E-waste extraction gold technology Gold extraction method
Pyrometallurgy technology is the earliest technology used to extract precious metals from electronic waste, and it is also the most used technology at present. The pyrometallurgical process is simple and easy to operate, and the yield of precious metals can reach more than 90%. However, the energy consumption is large, a large amount of organic matter cannot be comprehensively utilized, the equipment investment is large, and the economic benefit is low, which is far from the requirements for the harmless disposal of electronic waste. Common gold extraction techniques are as follows:
Nitric acid separation method
After preliminary pretreatment of the gold-plated waste, the gold-plated material is put into concentrated nitric acid or dilute nitric acid, the base metal is dissolved by heating, and after filtration, flake-shaped coarse gold is obtained, and then high-quality gold is obtained by purification.
Advantages: Simple operation.
Disadvantages: Strong corrosive acid is dangerous to people, and a large amount of toxic gas is generated during the production process.
Aqua regia dissolution method
This method also applies to the gold plating scrap in 1. Nitric acid and hydrochloric acid are prepared with aqua regia in a volume ratio of 1:3, the gold-plated waste to be treated is put into, and the reaction is finished and filtered, and the obtained solution is an aqua regia solution of gold and other various base metals. After heating to catch the nitrile, a small amount of metal with higher activity than gold is put in for replacement.
Advantages: The method is simple.
Disadvantages: It is difficult to extract a small amount of gold from various metal mixtures, the recovery rate is low, and the working environment is poor.
Sulfuric acid hydrogen peroxide method
The mixed solution of sulfuric acid and hydrogen peroxide is prepared in a certain proportion, put into the gold-plated waste to be treated, filtered to obtain crude gold after the reaction, and further purified to obtain gold of better quality.
Advantages: The treatment liquid is easy to filter and does not produce insoluble metal salts.
Disadvantages: high cost, slow speed, and difficult to handle waste acid.
Sodium cyanide hydrogen peroxide method
Take the aqueous solution of sodium cyanide as the main gold stripping solution, put the gold-plated waste into it, and then slowly add hydrogen peroxide around the gold-plated material until the gold-plated layer is completely peeled off, take out the gold-plated material quickly, and rinse it with water.
Advantages: less damage to the substrate, easy to recycle the substrate. (same as 1 and 2)
Disadvantages: high toxicity, dangerous operation, high cost; drugs are controlled substances and difficult to buy.
Sodium thiocyanate gold stripping method
Sodium thiocyanate, ferrous sulfate, hydrogen peroxide and sulfuric acid are prepared in the ratio of 125:100:25:75 per liter of water, adjust the pH value to about 5.5, the temperature is about 85, and put into the gold plating material at the ratio of 1:5, and heat it to 85 degree, the time is 1-5 hours, and the substrate is taken out and rinsed after completion.
Disadvantages: high cost, complex preparation of gold withdrawal liquid, unstable and slow.
0.1% potassium cyanide + 5% hydrogen peroxide + gold plating waste
Mix PH=9.5 hydrogen peroxide, potassium cyanide, gold plating waste, zinc powder, sulfuric acid, NaOH with NaOH. Iodide Gold Removal The aqueous solution of iodine and sodium iodide is used as gold stripping agent. This method has an ideal gold-returning effect, and has a good effect of non-toxic and normal temperature. It is a promising gold-returning method, but the price of medicines is high, it is more difficult to buy in areas with iodine deficiency, and the cost is extremely high.
Lead soot blowing method
Add a certain amount of coarse silver to the ash dish with dry cement, heat or blow the precious lead with a musket, the melted lead will be slowly absorbed by the ash dish or dry cement, and after the absorption is completed, the alloy of silver and gold can be obtained. The gold and silver are then separated into flakes with nitric acid.
Advantages: less pollution.
Disadvantages: long-term harm to people, easy to cause lead poisoning.
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