Removal properties of hexavalent chromium and hazardous trace elements in UCG condensate water by semi-cokes

• Published in: Coke and chemistry (New York, N.Y.) N.Y.), 2015-05, Vol.58 (5), p.188-195
• Main Authors: Xu, Bing, Chen, Lun-jian, Li, Long, Xing, Bao-lin, Huang, Guang-xu, Wang, Xiao-jiao, Yi, Gui-yun, Su, Yu, Zhang, Le
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Industrial Chemistry/Chemical Engineering; Industrial Safety
• ISSN: 1068-364X; 1934-8398
• DOI: 10.3103/S1068364X15050099

Underground coal gasification (UCG) is an attractive clean coal technology by converting coal into combustible gases in situ, but it also poses a potential environmental risk to groundwater pollution. In this paper, the Hebi pyrolysis/gasification semi-cokes were prepared by applying tubular resistance furnace, model test of UCG were also carried out. The porous characteristics of obtained semi-cokes were characterized by measuring the amount of N 2 adsorbed at 77 K, the removal of hexavalent chromium in simulated wastewater and hazardous trace elements in condensate water produced from UCG model test by pyrolysis semi-cokes were further investigated. The results indicate that the porous structure of semi-coke is closely related with applied preparation temperature and atmosphere (nitrogen, water vapor or CO 2 ). The specific surface area ( S BET ) of semi-coke gasified by CO 2 at 900°C reaches the largest, semi-coke pyrolyzed at 900°C (YM-900) then follows; Compared with CO 2 gasification semi-coke, a lower S BET and total pore volume ( V t ) and a larger pore with average pore width of 4.9 nm than 3.06 nm are observed in the water vapor gasification semi-coke; An increased S BET and V t of pyrolysis semi-cokes are initially observed as the temperature increases, the largest can be obtained at 900°C and then decrease at higher temperatures. The removal results show that the highest removal rate of Cr +6 in simulated wastewater can be obtained by using YM-900, subsequently by CO 2 gasification semi-coke; It is also found that hazardous trace elements in gas condensate water can be removed to certain extents by different pyrolysis semi-cokes, wherein the removal rates of Cd, Pb, Gr, Ni and Co can exceed 60%. However, parts of trace elements can be leached into groundwater from semi-coke samples, which should be paid more attention to.