The possibilities of using chitosan and its composites with transition metal oxides for arsenic removal from solutions with low concentrations are discussed. Methods for the formation of composite sorbents based on chitosan and molybdenum in a composition with a carbon fiber providing improved physical and chemical properties with respect to the recovered component are considered. The sorption properties of the obtained materials under dynamic conditions for the purification of solutions from arsenic are compared. It is shown that the preliminary modification of the carbon fiber with chitosan by ionic gelation using sulfate ion and then by adsorption with molybdate ion leads to the production of an efficient sorption material that provides the purification of 1600 column volumes of an arsenic solution at an initial concentration of 105 μg L –1 to a maximum permissible concentration of 50 μg L –1 . The calculation methods show that the gel ability of sulfate and molybdate ions is approximately the same.

The possibilities of producing low-ash crystalline graphite from high-carbon rocks of the southern Far East have been investigated. Promising setups for purifying the natural graphite from impurities using the processes of hydrothermal treatment of flotation concentrates have been developed.

Procedure for obtaining new hybrid sorbents based on carbon fibers and chitosan-carbon materials modified with molybdenum, which determines the affinity of the sorbents for arsenate ions, is described. The surface morphology was examined and a qualitative chemical analysis of the surface of the composite sorbents was made by the method of scanning electron microscopy–energy-dispersive analysis. Sorption isotherms were obtained for unmodified materials, carbon fibers and chitosan-carbon materials, and hybrid sorbents in twicedistilled and tap water at low As(V) concentrations.

Perspectives of use of activated carbon materials modified with transition metal oxides for purification of water from arsenic were considered. Sorption isotherms for two types of hybrid sorbents based on carbon fibers modified with manganese oxide as birnessite as well as on fiber and chitosan-carbon materials on its basic modified with molybdenum determining affinity of the sorbents to arsenate-ions are presented.

Sorption properties of poly(N-(5-methyl-4-imidazolyl)methylallylamine (PAA) and poly(N-(5-methyl-4-imidazolyl)methylethylenimine) (IMPEI) have been investigated and compared with those of imidazolylmethyl derivative of natural aminopolymer chitosan (IMC). We have shown that the structure of polymer backbone has a pronounced effect on sorption of both transition metal cations and noble metals by imidazolylmethyl derivatives. It was shown that sorption of Au(III) and Pt(IV) by all imidazolylmethyl derivatives is accompanied by changes in metal oxidation states. The highest content of more oxidized species – Au(III) and Pt(IV) was found in IMC, which showed the lowest sorption capacity. Efficacy of noble metals elution with HCl/thiourea solution changes in the row IMC > IMPAA > IMPEI, showing low applicability of IMPEI for recovery of gold and platinum ions in sorption/regeneration cycles despite its highest sorption capacity toward all noble metal ions. Sorption capacities toward transition metal cations change in the following row: IMPEI > IMC > IMPAA. The effect of polymer structure on sorption capacities of IMPEI, IMPAA, and IMC is much stronger for divalent cations than for monovalent silver ion. DFT calculations have shown that coordination of Ag+ ion by all derivatives occurs via formation of two Ag–N coordination bonds with N-atoms of imidazole ring and amino group of the polymer backbone, while contribution of electron–donor atoms of IMC and IMPEI backbone to coordination of divalent ions is remarkably higher.

Binding of Cu(2+), Ni(2+) and Ag(+) ions to polyallylamine (PAA), polyethylenimine (PEI), poly(N-2-(2-pyridyl)ethylallylamine) (PEPAA), poly(N-2-(2-pyridyl)ethylethylenimine) (PEPEI), and N-2-(2-pyridyl)ethylchitosan (PEC) has been investigated using batch sorption experiments, spectrophotometric titration, ESR, and XPS to elucidate how the structure of polymer precursors affects the ion binding efficiency of their pyridylethylated derivatives. It has been shown that pyridylethylation increases the sorption capacities of PAA and PEI cross-linked with epichlorohydrin toward Ag(+) and Ni(2+) ions, but does not improve or decrease that toward Cu(2+) ions. PEC was the most efficient material for Ag(+) ion sorption with the sorption capacity of 1.21 mmol g(-1). The highest sorption capacity for Ni(2+) (0.62 mmol g(-1)) was found for PEPEI. According to density functional theory (DFT) calculations, lower Cu(2+) binding efficiency to PEPEI results from the "looser" structure of this complex in comparison with unmodified PEI. DFT calculations have also suggested that the Cu(2+) ion is four-coordinated in the complexes with PEPAA and PAA and five-coordinated in all other complexes, which have the structures of distorted square pyramids with Cu-N bond lengths varying significantly depending on the ligand nature. The results of the theoretical investigations of the Cu(2+) complex structures were supported by the ESR data, which revealed the decrease of A‖ and the increase of g‖ values with increasing deviation from the square planar geometry of complexes in the ligands in the order PEI < PEPEI < PEPAA.

Manganese oxides have been prepared on the surface of carbon fiber by simple methods: coprecipitation of manganese salts of different valence in the presence of fiber as a support or electrodeposition from Mn(II) salt solution on a carbon fiber cathode, in the presence of chitosan including, under oxidation with air oxygen conditions. The obtained samples have been characterized by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Sorption properties of the composites toward As(V) have been studied. The relationships between sorption properties, structure, Mn valence, and manganese oxide surface morphology have been discussed.

Here we report the results of density functional theory (DFT) investigations of Ni2+ complexes with chitosan and its N-heterocyclic derivatives N-(2-pyridylethyl) chitosan (2-PEC), N-(4-pyridylethyl)-chitosan (4-PEC), and N-(5-methyl-4-imidazolyl)methyl chitosan (IMC). 11 model structures corresponding to 'bridge' and 'pendant' types of complexes have been calculated. We have shown that in most cases formation of 'pendant' complexes is more favorable. It was found that nitrogen atoms of chitosan and its N-heterocyclic derivatives played a governing role in Ni2+ binding and that the degree of charge transfer from the ligand to the central ion in the complexes correlated with the complex stability. A row of complexes stability depending on the type of functional substitute in chitosan macromolecules (IMC approximate to 2-PEC > chitosan > 4-PEC) was in a good agreement with experimental data obtained from the nickel ion sorption isotherms on chitosan, 2-PEC, 4-PEC and IMC. (C) 2015 Elsevier B.V. All rights reserved.

The electrochemical and thermal properties of composites prepared from carbon fiber modified by chitosan deposited on the fiber surface in various forms were investigated. The electrochemical behavior of a composite modified with chitosan in the sulfate form differed from that of starting carbon fiber and composites modified by electrochemical deposition of chitosan. The preparation conditions and subsequent electrochemical treatment affected the thermal oxidative stability of the composites. It was noted that cyclic cathodic-anodic and then cathodic treatment of the composites degraded them significantly. Cyclic voltammetry could be used to assess the surface condition of fibers modified with chitosan.

Here we report on the method of synthesis in gel of a new heterocyclic aminopolymer-N-2-(4-pyridyl)ethylchitosan (4-PEC) via direct addition of 4-vinylpyridine to chitosan that yields a derivative with the substitution degree (DS) up to 0.8. The comparison of reactivity, thermal, spectroscopic, and sorption properties of a new derivative and its isomer N-2-(2-pyridyl)ethylchitosan (2-PEC) is presented. 2-PEC has higher sorption capacity and forms more stable chelates with [PdCl4]2− and [PtCl6]2− ions than 4-PEC, but the latter shows higher selectivity to noble metals ions in the presence of Cl− ions. A gradual increase of the sorption capacities and the affinity coefficient for Cu2+ and Ni2+ in the row chitosan < 4-PEC < 2-PEC was related to the increase of electron donor nitrogen atoms content and chelating properties of 2-PEC. A nearly negligible increase of the 4-PEC sorption capacity for Ag+, as compared to plain chitosan, was suggested to be dependent on the difference in complexation models for 2-PEC and 4-PEC derivatives. The density functional theory (DFT) calculations have shown that the “pendant” model of the complex with Ag(I) is energetically favorable only for 2-PEC derivative, while in cases of chitosan and 4-PEC only “bridge” complexes can be formed that results in lower sorption capacity.

Brown coals with high Au and PGE concentrations from six deposits in the southern Russian Far East were analyzed for elemental composition, acid-base properties, and the molecular-size distribution of humic acids (HA). The ash contents of the coals were determined to be negatively correlated with their Au concentrations, and the content of “organic Au” (which is chemically bound to humic substances, HS) reaches 95%. The most probable mode of Au occurrence in the brown coals is submicrometer-sized particles of elemental gold stabilized by HA. Quantum-mechanical calculations of interactions between Au(0) clusters with model HS fragments confirm that HS could be originally strongly chemically adsorbed on the surface of elemental gold particles. Different stability of colloids during centrifuging of alkali extracts of the gold-bearing brown coals was proved to be likely responsible for the selective separation of free HA and those bound with gold particles, and this can be used to develop a technology for gold recovery from coals without decomposing their organic matrix.

The methods of the coprecipitation of chitosan and copper-containing particles on a carbon fiber used as a cathode and also of the precipitation of copper(II) on a carbon-fiber electrode preliminarily modified by chitosan were studied for feasibility of obtaining composites containing copper oxide/copper in a chitosan matrix. The composition, morphology, structure of the organic-mineral composites were studied by the methods of X-ray phase analysis, scanning electronic microscopy, X-ray photoelectron spectroscopy, and ESR spectroscopy.

The possibility of rhenium recovery from aqueous solutions by fibrous materials was investigated. Sorption characteristics of the following fibrous materials: carbon fibers (Busofite and Actylene), carbon fibers modified by electrochemical and chemical method (adsorption on the surface of natural polyelectrolyte - chitosan) and acrylic fibers FIBAN having the following anion-exchange groups: -N (CH2COO-)(2) (FIBAN A-6) and - =NH, -NH2, -COOH, =N (FIBAN AK-22) have been studied. The best capacity parameters for modified carbon materials prepared in the anodic region and at the open-circuit potential are observed. The half-conversion time tau(0.5) (3-10 min.) for them is much less than that for original carbon fibers (tau(0.5)-60-65 min). The degree of rhenium sorption by the ionites FIBAN.- 6 and AK-22 was equal 70.8 and 97.0 % accordingly. Elution characteristics for sorbent FIBAN AK-22 are better than for ionite FIBAN A-6.

The composite material nickel hydroxide (oxide)/carbon fiber has been obtained by hydroxide deposition on the surface of the activated carbon fiber (ACF) via urea hydrolysis in the presence of a surfactant. The organomineral composite NiO/CHIT/carbon fiber has been obtained by electrochemical deposition of nickel hydroxide on the ACF surface in combination with chitosan as well as by cathode deposition on a carbon fiber electrode preliminarily modified by chitosan. The surface of the obtained hybrid materials has been investigated by means of the methods of X-ray photoelectron spectroscopy (XPS), atomic force and scanning electron spectroscopy (AFM and SEM), and cyclic voltamperometry. The composition and properties of the obtained composites have been discussed.

In this work, consideration is given to the feasibility of using hydrothermal oxidation for the destruction of organic 60Co complexes during the course of the treatment of medium-level liquid radioactive wastes with a high salt content—evaporator concentrate in the reactor water cleanup system—formed at nuclear power plants (NPPs). It has been shown that hydrothermal oxidation makes it possible to effectively solve the problem of the selective extraction of the radionuclides of transition metals (60Co, 54Mn) with a minimum volume of solid radioactive wastes being formed. The results of laboratory experiments and pilot tests of the hydrothermal oxidation installation at the Novovoronezhskaya and the Kurskaya NPPs are presented. The general scheme of the hydrothermal technology of processing the evaporator concentrate at nuclear power plants is proposed.

Catalytic thermal destruction of ethylenediaminetetraacetic acid and its complexes with nickel, iron, and cobalt in nitrate solutions on carbon materials (activated unwoven material, sibunite, and BAU–A activated carbon) was studied. The activation energies of thermal destruction were calculated.