Which parameter must be monitored at all points in cyanide leaching operations?

• A. pH level
• B. Temperature
• C. Dissolved oxygen
• D. Pressure

Answer: (A)

The key idea is that keeping cyanide leaching operations in an alkaline environment is essential for both safety and effectiveness. Maintaining a high pH keeps cyanide predominantly in the cyanide ion form (CN−), which is necessary for dissolving gold as the soluble complex [Au(CN)2]−. If the pH falls, hydrogen cyanide gas (HCN) can form and escape, creating toxic exposure risk and causing cyanide losses that hurt leaching efficiency. Because this safety and chemistry balance must be maintained everywhere in the process—piles, tanks, solutions, and discharge streams—the pH must be monitored at all points. Temperature and dissolved oxygen matter for reaction rates and stability, but they do not pose the universal, immediate safety/operational constraint that pH does, and pressure is not a primary factor in the continuous monitoring across the leaching system.