Clerici solution

Clerici solution is an aqueous solution of equal parts of thallium formate (Tl(HCO2)) and thallium malonate (Tl(C3H3O4)). It is free-flowing and odorless. Its color fades from yellowish to colorless when diluted. At 4.25 g/cm3 at 20 °C (68 °F), saturated Clerici solution is one of the densest aqueous solutions. The solution was invented in 1907 by the Italian chemist Enrico Clerici (1862–1938).[1] Its value in mineralogy and gemology was reported in 1930s. It allows the separation of minerals by density with a traditional flotation method. Its advantages include transparency and an easily controllable density in the range 1–5 g/cm3[2][3][4] as a result of changes in solubility (and therefore density of the saturated solution) with temperature.

Clerici's solution
Names
IUPAC name
3-carboxylatooxy-3-oxopropanoate; thallium(1+)
Other names
Thallium(I) malonate/formate
Identifiers
3D model (JSmol)
  • InChI=1S/C4H4O6.2Tl/c5-2(6)1-3(7)10-4(8)9;;/h1H2,(H,5,6)(H,8,9);;/q;2*+1/p-2
    Key: QHRSTSUOSNUUHN-UHFFFAOYSA-L
  • C(C(=O)[O-])C(=O)OC(=O)[O-].[Tl+].[Tl+]
Properties
C4H2O6Tl2
Molar mass 554.82 g/mol
Appearance Colorless to yellow liquid
Density 4.25 g/mL (20 °C)
Fully soluble
Hazards
GHS labelling:
Danger
H301, H311, H315, H318, H331, H410
P261, P270, P280, P301+P310, P302+P352, P310, P332+P313, P403, P405
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Saturated Clerici solution is more dense than spinel, garnet, diamond, and corundum, as well as many other minerals.[3] A saturated Clerici solution at 20 °C (68 °F) can separate densities up to 4.2 g/cm3, while a saturated solution at 90 °C (194 °F) can separate densities up to 5.0 g/cm3.[4] The change in density is due to the increased solubility of the heavy thallium salts at the higher temperature. A range of solution densities between 1.0 and 5.0 g/cm3 can be achieved by diluting with water. The refractive index shows significant, linear and well reproducible variation with the density; it changes from 1.44 for 2 g/cm3 to 1.70 for 4.28 g/cm3. Thus the density can be easily measured by optical techniques.[2]

The color of the Clerici solution changes significantly upon minor dilution. In particular, at room temperature the concentrated solution with the density of 4.25 g/cm3 is amber-yellow. However, a minor dilution with water to the density of 4.0 g/cm3 makes it as colorless as glass or water (absorption threshold 350 nm).[5]

Procedure for determining mineral density using the Clerici solution are available.[2]

Two substantial drawbacks of the Clerici solution are its high toxicity and corrosiveness.[2][3] Today sodium polytungstate has been introduced as a replacement, but its solutions do not reach as high in density as the Clerici solution.

References
  1. Clerici, Enrico (1907). "Preparazione di liquidi per la separazione dei minerali" [Preparation of liquids for the separation of minerals]. Atti della Reale Accademia Nazionale dei Lincei: Memorie della Classe di Scienze Fisiche, Matematiche e Naturale. 5th series (in Italian). 16: 187–195.
  2. R. H. Jahns (1939). "Clerici solution for the specific gravity determination of small mineral grains" (PDF). American Mineralogist. 24: 116.
  3. Peter G. Read (1999). Gemmology. Butterworth-Heinemann. pp. 63–64. ISBN 0-7506-4411-7.
  4. B. A. Wills, T. Napier-Munn (2006). Wills' mineral processing technology: an introduction to the practical aspects of ore treatment and mineral recovery. Butterworth-Heinemann. p. 247. ISBN 0-7506-4450-8.
  5. A. Kusumegi (1982). "Total Absorption Counter and Viewing Shield by The Use of Heavy Liquids". Bull. Inst. Chem. Res., Kyoto Univ. 60 (2): 234. hdl:2433/76969.
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