Abstract
A double refractory gold ore contains gold particles locked in sulphides, solid-solution in arsenopyrite, and preg-robbing material such as carbonaceous matter, and so on. The diagnostic leach test (DLT) and preg-robbing (PR) approaches are widely used to investigate the occurrence and the distribution of refractory gold. DLT serves to qualitatively evaluate the gold occurrences within the ore. Preg-robbing, or the ore’s capacity to fix dissolved gold, is evaluated to determine physical surface interactions (preg-borrowing) and chemical interactions (preg-robbing). The objective of this project is to characterize the refractory gold in Agnico Eagle Mine’s Kittilä ore using the DLT and PRT approaches coupled with mineralogical analyses to confirm testing. The studied material was sampled from the metallurgical circuit following carbon in leach (CIL) treatment at the outlet of the autoclave in order to investigate the effect of the autoclave treatment on the occurrence and distribution of gold. Different reagents were used in the DLT procedure: sodium carbonate (Na2CO3), sodium hydroxide (NaOH), hydrochloric acid (HCl), and nitric acid (HNO3). The final residue was roasted at a temperature of around 900 °C. These reagents were selected based on the mineralogical composition of the studied samples. After each leaching test/roasting, cyanide leaching with activated carbon was required to recover gold cyanide. The results show that gold is present in two forms (native and/or refractory): to a small extent in its native form and in its refractory form as association with sulfide minerals (i.e., arsenopyrite and pyrite) and autoclave secondary minerals that have been produced during the oxidation and neutralization processes such as iron oxides, iron sulfates, and calcium sulfate (i.e., hematite and jarosite), along with carbonaceous matter. The results of DLT indicate that 25–35% of the gold in the tails is nonrecoverable, as it is locked in silicates, and 20–40% is autoclave products. A regrind can help to mitigate the gold losses by liberating the Au-bearing sulphide minerals encapsulated within silicates.
Highlights
The gold from the Kittilä mine is in a refractory form
The particle size distribution is of great importance in the assessment of diagnostic leach and preg-robbing tests
The results obtained for preg-robbing potential are similar to the results found in other sulfide ores where the preg-robbing was driven by sulfide minerals in the presence of free cyanide [41]
Summary
The gold from the Kittilä mine is in a refractory form. The refractory gold is called submicroscopic gold, which refers to atomic gold substituted into the matrix of otherMinerals 2019, 9, 557; doi:10.3390/min9090557 www.mdpi.com/journal/mineralsMinerals 2019, 9, 557 minerals such as arsenopyrite and pyrite [1]. The gold from the Kittilä mine is in a refractory form. It is reported that refractory gold-bearing sulphides are commonly associated with organic carbon (i.e., amorphous and graphite) [2,3,4,5]. The gold ore from the Kittilä mine is associated with carbonaceous matter, which could reduce the gold recovery owing to its sorption potential (preg-robbing phenomena) [6]. The physical (e.g., particle size and specific surface area) and mineralogical (e.g., degree of liberation) characterization of the organic carbon could affect the extraction of the refractory gold [9]. In the Kittilä case, the gold loss associated to carbon prefloat before the autoclave treatment is low because of the lack of the preg-robbing. Any gold losses during flotation would be the result of gold association in the original ore with the prefloat tails
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