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53.
Adsorption isotherm models for basic dye adsorption by peat in single and binary component systems 总被引:11,自引:0,他引:11
Colored effluents from textile industries are a problem in many rivers and waterways. Prediction of dye adsorption capacities is important in design considerations. The sorption of three basic dyes, namely Basic blue 3, Basic yellow 21, and Basic red 22, onto peat is reported. Equilibrium sorption isotherms have been measured for the three single-component systems. Equilibrium was achieved after 21 days. The experimental isotherm data were analyzed using Langmuir, Freundlich, Redlich-Peterson, Tempkin, and Toth isotherm equations. A detailed error analysis has been undertaken to investigate the effect of using different error criteria for the determination of the single-component isotherm parameters and hence obtain the best isotherm and isotherm parameters which describe the adsorption process. The linear transform model provided the highest R(2) regression coefficient with the Redlich-Peterson model. The Redlich-Peterson model also yielded the best fit to experimental data for all three dyes using the nonlinear error functions. An extended Langmuir model has been used to predict the isotherm data for the binary systems using the single component data. The correlation between theoretical and experimental data had only limited success due to competitive and interactive effects between the dyes and the dye-surface interactions. 相似文献
54.
钙矾石3CaO·Al2O3·3CaSO4·32H2O是水泥熟料水化的重要产物.它易被空气中的CO2 分解,常温下的分解反应为3CaO·Al2O3·3CaSO4·32H2O 3CO2 →3CaCO3 Al2O3·xH2O 3(CaSO4·2H2O) (26 -x)H2O分解机理[1 ,2]是:H2O先吸附在钙矾石表面的活性中心上,吸附态水再吸收CO2 成为H2CO3 ,然后碳酸与钙矾石反应,实现碳化(即分解).其分解速率[3]为v=kpco2 pH2o(1)可见水的吸附是钙矾石碳化分解的关键步骤,因此探讨… 相似文献
55.
Abstract Isothermal data in the (V, P)-plane are generally not sufficiently precise to determine the bulk modulus and its pressure derivative using finite differences. Instead the data are fit to an analytic expression and the derivatives of the analytic expression are used. The derivatives obtained in this fashion may be sensitive to the fitting form and the domain of data used for the fit. This point is illustrated by re-analyzing two data sets for β-HMX. With the third order Birch-Murnaghan equation and a Hugoniot based fitting form we show that the uncertainty in the modulus due to the fitting forms is greater than the statistical uncertainty of the fits associated with the experimental error bars. Moreover, there is a systematic difference between the two data sets. Both fitting forms give statistically good fits for both experiments, although the modulus at ambient pressure ranges from 10.6 to 17.5 GPa. The large variation in the initial value of the modulus is due in part to the lack of data in the low pressure regime (below 1 GPa) and to the property of a molecular crystal, in contrast to a metal or atomic crystals, to stiffen substantially under a small amount of compression. The values of the modulus and its derivative are an important issue for an explosive like HMX because they affect predictions of the Hugoniot locus in the regime of the Chapman-Jouget detonation pressure. 相似文献
56.
Lispro insulin (LPI), a widely used insulin analog, is produced on tons per year scale. Linear gradient reversed phase chromatography (RPC) is used in the production to separate LPI from two impurities, which differ from LPI by a single amino acid residue. A chromatography model for the ternary separation in this RPC process is unavailable from the literature. In this study, a parallel pore and surface diffusion model is developed and verified for LPI and the two impurities. The LPI can be recovered with high yield (≥95%) and high purity (>99.5%). A new method, which requires a small amount of materials and an order of magnitude fewer experiments, has been developed to estimate the solvent-modulated isotherm parameters. A modified reversed phase modulator model is developed to correlate the adsorption isotherms of LPI and impurities. A strategy has been developed for estimating the intrinsic pore diffusivity and surface diffusivity. Since the adsorption affinities decrease by more than three orders of magnitude as organic fraction (φ) increases from 0.19 to 0.40, the apparent diffusivities based on a pore diffusion model or a surface diffusion model can also vary by several orders of magnitude. For this reason, a pore diffusion model or a surface diffusion model with a constant apparent diffusivity cannot predict closely the chromatograms over the same range of organic fractions, concentrations, and loadings. The parallel pore and surface diffusion model with constant diffusivities can predict closely the frontal and elution profiles over a wide range of organic fractions (0.19-0.40), LPI concentrations (0.05-18 g/L), linear velocities (<10 cm/min), and loading volume (0.0004-13 CV). For large loading stepwise and linear gradient elution, the peaks of LPI and the impurities are strongly focused by self-sharpening and gradient focusing effects as a result of the steep decrease of adsorption affinity from the loading φ (0.19) to elution φ (≥0.27). When the ratio of diffusion rate to convection rate is greater than 10, spreading due to diffusion is largely compensated by the focusing effects. As a result, a pore diffusion model with a constant pore diffusivity can predict closely the elution profiles in stepwise and linear gradient elution. The experimental yield values (≥95%) can be predicted to within ±1% by the model. 相似文献
57.
Nanna Bjarnholt Bo Svensmark Hans Christian B. Hansen 《International journal of environmental analytical chemistry》2013,93(4):303-314
Pesticide metabolites are often found to be more mobile in soil than their parent compounds. Pyrethroids are bound strongly to soil and therefore sorption of the pyrethroid metabolite permethric acid (PA) to a typical soil sorbent, goethite, was investigated. An on-line solid-phase extraction (SPE)-HPLC-UV procedure was developed for quantification of trans- and cis-permethric acid in aqueous samples. Limits of detection (LOD) were 500 times lower than those obtained with conventional HPLC-UV, resulting in LODs of 1.4 and 0.3?nM for the trans- and cis-isomers, respectively. Sorption of nanomolar concentrations of PA to goethite was found to be specific up to less than 1% surface coverage. In this range the data was described by a Langmuir equation with K ads = 7.1 × 10?9?L/mol and Γmax = 7.1 × 10?9?mol/m2 for total PA (trans + cis) at pH = 3. K ads,?cis (1.4 × 106?L/mol) was approximately twice K ads,?trans (7.9 × 105?L/mol). At higher PA concentrations the slope of the sorption isotherm increased, which is ascribed to hydrophobic interactions between adsorbed and dissolved PA molecules. Based on comparison with reported K om values, metal oxides are expected to have a relatively greater significance to the retention of PA than soil organic matter. 相似文献
58.
John M. Zielinski Charles G. Coe Randy J. Nickel Anthony M. Romeo Alan C. Cooper Guido P. Pez 《Adsorption》2007,13(1):1-7
A differential pressure adsorption unit (DPAU) has been constructed which is capable of accurately measuring isotherm data
up to 2000 psia with as little as 100 mg of sample. This non-traditional adsorption/desorption method has been benchmarked
by comparing hydrogen and methane isotherms measured with standard volumetric and gravimetric instruments on a NaA (4A) zeolite
and an activated carbon at near ambient temperatures. The results from stability tests and well as the details of the mathematical
analysis for this differential pressure method are also provided. 相似文献
59.
In the present study a new low cost, easily available and environmentally friendly adsorbent was used for removal of Cr (VI).
The Cr (VI) removal efficiency of the adsorbent was studied as a function of contact time, pH, adsorbent dose, adsorbate concentration,
temperature and stirring speed. Different adsorption model equations for kinetics, isotherm and rate mechanism of the process
were used to find the best model, which fit well to the experimental data. A full factorial design of nk type was used to find a mathematical relation between the percentage of adsorption and variables affecting the adsorption
process such as time, pH, adsorbate concentration and temperature. Using the Students ‘t’ test, the significance of each term
of the derived equation was tested. The insignificant terms were removed from the derived equation. The adequacy of the equation
after removing the insignificant terms was tested using the Fisher adequacy test. From the factorial design analysis it is
found that pH has the most pronounced effect followed by time, temperature and the adsorbate concentration. A column study
was performed using the optimum operating conditions. 相似文献
60.
Pasqua D'Ambra 《Continuum Mechanics and Thermodynamics》1997,9(2):97-114
In this work we present some results of the numerical simulation of the growth of a crystal from its melt, taking into account
faceting. The simulation is based on a numerical solution of a three–dimensional generalized Stefan problem. That problem
arises from a non–local thermomechanical theory applied to a continuous system with an interface and embodies ideas from the
dislocation theory of crystal growth. In the model, the crystal surface is an isotherm and the growth velocity of a crystal
face depends on the velocities of the other faces and on the whole crystal configuration as well as on the temperature gradient.
A front fixing formulation of the model is considered. This is a conservative form of the Isotherm Migration Method [6, 7,
8, 9, 10, 11] in spherical coordinates. The numerical solution is based on an explicit finite difference discretization of
the resulting non–linear equations. We develop a theoretical analysis of the interface equations that drive the crystal face
motion. Numerical results, showing evolution of complex crystals with configuration changing during the growth, are in accord
with experimental results. Furthermore, numerical experiments offer useful information on the influence of certain parameters
in the model on the growth process.
Received: March 21, 1996 相似文献