LEACHING THERMODYNAMICS AND KINETICS OF OIL SHALE WASTE KEY COMPONENTS

Abstract

Estonia is strongly dependent on locally mined oil shale which is the main fuel for power and oil production. Vast amounts of solid wastes are formed from circulating fluidized bed (CFB), pulverized firing (PF), and solid heat carrier (SHC) technologies, and are currently wet deposited in open-air fields. Both the utilization of newly produced ash and the management of historical deposits require an accurate thermo- dynamic modelling of complex mixtures. The authors investigated the leach- ing of the main water-soluble Ca-compounds from three types of oil shale mineral waste and developed a kinetic model that was used to determine the equilibrium constants and kinetic parameters of dissolution reactions for all three ash-water systems over a wide range of solid-to-liquid (S/L) ratio. For this, we prepared binary (Ca(OH)2-CaSO4·2H2O-H2O) and ternary (Ca(OH)2-CaSO4·2H2O-CaS-H2O) model systems that reflect the composition of the three different ashes, and measured the kinetics of dissolution for both the model systems and industrial ash. Thermodynamic calculations were per- formed using HsC Chemistry ® 7.1 and Aspen Plus V8.6 while the leaching kinetics was simulated employing the MODEST 6.1 software package. By comparing the results obtained for our model systems with those obtained for industrial oil shale ash-water systems the authors were able to both verify that the model results coincided to a satisfactory degree with simulation data, and also propose models that may aid one to design shale ash processing technologies.