Growing Mechanism of Polysulfides and Elemental Sulfur Formation: Implications to Hindered Chalcopyrite Dissolution

Abstract

Metal-deficient polysulfides have been argued for a long time to be responsible for the low kinetics of chalcopyrite leaching to extract copper. It has been shown that chalcopyrite surfaces are the source of sulfur that is oxidized to form polysulfides and elemental sulfur. Electronic structure calculations were performed for H x S n x–2 (x = 0, 1, 2 and n = 1...20), aiming to understand the effect of the pH on the growing chains and the formation of elemental sulfur. The estimated pK a1 of the H2S n polysulfides converges from 4.2 (n = 3) to 3.4 (n ≥ 8), and the estimated pK a2 converges from 7.6 (n = 3) to 4.1 (n ≥ 8). The initial steps of the formation of polysulfide chains are more favored for protonated species. The elemental sulfur formation due to the decomposition of polysulfides to form smaller chains is mostly favored for protonated species with n smaller than 12. For larger chains, the decomposition is thermodynamically favored for polysulfides with any degree of protonation. The consequences of these results to the understanding of the mechanism of the chalcopyrite leaching process are discussed with the focus on the pH effect and the formation of elemental sulfur.

Atomic reconstruction and oxygen adsorption behavior of the pyrite (100) surface: a DFT study

“…2(e)). Literature 44 shows that S 2 is prone to polymerization to form polysulfide on the sulfide mineral surfaces. It can be considered that the (Fe–S–S–S–Fe) structure is the configuration of the S4 molecule adsorbed on the ideal surface with Fe as the adsorption site.…”

Leaching of Copper Concentrate with Iodized Salts in a Saline Acid Medium: Part 1—Effect of Concentrations

“…However, despite the wide variety of studies, there is still no clear conclusion on the process of formation and composition of this film. Among the hypotheses found are the formation of elemental sulfur (S 0 ) [ 18 , 19 , 20 , 21 ], disulfides (S 2 2− ) [ 20 , 22 , 23 ], polysulfides (S n 2− ) [ 20 , 24 ], metal-deficient sulfide [ 25 , 26 ], copper-rich polysulfides [ 27 ], and formation of iron hydroxides or jarosites on the surface of the ore [ 28 , 29 ].…”