A certain amount of base is usually added during the cyanidation operation to prevent hydrolysis loss of cyanide. However, when the amount of alkali is too high and the pH is too high, the dissolution rate of gold is significantly lowered. This is because at high pH, ​​the reaction kinetics of oxygen is detrimental to the dissolution of gold. In addition, in the presence of calcium ions, when the pH is increased, the dissolution rate of gold is significantly reduced by the formation of a calcium peroxide film on the metal surface (Fig. 1). Figure 1 Blocking effect of calcium ion on gold dissolution rate Numerous studies have shown that the optimum pH for gold cyanide leaching is 9.4. The optimum pH range for actual production operations can be between 9.4 and 10. If conditions permit, the cyanide leaching operation will take the lower limit, and the zinc replacement operation will take the upper limit. The latter pH value will increase the reaction advantage of zinc and water and reduce the consumption of zinc. The corresponding pH values ​​for different potassium cyanide concentrations are listed in the table below. The dissolution rates of gold and silver at different pH values ​​(ie different KOH concentrations) are shown in Fig. 2. It can be seen from the figure that the dissolution rate of the KOH concentration is 0.1 mol ∕L or more. Table The corresponding pH values ​​of various concentrations of KCN solution KCN∕% pH 0.01 10.16 0.02 10.31 0.05 10.40 0.10 10.51 0.15 10.66 0.20 10.81 Figure 2 Effect of pH value of solution on dissolution rate of gold and silver We supply high quality pliers which includes diagonal cutting pliers,long nose pliers, combination pliers, oil filter pliers etc. Wheel Weight Pliers,Stainless Pliers,Combination Pliers, Steel Wrench Ningbo Heyu Tire Repairs Co., Ltd. , https://www.auto-repair-tool.com