A Kinetic Study on Enhanced Cementation of Gold Ions by Galvanic Interactions between Aluminum (Al) as an Electron Donor and Activated Carbon (AC) as an Electron Mediator in Ammonium Thiosulfate System

The enhanced cementation technique by galvanic interaction of aluminum (Al; electron donor) and activated carbon (AC; electron mediator) to recover gold (Au) ions from the ammonium thiosulfate solution is a promising technique to eliminate the challenges of poor recovery in the system. This study presents the kinetics of Au ion cementation in an ammonium thiosulfate lixiviant as functions of initial Au concentration, size/amount of Al and AC, temperature, and shaking speed. The recovery results basically followed first order kinetics and showed that the cementation rate increased with a higher initial concentration of Au, smaller electron donor size, greater both electron donor and mediator quantity, decrease in temperature, and higher shaking speed in the system, while size of electron mediator did not significantly affect Au recovery.

Effects of Galvanic Interaction between Chalcopyrite and Monoclinic Pyrrhotite on Their Flotation Separation

The galvanic interaction between chalcopyrite and monoclinic pyrrhotite and its effect on flotation separation were studied using monomineral flotation tests, adsorption capacity tests, X-ray photoelectron spectroscopy (XPS) characterization, and scanning electron microscopy (SEM) test. These results showed that the interaction promoted the reduction of O2 on the cathodic chalcopyrite surface and accelerated the generation of Fe(OH)3, which was not conducive to collector adsorption; hence, the flotation recovery decreased by 10–16%. On the other hand, galvanic interaction accelerated the oxidation of S on the anodic monoclinic pyrrhotite surface to S0 or SO42− and produced a large amount of H+, thus preventing the formation of Fe(OH)3. Meanwhile, the Cu2+ eluted from chalcopyrite surface activated monoclinic pyrrhotite; hence, the flotation recovery increased by 3–10%. Galvanic interaction reduced the floatability difference between the two minerals, and the separation difficulty was significantly increased. Even with an increase in the amount of lime, the separation could not be improved.

Local electrochemical behaviour of friction stir welded Mg-Al-Mn alloy joints

Local scanning electrochemical microscopy (SECM), along with a scanning vibrating electrode technique (SVET), were employed to spatially map anodic and cathodic regions in a complex assembly including a friction stir lap welded joint between two Mg-Al-Mn alloys, namely AM60 and AM30. The assembly investigated herein was comprised of the two base materials (AM60 and AM30) and a stir zone (SZ). The transitory electrochemical characteristics of the three regions were perceived from different electrochemical tests and have been correlated to their respective microstructures. Potentiometric and voltametric SECM performed on the assembly in 0.01 M NaCl revealed that during the first few minutes of exposure, AM60 and SZ regions act as dominant anodic regions in the assembly whilst after 2 hours of exposure these regions transition to become cathodic relative to the AM30 region. Galvanic interaction between the different weld regions immersed in a significantly more conductive NaCl electrolyte was investigated by SVET. Under such conditions, filiform-like corrosion initiated, and propagated exclusively within the AM30 region, resulting in cathodic activation of the corroded surface. However, after approximately 5 hours of exposure, the AM60 region preferentially dissolves following sufficient cathodic activation of the AM30 region.