Oxide products formed from calcined carbonate powder for use as biocide, chemical detoxifier and catalyst support
products.
TECHNICAL FIELD
[0001] The present invention relates broadly to a process and apparatus for
manufacture of bio-active materials from calcined powders produced from the flash
calcination of materials, where the bioactivity applies to a broad spectrum of viruses,
bacteria, fungi and as either a biocide or probiotic depending on the target.
BACKGROUND
[0002] There has been an extensive development of nano-materials with biocide and
probiotic properties, and in particular, of nano-magnesia MgO and nano-zinc oxide ZnO.
An example of a biocide is "Antibacterial characteristics of magnesium oxide
powder", J . Sawei et. al. World Journal of Microbiology and Biotechnology , 16, Issue
2, pp 187-194 (2000) and T. Yin and Y. He, "Antibacterial activities of magnesium oxide
nanoparticles against foodborne pathogens" J . Nanopart. Res. 13, 6877-6885.
[0003] In the study by Sawai et al, the objective was to make high surface area MgO with
particle sizes below about 50 nm. In trials of these materials, the MgO particles rapidly
react with water to form nano-magnesium hydroxide Mg(OH)2 . Prior art references to
nano-MgO are ascribed herein to nano-MgOH)2. These hydrated nano-materials exhibit
broad spectrum bioactivity response to virus, bacteria and fungi. The powder, and the
hydrated nano-powder has as an ability to deactivate toxic materials such as chemical
warfare agents.
[0004] In a paper published by T. Yin and Y. Lu, it was demonstrated that nano-MgO
particles had a strong biocide activity against two foodborne pathogens, namely
Escherichia Coli and Salmonella. This work is important because nano-MgO/Mg(OH) 2 is
not believed to be toxic to humans or animals, and has a positive impact on plants
through the supply of magnesium as a fertilizer. For example, seven log reductions in E.
Coli were observed at a dosage rate of 8 g/litre solids, and dosages of 1 g/litre supressed
growth, and that 3 g/litre would kill all cells within 24 hrs. While Mg(OH)2 is relatively
insoluble, it rapidly dissolves in low pH environments, especially at the pH of digestive
systems. This would be true of nano-MgO/Mg(OH) 2 because the dissolution rate is faster
the higher the surface area.
[0005] US Patent No. 6,827,766 B2 claims a decontamination product comprising nanoparticles
including MgO and Mg(OH)2, selective biocides and a liquid carrier, including
water. The biocide properties are significantly enhanced by the presence of the nanoparticles.
The decontamination processes include a liquid spray, fog, aerosol paste, gel,
wipe, vapour or foam. While the claims are limited to the requirement of adding an
existing biocide as an adjuvant to the product, the examples disclosed teach that the nanoparticles,
in the liquid carriers, had an effective, long-term biocide activity without the
adjuvant. Specifically, their example 3 shows that 5/1 water/oil emulsion with 2% nano-
MgO, CaO, and ZnO solids had such properties, notably without the requirement of a
biocide.
[0006] The impact of the particle size would seem to be important. US Patent No.
2,576,731A (Thomson) discloses the use of magnesium hydroxide slurry, made from a
standard magnesium oxide, as the basis for a foliar spray as a carrier for active biocides
for both insects and fungi where the benefits are associated with the ability of the alkaline
particles to absorb active biocides to render them insoluble, and the strong adherence of
the particles on the leaves of the plants such that the biocide can act over many washings
of the leaf. That patent describes the role of the magnesium hydroxide as having no
insecticidal or germicidal activity. In the context of this invention, the important
teaching of that patent is the adherence of magnesium hydroxide.
[0007] This view was supported by a paper published by Motoike et. al "Antiviral
activities of heated dolomite powder" Biocontrol Sci. l3(4):131-8 2008 in which
processed dolomite is shown to exhibit anti-viral activity. Patent US20090041818 Al
claims an anti-viral agent which is a mixture of an oxide and a hydroxide, in which it is
taught that hydroxide ions are produced by the reaction of the oxide with a hydroxide. It
is claimed that many materials can provide the hydroxide, among which is Mg(OH)2, and
the oxide is preferably MgO. The relevant disclosure of this prior art is that the biocide
activity of such conventional slurries is primarily transient and thus a manufactured
magnesium hydroxide, or hydrated calcined dolomite slurry, does not have a significant
long term biocide effect. Without being limited by theory, this work suggests that the
active chemical species in such a hydroxide sl my are naturally present, but their
concentration is too low for a sustained impact on microbes. The present invention may
seek to overcome this limitation.
[0008] Insight into how the nano-Mg(OH) 2 has a significant bioactivity compared to
standard materials is gained at two levels.
[0009] Firstly, at the biological level, the most plausible theory of why pathological
fungal growth is suppressed by chemical processes is that the presence of Reactive
Oxygen Species (ROS). ROS have a high redox-potential, and include the superoxide ion
0 2 , which is known to generate hydroxyl radicals O , perhydroxyl anions H0 2 and
hydrogen peroxide H20 2 by hydrolysis with water. There are equilibria between these
species in water that is largely regulated by the pH, and at the pH near a nano-Mg(OH)
grain, around 10.4, the perhydroxyl anion dominates. Plants can ramp up the production
of ROS as a defence against pathogenic microbial attack, with the ROS attacking the
primitive cell walls of pathogenic fungus and bacteria. In response, fungus can produce
chemical species that react and neutralise the ROS, and the ROS attacks and destroys the
cell walls of pathogenic microbes. The same model for the activity is true of pathogenic
bacteria, in particular the anaerobic gram-negative bacteria. The ROS symbiosis is
associated with the relationship between the plant ROS and the beneficial gram positive
bacteria, which are essential to a healthy environment for growth. Gram positive bacteria
are generally beneficial and aerobic, and the ROS increases the oxygen level in the
environment. For example, as demonstrated in the case of rice blast fungus: Kun Huang,
Kirk J. Czymmek, Jeffrey L. Caplan, James A. Sweigard & Nicole M. Donofrio (201 1).
[0010] Secondly, at the atomic level, it is evident that the long term biological activity of
nano-Mg(OH) 2 slurry is associated with is ability to produce, and stabilise ROS. In
general terms, small crystal grains have, by definition, a high proportion of their
crystalline surfaces which are formed at the high energy surfaces, and it is well
understood that such surfaces are the source of energetic oxidants, such as the ROS
species. In the case of Mg(OH) , techniques such as Electron Paramagnetic Resonance
has detected all of the radical species described above on normal crystals, albeit at low
concentrations. ROS radicals in solution can recombine, and the bio-activity impact of
ROS would degrade by radial recombination. In the presence of Mg(OH)2, the ROS the
rate of dissipation can be substantially reduced, if not supressed by the generation of
magnesium peroxide Mg0 . Magnesium peroxide is a stable crystalline material, and is
usually formed in a mixture with hydrogen peroxide H2O2, water and excess MgO. It is
stable in this form at ambient temperature (I . I . Voi'nov , and E. I . Latysheva , "Thermal
stability of magnesium peroxide" Izvestiya Akademii Nauk SSSR, Seriya
Khimicheskaya, No. 1, pp. 13-18, January, 1970). Therefore, nano-Mg(OH) 2 can not
only form ROS at the grain boundaries but also the ROS species can be stabilized on the
grain surfaces. The ROS species are stored on the nano-grain surfaces, and would be
released by the change in the equilibria associated with pathogen attack, and general
dissolution of the nano-Mg(OH) 2 to supply magnesium to the plant as a fertilizer.
[001 1] In summary, a reasonable model for the bioactivity of nano-Mg(OH) 2 is that each
particle is a nanoscale crystalline grain that has a high concentration of ROS which is
stabilised on the energetic surfaces of the grain, and the bioactivity arises from the
enhancement of the plant's own natural defence systems which form ROS to provide the
aerobic environment that suppresses pathogenic microbes. This effect is enhanced by the
pH of the Mg(OH)2, at 10.4 which may neutralise acids extruded by pathogens; the net
positive particle charge from hydrolysis which attracts the particles to negatively charged
surfaces of certain microbes and cells; and the adherence of the particles onto the surfaces
of the microbes and cells of plants. By contrast, normal Mg(OH)2 with grain sizes of 0.1
to 100 microns generally have surfaces which are dominated by the stable 001 surface,
and the concentration of ROS would be small.
[0012] The same mechanisms ascribed above to nano-Mg(OH) may apply to other
bioactive materials based on metal oxides, such as nano-ZnO and AgO. Their nanograins
will also support a range of ROS species that depend on the specific defects at the
respective grain boundaries. For example, nano-ZnO is known to produce peroxyl and
hydroxyl radicals.
[0013] The mechanism for bio-activity of nano-grain particles is substantially different
from most other fungicides and bactericides, which use toxic compounds to target
pathogenic microbes. Firstly, the mechanism of ROS lies at the core differentiation
between aerobic and anaerobic microbes, and genetic evolution to limit the impact of the
bio-activity is unlikely. Secondly, the mechanism is an enhancement of the natural
processes whereby plants defend themselves against pathogenic attack. No new chemical
species are involved, and the products of the decomposition are essential nutrients or
micro-nutrients, and in the case of magnesium, it is an essential nutrient for the
production of chlorophyll. Plants absorb magnesium through stomata on the leaves, and
the aerobic/anaerobic contests between fungi, gram-positive and gram-negative microbes
and the plant cells take place both within the soil and on the leaves, for example, as
described by Susan S. Hirano and Christen D. Upper, Microbiol. Mol. Biol. Rev.
64, 3624-653 (2000).
[0014] A probiotic has been defined in proceeding of the US Trademark and Patent
Office, Trademark Trial and Appeals Board, Serial 77758863, (2013) a generic name for
a fertilizer using friendly bacteria in the soil producing microbial ecology means to bring
back symbiotic relationships to the soil. In this application, the definition is extended to
include symbiotic relationships on the plant leaves, and the symbiosis is specifically
associated with the relationship between the plant and the beneficial gram positive
bacteria, which are essential to a healthy environment for growth. Indeed, when nano-
Mg(OH)2 is applied onto leaves as a folia spray, the impact of magnesium absorption as a
fertilizer impact is noticeable through both the colour from increased chlorophyll, and the
increased leaf thickness. Thus at a technical level, the properties of nano-Mg(OH) 2
satisfies the requirements of being a probiotic soil or plant amendment.
[0015] The means of production of nano-materials use chemical synthesis, and the
materials are expensive to produce. Furthermore, the handling of very fine powders is
difficult because these powders have a tendency to readily float in air. Most importantly,
nano-materials are very difficult to filter from air using conventional air filters. Thus the
production processing of these materials requires expensive handling equipment to avoid
loss of the materials, and to meet safety, health and environmental regulations. These
costs are such that nano-materials have not made a substantial impact in the markets for
biocides. Equally important, there are concerns about nano-particles arising from their
ability to be absorbed through the skin, and inhaled into the lungs, by virtue of their small
size.
[0016] There is a need for a product that has the same desirable intrinsic biological
activity of nano-materials using a process that can produce significant volumes of
product, but also avoiding the materials handling issues of nano-materials, and their
potential for absorption and inhalation.
[0017] Any discussion of the prior art throughout the specification should in no way be
considered as an admission that such prior art is widely known or forms part of common
general knowledge in the field.
SUMMARY
[0018] PROBLEMS TO BE SOLVED
[0019] A problem to be solved may include the production of materials that have a high
concentration of bio-active species as do nano-particles, but which do not have the
undesirable features of nano-particles arising from their small size. It may be an object of
the present invention to overcome this disadvantage of the prior art.
[0020] A possible means for solving the problem is to, as a first step to produce a porous
nano-grain composite powder in which the particles in the powder are composed of
crystalline nano-grains of material, where the grain size of an nano-grain is on the nanoscale
so as to generate the active species responsible for biological activity.
[0021] The powder may be used directly, or may be hydrated in water to form a slurry
concentrate that can be diluted in water and sprayed to provide protection against
microbial activity.
[0022] The material on which the powder or spray is applied may be an agricultural or an
aquaculture crop, or a product such a seeds, vegetables, meat, or fish, or a processed food
product; or may be a surface that is to be decontaminated. It may be applied as a soil or
plant amendment.
[0023] The particles are required to be sufficiently porous, so that, in contact with the
microbes, the ROS species are readily made available to the particle surface by diffusion,
and/or by dissolution of the particle when applied to the product as a means of controlled
release to produce a sustained biological impact.
[0024] The particle size is preferably such that the powders are not breathable, and
cannot diffuse through the skin. Such particles are on the scale of 10-100 microns, and
are easily handled and processed by users.
[0025] The binding of the particles is such that they are mechanically stable, and do not
readily degrade to nano-particles that can be breathed or absorbed through the skin. The
particle are not weakly bonded aggregates of single nano-grain particles.
[0026] The particles are to be sufficiently porous that the ROS species formed and
stabilised on the grain surfaces can diffuse to, and impact on, microbes such as virus,
bacteria and fungus in the powder or hydrated form. The nano-composite is purposefully
not an aggregation of nano-particles, but is a material in which the constituent gains are
strongly bonded to each other, so as to resist mechanical disaggregation. A porosity of
about 0.5 for the particles in the powder may be desirable.
[0027] It is advantageous that the material is an oxide, such that the defect species
formed have a high oxidising power as measured by their redox potential; and it is further
desirable that the material has a basic pH such that it is gradually degraded in the acidic
media in which microbes thrive, so that fresh surfaces are continuously exposed so that
the bioactive response is maintained for a length of time until the particle are dissolved.
[0028] It may be advantageous that the material from which the nano-composite is
produced by the process described herein is a mineral.
[0029] It may be advantageous that the surfaces of the nano-composite material as a
powder or a hydrated material, adhere to both microbes and to cell walls to initiate the
desired activity to protect the material, and to minimise the loss of material from the
application of water.
[0030] It may be also advantageous that the hydrated nano-composite material is not
toxic to humans when and if consumed in small amounts, so that the material may not be
required to be washed off the product before consumption. When applied to plants, it is
even more preferable that the nano-composite degrades to a fertilizer and is absorbed by
the plant as a nutrient.
MEANS FOR SOLVING THE PROBLEM
[003 ] A first aspect of the present invention may include a process whereby the process
utilises the following steps to make the bioactive material:
a) Preparing a precursor material which is an inorganic compound powder which
contains one or more volatile constituents such as C0 2, in the form of metal carbonates,
¾ 0 in the form of metal hydroxides, bicarbonates, and NH3, in the form of amines or
organic ligands such as acetates or oxylates, such that, when heated these constituents are
driven off to give an oxide powder that has a high porosity, preferably in the range of 0.5
or higher. The powder formed by heating is a metal oxide, which generally will have a
known biological activity as a conventional nano-material, such as magnesium oxide or
zinc oxide. The standard measure of volatility of the precursor is the loss on ignition
when heated to a temperature of less than 1000°C. The loss on ignition should preferably
be about 50% of the precursor mass. There are a wide variety of production teclmiques to
make such inorganic precursor compounds, in which the powder is prepared as a
crystalline material, often precipitated from an aqueous solution, and which is ground to
the desired particle size of 10-100 microns. An alternative approach is to grind mineral
precursors, such a metal carbonates, hydroxides or hydroxycarbonates. As an example,
magnesium oxide mineral precursors include magnesite (MgC0 3), Brucite (Mg(OH) 2),
Hydromagnesite 4MgC0 3.Mg(OH) 2.4H 0), and Nesquehonite (MgHC0 3.OH. H20),
among others. Compounds include Magnesium Citrate Mg(C 6H607), and Magnesium
Oxalate Mg(C 0 ) . All these compounds decompose on heating to form MgO. Mixed
metal compounds can be either produced, or found as minerals, often as double salts,
such a dolomite.
b). Calcining the precursor to produce a porous nano-composite oxide powder. The
requirement of the flash calcining process is to rapidly vaporise the volatile constituents
to yield particles with the properties:-
(i) A particle size distribution in the range of 10-100 microns, as measured, for
example by light scattering using shear mixing to ensure that the particles are not weakly
bonded aggregates of conventional nano-particles;
(ii) A high porosity (from the voids left by the volatile constituents);
(iii) A nano-crystalline structure in which the characteristic length of the grains is
on the nanoscale, preferably 20 nm or less, as measured by the broadening of the X-ray
diffraction bands;
(iv) A surface area in the vicinity of 150 m2/gm or higher, as measured for
example, by the Bnmuer-Emmett-Teller(BET) method.
The surface area and porosity may be determined by techniques such as the BaiTett-Joyner-
Halenda (BJH) method, and by Small Angle X-Ray Scattering (SAXS). An important
condition of the calcination process to produce these properties is that it occurs at a low
temperature with a sufficiently small residence time that the particles do not sinter during
production, as such sintering rapidly leads to a loss of the desirable properties. The
particles may decrepitate during this production process, and such decrepitation is
tolerable and can be controlled by the design of the calcination process and the selection
of the precursor.
An example of a continuous production process include the calciner disclosed by Sceats
and Horley in Published PCT Patent Application No. WO2007045048 and included
herein in its entirety, in which the process occurs in a counterflow indirectly heating
process, and the reaction is complete in several seconds by the use of sufficiently high
temperature. Another example is a batch production process in which the calcination
takes place at a low temperature under vacuum over a long period of time.
(c). Hydrating the powder to produce a stable hydroxide sluny with a high solids fraction,
preferably in the range of 50-60%. The desirable property of the slurry is that it does
not settle rapidly, exhibits minimal syneresis, and has a low viscosity for dosing into a
spraying system for many applications. The hydration process is one in which the
hydrated product is also a nano-composite material. Such properties can be measured by
drying the slurry, and measuring the same properties as considered previously for the
calcined powder. The objective of the hydration process can be met by ensuring that the
hydration occurs within the particle such that the nano-crystals form the hydroxide
directly, rather than the traditional process where the hydroxide is precipitated from the
solution as crystals. The sluny composition to achieve this process may require the use
of co-solvents, temperature and pressure, to prevent the precipitation mechanism. The
objective is to ensure that the hydrated material contains the high energy surface defects
which are responsible for the bio-activity. Such defects occur on the hydrated grain
boundaries, and the confined hydration ensures that the concentration of the surface
defects is maximised. An example of the hydration process is that disclosed by Sceats
and Vincent for example in AU 2013904096 (incorporated herein by reference).
[0032] This present disclosure may also provide for a magnesium oxide powder or
slurry material that has long-lived biocide activity, and the process and apparatus for
production of such biocide slurries. In one form, the disclosure provides an intrinsic
biocide slurry or powder comprising particles in the range of 0.5-100 microns that
have been processed to be a bonded aggregate of nano-crystalline hydroxide or oxide
crystallites. When slurried in water, additives are used to stabilize the slurry to give a
long lifetime and a low resistance to shear thinning. The crystallites are
characterized by a high fraction of defects derived from superoxides formed in the
production process. The mineral precursor is preferably the mineral magnesite or
dolomite.
[0033] In another form or aspect of the present invention, the biocide response is
enhanced by adding adjuvant toxins including hydrogen peroxide, or ozone or
traditional molecular biocides or nano-particles which preferably absorb in the
particles and enhance the intrinsic biocidal properties.
[0034] In another form, the powder may be spread to provide an insecticide through
its dehydration effect, and the powder continues to provide a biocidal response after
hydration. The biocide benefits are specific to the intended application, where the
response to either or both dehydration and superoxide-derived defects may play a
role as an insecticide, fungicide, bactericide or viracide. For example, in the storage
and shipping of grains, it is preferable to maintain a low water vapour atmosphere, so
that a non-toxic biocide powder which achieves biocide action through dehydration
would be desirable. In other applications, such as an additive to processed food that
has high water content, the application of a slurry product would generally be
desirable.
[0035] In another form, the powder may be used in industrial applications for which a
nano-grain composite material may have advantageous properties, such as for
catalyst substrates and the like.
[0036] The powder or slurry product has preferably a shelf lifetime of several
months, and can be used as a feedstock for production of (a) a foliar spray for
agricultural application, or (b) an additive to food as an intrinsic non-toxic biocide, or
(c) as an additive to a fibre or polymer substrate to make a gauze or a wipe, or (d)
dried to produce a powder or a granular form, or (e) mixed with oils to form an
emulsion, or (f) aerated to produce a foam or fog, or (g) catalyst substrates.
[0037] A further aspect of the present invention may include: A process for
producing a biocide powder or a chemical detoxifier powder from a carbonate
compound, including the steps of: grinding the mineral to produce a powder with a
broad particle size distribution in the range of about 1-100 microns, with a mean
particle size of optionally about 10-20 microns, preferably about 10 microns;
calcining the powder in an externally heated counterflow flash calciner to produce an
oxide with a high surface area and a high degree of calcination.
[0038] This preferred process for producing a biocide slurry or a chemical detoxifier
sluny from a powder may also include forming a stable, readily thinned, sluny of the
hydrated oxide with about 60% solids in the final product after hydration, by the
process of mixing the powder with water, under conditions in which the temperature
is maintained at or near the boiling point of water until the hydration is completed,
shear mixing is applied, and a carboxylic acid or salt is added as the thinning agent;
quenching the slurry to below 60 C; cooling the sluny to ambient; and adding
additives to enhance the biocidal properties.
[0039] The preferred carbonate compound is magnesite, in which case the surface
area of the oxide is preferably greater than 150 m /gm, and even more preferably
greater than 190 m2/gm, with the degree of calcination being preferably greater than
90%. Preferably, the carbonate compound may also be dolomite, in which case the
degree of calcination is set to produce semidolime MgO.CaC0 3, with a surface area
preferably greater than 30 m /gm.
[0040] The process of Claims 1 or 2 in which Preferably, the carbonate compound
may also be a Magnesium Hydrocarbonate, including Hydromagnesite or
Nesquehonite, in which case the degree of calcination is set to produce magnesium
oxide MgO, with a surface area preferably greater than 230 m /gm. Preferably, the
carboxylic acid may also be acetic acid, and the carboxylic salt is magnesium or
calcium acetate. The preferred additive may be an aqueous solution of hydrogen
peroxide. The preferred additive may also be ozone, which is sparged into the slurry.
Further the preferred additive may be a molecular or nano-particle biocide.
Preferably, the additive is a dispersant.
[0041] Preferably, the slurry or powder is used to produce any of a spray, or mixed
with oil to form an emulsion, or processed into a foam or fog.
[0042] A further aspect of the present invention may include a reaction apparatus for
producing biocide powder or a chemical detoxifier powder from a carbonate mineral,
including: a grinder for carbonate minerals; an externally heated counter flow flash
calciner that produces high surface area oxides from the ground carbonate.
[0043] Preferably, the reaction apparatus for producing biocide slurry or a chemical
detoxifier slurry from a powder produced by the reaction apparatus of Claim 1 ,
including: a reaction vessel having an inlet for caustic calcined carbonate powder and
a water inlet; a shearing apparatus for shearing the reaction mixture; and a steam
outlet for release of steam from the reaction vessel, such that in vise the reaction is
controlled by allowing heat of hydration to raise the temperature of the reaction
mixture, allowing water to boil off from the reaction mixture as hydration proceeds,
and removing steam via the steam outlet to remove excess heat and control reaction
temperature at boiling point a means of quenching the slurry to below 60 C,
preferably by transfer of the slurry to a cooled container; a means of cooling the
slurry to ambient temperature; a means of adding solid or liquid additives to the
slurry if required; and a means of sparging the slurry with ozone if required.
[0044] A further preferred aspect of the present invention may include a chemical
composition adapted for use as a biocide, wherein the composition comprises: a
sprayable slurry of particle of calcined powder suspended in water, wherein the
particles have a porosity of greater than 0.5 and wherein the surface of the particles
includes microstructures defined by at least one nano-crystalline structure positioned
on the outer surface of the particles. Preferably, the calcined powder is magnesite.
[0045] The preferred particles may be adapted to allow the microstructures to be
released from the surface of each particle over a predefined time interval. Further, the
preferred particles may form nano-particles adapted to provide a high redox
potential.
[0046] Further forms of the invention will be apparent from the description and
drawings, and from the claims.
[0047] In the context of the present invention, the words "comprise", "comprising" and
the like are to be constraed in their inclusive, as opposed to their exclusive, sense, that is
in the sense of "including, but not limited to".
[0048] The invention is to be interpreted with reference to the at least one of the technical
problems described or affiliated with the background art. The present aims to solve or
ameliorate at least one of the technical problems and this may result in one or more
advantageous effects as defined by this specification and described in detail with
reference to the preferred embodiments of the present invention.
BRIEF DESCRIPTION OF THE FIGURES
[0049] Embodiments of the invention will be better understood and readily apparent
to one of ordinary skill in the art from the following written description, by way of
example only, and in conjunction with the drawings, in which:
[0050] Figure 1 shows a schematic drawing of a process for production of stable,
thin, high solids biocide slurry from powders of caustic calcined magnesia
DESCRIPTION OF THE INVENTION
[0051] Preferred embodiments of the invention will now be described with reference to
the accompanying drawings and non-limiting examples.
[0052] One example form of manufacture of the product can be described by
consideration of the process flow of Figure 1 for the case of magnesium hydroxide as a
probiotic or biocide.
[0053] In this embodiment, the first step is one in which the carbonate mineral is
magnesite, substantially MgC0 3, which is crushed and ground to the particle size
distribution that is close to that of particles found in the end product. This may be set by
the cut-off of the classifier, and the residence time in the grinder. Typically, the ground
material will have a lower particle size of about 1 micron, and upper particle size of about
100 micron, and an average particle size in the range of 10-20 microns. If required,
impurities in the mineral such as sand, talc and magnetic particles are extracted during
this process. The exact distribution depends on the mineral source, whether
macrocrystalline or cryptocrystalline, the impurities, the grinder and the grinder settings.
Most importantly, it is noted that there is no specification that there are any
nanocrystalline particles present (i.e. with a diameter less than 0.1 microns), and
generally such particles are undesirable because, as fines, they are difficult to filter from
the grinder air, and also to process in the steps described below, and to meet customer
and community concerns about the toxicity of nanoparticles in general. The grinder is
preferably a mill that entrains the ground particles in air, and which removes particles
above 1 micron before they can be further ground. This is a known art per se.
[0054] The second step of the process is that of calcination in which the magnesite is
calcined. It is important that the processed particles exhibit minimal sintering during the
calcination process, and achieve a degree of calcination that is preferably in excess of
95%. The most fundamental measure of the impact of sintering is the specific surface
area. This should be greater than 150 m /gm and preferably greater than 90 m2/gm.
The powder XRD analysis of the MgO exhibits a line-broadening which is a measure of
the crystalline structure of the particle, and for a powder with the surface areas quoted,
that width corresponds to a crystalline order of about 20 nm or less. This is the same
XRD profile observed in nano-materials. However, by contrast, the particle size of the
nano-MgO is commensurate with the crystallinity of the powder whereas with the
product of this invention, the particle size is several orders of magnitude higher than the
crystallinity, ie about 10 microns compared to 20 nm. The basic assertion of this
invention is that the biocide or probiotic activity arises from the crystallinity, rather than
the particle size.
[0055] The type of calciner is critical to achieving the properties described above. The
basic requirement is that the process is very fast to eliminate the effect of sintering, and
this should be preferably several seconds. This means that the process is flash
calcination. The second requirement is that the particles experience the lowest possible
temperature during this time. Conventional flash calciners drop the particles into a very
hot combustion gas, and from that time, the temperature of the gas decreases as the
reaction extract energy from the gas stream. Further, not all particles experience the
same conditions. The net result is that the outer surfaces of the particles are extensively
sintered, and it is difficult to achieve surface areas in excess of 50m /gm. The small
particles are most extensively sintered. The preferred calciner is that described by Sceats
and Horely, for example in WO2007/1 12496 (incorporated herein by reference), to give a
powder with a surface area preferably 150 m2/gm or larger, in which indirect
counterflow heat is used. In this case, the temperature of the particles flowing through
the calciner steadily increases for all particles, and the maximum temperature they
experience is the exhaust temperature. During the calcination, there is generally some
decrepitation of the input particles, and often a shoulder appears on the particle size
distribution in the region of 0.1-1 microns. Control of the external burners along the
calciner provides the desired heat transfer to the particles, and the degree of calcination
and surface area can be controlled. This system is known per se, and is capable of
operating at production levels of about 5 tonnes per hour for particles that are 95%
calcined with a surface area of 190 m /gm, and a crystallinity of 20 nm, and negligible
particles below 0.1 micron. These particles are strong, and resist grinding and do not
significantly disaggregate by ultrasonification. The particles are not agglomerates of
nano-particles. The crystallites, albeit porous, are strongly bonded.
[0056] The important factor which determines the biocidal impact is the high surface area
of the calcined powder. There are a range of stable magnesium hydrocarbonate
compounds such as hydromagnesite and nesquehonite of the form
(MgC03)x(Mg(OH) )y(H20 ) z that contain very large volume fractions of H 0 and C0 ,
and when these materials are calcined, they produce very high surface area magnesium
oxide, or order 500 m /gm. These compounds can be found as rare minerals, or can be
synthesised by sparging CO2 into magnesium hydroxide slurry described below,
separating and drying the powder prior to calcination. This approach provides a material
with a high biocidal impact.
[0057] The powder product from these two process steps may be used as a biocide
powder, where the desirable properties of dehydration are required. Where a slurry
product is desirable, the third step of the process is to hydrate the slurry. This process is
well described by Sceats and Vincent for example in AU 2013904096 (incorporated
herein by reference), as a process that can produce tonnes of slurry per hour to match the
production rate of the calciner described above. The high surface area of the particles is
such that the hydration reaction, when mixed vigorously, liberates a large amount of heat
and boils the water. This establishes a set point and the thermally activated hydration
occurs at the boiling point, and the excess heat is liberated by boiling. The application of
a shear mixer provides the agitation required for a uniform controlled process. During
the course of the reaction, acetic acid is added to the slurry to provide thinning necessary
for the shear mixer to operate. The reaction is complete when the temperature starts to
drop from the heat losses. It is preferred to quench the slurry quickly below 60 C, and
then let the slurry cool to ambient for the next processing step. The net result is a slurry
that has hydrated, and which is stable over many months with regard to sedimentation,
and which is readily shear thinned to allow pouring and processing. This slurry has the
same intrinsic biocide activity as has nano-particles when diluted in water for application
as a foliar spray. This will be considered below. Importantly, there is no significant loss
of biocide activity during over the slurry lifetime of several months.
[0058] The fourth step, if required, is to add adjuvants to either the powder or slurry
product in order to increase the biocide properties above that of the intrinsic biocide
response considered below. There are many such adjuvants. These can be hydrogen
peroxide, or ozone, which can be added to saturate the crystalline binding sites on the
Mg(OH) surfaces with the radical species being the superoxide ion, the hydroperoxide
anion, and oxygen radical, and the hydroxyl radical. In addition, the acetate ions may be
further converted to the peroxyacetate ion, which is stable at the pH of the slurry, at about
10.4. Impurity ions, such as Fe + and Fe3+ will have been removed during grinding to
reduce oxygen degradation of these radicals. The use of hydrogen peroxide or ozone
supplements the intrinsic radicals developed during calcination and hydration. Ozone is
added by sparging the slurry with ozonated air. Other adjuvents include a large number
of established biocides, including all those listed in US 6,827,766 B2 or nano-particles
such as AgO and ZnO. Depending on the specific adjuvant and the amount added, the
stability of the slurry may have to be re-established by the addition of dispersion agents.
The use of adjuvants is not generally preferred because it may make the product toxic to
humans, and increase the cost of production compared to the intrinsic biocide developed
in the previous steps.
[0059] The intrinsic biocide produced using steps 1-4 described above produces either a
powder of magnesium oxide or a 60% solids slurry of magnesium hydroxide particles
with a range of particle sizes from 0.4 microns to 50 microns as measured by a particle
size analyser. For the slurry, the particles are confirmed to be magnesium hydroxide by
drying the slurry at about 100 C, and measuring the TGA and DSC, and comparing these
with analytical grade magnesium hydroxide. The nano-crystallinity of the particles of
magnesium oxide or magnesium hydroxide is measured from the line broadening of
diffraction peaks from the dried slurry using Scherer's formula to be 20 nm. The
appearance of the dried magnesium hydroxide powder product under an SEM reveals
particle shapes not unlike those of the porous MgO powder produced by calcination, with
the pores filled in by the reaction with water. The surface area of the MgO powder was
measured to have a BET surface area of 190 m /gm, while that of the dried magnesium
hydroxide slurry was 20 m /gm.
[0060] The biocide activity of the intrinsic slurry has been established using in vitro
measurements and in preliminary crop trials. For invitro studies, the slurry is diluted to
1% by the addition of water, and is sprayed into a prepared Petri dish in which a dot of
the fungus, bacteria, or vims strain under test has been incubated and grown over 24
hours. The rate of growth of the radius is measured over a period, and the biocidal
impact is measured by the extent that the ring growth rate has been suppressed. Studies
were completed on a number of fungi, and a broad spectrum antifungal impact was
observed, and is comparable to commercial fungicides.
[0061] For preliminary crop trials, a number of crops such as grapes, avocados and
bananas exhibiting fungal outbreaks were sprayed with the diluted slurry, and the biocidal
impact measured by the healthiness of the crop, especially with regard to the presence of
fungi, compared to a field that was not sprayed. On inspection, after 7 days, the fungi
were not observable on the sprayed area. It was noted that the powder had a strong
adherence to leaves, and that the leaf appearance had improved indicating that the
magnesium was being adsorbed into the plant and promoting greater photosynthesis.
Such leaf characteristics include the colour and leaf thickness.
[0062] In trials of insecticide response, a sample of insect ridden wheat was dusted with
magnesium oxide powder. After several days, the insect count had decreased
considerably, and with a response that was similar to dehydrated diatomateous earth.
[0063] It is apparent that the diluted slurry has similar biological activity as reported for
nano-magnesum hydroxide. Without being bound by theory, it follows that the similarity
of the nano-crystalline grain properties of the MgO powders of this process, and the
crystalline properties of the single grain nano-MgO are the common feature. The
established propensity of crystal surfaces of MgO and Mg(OH)2 to stabilize radical
species such as superoxide, hydroxyl, atomic oxygen, and peroxyhydroxide that are
known to be active in breaking down the primitive epithelial cell walls of microbes is the
most likely explanation for this property. The high density of these sites and the
stabilization properties provide the basis for the long lived performance of the slurry, and
explain their resistance to decomposition of these radicals to produce oxygen, which
would otherwise have diminished the effectiveness over time. It is also apparent that the
trials with the powder product provided an insecticide response that was typical of
dehydration. Without being bound by theory, the response may be a combination of
dehydration and the superoxide response.
[0064] Naturally, the ability of the large particles to make intimate contact with the
surfaces of microbes is less than that of nano-particles. However, all particles of MgO
have negative charged surfaces, and the activity against gram-negative and gram-positive
microbes suggests that intimate contact is not required. A more likely explanation is that
the radical species are in equilibrium with the water, and transfer by diffusion from the
particle to the microbe. In the case of slurries, it is the surface area of the hydroxide
particles that will control the process, and it is noted that the surface area of hydrated
nanoparticles is of the order of 30 m2/gm, a similar result as measured for the powders
reported herein. The reports of increased activity of smaller nano-particles may simply
be a reflection of the increased geometric surface area of smaller particles. It is noted that
the propensity of nano-particles to aggregate is well established, and diagnostic tests of
the particle size is performed by ultrasonification of the dispersion before measurement
of particle size. The nano-powders in suspension deliver their biocide activity as
aggregates. This is not inconsistent with the premise of this invention that the particle
size is not the origin of the biocide properties. In the case of dehydration, the magnesium
oxide particle surface is about 190 m /gm. The high rates of dehydration are linked to
the surface area, and, in addition, the particle surface is very rough, and able to penetrate
the exoskeleton of insects.
[0065] The targets are not only microbes described above, but also chemicals. A different
application of the slurry is to deactivate toxic chemicals that would otherwise harm
plants, animals and humans. Nano-MgO has been used for this purpose, as a source of
radical species that attack and passify many such agents, such as those which can be
deployed as chemical and biochemical warfare agents. This is because many such
chemicals achieve their toxic effect by free radical generation, and the slurry, or a
dispersed slurry is a carrier of free radicals that can react and destroy these compounds.
The magnesium oxide power or slurry may be used to deactivate such chemicals.
[0066] The slurry described in this invention is not generally deployed as a biocide at
60% solids. It is a concentrate that is used to make biocides for different applications.
The means of application of biocides in agriculture is preferably through a sprinkling
system to avoid losses to the crop from wind. A common means is to use a slurry of the
materials, which is diluted by the spray water to about 1%. This foliar spray approach
has wide industry acceptance. In that case, a material based on magnesium hydroxide has
an added benefit of providing a source of magnesium, which is an essential nutrient for
photosynthesis. A spray should preferably have particles that are less than 100 microns,
and preferably 25 microns, diameter to avoid blockage of the nozzle. The use of a spray
may also be applicable for medical applications. However, in that area, there is also an
application for the incorporation of the material in a mask to reduce infection from
airborne microbes, or a wipe to remove microbes from surfaces.
[0067] MgO-laced gauze or other fabric materials can be made by reacting the powder or
a slurry of the material with various polymer forming materials and applying the mixture
to set on fabrics, with the objective being to adhere the particles on the gauze. In another
area of application, in the food industry, the non-toxic biocide magnesium hydroxide
slurry may be added into liquid products, or may be added as a powder to dried products.
There are known arts for slurry processing, such as grinding the dried product using
conventional processes to generate the desired particle size, or producing granules by
binding with appropriate materials suited for the application. It is noted that the MgO
powder may be applied to food because the process of hydration can occur by virtue of
the food product itself. In another application, the product should be able to be dispersed
into a spray, or fog, or foam to give a large area coverage, for example with spillages of
toxic chemicals.
[0068] In another application, the slurry should be mixed with existing biocides as
adjuvents. This includes conventional water soluble biocides, typically molecular, which
adsorb onto the particle to deliver a desired biocide activity. The formation of emulsions
with oils that contain oil soluble adjuvents is another such application.
[0069] Magnesium oxide is one particular oxide material that can be used, that has
the benefit of availability of a mineral precursor. Another embodiment uses dolomite
in which the degree of calcination of the magnesium site and the calcium site is
controlled to give the desired biocidal properties.
[0070] In this specification, the word "comprising" is to be understood in its "open"
sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is
the sense of "consisting only of. A corresponding meaning is to be attributed to the
corresponding words "comprise", "comprised" and "comprises" where they appear.
[0071] While particular embodiments of this invention have been described, it will be
evident to those skilled in the art that the present invention may be embodied in other
specific forms without departing from the essential characteristics thereof. The present
embodiments and examples are therefore to be considered in all respects as illustrative
and not restrictive, with all changes which come within the meaning and range of
equivalency therefore intended to be embraced therein. It will further be understood that
any reference herein to known prior art does not, unless the contrary indication appears,
constitute an admission that such prior art is commonly known by those skilled in the art
to which the invention relates.
[0072] In this specification, references to the term "probiotic" mean any material adapted
to beneficially promote or enhance the microbial balance within the treated area, location
or place.
[0073] A probiotic is also a generic name for a fertilizer using friendly bacteria in the soil
producing microbial ecology means to bring back symbiotic relationships to the soil ] . In
this application, we extend the definition to include symbiotic relationships on the plant
US Trademark and Patent Office, Trademark Trial and Appeals Board, Serial 77758863, (20 13)
leaves, noting that plants absorb applied magnesium as a fertilizer through the leaf
stomata. Indeed, when sprayed onto leaves as a folia spray, the impact of magnesium
absorption as a fertilizer impact is noticeable through both the colour from increased
chlorophyll, and the increased leaf thickness. The most plausible theory of why
pathological fungal growth is suppressed is that the presence of Reactive Oxygen
Species2. Plants can ramp up the production of ROS as a defence against microbial
attack, with the ROS attacking the primitive cell walls of fungi. In response, the fungi can
produce chemical species that react and neutralise the ROS . The ROS attacks and
destroys the cell walls of pathological fungi. The same model for the activity is true of
pathogenic bacteria, in particular the anaerobic gram-negative bacteria. The symbiosis is
associated with the relationship between the plant and the beneficial gram positive
bacteria, which are essential to a healthy environment for growth. These bacteria are
aerobic, and the ROS increases the oxygen level in the environment. Such bacteria exist
in the soil and on leaves 3 The probiotic effect is that the addition of nano-grains or
nano-grain composites of Mg(OH) increases the supply of ROS above that which the
plant provides. The slow dissolution of the grains by the acid environment leads to a
sustained supply of ROS for a long lasting biological activity. No new chemicals are
introduced in the process.
[0074] Although the invention has been described with reference to specific examples, it
will be appreciated by those skilled in the art that the invention may be embodied in
many other forms, in keeping with the broad principles and the spirit of the invention
described herein.
For example, in the case of rice blast fungus: Kun Huang, Kirk J . Czymmek, Jeffrey L. Caplan, James A.
Sweigard & Nicole M. Donofrio (201 1)
Suppression of plant-generated reactive oxygen species is required for successful infection by the rice blast
fungus, Virulence, 2:6, 559-562, DOI: 10.4 16l/viru.2.6. 18007
3 1 Bacteria in the Leaf Ecosystem with Emphasis nPse do o as syringae—a Pathogen, Ice Nucleus, and
Epiphyte
Susan S. Hirano and Christen D. Upper, Microbiol. Mol. Biol. Rev.September 64, 3624-653 (2000)
[0075] The present invention and the described preferred embodiments specifically
include at least one feature that is industrial applicable.
THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:
1. A process for producing a biocide powder or a chemical detoxifier powder or a
catalyst support from a carbonate compound, including the steps of:
a) Grinding the mineral to produce a powder with a broad particle size
distribution in the range of about 1-100 microns, with a mean particle size
of optionally about 10-20 microns, preferably about 0 microns;
b) Calcining the powder in an externally heated counterflow flash
calciner to produce an oxide with a high surface area, high porosity, and a
high degree of calcination.
2. The process of claim 1, further comprising the additional steps of:
a) Forming a stable, readily thinned, slurry of the hydrated oxide with
about 60% solids in the final product after hydration, by the process of
mixing the powder with water, under conditions in which the temperature
is maintained at or near the boiling point of water until the hydration is
completed, shear mixing is applied, and a carboxylic acid or salt is added
as the thinning agent;
b) Quenching the slurry to below 60 C;
c) Cooling the slurry to ambient;
d) Adding additives to enhance the biocidal properties.
3. The process of either claim 1 or 2, wherein the carbonate compound is magnesite,
with a surface area of the oxide is preferably greater than 150 m2/gm, and even
more preferably greater than 190 m2/gm, with the degree of calcination being
preferably greater than 90%;.
4. The process of either claim 1 or 2, wherein the carbonate compound is dolomite,
wherein a degree of calcination is set to produce semidolime MgO.CaC0 3, with a
surface area preferably greater than 30 m /gm.
5. The process of either claim 1 or 2, wherein the carbonate compound is a
magnesium hydrocarbonate, such as hydromagnesite or nesquehonite, in which
case the degree of calcination is set to produce magnesium oxide MgO, with a
surface area preferably greater than 230 m2/gm.
6. The process of claim 2, wherein the carboxylic acid is acetic acid, and the
carboxylic salt is magnesium or calcium acetate.
7. The process of claim 2, wherein the additive is an aqueous solution of hydrogen
peroxide.
8. The process of claim 2, wherein the additive is ozone, which is sparged into the
slurry.
9. The process of any one of claims 2 to 8, wherein the additive is a dispersant.
10. The process of any one of claims 1 to 8, wherein the slurry or powder is used to
produce any of a spray, or mixed with oil to form an emulsion, or processed into a
foam or fog.
11.A reaction apparatus for producing biocide powder or a chemical detoxifier
powder or a catalyst support from a carbonate mineral, including:
a . a grinder for carbonate minerals
b. an externally heated counter flow flash calciner that produces high
surface area oxides from the ground carbonate
12. The reaction apparatus of Claim 14, further comprising:
a) a second reaction vessel having an inlet for caustic calcined carbonate
powder and a water inlet;
b) a shearing apparatus for shearing the reaction mixture; and
c) a steam outlet for release of steam from the reaction vessel, such that
in use the reaction is controlled by allowing heat of hydration to raise the
temperature of the reaction mixture, allowing water to boil off from the
reaction mixture as hydration proceeds, and removing steam via the steam
outlet to remove excess heat and control reaction temperature at boiling
point.
d) a means of quenching the slurry to below 60 C, preferably by transfer
of the slurry to a cooled container.
e) a means of cooling the slurry to ambient temperature
f a means of adding solid or liquid additives to the slurry
g) a means of sparging the slurry with ozone
15. A chemical composition adapted for use as a biocide, wherein the composition
comprises: a sprayable slurry of particle of calcined carbonate powder suspended in
water, wherein the particles have a porosity of greater than 0.5 and wherein the
surface of the particles includes microstructures defined by at least one nanocrystalline
structure positioned on the outer surface of the particles.
16. The chemical composition of claim 15, wherein the carbonate powder is
magnesite.
17. The chemical composition of claim 16, wherein the particles are adapted to allow
the microstructures to be released from the surface of each particle over a predefined
time interval.
18. The chemical composition of claim 17, wherein the particles form nano particles
adapted to provide a high redox potential.
AMENDED CLAIMS
received by the International Bureau on 26 March 2015
THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:
1. A process for producing a biocide powder or a chemical detoxifier powder or a
catalyst support from a carbonate compound, comprising the steps of:
a) grinding the mineral to produce a powder with a broad particle size
distribution in the range of 1- 100 microns, with a mean particle size of
10-20 microns;
b) calcining the powder in an externally heated counterflow flash calciner
to produce an oxide with a high surface area, high porosity, and a high
degree of calcination;
c) forming a stable, readily thinned, shiny of the hydraled oxide with
about 60% solids in the final product after hydration, by the process of
mixing the powder with water, under conditions in which the temperature
is maintained at or near the boiling point of water until the hydration is
completed, shear mixing is applied, and a carboxylic acid or salt is added
as the thinning agent;
d) quenching the shiny to below 60°C;
e) cooling the slurry to ambient; and
adding additives to enhance the biocidal properties.
2. The process of claim 1, wherein the carbonate compound is magnesite, with a
surface area of the oxide is preferably greater than 150 m /gm, and even more
preferably greater than 190 m /gm, with the degree of calcination being
preferably greater than 90%.
3. The process of claim 1, wherein the carbonate compound is dolomite, wherein a
degree of calcination is set to produce semidolime MgO.CaC0 , with a surface
area preferably greater than 30 m /gm.
4. The process of claim 1, wherein the carbonate compound is a magnesium
hydrocarbonate in which case the degree of calcination is set to produce
magnesium oxide MgO, with a surface area preferably greater than 230 m2/gm.
5. The process of claim 1, wherein the carboxylic acid is acetic acid, and the
carboxylic salt is magnesium or calcium acetate.
6. The process of claim 1, wherein the additive is an aqueous solution of hydrogen
peroxide.
7. The process of claim 1, wherein the additive is ozone, which is sparged into the
slurry.
8. The process of any one of claims 1 to 7, wherein the additive is a dispersant.
9. The process of any one of claims 1 to 8, wherein e slurry or powder is used to
produce any of a spray, or mixed with oil to form an emulsion, or processed into a
foam or fog.
10. A reaction apparatus for producing biocide powder or a chemical detoxifier
powder or a catalyst support from a carbonate mineral, comprising:
a. a grinder for carbonate minerals;
b. an externally heated counter flow flash calciner that produces high
surface area oxides from the ground carbonate;
c . a second reaction vessel having an inlet for caustic calcined carbonate
powder and a water inlet;
d. a shearing apparatus for shearing the reaction mixture; and
e . a steam outlet for release of steam from the reaction vessel, such that
in use the reaction is controlled by allowing heat of hydration to raise
the temperature of the reaction mixture, allowing water to boil off from
the reaction mixture as hydration proceeds, and removing steam via the
steam outlet to remove excess heat and control reaction temperature at
boiling point.
f . a means of quenching the shiny to below 60°C, preferably by transfer
of the slurry to a cooled container.
g. a means of cooling the shiny to ambient temperature
h. a means of adding solid or liquid additives to the shiny
i . a means of sparging the slurry with ozone
11. A chemical composition adapted for use as a biocide, wherein the composition
comprises: a sprayablc s iny of particle of calcined carbonate powder suspended in
water, wherein the particles have a porosity of greater than 0.5 and wherein the
surface of the particles includes micros c res defined by at least one nanocrystalline
structure positioned on the outer surface of the particles.
12 . The chemical composition of claim 11, wherein the carbonate powder is
magnesite.
13. The chemical composition of claim 12, wherein the particles are adapted to allow
the lnicrostructures to be released from the surface of each particle over a predefined
time interval.
14. The chemical composition of claim 13, wherein the particles form nano particles
adapted to provide a high redox potential.