Synthesis of nickel-cobalt-iron supported alumina composite via electrolysis for palladium ions adsorption
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Date
2016
Authors
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Publisher
Universiti Teknologi Malaysia
Abstract
The discharge of palladium (Pd) effluents from industries may cause serious environmental effect to aquatic life and humans due to its toxicity and harmful effects. Thus, the removal of Pd from an aquatic system is very crucial and this process can be achieved by the adsorption method. In this study, nickel loaded alumina (Al2O3) was prepared by electrochemical (NiAl) and physical method for the adsorption of Pd from an aqueous solution. Due to the higher adsorptivity shown by the electrochemical method, the performance of electrochemically prepared cobalt (Co) and iron (Fe) onto NiAl with different metal loading (3-10 wt%) were also investigated. The adsorbents were characterized using x-ray diffraction, Fourier transform infrared spectroscopy, surface area analysis, transmission electron microscopy, electron spin resonance spectrometer, and vibrating sample magnetometer. The adsorption of Pd was conducted in a batch system under varying initial pH (3-8), adsorbent dosage (0.005- 0.05 g), initial concentration (10-100 mg L-1) and temperature (303-323 K). The adsorptivity of those adsorbents toward Pd ions is in the following order: FeCoNiAl > CoNiAl > NiAl > cobalt oxide > iron oxide > nickel oxide. The FeCoNiAl was able to remove the Pd with an adsorption capacity of 250 mg g-1 at pH 5 when using 0.05 g adsorbent, initial concentration of 75 mg L-1 at 303 K. The characterization result revealed that adsorptivity was significantly affected by the formation of metal spinel which induced the magnetism properties. Besides, the hydrogen atoms of hydroxyl (– OH) groups on the surface of Al2O3 also exchanged with the Pd ions. The consecutive addition of metals led to a greater formation of surface –OH, oxygen defects as well as spinel phases that contributed to a higher degree of magnetism, which provide more adsorption sites for the Pd ions. The equilibrium data followed the Langmuir model and the kinetics was best described by the pseudo-first-order model, while the thermodynamic study indicated that the adsorption was exothermic. Further optimization by the response surface methodology with a central composite design model was performed and the results showed that the reaction temperature plays a major role for the adsorption, which most probably affected the magnetism of the composites. This study provides a new perspective in the synthesis of composites with superior properties for the removal of Pd ions as well as for other applications
Description
Thesis (PhD. (Chemical Engineering))
Keywords
Palladium, Adsorption—Materials—Environmental aspects, Water—Purification—Adsorption