Abstract In the present study, we investigate the kinetics and mechanism of the leaching of calcium aluminate slag in Na2CO3 solution for alumina recovery. The slag consists of leachable phases, e.g., 12CaO·7Al2O3, CaO·Al2O3, 5CaO·3Al2O3, and a non-leachable phase that contains Ca-Al-Si-Ti oxides. A series of leaching treatment is done at different temperatures, leaching times, stirring rates, Na2CO3 concentrations, and different setups which includes wet-grinding and shaking-digestion reactor. The highest alumina recovery up to 90.5% is obtained after the slag is leached by 10 wt% Na2CO3 solution, at low temperatures (30–45 °C) within 90 min. It is shown that the rate of alumina recovery is high at the beginning of leaching and is then slow down due to the calcite layer product nucleation and growth at the surface of slag. The wet-grinding leaching and vigorous stirring increase the possibility of the collision between both particles and the stirrer that breaks the calcite layer, yielding less residue agglomeration and better recovery compared to the slow and mild agitations. A surface observation of the slag using electron microscopy shows that the calcite starts to nucleate at the non-leachable phase as the best deposition site, which has the least mass transfer barrier in the system. The apparent activation energy of the leaching reaction is calculated as 10.8–19.9 kJ/mol, which indicates the reaction is diffusion rate-limited as revealed by the applied kinetic models.

中文翻译：

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铝土矿冶炼还原氧化铝回收渣浸出动力学及机理

摘要 在本研究中，我们研究了在 Na2CO3 溶液中浸出铝酸钙渣以回收氧化铝的动力学和机理。炉渣由可浸出相组成，例如 12CaO·7Al2O3、CaO·Al2O3、5CaO·3Al2O3，以及包含 Ca-Al-Si-Ti 氧化物的不可浸出相。一系列浸出处理在不同温度、浸出时间、搅拌速率、Na2CO3 浓度和不同设置下完成，包括湿磨和振荡消化反应器。用 10 wt% Na2CO3 溶液浸出炉渣后，在低温 (30–45 °C) 下 90 分钟内，氧化铝回收率最高可达 90.5%。结果表明，氧化铝回收率在浸出开始时较高，然后由于方解石层产物在渣表面成核和生长而减慢。湿磨浸出和剧烈搅拌增加了两种颗粒与搅拌器之间发生碰撞的可能性，从而破坏了方解石层，与缓慢和温和的搅拌相比，产生更少的残留物结块和更好的恢复。使用电子显微镜对炉渣的表面观察表明，方解石在不可浸出相处开始成核，这是系统中传质障碍最小的最佳沉积位置。浸出反应的表观活化能计算为 10.8-19.9 kJ/mol，这表明反应是扩散速率限制的，如所应用的动力学模型所示。与缓慢和温和的搅拌相比，产生更少的残留物结块和更好的恢复。使用电子显微镜对炉渣的表面观察表明，方解石在不可浸出相处开始成核，这是系统中传质障碍最小的最佳沉积位置。浸出反应的表观活化能计算为 10.8-19.9 kJ/mol，这表明反应是扩散速率限制的，如所应用的动力学模型所示。与缓慢和温和的搅拌相比，产生更少的残留物结块和更好的恢复。使用电子显微镜对炉渣的表面观察表明，方解石在不可浸出相处开始成核，这是系统中传质障碍最小的最佳沉积位置。浸出反应的表观活化能计算为 10.8-19.9 kJ/mol，这表明反应是扩散速率限制的，如所应用的动力学模型所示。