Chromium-Doped Magnetite Nanoparticles for Permanganate Ion Removal: Advances in Environmental Remediation

Iron mines with manganese contamination, as well as manganese mines, are found in various locations worldwide. During manganese ore extraction, permanganate ions (MnO₄ ^-) are released into water bodies, imparting an intense purple coloration that reduces light penetration, which can disrupt photosynthetic processes and negatively impact aquatic life. Additionally, their cytotoxic properties pose severe environmental and health risks. This study investigates the adsorption of MnO₄ ^- onto Cr-doped magnetite nanoparticles (Cr-MNPs) as a potential remediation strategy for contaminated aqueous environments. Cr-MNPs and undoped magnetite nanoparticles were synthesized via the coprecipitation method and characterized using powder X-ray diffraction (XRD), revealing the presence of partially oxidized magnetite phases. X-ray photoelectron spectroscopy (XPS) analysis confirmed the high surface chemical purity of the materials, the presence of trivalent chromium at low concentrations, and the preservation of mixed Fe²⁺/Fe³⁺ surface species characteristic of magnetite, while revealing sample-dependent variations in surface oxygen species rather than a systematic increase in surface hydroxylation upon chromium incorporation. The adsorption process was evaluated by analyzing the effects of adsorbent dosage, contact time, and initial MnO₄ ^- concentration, along with kinetic and isotherm modeling. Equilibrium was reached within 100 min, and experimental data were best described by the pseudo-second-order kinetic model and the Langmuir isotherm, indicating monolayer adsorption on a homogeneous surface. These findings demonstrate that Cr-MNPs are a promising adsorbent for MnO₄ ^- removal, offering an efficient and sustainable solution for mitigating manganese contamination in aquatic environments, achieving a removal capacity of up to approximately 41 mg g^-1.