Recover gold from gold industry gold scrap

First, electronic industrial waste containing gold

(1) New waste

New waste generated when manufacturing electronic components and equipment is divided into waste components, boards, burrs, dust, punching chips and cuttings. In addition, due to the manufacturing process, additional precious metal-containing scraps, such as electroplating solutions, filter media, resin pastes and rags, are not real electronic wastes, which are also recovered in precious metal refineries.

(2) Old waste

Old waste is mainly from waste products, but also from the repair, quality upgrade and refurbishment of electronic components, electronic computers and communication equipment. Includes boards, connectors, wires and a different number of additional base metals and plastics.

(3) The content of precious metals

The precious metal content of electronic waste depends mainly on the source of the material and its original use and date of manufacture. From the 1960s to 1973, the production of circuit boards required gold content of 0.1% to 0.3%. Since 1973, the gold content has decreased. The current production of circuit boards requires gold content of 0.01% to 0.05%, usually 1 g of gold in circuit board waste. It will contain 2 to 3 g of silver , and a small amount of palladium (5 g of palladium per 100 g of gold) will appear.

Second, the processing of gold-containing waste

The processing of gold-containing scrap is as follows.

(1) Grinding - physical separation

Grinding is preparation for hydrometallurgy or pyrometallurgy. By magnetic screening, the magnetic portion is usually removed and the non-magnetic portion contains considerable gold and silver. The precious metal in the magnetic part will be lost.

(2) Calcination and smelting

Electronic waste calcination volatile components removed after melting soot, the noble metal ingots into the copper group, which may be a lot of processing all types of waste, the recovery rate is very high, this method outputs copper ingots, then standard electrolytic recovery of copper refining process Finally, the precious metal is recovered from the copper anode mud, and the process from calcination to recovery is mature, but the disadvantage of the method is that the investment required for the process equipment, especially the pollution control equipment is large.

1. Calcination

The precious metal scrap is calcined in a micro-oxidizing atmosphere at a low temperature of about 475 ° C. The soot and flue gas from the burner are burned at 920 ° C in a subsequent combustion chamber with 100% excess air to ensure complete oxidation of all volatiles. The air discharged from the rear combustion chamber is cooled, and the smoke is collected in the dust collector. Typical electronic waste loses about 30% of its weight when burned. Pay attention to the agitation during the burning process to avoid extinguishing the fire. After burning, remove iron and aluminum from the dust and recycle.

2, smelting

Out of the dust calciner and soda, borax together in a rotary kiln or a reverberatory furnace smelting. A flux such as quartz fluorite or saltpeter is added according to the composition of the soot. The purpose of the flux is to dissolve non-metallic components of the soot in a high temperature chemical reaction to form slag and carry away unwanted elements. At the time of melting, the atmosphere of the furnace is kept neutral (a micro-oxidizing atmosphere if iron is present). After the smelting was completed, the temperature of the furnace was about 1149 ° C, and the charge was discharged. The metal and slag are sampled by water quenching during slagging. According to the analysis results, it is determined whether the slag is remelted or discarded. The copper base is prepared for copper refining, and the flue gas cooling of the furnace is returned to the smelting by the collected soot.

3, refining

The ingots from the converter are not suitable for the anode plate for copper refining. Refined by fire, improve the grade of the ingot, and also incorporate copper ingots and other electronic waste before casting the anode plate. During the electrolytic refining of copper, the precious metal enters the anode mud, and the anode mud from the electrolytic cell is first leached to remove the base metal, and then the alloy is produced by smelting. The main component of the alloy is silver, and the silver is recovered by the traditional electrolytic silver method, that is, the nitrate-nitric acid is used. Copper-nitric acid dielectric. Recovering gold and platinum group elements from the silver anode slime electrolytic cell.

Three and five batches of electronic waste processing examples

The first batch of samples were filled boards, broken integrated circuits, cyanide dissolved metal materials and other electronic waste. The results are shown in Table 1.

Table 1 Overview of various electronic wastes

Copper grade (estimated) is 75%. The precious metal lost in the slag; gold 0.12%, silver 0.45%. Precious metals lost in soot: 0.08% gold and 0.41% silver. The treated material weighed 12008 kg.

The second batch of similar results is shown in Table 2. It is an overview of dealing with low-value mixed electronic waste. The composition of this batch is about 50% low-value telephone circuit board with gold-plated contactor removed, 20% of the current waste circuit board, 20% stripped circuit board, 4% of current integrated circuit board, 6% other Electronic waste.

Table 2 Overview of processing low-value mixed electronic waste

The third batch of samples contained a large amount of calculator waste, which included computers from 1970 to 1985 with a recovery rate of 95%. Typical recovery rates recovered from electronic computers are shown in Table 3.

Table 3 Typical recovery rate from processing 45360kg computer host

The fourth and fifth batches were recovered by hydrometallurgical methods.

Chemical leaching, especially the cyanide dissolution of circuit boards and iron, nickel -based products and components, can achieve good recovery. For example, the gold content of the processed circuit board is 0.08% to 0.50%, and the result of dissolving the four batches of scrap is 0.006%, 0.013%, 0.019%, 0.011%, and the average is 0.012% gold, and the recovery rate of gold is 90% to 95%. . Plus valuable metals can be recycled, so it is valuable. However, waste liquid is not easy to sell and handle. Moreover, flue gas scrubbers and wastewater treatment have involved actual investment, and most of their investment is repaid by amortization, so the plan should be compared.

IV. Example of recovering gold from gold-containing scrapped radio diodes

Plastic diodes use a small piece of gold when soldering, about 1g per 100. However, due to the generally low yield of diodes, these gold-containing diodes have also become waste. Many factories have accumulated a lot of time and are useless. It is now recycled in a very simple way. The steps are as follows:

(A) to plastic seal: the diode is placed in a common iron pot, then add concentrated sulfuric acid until the diode is fully immersed, heat the iron pot, stir while heating, and all the plastic seals will be carbonized off.

(2) Washing: Take the tube and rinse it in distilled water until it is black.

(C) copper nitrate to: Wash the stylet placed in a beaker, added at a concentration of 30% to 40% nitric acid, so that both ends of the stylet wire and solder copper is dissolved, the remaining silicon containing gold.

(4) Dissolution of aqua regia: Add aqua regia to the gold-containing silicon wafer, heat to boiling, and maintain for half an hour, while stirring while heating, to prevent localized overheated beaker from rupturing. At this point the gold dissolves in the aqua regia and the silicon remains in the bottom of the cup.

(5) Precipitating gold, adding an excess of ferrous sulfate to the above solution, heating to 70-75 ° C, maintaining 0.5 h, at this time there is reddish brown powdery gold.

(6) Washing and removing impurities: The upper layer waste liquid is removed by a pouring method, and the gold powder is repeatedly washed with distilled water until no sulfate (SO ₄ ^{2 -} ) is formed (dropped with a BaCl ₂ solution until no white precipitate is formed).

(7) Smelting into a block: The gold powder is poured into a quartz crucible and smelted into a molten state at 1200 ° C to pour out, which is a gold nugget.

The electronic waste is first dismantled by hand, hand-selected, then burned, and the precious metal parts are smelted to obtain the maximum recovery of the precious metal. In addition, the base metal is recovered in the form of maximum value. The treatment cost of this method is slightly higher than that of the grinding method, because the labor of disassembly is tight, but by increasing the recovery rate of precious metals, increasing the value of the metal scrap and the waste utilization potential of the secondary utilization components. The compensation obtained is higher than the increased cost.