Tungsten Based Heavy Liquids: SPT, LMT and LST

Two older isopolytungstate substitutes for bromoform and TBE have been available for some time, and are known as sodium metatungstate or sodium polytungstate (SPT) and lithium metatungstate (LMT). The tungsten anion for SPT and LMT is [H₂W₁₂O₄₀]^6- . They belong to a class of structures known in the literature as the 'Keggin' species.

Both SPT and LMT are relatively non-toxic and generally inert, but are considerably more viscous than bromoform and TBE at high densities. At a density of 2.85 g/mL, where TBE has a viscosity of 10 cP and bromoform has a viscosity of 2 cP, SPT has a viscosity of over 20 cP. This high viscosity results in considerably longer settling and filtration times when using SPT. SPT also has poor thermal stability above 80^oC, making recovery and concentration more difficult during the recycling of the heavy liquid.

A more thermally stable alternative of considerably lower viscosity is LST heavy liquid. LST can be used up to a density of 2.9 g/ml at room temperature, and up to a density of 3.5 g/ml at elevated temperatures.

Polyhedral representation of the 'Keggin' structure

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