Separation of radium and rare earth elements from monazite

Abstract

A method of chemically extracting radium-228, rare earth metals, thorium, the decay products of thorium, and phosphates from thorium-containing ores. The method involves breaking thorium-containing ore into fragments, wetting the fragments with a concentrated strong acid to make a slurry, heating the slurry, passing the heated solution through a first anion exchange column, retaining metals and radium-228 captured on the resin, allowing the radium-228 ions to decay to actinium-228, purifying the actinium-228 fraction, sending the actinium-228 fraction through a capture column, eluting the captured thorium-228 with acid, removing radium from the solution, retaining the radium-228 fraction for isomer in-growth, retaining decay products from the radium-228, separating the REEs from the process stream; and eluting and retaining the REEs.

Description

BACKGROUND OF THE INVENTION[0001]1. Technical Field[0002]The present invention relates generally to a novel method of chemical extraction fashioned to extract and separate rare earth metals, thorium, its decay products, and phosphates from thorium-containing ores. The novel process efficiently recovers phosphoric acid, radium-228, radium-228's decay sequence, including its isomers, actinium-228 and thorium-228, and the rare earth elements including lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium ytterbium, lutetium, yttrium and scandium from various thorium containing head ores or feed materials including monazite and bastnaesite.[0003]2. Background Art[0004]Radium-228 is present in small quantities, averaging approximately 3.5 grams per thousand tons of refined monazite sand. Radium-228 is a highly valuable material for medical applications as some of its natural or artificial decay products can b...

AI Technical Summary

Benefits of technology

[0009]The present invention removes radium-228 from the thorium-containing materials produced in the monazite mining waste stream to temporarily reduce the radioactivity of stockpiled thorium-containing materials. The process permits neutralized thorium to be stockpiled so that it can be recovered in the future for its nuclear energy content or later re-milked for its radium-228 content. Because the radioactive emissions from the thorium containing tailings are significantly reduced after the radium-228 is separated and removed, the remaining neutralized thorium in the tailings or stockpile will have significantly lower radioactivity until the natural decay of in the thorium replaces the radium-228 and the physical equilibrium of the decaying isotopes is restored. The process also removes the valuable REE so that these can be efficiently separated into pure metals or pure compounds. Finally, to the extent the ore contains phosphates, the inventive extraction process recovers the phosphates as phosphoric acid.

[0010]The inventive chemical separation process has the advantage that as radium-228 is collected, phosphoric acid is also collected, and each of the rare earth elements is collected in a highly purified form. The radium-228 is useful for medical isotope applications. When it is separated from thorium, thorium emissions are reduced so that in some jurisdictions it would be classified as the least regulated naturally occurring radioactive materials.

[0013]The separation of radium-228 from thorium-232 reduces potential liabilities associated with the possession of thorium for the mine operator for the period of time before sufficient new radium-228 “grows in” the thorium by the inexorable alpha decay. Immediately after the separations the remaining thorium-232 will have lower activity because significant quantities of radium-228 will have been removed. The radioactivity from radium-228 gradually returns in the thorium-232, but a mine operator will have sufficient time to permanently bury or otherwise properly dispose of the thorium-containing materials during the period of time when the rate of treated thorium-232 disintegrations is reduced, perhaps below the applicable regulatory threshold in some jurisdictions.

Problems solved by technology

Radioactive decay products from thorium-containing materials, including monazite mining tailings, add cost to monazite mining operations.

This stewardship cost for the rare earth, thorium, and phosphate extractive industries is a significant commercial expenditure.

Because thorium-containing materials are classified as low level radioactive waste, potential third party environmental, personal injury and property claims against the thorium possessor may ripen over time, exposing the possessor to liability and damages.

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