Mining High Volume Nanomaterials

A new technique in particle shape measurement has identified extremely large deposits of kaolin in Georgia that are 20 to 60 nm thick. Kaolin operations there now run as refineries where particle shapes and sizes are selected and “distilled off” for higher value applications such as barrier and higher-strength coatings. These could be considered as pragmatic nano-clays. However they represent a new dimension in kaolin research and have not been closely studied by many. 

Nanoclay, a 3-layer silicate mineral called montmorillionite or bentonite, has been shown to have remarkable properties in the world of nanocomposites but, with their high cost of purifying, dewatering and surface treatment, their cost of manufacture has constrained their use.

Kaolin

Kaolin, a 2-layer aluminosilicate, comprises a layers of silicon dioxide and aluminum hydroxide hydrogen bonded together and represents the most abundant clay mineral in the earth’s crust. A number of large deposits exist of white kaolin with low iron contents and are used in a wide range of applications, from porcelain to its most common usage in paper making. 

Georgia, USA, is the world’s largest producing region and has the added advantage of well developed road, rail and pipeline infrastructures together with an educated workforce. 
 

Kaolins have found extensive use in the paper industry where they provide flatter, whiter surfaces that allow excellent print quality. The commodity grade of kaolin is typically hexagonal platelets with an average diameter of 1 micron and 120 to 180 nm thick. In the last 10 years techniques have been developed that allow rapid measurement of an average aspect ratio which is allowing the industry to pinpoint large reserves of very high aspect ratio kaolins (60:1 to 100:1) that turn out to be comprised of platelets 20 to 50 nm thick. 

Kaolins with crystals as thin as 20 nm are now being produced for the paper industry to the extent of 100 KTons per year. Applications range from barrier coatings through stiffness enhancement and the production of smoother surfaces on paper and paperboard.

These can be categorized as a “pragmatic nanoclay” as they are abundant and of substantially lower cost to produce than classic nanoclays.

Georgia is the world’s largest production region for white kaolins but as the use of coated magazine and catalog papers declines in the face of a digital world we are seeing a corresponding decline in demand for these unique materials. We believe there is an opportunity to build on the learnings from nanoclay usage in nanocomposites to move these kaolins into wider use.

Very little work has been done with these thin crystal kaolins beyond that in paper coatings and the opportunity exists to take advantage of them in a wider range of materials applications. But few people know about their existence. Currently kaolin suspensions are stabilized in water with a sodium polyacrylate that provides added negative charge to keep the particle apart. However this hides a very interesting structure as the aluminum hydroxide surface is essentially hydrophilic while the silicon dioxide is expected to be hydrophobic. 

That is these are naturally occurring abundant janus nanoparticles that have the opportunity of behaving as a “mineral block co-polymer” with the associated opportunities to control self-assembly of useful structures.

biomimetics

In particular, advances being made in the world of biomimetics show the way to make high strength materials at low temperatures.  

Work at NorthWestern (Messersmith) and U Michigan (Kotov) have shown it possible to make ceramic strength materials at low temperatures.

Further work needs to be done both to characterize better the complex nature of kaolin as well as develop further the chemistry and surface interactions needed to optimize performance. Crystal thickness measurement, done by electron energy loss in a transmission electron microscope has identified clays in the ground with an thickness around 20 nm and are abundantly available

The USA is fortunate in having large reserves of these nanokaolins in Georgia as well as infrastructure in place that can be quickly transitioned to the manufacture of millions of tons per yr of thin crystal nano-kaolins. We have the opportunity to produce, economically, large volumes of useful nanoparticles that can lead to a major growth in jobs in the USA.

The manufacturing infrastructure is in place as well as pilot mineral processing facilities to allow the rapid scale up and manufacture of new product streams.

recommendations

1. Have these new thin crystal kaolin particles subjected to a more detailed thorough analysis using the tools that have been funded in the NNI program and by doing so make people more aware of their existence.
2. Have the kaolin industry make available large quantities of particle shape and size fractions for detailed evaluations.
3. Identify the details of the surface chemistry of kaolin taking into account the influence of isomorphic substitutions and other defect centers that will influence properties
4. Involve the major centers working on nanocomposites to develop applications relating to structural strength and barrier performance
5. Provide infrastructure to allow universities and government labs to take advantage of the mineral pilot plant facilities in industry to enable rapid scale up and commercialization of developments
6. Connect candidate end users, automotive, construction, consumer goods etc, so that they become aware of these unique materials and performance features