Chemical Oxidation of Pyrite by Strong Oxidizing Agents

finely disseminated throughout the matrix of refractory sulfide ores.
To improve the gold extraction, pyrite oxidation is required in order
to destroy the refractoriness behavior. This study investigated the use
of four oxidizing agents, 𝑆2𝑂8
2−, 𝐻2𝑂2
, 𝐶𝑙𝑂4
− and 𝐶𝑟2𝑂7
2−, to oxidize
pyrite. The objective was to enhance the oxidation efficiency of
pyrite by optimizing the pH and reaction time conditions.
Experimental results showed that the most efficient oxidant for pyrite
oxidation was peroxydisulfate 𝑆2𝑂8
2−, and the oxidation efficiency of
iron in pyrite varies in the following order: 𝑆2𝑂8
2− > 𝐻2𝑂2 > 𝐶𝑙𝑂4
− >
𝐶𝑟2𝑂7
2−. The optimum pH for the studied oxidizing agents were pH
= 6 for 𝑆2𝑂8
2−, 𝐻2𝑂2
, and 𝐶𝑙𝑂4
−, and pH = 2 for 𝐶𝑟2𝑂7
2−, for which
the oxidation efficiency reached respectively 76.51%, 20.19%,
16.83%, and 15.40% after 6 hours of reaction. The high oxidation
efficiency of pyrite by 𝑆2𝑂8
2− at pH = 6 is explained by the formation
of sulfate radical (𝑆𝑂4
•−) produced by the activation of 𝑆2𝑂8
2− with
Fe2+ released from pyrite. The mechanistic insights of the studied
oxidizing agents have been elucidated by analyzing the product
species after the oxidation reaction in the filtrate by Fourier
Transform Infrared (FTIR) spectroscopy and characterizing the solid
residue by X-ray diffraction (XRD) and scanning electron
microscope (SEM) coupled with energy-dispersive X-ray
spectroscopy (EDS). The obtained results suggest that 𝑆2𝑂8
2− is a
promising oxidizing agent for the oxidative pretreatment of
refractory pyritic gold ores.