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Title:
COLLOIDAL MESOPOROUS SILICA NANOPARTICLES (CMSNS) FOR TREATMENT OF MUNICIPAL SOLID WASTE INCINERATION (MSWI) ASH
Document Type and Number:
WIPO Patent Application WO/2017/171635
Kind Code:
A1
Abstract:
In the present application, colloidal mesoporous silica nanoparticles (CMSNs) are provided to sequester one or more inorganic compounds from municipal solid waste incineration (MSWI) ash, and therefore stabilising the ash. The CMSNs are synthesized by using triethanolamine (TEA) as the base and pores of said CMSNs are produced by subjecting the as-synthesized CMSNs to ethanolic solution of ammonium nitrate or hydrochloric acid, and therefore removing the templating surfactants. As a result, the surface of these CMSNs are covered by silanol groups, which then enable the CMSNs to stabilise the ash through substitution of the proton of the silanol groups with heavy metals in the ash.

Inventors:
GOH, Chee Keong (9 Woodlands Avenue 9, Singapore 4, 738964, SG)
TANG, Lok Hing (9 Woodlands Avenue 9, Singapore 4, 738964, SG)
Application Number:
SG2017/050107
Publication Date:
October 05, 2017
Filing Date:
March 07, 2017
Export Citation:
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Assignee:
REPUBLIC POLYTECHNIC (9 Woodlands Avenue 9, Singapore 4, 738964, SG)
International Classes:
B09B3/00
Domestic Patent References:
2011-07-07
Foreign References:
JPH09248540A1997-09-22
JPH0966278A1997-03-11
Other References:
MOLLER, K. ET AL.: "Colloidal Suspensions of Nanometer-Sized Mesoporous Silica", ADVANCED FUNCTIONAL MATERIALS, vol. 17, no. 4, 26 January 2007 (2007-01-26), pages 605 - 612, XP055067894, [retrieved on 20170526]
URATA, C. ET AL.: "Dialysis process for the removal of surfactants to form colloidal mesoporous silica nanoparticles", CHEMICAL COMMUNICATIONS, vol. 34, 29 July 2009 (2009-07-29), pages 5094 - 5096, [retrieved on 20170526]
BONTEMPI, E. ET AL.: "A new method for municipal solid waste incinerator (MSWI) fly ash inertization, based on colloidal silica", JOURNAL OF ENVIRONMENTAL MONITORING, vol. 12, no. 11, 20 October 2010 (2010-10-20), pages 2093 - 2099, [retrieved on 20170526]
Attorney, Agent or Firm:
DONALDSON & BURKINSHAW LLP (24 Raffles Place #15-00 Clifford Centre, Singapore 1, 048621, SG)
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Claims:
1 . An ash stabiliser comprising:

porous silica nanoparticles configured to sequester one or more inorganic compounds from ash,

wherein the porous silica nanoparticles have been pretreated with an ion-exchange process.

2. The ash stabiliser according to claim 1 , wherein said porous silica nanoparticles are substantially free from surfactants.

3. The ash stabiliser according to claim 1 or claim 2, wherein the porous silica nanoparticles are free from heat pre-treatment at a temperature of more than 150 °C.

4. The ash stabiliser according to any one of claims 1 -3, wherein the porous silica nanoparticles comprise an X-ray diffraction single broad peak between degree 2Θ = 16-32°.

The ash stabiliser according to any one of claims 1 -4, wherein the porous silica nanoparticles are dispersed in liquid medium as a colloidal suspension.

The ash stabiliser according to any one of claims 1 -5, wherein the ash stabiliser comprises from 0% to less than 45% by weight of organic residues.

The ash stabiliser according to any one of claims 1 -6, wherein the silica nanoparticles comprise precipitated silica nanoparticles precipitated from a mixture comprising at least one organic compound.

8. The ash stabiliser according to any one of claims 1 -7, wherein the porous silica nanoparticles comprise mesoporous silica nanoparticles.

9. The ash stabiliser according to any one of claims 1 -8, wherein the porous silica nanoparticles have particle sizes that are no more than 15 nm.

10. The ash stabiliser according to any one of claims 1 -9, wherein the porous silica nanoparticles comprise one or more of the following properties:

a) surface area of more than 400 m2/g;

b) pore volume of at least 1 .0 cm3/g; or

c) pore size of at least 1 .5 nm.

1 1 . The ash stabiliser according to any one of claims 1 -10, wherein the porous silica nanoparticles exhibit a type IV isotherm showing increasing nitrogen adsorption at a relative pressure of 0.8 or above.

12. A method of stabilising ash, the method comprising

contacting the ash with the ash stabiliser according to any one of the preceding claims to allow the porous silica nanoparticles to sequester one or more inorganic compounds present in the ash.

13. The method according to claim 1 1 , wherein the step of contacting the ash with the ash stabiliser comprises adding the ash stabiliser to the ash to form a mixture, wherein the ash stabiliser is added in an amount of up to less than 25% by weight of the mixture.

14. The method according to claim 13, wherein the inorganic compound comprises one or more metal selected from the group consisting of: arsenic, barium, cadmium, chromium, copper, mercury, molybdenum, nickel, lead, antimony, selenium, zinc, rubidium and/or one or more non-metal selected from the group consisting of: chloride, fluoride and sulphate.

15. A method of producing the ash stabiliser according to any one of claims 1 -10, the method comprising:

precipitating porous silica nanoparticles from a mixture of a silica source, a surfactant, a base and a liquid carrier; and

removing the surfactant from the porous silica nanoparticles by an ion- exchange process.

16. The method according to claim 15, wherein steps of the method are carried out at a temperature of less than 150°C.

17. The method according to claim 15 or claim 16, wherein the base comprises triethanolamine (TEA).

18. The method according to claim 17, wherein molar ratio of silicon in the silica source to TEA is no more than 1 :4.

19. The method according to any one of claims 15-18, wherein molar ratio of the surfactant to silicon in the silica source is no less than 0.17.

Description:
COLLOIDAL MESOPOROUS SILICA NANOPARTICLES (CMSNS) FOR TREATMENT OF MUNICIPAL SOLID WASTE INCINERATION (MSWI) ASH

TECHNICAL FIELD Various embodiments disclosed herein relate broadly to an ash stabiliser, method of stabilising ash, and method of producing the ash stabiliser.

BACKGROUND Municipal solid waste incineration (MSWI) ash of about 10% by volume or 20% by weight of original amount of solid waste is produced through the combustion of municipal solid waste, which is used to generate electricity. It is estimated by the World Bank that the global municipal solid waste generation is approximately 1 .3 billion tonnes per year. The amount of municipal solid waste generated is expected to grow faster in the coming decades, reaching 2.2 billion tons/year by 2025 and 4.2 billion by 2050. In general, the MSWI ash can be divided into two types, i.e. (1 ) incinerator bottom ash (IBA), which is solid residual material collected from the combustion chamber and (2) incinerator fly ash (IFA), which is solid residual material obtained from the clean-up of the flue gases.

MSWI ash is classified as hazardous waste. A major concern is the possible leaching of heavy metals such as cadmium and lead. Most regulatory agencies require the ash to be assessed for composition and potential leaching of hazardous compounds before it can be disposed or used.

Many techniques have been proposed to reduce the leaching of heavy metals from fly ash. These can be grouped into three classes: (a) Separation processes such as washing, electrochemical and thermal processes that allow the extraction or recovery of some metals from ash; (b)Solidification/ stabilisation (S/S) using additives or binders such as cement to physically and/or chemically immobilize hazardous components; (c) Thermal methods such as sintering and vitrification. However, these techniques have many limitations such as high cost, high-energy consumption and the generation of more waste. Geopolymerisation and accelerated carbonation processes are currently undergoing further research and development, to solve problems with high levels of soluble salts and the non-removal of some heavy metals such as cadmium. Thus, there is a need for an ash stabiliser, method of stabilising ash, and method of producing the ash stabiliser that seek to address or at least ameliorate one of the above problems.

SUMMARY

In one aspect, there is provided an ash stabiliser comprising porous silica nanoparticles configured to sequester one or more inorganic compounds from ash, wherein the porous silica nanoparticles have been pretreated with an ion-exchange process.

In one embodiment, said porous silica nanoparticles are substantially free from surfactants.

In one embodiment, the porous silica nanoparticles are free from heat pre- treatment at a temperature of more than 150 °C.

In one embodiment, the porous silica nanoparticles comprise an X-ray diffraction single broad peak between degree 2Θ = 16-32°. In one embodiment, the porous silica nanoparticles are dispersed in liquid medium as a colloidal suspension.

In one embodiment, the ash stabiliser comprises from 0% to less than 45% by weight of organic residues.

In one embodiment, the silica nanoparticles comprise precipitated silica nanoparticles precipitated from a mixture comprising at least one organic compound. In one embodiment, the porous silica nanoparticles comprise mesoporous silica nanoparticles.

In one embodiment, the porous silica nanoparticles have particle sizes that are no more than 15 nm.

In one embodiment, the porous silica nanoparticles comprise one or more of the following properties:

a) surface area of more than 400 m 2 /g;

b) pore volume of at least 1 .0 cm 3 /g; or

c) pore size of at least 1 .5 nm.

In one embodiment, the porous silica nanoparticles exhibit a type IV isotherm showing increasing nitrogen adsorption at a relative pressure of 0.8 or above.

In another aspect, there is provided a method of stabilising ash, the method comprising contacting the ash with the ash stabiliser according to any one of the above aspect or embodiments to allow the porous silica nanoparticles to sequester one or more inorganic compounds present in the ash.

In one embodiment, the step of contacting the ash with the ash stabiliser comprises adding the ash stabiliser to the ash to form a mixture, wherein the ash stabiliser is added in an amount of up to less than 25% by weight of the mixture. In one embodiment, the inorganic compound comprises one or more metal selected from the group consisting of: arsenic, barium, cadmium, chromium, copper, mercury, molybdenum, nickel, lead, antimony, selenium, zinc and rubidium and/or one or more non-metal selected from the group consisting of: chloride, fluoride and sulphate.

In another aspect, there is provided a method of producing the ash stabiliser according to any one of the above aspects or embodiments, the method comprising precipitating porous silica nanoparticles from a mixture of a silica source, a surfactant, a base and a liquid carrier; and removing the surfactant from the porous silica nanoparticles by an ion-exchange process.

In one embodiment, the steps of the method are carried out at a temperature of less than 150°C.

In one embodiment, the base comprises triethanolamine (TEA).

In one embodiment, the molar ratio of silicon in the silica source to TEA is no more than 1 :4.

In one embodiment, the molar ratio of the surfactant to silicon in the silica source is no less than 0.17. DEFINITIONS

The term "ash" as used herein broadly refers to residues produced from the combustion of matter. Likewise, the term "incinerator ash" as used herein broadly refers to residues produced from the combustion of matter in an incinerator. For example, the term includes but is not limited to, a composition of entirely incinerator ash, a mixture of incinerator ash and scrubbers residues, or a mixture of flyash and bottom ash, or combinations thereof; all of which are produced by an incinerator.

The term "ash stabiliser" as used herein refers to a compound or composition that contains one or more components that are configured to stabilise one or more matter (typically inorganic matter) present in ash. For example, the stabilising components may bind or sequester to the inorganic matter present in the ash and consequently, the ash stabiliser may reduce or prevent the leaching of inorganic compounds from the ash. The ash stabiliser disclosed herein may include solely the compound that are configured to stabilise one or more matter (typically inorganic matter) present in ash or a composition/mixture of the one or more components together with other additives, solvents etc. In various embodiments disclosed herein, the ash stabiliser includes porous silica nanoparticles.

The term "silica" as used herein refers to silicon dioxide (S1O2); and includes but is not limited to precipitated S1O2 and colloidal S1O2.

The term "porous" as used herein broadly refers a material with a plurality of pores (holes or openings). A "porous" material may be microporous, mesoporous or macroporous. "Microporous" materials may contain pores which diameters are less than 2 nm. "Mesoporous" materials may contain pores which diameters are in the range 2 - 50 nm, and "macroporous" materials may contain pores which diameters are more than 50 nm.

The term "inorganic compound" as used herein refers to a compound that does not contain carbon atoms in its structure. An "inorganic compound" may refer to a metal or a non-metal. Examples of a metal "inorganic compound" include but is not limited to arsenic, barium, cadmium, chromium, copper, mercury, molybdenum, nickel, lead, antimony, selenium, zinc and rubidium. Examples of a non-metal "inorganic compound" include but is not limited to chloride, fluoride and sulphate.

The term "residue" as used herein refers to matter that is remaining after an earlier process. For example, the term encompasses residual surfactant that remains after a removal process intended to remove the surfactant.

The term "nano" as used herein is to be interpreted broadly to include dimensions no more than about 1000 nm. Accordingly, the term "nanoparticles" as used herein may include particles of sizes that are no more than about 1000 nm, no more than about 900 nm, no more than about 800 nm, no more than about 700 nm, no more than about 600 nm, no more than about 500 nm, no more than about 400 nm, no more than about 300 nm, no more than about 200 nm, or no more than about 100 nm. The term "particle" as used herein broadly refers to a discrete entity or a discrete body. The particle desc ibed herein can include an organic, an inorganic or a biological particle. The particle used described herein may also be a macro-particle that is formed by an aggregate of a plurality of sub-particles or a fragment of a small object. The particle of the present disclosure may be spherical, substantially spherical, or non-spherical, such as irregularly shaped particles or ellipsoidally shaped particles.

The term "size" when used to refer to the particle broadly refers to the largest dimension of the particle. For example, when the particle is substantially spherical, the term "size" can refer to the diameter of the particle; or when the particle is substantially non-spherical, the term "size" can refer to the largest length of the particle.

The term "ion exchange" used herein broadly refers to refers to anion, cation, and chelate exchange. Ion exchange typically occur at temperatures lower than about 150°C, lower than about 140°C, lower than about 130°C, lower than about 120°C, lower than about 1 10°C, lower than about 100°C, lower than about 90°C, lower than about 80 C C, lower than about 70°C, lower than about 60°C, or lower than about 50 C C. In some examples, ion exchange may occur at ambient/room temperature and pressure. The term "surfactant" as used herein broadly refers to a substance or compound that reduces surface tension when dissolved in water or water solutions, or that reduces interfacial tension between two liquids, or between a liquid and a solid. The term "surfactant" thus includes anionic, cationic, nonionic, zwitterionic and/or amphoteric agents. An example of a surfactant includes cetyitrimethylammonium chloride.

The term "and/or", e.g., "X and/or Y" is understood to mean either "X and Y" or "X or Y" and should be taken to provide explicit support for both meanings or for either meaning. The terms "coupled" or "connected" when used in this description are intended to cover both directly connected or connected through one or more intermediate means, unless otherwise stated.

The term "associated with", used herein when referring to two elements refers to a broad relationship between the two elements. The relationship includes, but is not limited to a physical, a chemical or a biological relationship. For example, when element A is associated with element B, elements A and B may be directly or indirectly attached to each other or element A may contain element B or vice versa. Further, in the description herein, the word "substantially" whenever used is understood to include, but not restricted to, "entirely" or "completely" and the like. In addition, terms such as "comprising", "comprise", and the like whenever used, are intended to be non-restricting descriptive language in that they broadly include elements/components recited after such terms, in addition to other components not explicitly recited. Further, terms such as "about", "approximately" and the like whenever used, typically means a reasonable variation, for example a variation of +/- 5% of the disclosed value, or a variance of 4% of the disclosed value, or a variance of 3% of the disclosed value, a variance of 2% of the disclosed value or a variance of 1 % of the disclosed value.

Furthermore, in the description herein, certain values may be disclosed in a range. The values showing the end points of a range are intended to illustrate a preferred range. Whenever a range has been described, it is intended that the range covers and teaches all possible sub-ranges as well as individual numerical values within that range. That is, the end points of a range should not be interpreted as inflexible limitations. For example, a description of a range of 1 % to 5% is intended to have specifically disclosed sub-ranges 1 % to 2%, 1 % to 3%, 1 % to 4%, 2% to 3% etc., as well as individually, values within that range such as 1 %, 2%, 3%, 4% and 5%. The intention of the above specific disclosure is applicable to any depth/breadth of a range.

Additionally, when describing some embodiments, the disclosure may have disclosed a method and/or process as a particular sequence of steps. However, unless otherwise required, it will be appreciated the method or process should not be limited to the particular sequence of steps disclosed. Other sequences of steps may be possible. The particular order of the steps disclosed herein should not be construed as undue limitations. Unless otherwise required, a method and/or process disclosed herein should not be limited to the steps being carried out in the order written. The sequence of steps may be varied and still remain within the scope of the disclosure.

DESCRIPTION OF EMBODIMENTS

Exemplary, non-limiting embodiments of an ash stabiliser, a method of stabilising ash, and a method of producing the ash stabiliser are disclosed hereinafter.

In various embodiments, an ash stabiliser is provided. The ash stabiliser may comprise porous silica nanoparticles configured to sequester one or more inorganic compounds from an incinerator ash.

Advantageously, embodiments of the ash stabiliser disclosed herein allow toxic inorganic compounds present in incinerator ash to be removed. Without being bound by theory, it is believed that unwanted heavy metals may be entrapped by the porous silica nanoparticles through the substitution of protons of silanol surface groups by metal ions.

Even more advantageously, the porous nature together with the nano-sized particulate nature of the silica may increase the efficiency through which the toxic inorganic compounds may be removed. The inventors have found that commercially available silica are not desirable for use as ash stabilisers as they generally have a relatively low surface area of 200-250 m 2 /g and may have to be used in large amounts such as 25-35% by weight to achieve an optimised reaction. Accordingly, the inventors have surprisingly found that embodiments of the ash stabiliser disclosed herein provide an improved alternative to commercially available silica for the purposes of ash stabilisation. In various embodiments disclosed herein, the nanoparticles are substantially free from surfactants. The surface of the nanoparticles as well as the pores of the nanoparticles may be substantially free from surfactants. Without being bound by theory, it is believed that the presence of surfactants may reduce the surface available for sequestering unwanted inorganic compounds for binding to the heavy metals. In addition, the presence of surfactants remaining in the nanoparticles may present an environmental issue during disposal. For example, the surfactants may be toxic to aquatic life.

In various embodiments, the porous silica nanoparticles have particle sizes or average particle sizes of from about 1 nm to about 15 nm, from about 2 nm to about 15 nm, from about 3 nm to about 15 nm, from about 4 nm to about 15 nm, from about 4 nm to about 13 nm, from about 4 nm to about 1 1 nm, from about 4 nm to about 10 nm, from about 4 nm to about 9 nm, from about 4 nm to about 8 nm, from about 4 nm to about 7 nm, from about 4 nm to about 6 nm, or from about 4 nm to about 5 nm, no more than about 1 1 nm, no more than about 10 nm, no more than about 9 nm, no more than about 8 nm, no more than about 7 nm, no more than about 6 nm, no more than about 5 nm or no more than about 4 nm.

In one embodiment, the porous silica nanoparticles comprise mesoporous silica nanoparticles.

In various embodiments, the porous silica nanoparticles have pore sizes or average pore sizes of from about 1 nm to about 15 nm, from about 2 nm to about 13 nm, from about 2 nm to about 1 1 nm, from about 2 nm to about 9 nm, from about 2 nm to about 8 nm, from about 1 .5 nm to about 7 nm, from about 2 nm to about 6 nm, from about 2 nm to about 5 nm, from about 2 nm to about 4 nm, from about 2 nm to about 3 nm, no more than about 13 nm, no more than about 12 nm, no more than about 1 1 nm, no more than about 10 nm, no more than about 9 nm, no more than about 8 nm, no more than about 7 nm, no more than about 6 nm, no more than about 5 nm, no more than about 4 nm or no more than about 3 nm. In one embodiment, the porous silica nanoparticles have pore sizes or average pore sizes of from about 2 nm to about 15 nm.

In various embodiments, the porous silica nanoparticles have pore volumes or average pore volumes of from about 1 .0 to about 3.0 cm 3 /g, from about 1 .1 to about 2.8 cm 3 /g, from about 1 .1 to about 2.6 cm 3 /g , from about 1 .1 to about 2.5 cm 3 /g, about 1 .2 to about 2.3 cm 3 /g, about 1 .2 to about 2.2 cm 3 /g, about 1 .2 to about 2.1 cm 3 /g, about 1 .2 to about 2.0 cm 3 /g, about 1 .2 to about 1 .9 cm 3 /g, about 1 .2 to about 1 .8 cm 3 /g, about 1 .3 to about 1 .8 cm 3 /g, about 1 .4 to about 1 .8 cm 3 /g, about 1 .5 to about 1 .8 cm 3 /g, about 1 .6 to about 1 .8 cm 3 /g, about 1 .6 to about 1 .7 cm 3 /g, no less than about 1 .2 cm 3 /g, no less than about 1 .3 cm 3 /g, no less than about 1 .4 cm 3 /g, no less than about 1 .5 cm 3 /g, no less than about 1 .6 cm 3 /g or no less than about 1 .7 cm 3 /g.

As may be appreciated by a person skilled in the art, porous silica nanoparticles having pore volumes or average pore volumes that are different from those specified above may also be used, depending on their particle distribution, surface areas and average pore sizes.

Advantageously, the inventors have found out that porous silica nanoparticles with particle sizes or average particle sizes, pore sizes or average pore sizes and/or pore volumes or average pore volumes disclosed herein are capable of achieving high surface area of no less than about 400 m 2 /g, no less than about 500 m 2 /g, no less than about 600 m 2 /g, no less than about 700 m 2 /g, no less than about 800 m 2 /g, no less than about 900 m 2 /g, no less than about 1000 m 2 /g, no less than about 1 100 m 2 /g, no less than about 1200 m 2 /g or no less than about 1300 m 2 /g.

Advantageously, the inventors have found out that porous silica nanoparticles with particle sizes or average particle sizes, pore sizes or average pore sizes and/or pore volumes or average pore volumes disclosed herein are capable of achieving high surface area of about 800 m 2 /g to about 1200 m 2 /g. In various embodiments, the porous silica nanoparticles comprise porous silica nanoparticles pretreated with an ion-exchange process. In various embodiments, the porous silica nanoparticles are free from heat pre-treatment at a temperature of more than about 150 °C, more than about 140 °C, more than about 130 °C, more than about 120 °C, more than about 1 10 °C, more than about 100 °C, more than about 90 °C, more than about 80 °C, more than about 75 °C, more than about 70 °C, more than about 65 °C, more than about 60 °C, more than about 55 °C, more than about 50 °C, more than about 45 °C, or more than about 40 °C.

In certain embodiments, the porous silica nanoparticles disclosed herein have a high surface area of more than 1000 m 2 /g, and a framework-confined porosity made up of large mesopores.

The inventors have surprisingly found out that pre-treating the porous silica disclosed herein with an ion-exchange process may be an effective way to remove residual surfactant. Accordingly, various embodiments of the porous silica disclosed herein are pretreated with an ion-exchange process. Advantageously, when compared with thermal decomposition which is one possible way to remove the surfactants, ion- exchange process is comparatively lower in energy consumption and lower in cost. Contrary to the ion-exchange process, thermal decomposition is typically required to be carried at temperatures above 500°C in order to satisfactorily remove surfactants. This is energy inefficient and may drive up equipment costs as expensive equipment may be needed to withstand the high temperatures employed. This in turn can increase the overall production cost of the ash stabiliser and even more so when the production is made on an industrial scale. Accordingly, the present disclosure also provides porous silica nanoparticles that have not been subject to heat pre-treatment at a temperature of more than about 100 °C, more than about 200 °C, more than about 300 °C, more than about 400 °C, more than about 450 °C, more than about 500 °C, more than about 550 °C or more than about 600 °C.

The inventors have also found that high temperatures used in thermal decomposition can also result in the resultant porous silica having a high amount of organic residues, (typically 45-55% by weight) in the as-made porous materials, which is highly undesirable. Accordingly, in various embodiments, the ash stabiliser comprises from no more than about 45% by weight of organic residues, from about 0% to about 40% by weight of organic residues, from about 0% to about 35% by weight of organic residues, from about 0% to about 30% by weight of organic residues, from about 0% to about 25% by weight of organic residues, from about 0% to about 20% by weight of organic residues, from about 0% to about 15% by weight of organic residues, from about 0% to about 10% by weight of organic residues, from about 0% to about 5% by weight of organic residues, from about 0% to about 4% by weight of organic residues, from about 0% to about 3% by weight of organic residues, from about 0% to about 2% by weight of organic residues, from about 0% to about 1 % by weight of organic residues. In one embodiment, the porous silica is substantially free from organic residues and/or surfactants.

In one embodiment, the porous silica nanoparticles have an X-ray diffraction single broad peak between degree 2Θ = about 10°-50°, about 10°-40°, about 12°-40°, about 14°-40°, about 16°-40°, about 10°-38°, about 12°-38°, about 14°-38°, about 16°- 38°, about 10°-36°, about 12°-36°, about 14°-36°, about 16°-36°, about 10°-34°, about 12°-34°, about 14°-34°, about 16°-34°, about 10°-32°, about 12°-32°, about 14°-32°, or about 16-32°. Advantageously, the inventors have surprisingly found that porous silica nanoparticles having an X-ray diffraction single broad peak at degree 2Θ values disclosed above meet the requirements of being substantially free from surfactants as well as having the desired mesoporosity for the purposes of effective ash stabilisation.

Porous silica nanoparticles that have undergone surfactant removal treatment by ion-exchange have been surprisingly found to show a broad peak at degree 2Θ values disclosed above during X-ray diffraction. In various embodiments, the diffraction patterns are smooth without the appearance of more than one peak. In various embodiments, these broad peaks are characteristics of mesoporous silica oxide. In contrast, more than one peak in the diffraction pattern may be observed when silica nanoparticles are not washed or given treatment with an ion-exchange method. In one embodiment, the porous silica nanoparticles exhibit a type IV isotherm showing increasing nitrogen adsorption at a relative pressure of 0.8 or above. Advantageously, the inventors have found that this is a characteristic attributed to textural porosity, which is indicative of the existence of very small particles. In one embodiment, the porous silica nanoparticles are dispersed in liquid medium as a colloidal suspension. The liquid medium may be water, an organic solvent such as an alcohol or combinations thereof. In one embodiment, the alcohol is ethanol. The colloidal suspension may be an aqueous colloidal suspension. The colloidal suspension may be a stabile suspension with substantially uniform dispersions. The colloidal suspension may be substantially free from aggregates. The colloidal suspension may also be substantially free from flocculants.

In one embodiment, the porous silica nanoparticles comprises precipitated silica nanoparticles precipitated from a mixture comprising at least one organic compound.

In various embodiments, the ash stabiliser is an incinerator ash stabiliser. Advantageously, the ash stabiliser may be used in incinerator plants for stabilising fly ash and/or bottom ash generated therein.

Certain inorganic compounds such as heavy metal are hazardous and/or toxic. If allowed to leach from the incinerator ashes, these compounds may pollute the environment and/or harm living organisms. For example, mercury vapour, if inhaled by humans, may be toxic, fatal or lead to life threatening injuries to lungs and neurological systems. Inhalation of molybdenum fumes and dust may cause irritation of the eyes and the mucous membranes, and skin contact with molybdenum dust can cause irritation. If molybdenum is ingested in excessive amounts in humans through water and/or food, toxicity may also result. Likewise, certain inorganic compounds may also present problems in reuse applications. An example is chloride, which can accelerate the oxidation of reinforcing steel when chloride-containing incinerator ash is incorporated into building materials. In land reclamation projects, leached chloride from the incinerator ash may also contaminate local ecosystems. Accordingly, in various embodiments, there is provided a method of stabilising ash, the method comprising contacting the ash with the ash stabiliser as described herein to allow the porous silica nanoparticles to sequester one or more inorganic compounds present in the ash.

In various embodiments, the step of contacting the ash with the incinerator ash stabiliser comprises adding the incinerator ash stabiliser to the incinerator ash to form a reacting mixture, wherein the incinerator ash stabiliser is added in an amount of up to less than about 35% by weight of the reacting mixture, up to less than about 30% by weight of the reacting mixture, up to less than about 25% by weight of the reacting mixture, up to less than about 20% by weight of the reacting mixture, up to less than about 15% by weight of the reacting mixture or up to less than about 10% by weight of the reacting mixture. Advantageously, the inventors have found that embodiments of the method disclosed herein allow a significantly lower amount of nanoparticles to be added to achieve similar levels of ash stabilising effects when compared to commercially available colloidal particles, which have been found to only provide satisfactory results when a high amount of up to 25-35% by weight of such particles is used. In various embodiments, the method further comprises removing the nanoparticles that have sequestered the one or more inorganic compounds from the reacting mixture.

In various embodiments, the method does not require removing the nanoparticles that have sequestered the one or more inorganic compounds from the reacting mixture. In various embodiments, the nanoparticles are non-hazardous. In various embodiments, the obtained stabilised ash comprising the nanoparticles that have sequestered or trapped the one or more inorganic compounds can be safely reused for other applications. In various embodiments, the obtained stabilised ash is inert. Advantageously, embodiments of the method also allow for total recovery of soluble salts from the solid matrix by performing a washing step to remove chlorides and sulphates after metal stabilisation. In various embodiments, the obtained stabilised ash is mainly composed of calcium carbonate, calcium sulphate and silicon oxide, without any corrosive salts and toxic materials, making them extremely interesting for reuse applications.

In various embodiments, the stabilised ash obtained according to the method can be incorporated as filler in polymer matrix composite. Advantageously, the inventors have found that whilst the presence of a high amount of unmodified fly ash contents produces epoxy-based composites with low flexural and tensile strengths, embodiments of the method disclosed herein, comprising contacting the ash with the ash stabiliser, is capable of producing composites with improved mechanical properties including improved flexural and tensile strengths, and improved flexural and tensile moduli. Morphological findings also showed that the interfacial bonding of the treated ash with the epoxy polymer was significantly increased. Advantageously, embodiments of the method is capable of transforming waste materials like ash into value-added composites.

In various embodiments, said method of stabilising ash comprises reducing leaching of an inorganic compound from the ash.

In various embodiments, the inorganic compound comprises metal and/or non- metal. In various embodiments, the inorganic compound comprises heavy metal. In various embodiments, the inorganic compound is selected from the group consisting of one or more of arsenic, barium, cadmium, chromium, copper, mercury, molybdenum, nickel, lead, antimony, selenium, zinc, rubidium, chloride, fluoride, sulphate and combinations thereof. In various embodiments, the inorganic compound comprises an element or a substance which leaching limit is set out in the European Standard procedures EN12457-2. In various embodiments, said method of stabilising ash reduces leaching of rubidium in fly ash by at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 81 %, at least about 82%, at least about 83%, at least about 84%, or at least about 85% relative to a case where the ash stabiliser is not added.

In various embodiments, said method of stabilising ash reduces leaching of rubidium in bottom ash by at least about 50%, at least about 60%, at least about 61 %, at least about 62%, at least about 63%, at least about 64%, at least about 65%, at least about 66%, at least about 67%, at least about 68%, at least about 69%, at least about 70%, at least about 71 %, or at least about 72% relative to a case where the ash stabiliser is not added.

In various embodiments, said method of stabilising ash reduces leaching of barium in fly ash by at least about 50%, at least about 60%, at least about 61 %, at least about 62%, at least about 63%, at least about 64%, at least about 65%, at least about 66%, at least about 67%, at least about 68%, at least about 69%, at least about 70%, at least about 71 %, at least about 72%, at least about 73, at least about 74%, or at least about 75% relative to a case where the ash stabiliser is not added.

In various embodiments, said method of stabilising ash reduces leaching of chromium by at least about 50%, at least about 60%, at least about 68%, at least about 69%, at least about 70%, at least about 71 %, at least about 72%, at least about 73%, at least about 74% or at least about 75%, at least about 76%, at least about 77%, at least about 78%, at least about 79%, at least about 80%, at least about 81 %, at least about 82%, or at least about 83% relative to a case where the ash stabiliser is not added.

In various embodiments, said method of stabilising ash reduces leaching of molybdenum in fly ash by at least about 50%, at least about 60%, at least about 61 %, at least about 62%, at least about 63%, at least about 64%, at least about 65%, at least about 66%, at least about 67%, at least about 68%, at least about 69%, at least about 70%, at least about 71 %, at least about 72%, at least about 73%, at least about 74% or at least about 75%, at least about 76%, at least about 77%, at least about 78%, at least about 79%, at least about 80%, at least about 81 %, at least about 82%, at least about 83%, or at least about 84% relative to a case where the ash stabiliser is not added.

In various embodiments, said method of stabilising ash reduces leaching of lead in fly ash by at least about 50%, at least about 60%, at least about 67%, at least about 68%, at least about 69%, at least about 70%, at least about 71 %, at least about 72%, at least about 73%, at least about 74% or at least about 75%, at least about 76%, at least about 77%, at least about 78%, at least about 79%, at least about 80%, at least about 81 %, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, or at least about 88%, at least about 89%, at least about 90%, at least about 91 %, or at least about 92% relative to a case where the ash stabiliser is not added.

In various embodiments, said method of stabilising ash reduces leaching of zinc in fly ash by at least about 40%, at least about 41 %, at least about 42%, at least about 50%, at least about 60%, at least about 70%, at least about 71 %, at least about 72%, at least about 73%, at least about 74%, at least about 75%, at least about 76%, at least about 77%, at least about 78%, at least about 79%, at least about 80%, at least about 81 %, or at least about 82% relative to a case where the ash stabiliser is not added.

In various embodiments, said method of stabilising ash reduces leaching of chloride in fly ash by at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 91 %, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, at least about 99.1 %, at least about 99.2%, at least about 99.3%, at least about 99.4%, at least about 99.5%, at least about 99.6% or at least about 99.7% relative to a case where the ash stabiliser is not added. In various embodiments, said method of stabilising ash reduces leaching of fluoride in fly ash by at least about 50%, or at least about 60% relative to a case where the ash stabiliser is not added.

In various embodiments, said method of stabilising ash reduces leaching of sulphate in fly ash by at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 91 %, at least about 92%, at least about 93%, at least about 94% or at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, at least about 99.1 %, at least about 99.2%, at least about 99.3%, at least about 99.4%, at least about 99.5%, at least about 99.6% or at least about 99.7%, at least about 99.8%, at least about 99.9%, at least about 99.91 %, at least about 99.92%, at least about 99.93%, at least about 99.94%, or at least about 99.95% relative to a case where the ash stabiliser is not added. In various embodiments, said method of stabilising ash reduces leaching of barium in bottom ash by at least about 50%, at least about 60%, at least about 70%, at least about 71 %, at least about 72%, at least about 73%, at least about 74%, at least about 75%, at least about 76%, at least about 77%, at least about 78%, at least about 79%, at least about 80%, at least about 81 %, at least about 82%, at least about 83%, at least about 84%, at least about 85%, or at least about 86% relative to a case where the ash stabiliser is not added.

In various embodiments, said method of stabilising ash reduces leaching of copper in bottom ash by at least about 10%, at least about 15%, at least about 16%, at least about 17%, at least about 18%, at least about 20%, at least about 30%, or at least about 40%, at least about 41 %, at least about 42%, at least about 43%, at least about 44%, at least about 45%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 81 %, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91 %, at least about 92%, at least about 93%, at least about 94%, or at least about 95% relative to a case where the ash stabiliser is not added. In various embodiments, said method of stabilising ash reduces leaching of molybdenum in bottom ash by at least about 50%, at least about 52%, at least about 53%, at least about 54%, at least about 60%, at least about 70%, at least about 71 %, at least about 72%, at least about 73%, at least about 74%, at least about 75%, at least about 76%, at least about 77%, at least about 78%, at least about 79%, at least about 80%, at least about 81 %, at least about 82%, at least about 83%, or at least about 84%, at least about 85%, at least about 86%, at least about 87%, or at least about 88% relative to a case where the ash stabiliser is not added. In various embodiments, said method of stabilising ash reduces leaching of lead in bottom ash by at least about 50%, at least about 60%, at least about 70%, at least about 71 %, at least about 80%, at least about 90%, at least about 91 %, at least about 92% at least about 93%, at least about 94% or at least about 95%, at least about 96%, at least about 97%, at least about 98%, or at least about 99% relative to a case where the ash stabiliser is not added.

In various embodiments, said method of stabilising ash reduces leaching of zinc in bottom ash by at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 91 %, at least about 92% at least about 93%, at least about 94% or at least about 95%, or at least about 96% relative to a case where the ash stabiliser is not added.

In various embodiments, said method of stabilising ash reduces leaching of chloride in bottom ash by at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 91 %, at least about 92%, at least about 93, at least about 94%, at least about 95%, at least about 96% or at least about 97% relative to a case where the ash stabiliser is not added.

In various embodiments, said method of stabilising ash reduces leaching of sulphate in bottom ash by at least about 14%, at least about 15%, at least about 16%, at least about 50%, at least about 51 %, at least about 52%, at least about 53%, at least about 54%, at least about 55%, at least about 56%, at least about 57%, at least about 58%, at least about 59%, at least about 61 %, at least about 62%, at least about 63%, or at least about 64% relative to a case where the ash stabiliser is not added.

In various embodiments, there is provided a method of producing the ash stabiliser as described herein, the method comprising precipitating porous silica nanoparticles from a mixture of a silica source, a surfactant, a base and a liquid carrier; and removing the surfactant from the surface and/or the pores of the porous silica nanoparticles by an ion-exchange process.

In various embodiments, the silica source comprise organosilanes such as tetrabutoxysilane (TBOS), tetrapropoxysilane (TPOS), tetraethoxysilane (TEOS), tetramethoxysilane (TMOS) or the like. In one embodiment, the silica source comprises an alkoxysilane.

In various embodiments, the surfactant is one or more of the following selected from the group consisting of polyvinyl alcohol (PVA), dioctyl sodium sulfosuccinate, methyl cellulose, polysorbates, cetyltrimethylammonium bromide (CTAB), dodecylamine (DDA), 1 ,2-di-O-octadecenyl-3-trimethylammonium propane (DOTMA), hexadecyltrimethylammonium chloride (CTACI) and l,2-Dioleoyl-3- trimethylammonium-propane (DOTAP).

In one embodiment, the surfactant comprises a cationic surfactant. Advantageously, the cationic surfactants are capable of assembling with silicates having a high negatively-charged density though strong electrostatic interactions. In various embodiments, the base is selected from an alkali metal hydroxide and/or an amine. In various embodiments, the alkali metal hydroxide base is selected from the group consisting of potassium hydroxide, sodium hydroxide, lithium hydroxide, or a combination thereof. In one embodiment, the amine base comprises ammonia. In various embodiments, the amine base may be an organic amine base. In various embodiments, the organic amine base is selected from dimethyl amine, ethylamine, diethylamine, triethylamine, methylamine, dimethylamine, trimethylamine, ethanolamine, diethanolamine, and triethanolamine (TEA), morpholine, di-n- propylamine, butylamine, isopropylamine, cyclohexylamine, pentylamine or combination thereof.

In one embodiment, the base comprises triethanolamine (TEA). Advantageously, triethanolamine (TEA) is non-hazardous and the inventors have found that triethanolamine (TEA) may act as a complexing agent for the silicate species and additionally as a growth inhibitor for mesoporous particles, limiting its growth and aggregation of particles so that they can be in a size that is suitable for the purposes of an ash stabiliser.

In various embodiments, the liquid carrier may be selected from the group consisting of water, alcohols, halogenated hydrocarbon solvents, and combinations thereof.

In one embodiment, the method further comprises removing the surfactant from the porous silica nanoparticles by an ion-exchange process. The surfactant may be removed from the surface and/or the pores of the porous silica nanoparticles. Advantageously, the ion-exchange method is fast, cheap, efficient, low energy and able to remove surfactant and template residues completely without resorting to high temperatures. This is beneficial as the surfactant may be toxic, and its toxicity will likely damage the environment if the process is scaled up accordingly. As such, effective removal of the surfactant is therefore desired. Even more advantageously, the ion exchange method is also capable of preserving the structure and high surface area of the mesoporous materials. In one embodiment, the steps of the method are carried out at a temperature of no more than about 150 °C, no more than about 140 °C, no more than about 130 °C, no more than about 120 °C, no more than about 1 10 °C, no more than about 100°C, no more than about 90°C, no more than about 80°C, no more than 70°C, no more than about 60°C, no more than about 50°C, or no more than about 40°C. Advantageously, this may overcome or ameliorate the problems associated with the removal of surfactant by thermal decomposition or calcination as mentioned above. Accordingly, in one embodiment, the method is free from any thermal decomposition and/or calcination steps.

In various embodiments, the ion-exchange process is carried out using a solution of an acid or a cationic proton donor in ethanol. In various embodiments, the acid is selected from the group consisting of hydrochloric acid, sulfuric acid and nitric acid. In various embodiments, the cationic proton donor is selected from the group consisting of sodium nitrate, potassium nitrate, ammonium nitrate and any solution containing sodium ion, potassium ion and/or ammonium ion.

In one embodiment, said precipitating comprises centrifuging the mixture of a silica source, a surfactant, a base and a liquid carrier to recover the porous silica nanoparticles.

In various embodiments, the molar ratio of silicon in the silica source to TEA is no more than about 1 :1 , no more than about 1 :2, no more than about 1 :3, no more than about 1 :4, no more than about 1 :5, no more than about 1 :6, no more than about 1 :7, no more than about 1 :8, no more than about 1 :9, no more than about 1 :10, no more than about 1 :1 1 , no more than about 1 :12, no more than about 1 :13, no more than about 1 :14, no more than about 1 :15, no more than about 1 :16, no more than about 1 :17, no more than about 1 :18, no more than about 1 :19, no more than about 1 :20.

In various embodiments, the molar ratio of the surfactant to silicon in the silica source is no less than about 0.15, no less than about 0.16, no less than about 0.17, no less than about 0.18, no less than about 0.19, no less than about 0.20, no less than about 0.21 , no less than about 0.22, no less than about 0.23, no less than about 0.24, no less than about 0.25, no less than about 0.26 or no less than about 0.27.

In one embodiment, the method comprises an industrial method. BRIEF DESCRIPTION OF FIGURES

Fig. 1 is a schematic flowchart for illustrating a method of stabilising ash in an example embodiment. Fig. 2 is a schematic flowchart for illustrating a method of producing an ash stabiliser in an example embodiment.

Fig. 3 is a schematic diagram for illustrating a method of producing an ash stabiliser in an example embodiment.

Fig. 4 is a graph showing the variation of the surface area of mesoporous silica nanoparticles (MSNs) with increasing Si:TEA ratio at a Surf/Si ratio of 0.25 in accordance with various embodiments disclosed herein. Fig. 5 is a graph showing the variation of the surface area of MSNs with increasing Si:TEA ratio at a Surf/Si ratio of 0.17 in accordance with various embodiments disclosed herein.

Fig. 6 is an isotherm linear plot for one exemplary MSN (MSN 4A in Table 1 ) at Surf/Si = 0.25 in accordance with various embodiments disclosed herein.

Fig. 7 is an isotherm linear plot for another exemplary MSN (MSN 5B in Table 2) at Surf/Si = 0.17 in accordance with various embodiments disclosed herein. Figs. 8a and 8b are scanning electron microscopy (SEM) images of one exemplary MSN (MSN 4A in Table 1 ) (Si:TEA = 1 :12) at Surf/Si = 0.25 in accordance with various embodiments disclosed herein.

Figs. 9a and 9b show SEM Images of another exemplary MSN (MSN 5B in Table 2) (Si:TEA = 1 :14) At Surf/Si = 0.17 in accordance with various embodiments disclosed herein. Fig. 10 shows the X-ray diffraction (XRD) patterns for MSNs without surfactant removal, one exemplary MSN (MSN 4A in Table 1 ) (Si:TEA = 1 :12) at Surf/Si = 0.25 and another exemplary MSN (MSN 5B in Table 2) (Si:TEA = 1 :14) at Surf/Si = 0.17 in accordance with various embodiments disclosed herein. DETAILED DESCRIPTION OF FIGURES

Fig. 1 is a schematic flowchart 100 for illustrating a method of stabilising ash in an example embodiment. At step 102, ash is contacted with an ash stabiliser, to allow the porous silica nanoparticles to sequester one or more inorganic compounds. The ash stabiliser comprises porous silica nanoparticles and the porous silica nanoparticles have been pretreated with an ion-exchange process. Optionally, at step 104, the nanoparticles that have sequestered the one or more inorganic compounds are removed. Fig. 2 is a schematic flowchart 200 for illustrating a method of producing an ash stabiliser in an example embodiment. At step 202, porous silica nanoparticles are precipitated from a mixture of a silica source, a surfactant, a base and a liquid carrier. At step 204, surfactants are removed from pores of the porous silica nanoparticles by an ion-exchange process.

Fig. 3 is a schematic diagram for illustrating a method of producing an ash stabiliser in accordance with various embodiments disclosed herein. A silica source in the form of tetraethoxysilane (TEOS) 302 and a mixture 304 of a surfactant in the form of cetyltrimethylammonium chloride (CTACI) and a base in the form of triethanolamine (TEA) are added together and allowed to undergo hydrothermal reaction at room temperature shown by arrow 305 to produce colloidal mesoporous silica nanoparticles 306a, 306b and 306c, collectively known as precursor ash stabilisers 306, which contain the surfactant cetyltrimethylammonium chloride (CTACI). An ion-exchange process is then performed to remove surfactants from the surface and/or the pores of the precursor ash stabilisers 306 to produce colloidal mesoporous silica nanoparticles 308a, 308b and 308c, collectively known as ash stabilisers 308, which are capable of sequestering one or more inorganic compounds from ash and which have been pretreated with an ion-exchange process.

Fig. 4 is a graph showing the variation of the surface area of MSNs with increasing Si:TEA ratio at a Surf/Si ratio of 0.25. The surface area of the MSNs increases as the ratio of Si:TEA increases from MSN 1 A to MSN 6A as illustrated in Table 1 .

Fig. 5 is a graph showing the variation of the surface area of MSNs with increasing Si:TEA ratio at a Surf/Si ratio of 0.17. The surface area of the MSNs increases to a maximum as the ratio of Si:TEA increases from MSN 1 B to MSN 5B and then drops as the ratio of Si:TEA continues to increase in MSN 6B as illustrated in Table 2.

Fig. 6 is an isotherm linear plot for MSN 4A of Table 1 at Surf/Si =0.25 in accordance with an example embodiment disclosed herein. The plot resembles a type IV isotherm, showing an increase of adsorption at a high relative pressure (P/Po above 0.8). This is attributed by textural porosity, which is indicative of the existence of very small particles. Fig. 7 is an isotherm linear plot for MSN 5B of Table 2 at Surf/Si =0.17 in accordance with an example embodiment disclosed herein. The plot resembles a type IV isotherm, showing an increase of adsorption at a high relative pressure (P/Po above 0.8). This is attributed by textural porosity, which is indicative of the existence of very small particles.

Fig. 8a is an SEM image of MSN 4A of Table 1 (Si:Tea = 1 :12) at Surf/Si = 0.25 in accordance with an example embodiment disclosed herein. The image is taken at 10,ΟΟΟχ magnification. Fig. 8b is an SEM image of MSN 4A of Table 1 (Si:Tea = 1 :12) At Surf/Si = 0.25 taken at 50,000χ magnification. As shown, the MSNs are spheres of substantially uniform sizes with diameters that range in nano scale. Ion-exchange did not give rise to significant changes in the overall morphology of the MSNs. Fig. 9a is an SEM image of MSN 5B of Table 2 (Si:Tea = 1 :14) at Surf/Si = 0.17 in accordance with an example embodiment disclosed herein. The image is taken at 10,ΟΟΟχ magnification. Fig. 9b is an SEM image of MSN 5B of Table 2 (Si:Tea = 1 :14) at Surf/Si = 0.17 taken at 50,000χ magnification. As shown, the MSNs are of spheres of substantially uniform sizes with diameters that range in nano scales. Ion-exchange and varying molar ratios between the materials for synthesis did not give rise to significant changes in the overall morphology of the MSNs.

Fig. 10 shows the XRD patterns for MSNs without surfactant removal, MSN 4A of Table 1 (Si:TEA = 1 :12) at Surf/Si = 0.25 and MSN 5B (Si:TEA = 1 :14) of Table 2 at Surf/Si = 0.17 in accordance with example embodiments disclosed herein. Multiple small peaks could be observed when the MSNs are not washed or given treatment by ion-exchange method. After the MSNs undergo surfactant removal treatment (MSNs 4A and 5B), a broad and smooth peak, without multiple peaks appearance, between the degree 2Θ = 16-32° for each of MSN 4A and MSN 5B is observed. These broad peaks are representative of the silica particles being mesoporous.

EXAMPLES

Example embodiments of the disclosure will be better understood and readily apparent to one of ordinary skill in the art from the following examples, tables and if applicable, in conjunction with the figures.

Although studies on the interactions of surfactant, template, and silicas on synthesis of mesoporous silica nanoparticles (MSN) were conducted for many years, certain critical issues remained. The kinetic condition (pH, reaction temperature, concentration of materials etc.) remained of particular interest. Furthermore, scaling- up the quantity of mesoporous silica nanoparticles for commercial-scale applications was expected to present major challenges with regard to collection, uniformity, and reproducibility.

In the following examples, the inventors have shown the effects of varying the molar ratio of Si to template. The preferred concentration of TEA for the preparation of MSN for various applications is also discussed in the following examples. The examples demonstrate that a precise control of the reactants is capable of producing efficacious mesoporous nanoparticles, which are also translatable to an industrial scale. As will be shown in the following examples, it appears that more advantages may be observed by increasing the concentration of TEA instead of surfactants. Without being bound by theory, the surfactants are believed to enhance the dispersity of the alkoxysilanes in water and the hydrolysis rate of the alkoxysilanes become faster, leading to an increased nucleation as compared to the particle growth.

Example 1 - Synthesis of MSN

The synthesis of MSN is demonstrated in this Example at a laboratory scale to primarily prove the principles involved. It will be understood that a further scale-up of the method may be carried out, for example by scaling it to an industrial process. Briefly, 2.67 g of cetyltrimethylammonium chloride (CTACI) (25 wt% in water) from Sigma Aldrich as surfactant was dissolved in 24 g of water and heated to 60°C under 600 rpm stirring. The solution was subsequently added to a two-phase solution consisting of 1 .9 g (9 mmol) tetraethoxysilane as the silica source (TEOS) from Merck and 14.3 g (96 mmol) TEA from Merck as template (pre-heated at 90°C without stirring for 30 minutes). The mixture containing CTACI, TEOS, TEA and water was stirred at room temperature for about 2-3 hours at 600 rpm, the molar composition of TEOS:CTACI:TEA:H 2 O being 1 :0.17:8:120. After the reaction was completed, the precipitate of silica were obtained and collected by centrifuge (Sigma Sartorius 4K15 model). Colloidal mesostructured silica nanoparticles were thus obtained. The colloidal solution was further washed and centrifuged at 9000 rpm for 3 minutes two or three times repeatedly in ethanol to remove the free surfactants. An ion-exchange process is then carried out to remove TEA template and CTACI surfactant by adding, in a 1 :1 ratio, the colloidal solution in either 20 g/L ammonium nitrate in 100 ml ethanol/ 2 weight% ammonium nitrate in ethanol or 10 ml concentrated hydrochloric acid (37%) in 90 ml ethanol and stirred for either 8-10 hours at 70°C or 1 hour at 90°C at 1000 rpm. Then, the resulting solution was centrifuged to obtain the precipitate mesoporous silica nanoparticles. To replace the ammonium ions within the nanoparticles structure, the precipitate was washed again with a 100 ml solution of hydrochloric acid in ethanol (10 ml cone. HCI (37%) in 100 ml ethanol) for 1 hour at 90°C (1000 rpm). Following washing and centrifuging with pure ethanol, the obtained precipitate was redispersed in water and sonicated for 20 minutes to allow a stable colloidal aqueous suspension of mesoporous silica nanoparticles to form, resulting in the colloidal mesoporous silica nanoparticles product. To obtain a powder form of the nanoparticles product, after centrifuging, the precipitate may be directly dried in vacuum oven at 90°C overnight.

In this example, triethanolamine (TEA) was used to provide basicity in the synthesis of mesoporous silica nanoparticle as a substitute for the more common bases such as sodium hydroxide or ammonia to synthesize colloidal mesoporous silica with diameters of 20-150 nm. Triethanolamine (TEA) is non-hazardous and the inventors have found that triethanolamine (TEA) may act as a complexing agent for the silicate species and additionally as a growth inhibitor for mesoporous particles, limiting its growth and aggregation of particles. Furthermore, TEOS is fixed as the silica source as it is postulated that different alkoyxsilianes may not have a big impact on the particle size. Cationic surfactant is selected due to the alkaline conditions because silicates with a high negatively-charged density can assemble with the cationic surfactants though strong electrostatic interactions. Example 2 - Characterisation of MSN

In this Example, the morphology and sizes of mesoporous silica in accordance with various embodiments disclosed herein are studied by using Field Emission Scanning Electron Microscopy (FE-SEM). In addition, X-ray Diffraction (XRD) is used for phase composition identification of the silica. The Surface Area and Porosity Analyser is used to determine the textures of mesoporous silica. The models used in the Example are JEOL JSM-6701 F scanning electron microscope, X-Ray Diffraction System PANalytical X'pert PRO MPD and Micromeritic ASAP 2020. The inventors view that it is desirable to obtain a high surface area porous silica nanoparticles of more than 1000 m 2 /g and a framework-confined porosity made up of large mesopores. As demonstrated in this Example, this may be achieved by using different amounts of surfactant and TEOS under controlled reaction conditions (mixing temperature, reaction time, stirring speed, extraction time and extraction temperature). In this Example, two ratio of Surf/Si (0.17 and 0.25) are studied with different amount of TEA added in the synthesis of mesoporous silica nanoparticles (MSNs). In the medium Surf/Si ratio range, the surfactant may act as porogens (mesopores were further developed), particle size controllers, and flocculants.

Table 1 below shows the surface area of MSNs in different amount of TEA at fixed molar ratio Surf/Si = 0.25. Table 2 below shows the surface area of MSNs in different amount of TEA at fixed molar ratio Surf/Si = 0.17. When ratio of Si/TEA increased, the surface area of MSNs increased as well. Further, the molar ratio of surfactant to Si of alkoxysilanes (Surf/Si) is also demonstrated to affect the mesostructured formation such as the particle diameter and the dispersity of MSNs. In conclusion, high surface area of MSNs can be obtained by using the ion-exchange method together with the selection of an optimum ratio of the synthesis materials.

Table 1

Surf/Si =0.25

Pore

Volume Pore Size

Surface

MSNs Si:TEA (BJH (BJH

Area (m 2 /g)

Desorption, Desorption, Particle cm 3 /g) nm) Size (nm)

1 A 1 :04 613 2.3 1 1 10

2A 1 :08 783 2.1 8 8

3A 1 :10 927 1 .5 4 6

4A 1 :12 1221 1 .6 3 5

5A 1 :14 1274 1 .3 3 5

6A 1 :16 1275 1 .4 3 5 Table 2

The optimum molar ratio of Si to TEA required to obtain a high surface area of

MSNs is shown in Fig. 4 and 5. In particular, MSNs 4A for Surf/Si 0.25 (1221 m 2 /g) and MSNs 5B (1363 m 2 /g) for Surf/Si = 0.17 gave the significant promising surface area. A nitrogen adsorption analysis was conducted on the MSNs. Prior to the analysis, each sample was degassed at 90°C in nitrogen under vacuum for 24 hour. Nitrogen adsorption analysis was conducted with nitrogen at 77 K/-195.793°C and with relative pressure (P/Po) in the range of 0.1 -0.99. Specific surface area was calculated using Brunauer-Eimmett-Teller (BET) equation at P/Po < 0.3. Pore size distribution was calculated from the branch of the adsorption and desorption isotherm using Barrett-Joyner-Halenda (BJH) method. Primary total pore volume and pore size were determined at P/Po = 0.99. For both MSN 4A and MSN 5B, a type IV adsorption isotherm was observed, which, in addition to the pore condensation step, shows an increase of adsorption at a high relative pressure (p/po above 0.8) (see Figs 6 and 7). This was due to textural porosity, which is indicative of the existence of very small particles. Furthermore, it was observed that the more the TEA was added, the smaller the particle size of the resulting MSNs.

The MSNs in the Examples were of substantially spherical shapes with substantially uniform size and diameters that in the nanometer range. It was observed that the application of the ion-exchange method and the different molar ratio between the materials used for synthesis in this Example did not result in any significant changes in its overall morphology (see Figs 8 and 9). In X-ray diffraction analysis, diffraction patterns were obtained by employing

CuKa radiation (λ = 1 .54 A) generated by a Philip glass diffraction X-ray tube broad focus 2.7 kW types. The samples were continuously scanned at the range of 2Θ = 5- 90°C with a scanning rate of 1 minute. From the X-ray diffraction results, some peaks could be observed when the MSNs were not washed or treated with the ion-exchange method. After the MSNs had undergone surfactant removal treatment (MSNs 4A and 5B), the broad peak between the degree 2Θ = 16-32° were smooth without any peaks appearance. These broad peaks are representative of the silica particles being mesoporous (see Fig. 10). Example 3 - Use of MSNs in incinerator ash stabilisation

In this Example, the incineration ash was mixed with MSNs in accordance with various embodiments disclosed herein and the stabilised mixture was tested in accordance with the proposed European Standard procedures EN12457-2, which is the European standard tests for reuse application, to determine the mixture's suitability for use in further manufacturing methods. It is appreciated that the leaching behaviour of a waste material is related to its environmental exposure conditions such as the liquid-to-solid ratio {US). In this regard, the test procedures specified in the European EN12457-2 batch leaching tests was adopted for attaining information on the leaching behaviour under a broad spectrum of leaching pH values and L/S ratios, respectively. Test results 1 are obtained based on the test procedures of EN 12457-2 version 1 , where cumulative leaching is determined in a test where liquid is provided in a single batch manner to achieve a L/S ratio of 10L/kg. Test results 2 are obtained based on the test procedures of EN 12457-2 version 2, where cumulative leaching is determined in a test where liquid is provided in a two batch manner to collectively achieve a L/S ratio of 10L/kg. These standard leaching tests are currently adopted by Germany and Denmark. After the leaching procedures, the eluates were analysed by an inductively coupled plasma (ICP) spectrometer to measure heavy metals commonly present in incineration ash. Table 3 below shows the leaching test results performed in accordance with EN 12457-2 for fly ash that were stabilised, amongst others, with embodiments of the ash stabilisers disclosed herein. Table 4 below shows the leaching test results performed in accordance with EN 12457-2 for bottom ash that were stabilised, amongst others, with embodiments of the ash stabilisers disclosed herein.

Test results 1

The results in Tables 3 and 4 obtained based on EN 12457-2 version 1 below show that the harmful heavy metals such as lead (Pb), zinc (Zn) and rubidium (Rb) for both fly ash and bottom ash were successfully immobilised in embodiments of the mesoporous silica nanoparticles (MSNs) disclosed herein. This is because the amount of these harmful heavy metals was shown to be lower for incineration ash treated with embodiments of the mesoporous silica nanoparticles (MSNs) disclosed herein, as compared to untreated incineration ash. It is noteworthy that the amount of detected heavy metals was below the threshold value allowable under the EN 12457-2 standards for incineration ash treated with MSNs that were in accordance with various embodiments disclosed herein. Table 3

Note: ND- Not Detected

MSN4, MSN6 and MSN8 correspond respectively to 4% concentration, 6% concentration and 8% concentration of MSN 4A of Table 1 in aqueous colloidal suspension.

Table 4

Note: ND- Not Detected MSN4, MSN6 and MSN8 correspond respectively to 4% concentration, 6% concentration and 8% concentration of MSN 4A of Table 1 in aqueous colloidal suspension.

Test results 2

Tables 5 and 6 below show the second independent leaching test results obtained based on EN 12457-2 version 2 for both fly ash and bottom ash treated with embodiments of the mesoporous silica nanoparticles (MSNs) disclosed herein. Likewise, the amount of harmful heavy metals was shown to be lower for incineration ash treated with embodiments of the mesoporous silica nanoparticles (MSNs) disclosed herein, as compared to untreated incineration ash. The amount of detected heavy metals was also below the threshold value allowable under the EN 12457-2 standards for incineration ash treated with MSNs that were in accordance with various embodiments disclosed herein

Table 5

Cumulative leaching with L/S ratio lOL/kg for 24 hours (mg/kg)

Parameter Limit Raw Commerci MSN4- MSN6- j MSN8- j

Value Fly al MSNs- treated treated treated

Ash treated Fly Fly Ash Fly Ash j Fly Ash

Ash

As (arsenic) 0.5 j <0.02 <0.02 <0.02 <0.02 j <0.02 j

Ba (barium) 20 j 1.487 1.555 0.485 0.46 j 0.371

Cd (cadmium) 0.04 j <0.02 <0.02 <0.02 <0.02 j <0.02 j

Cr (chromium 0.5 j 0.123 0.038 0.027 0.025 1 <0.02 j

(total))

Cu(copper) 2 j <0.02 <0.02 0.115 0.124 j 0.066

Hg (mercury) 0.01 j <().()() 1 <().()() 1 <().()() 1 <().()() 1 j <().()() 1 j

Mo 0.5 j 0.127 0.032 0.045 0.038 j <0.02 j

(molybdenum)

Ni (nickel) 0.4 j <0.02 <0.02 <0.02 <0.02 j <0.02 j

Pb (lead) 0.5 j 4.584 1.442 1.053 1.074 j 0.351

Sb (antimony) 0.06 j <0.02 <0.02 <0.02 <0.02 j <0.02 j

Se (selenium) 0.1 j <0.02 <0.02 <0.02 <0.02 j <0.02 j

Zn (zinc) 4 j 0.135 0.079 0.032 0.03 j 0.024 CI (Chloride) 800 j 299 0.8 1.42 1.13 0.64

F (Fluoride) 10 0.05 <0.02 <0.02 <0.02 1 <0.02 j

S0 4 (Sulphate) 1000 j 285 0.14 0.23 0.13 0.13

Note : MSN4, MSN6 and MSN8 correspond respectively to 4% concentration, 6% concentration and 8% concentration of MSN 4A of Table 1 in aqueous colloidal suspension.

Table 6

Cumulative leaching with L/S ratio lOL/kg for 24 hours (mg/kg)

Parameter Limit Raw Commercial i MSN4- j MSN6- ! MSN8- j

Value i Bottom MSNs- treated i treated i treated ;

Ash treated Bottom i Bottom i Bottom ;

Bottom Ash Ash Ash Ash

As (arsenic) 0.5 ! <0.02 <0.02 <0.02 j <0.02 ! <0.02 j

Ba (barium) 20 I 0.580 0.076 0.079 ! 0.102 j 0.128 j

Cd (cadmium) 0.04 ! <0.02 <0.02 <0.02 j <0.02 ! <0.02 j

Cr (chromium 0.5 I 0.037 0.056 0.101 I 0.087 j 0.106 j (total))

Cu(copper) 2 j 1.642 0.224 0.169 j 0.077 \ 0.137 j

Hg (mercury) 0.01 I <().()() 1 <().()() 1 <0.001 j <().()() 1 j <().()() 1 j

Mo 0.5 j 0.299 0.139 0.039 I 0.033 j 0.070 j

(molybdenum)

Ni (nickel) 0.4 I <0.02 <0.02 <0.02 j <0.02 I <0.02 j

Pb (lead) 0.5 j 2.030 <0.02 <0.02 I <0.02 j <0.02 j

Sb (antimony) 0.06 I <0.02 0.037 0.072 j 0.077 I 0.035 j

Se (selenium) 0.1 j <0.02 <0.02 <0.02 ! <0.02 j <0.02 j

Zn (zinc) 4 ! 0.564 <0.02 <0.02 j <0.02 \ <0.02 j

CI (Chloride) 800 j 3.22 0.06 0.12 0.12 0.08

F (Fluoride) 10 ! <0.02 <0.02 <0.02 j <0.02 ! <0.02 j

S0 4 (Sulphate) 1000 j 1.76 1.49 0.63 0.73 0.62

Note : MSN4, MSN6 and MSN8 correspond respectively to 4% concentration, 6% concentration and 8% concentration of MSN 4A of Table 1 in aqueous colloidal suspension. APPLICATIONS

Various embodiments of the present disclosure provide porous, high-surface area silica nanoparticles which may be used in low amounts to bind and stabilise incineration ash, thereby keeping the cost of the process low. Further, various embodiments of the porous silica nanoparticles disclosed herein are relatively cheap to produce, highly reactive and non-toxic, thereby making the stabilisation process cost-effective on a large scale.

In various embodiments of the methods of stabilising ash disclosed herein, the chemical stabilisation reaction may be done through mixing the MSWI fly ash, bottom ash or their mixtures (at various ratios) with embodiments of the colloidal mesoporous silica disclosed herein.

Various embodiments of the methods of stabilising ash disclosed herein also qualify as a low energy process that can stabilise incinerator ash and lock up heavy metal contaminants by using embodiments of the colloidal MSNs disclosed herein. The stabilised ash may subsequently be used as a filler to create new and improved polymeric composite materials with a wide range of applications. The present disclosure has demonstrated the principles involved, and opens the way for further scale-up.

It will be appreciated by a person skilled in the art that other variations and/or modifications may be made to the embodiments disclosed herein without departing from the spirit or scope of the disclosure as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.