how do you seperate iridium from sand?

Answer 1

Iridium is the most dense element. If the iridium is in the form of small grains on the order of the same size as the sand, it can be separated by allowing it to fall in a tall tube with a slit on either side through which air is blown. This is analogous to separating chaff from wheat. Control the velocity of the air to deflect most of the sand through the opposite slit while allowing most of the iridium to fall to the bottom. There will be some sand still mixed with iridium at the bottom, so scoop the mixture up and repeat as necessary.

There are probably other mechanical separation methods based on the difference in density between iridium and sand, for example a centrifuge operating on a mixture of iridium and sand suspended in a viscous oil. That would be kind of messy though.

Iridium is electrically conductive while sand is not. If a mixture of sand and iridium is dropped through a strong magnetic field applied perpendicular to the vertical, the induced currents in the iridium will slow its descent compared to sand. You could devise a gate to catch the slower falling iridium after most of the sand was collected at the bottom of a tall tube.