Mg 2+ activity appeared to be in equilibrium with either diopside (CaMg[SiO 3 ] 2 ) or antigorite (Mg 2.825 Si 2 O 5 (OH) 3.65 ) and measured silica, but not with dolomite (CaMg[CO 3 ] 2 ) nor magnesite (MgCO 3 ). After 20 d of recarbonation for LANL, Mg 2+ solubility decreased from 10 −2.78 M to 10 −3.15 M . The experimental findings in this study further suggest that bubbling CO 2 (g) through retorted shales can reduce the concentrations of F and, in some cases Mo, in leachates.