Zinc powder displacement of gold is a method of extracting gold. Its processing object is gold-containing precious liquid. Its working principle is to use zinc powder as a reducing agent to displace gold from the precious liquid. In the order of metal activity, zinc (Zn) is more easily oxidized than gold (Au). Therefore, in an acidic environment, zinc can reduce gold ions to metallic gold, and zinc is oxidized to zinc ions. In addition, zinc powder can also be replaced by zinc wire. The replacement principles of the two are the same, and the process flow is also similar. This article mainly introduces the process flow of zinc powder displacement of gold, and the precautions during of the operation.
The process of zinc powder displacement gold mainly includes pretreatment, zinc powder addition, displacement reaction, solid-liquid separation and gold mud treatment, as follows:
1. Pretreatment: Preparation of gold-containing solution, including crushing, grinding, flotation or cyanide leaching, etc., to obtain gold-containing solution, and adjust the pH of the solution, remove impurity ions, etc.
2. Zinc powder addition: Determine the amount of zinc powder according to the gold content in the solution, and add it evenly to the gold-containing solution to ensure full contact.
3. Displacement reaction: Under suitable temperature, stirring intensity and reaction time, after zinc powder contacts with gold-containing solution, zinc will quickly undergo replacement reaction with gold ions to generate metallic gold precipitate and zinc ions.
4. Solid-liquid separation: After the replacement reaction is completed, the solid containing gold precipitate is separated from the solution. Common methods include filtration, thickening and centrifugation.
5. Gold mud process: The gold mud obtained after separation contains a certain amount of impurities, which needs to be cleaned, dried and smelted and purified to obtain high-purity gold.
1. The concentration of cyanide and alkali should be appropriate:
During the operation, the concentration of cyanide and alkali should be controlled within a reasonable range. Because when the cyanide concentration is low, zinc hydroxide and zinc cyanide precipitation will form on the zinc surface, which will hinder the replacement of gold; while when the concentration of cyanide and alkali is too high, it will accelerate the dissolution of zinc, which is conducive to the replacement of gold, but it will increase the consumption of zinc and increase the production cost.
2. Strict deoxidation:
During the operation of zinc powder replacement of gold, deoxidation must be strictly carried out. This is because the presence of oxygen will cause the precipitated gold to dissolve back. Not only that, oxygen will also accelerate the dissolution rate of zinc, increase the consumption of zinc, and produce zinc hydroxide and zinc cyanide precipitation on the surface of zinc, which will affect the effect of zinc replacement of gold. In addition, attention should be paid to airtightness to avoid air leakage affecting the replacement effect.
3. The role of lead salt:
In the replacement process, the main role of lead is to form a "zinc-lead couple" with zinc to dissolve gold. The commonly used lead salts in production are lead nitrate and lead acetate. The presence of lead can accelerate the replacement of gold, but excessive lead will cover the surface of zinc and slow down the replacement speed. If excessive lead enters the gold mud, it will also lead to a decrease in grade. Therefore, the amount of lead salt used in production should be appropriate.
4. Temperature and impurities in the solution:
Increased temperature will accelerate the replacement reaction. When the temperature is lower than 15°C, the replacement rate will be affected. Impurities in the solution include copper, mercury, nickel and soluble sulfides. Copper will produce a thin film on the surface of zinc powder, reducing the contact area; mercury complexes easily react with zinc to form alloys, making zinc brittle; soluble sulfides will react with zinc and lead, and form zinc sulfide and lead sulfide on the surface of zinc and lead. The above impurities will affect the replacement effect.
5. Cleanliness of precious solution (leaching solution):
The cleanliness of precious solution (leaching solution) is one of the important conditions affecting zinc powder replacement. Precious solution (leaching solution) is not allowed to contain suspended matter (mainly ore mud) and oil exceeding the requirements. The oil mixed in the precious liquid will form an oil film covering the surface of zinc, affecting the replacement effect; the presence of mineral mud will clog the filter cloth of the replacement equipment, affecting the replacement operation, and even affecting the quality of gold mud.
The above is an introduction to zinc powder replacement of gold and 5 precautions in the operation process. Only by strictly abiding by the operating procedures can the entire operation process be successfully completed and a better replacement effect be obtained.
