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The influencing factors of zinc replacement to deposite gold

2020-11-17 10:07

Introduction:The influencing factors of zinc replacement todepositegold The velocity of zinc replacement is related to temperature.When the temperature is below 10 ℃, the displacement speed will be significantly reduced.Zinc replacement deposit gold i

The influencing factors of zinc replacement to deposite gold

The velocity of zinc replacement is related to temperature.When the temperature is below 10 ℃, the displacement speed will be significantly reduced.Zinc replacement deposit gold is usually carried out at room temperature, and some heat preservation measures are only adopted in winter.
     The cyanogen concentration in the cyanide solution not only affects the consumption of metal zinc, but also affects the rate of gold replacement precipitation and recovery.Metallic zinc dissolves in cyanide solution and precipitates hydrogen:
             Zn+4NaCN+2H2O→Na2n(CN)4+2NaOH+H2
This reaction will increase the consumption of metallic zinc, but the hydrogen generated by this reaction can be combined with the dissolved oxygen in the cyanation solution to generate water, which can reduce the concentration of dissolved oxygen in the cyanation solution and prevent the reverse dissolution of gold and the oxidation of metallic zinc.Therefore, when the alkalinity and cyanide content of your liquid are high, the gold's replacement precipitation rate is higher and the replacement recovery rate is higher.Generally, the zinc powder replacement solution in production is deoxygenated through the deaeration tower, and the cyanide concentration in the solution should be controlled at about 0.02%.Generally, your liquid for zinc wire replacement does not deoxygenate through the degassing column, and the cyanide concentration in your liquid should be controlled higher, generally 0.05% ~ 0.08%.
Copper and mercury ions in the cyanation solution have adverse effects on zinc replacement of gold precipitation, and the reaction can be expressed as:
     Na2Cu(CN)3+Zn→Cu↓+Na2Zn(CN)4+2NaCN
   NaHg(CN)4+Zn→Hg+NaZn(CN)4
This reaction not only increases the consumption of metal zinc, but also produces copper film on the metal surface, which hinders the exchange precipitation of gold and silver.Mercury can be combined with zinc metal to form an alloy, making zinc metal brittle or passivation.
Soluble sulfide in cyanide solution can act with zinc and lead in solution, forming zinc sulfide film or lead sulfide film on the surface of zinc and lead, impeding the replacement precipitation of gold and silver.
Lead ions in cyanide solution can promote the exchange of zinc with gold.Due to the correction of the potential ratio of lead to zinc, lead and zinc can form a galvanic cell. At this time, zinc is anode area and lead is cathode area, and the surface of lead is hydrogenated continuously, while zinc is oxidized and dissolved continuously.Therefore, the lead in the metal zinc can promote the gold replacement precipitation, and the process of gold replacement precipitation can be judged from the hydrogen bubble.If there is no lead in the metallic zinc, since the reduction potential of hydrogen ions is much higher than that of the zinc-cyanogen ions in the expensive liquid, hydrogen bubbles will separate out on the surface of the metallic zinc as long as the zinc dissolves.Hydrogen, which is not combined with oxygen, precipitates on the surface of zinc to produce polarization and prevent the dissolution of zinc.In production, lead acetate or lead nitrate is often added to your solution or zinc wire is put into 10% lead acetate solution for 2 ~ 3 minutes, so that zinc wire lead.When zinc powder is replaced, zinc powder and lead nitrate or lead acetate are added into the mixing tank simultaneously.Adding lead salts to your solution can eliminate the harmful effects of soluble sulfide, but excessive lead salt will lead to increased zinc consumption, delaying the process of gold and silver replacement precipitation and reducing the recovery rate of gold and silver replacement, and lead hydroxide precipitation generated will reduce the grade of gold mud.Therefore, only 5 ~ 10 grams of lead nitrate is added per cubic meter.



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