Recycling of Catalytic Converters
As we have seen when an automobile is recycled, the catalytic converter is removed before the car is crushed and shredded.
The catalytic converters are cut from the exhaust system and sent to a specialist recycling plant.
Here, the outer stainless steel container is split to remove the honeycombed interior which has had several layers of aluminum wash-coats applied. This is to ensure optimum spread of the Palladium, Rhodium and Platinum which are impregnated into the wash-coat, and act as catalysts. It is important not only to remove the honeycomb interior but any remaining particles and dust which will have accumulated in the catalytic converter container.
Once there is sufficient materials accumulated the next stage of recycling can commence.
This entails the crushing of the honeycomb into small pieces that are then fed through grinding or hammer mills to produce a fine powder.
The powder is now fed into a vessel containing a solution such as sodium hydroxide (a caustic soda) and this dissolves the aluminum wash-coat fragments, leaving a solution of the three catalysts.
There are several processes that can be applied from this stage to separate the catalysts;
- Drying of the powder then separation of the metals by screening and filtration.
- Further chemical treatment.
Electrolysis (see my article on copper refining)
There is currently an innovative catalytic converter recycling process being researched and developed by the Japanese. Here, the whole catalytic converter unit is subjected to rapid heating in an electric arc furnace (see my article on recycling steel) then quenching in cold water. This separates the catalysts from the honeycomb, thus eliminating the need for immersion into caustic soda.