I have pumped millions of tons of rocks of all sizes, plus very fine magnetite iron ore.

I have toyed with the idea of plumbing some cast iron exhaust manifolds into either
magnetic separator discharge pipes,
or froth flotation tailing discharge pipes
to see how long it would take to “round out” the exhaust manifold interior edges and passages.

Seems a shame to pay high Extrude Hone prices when hundreds of mineral processing plants “have to” have abrasives flowing through pipes.

A few days ago I visited a site where a very small coal cleaning “package plant” was being erected. The young foreman told me he had never before worked in mining but had spent years building drag racing engines professionally. He was doing this job because his grandfather needed him. The grandfather drove up awhile later and it turned out his 1960s entry into the coal business was pumping sand out of a riverbed and separating coal from the sand before selling the sand for construction projects.

We both knew Harry Ranier of NASCAR and swapped stories of his risk taking and “salesmanship” both on and off track.

https://en.wikipedia.org/wiki/Ranier_Racing_with_MDM