Humic acid‐modified silica as a model aquifer material

Abstract

The sorption behavior of nonionic organic chemicals on humic acid-modified silica was examined to assess its possible use as a simplified model of natural low organic carbon aquifer materials. Column and batch sorption experiments were conducted on humic acid-coated silica (0.073% organic carbon), using tetrachloroethylene (PCE) and 1-methylnaphthalene (MN). Batch kinetic experiments showed that equilibrium was attained rapidly for PCE (-1 d), whereas several tens of days were required for MN. Batch experiment results indicated Freundlich (nonlinear) isotherm behavior when a wide concentration range was examined. Sorption coefficients derived from the column experiments were consistent with the batch-derived Freundlich isotherms, illustrating the importance of isotherm type on breakthrough curves and solute transport in ground water. Similarities exist between the sorption behavior observed in this study and that of a number of natural aquifer materials. Humic acid-modified silica serves as a simplified model for aquifer materials, which tend to be more complex and difficult to characterize and can be used to examine organic solute transport processes in ground water.

Time‐dependent isotherm shape of organic compounds in soil organic matter: Implications for sorption mechanism

“…3). This behavior is consistent with previous findings mentioned above that the ''resistant'' fraction is inversely related to the applied concentration [22][23][24][25]. This is important from the perspective of bioavailability and remediation because it may provide one mechanism for the oftenobserved drop-off in degradation rate [38,39].…”

“…Miller and Pedit [21] used model simulations to suggest that N of lindane in a soil measured at 732 h adequately described sorption thereafter. Other evidence suggests that the N s Ͻ N f ; in particular, desorption of small, nonpolar molecules from soils [22,23], silica [24], or humic-coated silica [25] left a ''resistant'' fraction (i.e., S s ) that became progressively more important to total sorption (i.e., S s expressed as percentage of total sorption increases) as the applied concentration was reduced.…”

Heterogeneous photochemical reactions of decabromodiphenyl ether

“…The organic carbon content of the HA-coated sand was measured at 0.071% with a Dohrmann TOC boat sampler (Santa Clara, CA, USA) and Horiba PIR-2000 CO 2 detector (Irvine, CA, USA). This result compared favorably to that found by Burris et al [23] of 0.073% for identically prepared material.…”

“…In several experiments, trace quantities of DBDPE were adsorbed onto humic acid (HA)-coated sand (between 50 and 70 mesh). The experimental procedures reported by Burris et al [23] were employed without modification for cleaning the sand and coating it with HA. The organic carbon content of the HA-coated sand was measured at 0.071% with a Dohrmann TOC boat sampler (Santa Clara, CA, USA) and Horiba PIR-2000 CO 2 detector (Irvine, CA, USA).…”

Using QSAR to evaluate phenomenological models for sorption of organic compounds by soil

“…To evaluate further the appropriateness of the polymer analog as a phenomenological model for sorption dynamics in soil, the a values obtained from the soil data were compared to a values obtained from several experiments that employed polymeric materials. These polymeric materials included styrene-butadiene-rubber [45], polyurethane [54], silicone rubber [ 5 5 ] , humic acid bonded to silica [56], humic acid [57,58], and nylon [59]. The rate data were scaled to a through use of Equation l ; data used in this analysis are presented in Table 3.…”