Abstract

Coal fly ash is a lightweight incombustible particulate generated during coal combustion. Alumina content in the fly ash is present in the mullite phase, and its high stability calls for alternative processing for conversion to reactive phase before leaching. Mechanical activation with sodium hydroxide was found unsatisfactory for the breakdown of mullite structure, whereas the mullite phase dissociated to sodium silicate and sodium aluminosilicate during the sodium hydroxide thermal treatment. Below 400 °C, hydroxycancrinite is formed, which leads to alumina loss, whereas above 600 °C, it dissociates to sodium aluminate and sodium silicate, facilitating the alumina extraction. Aluminum hydroxide was recovered by acid leaching followed by precipitation and calcination at 1000 °C to obtain gamma-alumina. The aluminum dissolution increased by incorporating thermal treatment from 5 to 80% in muffle and 89.4% in microwave routes. The acid–base precipitation process resulted in the recovery of ~ 98% dissolved aluminum values in the boehmite phase, leaving the solution with less than 50 ppm Al content suitable for leaching application. Microwave processing was found to be a promising and alternative economical route for the alumina extraction from fly ash.

Graphical Abstract

中文翻译：

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粉煤灰加工过程中氧化铝含量的提取

摘要

粉煤灰是在煤燃烧期间产生的轻质不可燃颗粒。粉煤灰中的氧化铝含量存在于莫来石相中，其高稳定性要求在浸出之前进行替代工艺以转化为反应相。发现用氢氧化钠的机械活化不能令人满意地破坏莫来石结构，而在氢氧化钠热处理期间，莫来石相解离为硅酸钠和铝硅酸钠。低于400°C，会形成羟基钙锰矿，从而导致氧化铝损失，而高于600°C，则会分解为铝酸钠和硅酸钠，从而促进氧化铝的萃取。通过酸浸回收氢氧化铝，然后在1000℃下沉淀和煅烧以获得γ-氧化铝。通过对马弗炉中的热处理和微波途径中的铝进行热处理，铝的溶解度从5％增加到80％，而铝的溶解度增加了89.4％。酸碱沉淀法导致勃姆石相中约98％的溶解铝值回收，使溶液中Al含量小于50 ppm的溶液适用于浸出。发现微波处理是从粉煤灰中提取氧化铝的一种有前途的替代经济途径。

图形概要