Adsorption studies of cerium on lead dioxide from aqueous solutions

The adsorption of cerium from aqueous solutions on lead dioxide has been investigated and optimized as a function of pH, equilibration time, sorbate and sorbent concentrations. The effect of other anions and cations on its adsorption has also been studied. Citrate, EDTA, tartrate, oxalate, U(VI), Th(IV), Pb(II), Cr(III) and Al(III) drastically reduce the adsorption. Adsorption of other metal ions on the same oxide has been measured under identical conditions. The distribution coefficient indicates that cerium can be separated from Fe(III), Tc(VII), In(III), Ag(I), Hg(II) and Ta(V). The data fitted very well to Freundlich as well as Dubinin-Raduskevich (D-R) isotherms. A mean free energy of sorption 11.62±0.2 kJ·mol^–1 was calculated, using the D-R equation and corresponds to an ion exchange reaction.     

Adsorption of the halogens on cerium dioxide

Summary CeO₂, alone or mixed with La₂O₃, is used as halogen adsorbent in the determination of carbon and hydrogen. Quantitative data are given on the adsorption of the single halogens on various samples of pure CeO₂ and La₂O₃. Retention of CO₂ and the influence of several parameters of special interest in the carbon and hydrogen determination, have been examined. It has been found that the conditions for optimum adsorption of the halogens are a large surface and relatively low adsorption temperature. Unfortunately these conditions cannot be applied in the determination of carbon and hydrogen.

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Zusammenfassung CeO₂ allein oder im Gemisch mit La₂O₃ wurde als Adsorbens für Halogen bei der CH-Bestimmung verwendet. Quantitative Angaben über die Adsorption der einzelnen Halogene an verschiedenen Mustern von reinem CeO₂ und La₂O₃ wurden gebracht. Die Retention von CO₂ und der Einfluß einzelner Parameter, die für die CH-Bestimmung von besonderem Interesse sind, wurden geprüft. Die besten Bedingungen für die Adsorption der Halogene sind große Oberfläche und relativ niedere Temperatur. Beide Bedingungen können leider bei der CH-Bestimmung nicht eingehalten werden.

     

Thermodynamics of carbofuran adsorption on pyrite

Thermodynamic parameters of carbofuran adsorption on pyrite were determined from experimental data. In order to minimize the dissolution of pyrite as well the degradation of carbofuran, all experiments were restricted to (15 to 20) min. The maximum adsorption capacity of carbofuran varied with both pH and temperature in the order: ${\left[{\Gamma }_{\text{carb}}^{\text{max}}\right]}_{\mathit{pH}1.77}>{\left[{\Gamma }_{\text{carb}}^{\text{max}}\right]}_{\mathit{pH}2.70}>{\left[{\Gamma }_{\text{carb}}^{\text{max}}\right]}_{\mathit{pH}4.01}$. The Dubinin–Radushkevick (D–R) model was used to assess the degree of site heterogeneity. The interactions between carbofuran and surface sites can largely be ascribed to specific chemical interactions.     

Thermodynamics of adsorption equilibrium

Russian Chemical Bulletin -     

Thermodynamics of the sorption of cerium complex compounds on anionite

Sorption of cerium in the form of complexes with Trilon B (EDTA) from acid media at pH 3 using weakly basic anionite D-403 in nitrate, chloride, or sulfate forms is studied. The equation of the mass action law is linearized for ion exchange reactions, allowing us to calculate the limiting sorption of ethylenediaminetetraacetate cerate (EDTA cerate) ions on anionite and the constants of the exchange of complex cerium ions by chloride, nitrate, and sulfate ions. The limiting sorption of EDTA cerate ions in the anionite phase transitioning to the sulfate form is lower than that of ions on nitrate or chloride anionite, due to the high ionic potential of the sulfate ions. A sorption series of EDTA cerate ions on anionite D-403 in different ion exchange forms is presented according to the Gibbs energy of the ion exchange equilibrium.     

Adsorption of amino acids on a cerium dioxide surface

Adsorption of glutamic, aspartic, and pteroylglutamic (folic) acids from aqueous solutions on the surface of nanocrystalline cerium dioxide has been studied as depending on the pH and ionic strength of the solutions. Stability constants have been calculated for surface complexes that result from the interaction of anionic forms of the amino acids with protonated surface groups of cerium dioxide. The structure of the surface complexes has been confirmed by IR spectroscopy.     

Electronic conductivity in nonstoichiometric cerium dioxide

The electrical conductivity of sintered specimens of nonstoichiometric CeO_2?x was measured as a function of temperature (750–1500°C) and oxygen pressure (1–10^?22 atm). The isothermal compositional dependence of the electrical conductivity of CeO_2?x was determined by combining recently obtained thermodynamic data, x = x(P_O2, T), with the conductivity data. The compositional and temperature dependence of the electrical conductivity may be represented by the expression

$\text{σ=410[x]e}{}^{\mathrm{<mtext>?(0.158+x)</mtext><mtext>kT</mtext>}}\text{(}\text{ohm cm}\text{)}{}^{\mathrm{?1}}$

over the temperature range 750–1500°C and from x = 0.001 to x = 0.1.This expression was rationalized in terms of the following simple relations for (a) the electron carrier concentration

$\text{n}{}_{\mathrm{ce}}\text{′}{}_{\mathrm{ce}}\text{=}\text{8x}\text{a}{}_0{}^3$

where n_Ce′Ce is the number of Ce′_Ce per cm³ and a₀ is the lattice parameter and (b) the electron mobility

$\text{μ=5.2(10}{}^{\mathrm{?2}}\text{)e}{}^{\mathrm{<mtext>?(0.158+x)</mtext><mtext>kT</mtext>}}\text{(}\text{cm}{}^2\text{/}\text{V sec}\text{)}$

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Properties of electrorheological fluids based on nanocrystalline cerium dioxide

Effect of conditions of nanocrystalline cerium dioxide preparation from aqueous solutions on its composition and physicochemical properties and on dielectric characteristics of CeO₂ suspensions in polydimethylsiloxane PMS-20 and the magnitude of electrorheological effect for these suspensions has been analyzed. Relationship between physicochemical properties of CeO₂ nanopowders and polarization and functional characteristics of electrorheological fluids derived therefrom has been established.     

Thermodynamics of mixed-ligand complexation of cerium group lanthanide ethylenediaminetetraacetates

The thermodynamic parameters (logK, Δ _r G ⁰, Δ _r H, and Δ _r S) for mixed-ligand complexation of LnEdta⁻ (Ln³⁺ = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Gd³⁺) with iminodiacetate and nitrilotriacetate ions in aqueous solution at 298.15 K and ionic strength I = 0.5 (KNO₃) were determined by calorimetry and pH-metry. The variation of the thermodynamic parameters of the reactions over the lanthanide series was discussed.     

Thermodynamics of vapour adsorption on heterogeneous microporous adsorbents

Fundamental thermodynamic functions have been derived for equations of adsorption isotherms including structural heterogeneity connected with micropore dimensions. Good agreement has been achieved between values of the differential molar enthalpy of adsorption and values of the isosteric adsorption heats obtained experimentally.     

Studies on the adsorption behaviour of trace amounts of cerium on manganese dioxide from aqueous solutions in the presence of complexing agents

Adsorption behaviour of trace amounts of cerium on manganese dioxide has been studied as a function of pH (1–10) in the presence of EDTA, oxalate, citrate, tartrate, cyanide and thiocyanate ions. The influence of their concentration on the adsorption has also been investigated. Maximum adsorption of cerium has been noticed at pH6. Under specific conditions, adsorption of other metal ions has been measured for comparison. Low distribution coefficients are obtained for Cs(I) and Hg(II) in the presence of oxalate, and for Cr(III) in the presence of thiocyanate ions. Based on these data, separation of cesium, chromium and mercury from rare earths and cerium scavenging in natural water or in waste water treatment can be achieved.     

Carbon dioxide adsorption on carbon nanomaterials

The adsorption of CO₂ on a number of activated carbons, thermal carbon black, and oxide materials at 195 K was studied using static and dynamic techniques. The landing surface areas ω(CO₂) ≈ 0.19 nm² on thermal carbon black and the absolute values of sorption for P/P ₀ < 0.4 were determined. The density of adsorbed CO₂ in the micropore volume was estimated at ρ(CO₂) = 0.91 g/cm³. It was demonstrated that the previously found effect of a weakening of the sorption interaction of nitrogen molecules with thin-walled materials (which manifested itself in an analysis of sorption isotherms by a comparative method) was pronounced to a lesser degree for the sorption of CO₂. At the same time, the presence of supermicropores in activated carbon samples resulted in overestimated values of surface areas. A dynamic method was proposed to measure the spectra of CO₂ desorption at 195–260 K using a SORBI-MS system for evaluating the binding energy of sorbate molecules with the surface.     

Thermodynamics of adsorption of organic vapours on carbon black

Summary An apparatus for gas adsorption on solids has been described and with the help of this apparatus specific surface area of carbon black was calculated by the adsorption of nitrogen gas on carbon black at liquid air temperature.The adsorption of methanol, methyl formate, methyl acetate, methyl cyanide, acetaldehyde and methyl ethyl ketone on carbon black has been measured at a number of temperatures between 0° and 40°, and qst the isosteric heat of adsorption, at different temperatures and coverages were computed by usingClausius-Clapeyron equation. The heats of adsorption are shown to be generally consistent with the idea of two adsorption processes occurring simultaneously, one with a small activation energy and one with a larger activation energy.

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Zusammenfassung Es wird eine Apparatur beschrieben, mit der die Adsorption von Gas an festen Körpern bestimmt werden kann. Mit ihrer Hilfe wurde die spezifische Oberfläche von Ruß berechnet, indem Stickstoff-Gas an Ruß bei der Temperatur von flüssiger Luft adsorbiert wurde.Ferner wurde die Adsorption von Methanol, Methylformiat, Methylazetat, Methylcyanid, Azetaldehyd sowie die der Methyl-Äthyl-Ketone für eine Reihe von Temperaturen zwischen 0° und 40° an Ruß gemessen. Dann wurde mit Hilfe derClausius-Clapeyronschen Gleichung die isosterische Wärme für die Adsorption berechnet. Die so gefundenen Adsorptionswärmen weisen auf zwei voneinander unabhängige Adsorptionsprozesse hin, die sich in der Aktivierungsenergie unterscheiden.

     

Thermodynamics of cerium(III) extraction with naphthenic acids

Cerium(III) extraction from dilute aqueous solutions with naphthenic acids in decane was studied. The dependence of the distribution ratio on the pH of the equilibrium aqueous phase was determined, and the extraction equilibrium constant and Gibbs energy were calculated.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 10, 2004, pp. 1630–1633.Original Russian Text Copyright © 2004 by Chirkst, Litvinova, Devyatkin, Zhadovskii.     

Thermodynamics of hydrogen adsorption on the zeolite Li-ZSM-5

Thermodynamic characterisation of the adsorption process (at a low temperature) of dihydrogen on the zeolite Li-ZSM-5 was carried out by means of variable-temperature infrared spectroscopy, with the simultaneous measurement of temperature and equilibrium pressure. Adsorption renders the H–H stretching mode infrared active, at 4092 cm⁻¹. The standard adsorption enthalpy and entropy resulted to be ΔH⁰=−6.5(±0.5) kJmol⁻¹ and ΔS⁰=−90(±5) Jmol⁻¹ K⁻¹, respectively. The adsorption enthalpy is significantly larger than the liquefaction heat, and this fact renders Li-ZSM-5 a potential cryoadsorbent for hydrogen storage.