Trung, Dao. “Research Application of K2CO3 Activated Coal Coal and Processing by HNO3 from Cake Shoulder to Process Methylene Blue Color”. VNUHCM Journal of Earth Science and Environment 4, no. 1 (June 30, 2020): 170-177. Accessed May 18, 2025. http://stdjsee.scienceandtechnology.com.vn/index.php/stdjsee/article/view/534.