The present study investigated the capability of magnetite nanoparticles (MNP) synthesized from the direct reduction iron sludge and green tea extract for the single and competitive adsorption of copper (Cu2+) and cadmium (Cd2+). Moreover, we assessed the desorption of Cu2+ and Cd2+ in a ten-day cycle (both single and competitive systems) to evaluate their release amount from the adsorbent's surface. The adsorption process was described using three well-known adsorption isotherms: Langmuir, Freundlich, and Dubinin-Radushkevich. The Freundlich isotherm was employed to describe the desorption process. The maximum adsorption capacity of Cu2+ and Cd2+ by MNP according to the Langmuir curve was 21.24 and 19.36mg/g, respectively. A significant difference was observed in the adsorbed value of heavy metals in the competitive mode and MNP selectively preferred Cu2+ against Cd2+. Results of energy-dispersive X-ray (EDX) and elemental mapping analyses corroborated the Cu2+ and Cd2+ adsorption in both single and competitive systems. The findings of Fourier-transform infrared spectroscopy (FTIR) analysis revealed the role of functional groups in Cu2+ and Cd2+ adsorption. The results of the desorption evaluation demonstrated the higher tendency of MNP to retain Cu2+ than Cd2+. We developed economical and environmentally friendly magnetite nanoparticles, promising in individual and competitive adsorption of Cu2+ from aqueous solutions while resisting to release it. Moreover, the adsorbent’s performance in singular removal of Cd2+ was noticeable.