In
chemistry, sparging, also known as gas flushing in
metallurgy, is a technique in which a
gas
Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma).
A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...
is bubbled through a
liquid in order to remove ''other''
dissolved gas(es) and/or dissolved
volatile liquid(s) from that liquid. It is a method of
degassing
Degassing, also known as degasification, is the removal of dissolved gases from liquids, especially water or aqueous solutions. There are numerous methods for removing gases from liquids.
Gases are removed for various reasons. Chemists remove ga ...
. According to
Henry's law
In physical chemistry, Henry's law is a gas law that states that the amount of dissolved gas in a liquid is directly proportional to its partial pressure above the liquid. The proportionality factor is called Henry's law constant. It was formulate ...
, the concentration of each gas in a liquid is proportional to the partial pressure of that gas (in the gaseous state) in contact with the liquid. Sparging introduces a gas that has little or no partial pressure of the gas(es) to be removed, and increases the area of the
gas-liquid interface, which encourages some of the dissolved gas(es) to
diffuse
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
into the sparging gas before the sparging gas escapes from the liquid. Many sparging processes, such as solvent removal, use air as the sparging gas. To remove oxygen, or for sensitive solutions or reactive molten metals, a chemically inert gas such as
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
,
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...
, or
helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
is used.
Liquid chromatography
Solvents used in
high-performance liquid chromatography
High-performance liquid chromatography (HPLC), formerly referred to as high-pressure liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify each component in a mixture. It relies on pumps to pa ...
(HPLC) are often sparged with helium.
Engineering
In
biochemical engineering
Biochemical engineering, also known as bioprocess engineering, is a field of study with roots stemming from chemical engineering and biological engineering. It mainly deals with the design, construction, and advancement of unit processes that inv ...
, sparging can remove low-boiling liquids from a solution. The low-boiling components evaporate more rapidly, so the gas bubbles remove more of them from the bulk solution containing higher-boiling components. It is an alternative to
distillation
Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heat ...
, and it does not require heat.
Environmental chemistry
In
environmental chemistry
Environmental chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places. It should not be confused with green chemistry, which seeks to reduce potential pollution at its source. It can be defined as ...
, air sparging is an ''in situ'' remediation technique that removes volatile pollutants from contaminated
groundwater
Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated ...
and soil.
Metallurgy
In
metallurgy, gas flushing removes dissolved gases from the
molten metal
Melting, or Enthalpy of fusion, fusion, is a physical process that results in the phase transition of a chemical substance, substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the appli ...
prior to the material being processed.
For example, before casting
aluminium alloy
An aluminium alloy (or aluminum alloy; see spelling differences) is an alloy in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin, nickel and zinc. There are two principa ...
s, argon bubbles are injected into liquid aluminium using a rotary
degasser
A degasser is a device used in the upstream oil industry to remove dissolved and entrained gases from a liquid. In drilling it is used to remove gasses from drilling fluid which could otherwise form bubbles. In a produced water treatment plant it i ...
. The argon bubbles rise to the surface, bringing with them some of the dissolved hydrogen. The degassing step reduces the occurrence of
hydrogen gas porosity
Hydrogen gas porosity is an aluminium casting defect in the form of a porosity or void in an aluminium casting caused by a high level of hydrogen gas (H2) dissolved in the aluminium at liquid phase. The solubility of hydrogen in solid aluminium is ...
. In the steel making process, this method is used very commonly for duplex steel and some high reactivity metals.
See also
*
Froth flotation
Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in mineral processing, paper recycling and waste-water treatment industries. Historically this was first used in the mining industry, wher ...
, the use of gas bubbles to separate or extract hydrophobic liquids and/or solids from hydrophilic liquids
References
{{Reflist
Laboratory techniques
Metallurgy