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Search Results: 1 - 10 of 87 matches for " Versiane Albis;Botaro "
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Adsor??o de metais pesados em serragem de madeira tratada com ácido cítrico
Rodrigues, Rafael Falco;Trevenzoli, Rafael Lopes;Santos, Luciano Rodrigo Gomes;Le?o, Versiane Albis;Botaro, Vagner Roberto;
Engenharia Sanitaria e Ambiental , 2006, DOI: 10.1590/S1413-41522006000100004
Abstract: in the present work, the exchange capacity of manilkara longifolia sawdust, chemically modified, was studied. the modification was carried out by a chemical treatment with citric acid, which introduced carboxilate groups in the material surface. the introduction of these groups was confirmed by infrared spectroscopy. cadmium and copper sorption was studied batchwise. isotherms were drawn and adjusted to the langmuir model. maximum loadings of 0.56 mmolcd/g and 0.94 mmolcu/g were achieved in single metal adsorption. cadmium uptake was reduced from 0.56 mmolcd/g to 0.21 mmolcd/g as the copper concentration increased in the reaction system. these results show that there is a competition between the two metals for the exchange sites.
Recupera??o de aminas, utilizadas na flota??o de minério de ferro, utilizando-se zeólitas naturais
Teodoro, Anderson Luiz;Le?o, Versiane Albis;
Rem: Revista Escola de Minas , 2004, DOI: 10.1590/S0370-44672004000300010
Abstract: the present work aimed at study the removal of amines applied in the iron ore industry, through their adsorption on zeolites. the experiments were carried out at bench scale as well as room temperatures applying two different type of amine: the monoamine flotigan eda-3b and the diamine f2835-2l. the effects of ph and amine concentration in solution over the adsorption were assessed. the amine concentration in the aqueous solution was determined at 409nm in a uv-visible spectrofotometer. the zeolite loadings were assessed by mass balance. overall extractions were between 95 and 98%. the electroforetic mobility showed surface charge reversal of both materials loaded with amine, suggesting that the loading took place initially through capillary condensation produced by electrostatic interactions followed by multilayer adsorption.
Lixivia??o da calcopirita com cloreto férrico e cloreto de sódio
Carneiro, Maria Fernanda Coimbra;Le?o, Versiane Albis;
Rem: Revista Escola de Minas , 2005, DOI: 10.1590/S0370-44672005000300009
Abstract: this work sought to study the behavior of chalcopyrite in dissolution with oxygenated solutions of ferric and sodium chloride. studied were the effects of the following process variables: ph, ferric ion concentration and sodium chloride concentration on copper dissolution. a morphologic characterization of reaction products was also performed by sem analyses along with specific surface area and porosity measurements. the dissolution of copper from chalcopyrite showed to be independent of ph, directly proportional to the sodium chloride concentration, and inversely proportional to the ferric ion concentration. the presence of sodium chloride changed the morphology of the product layer and contributed to the increase of copper dissolution in the reacting system.
Remo??o de sulfato de efluentes industriais por precipita??o
Ferreira, Bruno Christiano Silva;Lima, Rosa Malena Fernandes;Le?o, Versiane Albis;
Engenharia Sanitaria e Ambiental , 2011, DOI: 10.1590/S1413-41522011000400007
Abstract: the aim of this study was to develop alternative techniques for removing sulfate ions from mining/metallurgy effluents. sulfate removal processes are generally expensive and show low removal efficiency. two alternatives to treat sulfate-rich solutions were studied in this work. the first alternative was sulfate removal in acidic ph, as jarosite. moreover, the second precipitating alternative was tested in alkaline conditions, as ettringite. sulfate removal as ettringite was considered the preferable form for treating sulfate-containing wastewaters due to its low solubility in water, close to 10 mg/l at the ph of 11.5. chemical precipitation of sulfate in synthetic solutions containing 1,500 mg/l sulfate, at the temperature of 22±1o c, was thus investigated, and removals close to 85% in continuous precipitation systems were observed. this study showed sulfate reduction to final concentration values below 250 mg/l - lower than that recommended by environmental regulations.
Oxida??o de sulfetos de níquel com microorganismos mesófilos
Santos, Luciano Rodrigo Gomes;Barbosa, Alexandre Ferraz;Souza, Adelson Dias;Le?o, Versiane Albis;
Rem: Revista Escola de Minas , 2008, DOI: 10.1590/S0370-44672008000100008
Abstract: metallic sulphide oxidation has been associated to the generation of acid mine drainage, one of the most import environmental issues in the mining industry. bioleaching can be applied to accelerate sulphide oxidation, ceasing these impacts. this work sought to study the biooxidation of a complex nickel-iron sulphide (pentlandite and pyrrhotite) using acidophile iron-oxidizing bacteria. the effects of ph and solids concentration on the extraction of nickel were evaluated. a high nickel extraction (around 60%) can be achieved confirming the feasibility of nickel sulphide bioleaching. the ph has a negligible effect on nickel extraction being ph 2.0 the best value. nickel dissolution can be achieved at high solid percentages since gaseous transfer in the system is not strongly affected. it is suggested therefore that sulphide dissolution under these conditions is limited by the availability of carbon dioxide in the leaching system, which controls bacterial growth.
Compara??o de solu??es salinas na elui??o de resinas poliméricas de diferentes matrizes carregadas com cianocomplexos de ouro e cobre
Oliveira, Adélia Moreira;Le?o, Versiane Albis;Silva, Carlos Ant?nio da;
Rem: Revista Escola de Minas , 2006, DOI: 10.1590/S0370-44672006000100016
Abstract: ion exchange resins can be applied in cyanide recycling to address growing environmental concerns about the use of cyanide during gold extraction. although sorption with resins can be easily accomplished, elution is the key step and presents some problems. this work aims to study both loading and elution of two resins with different matrixes, purolite a500? and bayer ap247?, loaded with copper- and gold cyanocomplexes. both resins were loaded at 25oc (batchwise) and column elutions were performed at 50°c with either 1mol/l nano3 or nascn solutions. it has been found that 1mol/l nitrate solutions could not elute gold from polysterene resins(purolite a500?). conversely, both cyanocomplexes were removed from the bayer ap247? resin. for both resins, nascn (1mol/l) solutions increased metals yield as well as elution rates of both complexes.
Efeito estrutura da matriz na adsor??o de cianocomplexos metálicos em resinas de poliestireno
Riani, Josiane Costa;Carlos, Versiane Albis Le?o;Silva, Carlos Ant?nio da;
Rem: Revista Escola de Minas , 2004, DOI: 10.1590/S0370-44672004000200008
Abstract: this work aims the recycling of cyanide applying strong base ion exchange resins for the adsorption of metallic cyanocomplexes. the experiments were carried out with synthetic solutions simulating those found in the cyanidation of gold ores. the solutions are made up of copper, iron and zinc with concentrations raging from 50mg/l to 500mg/l. batch adsorption experiments were carried out with two commercial strong base resins: ionac sr-7 (polystyrene, tripropylammonium) and dowex 1x8 (gel type, polystyrene, trimethylammonium). the tripropilammonium resin ionac sr-7 presents a larger loading of zinc cyanide compared with those of copper and iron. the affinity sequence observed was zn>cu>fe. dowex 1x8 resin shows the highest uptake of both zinc and copper due to its high exchange capacity. the affinity sequence is similar to that of ionac sr-7 resin. the different affinities achieved are discussed based on both the physic-chemical features of the complexes and the resin structure.
Tecnologia limpa para redu??o de impacto ambiental do cianeto na minera??o de ouro
Riani, Josiani Costa;Pina, Pablo dos Santos;Le?o, Versiane Albis;
Rem: Revista Escola de Minas , 2007, DOI: 10.1590/S0370-44672007000100004
Abstract: a study on metal cyanocomplexes sorption on polyacrylic ion exchange resins has been undertaken. batch sorption experiments have shown that polyacrylic resins have a high affinity for zinc and iron cyanides compared to copper complexes. elution studies performed in column experiments have also depicted that 1mo/l sodium thiocyanate solutions can successfully extract the three metals. conversely, sodium nitrate solutions at the same concentration are not effective in eluting zinc cyanocomplexes. based on elution figures, it is proposed that copper and iron can be selectively eluted with nitrate before the zinc, this latter being recovered afterwards with thiocyanate solutions. both eluants were able to concentrate the cyanocomplexes in solution with a beneficial effect on the subsequent steps of cyanide recycling.
Influência da adi??o de fluorsilicato de sódio sobre a flotabilidade de minerais de manganês e quartzo com oleato de sódio
Andrade, Emily Mayer;Le?o, Versiane Albis;Lima, Rosa Malena Fernandes;
Rem: Revista Escola de Minas , 2011, DOI: 10.1590/S0370-44672011000200014
Abstract: this work presents and discusses results from zeta potential measurements and flotation response of rhodonite, rhodochrosite and quartz, in the presence of sodium fluorsilicate and sodium oleate. at concentrations of na2sif6 smaller than 10mg/l, at ph 9, quartz is more intensively depressed than rhodonite, whereas the flotation response of rhodochrosite is slightly affected either at ph 9 or ph 11. results from measurements of zeta potential versus ph indicate that iep of rhodonite (ph=2.8) is similar to those reported in literature, whereas the value o iep of quartz (ph<2.0) and rhodochrosite (ph=10,8) differ slightly from literature. zeta potential of rodonite, quartz and rhodochrosite, in the presence of sodium fluorsilicate and/or sodium oleate, become more negative at basic medium. based on the experimental results and collector (sodium oleate) plus depressant (sodium fluorsilicitate) speciation, some inference on the adsorption mechanisms of these reagents upon rhodonite, quartz and rhodochrosite is maintained.
Synthesis and Characterization of a New Cellulose Acetate-Propionate Gel: Crosslinking Density Determination  [PDF]
Patrícia Allue Dantas, Vagner Roberto Botaro
Open Journal of Polymer Chemistry (OJPChem) , 2012, DOI: 10.4236/ojpchem.2012.24019
Abstract: Crosslinking is one of the most commonly reactions used to improve the physical properties of cellulose derivatives. Cellulose Acetate Propionate (CAP) is a commercial ester obtained as a cellulose derivative and it can be used as basis for the synthesis of crosslinked chains as described in this work. Typical used crosslinkers are di-functional compounds, such as dianhydrides or diisocyanate. The formation of polymeric 3D structures as described in this work occurs typically by the reaction of the linear chains bearing free OH groups with crosslinking agents such as dianhydrides. These reactions are used to make a very absorbent material, typically a gel. The syntheses were performed in homogeneous medium with acetate propionate in a very dry atmosphere by employing PMDA (Pyromellitic Dianhydride) and BTDA (3,3’, 4,4’ Benzophenone Tetracarboxylated Dianhydride) as crosslinking agents in a reflux system. TGA analysis has shown the different thermal stability of the gels when compared with CAP. Typical TGA curves have demonstrated the lower stability of the crosslinked chains when compared to CAP as consequence of esther linkages formed in the gels structures. The Mc, which is the value for the molar mass between crosslinkings points in 3D structure, was determined according to Flory-Rehner theory. This important parameter has demonstrated greater reactivity of PMDA in comparison with the BTDA in the reactions conditions’ employed in this work.
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