In cyanide leaching operations, the pH level must be monitored and maintained not lower than which value?

In cyanide leaching operations, the pH level must be monitored and maintained not lower than which value?

• A. 9.5
• B. 7.0
• C. 8.5
• D. 10.0

Answer: (A)

Maintaining an alkaline pH is essential in cyanide leaching because it keeps cyanide in the dissolved CN− form and drastically reduces the release of toxic hydrogen cyanide gas. The minimum pH that should be maintained is not lower than 9.5, so the solution must stay at least at 9.5 or higher. If the pH falls below this level, the balance shifts toward HCN formation, increasing safety hazards and cyanide loss. The other values are either too low to prevent HCN formation (7.0 and 8.5) or simply represent a higher-than-necessary level (10.0) but do not define the minimum threshold that should be maintained.

Maintaining an alkaline pH is essential in cyanide leaching because it keeps cyanide in the dissolved CN− form and drastically reduces the release of toxic hydrogen cyanide gas. The minimum pH that should be maintained is not lower than 9.5, so the solution must stay at least at 9.5 or higher. If the pH falls below this level, the balance shifts toward HCN formation, increasing safety hazards and cyanide loss. The other values are either too low to prevent HCN formation (7.0 and 8.5) or simply represent a higher-than-necessary level (10.0) but do not define the minimum threshold that should be maintained.