Platinum leaves the mine mixed with the other platinum group metals, base metals and sulphides. Turning that mixture into refined metal is a long chemical process with consequences for supply.
The metals occur together and behave alike
Platinum, palladium, rhodium, ruthenium, iridium and osmium share chemical properties closely enough that they resist ordinary separation techniques.
They also occur intergrown with nickel and copper sulphides in the same ore, so the base metals must be dealt with before the precious ones can be addressed.
The similarity that makes them useful as catalysts is precisely what makes them difficult to separate from one another.
Smelting concentrates before chemistry begins
Crushed ore is first concentrated by flotation, which separates the metal bearing sulphides from the bulk of the waste rock.
The concentrate is smelted at high temperature into a matte, and the base metals are removed by leaching, leaving a residue enriched in the precious metals.
Only at that point does the material contain a high enough proportion of platinum group metal for the refinery to work on it economically.
Separation proceeds one metal at a time
The precious metal residue is dissolved and the metals are separated in sequence using solvent extraction and selective precipitation.
Each stage exploits a small difference in chemical behaviour, and each is followed by purification because small quantities of neighbouring metals carry through.
The sequence must run in order, which is why the whole circuit cannot be shortened by processing several metals at once.
The pipeline holds months of production
Metal in transit through smelting, leaching and refining is committed but not yet available for sale, and the volume held in that state is substantial.
A disruption at any stage backs up everything behind it, and clearing the backlog takes as long as the pipeline itself.
Producers report this inventory separately, because it represents metal that has been mined and paid for but cannot reach the market yet.
Recycling feeds into the same circuit
Spent autocatalysts are processed through similar smelting and refining steps, since the metals must again be separated from a mixed feed.
Recycled material competes with mine concentrate for the same limited refining capacity, so the two streams can constrain each other.
Where refining capacity is the binding limit, additional mine output or additional scrap collection does not increase available metal until that capacity expands.