How dangerous are rare earth processing by-products?

Question

A rare earth processing plant's waste could contain the element Thorium, which is radioactive.

I've pored through plenty of articles and Thorium by virtue of its long half-life has a very low amount of radioactivity. Proponents of rare earth processing cite this as a reason for the safety of rare earth processing. However, opponents claim that Thorium's decay products (in particular, Radium) are very radioactive and thus pose a major health hazard.

Here's an example of this type of quote from Rare Earth Investing News:

The production of rare earth oxides comes attached with a major problem: radioactive waste. The mining of the rare earths and the processing of the various elements produces large amounts of thorium as a byproduct. This material is radioactive and dangerous to human health.

However, in the Wikipedia article on Thorium, it was stated that the alpha radiation that natural Thorium (Th-232) emits cannot penetrate skin, or even a few inches of air.

Natural thorium decays very slowly compared to many other radioactive materials, and the alpha radiation emitted cannot penetrate human skin meaning owning and handling small amounts of thorium, such as a gas mantle, is considered safe.

Page 35 of a report from the IAEA commissioned for a rare earth processing plant in Malaysia indicated that predicted levels of radiation exposure to the public is around 0.002 mSv/year. Contrasting this figure with other examples of yearly dose figures it appears to be very insignificant.

Granted, the 0.002 mSv/year figure appears to be the dosage from radiation emitted by the plant rather than the waste products. However, Page 17 of the IAEA report claims that:

The radionuclide concentrations in the flue gas desulphurization and neutralization underflow residues are expected to be very low -- similar to the average values in normal rocks and soil worldwide (and in Malaysia)

(The main solid byproducts of this plant are flue gas desulphurization residue, neutralization underflow residue, and water leach purification residue.)

In light of the conflicting claims, how dangerous would the radiation from a buried cache of waste product be to the surrounding community?

Answer 1

I understand the issue is not the thorium itself, but what thorium yields in terms of decay products. This ANL report points out that Thorium 230 turns into radium 226, then radon 222, then polonium, etc. Thorium 228 has a similar decay chain. The decay products have much shorter half lives, but it is radon that one might fear the most since it will not stay in the ground, away from direct contact. As a gas, it will end up in the lungs of those who live in the area. Once in your lungs, radon is now a problem.