In this guide we will give a step by step process for the Recovery of Gold from fiber CPU's.
Fiber CPU's does differ in their design and materials from the ceramic type and therefore needs to be treated separately (see CPU's overview). Fiber CPU's are also different from each other, but they do have one thing in common; the leads (pins) are attached to the body of the CPU with regular solder.
Fiber CPU's contains recoverable gold mostly on the pins and sometimes on the inner side of the heat sink plate. On this article will discuss only on the recovery of the Gold plated pins.
Two more components to consider when dealing with fiber CPU's are; (1) The heat sinks that are sometimes Gold Plated (2) And the Monolithic Ceramic Capacitors (MCC's) that contain Palladium. Those two components are to be kept separately for later individual recovery of Gold or Palladium. Once the three components (pins, heat sink, MCC's) are removed from the CPU, discard it to your low grade e-scrap pile.
Abstract of the process:
A- Gold Plated Pins separation from the CPU body using a torch.
B- Gold and Base metals separation using a Hydrochloric Acid (HCL) leach.
A- Gold Plated Pins separation from the CPU body using a torch:
CPU's Pins are obviously Gold plated and usually gold plating thickness is 10-30 micro inches. Most new fiber CPU's does utilize 'Kovar' as base metal for the gold plating. Kovar is a strong alloy that composed of mostly Iron (Fe), Nickel (Ni) and Cobalt (Co). Older fiber CPU's may utilize a high copper alloy as base metal underneath gold plating. For this step you will need (see Amazon links): A Torch (A Small MAPP set will serve you well). Lock grip Pliers. Stainless Steel bowl
1- Grab the corner of the CPU with the pliers and start heating the pins on the far corner from the pliers. Use the lowest flame possible on your torch, the idea is to heat the solder enough to melt it without burning the fiber body of the CPU. You will know when the solder is molten once you hear and see it pops. At this point just swish the CPU's towards the bowl to create enough momentum for the pins to cut loose and land in the bowl. (See attached video) In some types of CPU's the pins will not detach from the body that easily, so just mount the pliers above the bowl, heat and scoop down the pins to the bowl with a small metal rod. COUTION: MOLTEN SOLDER, BURNING PLASTIC & EPOXY PRODUCE HIGHLY TOXIC FUMES!! PREFORME THIS STEP OUTDOORS OR UNDER FUMEHOOD. Note: Some people will perform this step with acids, the writer think that the use of acids at this stage will do more harm then good, that's including a possible loss of gold. (Addition 5/25/11: Loss of gold may occur not by dissolution in acid, but some of it will be trapped onto left over solids such as the CPU's body) With little practice and proper setup, using the torch method, one can easily do several dozens of CPU's in an hour.
B- Gold and Base metals separation using a Hydrochloric Acid (HCL) leach.
Now that you have the gold plated pins all separated from the body, it is time to separate the gold from the base metals. As said before, the most common base metals that are present in the pins are 'Kovar' (Fe+Co+Ni) alloy, the solder (Sn+Pb/Sn+Ag) and Copper. The separation is done chemically by boiling the pins in a solution of 32% Hydrochloric acid (HCl). Basic Principle 1: It is not recommended to dissolve gold with base metals in the same solution (i.e. Aqua Regia). Basic Principle 2: The combination of Tin (Sn) and nitric acid is an invitation for troubles. Stannous Nitrate (Sn(NO3)2) is a white gelatinous compound in solution and are to be avoided. For this step you will need (see Amazon links): Hot plate Erlenmeyer Flask Cork or Condenser Full strength Hydrochloric Acid 30-32% (buy locally)
1- Weight the pins and add them to the flask. 2- For each gram of pins calculate 12 ml of 32% HCL solution and add the amount to the pins, make sure the liquid level does not exceed half of the flask height. If needed, use a bigger flask (If bigger flask is unavailable, perform two or more consecutive leaches). 3- Place the flask on hotplate and slowly allow the solution to reach gentle boil. Careful not to add to much heat or it will boil over. 4- Place a cork of fit a condensation setup to keep evaporation to a minimum. 5- Let the solution boil for 3 hours. After three hours of boiling the solution will turn very dark blue, almost black. The black solution indicates saturation of the solution. You will also notice Gold Flakes and foils floating on top.
6- Decant the solution with all gold foils and powder to the filter, leaving any un-dissolved pins in the flask and allow complete draining. (Comment: Vacuum filtration shorten this step down to few minutes) You might see some left over un-dissolved pins that can still trap a bit of gold, you can add fresh acid to dissolve them or just wash them thoroughly with plenty of water and decant to the filter. Wash the foils and the filter well with water until its back to white color. You now have the gold foils and powder in the filter. With the gold, there will be small amount of un-dissolved base metals and left over organic matter.
This is the end of the Gold Recovery stage. On the next article we will explain the Gold Refining Stage of the foils.
