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Abstract(s)
A poluição do meio ambiente aumentou rapidamente durante os últimos anos, em particular a contaminação do solo e de águas subterrâneas. Entre os principais poluentes, os metais pesados são poluentes causadores de grande preocupação ambiental, pois são tóxicos, persistentes e não degradáveis. Reduzir a concentração destes poluentes presentes no solo é uma meta que se pretende atingir. Com este objetivo, têm sido desenvolvidos estudos e trabalhos utilizando diversas tecnologias, tanto químicas como biológicas.
Esta tese teve como objetivo geral estudar a remediação de solos contaminados com metais pesados recorrendo à utilização de nanopartículas de ferro zero valente ou nanoparticules zero-valent iron (nZVI). Em termos específicos procurou analisar-se se a utilização de nZVI “verdes” permitem, ou não, reduzir a concentração dos metais pesados cobre, zinco e crómio no solo e avaliar se esta técnica poderá vir a ser aplicadas em futuras descontaminações.
Para concretizar este objectivo, à escala laboratorial, procedeu-se ao estudo da eficiência das nZVI na degradação de metais pesados (Cobre, Crómio e Zinco). O estudo foi efectuado com dois tipos de nZVI diferentes: nZVI produzidas por síntese “verde” e nZVI comerciais (Nanofer 25S). A produção de nZVI verdes recorre a tecnologia “verde” de síntese destas nanopartículas. Esta tecnologia é bastante recente, não tendo ainda sido aplicada no campo de trabalho. Baseia-se no uso de extrato de cozedura da cortiça que reduz o ferro (III) a ferro zero valente, formando nZVI verdes.
Numa primeira fase estudou-se a produção, determinou-se a concentração ideal de nZVI verdes e optimizou-se de tempo da reacção para remediação do solo.
Posteriormente à optimização destes parâmetros foi feito um estudo comparativo com as nZVI comerciais para avaliar a eficiência dos diferentes tipos de nZVI. Os metais em estudo foram analisados por diferentes métodos: Cobre e Zinco por voltametria ciclíca e Crómio por Ultravioleta-visível (UV-vis).
Os ensaios em solos contaminados com estes metais revelaram que as nZVI verdes têm elevada capacidade para reduzir os metais, atingindo mesmo um grau de degradação de 55% para o crómio e 50% para o Zinco; já o cobre não é significativamente degradado com nenhuma das concentrações estudadas. Relativamente as nZVI comerciais a eficiência de degradação é inferior obtendo-se apenas 50% de degradação para o crómio e 26% para o Zinco. Com o estudo do parâmetro tempo de reacção conclui-se que para o zinco a eficiência das nZVI não se altera ao longo dos dias atingindo o estado estacionário com apenas um dia de reação, por sua vez o crómio atinge o estado estacionário ao fim de 4 dias de reacção.
Considera-se que o objectivo principal desta tese foi cumprido pois verificou-se que a utilização de nZVI permite reduzir a concentração de dois dos três metais estudados. As aplicações em casos reais poderão ser assim o próximo passo.
The environmental pollution has increased rapidly in recent years, in particular of soil and groundwater. Among the principles polluents, heavy metals are pollutants that cause a major environmental concern, since they are toxic, persistent and are not degradable. The reduce in the concentration of these pollutants in the soil is a goal to be achieved. With this aim have been developed several studies and work using various chemical technologies. This thesis aimed to study the remediation of contaminated soils with heavy metal through the use of zero-valent iron nanoparticles (nZVI); specifically it was investigated if the use of “green” nZVI allows, or not, the reduction of the concentration of heavy metals copper, zinc and chromium in soil and if it can be applied in the soils decontamination. To achieve this objective, at a laboratory scale, we proceeded to the study of the efficiency of nZVI in the degradation of heavy metals (copper, chromium and zinc). The study was performed with two different types of nZVI: nZVI produced by "green" synthesis and commercial nZVI (Nanofer 25S). This technology is quite recent, but it has not yet been applied in this field of work. It is based on the use of cork cooking extract which reduces iron (III) to iron zero valent, forming green nZVI. Initially the production of green nZVI was studied and its optimal concentration was also determined and the time reaction optimized. After the optimization of these parameters a comparative study was made using commercial nZVI to evaluate the efficiency of different types of nZVI. The metals in the study were analyzed by different methods: Copper and Zinc by cyclic voltammetry and chromium by Ultraviolet-visible (UV-vis) spectroscopy. Tests on soil contaminated (laboratory scale) with these metals have revealed that green nZVI has a high capacity to reduce metals, reaching 55% degradation for chromium and 50% for zinc; whereas copper is not significantly degraded at any of the concentrations studied. For the commercial nZVI degradation efficiency is inferior giving only 50% degradation for chromium and 26% for zinc. The optimization of reaction time parameter lead us to conclude that, for Zinc, efficiency of nZVI does not change throughout the day reaching a steady state with only one day of reaction, in turn the chromium reaches the steady state after 4 days reaction. The main aim of this thesis was fulfilled: It is possible to conclude that the use of nZVI reduces the concentration of two of the three metals studied. Applications into real cases could be well the next steps.
The environmental pollution has increased rapidly in recent years, in particular of soil and groundwater. Among the principles polluents, heavy metals are pollutants that cause a major environmental concern, since they are toxic, persistent and are not degradable. The reduce in the concentration of these pollutants in the soil is a goal to be achieved. With this aim have been developed several studies and work using various chemical technologies. This thesis aimed to study the remediation of contaminated soils with heavy metal through the use of zero-valent iron nanoparticles (nZVI); specifically it was investigated if the use of “green” nZVI allows, or not, the reduction of the concentration of heavy metals copper, zinc and chromium in soil and if it can be applied in the soils decontamination. To achieve this objective, at a laboratory scale, we proceeded to the study of the efficiency of nZVI in the degradation of heavy metals (copper, chromium and zinc). The study was performed with two different types of nZVI: nZVI produced by "green" synthesis and commercial nZVI (Nanofer 25S). This technology is quite recent, but it has not yet been applied in this field of work. It is based on the use of cork cooking extract which reduces iron (III) to iron zero valent, forming green nZVI. Initially the production of green nZVI was studied and its optimal concentration was also determined and the time reaction optimized. After the optimization of these parameters a comparative study was made using commercial nZVI to evaluate the efficiency of different types of nZVI. The metals in the study were analyzed by different methods: Copper and Zinc by cyclic voltammetry and chromium by Ultraviolet-visible (UV-vis) spectroscopy. Tests on soil contaminated (laboratory scale) with these metals have revealed that green nZVI has a high capacity to reduce metals, reaching 55% degradation for chromium and 50% for zinc; whereas copper is not significantly degraded at any of the concentrations studied. For the commercial nZVI degradation efficiency is inferior giving only 50% degradation for chromium and 26% for zinc. The optimization of reaction time parameter lead us to conclude that, for Zinc, efficiency of nZVI does not change throughout the day reaching a steady state with only one day of reaction, in turn the chromium reaches the steady state after 4 days reaction. The main aim of this thesis was fulfilled: It is possible to conclude that the use of nZVI reduces the concentration of two of the three metals studied. Applications into real cases could be well the next steps.
Description
Trabalho final de mestrado para obtenção do grau de Mestre em Engenharia Química
Keywords
Metais pesados Heavy metals Nanopatículas de ferro zero-valente Nanoparticles zero-valent iron Remediação de solos Remediation of soils
Citation
CORTES, Olga de Jesus Alves - Utilização de nZVI para remediação de solos contaminados com metais pesados . Lisboa: Instituto Superior de Engenharia de Lisboa, 2016. Dissertação de mestrado.
Publisher
Instituto Superior de Engenharia de Lisboa