New Sustainable Material for Metal Ions Removal: Adsorption Mechanism and Technological Innovations

In this study, a novel material was obtained by functionalizing shredded maize stalk (MS) with Alizarine Red S (ArS), a complexing agent that contains -OH and -C=O groups in its structure (MS-ArS). The obtained MS-ArS was employed in adsorption studies for Mn²⁺, Pb²⁺, Cu²⁺, Cr³⁺, Zn²⁺, and Fe³⁺ (Mⁿ⁺) removal from mixed aqueous matrices. Initially, complex formation between (Mⁿ⁺) and ArS in buffer solution at pH 4 and 10 was investigated using the UV-Vis spectrometric method. Continuous, the functionalization process of MS with ArS was tested at several pH values (2, 4, 6, 8, and 10) using a batch technique. It was observed that the best functionalization of MS with ArS was obtained at pH = 2. Subsequently, Mⁿ⁺ adsorption onto the MS-ArS mass was tested separately at pH 4 and 10. The study achieved that Mⁿ⁺ adsorption proved to be pH dependent. The results confirmed that at pH = 10, Mⁿ⁺ adsorption was increased, compared with pH = 4. MS-ArS has affinity for Mⁿ⁺ in the following order Fe³⁺ > Cu²⁺ > Zn²⁺ > Mn²⁺ > Pb²⁺ > Cr³⁺. Experimental data revealed remarkable desorption rates when 0.5 M HCl was used. After five adsorption/desorption cycles of Mⁿ⁺, the removal capability of MS-ArS was preserved. Overall, the potential of MS-ArS for effective Mⁿ⁺ removal/reuse makes it a sustainable polymer for wastewater treatment applications.