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 thermodynamic modelling of complex mixtures. The authors investigated the leaching 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-CaSO 4 •2H 2 O-H 2 O) and ternary (Ca(OH) 2-CaSO 4 •2H 2 O-CaSH 2 O) 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 performed 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.

The composition and properties of ash in the context of the modernisation of oil shale industry

“…As previous studies have shown, oil shale ash undergoes an alkaline reaction when it comes into contact with water [16,24,[53][54][55]. The water extracts of DeSOx and Auvere PP ashes exhibited the highest values of electric conductivity and pH.…”

Calcium Extraction From Estonian Industrial Wastes Based on Ammonium Solvents

“…The changes in water systems were less noticeable (up to 500 mg/L) due to much lower solubility of portlandite in water. Increasing S/L ratio to1/5 in OS ash-water systems had no effect in Ca leaching [12].…”

“…The main characteristics of the Ca dissolution process for OS ashes and the dissolution kinetics of main water-soluble Ca-compounds together with the dissolution mechanism has been described in previous studies [12], [24], [25].…”

“…Studies have shown that Ca(OH) 2 , CaSO 4 ·2H 2 O and CaS are the main water-soluble Ca and S species in OS ash aqueous systems [12]. Also, OS ashes contain secondary Ca(Mg)-silicate minerals, and an amorphous Al-Si glass phase [4].…”

Modelling and experimental measurement of the closed equilibrium system of H2O–SrS

“…For calculating the concentrations of unknown variables, the basedissociation or ionization constants (K b1 and K b2 ) are expressed as follows Eqs (6−7): (6) (7) In order to simplify the developed model of the closed equilibrium system of H 2 O−SrS, the charge balance equation in the liquid phase is presented as: (8) and the molar balance equation for calculating the mass of sulphur species as:…”