排序方式: 共有32条查询结果,搜索用时 0 毫秒
31.
Arsenic (As) pollutants generated by human activities in karst areas flow into subterranean streams and contaminate groundwater easily because of the unique hydrogeological characteristics of karst areas. To elucidate the reaction mechanisms of arsenic in karst subterranean streams, physical-chemical analysis was conducted by an inductively coupled plasma mass spectrometer and an X-ray fluorescence spectrometer. The results show that inorganic species account for most of the total arsenic, whereas organic arsenic is not detected or occurs in infinitesimal amounts. As(III) accounts for 51.0% ± 9.9% of the total inorganic arsenic. Arsenic attenuation occurs and the attenuation rates of total As, As(III) and As(V) in the Lihu subterranean stream are 51%, 36% and 59%, respectively. To fully explain the main geochemical factors influencing arsenic attenuation, SPSS 13.0 and CANOCO 4.5 bundled with CanoDraw for Windows were used for simple statistical analysis and redundancy analysis (RDA). Eight main factors, i.e., sediment iron (SFe), sediment aluminum (SAI), sediment calcium (SCa), sediment organic matter (SOM), sediment manganese (SMn), water calcium (WCa^2+), water magnesium (WMg^2+), and water bicarbonate ion (WILCOX) were extracted from thirteen indicators. Their impacts on arsenic content rank as: SFe〉SCa〉WCa^2+〉SAl〉wHCO3^-〉SMn〉SOM〉WMg^2+. Of these factors, SFe, SAl, SCa, SOM, SMn, WMg^2+ and WCa&2+ promote arsenic attenuation, whereas WHCO3^- inhibits it. Further investigation revealed that the redox potential (Eh) and pH are adverse to arsenic removal. The dramatic distinction between karst and non-karst terrain is that calcium and bicarbonate are the primary factors influencing arsenic migration in karst areas due to the high calcium concentration and alkalinity of karst water. 相似文献
32.
Cationic organobismuth complex as an effective catalyst for conversion of CO2 into cyclic carbonates
Xiaowen Zhang Weili Dai Shuangfeng Yin Shenglian Luo Chak-Tong Au 《Frontiers of Environmental Science & Engineering in China》2009,3(1):32-37
In order to achieve high-efficiency conversion of CO2 into valuable chemicals, and to exploit new applications of organobismuth compounds, cationic organobismuth complex with
5,6,7,12-tetrahydrodibenz[c,f][1,5] azabismocine framework was examined for the first time for the coupling of CO2 into cyclic carbonates, using terminal epoxides as substrates and tetrabutylammonium halide as co-catalyst in a solvent-free
environment under mild conditions. It is shown that the catalyst exhibited high activity and selectivity for the coupling
reaction of CO2 with a wide range of terminal epoxide. The selectivity of propylene carbonates could reach 100%, and the maximum turnover
frequency was up to 10740 h−1 at 120°C and 3 MPa CO2 pressure when tetrabutylammonium iodide was used as co-catalyst. Moreover, the catalyst is environment friendly, resistant
to air and water, and can be readily reused and recycled without any loss of activity, demonstrating a potential in industrial
application. 相似文献