Thermodynamical Study of the Removal of Molybdenum Using Dry Microalgae
| Autor: | CHIU, YI-CHUAN, 邱怡娟 |
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| Rok vydání: | 2017 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 105 In the previous studies, molybdenum is a well-known essential nutrient for algae; therefore, the potential to remove molybdenum with algae from the wastewater is worth being carefully evaluated. Two algae species, Chloroidium saccharophilum and Desmodesmus sp., were extracted from the wastewater in semiconductor plants and from the domestic sewage in National Chung Cheng University, respectively. Sorption experiments have been conducted for evaluating the efficiency of removing molybdenum under different values of pH, temperatures and initial molybdenum concentrations. The results confirm that the isotherm has an excellent agreement with Langmuir adsorption model, which has correlation coefficients (r2) of > 0.97. It demonstrates that the adsorption capacities (qmax) of both two algae species have an inverse relationship with pH value, which is consistent with the relationship of temperature. In addition, a similar experiment was also conducted for Desmodesmus sp. with domestic sewage instead of deionized water at the conditions of pH=6 and 20 oC. It obtained a lower value of qmax (2.5 x 106 mg kg-1) than that with deionized water (3.3 x 106 mg kg-1). It is believed that the anions in the domestic sewage, such as Cl-, NO3-, PO43- and SO42-, are capable of competing with HMoO4- and MoO42-; and, subsequently, the absorption capacity decreases. The results of kinetic analysis obtain a correlation coefficients of 0.96 for the pseudo-first order model, which are much greater than the simple first order (r2 = 0.89). The pseudo-first-order rate constant, kads(min-1), has an inverse relationship with pH value, which is consistent with the relationship of temperature. The calculated activation energy (Ea) is equal to 29.99 kJ/mole, which probably demonstrates the sorption reaction is related to chemical binding. The results also show that sorption processes is endothermic and the equilibrium constant increases with temperature. Positive change of enthalpy(ΔH), entropy (ΔS) and negative change of Gibb’s free energy(ΔG) confirm the sorption reaction is spontaneous and a process of adsorption of heat. Moreover, the sorption of rare earth element (REE) was also studied. The resaults show that alge prefers to absorb middle REE rather than LREE and HREE. However, HREE is the last to be absorbed on the algae surface. Key word： algae molybdenum |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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