By Joachim Schomburg,
Tom Conway, Gary Nelson
Different technologies have been developed to remove harmful or
foul-smelling gas components from polluted air or industrial
gas streams. Physisorption, or physical adsorption, effects of
inorganic or organic porous material are widely used within
these technologies.
Industrial used inorganic
adsorbents are:
- zeolites (synthetic,
natural)
- activated smectites (acid
activated, organophile)
- diatomaceous earth
Additionally, iron hydroxides
(goethite, limonite), titanium oxide (anatase, rutile) and
vermiculite are known as adsorbents from the patent
literature.
The major properties of mineral
adsorbents are:
- pore diameter (0.3 nm-400
nm)
¥ porosity (25-60%)
- specific surface (100-800
m²/g)
- pore volume (0.3-0.7
cm²/g)
Their advantages comparing with
organic adsorbents are:
- normally cheaper
- not flammable
- lower temperatures of
regeneration (< 300 ºC)
- no or low costs for reusing
or deposition of loaded mineral adsorbents
Halloysite granulates as gas adsorbents
In developing the potential of
halloysite nanotubes (HNT) for gas component adsorption,
several laboratory and pilot plant studies were performed with
different types of halloysite materials.
The halloysite materials were used
as granulates (1-6 mm), which can be prepared by sieving or
compaction of powdered material.
Halloysite reactivity differences
depend on the single tube morphology (length, outer and inner
diameter), the content and type of accompanying minerals, and
the content and type of heavy and trace elements (separate
catalytic activity).
In some cases the hydration stage
(ratio 10 A - and 7 A - halloysite) seems to be of
importance.
The HNT-granulates can be used as
single adsorbent material or in combination with low
Temperature Plasma Technology for treatment of gas streams or
polluted air (WO 2009/125004; WO 2011/128073).
Depending on the type of the
adsorbed harmful gas component, three ways of regeneration of
loaded HNT-granulates were successfully tested:
- thermal treatment (heating
up to 300 ¡C)
- low temperature plasma
treatment (up to 80 ¡C)
- oxygen flushing (very short
time)
Industrial applications
Halloysite nanotubes can act as an
interesting new adsorbent for several gas components. The first
industrial scale application has already been put into use.
HNT-adsorbent production will be a
part of I-Minerals’ product portfolio based on the
Helmer-Bovill Halloysite source located in North-Idaho,
USA.
Further reading
[1] MULLER; S.; K. SAULICH &
J. SCHOMBURG:
Plasmaregeneration mineralischer
Adsorbentien zur Formaldehydabscheidung aus Abgasen von
Biogas-Motoren.-
Proc. 7. Bioenergieforum, Rostock
21./22.06.2013, p. 117-125
[2] TYMCZYNA, L. et. al.:
Efficacy of a novel biofilter in Hatchery sanitation: II.
Removal of odorgenous pollutants.-
Ann. Agric. Environ. Med. 14
(2007), 151-157
[3] OPALINSKI, S. et. al.: Application of selected
alumosilicates for ammonia adsorption.- Przemysl chemiczny 88/5
(2009), Univ. Wroclawin, 2-5
I-Minerals Helmer-Bovill
project
I-Minerals’ Helmer-Bovil project is located in western
Idaho, and the company’s 2013 prefeasibility study
highlighted the potential of the property as having an after
tax NPV of $150m, 28% IRR, 3 year payback and $67m initial
CAPEX.
The prefeasibility study also
outlined potential CAPEX of $84m including life of mine
sustaining capital over the 26-year mine life.
Work so far has defined an inferred
resource of 38.4m tonnes primary clay comprised of an estimated
share of 6.6% hallyosite, 16.7% kaolin, 29.7% quartz and 13%
K-spar.
In March the US exploration company
completed the evaluation of drill core from its 2013 drilling
programme. The company expects that the most recent
drilling in the Kelly’s Hump
area will increase its halloysite reserves to about 20 years
when the prefeasibility study is
updated, up from previous estimates
of 10 years made in January 2013.
Relevant data has now been
submitted to mining consultant SRK, which designed the
programme in collaboration with I-Minerals, for resource
modelling, mining planning and reserve calculations.
Resource modelling will take places
using drill hole lithologic data, hole coordinates, material
balances information, and Scanning Electron Microscopy (SEM)
photographs.
This information will then be used to put together a mine
plan and calculation of quartz, potassium feldspar (K-spar),
kaolinite and halloysite.