Study On The Mechanism Of Trace Elements Adsorption On The Unburned Carbon

Trace elements emitted from coal combustion have become an increasingly important environmental concern due to its potential threats to human health, global agricultural and social sustainability. Among the toxic metals of interest are most volatile trace elements, Which could not be removed in polluted control equipments and produce direct atmosphere emission. The former research indicated that the fly ash carbon from coal combustion played an important role in the transformation of the trace elements, and it had the potential to control the emissions of the trace elements. But so far we have only a little acquaintanceship about the mechanisms of trace elements adsorption on the unburned carbon and there were even disputes on some crisis issues. Apparently it is necessary to have a deep study for the mechanisms of trace elements adsorption on the fly ash carbon.Based on Quantum Chemistry theory, the mechanisms of trace elements adsorption on the unburned carbon during coal combustion was studied in this paper by Quantum Chemistry Calculation.The cluster model of unburned carbon from fly ash was built rationally based on former researches at first. The Calculation used Density Functional Theory (DFT) B3PW91 methods and Stevens ECP basis in this paper.The adsorption mechanisms of mercury and mercury chloride on different types of unburned carbon surface have been investigated. We computed the the Bond Length, Bonding Energy and Bond Mulliken Population, and compared the differences between the different adsorption sites. The results indicated that the adsorption of elemental mercury on the unburned carbon is quite weak, which is mainly caused by physical adsorption. The presence of oxygen functionality and halogen species on the surface of fly ash carbons may greatly promote mercury adsorption, and make it seems like chemical adsorption. The adsorption of the mercury chloride on the unburned carbon is much stronger compared with the mercury adsorption.In another part, we discussed the adsorption mechanisms of selenium, arsenic and their oxide on the unburned carbon. The results indicated that the adsorption capability of the three trace elements on unburned carbon is in orders: Se>As>Hg. The adsorption of selenium, arsenic and their oxide may be chemical adsorption. Because of lacking literatures, more details need to be validated in the future work.