Influence of the post-granulation treatment on the thermal behaviour and leachability characteristics of Estonian oil shale ashes

Abstract

The power and heat production in Estonia is based over 90% on the combustion of a local solid fossil fuel—Estonian oil shale (OS), and at that 7–8 million tons of OS ash are formed annually. One promising possibility for large-scale utilization of cheap alkali ashes is the liming of acidic soils. In Estonia, there is 350,000 ha of agricultural land that needs permanent liming. To eliminate possible environmental contamination at liming of soils the oil shale ashes should be granulated. Thermal analysis was used for determination of the relationships between physico-mechanical and physico-chemical characteristics of granulated products and the post-granulation treatment conditions. For determination of leachability of ash components, the granulated products as well as the origin ashes were tested using laboratory lysimetries. Depending on OS ash and different post-granulation treatment used, it was possible to obtain granulated product with compressive strength between 5 and 15 N per granule. The leaching of Ca2+ decreased up to 26 and 34%, SO4 2− 70 and 53%, Mg2+ and K+ up to 7–12% for granulated CA and ESPA, respectively, comparing with original ashes. The results of soil analysis indicate that the use of OS ashes improved the pH level of soil significantly. pH increased equally with initial and granulated ash: from 4.7 up to 6.4 and 5.8, respectively, using for that CA and ESPA. Prolonged effect of soil neutralizing ability by granulated product (if compare with fine ashes) was proven by decrease in the content of leached ions in filtrate solutions as well as not mobile ions in soil.