Contrasting Effects of Catecholate and Hydroxamate Siderophores on Molybdenite Dissolution

Area of Science:

• Geochemistry
• Environmental Science
• Microbiology

Background:

• Molybdenum (Mo) is crucial for enzymes but often unavailable due to mineral sequestration.
• Metallophores are microbial and plant metabolites that enhance metal bioavailability by dissolving minerals.
• The interaction between metallophores and molybdenum-bearing minerals is not well understood.

Purpose of the Study:

• To investigate the effects of catecholate protochelin and hydroxamate desferrioxamine B (DFOB) on molybdenite (MoS2) dissolution.
• To elucidate the mechanisms of metallophore-molybdenite interactions under oxic and anoxic conditions.

Main Methods:

• Molybdenite dissolution experiments were conducted with protochelin and DFOB under varying oxygen conditions.
• Surface and solution analyses using Liquid Chromatography-Mass Spectrometry (LC-MS), X-ray Photoelectron Spectroscopy (XPS), and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS).
• Oxidation states of molybdenite and metallophores were manipulated to understand reaction pathways.

Main Results:

• Protochelin promoted molybdenite dissolution under oxic conditions, forming MoO3 and Mo-protochelin complexes, linked to oxidative degradation of both substances.
• Anoxic conditions prevented protochelin-mediated dissolution, but pre-oxidation of either protochelin or molybdenite enhanced it.
• DFOB inhibited molybdenite dissolution under both oxic and anoxic conditions, attributed to surface adsorption and weak Mo(VI) complexation.

Conclusions:

• Metallophore activity on molybdenite dissolution is condition-dependent, with protochelin acting as a promoter and DFOB as an inhibitor.
• Oxidation plays a critical role in protochelin-induced molybdenite dissolution.
• The study underscores the complex interplay of metallophore structure, environmental conditions, and mineral surface interactions in controlling molybdenum bioavailability.