Adsorpsi logam Pb (II) dengan Duckweed (Lemna Perpusilla Torr) yang diimmobilisasi pada nanopartikel oksida besi magnetite = Adsorption of Pb (II) with Duckweed (lemna Perpusilla Torr) that was immobilized on the iron oxide of magnetite nanoparticles / Stephanie Virgana