Cation Xanthated Exchangers from Colombian Sub-Bituminous Coals Effectively Removed Cadmium and Lead from Aqueous Solutions - Gómez-De-Arco, Lewis; Alzate-Rodríguez, Liliana; Colpas-Castillo , Fredy; Fernández-Maestre, Roberto (Universidad Autónoma de Nuevo León, 2011)