Gold is soluble in cyanide solutions, which has caused the cyanide leaching meth
ID: 929245 • Letter: G
Question
Gold is soluble in cyanide solutions, which has caused the cyanide leaching methods becoming the dominant form of gold mining these days. Basically, the gold ore is dumped onto a waterproof cement pad and then the cyanide solution is poured on the ore. The cyanide dissolves the gold in the ore and percolates to the bottom of the pad. The solution is collected and the gold removed by electrochemical processes. The cyanide solution is then recycled and poured back on the ore pile and the process repeats itself. The main reaction to dissolve the gold from the ore is:
Au(s) + 3CN(aq) = Au(CN)3(aq).
To increase production of gold, you need to increase the rate gold is dissolved from the ore. What processes might be tried to increase the rate of gold production (or the product yield) in this situation. You may select more than one answer.
Increase the concentration of cyanide in the solution.
Increase the pressure above the solution before Au(CN)3(aq) extration.
Add a powerful reducing agent to donate three electrons back to the gold that is in the Au(CN)3 state.
Remove as much gold as possible from the solution during the electrochemical processing step.
None of the changes listed here will increase the rate of gold production.
Acidify the solution to convert the CN(aq) to HCN(aq).
Increase the concentration of cyanide in the solution.
Increase the pressure above the solution before Au(CN)3(aq) extration.
Add a powerful reducing agent to donate three electrons back to the gold that is in the Au(CN)3 state.
Remove as much gold as possible from the solution during the electrochemical processing step.
None of the changes listed here will increase the rate of gold production.
Acidify the solution to convert the CN(aq) to HCN(aq).
Explanation / Answer
The only answer is to increase the concentration of CN- . If you increase the CN- appling the Le Chatelier's principle the system will reduce the Au concentration at the left of the equation producing more Au(CN)3(aq). In this way you are extracting more gold to be processed by the electrochemical technique.
Au(s) + 3CN(aq) = Au(CN)3(aq).
Acidify the solution will bring the opposite effect because you will be reducing the CN- concentration in the solution.
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