Common Methods for Separating Gold and Silver：

Chemical dissolution method: Gold can be dissolved in hydrochloric acid, while silver reacts with Cl⁻ ions to form a silver chloride precipitate during the dissolution process. After filtering, gold and silver are separated.

Aqua-regia solution method: Suitable for alloys with low silver content (silver typically below 10%), this method allows both gold and silver to dissolve. However, after dissolving, silver reacts with Cl⁻ ions to form a silverCommon Methods for Separating Gold and Silver chloride precipitate, enabling it to be separated from gold.

Chemical separation of gold and silver:

Using a single acid, it cannot dissolve gold but can dissolve silver, achieving the separation of gold and silver. Hydrochloric acid or sulfuric acid is commonly used. This method is typically used for gold-silver alloys with a gold content below 30%, while silver, copper, iron, and zinc can be dissolved in hydrochloric acid or sulfuric acid, whereas gold cannot. After filtering and washing, it can obtain gold with over 98% purity. For lead-containing alloys, hydrochloric acid is used for dissolution

Alloy gold: Alloy gold produced by roasting mercury paste on a mercury plate, alloy gold produced by melting gold paste in a converter, alloy gold produced by melting gold paste after removing impurities with nitric acid, alloy gold obtained by pyrometallurgical or hydrometallurgical treatment of copper lead anode paste, and other alloy gold produced in other gold and silver mines and rare and precious plants for non-ferrous metallurgy.

The gold content is 40%~99.9%, and the silver content is 40%~99.9%.

Extraction of Gold From Gold Mud:

Gold mud and heavy sand: about 3% of heavy sand selected from equipment such as zinc powder replacement gold mud, gold loaded carbon analytical electrolysis gold mud, gold loaded carbon incineration ash, Nielsen or shaker.

Gold content 5%~40%, silver content 5%~40

Copper wire (or copper chips) heating displacement method is used to recover gold：

Cyanide-containing solutions generally employ the copper wire (or copper chips) heating displacement method to recover gold. Additionally, for high-gold content plating waste solution, electrolytic methods can be employed to recover gold. 

For low-gold content solutions and rinse water, activated carbon adsorption and ion exchange adsorption methods are used to recover gold.

The cyanide-containing gold-bearing waste solution employs the zinc (or aluminum) displacement method (using zinc wire or powder) for gold recovery. Before the displacement process, zinc powder is first immersed in a 5%10% lead acetic acid solution for 35 minutes. 

Then, an amount of 810 g/L of zinc powder (chips) is added to the cyanide plating waste solution. The displacement process is continued for 10-15 days, with stirring performed once every 2 days, and zinc powder added once every 4-5 days.

To accelerate the reaction, heating or adding lead acetic acid catalyst can be employed. After the displacement is complete, the clear solution is removed, and the precipitate is treated with a 20% nitric acid solution for several minutes, then allowed to settle with the clear liquid repeatedly to obtain pure gold powder. 

The electronegativity of aluminum is greater than that of zinc. Using aluminum for the displacement of gold in cyanide solutions involves the same operations as with zinc, but the solution should be heated to 50-60°C for optimal results.

Sulfate Gold Ammonia Plating Waste Solution Utilizes pH Adjustment Technique for Gold Recovery：

The sulfide gold ammonia ion complex [Au¹(NH₃)₂(SO₃)₂]³⁻ is stable at a pH of 8~9 in solution and can be employed for electroplating gold. When the pH decreases, it decomposes into gold ions, sulfide ions, and ammonia; the sulfide ions facilitate the reduction of gold ions to metallic gold.

This method employs sulfuric acid adjustment to lower the pH to 2~3, thereby reducing gold into gold powder, which is subsequently filtered and washed for recovery.

Methods for Recovering Gold from Gold-Containing Waste Liquids:

Gold-containing waste liquids include electroplating waste liquids, which mainly consist of cyanide plating waste solutions and sulfuric acid gold plating solutions, as well as nitric acid waste solutions, chloride waste solutions, and various gold-containing wash waters. Electroplating waste solutions typically contain higher levels of gold, with acidic gold plating waste solutions commonly having 4~12 g/L of gold and alkaline gold plating waste solutions reaching up to 20 g/L.

Recycling Principle: The principle of recycling is based on electrochemistry, where gold ions dissolved in water are converted into metallic gold ions at the cathode, forming solid gold deposits.

Operation Method: A cyclic electroplating process is used. The water level in the tank is kept relatively low to minimize carryover to the next tank, aiming for higher recovery rates.

Recycling Efficiency: Achieves over 98% efficiency. In online cyclic recycling, levels can be maintained between 5-30 ppm, while offline single-recycling processes can reach as low as 0.5-10 ppm.