Thermodynamics and precipitation kinetics of lithium carbonate (Li2CO3)

Abstract

The objective of this thesis was to study thermodynamics and precipitation kinetics of lithium carbonate in liquid-liquid and gas-liquid system in a jacketed stirred tank reactor and study the influence of impeller speed, pump flow rate, residence time and ageing for precipitation of lithium carbonate in homogeneous system and gas flow rate, impeller speed, temperature, residence time and ageing for precipitation of lithium carbonate in heterogeneous system as operation variables. Filterability was studied to investigate efficient solid-liquid separation. The result obtained from homogeneous and heterogeneous reactive crystallization were investigated and compared.

Solubility study of Li2CO3 in Li2CO3-Li2SO4-H2O ternary system modeled with Pitzer thermodynamic model indicated the effects of other electrolytes on the Li2CO3 solubility behavior. Mixing conditions such as flow patterns and internal stirring speed were theoretically studied to have efficient mixing and avoid flooding of gas.

The crystals produced from crystallization in heterogeneous system and homogeneous system were characterized with scanning electron microscope (SEM), energy dispersion x-ray spectroscopy (EDS), and X-ray diffraction, particle size distribution. The crystals are mainly Li2CO3 that was identified by using HighScore software. Particles have flower-shape pellets and the size is in the range of 50-100 μm.

Overall, the study clearly shows that crystallization using CO2 gas in gas-liquid system and using Na2CO3 in liquid-liquid system can be used as a feasible way to recover lithium carbonate from lithium sulfate solution. It was noted that the high pH was necessary for the absorption of CO2 gas and to get the maximum crystals in heterogeneous reactive crystallization. In addition, the pH was dependent to the temperature which results difficulty in controlling the pH of the solution, product yield percentage, purity and uniform crystal shape. To predict the precipitation kinetics of Li2CO3, homogeneous reactive crystallization was easier because no pH adjustment required, rapid precipitation and more crystals obtained in less time as compared to the heterogeneous reactive crystallization.