Chemical Oxidation of Pyrite by Strong Oxidizing Agents: For Pretreatment of Refractory Pyritic Gold Ores

Pyrite is considered the major gold-bearing, in which gold is often 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, S_2 O_8^(2-), H_2 O_2, 〖ClO〗_4^- and 〖Cr〗_2 O_7^(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 S_2 O_8^(2-), and the oxidation efficiency of iron in pyrite varies in the following order: S_2 O_8^(2-) > H_2 O_2 >〖 ClO〗_4^- > 〖Cr〗_2 O_7^(2-). The optimum pH for the studied oxidizing agents were pH = 6 for S_2 O_8^(2-), H_2 O_2, and 〖ClO〗_4^-, and pH = 2 for 〖Cr〗_2 O_7^(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 S_2 O_8^(2-) at pH = 6 is explained by the formation of sulfate radical (〖SO〗_4^(•-)) produced by the activation of S_2 O_8^(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 S_2 O_8^(2-) is a promising oxidizing agent for the oxidative pretreatment of refractory pyritic gold ores.