Optimization of the extraction of aluminum sulfate and ammonium aluminum sulfate alums from aluminum dross tailings
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Optimization of the extraction of aluminum sulfate and ammonium aluminum sulfate alums from aluminum dross tailings M. A. Mohameda) Chemistry Department, Faculty of Science, South Valley University, Qena 83511, Egypt
M. E. Kassim Metallurgy Department, Faculty of Engineering, Assiut University, Assiut, Egypt
E. A. El-katatny Aluminium Company of Egypt, Nag-Hammady, Egypt (Received 9 December 1996; accepted 19 November 1997)
Aluminum dross tailings, an industrial waste from the Egyptian Aluminium Company (Egyptalum), were used to produce two types of alums, namely, aluminum sulfate alum and ammonium aluminum alum via two separate processes. The first process involved leaching the impurities using dilute H2 SO4 at different solidyliquid ratios and temperatures in the form of soluble sulfates. Some dissolved aluminum was recovered as ammonium aluminum sulfate. The second process involved extraction of aluminum sulfate from the purified dross produced after leaching. This was carried out under atmospheric pressure using different concentrations of H2 SO4 . Influence of temperature, time of reaction, and acid concentration on leaching and extraction processes were studied. X-ray diffraction, atomic absorption spectrometry, and thermal analysis techniques were used. I. INTRODUCTION
The use of industrial wastes to produce useful materials is a very important task for scientists all over the world, where billions of tons of industrial solid wastes were discarded, sometimes causing serious pollution of the environment. The aluminum industry is no exception in this respect where, for example, the aluminum wastes available in Egyptalum amounts annually to about 15,000 tons. Aluminum dross tailings, the parent material for the present study, represents 15% of this quantity. Several studies have been devoted to the production of aluminum sulfate alum from the by-product aluminum oxide.1–3 The double salt, ammonium aluminum sulfate, was also produced1 when the aluminum oxide by-product has a high content of aluminum nitride (AlN). In these studies,1–3 aluminum dross tailings were washed with water at elevated temperatures to remove the water soluble salts. Aluminum nitride (AlN) and aluminum carbide (Al4 C3 ) contaminants decompose to aluminum oxide trihydrate together with the volatile products, i.e., ammonia and methane. A slurry of dross and water was fed into an agitating vessel and heated between 60 and 70 ±C. H2 SO4 was gradually injected into the slurry where the temperature rose to 100–105 ±C. The reaction was maintained under liquification pressure
and agitation for 3–4 h while the reaction proceeded to completion. The binary salt of ammonia aluminum alum was crystallized out of the solution while the remaining liquor contained aluminum sulfate. In the present study, we have employed a new method for the treatment of aluminum dross tailings. Dilute H2 SO4 was used here as a leaching agent to dissolve the major impurities (e.g., AlN, Al4 C3 , CuO, Fe2 O3 , MnO, etc.) pres
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