Computational Results of the Ecotoxic Analysis of Fly and Bottom Ash from Oil Shale Power Plants and Shale Oil Production Facilities

Abstract

In Estonia, oil shale ash was considered as hazardous waste until the end of 2019 mainly due to its high content of calcium oxide. This limited the use and export of the produced ash. During 2018 and 2019, a study on the overall hazardous potential of Estonian oil shale ash was conducted. In this paper, we present the computational ecotoxic analysis results of fly and bottom ash from oil shale power plants and shale oil production plants. According to recommendations by the European Commission, computational methods are preferred for the evaluation of ecotoxicity. These methods take into account the concentrations of environmentally hazardous compounds. In order to evaluate ecotoxicity in light of hazardous property 14 (HP14, Ecotoxic), 14 different types of fly and bottom ash samples were collected and their trace element concentrations were measured using inductively coupled plasma mass spectrometry (ICP-MS) and X-ray fluorescence spectroscopy (XRF). This enabled analysing all major ash streams of the Estonian oil shale industry. In turn, the toxicity values were calculated according to European Union regulations. The results showed that oil shale ash samples should not be considered as hazardous regarding HP14 – the resulting summed concentrations remained around ten times under the limit values for all four different calculation methods. For example, the highest result was 3.918 % (for a limit value of 25 %), indicating the low concentrations of hazardous elements in the investigated material. As a result, oil shale ash, similarly to coal ash, is not consideret to be hazardous as of the beginning of 2020.