Halloysite can be used in sun screens,
nail varnish and toothpaste. (Source: Gerry
Halloysite is a naturally occurring alumino-silicate clay
mineral with the chemical formula
Al2Si2O5 (OH) 4. It
is similar to kaolinite, but crystalises as hollow tubes rather
than flat plates, or "books" of plates. Because the tubes are
very small they are known as halloysite nanotubes (HNT). These
are usually formed by the alteration of feldspars and/or micas
in acidic granites or volcanic rocks by hydrothermal and
Tube morphology varies from one halloysite deposit to
another. Tube length is typically 0.1 to 5 microns, but can
reach 10 microns or longer. External diameters can be anything
from 50 to 200 nanometres, while the hollow lumen is typically
The purity of commercial halloysite varies depending on the
geology of the deposit and refining techniques employed.
Properties such as tube morphology, chemistry and brightness
determine the mineral’s markets. Traditional
whiteware ceramics, for example, require low iron oxide
(Fe2O3) and titanium dioxide
(TiO2) content, while medical
applications require highly pure, non-toxic material with a
high (typically >90%) halloysite content, low levels of
heavy metals and zero dioxins.
Table 1. Leading halloysite
Ceramics; advanced ceramics
*Product is 50% halloysite: 50%
TEM and SEM images of HNTs. (Source:
Commercial halloysite suppliers
The number of halloysite suppliers globally is relatively
small. Some well-established halloysite are shown in Table
Large scale suppliers in China, Brazil, Thailand and
Argentina sell halloysite or halloysite/kaolin blends, mainly
for ceramic applications. Small deposits have been identified
in Kosovo, Korea, Japan and elsewhere.
In terms of new supply, US-based Applied Minerals Inc.
recently commenced halloysite refining activity at the Dragon
Mine in Utah, while Canada-headquartered I-Minerals Inc. is
developing a new deposit in Idaho, with first production
expected in early 2018.
High quality tableware ceramics are the
most important market for halloysite (Source: Christoph
Traditional ceramics applications
The most important market for halloysite is high quality
tableware ceramics, including porcelain, bone china, fine china
and glazed items. Its low Fe2O3 and
TiO2 content provides high whiteness and
translucency after firing, which, along with chip resistance,
texture and porosity, determine the finished quality of
Virtually all manufacturing companies prefer to use a blend
of halloysite and kaolin, rather than 100% halloysite, in their
recipes, to reduce costs and improve workability.
Typical raw material mixes and firing
temperatures for ceramic tableware are shown in Table
Porcelain is manufactured using high purity kaolin and
halloysite and has a low feldspar content compared to bone
china. It is thus more refractory and is fired twice at higher
temperatures. Finished porcelain is non-porous and translucent
with a cool white colour.
Bone china comprises approximately 50% bone ash produced
from de-gelatinised cattle bones, which have been calcined at
1,250⁰C and milled to powder. It is possible to make
thinner, more delicate pieces from bone china than from
porcelain, which are white and translucent but comparatively
Fine china is manufactured using a similar
raw material blend to porcelain but is only fired once at a
lower temperature. The finished product is opaque with a warmer
Halloysite can also be used in glaze preparation for all
types of tableware. The fine particle size provides good
suspension properties and the low Fe2O3
and TiO2 content helps to produce a clear
Halloysite is an established raw material for making
honeycomb catalyst supports for vehicle exhaust systems and
molecular sieves (often as a mixture with zeolite) for
applications such as water purification and separation of
gaseous and liquid mixtures.
Prices range from approximately $250/tonne for high volumes
of Chinese material up to around $650/tonne for high
performance, white firing New Zealand halloysite.
China is the world’s largest producer of
porcelain and Asia is the largest market for halloysite, with
high demand growth expected in China, India and the Middle
East. French industrial minerals producer Imerys SA supplies
significant tonnages to Europe, but volumes have declined since
2008 as many end users exited the market, moved to Asia or
switched from halloysite to less expensive kaolin.
Table 2: Ceramic tableware raw material
Demand prospects for HNTs are changing as potential
applications in non-ceramic industries are recognised. During
the last 10 years, there has been a significant amount of new
research across the world into HNTs, with special attention
being paid to their morphology. New markets have been
identified where HNTs can provide significant benefits and
command higher prices, notably as an alternative to carbon
nanotubes (CNT), which are expensive and come with health
concerns linked to respiratory conditions.
Two of the largest opportunities for HNTs are in polymers
and life sciences. Prices for HNTs used in these applications
are expected to be around $2-3/kg, compared to prices for CNT
which can be more than $500/kg.
The long tubes and high aspect ratio of HNTs provide
significant strength improvements when added to polymers such
as polypropylene and nylon. Fire resistance is also improved
due to a barrier effect and release of water of hydration.
Where HNTs replace glass or rock fibre additives, there is a
reduction in energy consumption, as these materials require
melting temperatures of around 1,400⁰C prior to spinning
or extruding the fibres.
HNTs added to polyethylene terephthalate (PET), high-density
polyethylene (HDPE), polyvinyl chloride (PVC) and
polystyrene used for food packaging acts as a barrier which
helps to keep carbonated drinks fizzy and prevents ingress of
air and water vapour to products such as milk, extending shelf
life. Tubes can also be loaded with anti microbial
Plastic pellets containing halloysite
The zeta potential (a measure of the magnitude of the
electrostatic or charge repulsion/attraction between particles,
affecting the stability of a material expressed as mV" of HNTs
is low at approximately -45mV, which allows for good colloidal
stability and dispersion in polar polymers, without the need
for expensive surface modification.
NaturalNano, a US nanomaterials company, imports halloysite
to its plant in Rochester, New York, where it is further
refined to remove impurities prior to incorporation into its
Pleximer range of polymers. Some Pleximer grades
contain 30% HNT and are sold to plastics manufacturers who
re-melt and dilute to their required specifications.
Life sciences include the cosmetics, medical, environmental,
agriculture and animal feed industries.
HNTs are a "generally regarded as safe" (GRAS) group of
materials and are biocompatible. They meet EU regulations for
use in cosmetics and animal feedstuffs and are Registration,
Evaluation, Authorisation and Restriction of Chemicals
(REACH)-exempt. HNTs are not biodegradable and therefore not
suitable for intravenous injections, however.
The ability to load the hollow tubes for slow release of
chemicals has led to opportunities in numerous fields,
including pharmaceuticals (delivery of drugs); paints (delivery
of corrosion inhibitors); cosmetics (delivery of moisturisers
and fragrances); and marine oil spills (delivery of
HNTs carry a negative charge on the outer tube, which
contains silicon dioxide (SiO2) and a positive
charge on the inner lumen surface, which is composed of
aluminium oxide (Al2O3), which promotes
loading with negative molecules. Lumen diameters are also the
right size to absorb large molecules such as proteins.
Researchers at Louisiana University in the US have developed
techniques to increase the volume of the hollow lumen by
etching it with acid and to extend release time by capping the
ends of the tubes.
Elsewhere, a team at the James Hutton Institute in Scotland
has come up with a statistical procedure using a scanning
electron microscope (SEM) to accurately measure tube length and
UltraHallopure impregnated onto textile
fibre for wound dressings. Plastic pellets
containing halloysite (Source:
According to I-Minerals, its HNTs are longer and have bigger
internal and external diameters than competitive commercial
products, offering potential advantages through their higher
aspect ratio for use in polymers and higher loadings of
chemical solutions for prolonged slow release in life science
In the cosmetics sector, HNTs are suitable for use in face
creams owing to their high oil absorption capacity, which helps
to remove grease and toxins to cleanse facial pores, while the
hollow tubes can release moisturiser such as glycerol. They can
also be used in sun screens, nail varnish (to improve adhesion
and flow) and toothpaste.
In May 2012, NaturalNano announced a three-year exclusive
agreement and licence to supply French nail polish makers
Fiabila with HNTs for use in nail-care products.
There is growing demand for non-woven textiles used in
sanitary items such as nappies and incontinence products.
Demand for the latter is increasing in line with rising life
expectancies. According to packaging producer Smithers Pira,
global sales of disposable nonwovens rose from $10bn in 2010 to
$14.1bn in 2014, at an annual growth rate of 7.1%. Hygienic
applications represent the largest sector of disposable
nonwovens and HNTs offer a number of improvements to these
fabrics, including odour removal by gas absorption,
particularly effective for ammonia, fluid absorption and
potential for slow release of fragrances or medicines.
Like kaolinite, halloysite has the ability to make blood clot
quickly. Additionally, the hollow tubes can be loaded with
antibiotics and other medicines, which are slowly released to
help to prevent infection. This makes HNTs especially effective
for treating burns as they reduce the frequency of bandage
In February this year, I-Minerals announced that its
UltraHallopure halloysite had been used in the development of a
new wound treatment by the Institute of Diabetes in Karlsburg
(IDK), Germany. This treatment utilises a new technology
developed by DURTEC GmbH in Neubrandenburg, allowing HNTs to be
impregnated into textile fibres.
HNTs can also be added to polymers such as
polymethylmethacrylate (PMMA), which are used to make dental
implants. HNTs form a scaffolding structure, improving
mechanical strength as well as helping the implants bond to the
gum and accelerating UV cure, but HNTs face strong competition
from synthetic TiO2 nanotubes in this field.
Research suggests that adding 5-8% HNTs to orthopedic-grade
PMMA bone cement used in hip and knee replacement surgery can
enhance structural integrity. Additionally, HNTs can be loaded
with an antibiotic such as gentamicin for sustained release for
up to 400 hours. Adding HNTs to calcium phosphate cements
offers similar improvements.
Tissue engineering is a new approach to treating damaged or
lost organs using patients’ own cells, grown on a
polymer support so that tissue parts can be regenerated. This
scaffold serves as an adhesive substrate for the implanted
cells and as a physical support to guide the formation of the
HNTs can be added to biodegradable polymers like PVA
chitosan or poly-lactic acid for the
preparation of tissue engineering scaffolds to improve
mechanical strength. Research into this area is being conducted
at the Slovak Institute of Technology in Bratislava.
In cancer treatment, researchers at Cornell University in
the US have improved the capture rate of circulating tumour and
leukemic cells using HNTs coated onto special micro tubes,
which selectively target, capture and destroy cancer cells,
delivering chemotherapeutics to circulating tumour cells in the
bloodstream, avoiding healthy cells.
Geomembrane installation is used as
part of the construction of a base liner system
of a landfill. (Source: Alan Levine/Flickr)
Due to their hollowness, high surface area and high
porosity, HNTs have the ability to absorb toxic materials from
both fluids and gases. They can be incorporated into honeycomb
catalyst supports used in the exhaust systems of motor vehicles
to clean exhaust gases, molecular sieves used to separate
liquids and gaseous mixtures and for water purification.
HNTs can absorb toxic gas such as carbon dioxide, hydrogen
sulphide (H2S) and ammonia (NH3) and
examples of application areas include biogas plants to remove
H2S and NH3; foundries for the fixation
of amine emissions; and farms for reduction of sulphur
compounds, amines and pathogenic bacteria.
In fluids, HNTs can help remove dyes used in textile, paper
or leather making from watercourses, as well as heavy metals
from mining activities.
In landfill management, geosynthetic clay liners consisting
of two layers of woven fabric usually filled with bentonite
absorb multivalent toxic metals from runoff and reduce
permeability, slowing the rate of leakage. However, if the
water flow stops, the bentonite may dry and crack, allowing
contaminated water to pass through untreated, once the flow
resumes. Blends of bentonite and halloysite have been reported
to prevent this problem and provide improved metal removal, as
HNTs have a strong affinity for monovalent cations, unlike
HNTs can be added to polymers such as polyacrylonitrile in
water filtration membranes to provide reinforcement and
improved filtration performance. Research suggests that HNTs
can also be effective in containing certain forms of nuclear
contamination and in cleaning up marine oil spills by
pre-loading the tubes with surfactants, which are slowly
released to reduce surface tension and help disperse the oil as
very small droplets, which eventually biodegrade.
HNTs loaded with fertilisers allow nutrients to be released
slowly, potentially reducing problems associated over use and
run off. They can also be used for the application of
pesticides and herbicides.
When added at low dose rates of approximately 0.5% into
animal feedstuffs, mycotoxins are absorbed and safely removed
from the animal’s system. HNTs and kaolins are
especially effective in removing Aflatoxin, the most prevalent
and toxic mycotoxin.
By absorbing ammonia contained in animal faeces, HNTs can
prevent leg burns in poultry and reduce odours.
*Frank Hart is the owner and director of
First Test Minerals Ltd.
Saif and Asif from Journal of the Chilean
Clay Nanotube/Poly(methyl methacrylate) Bone
Cement Composites with Sustained Antibiotic Release by Wenbo
Wei, Elshad Abdullayev, Anne Hollister, David Mills and Yuri M.
Selected properties of the halloysite as a
component of Geosynthetic Clay Liners (GCL) by P. Sakiewicz, R.
nowosielski, W. Pilarczk, K. Golumbek & M.