Kinetic Study of Ag Leaching from Arsenic Sulfosalts in the S2O32−-O2-NaOH System

In Zimapan, Mexico abundant mineral species have been identified. However, a significant number of these precious metals appear to be related to complex sulfides, as is the case of silver (Ag) in sulfosalts. In this work, a kinetic study of the formation of Ag complexes in the AgAsS2-S2O32−-O2-NaOH system from a Zn concentrate found in the Zimapan mining district was conducted. The kinetic model application on Ag leaching shows a linear adjustment in the valuation of the particle size effect. The rate of formation of Ag complexes is dependent of temperature, leaching agent concentration and OH− concentration. Furthermore, graphical verification of the kinetic models indicates that the kinetics of the formation of Ag complexes correspond to the shrinking core model with chemical controls as the controlling stage. The formation of Ag complexes was confirmed by Fourier transform infrared (FTIR) spectroscopy

Determination of Dissolution Rates of Ag Contained in Metallurgical and Mining Residues in the S2O32−-O2-Cu2+ System: Kinetic Analysis

The materials used to conduct kinetic study on the leaching of silver in the S2O32−-O2-Cu2+ system were mining residues (tailings) from the Dos Carlos site in the State of Hidalgo, Mexico, which have an estimated concentration of Ag = 71 g∙ton−1. The kinetic study presented in this paper assessed the effects of the following variables on Ag dissolution rate: particle diameter (d0), temperature (T), copper concentration [Cu2+], thiosulfate concentration [S2O32−], pH, [OH−], stirring rate (RPM), and partial pressure of oxygen (PO2). Temperature has a favorable effect on the leaching rate of Ag, obtaining an activation energy (Ea) = 43.5 kJ∙mol−1 in a range between 288 K (15 °C) and 328 K (55 °C), which indicates that the dissolution reaction is controlled by the chemical reaction. With a reaction order of n = 0.4, the addition of [Cu2+] had a catalytic effect on the leaching rate of silver, as opposed to not adding it. The dissolution rate is dependent on [S2O32−] in a range between 0.02 mol·L−1 and 0.06 mol·L−1. Under the studied conditions, variables d0, [OH−] and RPM did not have an effect on the overall rate of silver leaching

Influence of Temperature on the Formation of Ag Complexed in a S2O32−–O2 System

Metallic elements of higher economic value, occurring in the mineralogy of Zimapán, are Pb, Zn, Cu, and Fe; said elements are sold as concentrates, which, even after processing, generally include significant concentrations of Mo, Cd, Sb, Ag, and As that can be recovered through different leaching methods. In this work, the influence of temperature in the complexation of silver contained in a concentrate of Zn using the technology of thiosulfate with oxygen injection was studied. Chemical and mineralogical characterization of the mineral concentrate from the state of Hidalgo, Mexico confirmed the existence of silver contained in a sulfide of silver arsenic (AgAsS2) by X-ray Diffraction (XRD). The results obtained by Atomic Absorption Spectrophotometry (AAS) reported abundant metallic contents (% w/w) (48% Zn, 10.63% Fe, 1.97% Cu, 0.84% Pb, 0.78% As, and 0.25% Ag). These results corroborate the presence of metallic sulfides such as pyrite, chalcopyrite, and wurtzite; this last species was identified as the matrix of the concentrate by X-ray Diffraction (XRD) and Scanning Electron Microscopy-Energy-Dispersive X-ray Spectroscopy (SEM-EDS). Pourbaix diagrams were constructed for the AgAsS2–S2O32−–O2 system at different temperatures, which allowed the chemical reaction of leaching to be established, in addition to determining Eh-pH conditions in which to obtain silver in solution. The highest recoveries of the precious metal (97% Ag) were obtained at a temperature of 333 K and [S2O32−] = 0.5 M. The formation of silver dithiosulfate complex (Ag(S2O3)23−) was confirmed by the characterization of the leach liquors obtained from the experiments performed in the temperature range of 298 to 333 K using Fourier transform infrared spectroscopy (FTIR)