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Halide Leaching of Gold
Published in Sadia Ilyas, Jae-chun Lee, Gold Metallurgy and the Environment, 2018
Sadia Ilyas, Humma Akram Cheema, Jae-chun Lee
The stability of gold-halide complexes is dependent on the Eh-pH in the solution, composition (with respect to halide concentration), and the nature of ores to be processed (Sergent et al., 1992; Tran et al., 2001). A residual quantity of oxidant must be maintained to keep a high Eh in the solution, avoiding precipitation of metallic gold (Tran et al., 2001). Overall, the stability of halides is in the order of I− > Br− > Cl− > F−, whereas the rate of reaction is F− > Cl− > Br− > I−. Typical conditions used for leaching gold by halogens and their thermodynamic data are listed in Tables 6.1 and 6.2, respectively.
Urban Mining of Precious Metals with Halide as Lixiviant
Published in Sadia Ilyas, Hyunjung Kim, Rajiv Ranjan Srivastava, Sustainable Urban Mining of Precious Metals, 2021
Sadia Ilyas, Humma Akram Cheema, Hyunjung Kim, Rajiv Ranjan Srivastava
The stability of gold-halide complexes is dependent on the Eh-pH of the solution, the composition (with respect to halide concentration), and the nature of the material to be processed (Sergent et al., 1992; Tran et al., 2001). A residual quantity of oxidant must maintain a high solution Eh, avoiding precipitation of metallic gold (Tran et al., 2001).
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Published in Luis Liz-Marzán, Colloidal Synthesis of Plasmonic Nanometals, 2020
Marek Grzelczak, Jorge Pérez-Juste, Paul Mulvaney, Luis M. Liz-Marzán
Characterisation of the crystal structure is mandatory for a better understanding of the growth mechanism. It is well known that the main facets exhibited by the sides of gold nanoprisms are {111}-type facets, and detailed examination of the electron diffraction patterns displayed by the prisms indicates twinning in the [111] direction, perpendicular to the main facets of the nanoprism. This twinning produces convex and concave side crystal facets (see Fig. 6.4), which have different stabilities, and which could provide the driving force for 2D growth. Other driving forces have been postulated based on the differences in surface energies of the growing crystal. This mechanism, known as the silver halide model, was originally applied to silver and gold halide structures, and was investigated in detail by Lofton and Sigmund.6 They suggested that the silver halide model can be applied to fcc structures of gold and silver by considering the formation of twin planes on {111}-type faces, where the stacking fault energy is lower than in most metals, decreasing the energy required to form a twin plane. At the six surfaces where the twin plane terminates, the stacking fault of the twin plane causes {111} faces to form in alternating concave or convex orientations (Fig. 6.4a). On the convex side, an adatom attached to a surface has limited stabilisation energy due to the presence of only three nearest neighbours, so that it can be re-dissolved, thus slowing down the effective growth rate of this surface. On the concave side, where reentrant grooves are created that increase the number of nearest neighbours for an adatom, the stabilisation energy is increased and growth can be faster than on the convex side. This growth ratio causes the concave side to disappear, leaving a triangular prism. This model can explain not only the growth of trigonal prisms but also the evolution of a hexagonal plane structure, if one additionally assumes the presence of a second twin plane rotated 60° relative to the first twin plane. (Fig. 6.4b) The second twin plane leads to the presence of concave facets (re-entrant grooves) on all six sides. This leads to the regeneration of adjacent faces to it, allowing for fast growth in two dimensions.
A review of Preg-robbing and the impact of chloride ions in the pressure oxidation of double refractory ores
Published in Mineral Processing and Extractive Metallurgy Review, 2022
Wei Sung ng, Qiankun wang, Miao chen
Another potential method for processing preg-robbing ores is to use thiosulfate as a leaching agent over cyanide, as the resulting gold thiosulfate complexes have a low affinity for carbon (Gallagher et al. 1990). While a variety of gold leaching agents have been described in the literature, including chloride, bromide, iodide, thiourea, thiocyanate, and mixtures of two or more of the aforementioned lixiviants (Gökelma et al. 2016; Konyratbekova, Baikonurova and Akcil 2015; La Brooy, Linge and Walker 1994), the bulk of these studies has been focused on finding a less toxic replacement for cyanide rather than to tackle the issue of preg-robbing. Similar to gold cyanide, the soluble gold halide and gold thiocyanate complexes are recovered by adsorption to activated carbon, and preg-robbing remains an issue. In contrast, the soluble gold thiosulfate complex formed during the thiosulfate leaching of gold does not adsorb onto carbon; instead, gold is recovered from the pregnant liquor through cementation with copper, resin adsorption, solvent extraction, or electrowinning (Dong et al. 2017).