Abstract (EN):
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 µm, 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.
Idioma:
Inglês
Tipo (Avaliação Docente):
Científica
Nº de páginas:
10