The equilibrium constant (K0), change in free energy (△G), enthalpy (△H) and entropy (△S) of ammonium adsorption by a Cuban natural zeolite were estimated at the temperatures of 25, 35, 45 and 55℃ using ex...The equilibrium constant (K0), change in free energy (△G), enthalpy (△H) and entropy (△S) of ammonium adsorption by a Cuban natural zeolite were estimated at the temperatures of 25, 35, 45 and 55℃ using extensively used approaches. Equilibrium data were obtained in the concentration range 50-1,200 mg·L-1 of ammonium and used in the estimation of thermodynamic parameters. Freundlich's isotherm model was found as with the best adjustment to equilibrium data at 25, 45 and 55℃, whereas, Redlich-Peterson's model had a better performance at 35 ℃. A discontinuous and unusual behavior was observed on adsorption capacity of the zeolite, with an increase from 25 ℃ to 35 ℃ followed by a decrease from 35℃ to 55 ℃. K0 values presented differences that reached up to 105 from one methodology to other. Depending on the method considered, AS results indicated both increase or decrease in system degree of disorder and △G indicated both physisorption or chemisorption process, proving the poor correlation between the estimation proceedings of such important data. The results from Gaines and Thomas method were recognized as the most correlated to calorimetric studies, as well as to equilibrium data and observations related to system entropy.展开更多
The quantification of the sheltering and exposure effects of non-uniform sediments has been widely achieved through hiding function models. Big challenge exists so far in the model parameter that is highly variable an...The quantification of the sheltering and exposure effects of non-uniform sediments has been widely achieved through hiding function models. Big challenge exists so far in the model parameter that is highly variable and differs greatly between laboratory flumes and field streams. This paper presents an improved surface-based hiding fimction. The force balance for particle inception was formulated and the allocation of the overall bed shear stress into each group of sediments was mimicked. The new hiding function was examined against and agrees well with the documented field and flume data. It was shown that the hiding fimction is closely related to the relative flow depth and the reference elevation in the velocity profile in addition to the bed material gradation. The power law of velocity profile that applies to both flume flows and natural streams can link the flume and field data together. The hiding function with b = 1/6 and b = 1/2 is applicable to natural streams and laboratory flumes, respectively. The value orb = 0.263 also works well for gravel bed rivers. The range of the reference elevation, namely z0 = 0.4Dm-1.4Dm, is recommended for either the flume or field data. The new hiding function contributes to addressing clearer physical meanings and a useful perspective for further improvement.展开更多
文摘The equilibrium constant (K0), change in free energy (△G), enthalpy (△H) and entropy (△S) of ammonium adsorption by a Cuban natural zeolite were estimated at the temperatures of 25, 35, 45 and 55℃ using extensively used approaches. Equilibrium data were obtained in the concentration range 50-1,200 mg·L-1 of ammonium and used in the estimation of thermodynamic parameters. Freundlich's isotherm model was found as with the best adjustment to equilibrium data at 25, 45 and 55℃, whereas, Redlich-Peterson's model had a better performance at 35 ℃. A discontinuous and unusual behavior was observed on adsorption capacity of the zeolite, with an increase from 25 ℃ to 35 ℃ followed by a decrease from 35℃ to 55 ℃. K0 values presented differences that reached up to 105 from one methodology to other. Depending on the method considered, AS results indicated both increase or decrease in system degree of disorder and △G indicated both physisorption or chemisorption process, proving the poor correlation between the estimation proceedings of such important data. The results from Gaines and Thomas method were recognized as the most correlated to calorimetric studies, as well as to equilibrium data and observations related to system entropy.
基金the Beijing Municipal Science&Technology Project(Grant No.Z141100003614052)the National Natural Science Foundation of China(Grants No.51525901&51379100)as well as by China Ministry of Science and Technology(Grant No.2011CB409901)
文摘The quantification of the sheltering and exposure effects of non-uniform sediments has been widely achieved through hiding function models. Big challenge exists so far in the model parameter that is highly variable and differs greatly between laboratory flumes and field streams. This paper presents an improved surface-based hiding fimction. The force balance for particle inception was formulated and the allocation of the overall bed shear stress into each group of sediments was mimicked. The new hiding function was examined against and agrees well with the documented field and flume data. It was shown that the hiding fimction is closely related to the relative flow depth and the reference elevation in the velocity profile in addition to the bed material gradation. The power law of velocity profile that applies to both flume flows and natural streams can link the flume and field data together. The hiding function with b = 1/6 and b = 1/2 is applicable to natural streams and laboratory flumes, respectively. The value orb = 0.263 also works well for gravel bed rivers. The range of the reference elevation, namely z0 = 0.4Dm-1.4Dm, is recommended for either the flume or field data. The new hiding function contributes to addressing clearer physical meanings and a useful perspective for further improvement.