Lithium activation pretreatment mechanism and leaching process from coal fly ash

Abstract

As a result of the coal combustion process, high lithium enrichment in fly ash has been observed in some areas of China, which is considered to be a potential unconventional lithium resource. At present, most of the studies on lithium in fly ash focus on the leaching process, while there are fewer studies on the activation mechanism of roasting. In view of the above problems, the roasting activation mechanism of fly ash in the Pingshuo mining area (northern China) is investigated, and the leaching process of lithium is optimized. The activation pretreatment that destroys an inert composition of fly ash is necessary. In this study, fly ash and a mixed roasting agent (Na2CO3 and K2CO3 mass ratio of 3:1) were mixed at a mass ratio of 2:1 under 950 °C for 2 h. The results showed that the leaching rate of lithium increased by 70%. Direct acid leaching experiments show that 90% lithium in fly ash is related to insoluble aluminosilicate minerals. The mineralogical analysis of the calcined product shows that the stable aluminosilicate minerals in fly ash disappear and form nepheline KNa3(AlSiO4)3 which is soluble in acid, and the percentage of nepheline in the roasted product controls the leaching rate of lithium. The kinetic analysis of the acid leaching process of the roasting product shows that the lithium leaching process is mainly controlled by chemical reactions. Under the optimal leaching conditions, the leaching rate of lithium is 87.41%.