Heavy liquid
View on Wikipediafrom Wikipedia
A heavy liquid is a solution or liquid chemical substance with a high density and a relatively low viscosity. Heavy liquids are often used for determination of density in mineralogy, for density gradient centrifugation and for separating mixtures.
Uses
[edit]Common applications of heavy liquids include:
- Density gradient centrifugation
- Separating mixtures and sink/swim analysis
- Flotation process
- Determination of density
Toxicity
[edit]The classical heavy liquids like 1,1,2,2-tetrabromoethane (Muthmanns solution), potassium tetraiodomercurate(II) (Thoulets solution), bromoform or diiodomethane which are used in mineralogy are very toxic. These toxic chemicals are avoided today in consideration of the fact that there are alternative water based, non-toxic heavy liquids like sodium polytungstate solutions.[1] With this relatively new heavy liquid densities up to 3.1 g·cm−3 can be adjusted . Adding parts of pulverulent tungsten carbide increases the density to 4.6 g·cm−3.[2]
List of common heavy liquids with density > 2.0 g·cm−3
[edit]| Name | Density (g·cm−3) |
|---|---|
| 1,2-Dibromoethane | 2.180 |
| cis-1,2-Dibromoethene | 2.246 |
| trans-1,2-Dibromoethene | 2.231 |
| Dibromomethane | 2.477 |
| Bromal | 2.550 |
| Bromoform | 2.890 |
| 1,1,2,2-Tetrabromoethane (Muthmanns solution) | 2.967 |
| Sodium polytungstate | 3.100 |
| Bromine | 3.1028 |
| Thoulets solution | 3.196 |
| Diiodomethane | 3.325 |
| Indium(III) iodide | 3.40[3] |
| Barium tetraiodomercurate(II) | 3.57 |
| Thallium formate + thallium malonate (Clerici solution) | 4.25 |
| Galinstan (gallium, indium, tin alloy) | 6.44 |
| Mercury | 13.6 |
Mercury is the heaviest liquid at room temperature. But the heaviest liquid irrespective of temperature is liquid osmium (a rare metal) at its melting point (3033°C/5491.4°F), with a density of 22.59 g·cm−3, 1.65 times as heavy as mercury.[4]
References
[edit]- ^ Callahan J, A non-toxic heavy liquid and inexpensive filters for separation of mineral grains, in Journal of Sedimentary Petrology, 57/1987, S.765-6
- ^ CD Römpp Chemie Lexikon – Version 1.0: Schwerflüssigkeiten, Georg Thieme Verlag, 1995
- ^ Synthetic methods of organometallic and inorganic chemistry (Herrmann/Brauer). Vol. 2: Groups 1, 2, 13 and 14. Stuttgart: Georg Thieme Verlag. 1996–2002. ISBN 3-13-103021-6. OCLC 33665888.
- ^ See: https://www.aqua-calc.com/calculate/volume-to-weight/substance/liquid-blank-osmium
Literature
[edit]- Schnitzer W, Zur Problematik der Schwermineralanalyse am Beispiel triassischer Sedimentgesteine, in International Journal of Earth Sciences, 72/1983, S.67–75, ISSN 1437-3254 (Print) 1437-3262 (Online)
- Boenigk, Schwermineralanalyse, S.6–15, Stuttgart: Enke, 1983.
- Ney, Gesteinsaufbereitung im Labor, S.92–113, Stuttgart: Enke, 1986.
External links
[edit]
 | This chemistry-related article is a stub. You can help Wikipedia by adding missing information. |
Heavy liquid
View on Grokipediafrom Grokipedia
Fundamentals
Definition
A heavy liquid is a solution or liquid chemical substance characterized by a density significantly higher than that of water, typically ranging from about 2.5 to 3.3 g·cm⁻³, and relatively low viscosity to enable fluid handling and separation processes.[1] This classification emphasizes high specific gravity, which facilitates buoyancy-based applications in density separation, while distinguishing heavy liquids from dense solids or gases that lack fluid properties.[6] The term "heavy liquid" arises from its contrast to light liquids, such as water or common organic solvents, in contexts reliant on density differences for material differentiation.[7] The earliest uses of heavy liquids date to mid-19th-century mineralogy, where they served for specific gravity tests to assess and separate mineral samples.[7]Physical and Chemical Properties
Heavy liquids are characterized by their elevated densities, typically ranging from 2.0 to 3.1 g·cm⁻³, which distinguish them from common solvents and enable effective density-based separations.[8] This high density arises primarily from the incorporation of heavy atoms, such as iodine and bromine, which increase the mass per unit volume without proportionally expanding the molecular size.[8] In contrast, ordinary liquids like water have a density of approximately 1.0 g·cm⁻³ at standard conditions, underscoring the "heaviness" that allows heavy liquids to suspend or separate denser materials. The density (ρ) of a heavy liquid is fundamentally defined by the equation
where $ m $ represents the mass and $ V $ the volume of the substance.[8] Factors influencing this property include molecular weight, which correlates positively with density due to greater atomic mass contributions; intermolecular forces, such as van der Waals interactions, that promote closer molecular packing; and solvation effects in solution-based heavy liquids, where solute-solvent interactions modulate overall density.[8]
Viscosity in heavy liquids is generally low, often below 10 cP at room temperature, facilitating pourability, rapid mixing, and efficient flow during separation processes.[8] This low viscosity ensures minimal resistance to particle movement, enhancing the precision of density gradient techniques.[9]
Chemically, heavy liquids are commonly composed of halogenated organic compounds or aqueous solutions of inorganic salts, providing the necessary density while maintaining liquidity.[8] They exhibit good stability under ambient conditions, supporting repeated use in laboratory settings, though certain formulations may show sensitivity to light, which can induce photodegradation; heat, leading to thermal decomposition; or hydrolysis, particularly in aqueous environments.[8] These properties collectively ensure their utility in applications requiring controlled buoyancy without excessive reactivity.[10]
Types and Preparation
Common Examples
Heavy liquids are dense fluids used in laboratory techniques for separating minerals and materials based on specific gravity differences.[11] Common examples include organic compounds derived from halocarbons and aqueous inorganic solutions based on tungstate salts, selected for their stability and tunable densities in laboratory settings. Other inorganic options, such as zinc chloride solutions, are used in industrial applications despite their higher viscosity.[10] Organic heavy liquids, such as diiodomethane, bromoform, and tetrabromoethane, are widely used due to their high densities and low viscosities, though they pose toxicity risks from vapor inhalation and skin contact.[11] These are often preferred for precise separations but require careful handling. Aqueous inorganic heavy liquids, including sodium polytungstate, lithium heteropolytungstate, and Clerici solution, serve as lower-toxicity alternatives, particularly in environmental and safety-conscious applications, with densities adjustable via concentration.[11] The following table compares key examples, based on standard references for mineralogical separations.[11]| Name | Chemical Formula | Density Range (g·cm⁻³) | Typical Use Summary |
|---|---|---|---|
| Diiodomethane | CH₂I₂ | 3.32 (at 20°C) | High-density organic separations; oily, moderate toxicity |
| Bromoform | CHBr₃ | 2.89 (at 20°C) | Intermediate-density organic separations; cheaper but high vapor toxicity |
| Tetrabromoethane | C₂H₂Br₄ | 2.96 (at 20°C) | Organic separations; viscous, decomposes with metals |
| Sodium polytungstate | Na₆(H₂W₁₂O₄₀) | Up to 3.1 (at 25°C) | Non-toxic aqueous alternative; stable in water, low toxicity |
| Lithium heteropolytungstate | Aq. soln. of Li heteropolytungstates | Up to 2.95 (at 25°C) | Low-viscosity non-toxic aqueous; bulk availability for routine use |
| Clerici solution | Aq. soln. of Tl formate and malonate | 4.25–4.76 (at 20–90°C) | Ultra-high-density separations; highly toxic thallium-based, limited use |
| Zinc chloride | Aq. soln. of ZnCl₂ | Up to 2.9 (saturated) | Industrial separations; corrosive, higher viscosity |
Preparation Methods
Heavy liquids are prepared through distinct methods depending on whether they are organic or inorganic compounds, with approaches varying from laboratory-scale synthesis to industrial formulation. Organic heavy liquids, such as bromoform (CHBr₃), are typically synthesized via halogenation reactions, particularly the haloform reaction involving acetone and bromine in the presence of a base. In a standard laboratory procedure, acetone is mixed with a sodium carbonate solution, and bromine is added gradually, leading to the formation of bromoform through successive bromination and cleavage steps, represented by the overall reaction:
This method yields bromoform as a dense, colorless liquid with a density of approximately 2.89 g/cm³, often requiring distillation for purification.[13]
Inorganic heavy liquids, like sodium polytungstate (Na₆[H₂W₁₂O₄₀]), are prepared by dissolving the polytungstate salt in water to achieve the desired density. The salt is typically obtained commercially but can be synthesized from tungstic acid (H₂WO₄) and sodium hydroxide (NaOH) under controlled conditions to form the polyoxometalate structure, after which the powder is dissolved in deionized water while adjusting pH (typically neutral) and concentration—for instance, 133 g of sodium polytungstate in 22 g of water yields a maximum density of 3.10 g/cm³ at 20°C.[14]
Once prepared, heavy liquids undergo calibration and adjustment to ensure precise densities for specific applications. Techniques include incremental addition of solutes or solvents to fine-tune density, verified using a pycnometer by weighing a known volume of the liquid at a controlled temperature; for example, densities are adjusted by small additions of water or alcohol to organic liquids like bromoform. Stability is enhanced by incorporating stabilizers, such as 1-3% ethanol in bromoform to prevent decomposition upon exposure to light and air.[15][16]
Commercial production of heavy liquids has evolved since the mid-20th century, transitioning from custom laboratory reagents to standardized industrial grades supplied by specialized manufacturers. Companies like Cargille Laboratories offer precision-calibrated organic series liquids with densities ranging from 0.80 to 3.31 g/cm³, formulated for consistency and supplied in sets for mineralogical separations, while inorganic options like sodium polytungstate are produced at scale from tungsten ores and distributed as high-purity powders for on-site solution preparation.[15]
Applications
Density Separation Techniques
Density separation techniques using heavy liquids primarily rely on the sink-float method, a gravity-based process that exploits differences in particle density to separate minerals. In this method, ore particles are immersed in a heavy liquid medium with a specific gravity intermediate between that of the valuable mineral and the gangue. Particles denser than the liquid sink to the bottom, while less dense particles float to the surface, enabling effective beneficiation.[17][1] This separation is governed by Archimedes' principle, which states that the buoyant force $ F_b $ on a submerged object equals the weight of the displaced fluid:
where $ \rho_\text{liquid} $ is the density of the liquid, $ V_\text{displaced} $ is the volume of the displaced liquid, and $ g $ is the acceleration due to gravity. If the particle's density exceeds that of the liquid, the net downward force causes it to sink; otherwise, it floats.[17]
The setup for the sink-float method typically involves quiescent separation vessels, such as inverted truncated cones or pyramidal tanks, to minimize turbulence and allow clear stratification. Ore is fed into the vessel filled with the heavy liquid, and mechanical aids like paddles gently skim the floating fraction while the sunk material is removed via dredges or bucket elevators. Shaking tables may be used in some configurations to enhance separation for specific particle ranges, particularly in laboratory-scale operations.[17][18]
Heavy liquid density separation was introduced in the early 20th century for coal washing, marking a shift from manual jigs to more precise gravity methods. The technique gained industrial traction around 1931 with the commercialization of the deVooys process, which utilized suspensions for large-scale operations processing millions of tons annually. Refinements in the 1930s incorporated organic heavy liquids like bromoform, improving density control and applicability to a wider range of ores beyond coal.[17]
In mineral processing, the sink-float method is widely applied for ore beneficiation, particularly in separating high-value minerals from host rock. A key example is the recovery of diamonds from kimberlite ore using diiodomethane (methylene iodide), which has a specific gravity of approximately 3.32 and allows isolation of diamond concentrates from lower-density silicates in the 25–125 μm fraction after initial crushing. Efficiency depends on factors such as particle liberation and density contrast, with optimal performance for sizes typically between 0.1 and 10 mm, as finer particles may entrain or fail to stratify properly.[19][20][1]
The method offers high selectivity due to its ability to achieve sharp density cuts, even with differences as small as 0.1 g/cm³, making it ideal for preconcentrating ores and rejecting coarse gangue to reduce downstream processing costs. However, it is inherently a batch process with relatively low throughput compared to continuous methods, and separation efficiency diminishes for particles finer than 0.5 mm without additional centrifugal enhancements.[17][1]