Geochemical signature of superhigh organic sulphur Rasa coals and the mobility of toxic trace elements from combustion products and polluted soils near the Plomin coal-fired power station in Croatia

摘要

In the northern Adriatic coast of Croatia, combustion of super-high organic sulphur rich Rasa coal was common between 1970 and 2000. These Late Paleocene coals are enriched in a number of trace elements. This work aims to provide a detailed study on the distinctive geochemical patterns of the Rasa coal and investigate the environmental effects of the coal and combustion by-products on the area. Several analytical techniques were used to study the mode of occurrence, distribution, levels and solubility of major and trace elements in the Rasa coal, fly ash, slag and soils in an area within 10 km from the power station. Due to the sulphur-rich calcareous depositional environment of the Rasa coal, the combustion by-products are enriched in S and Ca. Fly ash and slag are enriched in potentially harmful trace elements i.e. Se, Mo, Hg, V and U. Similar enrichment pattern was found for soils suggesting that resuspension and deposition of airborne coal and fly ash particles, transport of gaseous species in the flue gas by dominant winds and/or leaching from ash deposits may have affected the wider environment. Whilst a large number of trace elements were found to be poorly soluble across samples, the leachable concentrations of Se, Cr and Mo in fly ash and slag are noteworthy. Their organic association in coal enhances volatilisation during combustion and then further condensation on ash particles as readily soluble oxyanionic species. Other oxyanionic metalloids such as As or V were insoluble in fly ash and slag, due to precipitation of solubility-limiting Ca-bearing species.