Adsorption Partition Coefficient Research Articles

Trace Metal Retention in the Incorporation Zone of Land-Applied Sludge

Recycling nutrients in wastewater sludge (biosolids) via land application is a desirable goal. However, potential movement of sludge-applied trace metals is of concern and an area of ongoing research. In this paper, the authors examine the first-order model used by the United States Environmental Protection Agency (US EPA) for predicting losses from the zone of incorporation as part of the risk assessment that undergirded the development of Part 503 regulations. The authors found that when empirical adsorption partition coefficients from the site are used as model inputs, the US EPA model for the incorporation zone is similar to that derived from preferential flow theory and simulates well the loss of metal from the surface soil layer at an orchard site where sludge was applied 15 years earlier.

Sodium Selective Ion-Exchange Properties of Zirconium Phosphate, HZr2(PO4)3, and Its Application for the Removal of Sodium Ions

Zirconium phosphate, HZr2(PO4)3 (NZP), in a powder form was synthesized from zirconium chloride oxide and sodium dihydrogenphosphate, and its ion exchange adsorption properties to alkali metal ions were studied. The ion-exchange adsorption partition coefficients of NZP to alkali metal ions at pH=3.4 were found to be 3.2×103 (Li*), 4.5×105 (Na+), 2.6 (K+), 12 (Rb+), and 380 (Cs+) cm3 g−1. The results indicate that NZP has a high adsorbability to sodium ions. Mixed granules of NZP and silica sol (NZP-P) were then prepared and applied for the selective removal of sodium ions by a column adsorption method.

The Influence of Organic Cosolvent (Methanol) on the Adsorption of Carbofuran on Three Different Types of Indian Soils

The adsorption of carbofuran on three different types of uncontaminated Indian soils (loam, silt clay loam, sandy loam) at various volume fractions (0.25, 0.50, 0.75, 1.0) of methanol (fS) has been studied by the batch shake technique. The adsorption of carbofuran was higher on loam soil, followed by silt clay loam and sandy loam soils, and decreased with increasing fS values on all soils. From the adsorption data, adsorption partition coefficients KD (ml/g) were evaluated and the KD values converted to mole-based partition coefficients Km (mol/g). These values were utilised to test the cosolvent theory. The Km values for soils, when normalised on foc, gave values of Kmoc, and a plot of log Kmoc versus fS resulted in a single line whose equation was determined by linear regression analysis as log Kmoc = –1.12 + 2.84; r2 = 0.96. The aqueous phase partition coefficient KDw (mol/g) normalised on f∞ for carbofuran extrapolated from this relationship was 4.1, The slope may be related to the effect of carbofuran solubility and to carbofuran–soil and solvent–soil interactions. The data presented suggested that methanol–soil interaction may not increase the accessibility of carbofuran to soil organic matter to the same extent as reported for less hydrophobic organic solutes.

Predicting soil sorption coefficients of organic chemicals using a neural network model

AbstractThe soil/sediment adsorption partition coefficient normalized to organic carbon (Koc) is extensively used to assess the fate of organic chemicals in hazardous waste sites. Several attempts have been made to estimate the value of Koc from chemical structure or its parameters. The primary purpose of this study was to develop a nonlinear model for estimating Koc applicable to polar and nonpolar organics based on artificial neural networks using the octanol/water partition coefficient (Kow) and water solubility (S). An analytic equation was obtained by starting with a neural network, converging the bias and weight values using the available data on water solubility, octanol/water partition coefficient, and the normalized soil/sediment adsorption partition coefficient, and then combining the equations for each node in the final neural network. For the 119 chemicals in the training set, estimates using the neural network equation lie outside the 2σ region (the standard deviation for the training set, σ = 0.52) for only five chemicals, while all the chemicals in the test set lie within the 2σ region. It was concluded that the neural network equation outperforms the linear models in fitting the Koc values for the training set and predicting them for the test set.

Characterization of Pesticide Sorption and Degradation in Macropore Linings and Soil Horizons of Thatuna Silt Loam

AbstractThe effect of changes in soil characteristics with depth because of soil horizonation and macroporosity on fate of pesticides is poorly understood. Soil from the surface A horizons (0–0.65 m), albic E horizons (1.05–1.35 m), argillic Bt horizons (1.4–3.5 m), and surface linings of macropores in the argillic horizons (Bt‐M, 1.4–3.5 m) of a Thatuna silt loam (fine‐silty, mixed, mesic Xeric Argialbolls) were characterized for their physical, chemical, and microbiological effects on adsorption, desorption, and mineralization of 2,4‐D, carbofuran, and metribuzin. Organic carbon (OC) contents decreased for soil materials in the order A (1.22%) > Bt‐M (0.36%) > Bt (0.25%) = E (0.20%), and were correlated with the number of soil microbial colony forming units (log CFU) that decreased in the order A (7.4) > Bt‐M (6.1) > E (5.6) = Bt (5.4). Percent macroporosity (pores 2–5 mm diam.) decreased in the order Bt (1.1%) > A (0.7%) > E (0.6%), which is the same order for decreases in saturated hydraulic conductivity (log m s−1), namely; Bt (−6) > A (−6.2) > E (−7.0). Freundlich adsorption partition coefficients (Kf− L kg−1) for A horizon soil with 2,4‐D (1.1), carbofuran (1.0), and metribuzin (1.6) were significantly greater than in subsurface E or Bt matrix material. Sorption Kf values in macropore linings with carbofuran (1.1) and metribuzin (2.0) were comparable to or greater than their respective values of 1.0 and 1.6 in A horizon material. Percent mineralization in the A horizon after 139 d for [U‐14C] 2,4‐D (81.8%) and carbofuran (14.7%) was significantly greater than in all subsurface soil materials. Mineralization in Bt macropore linings for 2,4‐D (17.0%) and carbofuran (8.4%) was significantly greater than in other subsurface soil materials. Mineralization of [U‐14C] metribuzin was negligible (<3%) in all soil materials after 139 d.

Adsorption and desorption of aliphatic amines, amino acids and acetate by clay minerals and marine sediments

The adsorption and desorption behavior of three aliphatic amines, three amino acids, and acetate by organic-free clay minerals (kaolinite and montmorillonite) and by marine sediment was studied in laboratory experiments using 14C-labeled compounds. These compounds were chosen to represent basic, neutral, and acidic functional groups. Adsorption partition coefficients ranged from < 0.5 to 4.2 for acetate, < 1 to 15 for monomethyl-, dimethyl- and trimethyl amine, and < 1 to 128 for alanine, glutamic acid and lysine. Single desorption experiments were conducted using these compounds to calculate desorption partition coefficients. Repetitive desorption experiments and a consecutive desorption model were used to calculate partition coefficients for the reversible and resistant components of desorption. Adsorption of the three positively-charged amines and lysine was mostly reversible, but glutamic acid, alanine and acetate exhibited irreversible association. This is most likely related to the different adsorption mechanisms caused by the different functional groups on these compounds. Ion exchange and electrostatic interactions are more important for the positively-charged compounds while chemical interactions with surface organic functional groups may be more important for the neutral and negatively-charged compounds. Adsorption of amines, amino acids and acetate is greater in sediments with a higher organic content although the acidic and neutral compounds were affected more than the basic compounds. Oxidation state of the sediments may also be an important factor in adsorption behavior.

Nonionic Organic Partitioning onto Organoclays

The adsorption of two nonionic organic compounds, nitrobenzene (NB) and 1,2-dichlorobenzene (DCB) onto five organoclays was studied. The results of the adsorption studies were compared to existing models (1-10) developed to predict nonionic organic adsorption onto the organic fraction of natural soils and sediments. The predictions by these models correlate the log of the normalized adsorption partition coefficient (Kom) and the log of the organic compound's octanol-water partition coefficient (Kow). The adsorption partition coefficient (Kp) is normalized by divided it by the soil's percent organic matter content (OM). The Kom values for NB and DCB adsorption by the organoclays was at least an order of magnitude higher than existing models would predict. This was most likely due to the greater efficiency of the organic fraction of the organoclays to adsorb nonionic organic compounds. A new model for nonionic adsorption onto organoclays is presented.

Herbicide Adsorption and Organic Carbon Contents on Adjacent Low‐Input Versus Conventional Farms

AbstractLittle quantitative information is available concerning the long‐term impact of alternative framing practices on herbicide adsorption and soil factors that control adsorption. The objective of this study was to evaluate the effects of long‐term conventional vs. long‐term, low‐input farming management practices on herbicide adsorption and soil properties that control adsorption at different landscape positions. Soil samples were collected at depths of 0 to 15 cm along a 350‐m boundary between adjacent long‐term conventional and low‐input farms near Spokane, WA. These samples were characterized for soil organic C (OC) and clay contents, soil pH, and linear adsorption partition coefficients (Kd) using the 14C radiolabeled herbicides metribuzin [4, amino‐6‐11,1‐dimethylethyl)‐3‐(methylthio)‐1,24‐triazine‐5(4,1,1)‐one], diuron, [3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea], 2,4‐D [(2,4‐dichlorophenoxy)acetic acid], and triallate [S‐(2,3,3‐trichloroally) diisopropylthiocarbamate]. Carbon contents were significantly higher on the low‐input farm than the conventional farm at all slope positions, with values at the bottom slope position of 19.4 g kg−1 on the low‐input farm and 12.2 g kg−1 on the conventional farm. Carbon contents also decreased significantly at upper slope positions, with values at the top slope of 9.0 g kg−1 on the low‐input farm and 6.0 g kg−1 on the conventional farm. The Kd values for the four herbicides studied were significantly larger on the low‐input farm than the conventional farm at all slope positions. Significant decreases in adsorption occurred on both farms at top‐slope positions relative to bottom‐slope positions. From 80 to 95% of the increase in Kd values could be explained by increases in OC contents, but the best‐fitting regression line had a large negative intercept for metribuzin, 2,4‐D, and diuron. We conclude from this that although the regression model may be used to estimate Kd values from measured OC contents at moderate to high values of OC, the model has no physicochemical significance and the slope of the model does not equate to a value for Koc.

Continuous ammonium enrichment of a woodland stream: uptake kinetics, leaf decomposition, and nitrification

In order to test for nitrogen limitation and examine ammonium uptake by stream sediments, ammonium hydroxide was added continuously at concentrations averaging 100 μg1‐1 for 70 days to a second‐ order reach of Walker Branch, an undisturbed woodland stream in Tennessee. Ammonium uptake during the first 4h of addition corresponded to adsorption kinetics rather than to first‐order uptake or to Michaelis‐ Menten kinetics. However, the calculated adsorption partition coefficient was two to four orders of magnitude greater than values reported for physical adsorption of ammonium, suggesting that the uptake was largely biotic. Mass balance indicated that the uptake of ammonium from the water could be accounted for by increased nitrogen content in benthic organic detritus. Nitrification, inferred from longitudinal gradients in NO3, began soon after enrichment and increased dramatically near the end of the experiment. Both ammonium and nitrate concentrations dropped quickly to near background levels when input ceased, indicating little desorption or nitrification of excess nitrogen stored in the reach. There was no evidence of nitrogen limitation as measured by weight loss, oxygen consumption, phosphorus content, and macroinvertebrate density of red oak leaf packs, or by chlorophyll content and aufwuchs biomass on plexiglass slides. A continuous phosphorus enrichment 1 year earlier had demonstrated phosphorus limitation in Walker Branch.

Transport of Organic Phosphate in Soil as Affected by Soil Type

Miscible displacement experiments were conducted on five soils using 7.5-cm diam and either 2.4- or 5.1-cm long columns. Glycerophosphate (771-2,195 ppm-P) and chloride (100 meq/liter) were applied in a 50-ml pulse to soil columns maintained at steady water contents slightly less than saturation. Two mathematical models were used in fitting the effluent concentration curves. The first was an analytical solution which consisted of first-order hydrolysis kinetics and reversible, instantaneous, linear adsorption reactions. The second was an explicit-implicit finite difference solution which consisted of first-order hydrolysis kinetics and two types of adsorption sites, one of which was reversible, instantaneous, and nonlinear; the other was reversible, kinetic, and nonlinear. The values of the partition coefficient and the exponent of the Freundlich isotherm used in the two-site model were determined by batch adsorption isotherm experiments. The rate coefficients of the adsorption-desorption reactions and hydrolysis reactions as well as the proportions of adsorption sites that were kinetic or equilibrium were determined by fitting calculated to measured glycerophosphate elution curves. Both the linear adsorption partition coefficient and the hydrolysis rate coefficient were determined by fitting elution curves of glycerophosphate using the linear, equilibrium model. The fitted partition coefficient was not in agreement with the batch adsorption isotherm indicating that the adsorption-desorption reactions were not instantaneous. Both mathematical models were capable of fitting the chloride effluent curves of all five soils quite well. The two-site model was capable of fitting the glycerophosphate effluent curves of all five soils more closely than the linear, equilibrium model. The two-site model, though, was incapable of accurately describing the adsorption-desorption reactions in two of the soils. This was apparently due to a wide range of kinetic rates of the reactions in these two soils.

Determination of soil adsorption partition coefficients of 14C-labeled carcinogenic organic chemicals by liquid scintillation

Determination of soil adsorption partition coefficients of 14C-labeled carcinogenic organic chemicals by liquid scintillation

Overall Capacity Coefficient of Mass Transfer between Bubble Phase and Emulsion Phase in Free and Eight-Step Fluid Beds

The residence time distribution curves of both non-adsorptive gas (helium) and adsorptive gas (carbon dioxide, Freon 12 and Freon 22) in 12 and 19 cm I.D. free and eight-step fluid beds (FCC catalyst-air system) are measured by impulse response technique.The overall capacity coefficient of mass transfer kobab between bubble phase and emulsion phase are calculated from these curves by applying a two-phase model in which physical gas adsorption equilibrium on solid particles is taken into account.It is found that the flow of gas approaches plug flow by dividing the fluid bed with baffles, and the values of kobab is dependent on the adsorption partition coefficient m and the bubble volume fraction εb. The following correlation is obtained : kobab/εb= (15m 1.8 + 229) / (m 1.8 + 191)