Pyrolysis chars at 500°C, 700°C, 900°C and coal combustion ashes were prepared to simulate the three zones residues of underground coal gasification. The contents of trace elements in solid residues, such as chromium, manganese, arsenic, cobalt, nickel and lead, were determined by using inductively coupled plasma mass spectroscopy (ICP-MS) and the enrichment factors were also calculated. By immersing the pyrolysis chars and coal combustion ashes in weakly acidic leaching liquid (pH=4, 5, 6), the leaching features of above trace elements and their potential threat on groundwater were characterized. Compared with the enrichment feature of Fe, the results indicate that CrMnCo stably exist in pyrolysis and combustion process; Ni and As get depleted in low-temperature pyrolysis chars, while enriched in 900°C chars and coal combustion ashes; Pb becomes enriched in ash, but gets depleted with the increase of pyrolysis temperature. The concentration of As in ash leachate is higher than the 5thclass of groundwater quality standard which may cause serious pollution; the concentration of Ni is below the 4thclass and may contaminate the groundwater; other elements in leachate have little influence on groundwater because of low concentrations below the 3rdclass of groundwater quality standard.
Valorization of non-balanced coal reserves in Serbia for underground coal gasification
