The Kinetics of Pyrite Dissolution in Nitric Acid Solution

Area of Science:

• Metallurgical Engineering
• Geochemistry
• Chemical Kinetics

Background:

• Refractory sulphidic ores containing gold within pyrite pose challenges for efficient gold extraction.
• Understanding pyrite dissolution mechanisms is crucial for unlocking trapped gold and improving recovery rates.

Purpose of the Study:

• To investigate the dissolution kinetics and mechanism of pyrite in nitric acid solutions.
• To identify optimal conditions for pyrite breakdown and enhance gold accessibility.

Main Methods:

• Pyrite dissolution experiments were conducted varying temperature (25–85 °C), nitric acid concentration (1–4 M), particle size (53–212 µm), and stirring speed.
• Dissolution rates were measured and analyzed using a shrinking core model.
• Solid residues were characterized using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Raman spectrometry.

Main Results:

• Increased temperature and nitric acid concentration significantly improved pyrite dissolution, with 95% iron extraction achieved.
• The dissolution process followed a mixed-controlled kinetics model, influenced by interfacial transfer and diffusion.
• Two distinct sulfur species (S₈ and S₆) were identified as byproducts of pyrite dissolution.

Conclusions:

• Pyrite dissolution in nitric acid is effectively enhanced by higher temperatures and acid concentrations.
• A novel shrinking core equation and a semi-empirical expression were developed to describe the reaction kinetics.
• The study provides critical insights into pyrite dissolution for optimizing gold extraction from complex ores.