Selectivity of thiourea dissolved gold

An organic complexing agent is thiourea, which may be combined with various metal ions to generate cationic complex. The following table is the dissociation constant for some metal thiourea complexes associated with thiourea leaching gold.

Table Dissociation constants (pK values) of some metal thiourea complex ions ¹

1 (tu) is an abbreviation for thiourea.

As can be seen from the data in the above table, thiourea has a high selectivity for the dissolution of gold and silver . However, when the raw material contains more mercury , copper and antimony , it will affect the efficiency of dissolving gold and silver in thiourea and increase the consumption of thiourea. The starting material contains more acid-soluble material (iron oxide, carbonate, copper oxide, etc.) and organic matter, should the case were pretreated with acid leaching, roasting or other processing methods remove. If it is a flotation concentrate, remove the drug as much as possible.

Regarding the effect of metal addition on the dissolution rate of gold and silver, CK Chen also added different concentrations of Ni ² in 0.5% H ₂ SO ₄ , 0.1% Fe ^{3 +} and 0.1% to 0.5% SCN ₂ H ₄ solutions at 25 ° C. ⁺ , Cu ^{2 +} , Zn ^{2 +} , As ^{3 +} , Sb ^{3 +} were tested. The results show that under the conditions of advancement, when the concentration of Cu ^{2 +} is higher than 1.0×10 ^-4 , the dissolution rate of gold and silver will be reduced; while other base metal ions can dissolve gold and silver at a concentration of up to 5.0×10 ^-4 . The impact of speed is minimal.

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