Low cost adsorbents for the removal of organic pollutants from wastewater.

Mass transfer between immobile and mobile zones is a consequence of simultaneous processes. We develop a “multirate” model that allows modeling of small-scale variation in rates and types of mass transfer by using a series of first-order equations to represent each of the mass transfer processes. The multirate model is incorporated into the advective-dispersive equation. First, we compare the multirate model to the standard first-order and diffusion models of mass transfer. The spherical, cylindrical, and layered diffusion models are all shown to be specific cases of the multirate model. Mixtures of diffusion from different geometries and first-order rate-limited mass transfer can be combined and represented exactly with the multirate model. Second, we develop solutions to the multirate equations under conditions of no flow, fast flow, and radial flow to a pumping well. Third, using the multirate model, it is possible to accurately predict rates of mass transfer in a bulk sample of the Borden sand containing a mixture of different grain sizes and diffusion rates. Fourth, we investigate the effects on aquifer remediation of having a heterogeneous mixture of types and rates of mass transfer. Under some circumstances, even in a relatively homogeneous aquifer such as at Borden, the mass transfer process is best modeled by a mixture of diffusion rates.

Multiple‐Rate Mass Transfer for Modeling Diffusion and Surface Reactions in Media with Pore‐Scale Heterogeneity

In this paper we investigate the probability of failure of a cohesive slope using both simple and more advanced probabilistic analysis tools. The influence of local averaging on the probability of failure of a test problem is thoroughly investigated. In the simple approach, classical slope stability analysis techniques are used, and the shear strength is treated as a single random variable. The advanced method, called the random finite-element method (RFEM), uses elastoplasticity combined with random field theory. The RFEM method is shown to offer many advantages over traditional probabilistic slope stability techniques, because it enables slope failure to develop naturally by “seeking out” the most critical mechanism. Of particular importance in this work is the conclusion that simplified probabilistic analysis, in which spatial variability is ignored by assuming perfect correlation, can lead to unconservative estimates of the probability of failure. This contradicts the findings of other investigators w...

/pdf/probabilistic-slope-stability-analysis-by-finite-elements-4i9novh51x.pdf

Probabilistic slope stability analysis by finite elements

http://www.ucalgaryreservoirsimulation.ca/wp-content/uploads/2014/07/J27-1-s2.0-S0009250907003144-main.pdf

Critical review of the impact of tortuosity on diffusion

Unsaturated soil mechanics has rapidly become a part of geotechnical engineering practice as a result of solutions that have emerged to a number of key problems (or challenges). The solutions have emerged from numerous research studies focusing on issues that have a hindrance to the usage of unsaturated soil mechanics. The primary challenges to the implementation of unsaturated soil mechanics can be stated as follows: (1) The need to understand the fundamental, theoretical behavior of an unsaturated soil; (2) the formulation of suitable constitutive equations and the testing for uniqueness of proposed constitutive relationships; (3) the ability to formulate and solve one or more nonlinear partial differential equations using numerical methods; (4) the determination of indirect techniques for the estimation of unsaturated soil property functions, and (5) in situ and laboratory devices for the measurement of a wide range of soil suctions. This paper explains the nature of each of the previous challenges and...

http://keshavarz.persiangig.com/document/Fredlund2006.pdf

Unsaturated Soil Mechanics in Engineering Practice

Evaluating the hydraulic conductivity of GCLs permeated with non-standard liquids

Recent studies suggest that diffusion may be an important, if not dominant, mechanism of contaminant transport through waste containment barriers. This paper represents the first of two papers pert...

Diffusion in Saturated Soil. I: Background

https://www.engr.colostate.edu/ce/homepages/shackel/Papers/6.pdf

Laboratory diffusion testing for waste disposal — A review

Hydraulic conductivity tests were conducted on a geosynthetic clay liner (GCL) for more than 2.5 years and as many as 686 pore volumes of flow (PVF) using single-species salt solutions (NaCl, KCl, or Ca Cl2 ) to (1) evaluate how the long-term hydraulic conductivity ( KL ) is affected by cation concentration and valence and (2) demonstrate the relevance and importance of termination criteria when measuring hydraulic conductivity of GCLs to salt solutions. Permeation with Ca Cl2 solutions resulted in an increase in the hydraulic conductivity of 1 order of magnitude or more. The rate at which these changes occurred depended on concentration, with slower changes (years and hundreds of PVF) occurring for weaker solutions. In contrast, permeation with 100 mM NaCl or KCl solutions or de-ionized (DI) water resulted in no appreciable change in hydraulic conductivity, regardless of the duration of permeation or number of pore volumes of flow. Hydraulic conductivities determined in accordance with ASTM D 5084 and D ...

https://www.engr.colostate.edu/ce/homepages/shackel/Papers/36.pdf

Long-term hydraulic conductivity of a geosynthetic clay liner permeated with inorganic salt solutions

The effective diffusion coefficients, \ID\N*, of three anions (Br\u-, Cl\u-, and I\u-) and three cations (Cd²\u+, K\u+, and Zn²\u+) diffusing in two compacted clay soils, kaolinite and Lufkin clay, are measured. The ions are contained in a simulated waste leachate. The effects of molding water content and method of compaction on the measured \ID\N* values are evaluated for kaolinite. The calculated \ID\N* values varied between 4 × 10\u-¹\u0 m²/s and 2 × 10\u-\u9 m²/s and, based on the results for chloride diffusion in kaolinite, are relatively insensitive to molding water content and compaction method. The measured \ID\N* values for Cl\u- and Br\u- in kaolinite are in excellent agreement with previous studies, but the \ID\N* values for the cations are relatively high. High \ID\N* values for the cations are attributed to nonlinear adsorption behavior at relatively high concentrations and to the possibility of chemical precipitation of the heavy metal species (Cd²\u+ and Zn²\u+). Also, \ID\N* values determined from reservoir concentrations typically are higher than \ID\N* values determined from soil concentration profiles.

Charles D. Shackelford

Papers

Evaluating the hydraulic conductivity of GCLs permeated with non-standard liquids

Diffusion in Saturated Soil. I: Background

Laboratory diffusion testing for waste disposal — A review

Long-term hydraulic conductivity of a geosynthetic clay liner permeated with inorganic salt solutions

Diffusion in saturated soil. ii: results for compacted clay