Sewwandi BGN, Vithanage M, Wijesekara SSRMDHR, Mowjood MIM, Hamamoto S, Kawamoto K. Adsorption of Cd (II) and Pb (II) onto Humic Acid–Treated Coconut (Cocos nucifera) Husk. Journal of Hazardous, Toxic, and Radioactive Waste. 2014;18(2):04014001.