The majority of rare earth elements (REEs) in coal fly ash (CFA) are associated with the aluminosilicate glassy phase, hindering their solubility in the acid leaching process. In this study, a sequential chemical roasting, water leaching, and acid leaching process was developed for the recovery of REEs from CFA. The effect of several roasting additives on the transformation of CFA phases into water or acid soluble phases was first studied. The reaction conditions for chemical roasting were selected based on a thermodynamic analysis. The selected reaction conditions were then validated experimentally. NaOH and Na₂CO₃ were the most effective additives to break the glassy phases to sodium silicate and sodium aluminosilicate, which can then be readily dissolved in water or acid. The reactions with NaOH was found to be spontaneous at ambient temperatures, while the reactions with Na₂CO₃ were spontaneous at elevated temperatures. Water leaching was very effective for the dissolution of the sodium silicate product, removal of the majority of silica, and for turning the glassy phases into a porous structure. As a result, mass transfer limitations were reduced, and acid could easily diffuse into the particles, dissolve the majority of remaining, and extract REEs along with other elements such as Al. This process significantly enhanced the REE recovery to 79% and 89% using NaOH and Na₂CO₃ roasting, respectively, compared to 20% REE recovery in baseline acid leaching.

粉煤灰（CFA）中的大多数稀土元素（REEs）与硅铝酸盐玻璃态相相关，从而阻碍了它们在酸浸过程中的溶解性。在这项研究中，开发了顺序化学焙烧，水浸和酸浸工艺，以回收CFA中的REE。首先研究了几种焙烧添加剂对CFA相转变为水相或酸溶相的影响。基于热力学分析选择化学焙烧的反应条件。然后通过实验验证所选的反应条件。NaOH和Na ₂ CO ₃是最有效的添加剂，可将玻璃相破碎成硅酸钠和硅铝酸钠，然后可以轻松溶于水或酸中。发现与NaOH的反应在环境温度下是自发的，而与Na ₂ CO ₃的反应在升高的温度下是自发的。水浸对于硅酸钠产品的溶解，去除大部分二氧化硅以及将玻璃相转变为多孔结构非常有效。结果，减少了传质限制​​，并且酸可以容易地扩散到颗粒中，溶解大部分残留物，并与其他元素（如Al）一起萃取REE。使用NaOH和Na _2可以大大提高REE的回收率，分别达到79％和89％与基线酸浸中20％REE回收相比，分别进行了CO ₃焙烧。