Effect of chemical heterogeneity on adsorbed solute dispersion at column scale

Abstract

in Wiley InterScience (www.interscience.wiley.com).Chemical heterogeneity seems to be responsible for spreading increase of adsorbed solute breakthrough curves. Adsorption in fixed beds assumes chemically homogeneous media. However, this is not always true, in particular when natural sands or mixed adsorbent filters are used in drinking water purification. Neglecting eventual effect of chemical heterogeneity may engender false modeling bases. So, considering homogeneous grain size distribution, the effect of chemical heterogeneity on global dispersion in porous media has been investigated experimentally in this article at column scale. Breakthroughs of adsorbed solute showed a visible effect of chemical heterogeneity on solute global dispersion increasing. The more heterogeneous the medium, the more spread the adsorbed solute breakthrough. Reduced variance showed a linear variation with the chemical heterogeneity scale at closely constant media global capacity. A pseudo-homogeneous model has been developed to simulate experimental data by increasing dispersion parameter.

A New Mixing-Cell-in-Series Model to Predict Breakthrough Curve in Chemically Heterogeneous Media at Column Scale

“…Considering kinetics, the model shows additive but independent effects of kinetics and hydrodynamics as in the case of chemically homogeneous media; it shows also independent kinetic effects from heterogeneity. Finally, modelling results were coherent with experimental observations made by Semra et al (2008). …”

“…It means that chemical heterogeneity is considered at such aggregate that could be close to or even greater than the one representing the hydrodynamic dispersivity. It is the case for heterogeneous media performed by Semra et al (2008) where chemical activity is different from one grain to another.…”

“…Considering chemical heterogeneity as non uniform distribution of active sites into the medium (in other words chemical activity distribution of the medium), a previous investigation (Semra et al, 2008) has shown, in fact, effect of chemical heterogeneity on solute dispersion. In Semra et al (2008), heterogeneous media were performed by mixing uniformly active grains and inert ones. Global capacity of media was kept constant whereas local capacity was varied with the number of active grains.…”

“…The investigation aimed essentially at finding out easily measured and controlled parameters that allow assessing of solute global dispersion into the medium and medium chemical heterogeneity. Considering Semra et al (2008) assumptions, the new model is based on the mixing-cell-in-series approach. This latter has already shown its efficiency in describing chromatographic processes.…”

Atrazine immobilization on sludge derived biochar and the interactive influence of coexisting Pb(II) or Cr(VI) ions

“…However, the different slopes at these two concentrations hint that diffusion may not be the only concentration-dependent mechanism that influences the sorption, and that kinetics may also be partially affected by the rate-limiting high-energy process. This was anticipated to make a greater contribution at a lower initial concentration among the heterogeneous sorption sites of the SDBC surface (Morelis et al, 2007;Semra et al, 2008;Zhang et al, 2013a,b). In addition, the H-bond has been reported to be stronger than organic partitioning with the hydrophobic tails of organic components (Lima et al, 2010), and therefore this may be dominant at a low loading.…”