The work of recycling gold and silver from waste raw materials has received widespread attention from countries around the world in recent decades. Take the United States as an example. In the early 1980s, there were more than 1,200 companies engaged in the recovery of precious metals such as gold and silver. In 1974, 2,400 tons of regenerated silver was recovered from waste materials, which was 2.28 times that of minerals in that year. Recycled gold is 80.6t, accounting for 5% of the annual gold production. In 1978, 5,660 tons of silver was recovered from scrap and currency, ranking first in the world. There are more than 150 companies that recycle silver from photo-based waste in Japan, and 300-400 tons of silver is recycled every year. In order to reclaim precious metals from used raw materials, Johnson Matthey invested more than $14 million to convert the gold refinery in Brinsdown, England, into a precious metal recycling facility for waste materials in 1977. plant. The plant was commissioned in October 1979. It is the world's largest waste raw material processing plant and the processing center for waste precious metals in the Western world.
Recovering gold and silver from waste raw materials, due to the wide range of raw materials, complex types, and disparity in grades (from tens of percent to 90% or more), in order to reduce processing and reduce production costs, the primary problem Different raw materials are classified according to the shape, type and grade of the materials, so that different treatment methods can be selected according to different raw materials. The main types of gold, silver, and gold and silver-containing waste materials and important treatment methods are summarized in Tables 1 and 2.
Table 1 Types of major silver and silver-containing waste materials and important treatment methods
species | Approach | species | Approach |
X-ray and photo film impression paper | Incineration method | currency jewelry Casting and processing debris Package (overlay) silver metal or alloy Silver plated metal products Silver battery Silver battery | Electrolysis 2. Acid dissolution |
Film, TV copy film factory Scrap | 2. Dissolution method | ||
Electrical switch contact | Electrolysis | ||
Silver solder | 2. Acid dissolution | ||
Telephone exchange device | 3. Slag smelting | ||
Integrated circuit board | After incineration (or drying) | Silver chloride Silver iodide Silver bromide Silver manganese Protein silver | 1. Add zinc and iron to the acid solution 2. Co-melting with soda 3. Ammonia or dimethyl sulfoxide dissolved |
A printed circuit board | Acid or fire enrichment | ||
Electrical appliances, resistance paste | |||
Mirror waste cotton | |||
Silver sulfide | 1. Smelting with soda and iron filings | ||
2. After the nitric acid is dissolved Electrolysis or precipitation | Mirror waste Thermos | Acid dissolution 2. Mechanical brushing | |
Fixer Film factory waste emulsion Plating solution Silver-containing wastewater Silver wash water | Chemical precipitation 2. Electrolysis 3. Replacement 4. Activated carbon adsorption 5. Ion exchange 6. Solvent extraction | ||
Waste silver nitrate | Recrystallization | ||
2. Electrolysis | |||
3. Copper or zinc replacement | |||
4. Chloride ion precipitation | |||
Silver catalyst | Alkali precipitation after acid dissolution | ||
Silver-containing garbage | Flotation | ||
Slag, demolition, Silver smelting | 2. After the crushing and screening, the fire method |
species | Approach | species | Approach |
Jewelry, decorations | 1. Fire enrichment | Platinum rhodium thermocouple wire | 1. Fire enrichment |
currency | Gold platinum spinneret | ||
Casting and processing debris, burrs, plating residues and scrap | 2. Chlorination smelting | Iridium nib | 2. Separation and purification after dissolving aqua regia |
Gold-plated electronic components, devices | 3. Liquid chlorination replacement | Gold, platinum, palladium , rhodium alloy | |
SCR contacts, base plates, Dental sleeves, alloys and plates, coated (overlay) gold metal and Alloy, gold nib | 4. Basket anodic electrolysis | ||
Gold-containing silicon electronic components | 1. Fire enrichment | ||
2. Silicon etchant in addition to silicon | |||
Gold-plated integrated circuit board | Fire enrichment or wet leaching after incineration | Alchemy Refractory lining Optical metal glass Cermet Resistance, capacitor | Classification and smelting after crushing and screening |
Gold-plated printed circuit board | |||
Gold couplet | |||
Gold signboard | |||
Dental plastic | Cyanide solution | 1. Zinc, copper replacement (or ferrous reduction) | |
Chlorinated solution | 2. Activated carbon adsorption | ||
Electroplated anode mud | Fire enrichment or Wet leaching | Wang Shui Liquid | 3. Ion exchange |
Various wash water | 4. Solvent extraction |
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