Equilibrium Study of Cr (VI) Removal from Aqueous Solution by Stalks from Three Tobacco Species (Nicotiana) Grown in Bulgaria. - Prokopov, Tsvetko; Nikolova, Milena; Ivanova, Tanya; Popova, Venelina; Dimov, Milen; Taneva, Donka (Environmental Research, Engineering & Management / Aplinkos Tyrimai, Inžinerija ir Vadyba, 2019)