Processing Lignite Fly Ash in Europe

Abstract

This study investigates environmental impacts of processing of lignite fly ash (LFA) in Europe. Lignite fly ash is a waste product from lignite-fired electricity production. Currently 95% of LFA is dumped in depleted lignite mines. However, there are alternatives. In this study the differences between two main processing options are examined. First, the environmental impacts of dumping LFA, which is a reference situation, are researched. Secondly, an alternative scenario of processing of LFA in concrete is researched. In order to see if utilization of LFA in concrete is a realistic possibility, LFA-concrete has been constructed. LFA samples from different production sites throughout Europe have been collected and characterized. These samples have been used to construct the LFA-concrete and research the leaching behavior of LFA deposits. In addition to assessment of the two main processing options, an indicative research on processing of LFA in geopolymers has been done. The geopolymer concept is an innovative approach in which polymer bonds are created to form a concrete-like material. This third processing alternative is however not an integrated part of the difference analysis and will be addressed separately. In order to determine the environmental impact of the processing options this study follows the standard protocol of life cycle assessment (LCA). The results show that there is a large variation in composition between the different types of LFA. As a consequence, there are differences in leaching behavior and strength development when processed in concrete. Although the LFA-concrete developed less strength than the reference concrete, 5 out of the 6 samples that were tested achieved over 90% of the reference compressive strength when replacing 15% of the cement with LFA. Due to the high uncertainty in both the emissions of dumping LFA and the effects of these emissions, it is hard to make a judgment about the extent of the overall adverse environmental effect. It can be concluded that processing of LFA in concrete reduces the environmental impact. The prevention of dumping of LFA and decrease in consumption of cement in concrete are the main sources of this reduction. Initial indicative results of the geopolymer research show great promise. The strength development of some LFA-geopolymer-concretes exceeded expectation. To discover full potential of utilization of LFA in geopolymers more research is necessary.