Mechanism and Modelling of Reactive Crystallization Process of Lithium Carbonate

• Main Authors: Shaolei Zhao, Jie Gao, Siyang Ma, Chao Li, Yiming Ma, Yang He, Junbo Gong, Fu Zhou, Bingyuan Zhang, Weiwei Tang
• Format: Article
• Language: English
• Published: MDPI AG 2019-04-01
• Series: Processes
• Subjects: lithium carbonate; reactive crystallization; crystallization mechanisms; multi-response optimization; response surface methodology
• Online Access: https://www.mdpi.com/2227-9717/7/5/248

The reactive crystallization of lithium carbonate (Li₂CO₃) from lithium sulfate (Li₂SO₄) and sodium carbonate (Na₂CO₃) solutions is a key process in harvesting solid lithium, whether from ores, brines, or clays. However, the process kinetics and mechanism remain poorly understood and the modelling of the reactive crystallization of Li₂CO₃ is not available. Hence, this work aims to determine the kinetics and mechanisms of the nucleation and growth of Li₂CO₃ reactive crystallization by induction time measurements and to model and optimize the crystallization process using response surface methodology. Induction time measurements were carried out as functions of initial supersaturation and temperature using a laser method. It was found that the primary nucleation mechanism of Li₂CO₃ varies with solution supersaturations, in which, expectedly, the heterogenous nucleation mechanism dominates at low supersaturations while the homogeneous nucleation mode governs at high supersaturations. The transition point between heterogenous and homogenous nucleation was found to vary with temperatures. Growth modes of Li₂CO₃ crystals were investigated by relating induction time data with various growth mechanisms, revealing a two-dimensional nucleation-mediated growth mechanism. The modelling and optimization of a complex reactive crystallization were performed by response surface methodology (RSM), and the effects of various crystallization parameters on product and process performances were examined. Solution concentration was found to be the critical factor determining the yield of crystallization, while stirring speed was found to play a dominant role in the particle size of Li₂CO₃ crystals. Our findings may provide a better understanding of the reactive crystallization process of Li₂CO₃ and are critical in relation to the crystallization design and control of Li₂CO₃ production from lithium sulfate sources.