Study of the optimization of the stereo-crystallization process with enhanced salinity-gradient solar pond for lithium extraction from Zabuye salt lake in Tibet

In recent years, the rapid development of new energy vehicles and energy storage technology, driven by the new energy industry, has led to rapid growth in lithium consumption. China has abundant lithium resources, especially in salt lake brine. Zabuye salt lake is the only salt lake in Tibet that has achieved the industrial development of lithium carbonate by using the lithium extraction technique with salinity-gradient solar pond (SGSP) so far. In this paper, the stereo-crystallization process is innovated and optimized based on an enhanced SGSP with nucleation matrix. The optimal processing parameters such as the structure design of the nucleation matrix, the spatial range of underutilized heterogeneous nucleation zone (UHNZ), and the appropriate area ratio of crystallization units have been obtained by experiments. The results show that the UHNZ should be about 0.80–2.00 m from the bottom of the pond, when the total depth of water body in the solar pond is controlled within 2.80–3.30 m and the thickness of the freshwater layer is between 0.30 and 0.60 m. For the best precipitation effect of lithium carbonate, it is suggested that the height of lower nucleation matrix (LNM) in the crystallization unit should be controlled above the height of about 0.80 m from the bottom of the pond, and the area ratio of crystallization units should be about 10%, when implementing the stereo-crystallization process. In 2022, the stereo-crystallization process with the enhanced SGSP has been fully promoted and implemented in Zabuye mining area of Tibet, increasing the output and grade of lithium concentrates significantly.