A printed circuit board contains metals such as copper, tin, silver, and lead along with minute quantities of gold. There are several methods that are used practically to extract gold from a printed circuit board. But before we can start the process we need to determine the amount of gold that the PCB contains. It can be done by a procedure which is known as "milling". You can mill the PCB yourself or you can take it to an assay laboratory for this purpose. There are a few ways to mill or break the PCB. The easiest way to mill the PCB is to use a wood chipper. The PCB can be broken into very small pieces of sizes around 140 mm. In some methods the edges of the microchips are removed and then it is melted to expose the gold inside the PCB. In this article we will discuss the most effective and easiest way to extract gold from a PCB.
Before you can start the process to extract gold from the PCB you will need a few instruments such as steel crucible, metal plates, metal plate holders, glass tank made of copper, glass beaker, glass dish, furnace, tweezers, and forceps. There are a couple of acids involved in the process so you should take necessary precautions for handling them. The acids involved are nitric acid and hydrochloric acid. The process involves a number of procedures which have to be carried out step by step. These steps are given below:
- After the milling is done, the metal that was separated out in pieces is put into the steel crucible. The furnace should be heated properly and the metal pieces are heated in it until they are completely melted. The molten liquid is then poured in the metal plate. It should be left to cool for some time.
- The glass tank should be filled completely with distilled water. Now take the plate holder and put one of the metal plates into it. The metal plate is then put in the glass tank filled with water. Now take the copper plate and put it in the same glass tank. The copper plate should be 1.5 inches away from the metal plate that was made. You have to apply charges to both plates. The copper plate should be given a negative charge and the metal plate should be given a positive charge. Then it should be kept like this for an hour. The copper that was present in your metal piece will get attracted to the metal plate and it will be drawn towards it. After the hour is complete, both the metal plates should be taken out from the glass tank.
- Now take a steel plate in place of the copper plate and apply the same procedure. A negative charge is given to the steel plate and a positive charge to your metal plate. The steel from the metal plate will be drawn towards the steel plate. Now remove both the plates from the glass tank.
- Now the only metal that your metal plate contains is gold. This metal plate should be left to dry for some time. Now take a glass beaker and pour some hydrochloric acid and nitric acid in it and mix them. The ratio of the acids should be 3:1 (Hydrochloric acid:Nitric acid). This mixture is called "Aqua regia." Now put the metal plate in the mixture and wait until the metal plate turns its color to orange. This step will make sure that the mixture is correct and the gold is dissolving. Now wait until the mixture becomes fuzzy orange. When it does, remove the plate. This process usually takes 60 minutes.
- Now put the residue in a glass dish and keep pouring the mixture in it until all the liquid has evaporated. In the end there will be some dusty residue left in the dish which is pure gold.