A new look at microbial leaching patterns on sulfide minerals.

Area of Science:

• Geochemistry
• Environmental Microbiology
• Mineralogy

Background:

• Sulfide minerals are crucial in various geological and industrial processes.
• Understanding microbial and abiotic leaching mechanisms is vital for resource recovery and environmental management.
• The role of microbial cells versus inorganic reactions in mineral surface evolution requires clarification.

Purpose of the Study:

• To investigate leaching patterns on pyrite, marcasite, and arsenopyrite using high-resolution scanning electron microscopy (SEM).
• To evaluate the relative contributions of inorganic surface reactions and cell-localized reactions to surface morphology changes.
• To determine the influence of cell type, crystal structure, and mineral dissolution rate on microbially induced pit formation.

Main Methods:

• Experiments involved reacting pyrite, marcasite, and arsenopyrite with iron-oxidizing bacteria (Acidithiobacillus ferrooxidans) and archaea (Ferroplasma acidarmanus).
• Abiotic reactions with Fe(3+) ions were conducted for comparison.
• High-resolution scanning electron microscopy (SEM) was used to analyze surface morphology and pit formation.

Main Results:

• Discrete, cell-sized elliptical pits formed on pyrite surfaces within a week, irrespective of attached cells, suggesting abiotic influence.
• Cell-induced, shallow pits conforming to cell shape were observed on arsenopyrite, but not on marcasite.
• Overall sulfide mineral dissolution appeared to be dominated by Fe(3+) surface reactions rather than cell-mineral interfaces.

Conclusions:

• Attached cells are not essential for pit formation on pyrite.
• Arsenopyrite's higher reactivity facilitated cell-induced pit formation.
• Inorganic reactions, especially with Fe(3+), likely play a more dominant role in overall sulfide mineral dissolution than direct microbial action.