Browsing by Author "Anwar Ul Haq, Rana"

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Lithium Carbonate Precipitation by Homogeneous and Heterogeneous Reactive Crystallization
(2020-08-01) Han, Bing; Anwar Ul Haq, Rana; Louhi-Kultanen, Marjatta
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Lithium carbonate precipitation from a Li2SO4 solution in a stirred crystallizer in semi-batch processes was investigated and compared using a heterogeneous CO2 reaction and homogeneous Na2CO3 reaction. Nucleation and crystal growth were successfully monitored by an inline Particle Track based on the focused beam reflectance measurement technique. The results obtained indicate that the particle size decreased with an increase in mixing speed for both precipitation processes. However, the CO2 feed rate in the heterogeneous reaction and the pumping rate of Na2CO3 in the homogeneous reaction did not have a significant impact on the particle size distribution. Temperature and the final pH play critical roles in precipitation when using CO2 as a reactant. High alkaline conditions are needed to induce heterogeneous precipitation. The lithium recovery with homogeneous precipitation was higher than with heterogeneous precipitation, probably due to the gas-liquid mass transfer phenomena of absorption influencing carbon dioxide conversion to carbonate ions in heterogeneous precipitation. Agglomerates of leaf-shaped primary crystals were mainly obtained.
Thermodynamics and precipitation kinetics of lithium carbonate (Li2CO3)
(2019-10-22) Anwar Ul Haq, Rana
Kemian tekniikan korkeakoulu | Master's thesis
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.