Abstract: In recent years, as the production of alumina in China has sharply increased, the available high-quality bauxite resources have fallen short for alumina in China. Meanwhile, the amount of low-grade bauxite resources, i.e., containing high-sulfur and carbon, with a low aluminum-to-silicon ratio, is underused due to the lack of available technology. The depletion of high-quality bauxite resources and the utilization problem of low-grade bauxite ores have become the main bottlenecks restricting the sustainable development of the alumina industry in China. Therefore, the effective utilization of low-grade bauxite resources is of great significance for the sustainable development of the alumina industry in China. To solve this issue, the present study employed a potential process of sodium nitrate pre-roasting activation coupled with leaching in low-alkali solution for low-grade bauxite. The bauxite and pre-roasted clinker were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), etc. The effects of technical parameters such as the temperature of pre-roasting bauxite alkali leaching, leaching time, and solid-liquid ratio on the leaching of alumina were studied in detail, focusing on the mechanism and kinetics of low-alkali leaching of pre-roasted bauxite. The results showed that after pre-roasting with sodium nitrate, the microstructure of the bauxite became loose, exhibiting a porous and grooved structure. Under the appropriate leaching conditions with a solid-to-liquid ratio of 300 g/L, using a lower concentration of caustic soda solution 160 g (Na2O)/L compared to the traditional Bayer process for 60 minutes at 270℃, 87.22% alumina of the pre-roasted bauxite with an original aluminum-to-silicon ratio of 3.57 was leached, and the aluminum-to-silicon ratio of red mud reduced to 0.88. This method could effectively improve the leaching rate of alumina in the bauxite and overcome the limitation of the theoretical leaching rate of Bayer process. The apparent activation energy for the leaching of alumina in the pre-roasted bauxite was regressed as 23.21 kJ/mol, the leaching process was controlled by mixed mechanisms.

Key words: bauxite, activation, roasting, leaching, kinetics

摘要： 近年来，随着氧化铝产量急剧增加，我国可供开发利用的优质铝土矿资源严重不足，多数为难处理的高硫高碳低品位一水硬铝石型铝土矿，优质铝土矿资源贫化与低品位铝土矿利用问题已成为制约我国氧化铝行业可持续发展的主要瓶颈。因此，低品位铝土矿资源的有效利用对我国氧化铝行业可持续发展具有重要意义。针对这一问题，本工作提出了一种硝酸钠与低品位铝土矿预焙烧活化耦合低碱溶液溶出的新方法。通过扫描电子显微镜(SEM)、X射线衍射(XRD)等技术手段对铝土矿及预焙烧制的熟料进行表征，详细研究了预焙烧铝土矿碱液溶出氧化铝的温度、溶出时间、固液比等技术参数的影响，重点研究了预焙烧铝土矿低碱溶液溶出的机理与动力学。研究结果表明，添加硝酸钠预焙烧后，促使铝土矿的微观结构变得疏松，呈现出孔洞和沟壑结构；铝硅比为3.57的铝土矿经活化预焙烧后，使用较传统拜耳法溶出浓度更低的160 g(Na2O)/L的低浓度苛性碱溶液溶出，在溶出温度为270℃、溶出时间为60 min、固液比为300 g/L的条件下，氧化铝的溶出率可达87.22%，赤泥的铝硅比可降至0.88，该方法能有效提高低品位铝土矿中氧化铝的溶出率，并突破了拜耳法理论溶出率的限制；其动力学研究表明，预焙烧熟料氧化铝溶出的表观活化能为23.21 kJ/mol，其溶出过程为混合控制。

关键词: 铝土矿, 活化, 焙烧, 溶出, 动力学