(A) Gold and silver in the are are not pure state, but they are alloyed with certain metals, mostly Au-Ag and Ag-S. The proper concentration of cyanide solution for dissolution of gold and silver in these alloyed states was obtained by expeiments as follows:
For Au-Ag alloys containing 10-20% Ag, 0.1-0.2% KCN,
For Au-Ag alloys containing 30-50% Ag, 0.2% KCN,
For Ag-S alloy containing 13% S, 0.35% or more KCN.
(B) To promote the dissolving power of cyanide solution, the writer invented the next improved cyanide process (Japanese Patent No. 127, 164): 0.005-0.5% of bleaching powder to gold are is added to the cyanide solution, the addition of 0.01-0.02% of bleaching powder being most effective for ordinary ores.
The results obtained by the improved cyanide process applied to Au-Ag, Ag-S, Au and Ag are as follows:-
1. The dissolution of Au-Ag alloy containing 10% Ag by 0.10% NaCN solution is remarkably promoted by adding 0.02-0.03% of bleaching powder, but it is interrupted by adding 0.08% or more of bleaching powder.
2. The dissolution of Ag-S alloy containing 13% S by 0.3% KCN solution becomes maximum when 0.03% of bleaching powder is added, but the dissolving power is weakened by adding 0.04% or more of bleaching powder.
3. The addition of bleaching powder up to 0.08% to 0.25% KCN solution does not effect upon the solubility of pure gold, but the addition of bleaching powder more than 0.08% gives bad effects.
4. The dissolution of pure silver by 0.25% KCN solution becomes maximum when 0.02% of bleaching powder is added, but it is weakened by adding 0.08% or more of bleaching powder.
From the above experiments, it may be concluded that the addition of a small quantity of bleaching powder to cyanide solution aids the dissolution of silver and silver alloys such as Ag-Au, Ag-S, etc., and, therefore, this improved cyanide process acts effectively upon the gold and the silver in ores.
The new process was applied to the gold ores of Sizukari, Motikosi and Kamiyosi Mines in laboratory experiments, and the next results were obtained.
The new process was applied to 100 ton plant at Huke, Japan, for the dissolution of flotation concentrate. By the addition of bleaching powder of 0.02% to flotation concentrate into the agitation tank, 99.3% of the gold and 94.4% of the silver were dissolved. The differences of dissolution % before and after the application of bleaching powder are 1.4% in gold and 17.2% in silver.

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