Adsorption behaviour of a number of metals on weakly basic ion-exchangers in methanol-hydrochloric acid mixtures

Many metals are not strongly adsorbed on DEAE-cellulose from aqueous hydrochloric acid media. However, some metals can be adsorbed on DEAE-cellulose from methanol-hydrochloric acid media. Distribution coefficients of Zn, Cd, Hg(II) and Bi(III), which show pronounced adsorption, are presented as functions of the methanol and the acid concentrations. Differences in the distribution coefficient between the four metals and a considerable number of other metals are large enough to permit good separations on columns. Among the platinum group metals, Pd(II), Ir(IV) and Pt(IV) are adsorbed from the mixed solvents and may be separated from large quantities of base metals such as Fe(III), Co(II), Ni and Cu(II).     

The chromatography of metals on DEAE-cellulose layers in phosphoric acid media

The adsorption behaviour of forty-eight metals on DEAE-cellulose thin layers has been examined in aqueous phosphoric acid media. R_F values are given as a function of phosphoric acid concentration over the range 0.01–1.0 M and are compared with those obtained in a similar manner with a crystalline cellulose, Avicel SF. Particularly strong retention on DEAE-cellulose occurred for Mo(VI), W(VI), Re(VII), the platinum group metals, Au(III) and Bi(III). Weak to moderate retention was also observed for several metals, such as V(V), Fe(III), Se(IV), In(III), the rare earths and U(VI), at lower concentrations of phosphoric acid (<0.1 M).     

Anion-exchange behaviour of metals on deae-cellulose in hydrochloric acid-acetic acid media

The anion-exchange behaviour of 35 metal ion species on a weakly basic cellulosic ion-exchanger (DEAE-cellulose) in mixed hydrochloric acid-acetic acid media has been investigated. The sorption of metal chloro-complexes on DEAE-cellulose is greatly enhanced with increasing concentration of acetic acid. Differences in sorbability of metals allow many useful analytical separations to be conducted on short columns, containing approximately 1 g of DEAE-cellulose(Cl(-)). Procedures for the chromatographic separations of two-, three-, four- and five-component mixtures are given.     

Anion-exchange behaviour of various metals on DEAE-cellulose in mixed acetic acid-nitric acid media

A number of nitrato complexes of metals have been found to be adsorbed on DEAE-cellulose from mixed acetic acid-nitric acid media, although none can be adsorbed from aqueous nitric acid solutions. The distribution coefficients of Sc, Mo, La, Sm, W, Re, Bi, Th and U are given as functions of acetic acid and nitric acid concentrations (sometimes in the presence of hydrogen peroxide to prevent hydrolytic precipitation). For 25 other metals column adsorption behaviour is described for a 90% acetic acid-10% 7.6M nitric acid mixture. Favourable differences in the distribution coefficients allow useful separations such as FeMoW and USmMoBiTh, to be achieved.     

Chromatographic behaviour of a number of metal ions on DEAE-cellulose layers in thiosulfate media

The adsorption behavior of 47 metal ions on DEAE-cellulose (Cl⁻) has been surveyed in aqueous thiosulfate solution by thin-layer chromatographic technique. The R_f values are measured as a function of thiosulfate concentration (0.010–2.0M) and are compared with those obtained on a microcrystalline cellulose Avicel SF. Generally, the ion-exchange adsorption of metal ions are weak or moderate over the thiosulfate concentration range tested except for a few metal ions like Mo(VI), Sb(III), Bi(III) etc., which have high preference to DEAE-cellulose. A variety of chromatographic distribution exhibited by metal ions allows to develop a number of separations of analytical and radiochemical interest.     

Anion-exchange separation of Te(IV) from Te(VI), Se(IV) and Se(VI) on deae-cellulose in mixed hydrochloric-acetic acid media

Te(IV) can be separated from Te(VI), Se(IV) and Se(VI) by adsorption of Te(IV) on a DEAE-cellulose column from a mixed 1M hydrochloric acid-acetic acid solution (1:9, v/v). This allows a selective separation of Te (IV) from the other three species in widely different mole ratios.     

Sorption of204Tl(III) from hydrochloric acid-water-organic solvent mixtures on deae-cellulose

The distribution coefficients of²⁰⁴Tl(III) between DEAE-cellulose and HCl-water-organic solvent (alcohols and ketones) mixtures have been determined using the statical method. The hydrochloric acid concentration as well as the nature and concentration of organic solvent in the mixtures have been widely varied. Sorption of Tl(III) takes place through a combined process of ion exchange and physical adsorption, its distribution between the anionic cellulose and solvent mixture depends on the tendency of the ionic association formation in these media.     

Concurrent dyes adsorption and photo-degradation on fly ash based substrates

Most of the dyes are organic compounds, with different degree of polarization and different groups with various steric effects, making their complete biodegradation slow or even impossible. Adsorption on fly ash and fly ash based substrates represents a possible alternative for simultaneous removal of dyes and heavy metals form wastewaters resulted in the textile industry. Adsorption (under visible light) and adsorption and photodegradation (under UV irradiation) studies were done on Methylene blue solutions and on their mixtures with heavy metals (copper and cadmium), in systems using fly ash as single substrate, or mixed with a wide band gap semiconductor (TiO₂). The titanium oxides and hematite content in fly ash proved to be responsible for photodegradation processes even in the absence of the TiO₂ powder, confirming that modified fly ash is a viable candidate in developing up scalable processes for advanced wastewater treatment. The kinetic and thermodynamic studies allow to calculate the parameters and to describe the complex mechanisms, involving competitive adsorption.     

Interfacial rheology of petroleum asphaltenes at the oil-water interface

A biconical bob interfacial shear rheometer was used to study the mechanical properties of asphaltenic films adsorbed at the oil-water interface. Solutions of asphaltenes isolated from four crude oils were dissolved in a model oil of heptane and toluene and allowed to adsorb and age in contact with water. Film elasticity (G') values were measured over a period of several days, and yield stresses and film masses were determined at the end of testing. The degree of film consolidation was determined from ratios of G'/film mass and yield stress/G'. Asphaltenes with higher concentrations of heavy metals (Ni, 330-360 ppm; V, 950-1000 ppm), lower aromaticity (H/C, 1.24-1.29), and higher polarity (N, 1.87-1.99) formed films of high elasticity, yield stress, and consolidation. Rapid adsorption kinetics and G' increases were seen when asphaltenes were near their solubility limit in heptane-toluene mixtures (approximately 50% (v/v) toluene). In solvents of greater aromaticity, adsorption kinetics and film masses were reduced at comparable aging times. Poor film forming asphaltenes had yield stress/G' values ((1.01-1.21) x 10(-2)) more than 4-fold lower than those of good film forming asphaltenes. n-heptane asphaltenes fractionated by filtering solutions prepared at low aromaticity (approximately 40% toluene in mixtures of heptane and toluene) possessed higher concentrations of heavy metals and nitrogen and higher aromaticity. The less soluble fractions of good film forming asphaltenes exhibited enhanced adsorption kinetics and higher G' and yield stress values in pure toluene. Replacing the asphaltene solutions with neat heptane-toluene highlighted the ability of films to consolidate and become more elastic over several hours. Adding resins in solution to a partially consolidated film caused a rapid reduction in elasticity followed by gradual but modest consolidation. This study is among the first to directly relate asphaltene chemistry to adsorption kinetics, adsorbed film mechanical properties, and consolidation kinetics.     

Preparative isolation of mono-, di- and tripurine nucleotides from hydrolysates of depyrimidinated herring sperm DNA

The purine nucleotides pdAp, pdGp, (dA)2, (dA-dG), (dG-dA), (dG)2, (dA)3, (dA-dG-dA), (dA-dA-dG), (dG-dA-dA), (dG-dA-dG) and known mixtures of purine nucleotide sequence isomers were separated by preparative scale chromatography of partial hydrolysates of depyrimidinated herring sperm DNA. Herring sperm DNA is first partially hydrolysed to a mixture of purine nucleotides. The low-molecular-weight oligonucleotides are then separated by column chromatography on DEAE-cellulose at pH 7.5, and fractionated by chromatography on QAE-Sephadex. Impurities which are not fully removed by column chromatography are separated by paper chromatography. The sequence of the isolated DNA fragments and the composition of the mixtures of sequence isomers were determined from the chromatographic data, absorption characteristics and by enzymatic degradation.     

Time-lapse STM studies of diastereomeric cinchona alkaloids on platinum metals

The adsorption of cinchonidine (CD) and cinchonine (CN) on Pt(111) and Pd(111) single crystals has been investigated by means of scanning tunneling microscopy (STM) in an ultrahigh vacuum system. In time-lapse series the mobilities of different adsorption species have been determined on a single molecule basis and with varying hydrogen background pressures in the system. The diastereomeric cinchona alkaloids, CD and CN, which are widely used as chiral modifiers of platinum group metals in catalytic enantioselective hydrogenation, showed similar adsorption modes and diffusion behavior on Pt(111), except that the flatly adsorbed CN molecules which were free (not in a dimer/cluster) were significantly more mobile than their CD analogues. CD adsorbed on Pd(111) showed similar adsorption modes as observed on Pt(111) but at considerably higher mobility of the flatly absorbed species already in the low-pressure region. The observed adsorption behaviors are discussed in the context of independent ATR-IR measurements and theoretical calculations. Special emphasis is put on the nonlinear effect observed in hydrogenation reactions with CD/CN mixtures. Our observations corroborate that this effect is mainly a consequence of the different adsorption strengths of CD and CN on Pt.     

A modification of the Doong-Yang model for gas mixture adsorption using the lewis relationship

The Doong-Yang model, which is used for predicting gas mixture adsorption equilibrium from pure-component isotherms of the Dubinin type, is modified by incorporating the Lewis relationship. The modified model is tested against experimental data for four binary systems, including a like-component (or nearly ideal) mixture, CH(4) + C(2)H(6), a moderately nonideal mixture, CO(2) + C(2)H(4), and two highly nonideal mixtures, CO(2) + C(3)H(8) and CO(2) + H(2)O. Comparisons are made with the ideal adsorbed solution (IAS) theory and the Bering model. Results show that the proposed model is the best for the like-component mixture and the moderately nonideal mixture. In contrast, for the highly nonideal mixtures, the original Doong-Yang model is the only one among the four models that can predict CO(2) + C(3)H(8) adsorption correctly. The IAS theory and the Bering model have similar predictions and are suitable only for like-component mixtures. The new model requires a simple numerical iteration but is easy to use; no new parameters are required. Theoretical reasons are given for the fact that the original Doong-Yang model is best for nonideal mixtures, whereas the modified Doong-Yang model is best for ideal mixtures.     

Sorption of the Pesticide Endosulphan on Two Indian Soils

Adsorption of endosulphan on uncontaminated sandy loam and silt clay loam soils in acetone-water and methanol-water mixtures at different f(s) values has been studied by the batch technique. Higher adsorption of endosulphan was observed on sandy loam soil than on silt clay loam soil, as was predicted from Freundlich constant K values and partition coefficient K(D) values. The K and K(D) values also confirm that adsorption of endosulphan was higher in acetone-water mixtures than in methanol-water mixtures and decreases with increases in the volume fraction of solvents (acetone, methanol), the f(s) values. The data were used to evaluate the cosolvent theory for describing adsorption of endosulphan in acetone-water and methanol-water mixtures. The aqueous phase partition coefficient K(DW) (mol/g) normalized on f(OC) (fraction of soil organic carbon) for endosulphan was evaluated by extrapolating to f(s)=0. Copyright 2000 Academic Press.     

On the nanostructure of polymer layers formed by adsorption from binary and ternary solutions on a solid SiO2: a combined adsorption and atomic force microscopy (AFM) study

The thickness of nanolayers formed by adsorption from dilute and semi-dilute solutions on a solid SiO₂ surface has been estimated from adsorption isotherms and atomic force microscopy (AFM) measurements for polystyrene, poly(butyl methacrylate), and their mixtures. The thickness of the adsorption layers depends strongly on the adsorption conditions and is controlled by several features of the adsorbing entities. In a low-concentration regime of adsorption, the length of polymer chains and the nature of their interaction with the substrate are the most important factors controlling the adsorption process. Above the critical concentration C*, macromolecular clusters (aggregates of several overlapping chains) are formed in a solution as a result of polymer chains self-assembly. Therefore, the final adsorption layer thickness is determined mainly by the size of the clusters in this concentrated regime of adsorption. We also demonstrate that in the case of polymer mixtures, the adsorption leads to formation of mosaic structures with alternation of the polymeric components in plane of the substrate and a characteristic domain size of approximately 200 nm for each of the components. AFM study reveals that the adsorbed layers are fractal structures whose fractal dimensions depend on the type of the polymer and the adsorption process. We demonstrate therefore that the structure of nanolayers of polymers and their mixtures on the solid surface can be regulated by variation of the adsorption conditions.     

Thin-layer chromatographic behavior of rare earths on silica gel with aqueous alkaline earth metal nitrate solutions as mobile phases

The TLC behavior of all the rare earths except Pm has been surveyed on silica gel (pH 7.0) pretreated with 0.1 mol L(-1) tris(hydroxymethyl)aminomethane and 0.1 mol L(-1) HCl with aqueous nitrate solutions of alkaline earth metals as mobile phases. The RF values of the lanthanides varied in a regular and characteristic way accompanied by the tetrad effect with increasing atomic number, and when the mobile phases were changed the RF values of each metal decreased in the order Mg2+ > Ca2+ > Sr2+ > Ba2+, as the crystal ionic radii of the alkaline earth metals increased. This adsorption sequence was not observed with alkali metal nitrate and alkali metal chloride mobile phases. A brief discussion concerning the effect on RF values of the solvent cations and the adsorption mechanism is included; also presented are typical chromatograms for the separation of multi-component mixtures containing adjacent lanthanides.     

Computational Study of Adsorption and Separation of CO(2), CH(4), and N(2) by an rht-Type Metal-Organic Framework

In this work, a computational study is performed to evaluate the adsorption-based separation of CO(2) from flue gas (mixtures of CO(2) and N(2)) and natural gas (mixtures of CO(2) and CH(4)) using microporous metal organic framework Cu-TDPAT as a sorbent material. The results show that electrostatic interactions can greatly enhance the separation efficiency of this MOF for gas mixtures of different components. Furthermore, the study also suggests that Cu-TDPAT is a promising material for the separation of CO(2) from N(2) and CH(4), and its macroscopic separation behavior can be elucidated on a molecular level to give insight into the underlying mechanisms. On the basis of the single-component CO(2), N(2), and CH(4) isotherms, binary mixture adsorption (CO(2)/N(2) and CO(2)/CH(4)) and ternary mixture adsorption (CO(2)/N(2)/CH(4)) were predicted using the ideal adsorbed solution theory (IAST). The effect of H(2)O vapor on the CO(2) adsorption selectivity and capacity was also examined. The applicability of IAST to this system was validated by performing GCMC simulations for both single-component and mixture adsorption processes.     

Simultaneous determination of traces of heavy metals by solid-phase spectrophotometry

A coupling sensitive solid phase spectrophotometric (SPS) procedure for determination of traces of heavy metals (Me-SPS) and multicomponent analysis by multiple linear regressions (MA), a simple methodology for simultaneous determination of metals in mixtures was inaugurated. The Me-SPS procedure is based on sorption of heavy metals on PAN-resin and direct absorbance measurements of colour product Me-PAN sorbed on a solid carrier in a 1-mm cell. This methodology (Me-SPS-MA) was checked by simultaneous determination of metals in synthetic mixtures with different compositions and contents of metals important in pharmaceutical practice: Zn, Pb, Cd, Cu, Co, and Ni. Good agreement between experimental and theoretical amounts of heavy metals is obtained from the recovery test (78.3–110.0%). The proposed method enables determination of particular metal ion at the ng mL⁻¹ level and it was successfully applied to the determination impurities from heavy metal traces in pharmaceutical substances (Cu in ascorbic acid, Pb in glucose, and Zn in insulin). The proposed procedure could be possible contribution to the development of pharmacopoeial methodology for a heavy metals test.     

Heterogeneous extended langmuir model with multiregion surfaces for adsorption of mixtures

The multiregion or multisite adsorption theory is applied to the heterogeneous extended Langmuir (HEL) model for predicting adsorption from mixtures. A new model, multiregion HEL (MR-HEL), is derived. MR-HEL is thermodynamically consistent. It uses the same three parameters for each component of the mixture as in the HEL model. Examples, including eight binary and one ternary systems, show that both MR-HEL and HEL yield satisfactory results for relatively ideal systems with like components. For nonideal and highly nonideal mixtures, however, MR-HEL reduces the total average deviation for the predicted amount adsorbed for each component by more than 50% in comparison with the original HEL model. The improvement by MR-HEL is significant. Moreover, the new model predicts not only an azeotrope for binary system CO(2)+C(3)H(8) that shows strong nonideal behavior but also the correct azeotropic composition.     

Quantitative separation of gold from cadmium, indium, zinc and other elements by cation-exchange chromatography in hydrochloric acid-acetone medium

Gold(III) can be separated from Cd, In. Zn, Ni, Cu(II), Mn(II), Co(II), Mg, Ca, Al, Fe(III), Ga and U(VI) by adsorbing these elements on a column of AG50W-X8 sulphonated polystyrene cation-exchange resin from 0.1M HCl containing 60% v v acetone, while Au(III) passes through and can be eluted with the same reagent. Separations are sharp and quantitative. The amounts of gold retained by the resin are between 1 and 2 orders of magnitude lower than encountered during adsorption from aqueous 0.1M HCl. Recoveries for mg amounts of gold are 99.9% or better and for ng amounts are still better than 99%, as shown by radioactive tracer methods. Hg(II), Bi, Sn(IV), the platinum metals and some elements which tend to form oxy-anions in dilute acid accompany gold. All other elements, though not investigated in detail, should be retained, according to their known distribution coefficients. Relevant elution curves, results of quantitative separations of binary mixtures and of recovery tests are presented.     

Biosorbents for hexavalent chromium elimination from industrial and municipal effluents

The presence of hexavalent chromium in wastewater is a potential hazard to aquatic animals and humans. There are various mechanisms proposed, kinetic models used and adsorption isotherms employed for the efficient removal of hexavalent chromium from industrial and municipal wastewaters using biosorbents. Biosorption of heavy metals is a most promising technology involved in the removal of toxic metals from industrial waste streams and natural waters. Metal removal treatment systems using microorganisms are cheap because of the low cost of sorbent materials used and may represent a practical replacement to conventional processes. The present review discusses hexavalent chromium biosorption properties of algae, bacteria, fungi, and agricultural products, as well as adsorption properties of non-living substances. Cell walls are responsible for biosorption of dead biomaterial; compositions of cell walls are discussed. Chemical modification of biosorbents, optimization of biosorption parameters, mixtures of different biosorbents and the study of biosorption mechanisms are the main keys to transfer the biosorption process from lab to industry.