1. The significance of recovering gold from gold-containing scrap
     In the production and action of gold or gold-containing products, a large amount of waste is generated and old products are used. The gold content of these wastes is much higher than that of ore, and the recycling process is much simpler than extracting gold directly from ore. And economically, it is also very cost-effective, so it makes sense to recover gold from it.
     Due to the needs of the development of the national economy, in recent years, all countries in the world have attached great importance to the recovery of gold from waste. In the United States, for example, in 1974, 80.6 tons of recycled gold was 56% of the annual gold output, showing that the economic benefits are considerable.
     2. Classification of gold-containing scrap
     Gold-containing waste can be broadly classified into the following categories:
     (1) Waste liquids: including cyanide waste liquid, chlorinated waste liquid, aqua regia waste liquid, various flushing water and laboratory gold-containing wastewater.
     (2) alloys include: Au - aluminum, gold - silicon, gold - antimony, gold - molybdenum - silicon, gold - B - Pt, Au - B - palladium alloy scrap scrap piece.
     (3) Gold plating: various scrapping components including electroless gold plating.
     (4) Sticking gold: including gold plaques, gold characters, gods, and costumes.
     (5) Dust: including polished ash and waste scraps from the gold pen factory, jewelry factory, gold foil factory, various gold-containing burnt ash (such as chimney ash in the gold-making room), and extremely mud generated from silver nitrate.
     (6) Garbage: including the garbage in the gold-making workshop, the dismantling of the alchemy furnace, and the removal of ancient construction waste with gold-plated and gold-plated parts.
3. Method for recovering gold from gold-containing waste liquid
     (1) Electrolysis method: Electrolysis separates tank electrolysis and closed-cell electrolysis. The principle is to introduce the gold-containing waste liquid into the electrolytic cell, and an ionization reaction is generated near the anode during electrolysis to dissociate the gold and deposit on the cathode.
     The slotting power is released to heat the waste liquid in the container to about 90 ° C, and the stainless steel is used as an electrode to perform electricity at a voltage of 5 to 6 volts. When the gold on the cathode is deposited to a certain thickness, it is scraped off and smelted to obtain a gold ingot.
     The closed cell electrolysis is carried out at a voltage of 2.5 volts. After the gold content in the solution is reduced to the required value, the new gold-containing waste liquid is exchanged for electrolysis until the gold deposit on the cathode is thick. Open the lifting device, scrape the gold mud from the cathode, and smelt the ingot after drying.
     (2) Displacement method: first acidify the gold-containing waste liquid to pH=1~2 with hydrochloric acid and then dilute it with distilled water 5 times (if it is flushing water, it will not be diluted), then replace it with zinc wire until it is completely reacted. Finally, the gold mud is collected, rinsed to neutral with distilled water, treated with sulfuric acid, and dried and cast into ingots.
     (3) Electrowinning method: The electrowinning method is a newly developed technology for obtaining pure gold directly from a solution rich in gold and silver. The electrodeposition tank uses stainless steel as the anode and steel wool as the cathode. Electrodeposition was carried out at room temperature. After direct current was applied, gold was deposited on the cathode, and steel wool deposited on the cathode was immersed in 1:1 industrial hydrochloric acid to remove stainless steel cotton. The treated gold powder is dried and placed in a crucible, and borax (8% to 25%), sodium carbonate (5% to 30%), silicon dioxide (5% to 25%), and appropriate amount of saltpeter are added, at 1200. The smelting at °C for 15 to 25 minutes yields a gold ingot with a purity of 92% to 93%.
     4. Method for recovering gold from alloy parts
     (1) Recovery of gold from gold-platinum (gold-palladium) alloy scrap: gold, platinum (palladium) is insoluble in nitric acid and soluble in aqua regia, after dissolving with aqua regia, separating platinum with NH4Cl, and recovering gold from the solution .
     (2) from the gold - iridium alloy scrap recovery of gold: after heating the alloy scrap with added sodium peroxide (or while adding caustic soda) was melted, poured cast iron plate sheet, the cooling water leaching, at this time a small amount of iridium The sodium salt enters the solution and most of it remains in the leaching residue. Injecting dilute hydrochloric acid into the leaching residue to thermally dissolve hydrazine, filtering the filtrate to pass chlorine gas, and adding saturated ammonium chloride solution to recover hydrazine, treating the slag with aqua regia and reducing the gold in the filtrate with ferrous iron.
     (3) Recovery of gold from gold-bismuth (gold-aluminum) alloy scrap: boiled and dissolved with rare aqua regia (acid: water = 1:3), and then recovered with SO2 gas to recover gold.
     5. Method for recovering gold from gold-plated scrap
     (1) Fire melt back: Fire melt-off i.e. a temperature melting point of lead is 327 deg.] C or more lead-gold extraction, generating expensive lead, then cupellation or electrolysis gold recovery, cupellation is silver and the process of separation of lead Silver method. At this time, gold lead, silver and lead can be mutually melted and gold and silver can form a gold-silver alloy, and the obtained precious lead is added to silver in proportion, so that the precious lead contains both gold and silver. The lead has a lower melting point, and the air is used to oxidize lead into the furnace ash, and then water quenching is performed to obtain gold and silver alloy particles. After the amount is determined by a nitric acid method, the gold powder is melt-cast into an ingot.
     (2) Chemical deplating: First, the deplating solution should be prepared. The deplating solution is a solution obtained by adding 75 g of sodium cyanide and 75 g of sodium m-nitrobenzenesulfonate in 1 liter of water. The gold-plated waste parts are placed in a deplating solution at a temperature of 90 ° C, and the gold plating is deplated in 1 to 2 minutes. If gold is saturated in the stripping solution, the newly prepared stripping solution should be used instead.
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