Application of manganese oxide minerals to treat acidic waters contaminated with vanadium

Vanadium (V) is both toxic environmental contaminant and a strategically valuable metal, increasingly being released from metallurgical and energy industries. Its high mobility and toxicity under acidic conditions challenge conventional remediation technologies, while its growing demand creates opportunities for selective recovery. This thesis investigated manganese(III/IV) oxides (MnOx) as sustainable, reuseable sorbents for V removal from acidic aqueous systems, combining mechanistic analysis with validation in real industrial wastewater. A systematic comparison of natural, commercial, synthetic, and biogenic MnOx revealed strong contrasts in V uptake that were governed primarily by surface chemistry rather than surface area. Under acidic conditions (pH 3), natural marine MnOx exhibited the highest mass-bassed adsorption capacity (54.0 mg/g), reflecting its amorphous, defect-rich structure and very low point of zero charge. Synthetic MnOx (SynMnO) showed slightly lower uptake (26.0 mg/g) but superior structural stability and reusability, retaining performance over multiple adsorption-desorption cycles. In contrast, commercial crystalline MnOx (ComMnO) displayed limited reactivity due to a lower density of accessible surface sites. Biogenic MnOx produced by the cyanobacterium Synechococcus leopoliensis displayed a distinct adsorption behaviour. Despite its low Brunauer-Emmett-Teller surface area, it achieved the highest area-normalised V uptake (18.1 mg/m2), outperforming abiogenic oxides (0.36 mg V/m2 for SynMnO and 0.77 mg V/m2 for ComMnO). This superior reactivity is attributed to its nanoscale, disordered structure, low point of zero charge (pHpzc = 2.0), and biologically derived surface functionalities, underscoring the importance of defect chemistry and surface composition in acidic conditions. However, the precise role of associated organic matter in stabilising reactive sites or influencing V binding remains equivocal and could not be fully resolved within this study. Application of SynMnO to a real acidic industrial effluent from V2O5 production (pH 2.1, V = 41.1 mg/L, Cr = 454 mg/L, high Cl-/SO42- background) demonstrated rapid and selective V removal, with >95 % V uptake achieved within 1 minute at optimised dosages, while Cr removal was slower and diffusion-limited. Mn loss was negligible (<0.2 %), and sorbent performance was maintained over multiple regeneration cycles, confirming robustness under complex chemical conditions. These results indicate that MnOx can preferentially capture V over competing oxyanions in strongly acidic matrices, enabling the coupling of wastewater treatment with potential resource recovery. Overall, this thesis provides the first systematic evaluation of MnOx for vanadium removal under industrially relevant acidic conditions, integrating abiogenic and biogenic materials with laboratory and real-effluent studies. It establishes surface protonation and defect-rich MnOx domains as key controls on V uptake, while identifying critical knowledge gaps, particularly regarding organic matter–metal–surface interactions—that warrant further investigation. The findings support MnOx, especially biogenic and hydrothermally synthesised forms, as promising platforms for sustainable V remediation and recovery in acidic waters.<p></p>

Author dc:creator

• Peirou Li (21065102)

• manganese oxide
• vanadium
• water contamination

Statement dc:rights

• All rights reserved
• Open Access after 2027-09-16

Identifier

10779/exe.31697368.v1

OAI identifier oai:identifier

oai:figshare.com:article/31697368