Element behavior during autoclave oxidation of polymetallic sulfide flotation concentrate containing tungsten and molybdenum

In this paper, we investigate the behavior of associated elements (tungsten, molybdenum, and bismuth) contained in a sulfide gold-bearing concentrate during its autoclave oxidation. The process is studied using a sulfide flotation concentrate, crushed to a particle sieve mesh size of minus 0.045 mm and containing 22.1 g/t of gold, 133.2 g/t of silver, 2.7% of tungsten, 13% of molybdenum, and 0.7% of bismuth. The process was carried out in a 2 dm³ autoclave at a temperature of 220ºC and an oxygen partial pressure of 0.7 MPa. The concentrations of sulfuric acid and iron ions in the solution were determined by titrimetric analysis. Inductively coupled plasma atomic emission spectroscopy was used to determine the concentrations of bismuth, tungsten, molybdenum, copper, silver, and arsenic in the solution, as well as the content of bismuth, tungsten, molybdenum, copper, arsenic, lead, and iron and sulfur forms in the cake. The cake was also examined using diffraction analysis. Experiments on cyanidation of oxidized cake were carried out in the pH range of 10.0–10.5 and a NaCN concentration of 1 g/dm³ with a PuroliteS992 ion exchange resin for 24 h. Autoclave oxidation experiments showed the sulfide oxidation degree to be higher than 99%. Extraction of molybdenum into solution in the form of [MoO₂(SO₄)n]^-(2n-2) and MoO ²⁺ amounted to 95%. The decrease in the solid mass led to an increase in the concentration of bismuth and tungsten in the cake, with their contents reaching 1.66% and 12.7%, respectively. The main phases in the cake were established to be scheelite, anhydrite, plumboyarosite, and bedantite. The extraction of precious metals at the subsequent cyanidation stage amounted to 97.5% of gold and 91.6% of silver. Therefore, autoclave cyanide processing of sulfide gold-containing concentrates leads to a molybdenum extraction in the autoclave oxidation solution at the level of 95%. During cyanidation, more than 90% of gold and silver are extracted. Due to the significant amount of tungsten (17%), bismuth (0.9%), lead (5.3%), and molybdenum (3.3%), the obtained cake cannot be considered a waste product.

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