The gold scraps may be recovered by calcination, electrolysis, pumice , etching, incineration, etc. depending on the material of the substrate. It is now described as follows:
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1. Calcination method: It is suitable for copper and brass gold scrap parts, such as copper Buddha, gods, goldware and so on.
The gold scrap was first coated with a paste of sulfur and diluted with concentrated hydrochloric acid, and then placed in a fume hood for 30 minutes. Then, it was placed in a horse-fee furnace and calcined at a temperature of 700 to 800 ° C for 30 minutes. As a result of this treatment, a layer of copper sulfide and copper is formed between the gold and the base metal to be peeled off from the copper and the brass, and the precipitate is collected, dried, and smelted.
2. Electrolysis method: Suitable for copper scrap metal scrap. The scrap as an anode paste, formulated into concentrated sulfuric acid electrolytic solution, with a lead plate as a cathode current density was controlled at 120 to 180 A / m 2. In electrolysis, to maintain current density, the cell voltage can be gradually increased from 5 volts to 25 volts. Even 50 volts. As a result of the electrolysis, gold is deposited in black to the bottom of the tank; part of the copper mud adheres to the metal surface.
After a period of electrolysis, the electrolyte was diluted with water and heated to boil, allowed to stand for 24 hours, filtered and washed with water. The obtained precipitate was dried, and the ingot was smelted to obtain a crude gold.
3. Pumice method: It is suitable for removing the gold from the large objects, that is, carefully scraping the gold with a pumice block, and removing the gold dust from the pumice block and the object with a wet sponge, and then washing the sponge Gold and pumice powder are mixed into the bottom of the bucket, and the precipitate is filtered, dried, and smelted into crude gold.
4. Etching method: It is suitable to recover gold from gold parts such as gold plaques, gold characters and signboards.
Every 10 to 15 minutes, the wet gold-plated material is etched with a hot concentrated sodium hydroxide solution. When the oil putty and the alkali are saponified, the gold is washed with a sponge or a brush. The washed gold is filtered, dried, and smelted into a crude gold.
5. Incineration method: Suitable for wood, paper and cloth. The waste to be treated paste into the iron pot, carefully burned. After the gold ash is smelted, crude gold can be obtained.