Showing papers on "Langmuir published in 1984"

Interlaboratory Comparison of a Standardized Phosphorus Adsorption Procedure

Abstract: A standard P adsorption procedure was proposed and the ability of four laboratories to produce consistent results over a wide range of soils was determined. For this procedure, 0.5 to 1.0 g of soil were shaken in 0.01 mol L CaCl at a soil/solution ratio of 1:25 in containers allowing a 50% head space for 24 h at 24 to 26°C on an end-over-end shaker. Initial dissolved inorganic P concentrations of 0 to 323 mol P L (as KHPO or NaHPO) were used and microbial activity inhibited by 20 g L chloroform. Excellent agreement between the four laboratories was obtained for the amount of P adsorbed by the 12 soils studied, with a mean coefficient of variation (CV) over all P levels and soils of 0.91%. The laboratories also exhibited a high degree of replication of individual treatments with no laboratory showing a strong consistent bias across all soils and P levels in terms of P adsorption. Langmuir, Freundlich, and Tempkin adsorption models were highly correlated with the adsorption data. Respective mean correlations for the 12 soils were 0.98, 0.97, and 0.95. The proposed method, therefore, has the potential to produce consistent results that can be used to predict partitioning of dissolved inorganic P between solid and solution phases in the environment.

Equilibrium adsorption of polycyclic aromatic hydrocarbons from water onto activated carbon.

Abstract: Adsorption isotherm data for 11 polycyclic aromatic hydrocarbons (PAH) from water onto Filtrasorb 400 activated carbon at 25/sup 0/C have been generated by batch shake testing. An evaluation of Henry's law, Langmuir, BET, Freundlich, and Redlich-Peterson equations indicates that the Langmuir equation is most useful for representing the data. Fitting the data to two linearized forms of the Langmuir equation provides estimates of the capacity term q/sup 0/ and the energy term b which apply over different equilibrium concentration (C/sub e/) ranges. The products of the parameters bq/sup 0/ obtained by using the low C/sub e/ linear form of the Langmuir equation approximate Henry's law adsorption constants. These values range from 2390 (mg/g)/(mg/L) for naphthalene to 326,000 (mg/g)/(mg/L) for chrysene. The parameter q/sup 0/ obtained by using the high C/sub e/ linear form of the Langmuir equation reflects limiting adsorption capacity. These values range from 580 mg/g for naphthalene to 14.7 mg/g for benz(a)anthracene. Both log (q/sup 0/) and log (bq/sup 0/) correlate with log (C/sub s/) and log (K/sub ow/), making it possible to predict relative adsorption of PAH from these latter properties. The adsorption of PAH onto activated carbon is (1) much stronger than is adsorption of PAHmore » onto soils, sediments, and suspended organic matter and (2) comparable to or greater than the adsorption of other hydrophobic organics onto activated carbon.« less

Competitive Adsorption of Phenols on Activated Carbon

Abstract: The adsorption of phenol and substituted phenols on activated carbon was examined. Mixtures of phenolic compounds were employed to test the Ideal Adsorbed Solution (IAS) theory using an improved method of calculation that had been developed for the description of multi‐component adsorption. This improved method of calculation allows for equilibrium concentrations to be calculated independent of the experimental observations as previously required in the original work. The IAS model with the modified calculation method was tested for its performance on ten sets of binary and tenary phenolic mixtures. The Langmuir competitive model was used for comparison. The IAS model was found to be successful in precisely describing the competitive adsorption behavior of phenolic mixtures and was proven to be superior to the Langmuir competitive model in all cases studied. The IAS model was also found to be relatively sensitive to the single‐component isotherm parameters input to the model calculation, particularly at l...

Sorption and transport of benzene in poly(ethylene terephthalate)

Abstract: The kinetics and equilibria of benzene sorption in poly(ethylene terephthalate) were measured at 40°C, 50°C, and 60°C, with benzene activities ranging from 0.02 to 0.3. At most experimental conditions, diffusion was found to be Fickian; however, evidence of non-Fickian transport was found at the highest activity levels. Values of the diffusion coefficient of benzene range from 10-14 cm2/s at 40°C to 10−12 cm2/s at 60°C in the limit of low concentrations. Nonlinear isotherms observed for benzene sorption were successfully interpreted in terms of the dual mode model for sorption in glassy polymers, whereby the sorbed penetrant exists as two populations: one sorbed according to Henry's law and the other following a Langmuir isotherm. Non-Fickian transport data were correlated with a model that superimposes diffusion of both the Henry's law and Langmuir populations (the “partial immobilization” model) upon first-order relaxation of the polymer matrix.

Sorption of phosphorus by some surface soils from Quebec in relation to their properties

Abstract: Surface horizons from Podzolic and Gleysolic soils were collected in various parts of the province of Quebec, Canada, and equilibrated with various amounts of KH2PO4 in 0.01 M CaCl2 for 48 hours. P sorption data conformed to the linear form of the Langmuir and Freundlich equations. P solubility isotherms showed evidence of hydroxyapatite formation in most samples studied, whereas equilibration solutions of only few samples were saturated with respect to either dicalcium phoshate dihydrate or octocalcium phosphate. These reaction products were associated to soil pH and levels of added phosphate. The average values of the Langmuir sorption maximum for these studied Gleysolic and Podzolic samples were 763 and 1096 μg/g respectively. These values were higher than those obtained by the segmented and modified Freundlich models. Relationships between the soil characteristics and P sorption parameters were evaluated by regression analysis. Among all variables, oxalate‐extractable Fe plus Al content of th...

Physical adsorption of gases on heterogeneous surfaces. Series expansion of isotherms using central moments of the adsorption energy distribution

Abstract: An alternative approach to the use of the usual integral equation for heterogeneous adsorption is developed. It provides a means of obtaining an explicit result for arbitrary local isotherms and distributions of energy of adsorption. The approximation is compared with exact numerical integrations, using the Langmuir local isotherm and a normal energy distribution. The series fails to converge for energy distributions that are very wide. Truncation of the expansion after the first-order term yields an equation which is capable of fitting experimental isotherm data.

Adsorption of Molybdate Anion (MoO42−) By Sodium-Saturated Kaolinite

Abstract: Adsorption of Mo(VI) on 2-0.2-um size fraction of sodium-saturated kaolinite at 25 _+ 2~ and at a constant pH of 7.00 _+ 0.05 was studied. The kaolinite sample was pretreated to remove any surface oxide and hydroxide coatings. The initial concentrations of Mo in solution ranged from 1 to 11 mg/liter in a NaC104 background electrolyte at a constant ionic strength of 0.09 _+ 0.01. Calculations of speciation using the GEOCHEM computer program indicated that under experimental conditions Mo(VI) was mainly in the MoO4 2- form. The experimental conditions were also shown to fulfill the requirements for applying the Langmuir equation in interpreting adsorption data. The Langmuir parameter for the adsorption maximum, n ~ and the affinity parameter, KMoO,2 -ao, were computed to be 3.33 x 10 -4 mole/ mole of adsorbent and 5.969 x 105, respectively. The large affinity parameter indicated that the Na- saturated kaolinite surface has a very high affinity for MoO42 ions relative to C10 4- ions.

Adsorption of gases on heterogeneous adsorbents

Abstract: A model to describe adsorbent heterogeneity has been developed by assuming that the adsorbent consists of a distribution of energetically different sites, the local isotherm on a site is of the Langmuir type and the energy distribution on the surface has a gamma probability density form. An analytic isotherm equation is derived. The parameters of the equation are m, the saturation adsorption capacity, and two energy distribution parameters, n and α. These parameters are found to be related to the Henry's-law constant, K. Thus there are only two adjustable parameters in the model when K is known from experimental data.The model has been used to describe isotherms for adsorption of N2, CH4, CO2 and C2H4 on the Calgon BPL activated carbon over large ranges of pressure and temperature. The carbon is found to be very heterogenous for the adsorption of these gases. Calculation of the probability density and the cumulative energy distribution functions indicates that the carbon exhibits a similar variance of surface energies for the adsorption of N2, CH4 and C2H4, although the isosteric heats of adsorption in the Henry's-law region for these gases are very different, decreasing in the order C2H4 > CH4 > N2. The isosteric heat of adsorption for CO2 is comparable to that of C2H4 but the carbon is more homogeneous for the adsorption of CO2 than for the other gases.

Chemical and XPS study of the adsorption of iron(III) onto porous silica

Abstract: Adsorption of iron(III) by porous silica has been measured from Fe(NO3)3 solutions. Three different adsorption processes can be distinguished. A Langmuir shape adsorption isotherm (plateau at 0.18 μmole/m2) is obtained for equilibrium concentrations up to 0.6 mF, corresponding to a pH range of 3.0 ± 0.2. In this concentration range, the final uptake per unit area is independent of silica/solution ratio, of solution age and of the duration of solid-solution contact. This process is attributed to adsorption of monomeric species. For higher concentration, the adsorbed amount increases; this additional uptake is markedly reduced if the solution is aged prior to the addition of the adsorbent. This process is due to the formation of oxyhydroxide polymers on the surface. XPS analysis shows that iron(III) is well distributed over the whole surface; however a slight enrichment observed on the outer surface of the particles may be attributed to adsorption of polymeric species.

Surface chemical and physical behavior of chrysotile asbestos in natural waters and water treatment

Abstract: Chrysotile asbestos fibers enter California waters from physical weathering of magnesium-silicate, serpentine rocks in mountains of the northern and central portions of the state. Chrysotile particles, initially positively charged below pH 8.9 because of their magnesium-hydroxide surface, become negatively charged due to dissolution and adsorption of organic matter. Chrysotile suspended in 0.1 M inorganic electrolyte at pH 7-10 for up to five days dissolves with magnesium being released in excess of the 3:2 Mg:Si to silica molar ratio in the solid. The rate of magnesium release exhibits a fractional dependence on hydrogen-ion concentration: r = k_1'[H^+]^(0.24) The observed rate constant, k_l', depends on dissolution mechanism, specific surface area of the solid and charge-potential relation at the surface. Interpreted in terms of a site-binding model for adsorption and desorption of protons on the surface, the fractional dependence implies that dissolution is limited by a chemical reaction involving an average of less than one adsorbed proton per magnesium ion released into solution. Silica release from chrysotile shows no clear pH dependence. The rate of magnesium release is independent of the anions NO^(3-), Cl^- , SO_4^(2-), HCO_3^-, oxalate or catechol. Oxalate inhibited and catechol slightly enhanced silica release over the pH range 7.5-8.5; other anions had no systematic effect. Chrysotile's dissolution rate (10^(-15.7) mol/cm^2·s at pH 8) is consistent with observations on other magnesium silicates and brucite. Catechol adsorption onto chrysotile or aluminum oxide (pH 7.5-8.5) does not reach equilibrium but increases over five days. After one day the maximum adsorption density (Langmuir adsorption equation) on chrysotile is 0.7 x 10^(-9) mol/cm^2 (50 x 10^(-6) mg C/cm^2), approximately one-third of the estimated number of surface sites available for proton exchange. The maximum adsorption density for natural organic matter was near 30 x 10^(-6) mg C/cm^2 on both chrysotile and aluminum oxide. Chrysotile adsorbs sufficient catechol, oxalate, phthalate or natural organic matter within one day to reverse its surface charge. The extent of reversal is larger than observed for adsorption of the same organics on aluminum oxide, because of selective dissolution of chrysoti1e's outer magnesium-hydroxide layer. In reservoirs, submicron-sized chrysoti1e particles coagulate with larger (>2 μm), negatively-charged particles that subsequently settle out. The rate at which freshly-suspended, positively-charged chrysotile fibers coagulate is at least ten-fold greater than the rate for aged, negatively-charged fibers coagulate. Removal of chrysotile particles in water treatment occurs by deposition of fibers onto sand grains in filtration. Capture efficiency for single fibers is low; removal is enhanced 10-fold or more by incorporating fibers into larger flocs. Removal of chrysotile fibers in water filtration to levels near detection limits (typically 10^5-10^6 fibers/L) is possible; consistent achievement of this level will require a higher removal efficiency than is routinely achieved in treatment plants receiving water from the California aqueduct.

Phosphorus Adsorption Characteristics of Some Acid and Alkaline Soils

Abstract: Acid soils adsorbed more P as compared with the alkaline ones irrespective of concentration of P in the equilibrium solution. The P adsorption showing a straight line Langmuir relationship was limited to a known solution concentration which varied with the soil. The treatment of citrate dithionite resulted in maximum reduction of P adsorption in acid soils and similar effect was found with ammonium acetate treatment in alkaline soils. In the former group of soils, more than 90% of the adsorbed P was as Fe and Al phosphate and in alkaline ones, about 40% was saloid bound. Phosphorus was adsorbed at two energy levels, the values of which varied with the nature of the soil.

Efficiency of Passive Sampling by Adsorbents

Abstract: The efficiency of passive samplers can be influenced strongly by the adsorption isotherm. In this study calculations of sampling efficiency were made in terms of dimensionless variables for adsorption controlled by the Langmuir, Freundlich, and Dubinin-Radushkevich isotherms, respectively. Of particular importance is that for the latter isotherm, which is often followed by activated charcoal for the adsorption of solvent vapors, passive sampling may remain highly efficient until a significant fraction of the capacity of the adsorbent has been utilized.

Solid adsorbents in batch fermentations

Abstract: The addition of a non-specific solid adsorbent reduces the liquid-phase substrate concentration at the start of a batch fermentation. Then, as product is generated, it displaces the substrate from the adsorbent, reducing liquid-phase product concentration. So both substrate and product inhibition can be reduced and the productivity of the fermentation increased. A mathematical model for this process is developed including a modified Langmuir bi-solute adsorption isotherm, and both growth- and non-growth-associated product formation. The model agrees well with experimental data on the effect of Linde JXC activated carbon on the fermentation of glucose to ethanol by S. cerevisiae. Only product inhibition is considered and NH3 is the sole nitrogen source to avoid complications arising from the adsorption of organic nitrogen compounds. Since ethanol is very hydrophilic and high concentrations of activated carbon are apparently toxic to yeast, there is little increase in volumetric productivity for this fermen...

A Thermodynamic Approach for Copper Adsorption on Some Danish Arable Soils

Abstract: For the investigated soils the Cu adsorption confirmed to the linear form of Langmuir isotherms. Cu adsorption is a pH dependent process increasing with soil pH and Cu solution concentration. Thermodynamically it exhibited an exothermic nature.

Diffusion of acid dyes in nylon film in the presence of inorganic salts

Abstract: The concentration-dependence measured by steady-state permeation and unsteady-state dyeing methods for a system of acid dye CIAcid Blue 182–nylon 6 film in the presence of inorganic salts such as NaCl, Na2SO4, and K2SO4, was analyzed in terms of parallel diffusion with simultaneous multimodal adsorption It would found that the dyeing process with added NaCl was governed by surface diffusion with two kinds of Langmuir adsorption, whereas with added Na2SO4 and K2SO4 it was governed by surface diffusion with three kinds of Langmuir adsorption

Zinc Adsorption Isotherms of Soils as Related to Soil Properties

Abstract: The Langmuir constants describing adsorption sites of dual mechanism for zinc on 10 surface samples covering five major soil types of Karnataka region were investigated. Adsorption maxima at b1 and b2 ranged from 0.13 to 0.49 and 0.54 to 3.69 with an average of 0.29 and 1.45 mg/g, respectively. On an average, the b1 and b2 values were equivalent to 3.7 and 18.3%, respectively of the cation exchange capacity (CEC). The values of adsorptive bond k1 and k2 varied from 0.220 to 1.026 and 0.012 to 0.068 with a mean of 0.454 and 0.037 ppm, respectively. With increased adsorption capacity there is a relative decrease in bonding energy coefficient and vice-versa. Inverse relations, C/C/x/m called as ‘breaks’ or inflection point of part I with part II of these soils expressed in μg/ml are 85 for saline, 124 and 138 for laterite, 180 and 204 for red, 218 and 227 for alluvial, 290 and 334 for black and 292 for sodic soils showing the direct relationship and ability of the soils to adsorb zinc. The Langmuir adsorption maxima (b2) were related to the soil properties viz, CEC, pH, clay content, organic carbon and calcium carbonate content in a decreasing order of significance.

An Analysis of Citrate Adsorption on Whewellite

Abstract: Adsorption at the whewellite-solution interface is important in urolithiasis because it affects rates of crystal growth and aggregation. Adsorption may also affect nucleation and apparent solubility (1). A number of substances in urine are adsorbed on whewellite and affect its growth and aggregation kinetics, so the adsorption process must be understood if we are to understand the kinetics of urolithiasis. It will be shown that Langmuir adsorption theory is not adequate to explain citrate adsorption on whewellite when conditions of pH and calcium ion activity are varied. Consideration of the electric double layer of whewellite in aqueous suspension yields an improved but not perfect description of citrate adsorption on whewellite under these conditions.

Langmuir solitons of the Bernstein--Green--Kruskal type

Abstract: A Langmuir soliton with a negative potential for ions is analyzed. The possible existence of trapped ions in such a soliton is considered. The distribution function of the trapped particles is derived.

Thermal etching of ZnS

Abstract: The thermal etching and the evaporation of ZnS single crystals were studied in vacuum. The Langmuir and the Knudsen evaporation processes on (111), (0001), (1010) and (1120) faces were investigated. In the Langmuir case on cationic polar faces etch pits are formed, whilst on anionic close packaged planes hillocks are observed. Rapid spiral decomposition on the A-surfaces and growth spirals on the B-surfaces are described. In these etch-features symmetrical stress fields are pointed out. From the elimination of different faces and temperature dependent etch pattern anisotropies the relation of the different evaporation rates can be approximated. For Knudsen evaporation the resulting near-equilibrium morphologies are also given. On the basis of the interferometric examination of the morphology it is supposed that the rate determining step for Langmuir evaporation is the generation of kinks.

Langmuir on the theory and application of the vacuum tube

Abstract: In this classic paper, Irving Langmuir presented his mathematical theory of space charge in high-vacuum electronic tubes to the Institute of Radio Engineers that had been organized three years earlier in 1912. The revolutionary merger of electronics and radio was just beginning when Langmuir delivered the paper that reported on theoretical and experimental research at the General Electric Research Laboratory. Only’a few weeks before, Edwin H. Armstrong, a radio enthusiast and recent graduate of Columbia University, had presented an IRE paper on the principles of vacuum-tube amplifiers and oscillators and their use in radio receivers. In his paper, Langmuir reviewed the history of research on thermonic currents including the theory of Owen W. Richardson and how space charge had been found to cause deviation from the volt-ampere characteristics calculated using the Richardson equation. Langmuir emphasized that “with the elimination of the gas effects, all of the irregularities which had previously been thought inherent in vacuum discharges from hot cathodes were found to disappear.” He also explained the new nomenclature for high-vacuum tubes that was being used at General Electric with terms such as “kenotron” and “pliotron,” a nomenclature that Lee de Forest later characterized as “Greeko-Schenectady.” During the discussion of Langmuir’s paper, de Forest praised the quality of the electronics work being done at General Electric but raised the issue of whether a new name for the ”audion” was justified simply because a higher vacuum had been achieved.