Adsorption. Surfactant Surfactant adsorption can be an important mechanism for a SEAR process since it causes retardation and consumption of surfactant. The remaining adsorbed surfactant after flushing with water at the end of the remediation process may also be important even for food grade surfactants and even though the mass concentration in the porous media at this time is likely to be very low on the order of the CMC. Some additional time will be required for this remaining surfactant to biodegrade and this will depend on the surfactant concentration among other variables. Surfactant adsorption has been the subject of extensive study for many decades and is now very well understood, especially for the types of surfactants and porous media of interest to SEAR. Xxxxx et al. [1993] and Xxxxx and Xxxxx [1994] are examples of recent studies done to compare the adsorption of different types of surfactant on soils. Xxxxxxxxxxxx and Xxxxx [1977] and Xxxxxxxxx et al. [1982] are examples among the hundreds of studies done to evaluate the adsorption of surfactants on porous media in the context of surfactant enhanced oil recovery. These studies show that surfactant adsorption isotherms are very complex in general. This is especially true when the surfactant is not isomerically pure and the substrate is not a pure mineral. However, we and others have found that for many if not most conditions of interest to us the general tendency is for the surfactant isotherm to reach a plateau at some sufficiently large surfactant concentration. For pure surfactants, this concentration is in fact the CMC, which is often 100 times or more below the injected surfactant concentration. Thus, the complex detailed shape of the isotherm below the CMC has little practical impact on the transport and effectiveness of the surfactant and for this reason it has been found that a Langmuir-type isotherm can be used to capture the essential features of the adsorption isotherm for this purpose. Xxxxxxxxx et al. [1987a] illustrate this by simulating an oil recovery experiment and Xxxx et al. [1989] by successfully simulating a surfactant field project using this approach. We also used a Langmuir-type adsorption isotherm for the simulation of the surfactant remediation of the Xxxxxx cell test illustrated below. UTCHEM uses a Langmuir-type isotherm to describe the adsorption level of surfactant which takes into account the salinity, surfactant concentration, and soil permeability (Xxxxxxxx and Xxxx, 1974). ...
Adsorption. The tracer adsorption for any type of tracer is assumed to be linear and can be modeled using an input retardation factor parameter (Ds) as Ds = CT CTℓ = (1 − φ)ρraT φρℓCTℓ ℓ = 1 or 4 (4.11) where aT is the mass of adsorbed tracer divided by the mass of rock. ρr and ρℓ are the rock and water ( ℓ = 1) or gas phase (ℓ = 4) densities. CT is the adsorbed tracer concentration. The adsorption is applied to total tracer flux (convective and dispersive ) and modeled as (Vt )ret . = u ⎛⎜ 1 ⎞⎟ (4.12) φSℓ ⎝ 1 + Ds ⎠ where u is the Xxxxx flux in ft/d and φ is the porosity.
Adsorption. As an alternative to cation exchange, the retention of chromium has also been modeled as a "Langmuir- type" isotherm in UTCHEM. Cˆ 14 = a14 C14,1 1 + b14 C14,1 (6.6)
