Spodumene being a major source of lithium, extraction of lithium from this mineral has attracted significant attention with the main aim of reducing the economic cost of the extraction processes. Generally, lithium is extracted from spodumene by converting the α-spodumene to β-spodumene at high temperatures followed by roasting β-spodumene in the presence of concentrated sulphuric acid.. However, in response to climate change and mitigation measure on energy conservation as well as the trend of cost minimization, different heating technologies have been applied to improve the acid roasting process. Thus, the microwave has been identified as a potential source of alternative energy following its success in other applications such as coal processing.
Murdoch University researchers; Nasim Salakjani (PhD candidate, Professor Pritam Singh and Professor Aleksandar Nikoloski from the Department of Engineering and Energy recently investigated the use of microwave oven in acid roasting process of lithium extraction and compared it with conventional furnace heating. Specifically, they evaluated the effects of very key parameters such as temperature and concentration levels. Their work is currently published in the research journal, Minerals Engineering.
The research team observed that conventional acid roasting of β-spodumene for lithium extraction was highly effective at 250°C for 60 minutes in the presence of 80% excess concentrated sulphuric acid. Additionally, a complete lithium recovery was achieved with 20s of microwave irradiation. Furthermore, it was necessary to investigate the potential of reducing the amount of required excess acid by grinding the sample to reduce the particle size. Here, a complete recovery was observed with only 15% of excess acid.
When the sample was exposed to microwave irradiation for longer than 20s, a reduction in lithium extraction was noted. For instance, the lowest extracted lithium value was recorded as 42% after 240s of the microwave irradiation. These effects were attributed to the mechanism of heating and reverse reaction of lithium and hydrogen ions. Furthermore, the heating energy consumption of the microwave and conventional muffle furnace was evaluated and compared. For the sample percentage of lithium extracted from the β-spodumene, conventional muffle furnace heating consumed 10.4MJ which was significantly higher than microwave energy which only consumed 15.4kJ.
Microwave energy exhibited several advantages as compared to conventional muffle heating processes. For instance, it is a cleaner and environmentally friendly process that can be extended to various processing applications. In addition, it consumes less energy and thus more efficient. This was attributed to the fact that significant time required for the muffle furnace interior to reach the target temperature, unlike the microwave oven where the sulphuric acid heats in a very short time to reach the reaction temperature. Furthermore, it was worth noting that the reduction in the amount of acid required by microwave heating reduces the overall production cost.
In summary, Murdoch University scientists conducted a thorough study comparing the lithium extraction process using microwave heating and conventional heating methods. Whereas conventional methods are commonly used, microwave oven proved a potential alternative method with increased efficiency in terms of cost reduction, less energy consumption and less impact on the environment.
Salakjani, N., Singh, P., & Nikoloski, A. (2019). Acid roasting of spodumene: Microwave vs. conventional heating. Minerals Engineering, 138, 161-167.Go To Minerals Engineering