Extraction of Lithium from Spodumene by Alkali fusion

Abstract

The most common process of extracting lithium from spodumene is the sulfuric acid roasting process. In this process, spodumene is roasted with sulfuric acid at 250 °C followed by leaching with water to extract lithium in the solution. However, this process is preceded by a calcination step at a temperature of over 1000 °C to transform α–spodumene to β–spodumene before the roasting stage. This calcination step consumes a large amount of energy. Many studies have been conducted to develop a novel process for extracting lithium from spodumene, however, most studies only dealt with β-spodumene formed after the transformation stage. Only a few studies made use of α-spodumene.

Hence, in this study, lithium was extracted from α-spodumene directly without the phase-transformation at temperature over 1000 °C. For this process, the alkali fusion method was chosen because it is the typical pre-treatment method for silicate minerals. This study is divided into two parts: (1) sodium hydroxide (NaOH) fusion, (2) sodium carbonate (Na2CO3) fusion. Experiments were conducted at various conditions to determine the optimum condition for extracting lithium.

In the NaOH fusion test, the optimum fusion conditions were 600 °C fusion temperature, 60min fusion time, and 1.5:1 NaOH/sample ratio

furthermore, the leaching conditions were 5min leaching time and 25 °C leaching temperature. The extraction efficiency of lithium under these conditions was 63.88%.

In the Na2CO3 fusion test, the fusion temperature was fixed at 850 °C. At this fusion temperature, the optimum fusion conditions for were 60 min fusion time and 1:1 Na2CO3/sample. The leaching conditions were 5 h leaching time and 1.5 M sulfuric acid concentration. The results of the sodium carbonate fusion test under these conditions show that 99.98% of the lithium in the samples was extracted. However, all the silicon and 75% of the aluminum in the sample was extracted along with lithium. After leaching with 1.5M hydrochloric acid under the same fusion conditions, the lithium extraction was lower than sulfuric acid. However, it was possible to remove silicon and aluminum by adding Na2CO3 into the leachate.

In summary, the optimum fusion and leaching conditions were investigated to extract a high percentage of lithium from spodumene by the alkali fusion method. The results show that almost of the 100% lithium in the samples was extracted with Na2CO3 fusion and sulfuric acid leaching. However considering impurities, the optimum conditions were using 1.5M of hydrochloric acid in the leaching stage followed by removal of Si and Al by adding Na2CO3. This experiment was conducted at a lower temperature than that of the existing processes with no phase-conversion stage. Therefore, it is a better process in terms of the energy consumption and simplicity of the process.