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The iodine-assisted heap leaching of chalcopyrite involves the addition of iodide in ferric sulfate media to accelerate the dissolution of chalcopyrite at ambient temperature. The previous studies using reactor leaching tests identified the solution potential, the amount of iodide added, and temperature as the factors controlling the process performance. In the present study, the iodine-assisted chalcopyrite leaching process was scaled up from reactors to 1-m and 6-m columns to further understand how these parameters control the process performance at a larger scale. This is essential to optimize the process in industrial-scale heap leach pads. The HeapSim-2D model was calibrated with the 1-m and 6-m column leach tests together with the kinetic parameter values obtained in the previous reactor leaching tests. When the iodine-assisted chalcopyrite leaching was scaled up from reactors to 1-m and 6-m columns, the leaching became slower because the ore used in the column leaching tests had larger particle sizes with partially-liberated chalcopyrite particles. The calibrated model was then used to carry out the sensitivity analyses to assess the response of the process performance to key design and operating variables, including irrigation rate, ferric concentration, total iodide concentration, temperature, and heap height. The analyses show that the copper extraction could be optimized by adjusting these key design and operating parameters. • The iodine-assisted chalcopyrite leaching was slower at a larger scale. • Conventional ferric sulfate leaching prevailed at insufficient ferric levels. • The slower leaching was attributed to partial liberation of chalcopyrite particles. • The HeapSim 2D model was calibrated with the 1-m and 6-m column test results. • Copper extraction could be optimized by adjusting key design and operating parameters. [ABSTRACT FROM AUTHOR]

Uranous sulfate x -hydrate will thermally decompose into uranium oxide at high temperature, releasing SO 2 gas that can be recovered as sulfuric acid. The recovered acid can be recycled back to the prior hydrometallurgical crystallization step, thus offsetting the net acid consumption of the process while at the same time producing a more readily marketable oxide product. A thorough understanding of the thermal decomposition pathways of the various uranous sulfate x -hydrates is critical to the proper design of such a calcining process. The thermal decomposition pathways of uranous sulfate tetra-, hexa-, and octahydrate, including decomposition temperatures and intermediary products, were determined theoretically using thermodynamic data, and then verified experimentally using thermogravimetric analysis. All three hydrates were found to proceed through similar stages of decomposition: multi-step water loss, oxidation to uranyl sulfate, and finally decomposition to U 3 O 8 . These thermal events were observed to occur at markedly different temperatures for each of the hydrates, suggesting that differences in structural arrangement play a role in thermal stability. A decomposition mechanism is proposed based on theoretical and experimental data, and an explanation for the different behaviours of the three hydrates based on structural differences is postulated. [ABSTRACT FROM AUTHOR]

The addition of iodide has been found to significantly accelerate chalcopyrite leaching in ferric sulfate media at ambient conditions. Solution potential is the principal factor determining the leaching performance through controlling the iodine speciation. In order to develop a kinetic equation that incorporates the iodine speciation, a series of leaching tests were carried out in specially-designed sealed reactors that allows the solution potential together with other leaching parameters to be fully controlled. The experimental results showed that the rate of copper dissolution was increased by increasing the solution potential in the range of 669 to 769 mV vs. SHE), increasing the total iodide concentration in the range of 50 to 200 mg/L, and increasing the temperature between 25 and 40 °C. The formation of elemental sulfur and jarosite did not hinder the leaching reaction. A kinetic model was developed that relates the rate of copper extraction to the solution potential with a reaction order of 0.32, the diiodine concentration with a reaction order of 1.17, and temperature with an activation energy of 43.1 kJ/mol. The kinetic analysis supported that the leaching process was controlled by surface chemical reaction. • Iodine presence in ferric sulfate media enhanced chalcopyrite leaching kinetics. • Solution potential was the primary factor determining the leaching kinetics. • Effect of temperature manifested itself only at sufficiently high redox potential. • Iron precipitates and elemental sulfur do not hinder the dissolution reaction. • Kinetic modelling supported that the leaching was controlled by chemical reaction. [ABSTRACT FROM AUTHOR]

Chalcopyrite leaching at moderate temperature exhibits slow kinetics due to surface passivation. The presence of iodine has been reported to significantly enhance copper dissolution from chalcopyrite in ferric sulfate media at ambient temperature. However, the key factors controlling the reaction rate and the mechanisms have not been well understood. This study quantified the effect of different parameters on the kinetics of copper extraction in the presence of iodine and elucidated the possible rate-limiting steps. A series of leaching tests was carried out in PTFE (polytetrafluoroethylene) bottles with high chemical resistance to investigate the effect of solution potential (673–769 mV vs SHE), total iodide concentration (50–200 mg/L), particle size (53–90 μm), and temperature (25–45 °C) on chalcopyrite concentrate leaching. PTFE bottles were used to prevent iodine loss via evaporation and iodine corrosion of the experimental apparatus. The experimental results show that redox potential was the principal factor determining the leaching performance via controlling the aqueous iodine speciation. In the potential range where triiodide or diiodine dominates, the copper extraction increased with increasing potential, increasing total iodide concentration, and increasing temperature. Particle size did not affect the kinetics, possibly resulting from the narrow size ranged used. A preliminary kinetic model shows that the reaction orders with respect to Fe(III)/Fe(II) concentration ratio and the total iodide concentration were 0.36 and 0.91, respectively. The activation energy (47 kJ/mol) was significantly lower than those reported for the conventional chalcopyrite leaching in ferric sulfate media, suggesting that the presence of iodine changed the reaction mechanism. Further investigation is required to uncover the exact role of different iodine species in the leaching process. • Iodide addition in ferric sulfate media enhanced chalcopyrite leaching kinetics. • Solution potential was the primary factor determining the leaching kinetics. • Effect of temperature manifested itself only at sufficiently high redox potential. • Triiodide and diiodine were the active species responsible for chalcopyrite leaching. • Kinetic modelling supported that the leaching was controlled by chemical reaction. [ABSTRACT FROM AUTHOR]

Uranous sulfate is known to crystallize from uranium(IV) sulfate solutions upon the addition of sulfuric acid and the application of heat. This phenomenon, when coupled with a prior reduction process, could be exploited as a new way to selectively separate uranium from impurities in a high-grade leach solution. In the present work, the selectivity of uranous sulfate precipitation in the presence of the impurities Al, Cu, Fe, and Ni is demonstrated. A process employing this concept, including electrolytic reduction, precipitation, washing, drying, and calcining, has been tested on the bench scale from beginning to end, demonstrating that the process is technically viable. [ABSTRACT FROM AUTHOR]