| Summary: | 碩士 === 國立高雄應用科技大學 === 化學工程與材料工程系博碩士班 === 103 === ABSTRACT
In Taiwan, aluminum wastes are remelted to form aluminum metal and scrap scum (or called primary aluminum dross). The aluminum dross is re-refined until the residues contain only 30-50% of aluminum value. The residues are called secondary aluminum dross and are disposed in the landfill. Due to moist air, aluminum nitride (AlN) in the aluminum dross will be hydrolyzed slowly, resulting in the formation of odorous ammonia. Ammonia can be dissolved in water, so the water body will be somewhat alkaline.
In this study, the rapid hydrolysis of AlN in aluminum dross via ultrasonic wave-enhanced process was carried out. The effects of operating parameters, including the final hydrolysis temperature (50℃ or 70℃), reaction time (30-180 min), and the initial molar ratio of Na (by adding NaOH) to Al (in aluminum dross) (= 7.7 or 12.9), were discussed. Moreover, the removal of impurities (Si and Cr) in aluminum dross, as well as the production of aluminum hydroxide were also carried out.
The result showed that the content of Al and AlN in aluminum dross was 37.2% and 9.8, respectively. After the alkali dissolution, the optimal operating conditions were as follows: at 70℃, reaction time = 60 min, and initial Na/Al molar ratio =12.9. The dissolution ratio of Al from aluminum dross into sodium aluminate was about 46.2~49.4%. Moreover, after the removal of impurities (Si and Cr) in aluminum dross, aluminum hydroxide was produced with a yield of 24.9~37.9% of Al element on a basis of aluminum dross.
Keywords: Aluminum dross, Alkali dissolution, Desilication, Chromium depletion Aluminum hydroxide.
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