Browsing by Author "Oliveira, F. D."
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- Copper and lead removal by peanut hulls: equilibrium and kinetic studiesPublication . Oliveira, F. D.; Paula, J. H.; Freitas, Olga M.; Figueiredo, Sónia AdrianaThis research work aims to study the use of peanut hulls, an agricultural and food industry waste, for copper and lead removal through equilibrium and kinetic parameters evaluation. Equilibrium batch studies were performed in a batch adsorber. The influence of initial pH was evaluated (3–5) and it was selected between 4.0 and 4.5. The maximum sorption capacities obtained for the Langmuir model were 0.21 ± 0.03 and 0.18 ± 0.02 mmol/g, respectively for copper and lead. In bi-component systems, competitive sorption of copper and lead was verified, the total amount adsorbed being around 0.21 mmol of metal per gram of material in both mono and bi-component systems. In the kinetic studies equilibrium was reached after 200 min contact time using a 400 rpm stirring rate, achieving 78% and 58% removal, in mono-component system, for copper and lead respectively. Their removal follows a pseudo-second-order kinetics. These studies show that most of the metals removal occurred in the first 20 min of contact, which shows a good uptake rate in all systems.
- Copper, nickel and zinc removal by peanut hulls: batch and column studies in mono, tri-component systems and with real effluentPublication . Oliveira, F. D.; Soares, A. D.; Freitas, Olga M.; Figueiredo, Sónia AdrianaThe main goal of this research study was the removal of Cu(II), Ni(II) and Zn(II) from aqueous solutions using peanut hulls. This work was mainly focused on the following aspects: chemical characterization of the biosorbent, kinetic studies, study of the pH influence in mono-component systems, equilibrium isotherms and column studies, both in mono and tri-component systems, and with a real industrial effluent from the electroplating industry. The chemical characterization of peanut hulls showed a high cellulose (44.8%) and lignin (36.1%) content, which favours biosorption of metal cations. The kinetic studies performed indicate that most of the sorption occurs in the first 30 min for all systems. In general, a pseudo-second order kinetics was followed, both in mono and tri-component systems. The equilibrium isotherms were better described by Freundlich model in all systems. Peanut hulls showed higher affinity for copper than for nickel and zinc when they are both present. The pH value between 5 and 6 was the most favourable for all systems. The sorbent capacity in column was 0.028 and 0.025 mmol g-1 for copper, respectively in mono and tri-component systems. A decrease of capacity for copper (50%) was observed when dealing with the real effluent. The Yoon-Nelson, Thomas and Yan’s models were fitted to the experimental data, being the latter the best fit.
- Remoção de metais usando casca de amendoimPublication . Oliveira, F. D.; Figueiredo, Sónia Adriana Ribeiro da Cunha; Freitas, Olga Manuela Matos deNo presente trabalho pretendeu-se estudar a viabilidade da utilização de um resíduo agrícola – casca de amendoim – como biossorvente na remoção de metais pesados – cobre (II), níquel (II) e zinco (II) – em solução aquosa. A escolha deste biossorvente baseou-se no facto de se saber que se trata de um material natural que revela aptidão para a fixação de iões metálicos, bastante abundante e de baixo custo, podendo vir a ser uma potencial alternativa aos materiais actualmente utilizados. O trabalho contemplou os seguintes aspectos: caracterização do biossorvente, estudo da influência da granulometria, ensaios cinéticos num adsorvedor perfeitamente agitado, estudo da influência do pH nos sistemas mono-componente, planeamento factorial para o estudo da influência da força iónica e da razão massa biossorvente/metal, isotérmicas de equilíbrio e ensaios em coluna mono e tricomponente. Seleccionou-se a granulometria de 1,0-2,0 mm para o trabalho experimental. No ensaios cinéticos o modelo que melhor se ajustou aos dados experimentais do cobre e do zinco foi o de pseudo-primeira ordem, sendo o de pseudo-segunda-ordem o mais adequado para o níquel. O estudo da influência do pH permitiu concluir que o valor de pH 5 seria adequado para todos os sistemas. O planeamento factorial incidiu sobre os sistemas mono-componente, sendo os factores – força iónica e concentração de adsorvente – o objecto de estudo. A partir dos resultados obtidos verificou-se que a capacidade de biossorção aumenta com o aumento da concentração da casca de amendoim e com a força iónica, apresentando esta uma forte influência. Os estudos de equilíbrio foram adequadamente descritos pelo modelo de Freundlich, verificando-se uma maior afinidade da casca de amendoim para o cobre. Nos ensaios em coluna de leito fixo, para o cobre nos sistemas mono e tricomponente, verifica-se que o modelo de Yan é o que melhor descreve a curva de ruptura experimental.