In the manufacture and use of products containing gold, will produce some of the material used or waste products. The gold grade in these waste materials is sometimes much higher than the gold grade in the ore, and the treatment process is relatively simple, and the economic benefits of recovery are significant, so it is the second resource for extracting gold. However, there are many kinds of gold-containing scraps, and their properties and compositions are different. It is necessary to select suitable recycling methods according to different objects and requirements.

1. Recovery of gold from gold-plated scrap

For plated parts with high gold content, gold plating can be removed from the gold-plated scraps before the gold is purified and recovered. There are several ways to remove gold plating:

(1) Lead melting method

The treated gold-plated waste is placed in molten lead liquid to allow gold to penetrate into the lead liquid. Remove the waste parts after the withdrawal of gold, cast the gold-containing lead liquid into a precious lead plate, and then recover the gold from the precious lead by electrolysis or ash blowing.

(2) Thermal expansion method

The difference between the expansion coefficient of the gold and the base alloy is heated to create a gap between the gold plating layer and the substrate. Then, it is boiled in dilute sulfuric acid to completely remove the gold plating layer, and then the gold is dissolved and purified.

(3) Chemical dissolution method

There are many types of deplating solutions, such as iodine -potassium iodide solution, sodium cyanide-m-nitrobenzenesulfonate solution, and the like. The method of dissolving the base alloy by nitric acid may also cause the gold plating layer to fall off and remain in the insoluble matter, and then the insoluble matter may be treated to recover gold.

(4) Electrolysis

The thiourea and sodium sulfite are used as the electrolyte, the graphite is used as the cathode, and the gold-plated waste is used as the anode for electrolytic degreasing. After the anode is oxidized, the thiourea reacts with thiourea to form a complex cation into the solution, which is then reduced to gold by sodium sulfite in the solution, and precipitated at the bottom of the electrolytic cell, and the gold precipitate is separated and purified to recover gold.

2. Recovery of gold from gold-containing waste liquid

According to the chemical composition of waste liquid, gold-containing waste liquid can be divided into gold-plated waste liquid, aqua regia waste liquid and various gold-containing washing water. Generally, the acid gold plating solution contains gold liquid 4 to 12 g/L, the neutral gold plating liquid contains gold 4 g/L, and the alkaline gold plating liquid contains gold 20 g/L, most of which contain cyanide. Aqua regia or iodine corrosion solution in the production of electronic components is one of the main gold-containing waste liquids.

(1) Gold-plated waste liquid

Depending on their composition and may be gold concentration, respectively electrolysis (electrolytic slotted or closed electrolysis tank), zinc powder replacement method, activated carbon adsorption or ion exchange method. After the recovered tail liquid, cyanide should be further processed to meet the emission standards.

(2) Wangshui Corrosion Solution

Recovering gold which is typically a reduction method, including ferrous sulfate reduction, reduction of sodium sulfite, sodium bisulfite or formic acid reduction reduction method. Zinc powder replacement method is sometimes used, but the feed liquid is required to remove nitric acid in advance to increase the recovery rate of gold.

(3) Iodine corrosion solution

The gold can be recovered by a sodium sulfite reduction method. When a saturated sodium sulfite solution is added to the feed liquid, the iodine solution changes from a purple color to a pale yellow color, which is naturally clarified and filtered to obtain a crude gold product.

3. Recovery of gold from gold-containing alloy scrap

Including various electronic components, electrical contacts, circuit boards, couplings, etc., which are discarded in the electronics industry. For example, in the circuit boards produced between the 1960s and the mid-1970s, gold was as high as 0.1% to 0.3%, and the current production of circuit boards contained gold to be reduced to 0.01% to 0.05%. There are many types of alloys containing gold, and the composition varies greatly. For example, there are alloys such as Au-Ag, Au-Cu, Au-Sb, Au-Al, Au-Pt, Au-Pd, Au-Ir, Au-Pd-Ag, and Au-Cu-Ag. The method of treatment is usually carried out by sorting, sorting, grinding and physical treatment, and then performing chemical treatment, including calcination, smelting, initial dissolution and separation, reduction, electrolytic refining and the like. For solid waste with higher gold content, it can be smelted into precious lead and further refined to recover gold. For solid waste with lower gold content, wet treatment can be used, that is, solvent and gold can be selectively dissolved in gold-containing waste, and then separated by solvent extraction, ion exchange, liquid membrane method or activated carbon adsorption. , enrichment and purification, and finally recover gold and other valuable metals from the solution by reduction or electrolysis.

4. Recover gold from gold-containing jewelry waste

Jewelry waste often contains an objective amount of precious metals such as gold and silver , which can be recovered by hydrometallurgical methods. Usually, the thermal degradation treatment is carried out first; then the first stage leaching is carried out with a nitric acid solution to separate silver and other metals; the second stage leaching gold is treated with aqua regia; the gold-containing solution is extracted with a selective solvent of diethyl malonate. Gold; finally, the metal gold product is separated from the organic phase by a reduction method. A typical hydrometallurgy process for recovering gold and silver from gold-containing jewelry waste is shown in the figure below.

Figure Hydrometallurgical process for recovering gold from jewelry waste

      Auxiliary equipment for activated carbon production includes screening equipment, dust removal equipment, packaging equipment, conveying equipment, crushing equipment and drying equipment.