Which reason is correct for the following statement? (1) Bauxite ore is leached by aqueous solution of Na2CO3 or NaOH because_________
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Different ways for alkaline recovery of aluminum from bauxite residue are considered from the literature and examined in experiments. The advantages and disadvantages of a high-temperature digestion via Bayer process and soda-lime sintering process are elaborated and compared. As a hybrid process, bauxite residue undergoes a reductive smelting process with lime addition in an electric arc furnace in order to generate alumina-enriched slag. This slag is subsequently treated with high-pressure caustic leaching at moderated (200–300 g/l) and high (572–762 g/l) sodium hydroxide concentrations. The aluminum extractions are related to phase transitions in mineralogy caused by the process parameter and are analyzed and proofed by x-ray diffraction. The results show moderate aluminum recoveries of 70 % in case of the use of Bayer process, extremely high aluminum extractions of 95 % in case of slag leaching at high NaOH concentrations, and even high recoveries of almost 90 % achieved by an optimized sinter process with subsequent leaching at 50 °C with water. Special focus throughout all experiments is set on the dissolution of silicon as major impurity in the leachate.
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