Sodium Polytungstate (SPT)
Definition
An aqueous inorganic salt solution used as a non-toxic alternative to bromoform for density separation. Density is tunable by concentration; the 2.85-2.90 g/cm3 working solution is standard for heavy-mineral work. Recovered by drying and redissolving, making it economical and environmentally preferable.
- Type
- Aqueous inorganic salt solution
- Replaces
- Bromoform (toxic solvent)
- Working density
- About 2.85-2.90 g/cm3
- Recovery method
- Drying and redissolving
Common questions
Why was sodium polytungstate adopted in place of bromoform for density separation?+
Bromoform is a toxic, volatile halogenated solvent that poses health and disposal hazards in a laboratory setting. Sodium polytungstate achieves the same heavy-liquid separation function while being non-toxic to handle and far easier to dispose of or recover safely.
How is the working density of an SPT solution adjusted for a particular separation?+
The density is controlled by the concentration of dissolved sodium polytungstate in water, so a technician dilutes or concentrates the stock solution to reach the target density needed to float or sink the mineral fraction of interest, commonly around 2.85 to 2.90 g/cm3 for heavy-mineral work.
What makes SPT more economical than a single-use heavy liquid?+
Because it is water-soluble, spent SPT solution can be recovered by evaporating the water and redissolving the residual salt for reuse, rather than being consumed or discarded after a single separation, which lowers ongoing reagent cost.
Related terms
- ATi Index
- Apatite to Tourmaline index: [apatite/(apatite + tourmaline)] x 100. Low values indicate advanced weathering or sediment recycling because apatite is dissolved by...
- Bromoform (CHBr3)
- Tribromomethane, density 2.89 g/cm3, historically the standard heavy-separation liquid. Now largely displaced by sodium polytungstate because of its toxicity and regulatory requirements,...
- Heavy Minerals
- Minerals with density greater than 2.85 g/cm3, separated from a soil or sediment by a heavy liquid. They typically form 0.1-5% of...
- Provenance
- The documented origin of a media file: the device that captured it, the time and location of capture, the chain of custody...
- ZTR Index
- Zircon-Tourmaline-Rutile index: [(zircon + tourmaline + rutile)/total transparent non-opaques] x 100. High values mark texturally and chemically mature sediments that have lost...