Convective transport of acids and bases in porous media

Abstract

We present a convective description of acid‐base transport in porous media which is based on classical one‐component nonlinear Chromatographic theory applied to the acidity of the system. In the mobile phase the solution acidity is given by c = [H+]t ‐ [OH−]t, where [H+]t and [OH−]t are the total solution concentrations of H+ and OH−, respectively. In the stationary phase the surface acidity corresponds to the charge density σ, which is commonly presented as a function of pH of the solution. The response of a Chromatographic column to a step pH change at column inlet results in a pH breakthrough curve which consists of a combined Chromatographic front. This combined front begins with a diffuse subfront and ends with a self‐sharpening subfront. The present Chromatographic theory is used to predict experimentally observed pH breakthrough curves for columns filled with materials of known pH‐dependent charging behavior. Good agreement between theoretical predictions and experimental results is observed. Essentially, the same Chromatographic theory is used to explain pH breakthrough curves when the salinity of the input solution is changed. This situation leads usually to an additional nonretarded front where a change in pH occurs.

Adsorption of naphthalene from aqueous solution on activated carbons obtained from bean pods

“…Moreover, proton binding may also occur between water molecules and oxides on the carbon surface, particularly in carbons with high content of mineral matter, as those reported in this work. Such interactions would largely suppress the retention of the targeted probe (i.e., naphthalene) at low concentrations, leading to the S-class isotherm [34,35]. Table 4 Freundlich adsorption parameters and correlation coefficient for naphthalene removal The adsorptive capacity of the carbons was obtained by fitting the experimental data to the Freundlich approach, in terms of the amount of naphthalene adsorbed per unit mass of adsorbent.…”

Experimental investigation of transport of strongly retained species by soil columns

“…From the figure it can be noted a sequence of both diffuse-sharp adsorption and diffuse-sharp desorption fronts. Similar pHbreakthrough curves have been presented for other sorbent materials where silica was the main component Scheidegger et al, 1994). This behaviour corresponds to an adsorption isotherm that is S-shaped in terms of proton concentration (Schweich and Sardin, 1981), like it is generally in the case of soils.…”

“…Moreover, it is noteworthy that the faster breakthrough front observed in the NaC1 solution is also clearly spreader than in the other matrixes. Being the flow rate the same in all the experiments, the spread-out of the breakthrough curve can not be explained in terms of kinetic effects due to lower transport and sorption rate with respect to advection and dispersion (Schwarzenbach and Westall, 1981). Considering that in all the matrixes the sorbing species is the same (free lead), the observed effect can be explained in terms of different kinetics of complexation equilibria in the liquid phase: according to this hypothesis, the spread-out of the breakthrough front should indicate a slower dissociation kinetics of lead chloride complexes (essentially PbCI + and PbC12(aq)) than of lead nitrate one.…”

Miscible displacement of salinity fronts: Implications for colloid mobilization

“…The displacement of a high with a low concentration electrolyte solution causes cation exchange according to the mass action where Na is sodium, H is a proton, and X the sorbent. This ion exchange consumes H, and causes pH fronts to develop [ Schweich et al , 1993b; Scheidegger et al , 1994].…”

“…The second, retarded front is diffuse and has a pronounced tailing. The shape of the pH fronts is determined by the acidity isotherms [ Scheidegger et al , 1994]. In the case of the hydrodynamically unstable salinity front displacement, the nonretarded pH front shows several humps (Figure 4).…”