LST Heavy Liquid - Comparison with other heavy liquids

Why use LST?

LST Heavy Liquid is a premium low toxicity, low viscosity, heat stable heavy liquid for density separations in industry and research. It produces no noxious fumes under normal use and can be very efficiently recycled.

Organic Heavy Liquids

The organic heavy liquids form the "older" generation of heavy liquids. Two of the organic heavy liquids most commonly in use are bromoform and tetrabromoethane (TBE). Of these, bromoform has the lower viscosity (1.8 cP) but is considered more hazardous to work with because it has the higher vapour pressure (5.9 mm Hg at 25° C). TBE has a higher viscosity (9 cP) and a lower vapour pressure (0.02 mm Hg at 25° C).

Another organic heavy liquid, used when higher densities are required, is diiodomethane. Diiodomethane has a density of 3.31 g/ml, a vapour pressure of 1.2 mm Hg at 25° C, and a low viscosity of 2.6 cP.

The three commonly used organic heavy liquids all have problems with toxicity, and must be handled in a fume hood. Diiodomethane is moderately toxic by subcutaneous and other routes. Bromoform has been shown to cause severe liver damage and is poisonous by ingestion. There is evidence that it is a human mutagen and a neoplastigen on experimental animals, so it is potentially carcinogenic. TBE is poisonous by inhalation or ingestion and is a moderate irritant to the skin. It is a neoplastigen and mutagen with animals.

These liquids have the problem of being volatile and potentially causing health problems.

Tungsten based heavy liquids: SPT, LMT and LST

Two low-toxicity substitutes for the organic heavy liquids bromoform and tetrabromoethane (TBE) have been available for some time. They are SPT (sodium polytungstate, or sodium metatungstate) and the lithium equivalent, LMT. These are inorganic compounds, based on the [H₂W₁₂O₄₀]^6- anion, which is dissolved in water to form very dense solutions.

SPT and LMT are not used by as many mineral labs which need a heavy liquid with a density of 2.8 g/ml or more, because their solutions at these densities are too viscous. Typically the viscosity of these liquids is greater than 25 cP, or more than 25 times the viscosity of water. Another disadvantage of SPT and LMT is their lower thermal stability above 80° C. The lower thermal stability means that solutions of SPT or LMT cannot be evaporated by boiling, so the recirculation and regeneration of these liquids is requires special equipment, and/or is quite time consuming.

The most recent development is the low-toxicity heavy liquid called LST Heavy Liquid. LST Heavy Liquid has a low viscosity and excellent thermal stability. LST Heavy Liquid is typically used up at a density of 2.85 g/ml at room temperature, and up to a density of 3.5 g/ml at elevated temperatures.