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The Solubility Relationships of Calcium and Magnesium Minerals in Processed Oil Shales¹

ABSTRACT

One of the major problems occurring with the oil shale industry is the production of large amounts of solid wastes (spent shale). The high alkalinity of these waste materials often presents problems for successful management practices to minimize overall pollution impact on the environment. The objective of this study was to determine solubility of calcium and magnesium minerals to explain high alkalinity of spent shales. Two oil shales, one processed by Los Alamos National Laboratory (LANL) and another processed by Lurgi Ruhrgas (Lurgi) were examined in this study. The x-ray diffraction analysis was used to identify different mineral phases of spent oil shales. The results indicate that processing oil shales at high temperature destroyed carbonate minerals and formed silicate minerals including wollastonite (CaSiO₃), clinoenstatite (MgSiO₃), or diopside (CaMg(SiO₃)₂). These minerals buffered pH above 11.00 and controlled Ca²⁺ and Mg²⁺ activities in solution. The experimental findings in this study further suggest that oxides or hydroxides of Ca and Mg produced initially from processing oil shales did not persist after moisture was allowed to contact the spent shale.

Key Words: high temperatures • alkalinity • dissolution • precipitation • silicate minerals • activity

¹ Contribution from the Colorado State Univ. Exp. Stn. and published as Scientific Series paper no. 3011 supported in part by DOE Grant no. EV/4018-7.

² Graduate Research Assistant and Professor, respectively, Dep. of Agronomy, Colorado State Univ., Fort Collins, CO 80523.

Received for publication April 29, 1985.