Question

Lanthanoids occur together in nature and difficult to separate why

Answer 1

Apart from a few metals, rare earth elements are restricted to the 3+ oxidation state (except in very specific circumstances). Chemically speaking the rare earths are very similar to each other. The only major differentiating factor is their size.

The poor shielding ability of 4f electrons means that the lanthanides contract more than would otherwise be expected. Despite this relatively large difference between lanthanum and lutetium there are 13 other elements in between. From one rare earth to the next there is minimal difference.

It's hard to separate thinga that are essentially the same.

Thank you...