Production and mechanism analysis of clean coal from low-rank coal

There are abundant low-rank coal resources in China. However, its higher AAEMs (alkali and alkaline earth metals) content and the release of AAEMs during combustion cause serious fouling and slagging problems. In this paper, a method of removing AAEMs and ash from low-rank coal to produce clean coal by organic acid leaching was proposed. The leaching effects of four organic acids were compared, the leaching mechanism of citric acid was analyzed, and the removal behavior of AAEMs and ash was investigated. The results show the effect of citric acid is better than others. During the leaching process, the citric acid ionizes H+, which reacts with inorganic minerals of AAEMs, completes ion exchange with AAEMs Organics. Under the relative optimized experimental conditions, the content of Na2O in coal ash is 0.9%, which is in line with the standard of power coal in China. The removal efficiency of alkaline earth metals Ca and Mg are significantly lower than those of alkali metals Na and K. The trend in the removal efficiency of Ca and ash are consistent. Citric acid leaching is an effective and promising method to produce clean coal from low-rank coal.