| Cementation was investigated to recover gold and silver from the acidic thiourea solution with zinc, aluminum and iron powders. The results showed that the zinc powder was not of practical use in acidic solution because of the great consumption of zinc and thiourea decomposition, while aluminum and iron powders were substantially effective in practical aspects in comparison with zinc. Iron was found to be the most effective precipitant due to its little consumption and low cost. The dissolved oxygen becomes detrimental to cementation of precious metals in acidic thiourea solution. When the oxygen was expelled by introducing nitrogen gas, the fast cementation was carried out effectively with the decrease of metal consumption as cementing agents. In the cementation with iron powder, the activation energy of gold and silver were 4.4 ㎉/㏖ and 13.1 ㎉/㏖, respectively. Accordingly the reaction was controlled by mass transfer for the cementation of gold and by surface chemical reaction for the cementation of silver. |
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