Thorium(IV) Nitrate
Properties
| State | Solid (commonly hydrated) |
| Color | White to colorless |
| Solubility | Very soluble in water and alcohols; soluble in TBP/kerosene (extraction solvent) |
| Melting Point | 55 °C (tetrahydrate, decomposes on further heating) |
About Thorium(IV) Nitrate
Thorium(IV) nitrate is the aqueous-soluble form of thorium and the universal feedstock for separating Th from the rare-earth elements it co-occurs with in monazite ore. Monazite — the principal commercial thorium mineral — is a mixed (Ce,La,Nd,Th)PO4 phosphate that contains 4-12% ThO2 alongside the light rare earths. Industrial separation begins by digesting monazite in hot 50% NaOH to break down the phosphate matrix, dissolving the resulting hydroxide cake in concentrated HNO3, and then running the nitric-acid solution through a tributyl phosphate (TBP) in kerosene solvent-extraction circuit. TBP·Th(NO3)4·xH2O extracts into the organic phase with separation factors above 1000 from the trivalent rare earths, which stay in the aqueous raffinate. The same TBP-nitrate chemistry is the backbone of the PUREX process for spent uranium fuel and the THOREX process for spent thorium fuel, so monazite separation and reactor reprocessing share their core chemistry. Th(NO3)4 itself is hygroscopic and is normally sold as the tetrahydrate Th(NO3)4·4H2O or pentahydrate, both colorless to white crystalline solids that crystallize from concentrated nitric solution. Calcining the nitrate at 700°C is the cleanest synthesis route to ThO2 powder of high purity. Aqueous Th(IV) is heavily hydrolyzed above pH 3, forming a sequence of polynuclear hydroxy-clusters [Th2(OH)2]6+, [Th4(OH)8]8+, and [Th6(OH)15]9+ before precipitation of amorphous ThO2·xH2O sets in.
Where you'll encounter it
If you've ever held an antique Welsbach gas-camping mantle from the 1920s or a vintage Coleman lantern made before the 1990s, the bright white incandescence came from a fabric mesh impregnated with Th(NO3)4 solution and then fired off in the gas flame — the burn left behind a porous ThO2 lattice that emits brilliantly at the gas-flame temperature. The mantles are mildly radioactive, and walking through an antique store with a pancake-probe Geiger counter still picks them out across the room. In a modern reprocessing or rare-earth-separation plant, Th(NO3)4 is the actual aqueous feed entering the TBP solvent-extraction circuit, where it partitions into the organic phase and the rare earths stay behind. India's Indian Rare Earths Limited at Aluva runs exactly this chemistry on monazite from Kerala beach sands, generating thorium nitrate that is then calcined to ThO2 fuel-form material for the country's three-stage thorium-reactor program.
Common Uses
- Aqueous feed for TBP-kerosene solvent-extraction separation of Th from rare earths in monazite processing
- Calcination precursor for high-purity ThO2 fuel-form powder (calcine at 700°C in air)
- Historical impregnation solution for Welsbach incandescent gas mantles (1885-1990s)
- Standard aqueous feed for the THOREX spent-thorium-fuel reprocessing scheme
- Precursor for thorium-doped scintillator and laser-host single-crystal growth research
- Source compound for preparation of other Th(IV) salts (ThCl4·8H2O, ThF4) by ion-exchange or precipitation
- Standard reference solution for ICP-MS calibration in actinide trace-analysis labs
- Catalyst-research feedstock for petroleum hydrocracking studies
Safety Information
GHS: H272 oxidizer (Category 2), H302 harmful if swallowed (Category 4), H350 may cause cancer (Category 1A). Dual hazard — chemical oxidizer and radioactive source. As an oxidizer, Th(NO3)4 is incompatible with organic fuels, reducing agents, finely divided metals, and combustible packaging; spills onto sawdust, paper, or organic absorbents can ignite spontaneously. As a radioactive material, the 232Th decay chain delivers alpha dose from inhaled or ingested compound and external gamma dose from the Tl-208 daughter; long-term internal contamination concentrates in liver and bone. NRC source-material license required above 6.8 kg elemental Th per facility. OSHA PEL for soluble Th compounds is 0.05 mg/m3 as Th, 8-hour TWA. Store in tightly closed glass or polyethylene containers segregated from organic chemicals, in a HEPA-vented cabinet, with secondary containment to catch any leak.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.