PCB circuit board electroplating waste liquid precious metals
In the long run, comprehensive utilization of land and investment in PCB electroplating waste liquid can save money and reduce costs Various chEMIcal products are used for PCB electroplating The waste liquid produced by these chemICal products, after comprehensive utilization and treatment, is a useful raw material for chemical production. Once discharged from the production process, it becoMES the most harmful substance The comprehensive utilization of PCB electroplating waste liquid is not only to reduce the loss caused by discharge, but also significant from the perspective of preventing pollution and reducing the cost of sewage treatment
Precious metal recovery technology PCB electroplating waste liquid
Gold recovery rate
Gold is the most chemically stable metal. It has good decoration, corrosion resistance, wear resistance, color change resistance and high temperature oxidation. It also has low contact resistance and excellent welding efficiency. Because its output is very SMAll, when using it, we must consider how to maximize its content with the minimum amount.
1. Recycling process:
(1) Pickling and water washing: add 1:2.5 hydrochloric acid solution to the gold powder, boil, stir for 5 minutes, pour out the upper layer of solution, and repeat for 3 to 5 times until it is not yellow. Rinse the gold powder with distilLED water several times until the pH value of the rinsing water is about 7
(2) Heat the waste liquid containing gold to 80 to 90 ℃, and slowly add ferrous chloride solution with constant stirring. The reaction is as follows:;
Au3++3Fe2+==3Fe3++Au
As the gold ions decrease, 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 stand for several hours. Take two drops of static layering solution and add two drops of 1% red blood salt. The color is blue, indicating that the gold has been completely reduced. Pour the clear liquid from the upper part, vacuum suction filtration, and the lower part is the ochre gold powder precipitation.
(3) Melting and casting: put the gold powder into a quartz crucible, heat it to about 1200 ° C in a high temperature tubular electric furnace, melt it, inject it into a graphite mold, and cast it into gold ingots. If the gold powder is not blunt, borax can be added when melting, but quartz crucible is not suitable. Gold powder can be cast in graphite crucible.
(4) Drying: put the cleaned gold powder into the drying box to dry, and obtain orange sponge shaped granular gold slag.
Circuit board

2. With good ventilation, adjust the pH value of the waste gold plating solution to about 1 with hydrochloric acid. Heat the solution to 70-80 ℃, 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 treatment method is the same as (2).
3. Under the condition of good ventilation, pour the waste gold plating solution into the porcelain plate, heat and evaporate until it is viscous, dilute it with five times distilled water, stir continuously, and add ferrous sulfate acidified by hydrochloric acid until it does not precipitate, until it precipitates. Gold is a black powder, deposited on the bottom of the porcelain plate. The precipitate is first boiled with hydrochloric acid, then with nitric acid, and then washed and dried. It is better to burn at 700-800 ℃ for 30 minutes.
4. Removal of unqualified gold plating Unqualified gold plating shall be re plated as much as possible and can only be removed when rescue is impossible Unqualified gold plated PCB can be removed with alkaline gold solution containing 50~60g cyanide/l This gold stripping solution is fast and will not damage the nickel substrate The amount of gold dissolved can reach 25g/l The operating temperature is 30-50 ℃

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