Showing papers on "Freundlich equation published in 1977"
TL;DR: In this article, a combination of equilibrium and kinetic adsorption models is proposed to describe the nature of the overall reaction in a given chemical reaction in soil. But, the model is not applicable to agricultural applications.
Abstract: A given chemical may react at different rates with various soil constituents and be involved in several kinds of reactions. A combination of equilibrium and kinetic adsorption models is hypothesized to describe the nature of the overall reaction. An analytical solution to the one-dimensional convectivedispersive transport equation with a combination linear Freundlich isotherm and first-order reversible kinetic adsorption model is developed. The individual and combined effects of the model parameters on the breakthrough curves and retention profiles are examined. The combination equilibrium-kinetic model is shown to be applicable to pesticide, nutrient, and metal transport in soils.
369 citations
232 citations
TL;DR: Adsorption and precipitation of cadmium in soil suspensions were investigated as possible factors controlling Cd/sup 2 +/ levels in soils as mentioned in this paper, and the results showed that Cd+/ activity decreased approximately 100-fold for each unit increase in pH.
Abstract: Adsorption and precipitation of Cd/sup 2 +/ in soil suspensions were investigated as possible factors controlling Cd/sup 2 +/ levels in soils. Both adsorption of Cd/sup 2 +/ onto soils surfaces and possibly precipitation of cadmium minerals were evident in this study. At low cadmium levels solubility relationships in soils are best described by adsorption and fit the empirical Freundlich adsorption isotherm. Based on current thermodynamic data the solid phases CdCO/sub 3/ and Cd/sub 3/(PO/sub 4/)/sub 2/ most likely limit Cd/sup 2 +/ activities in soils. Under alkaline conditions, Cd/sup 2 +/ activity decreased approximately 100-fold for each unit increase in pH. CdCO/sub 3/ precipitated in sandy soils having low cation exchange capacity (CEC), low organic matter, and pH values >7.0. DTPA-extractable cadmium levels in soils were highly correlated (r = 0.96) with Cd concentrations in corn (Zea mays L.) seedlings grown in soils amended with Cd solutions, sewage sludge, or Cd-spiked sewage sludge. Increasing Cd additions to the soil increased plant Cd regardless of the form of Cd added. Addition of inorganic Cd to the soil increased the Cd concentration of corn seedlings more than equivalent Cd additions in the form of sewage sludge or Cd-spiked sludge.
160 citations
TL;DR: In this paper, the authors measured the adsorption capacity of 14 surface and 6 subsurface horizons of Illinois soils with respect to the amount of F− with release of OH− at low concentrations, and found that F− was due to amorphous aluminum oxyhydroxides which are common weathering products in these soils.
Abstract: Summary
Fourteen surface and 6 subsurface horizons of Illinois soils adsorbed significant amounts of F− with release of OH−. At low concentrations, adsorption was described by both Langmuir and Freundlich isotherms. The calculated Langmuir adsorption capacities were related to pH, clay, organic carbon, and amorphous aluminum contents.
Two soils with different gross chemical properties behaved in essentially the same manner, with adsorption maxima occuring between pH 5.5 and 6.5. The similarity between adsorption at different pH values for the soils and those for bauxite, allophane and synthesized ‘soil chlorite’, and the lack of adsorption maxima between pH 5.5 and 6.5 for pure kaolinite and montmorillonite, suggest that F− adsorption in the soils is due primarily to the presence of amorphous aluminum oxyhydroxides which are common weathering products in these soils.
117 citations
01 Jan 1977
TL;DR: In this paper, the theory of regular solid solutions was applied to exchange adsorption of ions in soil and some approximative equations of practical interest were derived for the possible role of oxides of Fe and Mn in the binding of other heavy metals.
Abstract: Fractions of Zn, Cd, Cu, Pb, Fe and Mn extractable with water, a salt solution and dilute acid, and residual fractions were determined in soils with raised contents of heavy metals, near zinc smelters, along a river formerly discharging heavy metals, and in a sewage farm. Special attention was paid to the role of oxides of Fe and Mn in the binding of other heavy metals. The theory of regular solid solutions was applied to exchange adsorption of ions in soil and some approximative equations of practical interest were derived. The possible role. of hydrolysis and the adsorption of hydrolysis products was studied. Ion exchange in soil was described in terms of sites of high and low selectivity (two-site model) giving rise to a decreasing free enthalpy of adsorption with increasing surface coverage (Freundlich behaviour). Cation-exchange experiments with Ca 2+ , Zn 2+ , Cd 2+ , Cu 2+ and Pb 2+ on Winsum clay soil showed that heavy metals were subject to regular and selective (specific) exchange adsorption, and to superequivalent adsorption. A pronounced lowering of pH upon adsorption of heavy metals was assumed to be by desorption of weakly acidic protons or selective adsorption of hydrolysis products, in combination with a diminished acid-neutralizing capacity. Results may be of interest for environmental control of heavy metals.
84 citations
TL;DR: In this article, a preliminary model was formulated to describe the relation between the daily regenerated adsorptive capacity and influent organic matter concentration in plug-flow activated sludge units maintained at sludge ages of 3, 5, 10 and 15 days.
40 citations
TL;DR: In this paper, rate models for adsorption and desorption on a non-uniform surface are derived using the "Extent of Reaction Effect" which describes the behaviour of large systems of parallel reactions.
Abstract: Rate models for adsorption and desorption on a non-uniform surface are derived using the “Extent of Reaction Effect” which describes the behaviour of large systems of parallel reactions. When the rate models and the resulting isotherm are fitted to data taken from the literature, very good agreement is found between the fitted model and the data. The new isotherm also provides an explanation for cases where physisorption is observed to follow Langmuir's dissociative chemisorption isotherm.Extensions of our rate model are presented for the case where a precursor state exists. This approach leads to two well-established isotherms: the Freundlich isotherm and the “generalized Freundlich” isotherm proposed by Sips.
30 citations
TL;DR: Time-dependent batch equilibrium studies for Cu, Zn, and Cd were conducted to determine the sorbing properties for these metals on the upper 30 cm of a forest soil as discussed by the authors.
Abstract: Time-dependent batch equilibrium studies for Cu, Zn, and Cd were conducted to determine the sorbing properties for these metals on the upper 30 cm of a forest soil. Major cations were added to equilibrating solutions in an attempt to match to cationic matrix of a sewage sludge. Essentially all of the Cu was adsorbed by the soil in the first 0.3 hour of equilibration. Copper adsorption data fit the Freundlich isotherm better than the Langmuir isotherm. Adsorption of Zn and Cd was more time dependent than Cu, especially for the 0 to 7.5 cm depth of soil, and was described with some success by the empirical kinetic equation, delta S/delta t = aC/sup b/S/sup c/, where S is ..mu..g metal absorbed per g soil, C is concentration of metal in final equilibrating solution, t is time, and a, b, and c are constants. Batch data taken at 3 hours of equilibration for Zn and Cd also fit the Freundlich isotherm better than the Langmuir isotherm. For Cu, Zn, and Cd adsorption, Freundlich constants (K) were higher for the 0 to 7.5 cm depth than for the 7.5 to 15 cm depth, indicating the binding effects of the higher level ofmore » organic matter in the surface 7.5 cm of forest soil.« less
25 citations
TL;DR: The transport model based on the adsorption of cationic forms of Cu, Zn, and Cd severely underpredicted the movement of these metals in both the 15- and 120-cm percolate when compared to previously observed field data, indicating that transport processes other than accelerated movement of chelated compounds, such as ''channelization,'' may be involved in the field.
Abstract: A transport model was developed to study the movement of Cu, Zn, and Cd in a forest soil. Adsorption of cationic forms of these metals by the soil was described by Freundlich adsorption isotherms. Two slug inputs of heavy metals were introduced during the first 37 days and between the 168th and 196th days of the 17-month simulation period. The transport model based on the adsorption of cationic forms of Cu, Zn, and Cd severely underpredicted the movement of these metals in both the 15- and 120-cm percolate when compared to previously observed field data. With the addition of assumed levels of less highly adsorbed chelated components to the model, percolate metal concentrations were roughly predicted at the 15-cm depth. However, data generated by the partitioned (chelate component) model also underpredicted movement of heavy metals to the 120-cm depth, indicating that transport processes other than accelerated movement of chelated compounds, such as ''channelization,'' may be involved in the field.
25 citations
TL;DR: In this article, it was found that the adsorption isotherms describing the adaption of sodium 4-hexadecyl-oxytolyl2-sulfonate and sodium dodecyl-benzene-4-sulphonate at different solid surfaces revealed maxima at the range of CMC.
Abstract: It has been found that adsorption isotherms describing the adsorption of sodium 4-hexadecyl-oxytolyl2-sulfonate and sodium dodecyl-benzene-4-sulfonate at different solid surfaces revealed maxima at the range of CMC. Similar maxima also occurred on the curves χ/c.
22 citations
TL;DR: In this article, the effects of temperature and pressure on the amount adsorbed were investigated and the authors applied the heterogeneous surface model applied in Part 2 to the kinetics.
Abstract: The heterogeneous-surface model applied in Part 2 to the kinetics, is now applied to the effects of temperature and pressure on the amount adsorbed. It predicts isobars with a maximum that is displaced towards higher temperatures at higher pressures. The low-temperature, pseudo-equilibrium isotherms obey the Freundlich equation. Increase in temperature or decrease in pressure produce desorption followed by readsorption. Temperature-programmed desorption gives one peak when heating is slow and two peaks when heating is rapid. When isotopes are successively adsorbed, the isotope adsorbed last is desorbed at lower temperature. The distribution of the adsorbate, according to the regions of various energy on the adsorbent, depends on temperature, pressure and time and is given by a discontinuous function with a maximum.
TL;DR: In this article, the authors used the gas chromatographic method of Cremer and Huber to investigate the adsorption isotherms on γ-alumina of hydrocarbons with up to eight carbon-atoms.
01 Apr 1977
TL;DR: In this paper, the surface homogeneity and heterogeneity for the adsorbents of binary gas mixtures measured at constant total pressure is discussed by assuming the surface heterogeneity and heterogeneity of the adorbents.
Abstract: Adsorption of binary gas mixtures measured at constant total pressure is discussed by assuming the surface homogeneity and heterogeneity for the adsorbents. Similarly as for mixed-gas adsorption at constant adsorbed amount of one of the components, the equations for partial adsorption isotherms at constant total pressure can be expressed as functions of the partial pressures, i.e., partial adsorption vs partial pressures. For full monolayer coverage these equations assume a form similar to that describing the adsorption from ideal solutions. The analogy between adsorption from gas mixtures and adsorption from ideal solutions is discussed on the basis of the derived equations. Experimental data concerning the adsorption from hydrocarbon mixtures on charcoal, activated carbon, and silica gel are analyzed by using the derived equations.
TL;DR: Different models of adsorption isotherm have been applied to the study of benzene and cyclohexane on graphitized thermal carbon black by the step and pulse gas chromatographic method.
TL;DR: In this paper, the problem of determining adsorption from binary gaseous mixtures on the basis of pure-gas adorption parameters has been theoretically discussed and analyzed.
Abstract: In this paper the problem of determining adsorption from binary gaseous mixtures on the basis of pure-gas adsorption parameters has been theoretically discussed. The author analysed adsorption systems whose adsorption from pure gases is in agreement with the equation ofToth, Freundlich orLangmuir.
TL;DR: In this article, the relationship between the adsorption of p-chloroaniline and the original adsorbate concentration was investigated for five soils ranging in organic matter content from 1.7 to 8.1 per cent and in clay content from 0.5 to 21 per cent.
Abstract: Summary
Relationships between the adsorption of p-chloroaniline and the original adsorbate concentration were investigated for five soils ranging in organic matter content from 1.7 to 8.1 per cent and in clay content from 0.5 to 21 per cent. Adsorption data were analyzed applying the linear form of the Freundlich equation. To evaluate the general relationship between adsorption of p-chloroaniline by soils and the solution concentration (C0), values of partition coefficient (Kp), reflecting the magnitude of distribution of chemical at equilibrium between soil colloids and solution were calculated.
The experiments showed that the regression parameters were significantly correlated with the soil organic matter content. A comparison of the experimental results obtained with other soils and the calculated values gave satisfactory agreement.
TL;DR: In this article, the adsorption of Dyfonate (O-ethyl-S-phenyl ethylphosphonodithioate) was studied on humic acid saturated with various cations (Fe3+, Al3+, Cu2+, Zn2+, Co2+, Mn2+, Ni2+, Ca2+, Mg2+, and H+).
Abstract: The adsorption of Dyfonate (O-ethyl-S-phenyl ethylphosphonodithioate) was studied on humic acid (HA) saturated with various cations (Fe3+, Al3+, Cu2+, Zn2+, Co2+, Mn2+, Ni2+, Ca2+, Mg2+, and H+). The amount of Dyfonate adsorbed was affected by the cation with which the HA was saturated. The adsorption process could be described empirically by a Freundlich-type isotherm. The K and constants of the Freundlich equation decreased and increased, respectively, with increase in temperature. The data suggest a physical type of adsorption.
TL;DR: In this paper, the dispersion and adsorption of solute in multilayer saturated porous media with constant specific discharge were examined and a general nonlinear equilibrium adaption isotherm of the Freundlich type was considered.
Abstract: Dispersion and adsorption of solute in multilayer saturated porous media with constant specific discharge are examined in the present work. Differential equations are formulated for describing the solute concentration in two-layer porous media. A general nonlinear equilibrium adsorption isotherm of the Freundlich type is considered. The nonlinear coupled differential equations are solved by the orthogonal collocation method to give the solute concentration distributions in the media when subject to a step-change or an exponential input. It is found that under many circumstances, the general dispersion model can be reduced to a simpler plug-flow model by neglecting the dispersion component in the governing differential equations. A criterion for this simplification is also suggested.
TL;DR: In this article, a new excess isotherm is derived for multilayer adsorption from binary liquid mixtures on solid surfaces by applying the Myers and Sircar's theoretical procedure.
Abstract: A new excess isotherm is derived for multilayer adsorption from binary liquid mixtures on solid surfaces. This is done by applying the Myers and Sircar's theoretical procedure, and assuming that the adsorption of single components is described by the BET isotherm equation, as modified by Brunauer, Skalny and Bodor. The derived excess equation is next generalized for the case of patchwise heterogeneous solid surfaces. The illustrative calculations presented here include both model investigations and an investigation of two real adsorption systems. It is drawn as a general conclusion that the heterogeneity effects in adsorption from solutions play a greater role than previously supposed.
TL;DR: In this paper, two exponential adorption isotherms are discussed with regard to adsorption on microporous adsorbents at low and moderate surface coverages, one of them may be treated as a certain generalization of Dubinin isotherm.
TL;DR: Adsorption of some phenylcarbamates, phenylureas and anilide pesticides on powdered activated carbon was investigated in this article, and the studied phenylamides proceeds in accordance with the Freundlich model.
TL;DR: In this article, a method was developed to obtain adsorption isotherms by analyzing spreading pressure-surface charge data obtained throughout a range of potentials in aqueous electrolyte solutions.
TL;DR: In this paper, four soils sampled at two depths were equilibrated with Mn solutions to test the conformity to the Langmuir isotherm and to relate the Langevin coefficents to soil properties.
Abstract: Four soils sampled at two depths were equilibrated with Mn solutions to test the conformity to the Langmuir isotherm and to relate the Langmuir coefficents to soil properties. The data conformed to the Langmuir isotherm over the entire Mn concentration range tested (2 to 64 μg Mn/ml) except where there was very low adsorption by sandy, low organic matter top soils. In those soils the isotherm was followed only up to 16 μg Mn/ml in the original solution. Adsorption capacities for Mn were higher for the finer-textured, high organic matter soils and generally followed the CEC of the soils. However, the Mn adsorption maximum was less than 40 percent in all cases and for the sandy top soils only 6 percent of the CEC. There was an inverse relationship between the bonding energies of the soils for Mn and the Mn adsorption capacities. For a relatively constant pH, clay and organic matter contents (and the subsequent CEC) were the soil properties more closely related to Mn adsorption by soils.
01 Jan 1977
TL;DR: In this paper, the effects of 14C-atrazine on freshwater invertebrates were studied and the results showed that mortality increased with increasing observation time, even at low concentrations of 1 ppm.
Abstract: Effects of the herbicide atrazine on freshwater invertebrates were studied. Long-term studies are urgently recommended for any evaluation of the toxicity of herbicides. Mortality increased with increasing observation time, even at low concentrations of 1 ppm. 14C-atrazine is taken up from water according to a hyperbolic function of time and reaches a maximum value within a few hours. Total adsorption capacity increased with increasing concentration in the water according to the Freundlich adsorption isotherm. Elimination was observed to occur within 24 hours in leeches. Within the animal atrazine is distributed according to the lipid content of the organs. The other herbicides studied, 2,4 — D and Paraquat, showed another distribution.
TL;DR: In this paper, the consequences of assuming Jovanovic local adorption isotherm are discussed on the basis of integral adsorption equation for heterogeneous surfaces, and analytical solutions are presented for Dubinin-Radushkevich adsorem.
Abstract: The consequences of assuming Jovanovic local adsorption isotherm are discussed on the basis of integral adsorption equation for heterogeneous surfaces. Analytical solutions are presented for Dubinin-Radushkevich adsorption isotherm.
TL;DR: In this paper, the critical deposition potential was determined from the amount deposited in the equilibrium state and from the potential-dependence of the rate constant for the deposition of 54 Mn.