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This week in Core Elements, we will touch on bentonites and carbonites. Hope you enjoy!
Rasoul Sorkhabi
Editor, Core Elements
Bentonite and Its Applications in the Petroleum Industry
Bentonite Hills/ Greg Willis/ Shutterstock.com
In Reviews in Chemical Engineering, Hosseini and colleagues review the properties and applications of bentonite. Here are some highlights.
Word origin:
Geologist Wilbur Knight suggested the term bentonite in 1898 after the Cretaceous Benton Shale outcrop near Rock River in Wyoming.
The Benton Shale was named earlier by Fielding Meek and Ferdinand Hayden after Fort Benton in Montana.
Mineralogy:
Bentonite is a type of natural claystone composed mainly of montmorillonite, an aluminum phyllosilicate clay mineral in the smectite group.
Montmorillonite forms by weathering and diagenesis of volcanic ash settled in a marine or lacustrine basin.
The layered clay structure of bentonite consists of TOT layer units. These units are octahedral sheets of alumina sandwiched between tetrahedral sheets of silica.
The distinctive properties of bentonite include its plasticity, water absorption (swelling), sorption, and cation exchange capacity. They result from its mineralogical, chemical, and TOT layering characteristics.
Types of bentonites:
Swelling or sodium bentonite
Non-swelling or calcium bentonite
Mixed sodium-calcium bentonite
Potassium bentonite: Transformation of smectite into illite produces K-bentonite, which is used for tephrochronology or dating volcanic ashes.
Ten applications of bentonites in the petroleum industry:
High-salinity and high-temperature subsurface environments can make sodium bentonites degradable and require activation and modification engineering.
Oil-based (non-aqueous) drilling fluid cannot use the natural hydrophilic bentonite, and instead, uses engineered “organic bentonite” by ion-exchanging of inorganic cations (sodium and calcium) with ammonium salts.
Producing countries:
The United States, China, and India are the leading bentonite producers, followed by Turkey, Iran, Greece, and Russia.
In the United States, sodium bentonite mainly comes from Wyoming’s Bighorn Basin and South Dakota’s Black Hills, and calcium bentonite comes from Mississippi and Alabama.
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Plate Tectonics of Carbonatites and Rare Earth Ores
Magnesiocarbonatites. Photo by Creative Commons Attribution 2.0/ Wikimedia Commons
Carbonatites are enigmatic igneous rocks because they are carbonates rather than silicates. They are also extremely rich in rare-earth-elements (REEs).
Read more: See my previous coverage of carbonatites here and here.
Recently, I came across another interesting paper in Science Advances that relates the origin of carbonatites and rare-earth ores to plate tectonics.
Big questions:
Mantle plumes account for the origin of within-plate magmatic activities, but they are too hot to explain the low-temperature alkaline magmas such as carbonatites.
Plate tectonics is a well-established framework for plate-margin magmatism, but its linkage to the generation of REE-rich carbonatite melts is less studied.
What the researchers did: Carl Spandler and his colleagues from Adelaide University….
Compiled a database of continental carbonatites (304) and magma-related REE ore deposits (108).
They then used the GPlates software to map fertilized mantle lithosphere (FML) polygons, integrating carbonatites, REE ore deposits, and tectonic configurations for the past 2 billion years.
The researchers considered converging plate tectonics that lasted continuously for more than 100 million years.
What they found:
The compared FML domains for the past two billion years captured 67 percent of carbonatites, 72 percent of all REE deposits, and 92 percent of Precambrian REE deposits.
The kinematic plate modeling shows that about 35 percent of the present-day subcontinental lithospheric mantle has experienced substantial subduction-related fertilization.
The study supports the idea that alkaline magmatism in intraplate rifts forms via melting of FML that was metasomatized by plate subduction before the magmatism itself.
Limitations of the study: The study did not consider short-duration subduction or mantle-plume-lithosphere interactions that may also generate metasomatized mantle lithosphere.
The Lighthearted Layer
James Hutton/Art by James Raeburn
3 June marked the 300th birthday for James Hutton, one of the founding fathers of modern geology. I loved watching these two YouTube clips on the Hutton anniversary:
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