الفهرس 
CHAPTER I LITERATURE SURVEYOnly 14 pages are availabe for public view
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Abstract
Among separation processes such as solvent extraction, ion exchange, precipitation and others, the adsorption of metals on various inorganic and organic adsorbents shows a lot of advantages from the viewpoint of environmental protection. Chelating polymer adsorbents have received considerable attention in the separation of metal ions owing to their inherent advantages over simple ion-exchange resins, e.g. their greater selectivity to bind heavy metal ions. Polymers with specific functionalities can be obtained by either synthesizing new monomers carrying the functional groups capable of interacting with the target metal ions followed by polymerization or copolymers with suitable reactants into the desired functional groups or by converting groups on existing polymers. In the present work, the main target is based on four steps:
1. Synthesis of a crosslinked acrylonitrile (AN) acrylic acid(AA) resin. The nitrile group of resin was converted to amidoxime group to produce acrylamidoxime acrylic acid polymer.
2. characterization of the prepared resins by IR and SEM techniques.
3. Measuring the swelling characteristics of the prepared resin in aqueous media.
4. Application of the prepared resins to extract uranyl ions from ores.
The present work deals with synthesis of crosslinked AN/AA network in the presence of N, N´- methylenebisacrylamide (MBA) and divinylbenzene (DVB) as crosslinking agents with different mol ratios of monomers were carried out in the presence of water as a solvent. Potassium persulfate and sodium metabisulfite were used as redox initiators. Poly (vinyl alcohol) was added as surfactant. The AN/AA monomers with ratios 95/; 80/ 20 ; 50/ 50 and 20/ 80 were prepared.
Molar ratio of AN/AA, 20/ 80, was excluded from other steps due to formation of gel. The hydroxyl amine solution was added to acrylonitrile acrylic acid resins to convert nitrile groups to amidoxime to prepare acrylamidoxime acrylic acid copolymers Am/AA. The reaction carried out at 70o C for two hours.
The chemical structure of the produced polymers was confirmed by FTIR analysis. The amidoxime contents of AN/AA were evaluated from FTIR analysis. The morphology of the prepared networks can be examined with a scanning electron microscope (SEM). The effect of copolymer composition and type of crosslinker on the porosity of the networks was evaluated from SEM micrographs. SEM illustrates the development of the heterogeneity in the networks which depend on the crosslinker type and AN content. If the crosslinker DVB, the morphology changes drastically and a structure consisting of aggregates of spherical domains appears. As the AA content further increases from 20 to 50 mol %, the morphology changes from a structure of large aggregates of poorly defined microspheres to one consisting of aggregates of well defined microspheres. The structure looks like cauliflowers, typical for a macroporous copolymer network. The SEM photographs of Am/AA crosslinked with MBA is different than that crosslinked with DVB. SEM photographs indicate that large pores were formed with increasing AN content in copolymer when crosslinked with DVB crosslinker.
The crosslinked copolymers amidoximated under optimal conditions (Am/AA) were left in the uranyl ion solutions, until they reach their maximum adsorption equilibrium. FTIR was ocurred on loaded Am/AA copolymers with UO22+ ion also to resin after elution with strong acid media as 4 N HCl to elucidate that strong acid not affect on chemical structure of resins used. The FTIR also show that the bands due to COOH, amide carbonyl and hydroxyl groups decrease in transmittance after the chelation of uranyl ions. The SEM micrographs of the Am/AA resins after absorbing UO2 2+ ions, showed a different morphology in which the pores are not observed. It seems that the introduction of metal ions inside the matrix causes a large disruption to the surface. It is clear that the UO22+ ions uptake decrease with the decrease of AA percentage of the copolymer, this indicates that, the AA comonomer in the hydrogel structure is primarily responsible for the specific binding of the UO2 2+ ions due to the coordination between UO2 2+ ions and the carboxylic acid groups. AA rich compositions possess high metal uptake that it possess high degree of swelling at UO2 2+ ions feed solutions, which assist the diffusion of the metal ions inside the hydrogel i.e. to reach to the chelating functional groups of the hydrogel. As the AA content in the hydrogel increases, the swelling ability of the hydrogel increases. The metal ion uptakes for the various samples are in the order of their hydrophilic character. Higher water uptake of the sorbent shows higher metal ion uptake. The variation of UO22+ ions uptake with crosslinker percentage and type in the hydrogels at pH=6. It is clear that the UO22+ ions uptake decrease with the increment of crosslinker percentage of the copolymer, this indicates that, the crosslinker contents in the hydrogel structure are primarily responsible for the specific binding of the UO22+ions due to the coordination between UO22+ ions and the active functional groups of the networks. It was found that, crosslinker rich compositions did not possess high metal uptake that it possess low degree of swelling at UO22+ions feed solutions, which prevent the diffusion of the metal ions inside the hydrogel. It was also observed that the incorporation of DVB crosslinker instead of MBA in the network structure increases the UO22+ ions uptakes. It is obvious that the adsorption of UO2 2+ onto the Am/ AA hydrogels is pH dependent. The results show that uranium adsorption by the hydrogels is low at pH 3.0, but increased with increasing pH and then reached the maximum at pH 8.0. Uptake of UO2 +2 by hydrogels at neutral or slightly acidic conditions may be explained to proceed via complex formation between the metal ions and the active sites on the resins.
To repeatedly reuse the hydrogels for the recovery of uranium, uranium adsorbed on the resin must be easily eluted with a certain kind of eluents. Regeneration calculated after 6 cycles for all crosslinked Am/AA polymers. The elution was investigated by batch method using 2 M HNO3, 4 M HCl and 1M Na2CO3, respectively. UO2
+2 ions adsorbed on the hydrogels show a higher elution in acidic media than in basic media. UO2
+2 ions adsorbed on the hydrogels were eluted close to 80% by nitric acid, 90% by hydrochloric acid and 70% by sodium carbonate.