The Kinetics of Pyrite Dissolution in Nitric Acid Solution

Abstract

Refractory sulphidic ore with gold captured in pyrite has motivated researchers to find efficient means to break down pyrite to make gold accessible and, ultimately, improve gold extraction. Thus, the dissolution of pyrite was investigated to understand the mechanism and find the corresponding kinetics in a nitric acid solution. To carry this out, the temperature (25 to 85 °C), nitric acid concentration (1 to 4 M), the particle size of pyrite from 53 to 212 µm, and different stirring speeds were examined to observe their effect on pyrite dissolution. An increase in temperature and nitric acid concentration were influential parameters to obtaining a substantial improvement in pyrite dissolution (95% Fe extraction achieved). The new shrinking core equation (1/3ln (1 − X) + [(1 − X)−1/3 − 1)]) = kt) fit the measured rates of dissolution well. Thus, the mixed–controlled kinetics model describing the interfacial transfer and diffusion governed the reaction kinetics of pyrite. The activation energies (Ea) were 145.2 kJ/mol at 25–45 °C and 44.3 kJ/mol at higher temperatures (55–85 °C). A semiempirical expression describing the reaction of pyrite dissolution under the conditions studied was proposed: 1/3ln(1 − X) + [(1 − X)−1/3 − 1)] = 88.3 [HNO3]2.6 r0−1.3 e−44280/RT t. The solid residue was analysed using SEM, XRD, and Raman spectrometry, which all identified sulphur formation as the pyrite dissolved. Interestingly, two sulphur species, i.e., S8 and S6, formed during the dissolution process, which were detected using XRD Rietveld refinement.

A New Hydrometallurgical Process for Metal Extraction from Electric Arc Furnace Dust Using Ionic Liquids

“…Depending on the mineralogy of materials, a high amount of solid in the leaching solution can sometimes contribute to ineffective mixing within the solution. This is due to the higher-density mixture causing ineffective dispersion and mass transfer within the mixture [ 32 , 33 , 34 , 35 ]. With a high amount of solid in the mixture, the amount of the ionic liquid solution can also be a limiting reagent in the dissolution reaction.…”

A comparison of the electrochemical oxidative dissolution of pyrite and chalcopyrite in diluted nitric acid solution

“…• The previous study by Teimouri et al (2022) [22] showed that when nitric acid concentration is above 2 M, it has powerful oxidative ability to dissolve pyrite.…”

“…(ii) Pyrite dissolves faster in HNO3 than H2SO4, however, the latter is more suitable for chalcopyrite dissolution. This is due to the passive layer formed on chalcopyrite dissolving more readily in H2SO4 than HNO3, although higher potentials are required in H2SO4 (as compared to that in in HNO3) [22,34] (iii) The dissolution kinetics for both pyrite and chalcopyrite is diffusion-controlled in HNO3 and H2SO4. (iv)…”

“…However, a substantial portion of this residual gold is refractory in nature and encapsulated in mostly pyrite particles and to a lesser extent chalcopyrite. A previous paper by Teimouri et al [22] considered the dissolution kinetics of the mine tailings (which contain mostly pyrite) in nitric acid as a potential route to improve the recovery of gold from them. This research aims to examine and compare the mechanism of dissolution of both pyrite and chalcopyrite through investigations of their electrochemical behaviour in 0.5 M nitric acid solution.…”