Open-Air Deposition of Estonian Oil Shale Ash: Formation, State of Art, Problems and Prospects for the Abatement of Environmental Impact

Abstract

Abstract. The growing demand for the world energy supply necessitates the employment of local low-grade fossil fuels like oil shale (OS

Leaching Behaviour of Estonian Oil Shale Ash-Based Construction Mortars

“…Kuusik et al [3] and Bitjukova et al [4] demonstrated that all OSA fractions are dominated by the presence of CaO total , whose proportion varies from 26 to 55% in PF ash and from 26 to 49 % in CFB ash. As reported [2,3,6,7], OSA is rich in free lime (CaO free ), anhydrite (CaSO 4 ), secondary Ca(Mg)-silicate minerals and, especially in PF ashes, an amorphous Al-Si glass phase.…”

“…According to Kuusik et al [7], variations in the mineral composition of ash fractions are related to those in the lime, the proportion of which varies from about 1.6% in CFB ash to a maximum of 24.6% in PF ash. Due to the significant difference (1.5-1.8-fold) in their combustion temperatures, the difference in amorphous-glassy phase content between PF and CFB ashes is also evident.…”

Leaching Thermodynamics and Kinetics of Oil Shale Waste Key Components

“…The estimated values of the rate constants k 41 (2.01 × 10 -4 s -1 ) and k 51 (8.66 × 10 -5 s -1 ) were one order of magnitude higher than the results reported by Mölder et al [36] who investigated the rate of hydrolysis and oxidation (saturating the suspension with air) of CaS in a hydraulic ash disposal system. They reported rate constants for reactions (4) and (5) to be about 1 × 10 -5 s -1 and approximately 4 × 10 -6 s -1 , respectively. The reaction rate constants k 61 and k 71 at S/L ratios ranging from 0.004 to 0.2 were determined using the parameter estimation procedure that iteratively solved the proposed model equations and minimized the difference between these predictions and data obtained in batch experiments.…”

“…The oil shale ash (OSA) from thermal power plants contains mainly free lime (CaO free ), Ca-sulfate, secondary Ca(Mg)-silicate minerals, and an amorphous Al-Si glass phase [3][4][5]. Both the high temperatures and thermal processing conditions as well as combustion conditions (> 750 °C, residence time, combustion regime -pulverized firing (PF) or circulating fluidized bed (CFB) combustion) ensure that all of the organic matter (mainly kerogen) in OS (up to 65% [6]) is burnt out [1].…”

“…Today, about 90% of oil shale ash is wet deposited in ash fields near the power plants. Only a small percentage of OSA is utilized, either in the building materials industry, in agriculture as a liming agent, or in road construction [5]. OSA is classified as a "hazardous waste" mainly due to the high alkalinity of leachates (pH values [12][13], contributed by the dissolution of free lime (up to 30 wt%).…”