Herrera, A., 		Bion, H., 		Magpantay, C., 		Quilao, A., 		Balais, W., 		Abarquez, F., 		Pugal, D., 		Yamada, K., 		Takeda, S., 		Tsurue, T., AND 		Ishizaki, K..
" Highly Active Absorbent for SO₂ Removal Prepared from Coal Ash (Part 3)" <em>Philippine Engineering Journal</em> [Online], Volume 20 Number 1 (25 August 2021)