First, let me start by saying that Ceramic CPU's and chips are barely used or manufactured anymore. Therefore, the time will come when they will extinct from your regular electronic scrap stream.
Scrap Ceramic CPU may have two values: one value for scrap, which represents the gold (and Silver) content and the other value, a collector's value.
Yes, there are folks out there who collect CPUs and are willing to pay you for them, usually far more than the Gold and Silver content worth. Don't deprive them of that pleasure. I will not go into this subject further than this, just remember, whenever quirky and funky-looking ceramic CPU or Chip arrive, you better keep them intact and check it online. Use the serial numbers printed on it. Ceramic CPU's are well worth their own tutorial as they are the little jewels of the electronic scrap world. The best-yielding CPUs may hold up to 0.4-0.5 grams of gold per unit! Some other small ceramic chips may contain several grams of gold per lb. Here, offered a method of a direct dissolution of all metals in Aqua Regia, this kind of Gold Recovery Process is not recommended for most other types of electronic scrap. Ceramic CPUs are unique in terms of the base metals composition and the base metals to Gold (and Silver) ratio, which can provide an efficient and cheap process, despite it being a bit messy.
SAFETY NOTIFICATION: The process described in this article involves using toxic chemicals and gasses. All precautionary measures should be taken beforehand while dealing with chemicals, including Eyes protection, chemical resistant gloves and means to vent any gasses (e.g. fume hood).
Abstract of the Gold and Silver recovery process: - Size reduction and lids removal. - Dissolving the metals with Aqua Regia. - Silver/Lead removal from solution. - Precipitation of Gold Powder.
Size reduction and lids removal. First, remove thermal grease, dirt and any other debris from the CPU's as much as possible. To fit many CPU's into your reaction beaker, you would have to break the CPU's down to around 1/4-1/2" size pieces. This can be done with a simple hammer and anvil or any other creative way you can come up with. While breaking the CPU's, there are a few points you should remember to ensure the success of the recovery process:
- Metallic bottom lids should be removed and processed individually. - Make sure the silicon chip in the center is broken in half or more. - If there's a Gold plated heat spreader, smack it with a hammer; if it breaks apart, then it is most likely composed of a high Tungsten alloy. If that's the case, it is safe to include the heat spreader with the main batch and the rest of the CPU's. Once the gold plating dissolves away from the heat spreader surface, the high Tungsten content will react with the Aqua Regia to form a passive coating of yellowish Tungsten (IV) Oxide (WO2). If the top heat spreader doesn't break and only gets bent slightly, you should not include it in the main batch as it is mostly Copper.
High Tungsten heat spreader (left). Kovar based metallic bottom lid (right)
Dissolving the metals with Aqua Regia. Once the CPU's are cleaned and broken, place them in your vessel of choice and cover them with Hydrochloric Acid (HCl 32 -36%). A Griffin Beaker is usually the best choice for that. It is somewhat impossible to know exactly how much HCl is needed in order to achieve complete digestion, and on the other hand, avoid excess usage of acid. It is the writer's experience that, 20-30 ml of HCl for each CPU is sufficient for most Ceramic CPU's types. If the batch is composed of small ceramic chips or CPU's, you should probably use more HCl. So, once the CPU's are covered with HCl, carefully dilute it with some water, add about 1/5-1/4 of the acid volume (example: for 100ml of acid, add 20-25ml water). This is done to help accommodate all the metals ions in the solution but without affecting the speed of the process (too much). The liquid level should never exceed 2/3 the height of your reaction vessel! Preferably, be it only 1/2 its height. The vessel is now placed on a heat source such as a hot plate or a mantle and the solution temperature is raised to 176-194 F (80-90 C). Safety Note: Remember this process should be done outdoors or in a fume hood.