Roasting gold ores

Roasted gold ore, magnetite, hematite, maghemite, cyanide, passivation, galvanic corrosion, XPS, SEM-EDS... 

The gold ore sample was obtained from Barrick Gold Corp. This was the calcine after roasting of refractory gold ore. In roasted gold ore sample, gold is mainly associated with iron oxides (Figure 1) such as... 

Figure 1 - Fe-oxides identified by SEM analysis from the received roasted gold ore sample Material and Preparation of Electrodes...

Figure 2 - Cyclic voltammetry (CV) of different electrodes (a) Au (pure gold), (b) RGO (roasted gold ore), (c) Mag (magnetite), (d) Hem (hematite) disc electrodes in 0.04 M NaCN solution at pH 10.5 with scan rate of 10 mV/s, argon bubbling onto the surface of electrolyte at 25 °C...

Figure 3- Potentiodynamic cathodic polarization of gold (Au), and roasted gold ore (RGO) with scan rate of 0.166 mV/s at pH 10.5, 100 rpm agitation, atmospheric oxygen, and 25 °C...

Figure 4 - The influence of agitation speed on the galvanic potential (a) and current (b) between gold (Au) and roasted gold ore (RGO) electrodes, pH 10.5,25 °C, cyanide cone. 0.01 M, 25 °C, saturated atmospheric oxygen, Au electrode surface area 0.25 cm2, RGO area 4.9 cm2...

Figure 6 - Galvanic couple potential and ZRA vs. time at 100 rpm agitation, pH 10.5, 0.01 M cyanide cone., saturated atmospheric oxygen, 25 °C, (a) RGO (roasted gold ore electrode 4.9 cm2) and Mag (magnetite disc electrode 4.9 cm2) (b) RGO (roasted gold ore electrode 4.9 cm2) and Hem (hematite disc electrode 4.9 cm2)...

Corrosion potentials of hematite, magnetite, maghemite, and roasted gold ore indicated that they can act as a cathode and could potentially or at least temporarily promote the dissolution of gold in galvanic coupling. 

Bas, A.D., Gavril, L. Ghali, E. (2014). Electrochemical behavior of roasted gold ore (Technical report 2). Submitted to Barrick Gold Corp. p. 70. 

Gold ores can be concentrated by froth flotation, the resulting concentrate being roasted at 600-800°C to oxidize off sulphur and arsenic as their oxides. The product is extracted with cyanide under oxidizing conditions (using either peroxide or air itself) before displacement with powdered zinc. More reactive metals (silver etc.) can be removed by chlorination of molten gold. 

Prior to gold extraction by cyanidation, refractory gold ores are either roasted or pressure oxidized to liberate the gold contained as submicroscopic particles or in solid solution in arsenopyrite and arsenic-rich pyrite. Gold extraction from such ores require roasting or pressure oxidation or bacterial oxidation prior to cyanidation to destroy the sulfide structure. 

Paktunc, D. Kingston, D., Pratt, A., Mcmullen, J. 2006. Distribution of gold in pyrite and in products of its transformation resulting from roasting of refractory gold ore. Canadian Mineralogist, 44, 213-227. 

Tellurium occurs chiefly as telluride in gold, silver, copper, lead, and nickel ores in Colorado. California, Ontario, Mexico, and Peru, and infrequently as free tellurium and tellurite (tellurium dioxide, Te02) The anode mud from copper and lead refineries, or the flue dust from roasting telluride gold ores is treated by fusion with sodium nitrate and carbonate and the melt extracted with water. The resulting solution is acidified carefully with H2S04, whereupon tellurium dioxide is precipitated, and die dioxide reduced to free tellurium by heating with carbon. 

Sources related to current human activities from mobilization of mercury impurities in raw materials such as fossil fuels (particularly coal and, to a lesser extent, gas and oil), other material processing (e.g., cement kilns, waste incineration) and mining of mercury, ore roasting, gold mining. 

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