Recycling precious metals (platinum-iridium) from spark plugs

Recycling precious metals (platinum-iridium) from spark plugs

1. Precious metal components in spark plugs
   Iridium
   Iridium is usually found at the tip of the center electrode of a spark plug, in the form of a coating or micro-electrode.

   Its content is about 0.5%-1%, and it is the preferred material for high-end spark plugs due to its high melting point

   (2446°C) and excellent corrosion resistance.

   Platinum
   Platinum is used as an electrode material in some spark plugs due to its excellent oxidation resistance and durability.

   Its content is usually less than 1%, and it is often used in combination with iridium to improve performance.

2. Precious metal recycling process
   1. Collection and pretreatment
   Physical separation: crush the waste spark plugs and use magnetic separation technology to remove impurities such as ceramics and steel shells.
   Screening and classification: retain the part rich in precious metals to prepare for subsequent chemical treatment.
   2. Chemical extraction
   Acid dissolution: dissolve the precious metals in the spark plug electrode in concentrated nitric acid or aqua regia to generate soluble compounds of iridium and platinum.
   Electrolytic separation: separate metal ions from the solution through electrolysis to obtain high-purity precious metals.
   3. Smelting and purification
   High-temperature smelting: heat the separated precious metal compounds to above their melting point to separate metals such as iridium and platinum.
   Refining process: further improve the purity of precious metals through precipitation or centrifugal separation technology to reach the industrial standard of 99.9%.
   4. Recycling and reuse
   The purified precious metals can be made into various industrial application materials to further exert their high added value.