Name: | Description: | Size: | Format: | |
---|---|---|---|---|
3.02 MB | Adobe PDF | |||
2.88 MB | Adobe PDF |
Advisor(s)
Abstract(s)
Os resíduos produzidos em Estações de Tratamento de água (ETA), resíduos de ETA
(RETA), podem ser valorizados como adsorventes para a remoção de metais pesados
de águas de escorrências de estradas (AEE). Estes efluentes transportam uma série
de poluentes, entre eles crómio (Cr), chumbo (Pb), níquel (Ni) e zinco (Zn), que
podem causar importantes impactos ambientais, bem como graves problemas de
saúde e a sua valorização pode evitar estes problemas e produzir um adsorvente para
controlo da poluição que pode ser comercializado.
Um amostra de RETA, retirada da ETA do Caldeirão (Guarda) e calcinada a 700 ºC
para eliminar o seu conteúdo orgânico, foi caracterizada física e quimicamente (EDS
e XRD) e foram ainda determinadas propriedades como a análise granulométrica,
densidade, massa volúmica, superfície específica e capacidade de troca catiónica. Os
resultados indicam tratar-se de um material de estrutura um pouco cristalina, com
elevada capacidade para trocar catiões, elevada superfície específica e com argilas e
siltes na sua composição.
Realizaram-se 4 fases de ensaios experimentais para avaliar a capacidade do RETA
para remover os metais pesados Cr, Pb, Ni e Zn, comuns nas AEE, e para poder ser
reutilizado como material adsorvente no controlo da poluição associada à deposição
destes efluentes em massas de água. Os resultados mostram que o RETA tem muito
boa capacidade para remover os metais Pb, Ni e Zn, mas é pouco eficaz para
remover o crómio, para concentrações entre 3 mg/l e 10 mg/l, e um tempo de
contacto de 5 horas. Esta circunstância está associada à faixa de pH observada nos
ensaios (entre 7 e 8), que é favorável para a remoção de Pb, Ni e Zn por adsorção e
complexação-precipitação, mas é desfavorável para a remoção de Cr, uma vez que
este metal é melhor adsorvido para pH menor que 7.
A remoção mais elevada foi do Zn (entre 83,5% e 96,7%), seguindo-se o Pb (entre
70,9% e 89,2%) e o Ni (entre 73,1% e 75,4%), e entre 70% e 90% da remoção observouse
nas 2 primeiras horas de contacto, onde também se atingiu o equilíbrio de sorção.
A remoção de Cr variou entre 9,8% e 22,6%.
O modelo de pseudo-primeira ordem explica adequadamente a cinética de sorção
para os quatro metais.
The waste produced in water treatment plants (ETA), waste of ETA (RETA), can be valorised as adsorbent for the removal of heavy metals from road runoff water (AEE). These effluents carry a variety of pollutants, including chromium (Cr), lead (Pb), nickel (Ni) and zinc (Zn), which can cause significant environmental impacts and serious health problems and their removal and control can avoid these problems and also allow producing a good adsorbent for controlling pollution that can be commercialized. A sample of RETA, from the ETA of Caldeirão (Guarda), and burned at 700 °C for removing its organic content, was characterized physically and chemically (EDS and XRD) and certain properties was analysed (such as particle size analysis, density, specific surface and cation exchange capacity). The results indicate that its structure is slightly crystalline with a high both cation exchange capacity and surface area and with silts and clays in their composition. Four experimental phases of tests were developed for evaluating its ability for removing the heavy metals Cr, Pb, Ni and Zn, common in the AEE, and its potential for being reused as an adsorbent material in the control of the pollution associated with these effluents. The results show that the residue has a very good ability for removing Pb, Ni and Zn, but it is ineffective in the remove the Cr, for metal concentrations between 3 mg/l and 10 mg/l, and a contact time of 5 hours. These results are mainly associated with the pH range observed in the tests (between 7 and 8), which is favourable for the removal of Pb, Ni and Zn by adsorbing and complexing, precipitating, but it is unfavourable for the removal of Cr, since this metal is better adsorbed for pH lower than 7. The highest removal was for Zn (between 83.5% and 96.7%), followed by Pb (between 70.9% and 89.2%) and Ni (between 73.1% and 75.4 %), and between 70% and 90% of the removal was observed in the first 2 hours of contact, where also the sorption equilibrium was reached. The removal of Cr ranged between 9.8% and 22.6%. The pseudo-first-order model adequately explains the sorption kinetics for the four metals.
The waste produced in water treatment plants (ETA), waste of ETA (RETA), can be valorised as adsorbent for the removal of heavy metals from road runoff water (AEE). These effluents carry a variety of pollutants, including chromium (Cr), lead (Pb), nickel (Ni) and zinc (Zn), which can cause significant environmental impacts and serious health problems and their removal and control can avoid these problems and also allow producing a good adsorbent for controlling pollution that can be commercialized. A sample of RETA, from the ETA of Caldeirão (Guarda), and burned at 700 °C for removing its organic content, was characterized physically and chemically (EDS and XRD) and certain properties was analysed (such as particle size analysis, density, specific surface and cation exchange capacity). The results indicate that its structure is slightly crystalline with a high both cation exchange capacity and surface area and with silts and clays in their composition. Four experimental phases of tests were developed for evaluating its ability for removing the heavy metals Cr, Pb, Ni and Zn, common in the AEE, and its potential for being reused as an adsorbent material in the control of the pollution associated with these effluents. The results show that the residue has a very good ability for removing Pb, Ni and Zn, but it is ineffective in the remove the Cr, for metal concentrations between 3 mg/l and 10 mg/l, and a contact time of 5 hours. These results are mainly associated with the pH range observed in the tests (between 7 and 8), which is favourable for the removal of Pb, Ni and Zn by adsorbing and complexing, precipitating, but it is unfavourable for the removal of Cr, since this metal is better adsorbed for pH lower than 7. The highest removal was for Zn (between 83.5% and 96.7%), followed by Pb (between 70.9% and 89.2%) and Ni (between 73.1% and 75.4 %), and between 70% and 90% of the removal was observed in the first 2 hours of contact, where also the sorption equilibrium was reached. The removal of Cr ranged between 9.8% and 22.6%. The pseudo-first-order model adequately explains the sorption kinetics for the four metals.
Description
Keywords
Águas de Escorrência de Estradas Estação de Tratamento de Água Metais Pesados Resíduo Sorção