Recovery technology of precious metal from electroplating waste liquid of PCB circuit board

In the long run, PCB plating waste liquid in the comprehensive utilization of investment, can save money to reduce costs. PCB plating using a variety of chemical products. The waste liquid produced by these chemical products is a useful material for the chemical industry, and once it is discharged from the production process, it becomes the most harmful substance. The comprehensive utilization of PCB plating waste liquid is not only to reduce the loss caused by discharge, but also very meaningful to prevent pollution and reduce the cost of sewage treatment.


Gold recovery


Gold is one of the most stable metals in chemistry. It has the advantages of good decoration, corrosion resistance, abrasion resistance, color resistance and oxidation resistance. Because of its very low yield, it is necessary to consider how to maximize its properties with the least amount of time.


Recovery process:

(I),

(1) the gold containing waste liquid is heated to 80-90 DEG C, and the ferrous chloride solution is slowly added under stirring;


Au3++3Fe2+==3Fe3++Au:

With the continuous reduction of gold ions, the color of the solution changed from yellow to red. Continue to add excessive ferrous oxide solution, static for several hours. Take the static stratified liquid two plus 1% drops, two drops of red, blue, gold that has been completely reduced. Go down the upper clear liquid, pressure filtration, the lower soil yellow gold precipitation.

(2) pickling, washing: add: 1: 2.5 hydrochloric acid solution into the gold powder, boil, stirring for about 5 minutes, pour the upper solution, so repeated for 3 or 5 times, until the yellow. Rinse gold powder with distilled water several times, until the pH value of water is about 7

(3) drying: the washed gold powder is placed in a drying box for drying, and the orange sponge granular gold residue is obtained.

(4): casting gold powder in the quartz crucible, in high temperature tube furnace heated to 1200 DEG C, melted in graphite mold cast ingots for injection. If the gold powder is not blunt, melting can be added borax, but not suitable for the use of quartz crucible, the gold powder can be placed in the graphite crucible melting.

(two),

In good ventilation conditions, the waste liquid is injected into the gold plating porcelain dish, heating evaporation to viscous, diluted five times with distilled water, acidified with hydrochloric acid before adding ferrous sulfate under continuous stirring, until now no longer precipitation. Gold presents a black powdery precipitate at the bottom of the porcelain dish. The precipitate was first prepared with hydrochloric acid, then boiled with nitric acid, and then dried. If you can bake for 30 minutes at a temperature of 700 to 800.

(three) under the condition of good ventilation, the PH=1 of the waste gold plating solution was adjusted with hydrochloric acid. The solution is heated to 70-80 deg.c zinc powder under continuous stirring, until the solution becomes transparent white, there are a lot of gold powder was settling down so far. In this process, keep around PH=1. The subsequent treatment method is the same as (two).

(four) the removal of unqualified gold plating, unqualified gold plating should be as far as possible plating, only in the case can not be saved when the retreat. PCB unqualified gold coating can be removed with the basic gold removal solution containing 50 60g/l. This kind of gold plating solution is fast and does not damage the nickel matrix, the amount of gold can be up to 25g/l, after the operation temperature of 30--50 DEG C, the nickel plating can be continued after the plating.


Silver recovery


Silver is also one of the precious metals, silver recovery of the waste liquid method is as follows:

The waste liquid with 20% sodium hydroxide to adjust pH value between 8-9, and then add sodium sulfide solution, so that the formation of silver sulfide precipitation;

2Ag++Na2S==Ag2S:: +2Na+

(2) water washed silver sulfide precipitate to residual sulfide, filtered water, the silver sulfide in the crucible, heating to 800-900 DEG C for desulfurization, remove the cooling.

(3) to 100 (weight) silver slag, add borax 10, sodium chloride 5 mix and then burning to crude silver crucible.

(4) dissolve the crude silver with nitric acid, make it into a silver nitrate solution, and then use activated carbon to decolorization and filtration.

(5) when the filtrate is concentrated to the precipitation of silver nitrate crystals, the absorption and filtration method is used to precipitate all the silver nitrate. Finally, the crystal of silver nitrate in the dryer after drying, you can use. If the purity of the silver nitrate is not high, the purity can be improved by multiple crystallization.


Copper recovery


(1) recovery of copper from copper containing waste liquid containing no chelate.

The addition of excess iron in copper containing waste liquid, temperature control solution of 30--50 C, 1 hours after the reaction reaction to remove iron, copper, filtering, washing and baking to obtain the replacement of copper powder, the purity is more than 99%.

(2) recovery of copper from copper containing waste liquor containing chelating agent.

In copper containing waste liquid, adjust pH to 11 or more, more than the amount of calcium hydroxide added copper ions, while stirring the solution, generating, filtering, washing, hydroxide precipitation. The amount of sulfuric acid is added to the precipitate and then evaporated. Take out the crystal, and then get the copper sulfate crystal.


 

(Source: internal information)

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