Leaching of a gold bearing partially roasted sulphide. Laboratory scale studies

Abstract

This research aimed at defining a route for recovering precious metals from a very heterogeneous gold bearing sulphide and arsenide concentrate that was partially roasted and dumped by the 1960s when Santo António mine closed. Gold occurs in this concentrate as free particles in the range of 10-100 mum, most of them still enclosed in the pyrite and arsenopyrite matrix. Its content varies from 20 to 150 g of Au/ton, being higher at the dump upper levels and in the finer concentrate fractions. Preliminary tests demonstrated the refractoriness of this product, since the leaching with conventional cyanide solutions and with other leaching solutions gave very low recoveries. However, high concentrated cyanide solutions recover more than 60% of Au, although with high NaCN and lime consumptions and poor settling characteristics. Iron was shown to be highly dissolved in these solutions. Some prior treatments clearly favoured the cyanidation process, in particular a roasting step. Thus, a large number of roasting experiments was carried out to define the most favourable conditions for recovering gold. However, no clear relationship between roasting conditions and gold dissolution was found due to the heterogeneity of the product and high variance of gold experimental recoveries. These recoveries were calculated considering gold contained in both the leaching residues and leachates, and uncertainties of these results are relatively high. Roasting the product at 450-700 °C for 1 h guarantees a high probability to dissolve at least 74% Au in a highly concentrated NaCN solution stirred for 24 h. The 600-700 °C roasting range is clearly preferable for consuming less cyanide and lime. Pre-washing the roasted product seems not to reduce the cyanide consumption. Regarding the silver recovery, the NaCN and lime consumption are higher while using the products roasted at the lowest tested temperatures. Products roasted at higher temperatures have better settling performance

Rietveld refinement study of pyrite crystals

“…[23,24]. Some pyrite ores include impurities (inclusions) of noble metals (gold, silver) [1,[25][26][27][28] and can be used for gold recovery; pyrite itself is a frequent (harmful) impurity phase in coal [1]. One of studied applications is the soil improvement/amendment [29][30][31].…”

Developed Process Circuit Flowsheet of Al Amar Ore for Production of Nanocrystalline Ferrite and Improving Gold Recovery

“…In agreement with these results, Liu et al stated that gold recovery from roasted sulfidic-ores remained well below the acceptable levels . Although roasting is a common practice for the pretreatment of sulfidic gold ores, it may be insufficient to achieve a satisfactory gold recovery. , This may be due to partial liberation of gold and insufficient contact with the leaching medium.…”

“… 4 Although roasting is a common practice for the pretreatment of sulfidic gold ores, it may be insufficient to achieve a satisfactory gold recovery. 5 , 6 This may be due to partial liberation of gold and insufficient contact with the leaching medium.…”

The Application of Flame Atomic Absorption Spectrometry for Gold Determination in Some of Its Bearing Rocks

“…The optimum temperature stated for sulphide minerals was 650˚C where above this temperature low gold assays was reported, owing to the partial volatilization of gold [29]. Sodium cyanide needed to leach the roasted samples was less than that for the non-roasted ones; beside, its consumption increased for samples roasted at lower temperatures [30].…”