The tailing liquid or tailing salt resulting from the lithium extraction process of ores (lepidolite and spodumene) contains significant quantities of strategically important elements, including lithium, rubidium, and cesium. Currently, there is a lack of cost-effective recycling methods for these strategic elements. In this study, a comprehensive solvent extraction separation process was developed to achieve the efficient and synergistic recovery of rubidium, cesium, and lithium from lithium tailings derived from ore processing.
Firstly, 4-tert-butyl-(α-methylbenzyl)phenol (t-BAMBP) was employed as the extraction agent to extract cesium under low alkalinity conditions (approximately 0.05 mol/L OH⁻). Through the optimization of the extraction-scrubbing-stripping process, efficient recovery of cesium was achieved, resulting in high-purity cesium salt products. In the process amplification tests conducted using mixing-settling extraction tanks and centrifugal extractors, the cesium recovery rate exceeded 96%, and the purity of the cesium chloride product reached over 99.4%. A synergy extraction system, consisting of a substituted phenol and an organic phosphoric acid extractant, has been developed to achieve cesium extraction without alkali consumption. This system is anticipated to be applicable for the separation of cesium from salt lake brine systems characterized by low cesium concentrations and high calcium and magnesium contents.
Rubidium salt could be further separated by increasing the alkali concentration of the raffinate following cesium extraction, with t-BAMBP extractant employed and process conditions optimized. Through amplification verification of the mixing-settling extraction tanks, the recovery rate of rubidium reached 93%, while the purity of the resulting rubidium salt product exceeded 99%. By employing specialized resin adsorption, organic compounds (primarily component t-BAMBP) dissolved in the high-basicity rubidium extraction residual solution could be effectively recovered. This approach facilitated the recycling and reuse of the dissolved extractant, thereby reducing production costs and minimizing potential environmental risks.
The tail liquid resulting from rubidium extraction process contains a notable amount of lithium and alkali as well as significant quantities of alkali metals, including sodium and potassium. The discarding of this tail liquid would not only lead to the wastage of valuable resources but also pose potential environmental concerns. Therefore, we have developed an extraction system capable of selectively separating lithium from liquid feedstocks with high alkalinity and significant sodium and potassium content. This system exhibits high lithium selectivity and excellent acid and alkali stability. After multistage countercurrent extraction, the extraction efficiency of lithium could exceed 99.5%, while the separation coefficients of lithium-sodium and lithium-potassium reached 5000 and 20000, respectively. A range of high-purity lithium salt products could be produced through various impurity scrubbing and stripping processes. Specifically, the sulfuric acid process enables the production of lithium sulfate with a purity exceeding 99.9%, while the hydrochloric acid process yields lithium chloride at a similar purity level. Additionally, the carbonic acid stripping process produces battery-grade lithium carbonate with a purity greater than 99.5%. Lithium chloride or lithium sulfate enrichment liquid derived from the extraction process could also be used to prepare battery-grade lithium carbonate product through reaction-crystallization with sodium carbonate. Furthermore, lithium hydroxide products could be obtained via the bipolar membrane electrolysis process. This lithium extraction system enables the efficient recovery of lithium and, when integrated with various subsequent processes, facilitates the production of diverse high-purity lithium salt products. Consequently, this system demonstrates significant potential for widespread adoption and application.
This systematic research has offered a viable solution for the efficient recovery of rubidium, cesium, and lithium resources from the tailing liquid of the lithium extraction process from ores. We will continue to endeavor to optimize the process, minimize costs, enhance product quality, and anticipate that our research findings will be translated into large-scale production applications.