Experimental study on improving lithium extraction efficiency of salinity-gradient solar pond through sodium carbonate addition and agitation

Abstract

The use of salinity-gradient solar ponds (SGSPs) to extract lithium from carbonate salt brine has expanded their applications beyond thermal extraction and into direct mineral exploitation. SGSPs play a significant role in lithium extraction, but the CO32- concentration will decease significantly after a cold winter, resulting in low precipitation efficiency of lithium in SGSPs. Analyzing the characteristics of the brine in the lower convective zone shows the key causative factors of this reduced extraction efficiency to be the imbalances in lithium carbonate concentration and metastability of the water at low temperatures. In this study, this problem was solved by adding sodium carbonate and agitating the LCZ. First, the proportion of sodium carbonate was determined through experiments and the practicality was further verified using SGSPs. Meanwhile, system changes caused by sodium carbonate in the LCZ were investigated and numerical simulation was carried out for thermal efficiency and salt diffusion process. This study found that the addition of sodium carbonate improved the quality of the brine and the seasonally-induced concentration imbalances between the Li+ and CO32-. By agitating the LCZ, the stable low convection state of the brine was broken, the ions were remixed evenly, and the supersaturation of lithium carbonate was increased. By adding 5 % sodium carbonate to the SGSPs and agitating the brine, the ponds’ average lithium yield was increased by 48.3 %, and the grade of the lithium carbonate was increased to over 80 %. This study enriches the application of SGSPs as an industrial tool for mineral exploitation.