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Adsorption of Ni2+, As5+, Pb2+ on graphene oxide modified biochars derived from rice husks and sewage sludge

Vosnaki Olga

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Year 2021
Type of Item Diploma Work
Bibliographic Citation Olga Vosnaki, "Adsorption of Ni2+, As5+, Pb2+ on graphene oxide modified biochars derived from rice husks and sewage sludge", Diploma Work, School of Chemical and Environmental Engineering, Technical University of Crete, Chania, Greece, 2021
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The aim of this thesis is to study the adsorption of the heavy metals Ni2+, Pb2+ and As5+. Biochar is a carbonaceous material that is produced through the pyrolysis of biomass. In this study two different waste types of biomass feedstock were used: a) Rice husks (RH) and b) Sewage sludge (SS). Both of them were used to generate biochar through pyrolysis at two different temperatures, i.e. 400oC and 600oC, under specific conditions. Thus, four types of biochars were produced. The second step was the modification of biochars. Graphene oxide was the nano-material used in this coating procedure. The modification happened in two distinct doses of 0.1% and 1%, respectively. In the end, twenty biochars were produced which were either modified or not with unique capabilities. All biochar samples were characterized for the following properties: Yield, Ash content, pH, pHpzc (point zero charge), Electrical Conducivity (EC), Cation Exchange Capacity (CEC), BET surface area, Total organic carbon (TOC). According to the measured values, the RH_GO0.1_600 from rice husks and the SS_GO0.1_600 from sewage sludge were the most promising for adsorption. The next part in this study was the process of adsorption. The stock solution with the intended concentrations was prepared prior to the adsorption experiments. Adsorption kinetic experiments took place in order to understand the behavior of the biochar samples. In addition, kinetic models such as the pseudo-1st order and the pseudo-2nd order were investigated, with the best description given by the pseudo-2nd order for all metals.In conclusion, both biochars, modified or not, had considerable removal capacity without any remarkable differences among them. Maybe the sewage sludge biochars have a bit better adsorption behavior in As5+ and Pb2+ than the biochars of rice husk because of their organic origin.

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