Gradiation grafted sulfonic acid membrance for removal of heavy metal ions from aqueous solutions / by Hamdani Saidi, 1953-, author, Mohamed Mahmoud El-Sayed Nasef, author, Zaini Ujang, Prof. Dato' Ir. Dr., 1965-, author, Khairulzaman Mohd. Dahlan, author, International Conference on Membrane Science & Technology (7th: 2009: Kuala Lumpur)