Sorption of heavy metals by untreated red fir sawdust

Applied Biochemistry and Biotechnology - Equilibrium and rate relationships have been determined for the sorption of divalent copper (Cu2+) and hexavalent chromium (Cr6+) onto untreated Red Fir...     

Sorption and preconcentration of some heavy metals by 2-mercaptobenzothiazole-clay

2-Mercaptobenzothiazole loaded on previously treated clay was prepared, characterized and used for sorption and preconcentration of Hg(II), Pb(II), Zn(II), Cd(II), Cu(II) and Mn(II) from an aqueous solution. The support used was a natural clay previously treated with sulphuric acid solution. Adsorption isotherms of metal ions from aqueous solutions as function of pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The chemically treated clay was very selective to Hg(II) in solution in which Zn(II), Cd(II), Pb(II), Cu(II) and Mn(II) were also present.     

Sorption of atrazine on conventional and surface modified activated carbons

The sorption of atrazine from water has been studied using a conventional activated carbon, F400, an annealed carbon sample, F400AN, and an aminated carbon sample, F400NH(2). Characterisation of the carbon samples showed that sample F400NH(2) had the highest proportion of micropores, but had the lowest values of point of zero charge (PZC) and iso-electric point (IEP). This was attributed to the existence of a high proportion of oxygen containing functional groups. Sorption data showed that sample F400AN was superior in the sorption of atrazine to samples F400 and F400NH(2). It was noted that pore size distribution alone was not the only contributing factor for the uptake of atrazine onto the activated carbons. The sorption data were fitted well using the Freundlich isotherm. The free energy change showed that sorption of atrazine on activated carbons is a spontaneous process. A pseudo-second order kinetic model was used for analysing the kinetic data, and it was concluded that adsorption of atrazine was controlled by a film diffusion mechanism.     

Sorption of heavy metal ions with activated carbons obtained from polyethylene terephthalate waste

The sorption capacity of activated carbons obtained from polyethylene terephthalate containers and packages with respect to heavy metal ions was examined. Based on the sorption capacities for Co²⁺, Mn²⁺, Ni²⁺, Cu²⁺, and Zn²⁺, the selectivity series were established for the samples prepared by conventional steam and gas activation and by the procedure involving pretreatment with sulfuric acid.     

Sorption of uranium and other heavy metals on hydroxyapatite

The immobilization of U^VI and Pb^II from aqueous solutions in a solid phase by interaction with calcium hydroxyapatite has been studied in batch experiments with increasing contact times. The results were compared with those previously found for Cd^II. All these elements are able to be efficiently immobilized by such a method. The sorbed quantities vary in the order Pb>U>Cd. The sorption mechanisms are element dependent. The dominant mechanisms are: dissolutionprecipitation with formation of an amorphous or microcrystalline phase for U, dissolution-precipitation with the formation of two new crystalline phases and with possible incorporation into the initial apatite for Pb, and intracrystalline diffusion and exchange for Cd.     

Adsorption of anionic and cationic dyes by activated carbons, PVA hydrogels, and PVA/AC composite

The textural and adsorption characteristics of a series of activated carbons (ACs), porous poly(vinyl alcohol) (PVA) gels, and PVA/AC composites were studied using scanning electron microscopy, mercury porosimetry, adsorption of nitrogen (at 77.4 K), cationic methylene blue (MB), anionic methyl orange (MO), and Congo red (CR) from the aqueous solutions. Dye-PVA-AC-water interactions were modeled using the semiempirical quantum chemical method PM6. The percentage of dye removed (C(rem)) by the ACs was close to 100% at an equilibrium concentration (C(eq)) of less than 0.1 mM but decreased with increasing dye concentration. This decrease was stronger at C(eq) of less than 1 mM, and C(rem) was less than 50% at a C(eq) of 10-20 mM. For PVA and the PVA/AC composite containing C-7, the C(rem) values were minimal (<75%). The free energy distribution functions (f(ΔG)) for dye adsorption include one to three peaks in the -ΔG range of 1-60 kJ/mol, depending on the dye concentration range used and the spatial, charge symmetry of the hydrated dye ions and the structural characteristics of the adsorbents. The f(ΔG) shape is most complex for MO with the most asymmetrical geometry and charge distribution and adsorbed at concentrations over a large C(eq) range. For symmetrical CR ions, adsorbed over a narrow C(eq) range, the f(ΔG) plot includes mainly one narrow peak. MB has a minimal molecular size at a planar geometry (especially important for effective adsorption in slit-shaped pores) which explains its greater adsorptive capacity over that of MO or CR. Dye adsorption was greatest for ACs with the largest surface area but as molecular size increases adsorption depends to a greater extent on the pore size distribution in addition to total and nanopore surface areas and pore volume.     

Collection of trace metals with cationic surfactant-silica particles followed by flotation with an anionic surfactant for seawater analysis

The analysis of seawater for trace metals is important for pollution monitoring and better understanding of marine systems. The present paper describes an efficient preconcentration method for the determination of trace metals in seawater. Trace metals [Ni(II), Cu(II), Ga(III), Cd(II), Pb(II), and Bi(III)] in 1,000 mL of seawater sample were complexed with ammonium pyrrolidinedithiocarbamate and sorbed onto silica particles covered with cetyltrimethylammonium chloride. After the addition of sodium dodecyl sulfate, the particles were floated to the solution surface by bubbling and then collected by suction. The trace metals were desorbed with dilute nitric acid and determined by inductively coupled plasma–mass spectrometry. The rapid 200-fold preconcentration was demonstrated with certified seawater samples.     

Sorption capacity of acetylacetonated humin-like compounds with respect to cations of heavy metals

A method of synthesis of acetylacetonated humin-like compounds was developed. The effect of modification on the sorption capacity of humin-like compounds with respect to heavy metals was studied.     

Layer-by-layer composite of anionic and cationic clays by metathesis

An alternately stacked layer-by-layer composite of oppositely charged layered solids was obtained by solvothermal treatment of the monolayer colloidal dispersions of dodecylsulfate intercalated nickel aluminum LDH and cetyl trimethylammonium intercalated smectite in 1-octanol. This composite shows altered thermal decomposition behavior compared to the parent solids. On heating the LDH component of the composite decomposes to NiO, while the layer structure of the cationic clay is retained up to 800°C.     

Silicas modified by polyelectrolyte complexes for the ion chromatography of anionic complexes of transition metals

An approach, which is based on the fact that an anion-exchange layer may be bound at the surface of a cation-exchanger by electrostatic interaction of reversibly-charged functional groups, was used for producing polyelectrolyte anion-exchangers. Water-soluble polymers containing positively charged nitrogen atoms were used instead of anion-exchanging latex. A sulfonated co-polymer of styrene and divinylbenzene was replaced with a sorbent for reversed-phase chromatography (silica coated with dodecylbenzenesulfonic acid). The ion-chromatographic behavior of transition metal complexes with ethylenediaminetetraacetic acid (EDTA) and cyclohexanediaminetetraacetic acid (CDTA) separated on sorbent Silasorb-C₁₈, modified by polyvinylpyridinium bromide (PEVP), polydimetyldiallylammonium chloride (PDMDAA), and polyhexamethyleneguanidine chloride (PGMG) was investigated. The limits of detection were 0.1–1 mg/L and 0.01–0.05 mg/L for single and dual-columns, respectively. A comparison of synthesised Silasorb C₁₈-DBSA-PEVP anion-exchanger with several commercial packed materials (Hiks-1, Anieks, TSK gel IC-Anion-PW, TSK gel IC-Anion-SW, BT XI An, Nucleosil 10 SB) was carried out. It was shown that BT I An and BT II An anion-exchangers cannot be used in determining transition metal complexes with EDTA due to high non-ion-exchange sorption of hydrophobic complex anions on the polymer matrix. Silasorb C₁₈-DBSA-PEVP showed the highest selectivity in separating anion complexes of transition metals with EDTA. Received: 17 July 1997 / Revised: 21 January 1998 / Accepted: 23 January 1998     

Silicas modified by polyelectrolyte complexes for the ion chromatography of anionic complexes of transition metals

An approach, which is based on the fact that an anion-exchange layer may be bound at the surface of a cation-exchanger by electrostatic interaction of reversibly-charged functional groups, was used for producing polyelectrolyte anion-exchangers. Water-soluble polymers containing positively charged nitrogen atoms were used instead of anion-exchanging latex. A sulfonated co-polymer of styrene and divinylbenzene was replaced with a sorbent for reversed-phase chromatography (silica coated with dodecylbenzenesulfonic acid). The ion-chromatographic behavior of transition metal complexes with ethylenediaminetetraacetic acid (EDTA) and cyclohexanediaminetetraacetic acid (CDTA) separated on sorbent Silasorb-C₁₈, modified by polyvinylpyridinium bromide (PEVP), polydimetyldiallylammonium chloride (PDMDAA), and polyhexamethyleneguanidine chloride (PGMG) was investigated. The limits of detection were 0.1–1 mg/L and 0.01–0.05 mg/L for single and dual-columns, respectively. A comparison of synthesised Silasorb C₁₈-DBSA-PEVP anion-exchanger with several commercial packed materials (Hiks-1, Anieks, TSK gel IC-Anion-PW, TSK gel IC-Anion-SW, BT XI An, Nucleosil 10 SB) was carried out. It was shown that BT I An and BT II An anion-exchangers cannot be used in determining transition metal complexes with EDTA due to high non-ion-exchange sorption of hydrophobic complex anions on the polymer matrix. Silasorb C₁₈-DBSA-PEVP showed the highest selectivity in separating anion complexes of transition metals with EDTA. Received: 17 July 1997 / Revised: 21 January 1998 / Accepted: 23 January 1998     

Separation of basic, acidic and neutral compounds by capillary electrochromatography using uncharged monolithic capillary columns modified with anionic and cationic surfactants

A mode of capillary electrochromatography (CEC), based on the dynamical adsorption of surfactants on the uncharged monolithic stationary phases has been developed. The monolithic stationary phase, obtained by the in situ polymerization of butyl methacrylate with ethylene dimethacrylate, was dynamically modified with an ionic surfactant such as the long-chain quaternary ammonium salt of cetyltrimethylammonium bromide (CTAB) and long-chain sodium sulfate of sodium dodecyl sulfate (SDS). The ionic surfactant was adsorbed on the surface of polymeric monolith by hydrophobic interaction, and the ionic groups used to generate the electroosmotic flow (EOF). The electroosmotic mobility through these capillary columns increased with increasing the content of ionic surfactants in the mobile phase. In this way, the synthesis of the monolithic stationary phase with binary monomers can be controlled more easily than that with ternary monomers, one of which should be an ionic monomer to generate EOF. Furthermore, it is more convenient to change the direction and magnitude of EOF by changing the concentration of cationic or anionic surfactants in this system. An efficiency of monolithic capillary columns with more than 140000 plates per meter for neutral compounds has been obtained, and the relative standard deviations observed for to and retention factors of neutral solutes were about 0.22% and less than 0.56% for ten consecutive runs, respectively. Effects of mobile phase composition on the EOF of the column and the retention values of the neutral solutes were investigated. Simultaneous separation of basic, neutral and acidic compounds has been achieved.     

Interpretation of synchrotron radiation circular dichroism spectra of anionic, cationic, and zwitterionic dialanine forms

Electronic absorption and synchrotron radiation circular dichroism (SRCD) spectra of the anionic, cationic, and zwitterionic forms of L-alanyl-L-alanine (AA) in aqueous solutions were measured and interpreted by molecular dynamics (MD) and ab initio computations. Time-dependent density functional theory (TD DFT) was applied to predict the electronic excited states. The modeling enabled the assessment of the role of molecular conformation, charge, and interaction with the polar environment in the formation of the spectral shapes. Particularly, inclusion of explicit solvent molecules in the computations appeared to be imperative because of the participation of water orbitals in the amide electronic structure. Implicit dielectric continuum solvent models gave inferior results for clusters, especially at low-energy transitions. Because of the dispersion of transition energies, tens of water/AA clusters had to be averaged in order to obtain reasonable spectral shapes with a more realistic inhomogeneous broadening. The modeling explained most of the observed differences, as the anionic and zwitterionic SRCD spectra were similar and significantly different from the cationic spectrum. The greatest deviation between the experimental and theoretical curves observed for the lowest-energy negative anion signal can be explained by the limited precision of the TD DFT method, but also by the complex dynamics of the amine group. The results also indicate that differences in the experimental spectral shapes do not directly correlate with the peptide main-chain conformation. Future peptide and protein conformational studies based on circular dichroic spectroscopy can be reliable only if such effects of molecular dynamics, solvent structure, and polar solvent-solute interactions are taken into account.     

Catalytic oxidation with air of cyclohexanone to dicarboxylic acids on synthetic carbons. Effect of supported metals and solvents

The oxidation with air of cyclohexanone was conducted in the presence of synthetic carbons catalysts. The effect of carbon activation treatment (CO2 or air burnoff), phosphorus additive, platinum loading, and nature of the solvent (water or water/acetic acid mixture) were studied. Cyclohexanone oxidation at 140 degrees C yielded a mixture of C6, C5, and C4 dicarboxylic acids. Air activated carbons, including those containing phosphorus or those supporting platinum, resulted in a higher yield of adipic acid. The activity and selectivity was associated with the oxygenated functional groups, essentially carbonyl/quinone groups, created during air activation of the carbon. The incorporation of phosphorus into the carbon increased slightly the selectivity to 34.3%, probably because this additive increased the density of oxygenated functional groups. The deposition of platinum by impregnation and liquid-phase reduction with formaldehyde increased the reaction rate and improved the selectivity to adipic acid, where the highest figure was 38.8%. It was suggested that platinum contributed to molecular oxygen activation. In contrast platinum deposition by cationic exchange followed by reduction under H2 resulted often in a detrimental effect probably because the density of the oxygenated groups on carbon is decreased upon H2 reduction in the presence of platinum. When the oxidation of cyclohexanone was carried out in mixtures of water/acetic acid, the selectivity given by the different samples were quite close and generally smaller than those obtained in water which indicates that acetic acid interacts with the oxygenated surface functional groups responsible for the activity and selectivity. Oxidation experiments with methyl-labeled 4-methylcyclohexanone indicated that glutaric acid was produced by oxidative decarbonylation of both the C1 and C2 carbon atoms of the molecule.     

Ion decontamination with a mixture of cationic and anionic surfactants

The composition of mixed micelles and mixed micelle — solution interfaces changes with the concentration and molar ratio of the cationic and anionic surfactants present. The micelle — solution interface includes besides the headgroups of both surfactants, the counterions of the surfactant in excess. The finding of an enhanced binding of counterions to mixed micelles may be of some practical importance in decontamination.     

Stripping voltammetric determination of platinum metals at a carbon paste electrode modified with cationic surfactants

In this contribution, a novel method is described for the determination of platinum metals. The procedure developed employs a carbon paste electrode modified in situ with cationic surfactants of the quaternary ammonium salt type. The pre-concentration step is based on a specific accumulation mechanism involving ion-pair formation; the detection being performed by cathodic scanning in the differential pulse voltammetric mode. Regarding the individual forms of platinum metals, the method has been found convenient for the determination of three heavy platinum metals in the form of Pt(IV), Ir(III) and Os(IV), whereas for the remaining elements (Ru, Rh, and Pd) was almost inapplicable. Platinum metals of the former group can be pre-concentrated in chloride-containing supporting media via PtCl₆²⁻, IrCl₆³⁻ and OsCl₆²⁻ complex anions, the central atom of each species being fairly reducible during the voltammetric scan. Stripping signals for both platinum and iridium were proportional to the concentration in a range of 1-10 × 10⁻⁶ M Pt(IV) and Ir(III); the response for osmium being linear within 0.1-6 × 10⁻⁷ M Os(IV) with a detection limit of about 5 × 10⁻⁹ mol l⁻¹. During optimisation, special attention was paid to the accumulation mechanism, choice of key experimental conditions, and to interference effects from foreign ions with potentially ion-pairing capabilities (AuCl₄⁻, TlCl₄⁻, CrO₄²⁻, MnO₄⁻, SCN⁻, and I⁻). The method elaborated has been tested on both model solutions and real samples of industrial waste water, showing in both cases satisfactory analytical performance.     

Sorption of 2-naphthol and copper ions by cationic surfactant-adsorbed laponite

As one of applications of adsolubilization, a simultaneous sorption of 2-naphthol and copper ions by cationic surfactant-adsorbed laponite was carried out. Both the surfactant-adsorbed laponite using dodecyl trimethylammonium bromide (DTAB) and 1,2-bis(dodecyldimethylammonio) ethane dibromide (2RenQ) retained a high sorption capacity for copper ions, while the 2RenQ-adsorbed laponite completely adsolubilized 2-naphthol in a whole concentration region, but the DTAB-adsorbed laponite one decreased the adsolubilization gradually above the cmc of DTAB. Thus, it was found that laponite having cationic surfactant-adsorbed layer has a great capacity for a simultaneous removal of both toxic nonionic and ionic compounds.     

Synergism in mixtures of cationic surfactant and anionic copolymers

Surface tension measurements have been made in aqueous solutions of anionic hemiesters of an alternating copolymer of maleic acid and styrene, MAS-n with n=0-12, in the presence of dodecyltrimethylammonium bromide, DTAB. A synergistic aspect of surface tension reduction efficiency was observed for all systems studied. The pseudo-phase separation approach and regular solution approximation have been applied, and the interaction parameter, beta, and the mole fraction of DTAB in the adsorbed layer (on a surfactant/repetitive unit basis), X, were obtained. Negative values of beta, ranging from -3 to -11, were calculated. On the other hand, the molar fraction of DTAB varies from 0.52 to 0.26. These results are discussed in terms of hydrophobic effects on the distribution of the aggregates between the interface and the bulk of the solution. The conditions predicted by the model to obtain synergism in the tension reduction efficiency are completely satisfied in all cases.