Zhengzhou Zhengyang Machinery Equipment Co., Ltd

Waste circuit board precious metal recovery method


Precious Metal Refining Machine
Precious Metal Refining Machine

(1) The gold-containing waste liquid is heated to 80-90°C, and ferrous chloride solution is slowly added under constant stirring. The reaction is as follows;


As the gold ions are continuously reduced, the color of the solution gradually changes from yellow to red, and the gold powder sinks to the bottom. Continue to add excess ferrous oxide solution and let it stand for several hours. Take two drops of the static stratified liquid, add two drops of 1% red blood salt, the color is blue, indicating that the gold has been fully reduced. Pour the clear liquid from the upper part, and filter by suction under reduced pressure, and the lower part is the precipitation of ocher gold powder.

(2) Pickling and water washing: add 1:2.5 hydrochloric acid solution to the gold powder and boil, stir for 5 minutes, pour off the upper solution, repeat this 3-5 times, until it does not appear yellow. Rinse the gold powder several times with distilled water until the pH value of the washed water is about 7 o'clock

(3) Drying: Put the washed gold powder in a drying box for drying to obtain orange sponge granular gold slag.

(4) Melting casting: Place the gold powder in a quartz crucible, heat it to about 1200°C in a high-temperature tubular electric furnace, melt it and inject it into a graphite mold to cast it into a gold ingot. If the gold powder is not blunt, borax can be added when melting, but it is not suitable to use a quartz crucible. The gold powder can be cast in a graphite crucible.


Under good ventilation, pour the waste gold plating solution into a porcelain dish, heat and evaporate until it becomes viscous, dilute it with five times distilled water, and add ferrous sulfate acidified with hydrochloric acid under constant stirring until no more precipitation occurs. . The gold is black and powdery and settles on the bottom of the porcelain dish. The precipitate is first boiled with hydrochloric acid and then with nitric acid, and then washed and dried. It is better if it can be fired at 700-800°C for 30 minutes.

(3) Under good ventilation, use hydrochloric acid to adjust the pH of the spent gold plating solution to about 1. Heat the solution to 70-80°C and add zinc powder under constant stirring until the solution becomes transparent yellow-white and a large amount of gold powder is precipitated. During this process, keep PH=1 or so. The subsequent processing method is the same as (2).

(4) Removal of unqualified gold plating. Unqualified gold plating should be re-plated as much as possible, and only removed when it cannot be saved. Unqualified gold plating on PCB can be removed with alkaline gold removing liquid containing cyanide 50-60g/l. This kind of gold stripping solution has a fast stripping speed and does not damage the nickel substrate. The amount of gold dissolved can reach 25g/l, and the operating temperature is 30-50℃. After the gold has been stripped, the nickel plating can continue to be gold-plated.

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