That analysis has an error - Its OK to take 5 tonnes/cubic metre...

That analysis has an error -
Its OK to take 5 tonnes/cubic metre for Iluka's monazite pile (because it is assumed to be all monazite, which has a specific gravity of ~4.6 - 5.4) but for AHK's situation we should use the density of the bulk sand as it exists in situ. - say maybe 3 tonnes/cubic metre.
That drops the tonnage of monazite recoverable from 3% of the prospective area to 277,000. - Or if extended over the whole area to 9.2 million tonnes.

But as I say these are only rough calcs, and the density of sand depends on how compacted it is, as well as the actual minerals contained. To say the density is 3 units allows for strong compaction over many years, and known dense minerals. However the result is still only a guide to possible outcomes.

Please make your own judgements.