The effect of background anion on cation exchange reactions, suchas Na-Ca and Na-Cu exchange reac- tions, on montmorillonites has beenstudied, but the results are not always clear and discrepancies existin the literat...The effect of background anion on cation exchange reactions, suchas Na-Ca and Na-Cu exchange reac- tions, on montmorillonites has beenstudied, but the results are not always clear and discrepancies existin the literature. In this study, the exchange of zinc (Zn^2+) forsodium (Na^+) on Wyoming montmorillonite was investigated at 298 deg.K using Cl^-, ClO_4^-, NO_3^-, Oac^-, and SO_4~2- solution media at aconstant total metal charge concentration of 0.02000 mol_c L^-1.Results indicated that the clay CEC values were essential similar forCl^-, ClO_4^-, NO_3^- and SO_4~2- solution media with an average CECof 0.856±0.008 mol_c kg^-1; in an OAc^- solution the clay CEC wasmuch higher than that in other anion media.展开更多
Stochastic approaches are useful to quantitatively describe transportbehavior over large temporal and spatial scales while accounting for the influence of small-scalevariabilities. Numerous solutions have been develop...Stochastic approaches are useful to quantitatively describe transportbehavior over large temporal and spatial scales while accounting for the influence of small-scalevariabilities. Numerous solutions have been developed for unsatu-rated soil water flow based on thelognormal distribution of soil hydraulic conductivity. To our knowledge, no available stochasticsolutions for unsaturated flow have been derived on the basis of the normal distribution ofhydraulic conductivity. In this paper, stochastic solutions were developed for unsaturated flow byassuming the normal distribution of saturated hydraulic conductivity (K_s). Under the assumptionthat soil hydraulic properties are second-order stationary, analytical expressions for capillarytension head variance (σ_h^2 ) and effective hydraulic conductivity (K_ii~*) in stratified soilswere derived using the perturbation method. The dependence of σ_h^2 and K_ii~* on soil variabilityand mean flow variables (the mean capillary tension head and its temporal and spatial gradients) andmean flow conditions (wetting and drying) were systematically analyzed. The calculated variance ofcapillary tension head with the analytical solution derived in this paper was compared with fieldexperimental data. The good agreement indicates that the analytical solution is applicable toevaluate the variance of capillary tension head of field soils with moderate variability.展开更多
文摘The effect of background anion on cation exchange reactions, suchas Na-Ca and Na-Cu exchange reac- tions, on montmorillonites has beenstudied, but the results are not always clear and discrepancies existin the literature. In this study, the exchange of zinc (Zn^2+) forsodium (Na^+) on Wyoming montmorillonite was investigated at 298 deg.K using Cl^-, ClO_4^-, NO_3^-, Oac^-, and SO_4~2- solution media at aconstant total metal charge concentration of 0.02000 mol_c L^-1.Results indicated that the clay CEC values were essential similar forCl^-, ClO_4^-, NO_3^- and SO_4~2- solution media with an average CECof 0.856±0.008 mol_c kg^-1; in an OAc^- solution the clay CEC wasmuch higher than that in other anion media.
基金This work was supported by the National NaturaI Science Foundation of China(Grant Nos:59509007,59879028)the Major State Basic Research Development Program of China(Grant No:G1999045700)the Fok Ying Tung Education Foundation.(Grant No:71027)
文摘Stochastic approaches are useful to quantitatively describe transportbehavior over large temporal and spatial scales while accounting for the influence of small-scalevariabilities. Numerous solutions have been developed for unsatu-rated soil water flow based on thelognormal distribution of soil hydraulic conductivity. To our knowledge, no available stochasticsolutions for unsaturated flow have been derived on the basis of the normal distribution ofhydraulic conductivity. In this paper, stochastic solutions were developed for unsaturated flow byassuming the normal distribution of saturated hydraulic conductivity (K_s). Under the assumptionthat soil hydraulic properties are second-order stationary, analytical expressions for capillarytension head variance (σ_h^2 ) and effective hydraulic conductivity (K_ii~*) in stratified soilswere derived using the perturbation method. The dependence of σ_h^2 and K_ii~* on soil variabilityand mean flow variables (the mean capillary tension head and its temporal and spatial gradients) andmean flow conditions (wetting and drying) were systematically analyzed. The calculated variance ofcapillary tension head with the analytical solution derived in this paper was compared with fieldexperimental data. The good agreement indicates that the analytical solution is applicable toevaluate the variance of capillary tension head of field soils with moderate variability.
