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O trabalho desenvolvido pretendeu estudar a viabilidade do uso de argilas, adsorventes naturais, vermiculite e hidrotalcite, na remoção de fármacos presentes em águas por sorção. Foram selecionados três fármacos pertencentes a grupos terapêuticos diferentes com base no seu consumo e persistência ambiental: venlafaxina (antidepressivo), a carbamazepina (tratamento da epilepsia) e o ibuprofeno (anti-inflamatório).
Foram realizados estudos para a vermiculite e para a hidrotalcite na sua forma bruta e após tratamentos químicos ou térmicos. A escolha dos sistemas adsorvente/adsorvato foi baseada na sua afinidade em termos de carga.
A remoção da venlafaxina foi estudada para as vermiculites bruta (W), expandida (Ve), após tratamento com hidróxido de sódio (WNaOH) e após tratamento com ácido nítrico e hidróxido de sódio (WNOH). Os ensaios demostraram que o equilíbrio se atingia rapidamente, permitindo obter elevadas eficiências de remoção, tal como era esperado atendendo à afinidade de carga entre o adsorvente e o adsorvato. Os modelos que melhor se ajustaram aos resultados dos ensaios de cinética foram: para a vermiculite bruta o modelo de Elovich e para as restantes vermiculites (Ve, WNaOH e WNOH) foi o modelo pseudo 2ª ordem. Nos resultados obtidos nos estudos de equilíbrio o melhor ajuste para o sistema de venlafaxina/vermiculite bruta e WNaOH foi o modelo de Redlich & Peterson, enquanto que para os sistemas venlafaxina/Ve e WNOH foi o modelo de Langmuir. De acordo com o modelo de Langmuir, a capacidade máxima de sorção mais elevada foi obtida, para a vermiculite WNOH (33 ± 4 mg/g) seguida da vermiculite WNaOH (6,3±0,5 mg/g), da vermiculite bruta (5,8±0,7 mg/g), e da vermiculite expandida (3,9±0,2 mg/g). As eficiências de remoção obtidas foram de 87 % para a vermiculite bruta, 76 % para a expandida, 75 % para a WNaOH e de 97% para a WNOH.
No estudo cinético realizado com a carbamazepina e a vermiculite expandida, não se verificou remoção do composto, o que pode ser explicado pela carga neutra deste fármaco.
A remoção do ibuprofeno foi estudada para as duas hidrotalcites, a bruta (HT) e a tratada termicamente a 450 ºC (HTC450). Os ensaios cinéticos demostraram que o equilíbrio se atingia rapidamente. O modelo cinético que melhor descreve os resultados experimentais, para as duas hidrotalcites em estudo, foi o de pseudo 2ª ordem. Nestes estudos foram obtidas boas eficiências de remoção, o pode ser relacionado com a afinidade entre a carga negativa do ibuprofeno e carga superficial do adsorvente. Foi verificada uma forte influência do pH na medida em que pequenas variações de pH levam a uma alteração significativa da capacidade de adsorção da hidrotalcite. Esta forte dependência do pH conduziu uma elevada variabilidade nos resultados dos ensaios de equilíbrio, não permitindo o ajuste de modelos. A capacidade mais elevada de sorção da hidrotalcite bruta, 3,73 mg .g-1, foi obtida para um pH inicial próximo de 2,4. Para o ensaio da HTC450 a melhor capacidade de sorção obtida foi de 14,1 mg .g-1, para um valor de pH inicial de 2,6.
Atendendo às elevadas eficiências de remoção e às rápidas cinéticas observadas para os materiais tratados, WNOH e HTC450, considera-se que a aplicação destes adsorventes de origem natural poderá ser viável à escala industrial. Contudo, este é um estudo inicial que ainda necessita de ser aprofundado.
The work aimed to study the feasibility of the use of clays, natural adsorbents, vermiculite and hydrotalcite, in the removal of pharmaceuticals present in water by sorption. Three pharmaceuticals belonging to different therapeutic groups were selected based on their consumption and environmental persistence: venlafaxine (antidepressant), carbamazepine (treatment of epilepsy) and ibuprofen (antiinflammatory). Studies were carried out for vermiculite and hydrotalcite, in their natural form and after chemical or thermal treatments. The choice of adsorbent/adsorbate systems was based on their affinity in terms of charge. Removal of venlafaxine was studied for diferente vermiculites: raw (W), expanded (Ve), after treatment with sodium hydroxide (WNaOH) and after treatment with nitric acid and sodium hydroxide (WNOH). The assays demonstrated that the equilibrium was reached rapidly, allowing high removal efficiencies, as expected given the affinity of charge between the adsorbent and the adsorbate. The models that best fit the results of the kinetic tests were: for raw vermiculite it was the Elovich’s model and for the remaining vermiculites (Ve, WNaOH and WNOH) it was the pseudo 2nd order model. In the results obtained for the equilibrium studies the best fit for the systems venlafaxine/raw vermiculite and WNaOH was the Redlich & Peterson’s model, while for the systems venlafaxine/Ve and WNOH was the Langmuir’s model. According to this model, the highest maximum sorption capacity was obtained for vermiculite WNOH (33 ± 4 mg.g-1 ) followed by vermiculite WNaOH (6.3 ± 0.5 mg.g-1 ), raw vermiculite (5.8 ± 0.7 mg.g -1) and expanded vermiculite (3.9 ± 0.2 mg.g-1). The removal efficiencies obtained were 87% for raw vermiculite, 76% for expanded vermiculite, 75% for WNaOH and 97% for WNOH. In the kinetic study performed with carbamazepine and expanded vermiculite, there was no removal of the compound, which can be explained by the neutral charge of this pharmaceutical. The removal of ibuprofen was studied for the two hydrotalcites, raw (HT) and thermally treated at 450 ºC (HTC450). Kinetic tests showed that equilibrium was rapidly achieved. The kinetic model that best describes the experimental results for the two hydrotalcites under study was the pseudo 2nd order. In these studies, good removal efficiencies were obtained, which can be related to the affinity between the negative charge of the ibuprofen and the surface charge of the adsorbent. A strong influence of the pH was verified, therefore small variations of pH lead to significant changes in the adsorption capacity of hydrotalcite. This strong pH dependence led to a high variability in the results of the equilibrium assays, not allowing model adjustment. The highest sorption capacity of the raw hydrotalcite, 3.73 mg.g-1, was obtained at an initial pH of about 2.4. For the system ibuprofen/HTC450 the best sorption capacity obtained was 14.1 mg.g-1 , for an initial pH value of 2.6. Given the high removal efficiencies and fast kinetics observed for the treated materials, WNOH and HTC450, the application of these naturally occurring adsorbents may be feasible at industrial scale. However, this is an initial study that still needs to be futher developed.
The work aimed to study the feasibility of the use of clays, natural adsorbents, vermiculite and hydrotalcite, in the removal of pharmaceuticals present in water by sorption. Three pharmaceuticals belonging to different therapeutic groups were selected based on their consumption and environmental persistence: venlafaxine (antidepressant), carbamazepine (treatment of epilepsy) and ibuprofen (antiinflammatory). Studies were carried out for vermiculite and hydrotalcite, in their natural form and after chemical or thermal treatments. The choice of adsorbent/adsorbate systems was based on their affinity in terms of charge. Removal of venlafaxine was studied for diferente vermiculites: raw (W), expanded (Ve), after treatment with sodium hydroxide (WNaOH) and after treatment with nitric acid and sodium hydroxide (WNOH). The assays demonstrated that the equilibrium was reached rapidly, allowing high removal efficiencies, as expected given the affinity of charge between the adsorbent and the adsorbate. The models that best fit the results of the kinetic tests were: for raw vermiculite it was the Elovich’s model and for the remaining vermiculites (Ve, WNaOH and WNOH) it was the pseudo 2nd order model. In the results obtained for the equilibrium studies the best fit for the systems venlafaxine/raw vermiculite and WNaOH was the Redlich & Peterson’s model, while for the systems venlafaxine/Ve and WNOH was the Langmuir’s model. According to this model, the highest maximum sorption capacity was obtained for vermiculite WNOH (33 ± 4 mg.g-1 ) followed by vermiculite WNaOH (6.3 ± 0.5 mg.g-1 ), raw vermiculite (5.8 ± 0.7 mg.g -1) and expanded vermiculite (3.9 ± 0.2 mg.g-1). The removal efficiencies obtained were 87% for raw vermiculite, 76% for expanded vermiculite, 75% for WNaOH and 97% for WNOH. In the kinetic study performed with carbamazepine and expanded vermiculite, there was no removal of the compound, which can be explained by the neutral charge of this pharmaceutical. The removal of ibuprofen was studied for the two hydrotalcites, raw (HT) and thermally treated at 450 ºC (HTC450). Kinetic tests showed that equilibrium was rapidly achieved. The kinetic model that best describes the experimental results for the two hydrotalcites under study was the pseudo 2nd order. In these studies, good removal efficiencies were obtained, which can be related to the affinity between the negative charge of the ibuprofen and the surface charge of the adsorbent. A strong influence of the pH was verified, therefore small variations of pH lead to significant changes in the adsorption capacity of hydrotalcite. This strong pH dependence led to a high variability in the results of the equilibrium assays, not allowing model adjustment. The highest sorption capacity of the raw hydrotalcite, 3.73 mg.g-1, was obtained at an initial pH of about 2.4. For the system ibuprofen/HTC450 the best sorption capacity obtained was 14.1 mg.g-1 , for an initial pH value of 2.6. Given the high removal efficiencies and fast kinetics observed for the treated materials, WNOH and HTC450, the application of these naturally occurring adsorbents may be feasible at industrial scale. However, this is an initial study that still needs to be futher developed.
Description
Keywords
Pharmaceuticals Vermiculite hHydrotalcite Sorption Venlafaxine Ibuprofen Carbamazepine