| Summary: | 碩士 === 弘光科技大學 === 職業安全與防災研究所 === 99 === Gallium, indium and its compounds have numerous industrial applications in the manufacture of optoelectronics and semiconductors. Two separate parts are represented as the main body of this thesis. In first part, we used batch adsorption techniques to evaluate the potential suitability of tea waste as an environmentally friendly adsorbent for the removal of gallium, indium ions from aqueous solution. In addition, we also investigated the effects of process parameters, such as the solution pH, initial concentration of gallium, indium ions, adsorbent dose and temperature on adsorption performance. The experimental data were fitted with several adsorption isotherm models to describe the adsorption process of gallium, indium ions onto the tea waste. This study indicated that tea waste could be used as an effective and environmentally friendly adsorbent for the treatment of gallium, indium-containing aqueous solutions. The tea waste at pH 4.0 gave the greatest zeta potential value. Therefore, adsorption of gallium, indium ions onto tea waste is at optimum in the pH range 4-5. Thermodynamic parameters, including the Gibbs free energy, enthalpy, and entropy, indicated that the gallium, indium adsorption of aqueous solutions onto tea waste was feasible, spontaneous and endothermic in the temperature range of 288 K to 318 K. The experimental data were fitted with several adsorption isotherm models to describe the adsorption process of gallium, indium ions onto the tea waste. The predictions of the Freundlich isotherm model satisfactorily matched the experimental observations. In addition, the kinetic data obtained at different initial concentrations were analyzed using pseudo-first-order and pseudo-second-order kinetic models. A pseudo-second-order model provided a good fit to the experimental results with correlation coefficients greater than 0.99.
The second part in this thesis is to investigate the effect of process parameters on the removal of indium ions from aqueous solutions using iron electrocoagulation. Various operating parameters that could potentially affect the removal efficiency were investigated, including the current density, pH variation, supporting electrolyte, initial concentration, and temperature. The optimum current density, supporting electrolyte concentration, and temperature were found to be 6.4 mA cm-2, 0.003 N NaCl, and 298 K, respectively. When the pH values lower than 6.1, the removal efficiencies of indium ions via electrocoagulation were up to 5 times greater than those by adding sodium hydroxide. The adsorption of indium ions preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules.
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