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Abstract(s)
A tecnologia de barreiras reactivas é uma alternativa possível de ser implementada
para tratamento de águas contaminadas com compostos organoclorados, nomeadamente
o tricloroetileno (TCE). O recurso a ferro zerovalente (Fe0) como meio reactivo tem na
actualidade inúmeras aplicações, tratando-se de uma reacção de desalogenação por
mecanismo de oxidação-redução.
Neste trabalho fizeram-se estudos em batch da reacção entre o Fe0 e o TCE de
forma a conhecer os parâmetros cinéticos. A natureza e a área da superfície do ferro
provaram ser determinantes na velocidade da reacção. Foi possível verificar que para o
sistema ferro comercial / TCE a ordem da reacção é inferior a um, e a constante cinética
da ordem de 10-2 Lm-2h-1.
Para simular uma barreira reactiva, projectaram-se e construíram-se colunas, as
quais foram cheias com areia e ferro depois de devidamente misturados, uma vez que se
tratou da disposição a que corresponderam melhores eficiências de redução do TCE.
Não foi possível estabelecer o mecanismo da reacção, nem conhecer os parâmetros
cinéticos, pelas dificuldades experimentais encontradas na análise do TCE e pelo facto
de se tratar de uma reacção muito lenta.
A cromatografia gasosa com detector de ionização de chama provou ser o método
mais apropriado para doseamento do TCE em águas contaminadas, nas condições
usadas neste estudo. A elevada volatilização do TCE e a baixa solubilidade em água
contribuíram para as dificuldades operacionais encontradas.
Reactive permeable barriers have been extensive to the treatment of waters contaminated with organochlorine compounds, namely trichloroethene (TCE). Nowadays, the use of zerovalent iron (Fe0) as the reactive medium has many applications and it is based on an oxidation-reduction reaction. In this work the reaction between commercial Fe0 and TCE was studied in order to establish kinetic parameters. The reaction that occurs at the iron surface has been interpretated and a less first order kinetics based on classic approach for homogeneous solutions was found. A value close to 10-2 Lm-2h-1 was obtained for rate constant. To simulate a reactive barrier, columns were projected and constructed. A mixture of granular iron and sand was installed into the column since it corresponds to the performance that leads to high TCE reduction efficiencies. It was not possible to establish the mechanism of the reaction and to obtain kinetic parameters, in consequence of experimental difficulties found in the TCE analysis and slowness of the reaction kinetics. Gas chromatography coupled with Flame Ionization Detector proved to be the most suitable method for determination of TCE in contaminated water under the conditions used in this study. The high volatilization of the TCE and his low solubility in water contributed to the operational difficulties found.
Reactive permeable barriers have been extensive to the treatment of waters contaminated with organochlorine compounds, namely trichloroethene (TCE). Nowadays, the use of zerovalent iron (Fe0) as the reactive medium has many applications and it is based on an oxidation-reduction reaction. In this work the reaction between commercial Fe0 and TCE was studied in order to establish kinetic parameters. The reaction that occurs at the iron surface has been interpretated and a less first order kinetics based on classic approach for homogeneous solutions was found. A value close to 10-2 Lm-2h-1 was obtained for rate constant. To simulate a reactive barrier, columns were projected and constructed. A mixture of granular iron and sand was installed into the column since it corresponds to the performance that leads to high TCE reduction efficiencies. It was not possible to establish the mechanism of the reaction and to obtain kinetic parameters, in consequence of experimental difficulties found in the TCE analysis and slowness of the reaction kinetics. Gas chromatography coupled with Flame Ionization Detector proved to be the most suitable method for determination of TCE in contaminated water under the conditions used in this study. The high volatilization of the TCE and his low solubility in water contributed to the operational difficulties found.
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Instituto Politécnico do Porto. Instituto Superior de Engenharia do Porto