Basic properties of fly ash samples from different urban waste combustion facilities in China were analyzed using as X-ray fluorescence （XRF）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）. The lea...Basic properties of fly ash samples from different urban waste combustion facilities in China were analyzed using as X-ray fluorescence （XRF）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）. The leaching toxicity procedure and some factors influencing heavy metals distribution in fly ash were further investigated. Experimental results indicate that the fly ash structures are complex and its properties are variable. The results of XRF and SEM revealed that the major elements （〉10000 mg/kg, listed in decreasing order of abundance） in fly ash are O, Ca, Cl, Si, S, K, Na, Al, Fe and Zn. These elements account for 93% to 97%, and the content of Cl ranges from 6.93% to 29.18 %, while that of SiO2 does from 4.48% to 24.84%. The minor elements （1000 to 10000 mg/kg） include Cr, Cu and Pb. Primary heavy metals in fly ash include Zn, Pb, Cr, Cu etc. According to standard leaching test, heavy metal leaching levels vary from 0 to 163.10 mg/L （Pb） and from 0.049 to 164.90 mg/L （Zn）, mostly exceeding the Chinese Identification Standard for hazardous wastes. Morphology of fly ash is irregular, with both amorphous structures and polycrystalline aggregates. Further research showed that heavy metals were volatilized at a high furnace temperature, condensed when cooling down during the post-furnace system and captured at air pollution control systems. Generally, heavy metals are mainly present in the forms of aerosol particulates or tiny particulates enriched on surfaces of fly ash particles. The properties of fly ash are greatly influenced by the treatment capacities of incinerators or the variation of waste retention time in chamber. Fly ash from combustors of larger capacities generally has higher contents of volatile component and higher leaching toxicity, while those of smaller capacities often produce fly ash containing higher levels of nonvolatile components and has lower toxicity. The content of heavy metals and leaching toxicity maybe have no convincing correlation, and high alkali content of CaO greatly contribute to leaching toxicity of heavy metal and acid neutralization capacity against acid rain.展开更多
One of the reasons for many social tragedies resulted from land expropriation in China is failure of the constitution to bring into play its due functions in standardizing land expropriation power of the government an...One of the reasons for many social tragedies resulted from land expropriation in China is failure of the constitution to bring into play its due functions in standardizing land expropriation power of the government and protecting farmers' rights.In the existing land expropriation system,government is not only a policy maker of land expropriation,but also a "referee" of dispute over land expropriation.Government' land expropriation power and land-expropriated farmers' rights become out of balance.As a result,some local governments do not attach importance to farmers' rights,making land-expropriated farmers dissatisfied and consequently leading to some social tragedies unfavorable for harmony and stability.To fundamentally settle disputes over land expropriation and realize win-win of farmers' right and state interest,it should bring into full play functions of the constitution through protecting farmers' right to participate in land expropriation and establishing constitution evaluation mechanism.展开更多
基金Project supported by the Hi-Tech Research and Development Program (863) of China (No. 2002AA644010) the National Tenth-Five Year Program of China (No. 2003BA604A-11-07).
文摘Basic properties of fly ash samples from different urban waste combustion facilities in China were analyzed using as X-ray fluorescence （XRF）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）. The leaching toxicity procedure and some factors influencing heavy metals distribution in fly ash were further investigated. Experimental results indicate that the fly ash structures are complex and its properties are variable. The results of XRF and SEM revealed that the major elements （〉10000 mg/kg, listed in decreasing order of abundance） in fly ash are O, Ca, Cl, Si, S, K, Na, Al, Fe and Zn. These elements account for 93% to 97%, and the content of Cl ranges from 6.93% to 29.18 %, while that of SiO2 does from 4.48% to 24.84%. The minor elements （1000 to 10000 mg/kg） include Cr, Cu and Pb. Primary heavy metals in fly ash include Zn, Pb, Cr, Cu etc. According to standard leaching test, heavy metal leaching levels vary from 0 to 163.10 mg/L （Pb） and from 0.049 to 164.90 mg/L （Zn）, mostly exceeding the Chinese Identification Standard for hazardous wastes. Morphology of fly ash is irregular, with both amorphous structures and polycrystalline aggregates. Further research showed that heavy metals were volatilized at a high furnace temperature, condensed when cooling down during the post-furnace system and captured at air pollution control systems. Generally, heavy metals are mainly present in the forms of aerosol particulates or tiny particulates enriched on surfaces of fly ash particles. The properties of fly ash are greatly influenced by the treatment capacities of incinerators or the variation of waste retention time in chamber. Fly ash from combustors of larger capacities generally has higher contents of volatile component and higher leaching toxicity, while those of smaller capacities often produce fly ash containing higher levels of nonvolatile components and has lower toxicity. The content of heavy metals and leaching toxicity maybe have no convincing correlation, and high alkali content of CaO greatly contribute to leaching toxicity of heavy metal and acid neutralization capacity against acid rain.
基金Key Project of National Social Science Foundation (09AFX001) in 2009 Decision Research Project of Henan Provincial Government (B543)
文摘One of the reasons for many social tragedies resulted from land expropriation in China is failure of the constitution to bring into play its due functions in standardizing land expropriation power of the government and protecting farmers' rights.In the existing land expropriation system,government is not only a policy maker of land expropriation,but also a "referee" of dispute over land expropriation.Government' land expropriation power and land-expropriated farmers' rights become out of balance.As a result,some local governments do not attach importance to farmers' rights,making land-expropriated farmers dissatisfied and consequently leading to some social tragedies unfavorable for harmony and stability.To fundamentally settle disputes over land expropriation and realize win-win of farmers' right and state interest,it should bring into full play functions of the constitution through protecting farmers' right to participate in land expropriation and establishing constitution evaluation mechanism.
