Interesting claim, but to justify a few milligrams of metals is worse than literally tons of metal and cement is going to require a quantitative argument.
99.99%, even if you’re right, only gets us to 10kg equivalent if you start with 1 gram.
(And keep in mind that these processes to make bulk materials themselves use alloying agents and specialty materials in cutting heads, etc, to fabricate them.)
It requires tonnes of ore processed to produce ounces of gold (I read roughly 13 tonnes on average, but it's highly dependent on the quality of the deposit and refinement difficulty), there are metrics and studies: https://www.businessinsider.com/tons-of-rock-for-an-ounce-of...
Keep in mind your conventional car’s catalytic converter contains grams of platinum group metals, worth about $1000 or so now ($3000 for older, larger catalytic converters). Due in large part to the spike in rhodium prices.
Platinum is extracted as a by-product of nickel and copper mining (as are other elements) as it's primary source, unlike gold and copper which are mined for their element directly. Not arguing your point (45% of platinum is used in auto) only that how we get Pt and Pd is already in progress to get at the other elements like Cu, Au and Ag.
