Wannawek, A., Pookmanee, P., Satienperakul, S., Putharod, R., Laorodphan, N., & Phanichphant, S. (2016). Removable Pb (II) from aqueous solutions by adsorption onto natural and modified leonardite. Engineering and Applied Science Research, 43, 477–479. Retrieved from https://ph01.tci-thaijo.org/index.php/easr/article/view/70839