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different leaching kinetics. When gold is directly exposed to the surrounding phase it has a fast leaching kinetic. On the other hand, gold attacked through ore porosity, like in heap leaching, exhibits slow dissolution kinetics. Figure 1 shows four different classes of gold, each one having a different leaching behaviour. One can see that gold
CYANIDATION IN GOLD PROCESSING ALTERNATIVES TO CYANIDE IN GOLD PROCESSING THIOSULPHATE LEACHING Thiosulphate leaching is a process that removes gold from gold bearing ores without the use of cyanide. Although not as aggressive a leaching agent as cyanide, thiosulphate offers several technological advantages including its lower toxicity
#0183;#32;Gold mostly concentrates in highsulphidation systems at 300 #176;C at low pH (lt;2) and high log f(O 2)(28). For example, the concentration of Au in the vapor phase is ppb at pH = 2 and log f (O 2 ) = 28 ( Archibald et al., 2001 ).
The lower limit of oxidation potential varies with pH but is a minimum of about V occurs between pH 4 and 9. Leaching gold with thiosulfate, however, was found to be sensitive to the concentration of copper, thiourea, and temperature of the solution. The relationship between gold dissolution and copper concentration is complex and involves
lower pH values2. Lcysteine increased goldcyanide bi osorption of Bacillus, PenicilliulIl, and SargassumlR At pH 2, the max imum gold uptakes were g Au/kg OW fo r bacteri a, g/kg fo r fungus, and g/kg fo r seaweed, or 150250% greater than in the absence of cysteine. The anionic gold cyanide species were
If further leaching of gold by cyanidation or the chloridehypochlorite method is assumed, then the process is carried out in a relatively neutral medium: at a pulp pH above For the neutralization resulting from the oxidation of the reactions (1) and (4) of sulfuric acid, the cheapest reagent is used limestone and / or soda.
A gold leaching process by using oxidation products of elemental sulfur in alkaline solutions was proposed and investigated. A gold concentrate and a residue from an arsenic refractory gold
Lime sulphur synthetic solution (LSSS) method was applied in gold concentrates leaching. The effect of mass ratio of sulphur, lime and water and synthetic time on sulfur conversion rate and pH
#0183;#32;Sulfur (surface) oxidation to sulfate proceeds through the formation of an intermediate SOH species followed by the formation of thiosulfate, sulfite and finally sulfate .The bulk disulfide is not directly oxidised, however there may be transfer of electrons from the bulk disulfide to surface Fe 3+ .This leads to the formation of electrondeficient disulfide which may rearrange to form
sulfur lowers ph in gold leaching HFC Refrigerants (55) HST Hydraulic Cone CrusherHST series hydraulic cone crusher is combined with technology such as machinery, hydraulic pressure, electricity, automation, intelligent control, etc., representing the most advanced crusher technology in the world.
solution also contains polysulfide, it is likely that this species is the oxidant for gold leaching. The potential of the sulfide / polysulfide system can be conveniently represented by an EpH diagram. A metastable EpH diagram for sulfur in alkaline solutions was generated using the StabCal thermochemistry package (Huang
received attention and new rate equations expressing the gold leaching are still developed. The effect of leaching parameters on gold cyanidation is studied in this work in order to optimize the leaching process. A gold leaching model, based on the wellknown shrinkingcore model, is presented in this work. It is proposed that
The optimal pH range for the most common types of bacteria used in gold bioleaching range from 1 to 2. 2 [2]. The pH should be closely monitered and lime or acid should be added accordingly. Redox is the oxidationreduction potential for a given leaching environment.
sulfide solutions be recovered. As shown in Figure 3, gold is soluble in the alkaline sulfide system. Gold lixiviation is the result of leaching by polysulfides and sulfides as shown in equation 8. 2Au + S2 2+ 2S2 2AuS+2S2(8) Figure 3. Equilibrium Species EhpH Diagram for Sulfur and Alkaline Sulfide Gold
As shown in Figure 1, when the gold electrode was submerged in the /L thiosulfate solution, the observed peak at V is mainly related to the oxidation of thiosulfate to form polysulfides, and this was confirmed by related research. 11, 22, 23 In the gold thiosulfate leaching, both gold dissolution and thiosulfate oxidation occur during the anodic process.
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