Heavy Metal Ions Cu (II), Co (II) and Cr (III) Bifunctionally Improved with Hydroxamic and Amidoxime Groups Chelating Ion Exchangers - WENKERT, R.; MOISA, S.; TOFAN, L.; PADURARU, C. (The Annals of “Dunarea de Jos” University of Galati. Fascicle IX, Metallurgy and Materials Science, 2009)