WO2016133463A1

WO2016133463A1 - Method of manufacturing a lightweight material

Info

Publication number: WO2016133463A1
Application number: PCT/SG2016/050082
Authority: WO
Inventors: Thatt Yang Timothy TAN; Qingchi XU
Original assignee: Nanyang Technological University
Priority date: 2015-02-17
Filing date: 2016-02-17
Publication date: 2016-08-25
Also published as: CN107921492A; CN107921492B

Abstract

A method of manufacturing a lightweight material is provided. The method comprises a) dispersing a solid waste comprising at least one of a contaminated solid waste, marine clay, mud, waste glass, or ash obtained from incineration of waste in an aqueous reagent to form a dispersion; b) mixing the dispersion with an additive comprising a foaming agent and a metal silicate to form a mixture; and c) curing the mixture to obtain the lightweight material. A lightweight material manufactured by the method, and use of the method in the manufacture of a lightweight aggregate, a thermal insulative panel, a lightweight partition wall, or a lightweight brick are also provided.

Description

METHOD OF MANUFACTURING A LIGHTWEIGHT MATERIAL

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore patent application No. 10201501250S filed on 17 February 2015, the content of which is incorporated herein by reference in its entirety for all purposes.

TECHNICAL FIELD

[0002] Various embodiments relate to the manufacture of lightweight materials using solid wastes, including contaminated solid waste, marine clay, mud, waste glass, and/or ash obtained from incineration of waste.

BACKGROUND

[0003] Due to rapid urbanization, large amounts of sewage sludge and municipal solid waste (MSW) are being generated world-wide annually, and the numbers are growing rapidly. In USA alone, annual generation of municipal solid waste amounts to 200 to 400 million tons. These constitute serious global environment problems.

[0004] To manage the wastes, incineration has been used in most developed countries, including Singapore and Europe. By incineration, about 70 % to 90 % in mass of sewage sludge and MSW may be reduced before they are sent for landfill. The method has an added advantage that pathogens and organic pollutants may be burnt off in the process. Notwithstanding the above, it is estimated that approximately 1.7 million tons of sewage sludge incineration ash are produced annually world-wide, and this number is likely to increase rapidly in the future. In Singapore, for example, an estimated 500,000 tons of MSW incineration ash and 18,000 tons of sewage sludge incineration ash are respectively generated from burning MSW and sewage sludge annually. The incineration ashes are disposed off at Pulau Semakau landfill, which is projected to be exhausted by 2045, and recycling rate of both incineration ashes in Singapore is currently at 0 %.

[0005] Most studies on incineration ash have been focused on its safe disposal, but not on conversion of the incineration ash to resources. Development of technologies that can convert incineration ash to green products is important to protect precious land and water resources. In addition, tighter legislation and higher disposal costs provide greater incentives to develop economically viable reuse and recycling alternatives.

[0006] Apart from incineration ash, marine clay, which may be found in coastal and offshore regions around the world, is another major source of solid waste. Taking Singapore as an example, a large quantity of marine clay is removed from construction sites every year, in particular construction sites for underground rail or road systems. Swelling and shrinkage behaviors of marine clay may impose foundation problems to result in excessive settlements, such as that seen by the Nicoll Highway collapse in 2004. A large quantity of marine clay was excavated during construction of the Marina Barrage, which had to be removed to ensure its stability. Furthermore, marine clay is susceptible to contamination with heavy metals due to industrial waste discharge into the sea, or oil slicks from tankers. Legislation in Singapore prohibits disposal of contaminated marine clay in landfill, and the marine clay is currently sent to staging ground in Changi East. This is, however, not a sustainable solution.

[0007] Mud slurry also constitutes a main source of waste generated in Singapore. Recycling of the mud slurry is difficult due mainly to its high water content. Management of mud slurry has thus become a social and environmental problem. There is no feasible and sustainable technology which may be used to recycle the mud slurry in Singapore. Currently, the mud slurry is disposed at Sungei Tengah Road location and the disposal cost is around S$20 per ton.

[0008] Waste glass, which may be derived from consumer electronics such as televisions and computers, may pose problems in disposal as glass is not biodegradable and only a small fraction of waste glass may be recycled or reused such as in the bottling and container industry. New products utilizing recycled waste glass are therefore needed to further promote glass recycling, because only a limited amount of glass can be remelted to make new containers, which is currently the primary use of recycled glass.

[0009] Green building materials are materials recycled from wastes which have specific benefits such as energy conservation. They have attracted strong interests due to growing awareness of environmental preservation and resource depletion. Other driving forces for the development and use of green building materials include social and economic factors such as environmental responsibility, resource efficiency and enhanced corporate image. In Singapore, incentives of using certified green building materials in residential and nonresidential buildings include awarding of green mark points by the relevant authorities. [0010] Commercially available artificial lightweight green building materials (inorganic) include foam glass and foam ceramic, which have properties of lightweight (resource efficient), low thermal conductivity (energy conservation), high thermal stability, and nonflammable (environmentally responsible). Foam glass and foam ceramic, however, are relatively expensive due in part to high raw material costs, as recycled glass or ceramics are usually not used to produce the foam glass and foam ceramic, due to complexity and high costs associated with sorting the recycled glass and ceramics.

[0011] In view of the above, there exists a need for improved methods of utilizing the solid waste, such as in the manufacture of lightweight material, that overcome or at least alleviate one or more of the above-mentioned problems.

SUMMARY

[0012] In a first aspect, a method of manufacturing a lightweight material is provided. The method comprises

a) dispersing a solid waste comprising at least one of a contaminated solid waste, marine clay, mud, waste glass, or ash obtained from incineration of waste in an aqueous reagent to form a dispersion;

b) mixing the dispersion with an additive comprising a foaming agent and a metal silicate to form a mixture; and

c) curing the mixture to obtain the lightweight material.

[0013] In a second aspect, a lightweight material manufactured by a method according to the first aspect is provided.

[0014] In a third aspect, use of a method according to the first aspect in the manufacture of a lightweight aggregate, a thermal insulative panel, a lightweight partition wall, or a lightweight brick is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The invention will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and the accompanying drawings, in which: [0016] FIG. 1 shows photographs depicting possible applications of lightweight aggregates as (A) a wallboard, (B) drainage layer, (C) lightweight brick, (D) roof, (E) oil- subwell, (F) road and pavement, (G) concrete, and (H) bridge.

[0017] FIG. 2 shows lightweight aggregate prototypes according to embodiments. The lightweight aggregate has inherent merits such as low thermal conductivity, sound proof, non-flammable and high thermal stability, low density, non-toxic, rodent and insect resistant, bacteria resistant, and UV stable.

[0018] FIG. 3 is a schematic diagram showing production of lightweight aggregate according to embodiments. Foaming agent and additives are added to a solid waste mixture, and the resultant mixture is ball milled to obtain a fine mixture. The fine mixture is subjected to glomeration and foaming to form a lightweight aggregate.

[0019] FIG. 4 is a graph showing apparent densities of the lightweight aggregates produced without the addition of sodium metasilicate at different foaming temperatures for comparison purposes.

[0020] FIG. 5 is a graph showing apparent densities of the lightweight aggregates produced at different foaming temperatures according to embodiments.

[0021] FIG. 6 is a graph showing water adsorption rate of the lightweight aggregates produced at different sintering temperatures according to embodiments.

[0022] FIG. 7 is a graph showing apparent densities of the lightweight aggregates produced at different sintering temperatures using different silicate of sodium metasilicate, aluminum silicate, and calcium silicate (all at 3 %) as additive according to embodiments.

[0023] FIG. 8 depicts the Riley's ternary diagram.

[0024] FIG. 9 is a graph showing apparent densities of the lightweight aggregates produced at different foaming temperatures according to embodiments.

[0025] FIG. 10 is a graph showing water adsorption rate of the lightweight aggregates produced at different foaming temperatures according to embodiments.

[0026] FIG. 11 is a photograph showing applications of foam materials in A) building (exterior wall), and B) industrial chimney and pipeline.

[0027] FIG. 12 shows a prototype of the thermal insulative panel according to embodiments.

[0028] FIG. 13 is a schematic diagram of the production of thermal insulative panel according to embodiments. Foaming agent and additives are added to a solid waste mixture, and the resultant mixture is ball milled to obtain a fine mixture. The fine mixture is subjected to glomeration, during which a binder is added. This is followed by (i) moulding and compression, and (ii) demoulding and foaming to form an insulative panel.

[0029] FIG. 14 is a photograph showing a prototype of the lightweight partition wall according to embodiments.

[0030] FIG. 15 is a photograph taken in Singapore of a building under construction.

[0031] FIG. 16 is a photograph showing a prototype of the lightweight brick according to embodiments.

[0032] FIG. 17 is a graph showing energy consumptions of formulations 1, 2, and 3 (Fl, F2, and F3) for producing lightweight aggregates of two similar densities ((i) 0.61 g/cm³ to 1.1 g/cm³, and (ii) 0.50 g/cm³ to 0.61g/cm³).

DETAILED DESCRIPTION

[0033] Various embodiments refer in a first aspect to a method of manufacturing a lightweight material using solid waste. The term "solid waste" as used herein refers to solid, semi- solid or solid-containing inorganic or organic materials which are discarded from industrial, commercial, mining, or agricultural operations, and/or from community activities.

[0034] Examples of solid waste may include, but are not limited to, garbage, construction debris, demolition wastes, industrial or agricultural wastes, production waste, commercial refuse, sludge from water supply or waste treatment plants, or air pollution control facilities, sewage sludge, agricultural refuse, mining residues, and may include items such as waste paper, scrap wood, and/or plastic waste.

[0035] The solid waste may be contaminated with a hazardous substance or a contaminant. The terms "hazardous substance" or "contaminant" as used herein refer to an unwanted substance which is present in the solid waste in an amount which is toxic or detrimental to health and/or the environment. An example of a hazardous substance or contaminant is a toxic heavy metal. The term "heavy metal" as used herein refers to a compound or complex of a metal which may be considered toxic if ingested or absorbed into the body in more than miniscule amounts, such as, but not limited to, compounds or complexes of d-block metals such as mercury, cadmium, gold, silver, platinum, nickel, chromium, and molybdenum. Further examples of contaminants include chalcogens, lead, bismuth, arsenic, aluminum, cyanides, sulfates, and/or phosphates. In such embodiments, the solid waste may be termed as a "contaminated solid waste". Advantageously, the method disclosed herein is able to lock in the hazardous substance within the lightweight material obtained, such that the hazardous substance is not able to leach out after conversion of the solid waste to the lightweight material.

[0036] The method disclosed herein may also provide a less energy intensive process as compared to state of the art methods due to its lower sintering temperatures and shorter holding times. This results in significant energy savings. Using a method disclosed herein, solid wastes such as contaminated solid wastes, marine clay, mud, waste glass, or ash obtained from incineration of waste may be converted or used to manufacture a lightweight material such as lightweight aggregates, thermal insulative panels, lightweight partition walls, and/or lightweight bricks. More than 95 % of the lightweight material may be formed from the solid waste material.

[0037] The lightweight material disclosed herein may have a density of about 0.25 g/cm³ to about 0.9 g/cm³, a low water adsorption rate of less than 2 % or less than 1 %, uniform pore size of about 0.1 mm to about 2 mm, and a high compressive strength of about 0.8 MPa to about 18 MPa. These properties render the lightweight materials suitable for structural use such as in buildings and roads, thermal insulation such as roof insulation, and other insulating purposes. In particular, the lightweight material disclosed herein may have a high thermal stability of greater than 800 °C, a thermal conductivity of about 0.12 W/m-k to about 0.2 W/m-k, and is non-flammable, which provides for applications in thermal insulation. Its sound absorption coefficient of about 0.35 to about 0.5 may also render its suitability for sound-proofing applications.

[0038] With the above in mind, a method of manufacturing a lightweight material is disclosed herein. The method comprises dispersing a solid waste comprising at least one of a contaminated solid waste, marine clay, mud, waste glass, or ash obtained from incineration of waste in an aqueous reagent to form a dispersion.

[0039] Marine clay refers generally to a type of clay that may be found in coastal and offshore regions around the world. In urbanized countries such as Singapore, a large quantity of marine clay is excavated at construction sites each year, especially at sites for construction of underground rail or road systems, and which needs to be disposed off. As in the case for marine clay, mud or mud slurry may result from the excavation activities, and which needs to be disposed off. [0040] Waste glass, which may be primarily formed of silicon dioxide, may be derived from consumer electronics such as television sets, monitors, fluorescent tubes and/or energy- efficient lamps and/or photovoltaic systems.

[0041] Generally, ash obtained from incineration of waste, or incinerator ash, may be classified as bottom ash and fly ash. The term "bottom ash", otherwise termed herein as "incinerator bottom ash", IBA, refers to ash that is collected at the bottom of a combustion chamber or incinerator. Typically, bottom ash contains a heterogeneous mixture of slag, glass, ceramics, ferrous and non-ferrous metals, minerals, non-combustibles, and unburnt organic matter. Fly ash, on the other hand, refers to ash that is lighter than bottom ash and which is collected mainly in the discharge gas processing system connected to the incinerator or in a dust collector provided in the discharge gas processing system. Bottom ash and fly ash have significantly different properties and compositions, with fly ash having a smaller specific weight and containing more volatile components than bottom ash.

[0042] TABLE 1 provides an exemplary chemical composition of incineration ash, marine clay, waste glass, and solid waste ("mixture") disclosed herein, as measured by Energy-dispersive X-ray spectroscopy (EDX).

[0043] TABLE 1: Chemical compositions of incineration ash, marine clay, waste glass, and solid waste ("mixture")

Mixture is made up of 50 % incineration ash, 30 % waste glass and 20 % marine clay, which are the weight ratios of the different components.

[0044] In specific embodiments, the solid waste comprises at least one of marine clay, mud, waste glass, or ash obtained from incineration of waste.

[0045] In various embodiments, the solid waste comprising at least one of a contaminated solid waste, marine clay, mud, waste glass, or ash obtained from incineration of waste comprises at least about 40 wt% silicon dioxide. For example, the solid waste comprising at least one of a contaminated solid waste, marine clay, mud, waste glass, or ash obtained from incineration of waste may comprise at least about 45 wt% silicon dioxide, such as at least about 50 wt%, about 53 wt%, about 56 wt%, or at least about 60 wt% silicon dioxide.

[0046] In some embodiments, the solid waste comprising at least one of a contaminated solid waste, marine clay, mud, waste glass, or ash obtained from incineration of waste comprises aluminum oxide. Generally, amount of aluminum oxide in the solid waste may be in the range of about 0.5 wt% to about 40 wt% of the solid waste.

[0047] As mentioned above, the solid waste may be contaminated with a hazardous substance or contaminant such as toxic heavy metals. In various embodiments, the solid waste comprises one or more contaminants. The one or more contaminants may be selected from the group consisting of a heavy metal, chalcogens, lead, bismuth, arsenic, aluminum, cyanides, sulfates, phosphates, and combinations thereof. Apart from or in addition to that contained in the contaminated solid waste, the one or more contaminants may be contained in the marine clay, mud, waste glass, and/or ash obtained from incineration of waste. Using a method according to embodiments disclosed herein, a lightweight material possessing a unique, close cellular structure with very low density and water adsorption rate may be obtained. The close cellular structure may function to secure or to lock-in the hazardous substance within the lightweight material such that the hazardous substance does not leach out, thereby avoiding health or environmental issues that may arise through use of the solid waste.

[0048] The at least one of a contaminated solid waste, marine clay, mud, waste glass, or ash obtained from incineration of waste may be comprised in the solid waste in any suitable combination depending on their chemical composition and/or intended application of the lightweight material. For example, when the lightweight material is a lightweight aggregate, the solid waste may comprise incinerator ash and waste glass in a weight ratio of about 3:2. In alternative embodiments where mud is present, the solid waste may comprise mud, incinerator ash and waste glass in a weight ratio of about 5:3:2.

[0049] In various embodiments, the solid waste comprises mud, ash obtained from incineration of waste, and waste glass in a weight ratio in the range of about 0:3:2 to about 5:3:2, such as about 1:3:2 to about 5:3:2, about 2:3:2 to about 5:3:2, or about 3:3:2 to about 5:3:2. [0050] The solid waste is dispersed in an aqueous reagent to form a dispersion. As used herein, the term "aqueous reagent" refers to a liquid containing water, or a liquid reagent which is based primarily on water. Examples of an aqueous reagent include aqueous liquids such as water, buffer solutions, alkaline or acidic solutions, salt solutions, or a mixture of water and a water-miscible liquid, which may for example, be a lower alkanol, such as methanol, ethanol and/or propanol; an ether such as diethyl ether and/or diethylene glycol methylether, and/or a lower ketone such as acetone and/or methyl ethyl ketone. In specific embodiments, the aqueous reagent is water. Dispersing of the solid waste in the aqueous reagent may be carried out using any suitable agitation methods such as sonication, stirring, and/or shaking.

[0051] By forming the dispersion, and adding an additive comprising a foaming agent and a metal silicate such as water soluble sodium metasilicate to the dispersion, a low energy process with low foaming temperature and low holding time as disclosed herein to manufacture a lightweight material may result, giving rise to a lightweight material having a unique, close cellular structure with very low density and water adsorption rate.

[0052] The solid waste may be subjected to a size reduction process prior to dispersing the solid waste in the aqueous reagent. By reducing particle size of the solid waste, processability of the solid waste may be improved. Examples of suitable size reduction process include, but are not limited to, milling, ball-milling, grinding, crushing, cutting, and combinations thereof.

[0053] In various embodiments, the solid waste is subjected to a ball milling process prior to dispersing the solid waste in the aqueous reagent. The ball milling may be carried out, for example, at a speed in the range of about 300 rpm to about 400 rpm, and for a time period in the range of about 5 minutes to about 30 minutes.

[0054] The ball milling may be carried out for a time period sufficient to reduce particle size of the mixture to an average particle size of about 500 μιη or less. For example, particle size of the mixture may be reduced to an average particle size in the range of about 20 μιη to about 500 μιη, such as about 40 μιη to about 500 μιη, about 100 μιη to about 500 μιη, about 150 μιη to about 500 μιη, about 200 μιη to about 500 μιη, about 300 μιη to about 500 μιη, about 400 μιη to about 500 μιη, about 20 μιη to about 400 μιη, about 20 μιη to about 300 μιη, about 20 μιη to about 200 μιη, about 20 μιη to about 100 μιη, about 20 μιη to about 50 μιη, or about 30 μιη to about 50 μιη. [0055] The dispersion is mixed with an additive comprising a foaming agent and a metal silicate to form a mixture. As used herein, the term "foaming agent" refers to a substance that may be added to generate gas in the mixture. When used in conjunction with a metal silicate which is comprised in the additive, a cellular structure may be formed in the resultant lightweight material.

[0056] The foaming agent may be selected from a variety of substances that are able to decompose to give off gas at curing temperature of the mixture. In various embodiments, the foaming agent is selected from the group consisting of silicon carbide, ferric oxide, calcium sulfate, calcium carbonate, sodium carbonate, carbon black, and combinations thereof. In specific embodiments, the foaming agent comprises or consists of silicon carbide.

[0057] Amount of the foaming agent in the mixture may depend on factors such as porosity requirements of the resultant lightweight material and type of foaming agent used. Generally, amount of the foaming agent in the mixture may be in the range of about 0.1 wt% to about 2 wt% of the mixture, such as about 0.4 wt% to about 2 wt%, about 0.8 wt% to about 2 wt%, about 1.2 wt% to about 2 wt%, about 1.5 wt% to about 2 wt%, about 1.8 wt% to about 2 wt%, about 0.1 wt% to about 1.8 wt%, about 0.1 wt% to about 1.5 wt%, about 0.1 wt% to about 1.3 wt%, about 0.1 wt% to about 1 wt%, about 0.1 wt% to about 0.8 wt%, about 0.1 wt% to about 0.5 wt%, about 0.3 wt% to about 1.8 wt%, about 0.5 wt% to about 1.5 wt%, about 0.8 wt% to about 1.2 wt%, or about 0.2 wt% to about 0.5 wt%.

[0058] Apart from the foaming agent, the additive also contains a metal silicate. Advantageously, the metal silicate may reduce curing temperature of the mixture in forming the lightweight material, while reducing density of the lightweight material that is formed.

[0059] In various embodiments, the metal silicate is a water-soluble metal silicate. The water-soluble metal silicate may dissolve in water to form a viscous solution, thereby acting as a binder of the solid granular materials of the solid waste material to prevent escape of generated gases due to action of the foaming agent on the solid waste material during curing. As mentioned above, the metal silicate may reduce curing temperature of the mixture in forming the lightweight material while reducing density of the lightweight material that is formed. The water-soluble metal silicate may further improve on these, to allow formation of a lower density lightweight material at a lower curing temperature. [0060] In various embodiments, the metal silicate comprises or consists of an alkali metal silicate. The alkali metal silicate may, for example, be at least one of lithium silicate, sodium silicate, potassium silicate, rubidium silicate, cesium silicate, or francium silicate.

[0061] In some embodiments, the metal silicate is selected from the group consisting of sodium metasilicate, calcium silicate, aluminum silicate, and mixtures thereof.

[0062] In specific embodiments, the metal silicate is sodium metasilicate. Advantageously, it has been surprisingly found by the inventors that sodium metasilicate is able to substantially decrease the temperature at which the mixture foams, and form a lightweight material having a much lower density, as compared to other metal silicates such as aluminum silicate and calcium silicate. In various embodiments, the sodium metasilicate creates a cellular structure in the resultant lightweight material, which is able to prevent leaching of toxic materials such as hazardous toxic heavy metals that may be present in the solid waste that is used to form the lightweight material.

[0063] Amount of the metal silicate in the mixture may be in the range of about 1 wt% to about 10 wt% of the mixture. For example, amount of metal silicate in the mixture may be in the range of about 3 wt% to about 10 wt% of the mixture, such as about 5 wt% to about 10 wt%, about 7 wt% to about 10 wt%, about 1 wt% to about 8 wt%, about 1 wt% to about 5 wt%, about 1 wt% to about 3 wt%, about 2 wt% to about 8 wt%, or about 3 wt% to about 7 wt%.

[0064] Apart from the foaming agent and the metal silicate, the additive may further comprise a fluxing agent. As used herein, the term "fluxing agent" refers to a substance that is added to decrease temperature at which the mixture melts, or temperature at which a melt is formed in the system. In embodiments wherein mud is used for example, due to the high melting point of mud, a fluxing agent such as borax may be used to reduce temperature at which the mixture melts. In various embodiments, the fluxing agent is selected from the group comprising sodium borate, boric acid, sodium carbonate, potassium carbonate, coke, lime, and combinations thereof. In specific embodiments, the fluxing agent comprises or consists of sodium borate, otherwise known as borax.

[0065] Amount of the fluxing agent in the mixture may be about 5 wt% or less. For example, amount of the fluxing agent may be in the range of about 0.1 wt% to about 5 wt% of the mixture, such as about 0.5 wt% to about 5 wt%, about 1 wt% to about 5 wt%, about 2 wt% to about 5 wt%, about 3 wt% to about 5 wt%, about 0.1 wt% to about 4 wt%, about 0.1 wt% to about 3 wt%, or about 1 wt% to about 4 wt%.

[0066] In various embodiments, the additive may further comprise a binder. The term "binder" as used herein refers to a material that is capable of attaching two or more materials to one another such that the two or more materials are held together. In various embodiments, the binder comprises S1O2 and/or a silicate such as sodium silicate and/or potassium silicate, and a hydroxide selected from the group consisting of an alkali-metal hydroxide such as sodium hydroxide and/or potassium hydroxide, an alkaline earth metal hydroxide, ammonium hydroxide, and combinations thereof.

[0067] Examples of silicate that may be used have already been mentioned above. Examples of an alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, francium hydroxide, or combinations thereof. Examples of an alkaline earth metal hydroxide include beryllium hydroxide, beryllium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, or combinations thereof.

[0068] In specific embodiments, the binder comprises an aqueous alkaline solution of sodium silicate.

[0069] Amount of the binder in the mixture may be about 5 wt% or less. For example, amount of the binder may be in the range of about 0.1 wt% to about 5 wt% of the mixture, such as about 0.5 wt% to about 5 wt%, about 1 wt% to about 5 wt%, about 2 wt% to about 5 wt%, about 3 wt% to about 5 wt%, about 0.1 wt% to about 4 wt%, about 0.1 wt% to about 3 wt%, or about 1 wt% to about 4 wt%.

[0070] As mentioned above, the dispersion and the additive are mixed to form a mixture. In various embodiments, mixing the dispersion with the additive comprises agglomerating the mixture to obtain one or more aggregates of the mixture. As used herein, the term "agglomerating" refers to a process whereby a plurality of particles are physically and/or chemically adhered or clustered together to form a discrete body of matter or an aggregate.

[0071] The one or more aggregates may have an average size in the range of about 0.5 cm to about 5 cm. In various embodiments, the one or more aggregates have an average size in the range of about 1 cm to about 5 cm, such as about 1.5 cm to about 5 cm, about 2 cm to about 5 cm, about 2.5 cm to about 5 cm, about 3 cm to about 5 cm, about 3.5 cm to about 5 cm, about 4 cm to about 5 cm, about 1 cm to about 4 cm, about 1 cm to about 3 cm, about 1 cm to about 2 cm, about 2 cm to about 4 cm, about 2 cm to about 3 cm, or about 1.5 cm to about 4.5 cm.

[0072] While agglomerating the mixture, a second binder may be added to the mixture. Examples of suitable binders that may be used have already been mentioned above. In various embodiments, the second binder comprises a silicate and a hydroxide selected from the group consisting of an alkali-metal hydroxide, an alkaline earth metal hydroxide, ammonium hydroxide, and combinations thereof. In specific embodiments, the second binder comprises an aqueous alkaline solution of sodium silicate.

[0073] Amount of the second binder in the mixture may be about 5 wt% or less. For example, amount of the second binder may be in the range of about 0.1 wt% to about 5 wt% of the mixture, such as about 0.5 wt% to about 5 wt%, about 1 wt% to about 5 wt%, about 2 wt% to about 5 wt%, about 3 wt% to about 5 wt%, about 0.1 wt% to about 4 wt%, about 0.1 wt% to about 3 wt%, or about 1 wt% to about 4 wt%.

[0074] The method disclosed herein comprises curing the mixture to obtain the lightweight material. In various embodiments, curing the mixture to obtain the lightweight material is carried out at a temperature in the range of about 1000 °C to about 1150 °C. For example, curing the mixture to obtain the lightweight material may be carried out at a temperature in the range of about 1025 °C to about 1150 °C, about 1050 °C to about 1150 °C, about 1075 °C to about 1150 °C, about 1100 °C to about 1150 °C, about 1125 °C to about 1150 °C, about 1000 °C to about 1125 °C, about 1000 °C to about 1100 °C, about 1000 °C to about 1075 °C, about 1000 °C to about 1050 °C, about 1000 °C to about 1025 °C, about 1050 °C to about 1100 °C, or about 1075 °C to about 1125 °C.

[0075] In some embodiments, curing the mixture to obtain the lightweight material is carried out at a temperature in the range of about 1100 °C to about 1125 °C. It has been surprisingly found by the inventors that curing the mixture at a temperature in the range of about 1100 °C to about 1125 °C may result in lightweight materials such as lightweight aggregates with very low density. In particular, a temperature of about 1100 °C may be considered as an optimal temperature to produce lightweight material with very low density.

[0076] Curing the mixture to obtain the lightweight material may be carried out for any suitable time period that is sufficient to obtain the lightweight material. In various embodiments, curing the mixture to obtain the lightweight material may be carried out for a time period in the range of about 1 minute to about 15 minutes, such as about 3 minutes to about 15 minutes, about 8 minute to about 15 minutes, about 10 minutes to about 15 minutes, about 1 minute to about 12 minutes, about 1 minute to about 10 minutes, about 1 minute to about 8 minutes, about 1 minute to about 5 minutes, about 1 minute to about 3 minutes, about 1 minute to about 2 minutes, about 3 minute to about 10 minutes, or about 5 minute to about 10 minutes.

[0077] In some embodiments, curing the mixture to obtain the lightweight material is carried out by heating the mixture to a temperature in the range of about 1100 °C to about 1125 °C, holding the mixture at the temperature for about 1 minute to about 2 minutes, and thereafter cooling the mixture to room temperature. Heating the mixture to a temperature in the range of about 1100 °C to about 1125 °C may be carried out using a heating rate in the range of about 10 °C/min to about 20 °C/min.

[0078] As mentioned above, the method disclosed herein may be carried out using a lower foaming temperature such as in the range of about 1000 °C to 1100 °C or in the range of about 1100 °C to about 1125 °C. Coupled with the short holding time of less than 2 minutes, significant energy savings may be realized using a method disclosed herein for the manufacture of a lightweight material.

[0079] In some embodiments, the mixture may be compressed and/or molded prior to curing. The compression and/or molding step may be carried out in embodiments where the lightweight material is a thermal insulative panel, for example, and may similarly be used where the lightweight material is a lightweight partition wall or a lightweight brick.

[0080] The mixture may, for example, be compressed at a pressure in the range of about 5 MPa to about 20 MPa, such as about 5 MPa to about 18 MPa, about 5 MPa to about 15 MPa, about 5 MPa to about 10 MPa, about 5 MPa to about 8 MPa, about 8 MPa to about 20 MPa, about 12 MPa to about 20 MPa, about 15 MPa to about 20 MPa, about 8 MPa to about 16 MPa, about 10 MPa to about 18 MPa, or about 5 MPa to about 10 MPa. The compression may be carried out in a press machine such as a hydraulic presser.

[0081] The compression may be carried out for any suitable time period, and may generally be compressed for a time period in the range of about 1 minute to about 10 minutes, such as about 3 minutes to about 10 minutes, about 5 minutes to about 10 minutes, about 7 minutes to about 10 minutes, about 1 minute to about 8 minutes, about 1 minute to about 5 minutes, about 1 minute to about 3 minutes, about 3 minutes to about 8 minutes, or about 2 minute to about 7 minutes. [0082] Various embodiments refer in a second aspect to a lightweight material manufactured by a method according to the first aspect, and in a further aspect to use of a method according to the first aspect in the manufacture of a lightweight aggregate, a thermal insulative panel, a lightweight partition wall, or a lightweight brick.

[0083] Lightweight aggregate (LA) is one of the green building materials which is in high demand in the construction industries for a diverse range of application, for example in lightweight concrete, bricks, and insulation in industries. In tall building structures, density of building materials becomes critical and the use of lightweight aggregates in concrete is one way to address this issue. Use of lightweight aggregates incorporated into building materials may substantially reduce the energy consumption and hence the carbon dioxide footprint of buildings.

[0084] As mentioned above, the lightweight material disclosed herein may have a density of about 0.25 g/cm³ to about 0.9 g/cm³, a low water adsorption rate of less than 2 % or less than 1 %, uniform pore size of about 0.1 mm to about 2 mm, and a high compressive strength of about 0.8 MPa to about 18 MPa. These properties render the lightweight materials suitable for structural use such as in buildings and roads, thermal insulation such as roof insulation, and other insulating purposes. In particular, the lightweight material disclosed herein may have a high thermal stability of greater than 800 °C, a thermal conductivity of about 0.12 W/m-k to about 0.2 W/m-k, and is non-flammable, which provides for applications in thermal insulation. Its sound absorption coefficient of about 0.35 to about 0.5 may also render its suitability for sound-proofing applications.

[0085] Hereinafter, the present invention will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, lengths and sizes of layers and regions may be exaggerated for clarity.

[0086] As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. The invention illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms "comprising", "including", "containing", etc. shall be read expansively and without limitation. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the inventions embodied therein herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention.

[0087] The invention has been described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

[0088] Other embodiments are within the following claims and non- limiting examples. In addition, where features or aspects of the invention are described in terms of Markush groups, those skilled in the art will recognize that the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group.

EXPERIMENTAL SECTION

[0089] Various embodiments disclose a technology that involves a simple and less energy intensive conversion of contaminated solid waste materials (marine clay, incineration ash and mud) to green building materials. Different type of hazardous solid waste materials existing in liquid suspension may be converted to value-added green building materials through a low-energy process. The hazardous solid waste materials include contaminated marine clay and mud, incineration ash, and waste glass. The green building materials produced are lightweight aggregates, lightweight partition wall, thermal insulative panel and lightweight brick. The key of this technology is the use of water soluble sodium metasilicate in the process, which has the unique ability to create close cellular structure lightweight materials with very low density and water adsorption rate at a lower foaming temperature and holding time (TABLE 1) when mixed with other additives. This enables a simple mixing of various waste components and the additives in a single production line process. The commercial attractiveness of this technology arises from its lower energy requirement and simple process line for the production of environmental friendly building materials.

[0090] Incineration ash represents a major environmental hazard when it is sent to landfill, due to potential leaching of its heavy metal contents into agricultural soil and underground water. Marine clay and mud are other potentially solid wastes generated in Singapore and the current management method, i.e. disposal to landfill or staging ground, is not sustainable especially for land-scarce nation like Singapore. The technology disclosed herein is able to convert environmentally hazardous incineration ash, marine clay and mud to value-added green building materials, including lightweight aggregates, lightweight partition wall, thermal insulative panel and lightweight brick. These materials will be made to "lock-in" and stabilize the heavy metal content by rendering close-pores structure with low water absorption, which means they can be disposed safely after their lifespan. The densities and water adsorption rates of the green building materials are low, which are comparable with current commercial products or even better than that of the commercial products. In addition, their production process will have minimal environmental impact due to minimal C0₂ generated and short holding time at foaming temperature is only about 1 to about 2 min, which means the process does not require high energy consumption.

[0091] Example 1; Lightweight aggregates (LAs)

[0092] This technology converts incineration ash or marine clay or mud or their mixture to lightweight aggregate with low density (0.25 g/cm³ to 0.8 g/cm³), low water adsorption rate (less than 1 %), uniform pore size (0.2 mm to 1.0 mm) and high mechanical strength (1.5 MPa to 10 MPa). The main components of the incineration ashes, marine clay and mud are S1O2, CaO, AI2O3, Na20 and Fe20₃, which are similar to that of glass and clay. Therefore, incineration ash and marine clay may be used as the raw materials to produce lightweight aggregates.

[0093] Content of the contaminated solid waste (incineration ash/marine clay/mud/waste glass or their mixture) is up to 98 %. In addition, sintering temperature for producing lightweight aggregate is in the range of 1000 °C to 1100 °C with a low holding time of 1 minute, which will not cause high energy consumption. This technology is timely and fitting to Singapore's and global efforts of sustainable development through waste-to-resources recycling. [0094] Some studies on lightweight aggregate conversion from incineration ash have been conducted but their properties remain poor (TABLE 2).

[0095] TABLE 2: Results of using incineration ash to produce lightweight aggregate (LA).

* 22% of boric acid was used in the formulation, which increase the cost greatly References:

[1] D. J. Tonjes, K. L. Greene, Waste Management & Research, 30 (8) (2012)758.

[2] B. Gonzalez-Corrochano, J. Alonso-Azcarate, M. Rodas, Cement & Concrete Composites, 32 (2010) 694.

[3] S. H. Hu, S. C. Hu, Y. P. Fu, Environmental Progress & Sustainable Energy, 32 (2012) 740.

[4] N. U. Kockal, T. Ozturan, Materials & Design, 32 (2011) 3586.

[5] B. Gonzalez-Corrochano, J. Alonso-Azcarate, M. Rodas, J. F. Barrenechea, F. J. Luque, Construction and Building Materials, 25 (2011) 3591.

[6] C. R. Cheeseman, A. Makinde, S. Bethanis, Resources, Conservation and Recycling, 43 (2005) 147.

[7] H. J. Chen, S. Y. Wang, C. W. Tang, Construction and Building Materials, 24 (2010) 46.

[8] J. Latosi ska, M. Zygadlo, Environmental Technology, 32 (2011) 1471. [0096] FIG. 2 shows the prototypes of lightweight aggregates produced using incineration ash as raw materials.

[0097] FIG. 3 shows the methodology of producing lightweight aggregate. Solid wastes, including incineration ash, marine clay, mud and waste glass, are the main raw materials. Firstly, two or three types of solid wastes are mixed at various ratios. Then, the appropriate amount of foaming agent and additives are added in the solid waste mixture. The foaming agent and additives can be SiC, borax, sodium dihydrogen phosphate, sodium metasilicate and aqueous alkaline solution of sodium silicate. After that, the mixture is ball-milled at speed of 350 rpm for 10 min. After the glomeration process, the particles are heated up to a temperature of about 1000 °C to about 1100 °C at heating rate of about 10 °C to about 20 °C/min and hold at this temperature for 1 to 2 min. The lightweight aggregates are obtained after being cooled down to room temperature.

[0098] Example 1.1: Production of LA without sodium metasilicate

[0099] Example 1.1.1: Processing conditions and materials used

[00100] Solid Waste Mixture: Incineration ash/waste glass = 3/2 (weight ratio)

[00101] Additives: 0.25 wt.% SiC

[00102] Heating rate : 10 °C/min

[00103] Holding time at optimal temperature: 2 mins

[00104] Example 1.1.2: Results and Discussion

[00105] Lightweight aggregate without addition of sodium metasilicate was first prepared. Apparent density is one of the most important parameters to evaluate the quality of lightweight aggregate. Normally, lower density of the lightweight aggregate results in lower thermal conductivity and lower building dead load. During the sintering process, the solid waste may melt and the foaming agents (SiC) may generate gas to bloat the lightweight aggregates and generate a cellular structure.

[00106] FIG. 4 shows apparent densities of the lightweight aggregates produced at different foaming temperatures without addition of sodium metasilicate. With the increase of foaming temperature from 1000 °C to 1150 °C, apparent density of the lightweight aggregate decreased gradually from 2.0 g/cm³ to 0.85 g/cm³.

[00107] Foaming temperature and apparent density of the lightweight aggregates without the addition of sodium metasilicate were quite high, thus the process was not energy saving. In addition, the water adsorption rate of the lightweight aggregate (0.85 g/cm³) without the addition of sodium metasilicate at 1150 °C was greater than 5.0 %, which was higher than that of the lightweight aggregate with the addition of sodium metasilicate at 1025 °C to 1125 °C.

[00108] Example 1.2: Production of LA in the presence of SiC and sodium metasilicate

[00109] Example 1.2.1: Processing conditions and materials used

[00110] Solid Waste Mixture: Incineration ash/waste glass = 3/2 (weight ratio)

[00111] Additives: 0.25 wt.% SiC and 2.0 wt% sodium metasilicate

[00112] Heating rate : 10 °C/min

[00113] Holding time at optimal temperature: 2 mins

[00114] Example 1.2.2: Results and Discussion

[00115] FIG. 5 shows the apparent densities of the lightweight aggregates produced at different foaming temperatures. With increase in foaming temperature from 1000 °C to 1100 °C, apparent density of the lightweight aggregate decreased gradually from 0.95 g/cm³ to 0.25 g/cm³. This may be attributed to the decrease in viscosity of the melting material and the increase of gas pressure. However, further increase of the foaming temperature to 1150 °C leads to the increase of the apparent density to 0.39 g/cm³. At higher foaming temperature, viscosity of the melting material decreases and gas pressure further increases, which may lead to escape of gas and increase in apparent density. Herein, 1100 °C may be considered as the optimal temperature to produce lightweight aggregate with very low density. Sodium metasilicate may decrease the foaming temperature and create close cellular structure, which prevents leaching of hazardous toxic heavy metals.

[00116] The water adsorption rate may be considered as another important parameter to evaluate the quality of lightweight aggregate. Normally, the water adsorption rate of the normal weight aggregate (stone) is less than 2.0 wt.%. If the water adsorption rate of lightweight aggregate is high, it will adsorb more water and reduce the workability of concrete. In additional, thermal conductivity of lightweight aggregate greatly increase after adsorbing water. FIG. 6 shows the water adsorption rate of the lightweight aggregates produced at different foaming temperatures. The water adsorption rates of the lightweight aggregates produced at foaming temperature in the range of 1000 °C to 1100 °C are less than 1.0 wt.%, which are lower than normal commercial lightweight aggregate and comparable with normal weight aggregates. Further increase in the foaming temperature leads to high water adsorption rate, which is attributed to the open cellular structure generated by the escape of gas at high temperature. The water adsorption rate at 1150 °C is around 8.5%.

[00117] Example 1.3; Production of LA with sodium metasilicate and other silicate additive; A comparative study

[00118] Example 1.3.1: Processing conditions and materials used

[00119] Solid Waste Mixture: Incineration ash/waste glass = 3/2 (weight ratio)

[00120] Additives: 0.25 wt.% SiC and 3.0 wt.% sodium metasilicate, aluminum silicate or calcium silicate

[00121 ] Heating rate : 10 °C/min

[00122] Holding time at optimal temperature: 2 mins

[00123] Example 1.3.2: Results and Discussion

[00124] To investigate how the other silicate additive affects the density of lightweight aggregates and understand why the addition of sodium metasilicate can greatly decrease the density of lightweight aggregate and sintering temperature, lightweight aggregates with other silicate additives were prepared for comparison. FIG. 7 shows the apparent densities of the lightweight aggregates produced at different sintering temperatures using different silicate as additive. Compared with the lightweight aggregates without silicate additive (FIG. 4), the lightweight aggregates with aluminum silicate or calcium silicate additive also shows much lower apparent density at the same sintering temperatures (versus 0.86 g/cm³ or 1.09 g/cm³ to 2.0 g/cm³ at 1000 °C).

[00125] According to the Riley's ternary diagram (FIG. 8), to produce foam materials such as lightweight aggregates, the chemical composition of the solid wastes should be in the area of the expandable region. Normally, the chemical composition of the incineration ash is not in the limits of the expandable region of the ternary diagram due to the low content of S1O2. The addition of silicates (sodium metasilicate or aluminum silicate or calcium silicate) can increase the content of Si0₂ and probably leads to the decrease in sintering temperature.

[00126] TABLE 1 lists the percentage amount of the various contents, which should be the optimal composition which results in the most energy efficient process to produce the lightweight aggregates.

[00127] Additionally, compared with lightweight aggregate with aluminum silicate or calcium silicate, the lightweight aggregate with sodium metasilicate shows much lower apparent density at lower sintering temperatures (975 °C to 1000 °C). The sodium metasilicate can dissolve in water to form viscous solution, while both aluminum silicate and calcium silicate cannot dissolve in water. It is probably due to the fact that the sodium metasilicate viscous solution can act as a binder of the solid granular materials to prevent the escape of generated gas at lower sintering temperature, which will lead to the formation of low density lightweight aggregate at lower the sintering temperature.

[00128] Example 1.4: Production of in the presence of SiC, borax and sodium metasilicate

[00129] Example 1.4.1: Processing conditions and materials used

[00130] Solid Waste Mixture: Mud/Incineration ash/waste glass = 5/3/2 (weight ratio)

[00131] Additives: 0.25 wt.% SiC, 1.0 wt% borax and 3.0 wt% sodium metasilicate

[00132] Heating rate: 10 °C/min

[00133] Holding time at optimal temperature: 2 mins

[00134] Example 1.4.2: Results and Discussion

[00135] In this formulation, the borax is used as a fluxing agent, which is due to the high melting point of the mud. FIG. 9 shows the apparent densities of the lightweight aggregates produced at different foaming temperatures. The mixture of mud, incineration ash and waste glass is used as the main raw material. With the increase of foaming temperature from 1050 °C to 1150 °C, the apparent density of the lightweight aggregate decreased gradually from 1.5 g/cm³ to 0.3 g/cm³. This may be attributed to the decrease of viscosity of the melting material and the increase of gas pressure. However, further increase the foaming temperature to 1175 °C led to the increase of the apparent density to 0.51 g/cm³. At higher foaming temperature, the viscosity of the melting material decreases and the gas pressure further increases which lead to the escape of gas and the increase of apparent density.

[00136] FIG. 10 shows the water adsorption rate of the lightweight aggregates produced at different foaming temperatures, using the mixture of mud, incineration ash and waste window glass as raw material. The water adsorption rates of the lightweight aggregates produced at foaming temperature in the range of 1050 °C to 1125 °C are less than 1.0 wt.%, which are lower than normal commercial lightweight aggregate and comparable with normal weight aggregates. Further increase the foaming temperature leads to high water adsorption rate, which is attributed to the open cellular structure generated by the escape of gas at high temperature. The water adsorption rate at 1150 °C is around 1.2%.

[00137] Example 1.4.3: Role of additives [00138] The formulation (Fl) with the three additives: 1 % SiC, 2 % sodium metasilicate and 2 % borax, gave the lowest density, which is a desired property of lightweight aggregates.

[00139] SiC is a foaming agent and was able to react with AI2O3 contained in the marine clay when heated to a high temperature. At high temperatures, gases were generated and released during the process, which increased porosity of the aggregates. Sodium metasilicate, which has a melting point of 1088 °C, may co-melt with S1O2 at a temperature in the range of about 1000 °C to 1350 °C, and may hence function to lower the co-melting temperature of the solid waste (marine clay, waste glass and incineration ash). This greatly decreased the sintering temperature of Fl, making it easy to produce very low-density lightweight aggregates at a much lower temperature at 1050 °C.

[00140] Meanwhile, borax was used as a fluxing agent to mix with waste melt, forming a dense shell. The shell may prevent the escape of generated gas obtaining high porosity light LAs, and obstruct permeation of water into LAs, which may show up in the form of low water adsorption. The dense shell may further function to improve compressive strength and lock-in toxic heavy metals in the LAs.

[00141] Example 1.4.4: Energy savings

[00142] Further experiments were carried out using Fl at lower sintering temperatures to determine the density and energy consumptions of the production process. TABLE 3 summarizes the aggregates properties produced at 1000 °C to 1050 °C using Fl. At a lower sintering temperature of 1000 °C, the density achieved was about 0.859 g/cm³, which is still a desirable value for LAs (density < 0.9 g/cm³).

[00143] In addition, the energy savings derived from the production using Fl was compared with those of similar density lightweight aggregates using two other formulations F2 and F3 respectively. It is to note that current industries employ the same additives as that used in F2, and therefore offer a realistic comparison with the LA produced from Fl in the studies conducted by the inventors.

[00144] TABLE 3: Formulation 1 (Fl) - Lightweight aggregates properties and production parameters

Water Energy

Sintering Holding time Density

adsorption consumption temperature (°C) (mins) (g/cm³)

(%) (kWh)^a

1000 2 0.859 3.624 0.216 1025 2 0.733 4.154 0.342

1050 2 0.535 4.347 0.362

Note:

a: all energy consumption is for 5 g balls (before sintering)

Fl: 50 g marine clay + 30 g waste glass + 20 g incineration ash + 1 g SiC + 2 g sodium metasilicate (SM) + 2 g borax

F2: 50 g marine clay + 30 g waste glass + 20 g incineration ash + 1 g SiC + 2 g calcium silicate (CS) + 2 g NaH₂P0₄

F3: 50 g marine clay + 30 g waste glass + 20 g incineration ash + 1 g SiC + 2 g aluminum silicate (AS) + 2 g Na₂C0₃

[00145] Density of the aggregates decreased when sintering temperature was increased and holding time was extended. To provide a fair comparison, sintering temperature and holding time were varied so as to prepare LAs of similar densities. Lightweight aggregates with densities of 0.572 g/cm³ and 0.603 g/cm³ were obtained at 1200 °C for 15 mins for F2 and F3, respectively. LAs from F2 and F3 with respective density of 0.873 g/cm³ and 1.005 g/cm³ were obtained at 1100 °C for 15 mins. TABLE 4 compares the sintering temperature, holding time, and density of the three formulations. From the results obtained, it is evident that energy consumption greatly increased for F2 and F3 by increasing the sintering temperature and holding time to obtain the low-density aggregates. The energy consumption increased by about 8 to 14 times as shown in FIG. 17.

[00146] Energy consumptions of the three formulations were compared for two density ranges: 0.8 g/cm³ to 1.0 g/cm³ and 0.5 g/cm³ to 0.6 g/cm³. From TABLE 4 and FIG. 17, energy consumptions for F2 and F3 increased by 12.86 times and 13.80 times, respectively, for producing aggregates having a density range of 0.8 g/cm³ to 1.0 g/cm³. This is because the sintering temperature increased from 1000 °C to 1100 °C and the holding time extended to 7.5 times compared to formulation 1 (Fl). Energy consumptions for those using F2 and F3 increased 8.85 times and 9.54 times with density range of 0.5 g/cm³ to 0.6 g/cm³. It is evident that the lightweight aggregate produced using Fl has significant energy saving compared to existing other similar reported methods.

[00147] TABLE 4: Comparison of lightweight aggregates properties and production parameters of Fl, F2 and F3 Energy

Density Sintering Holding

Formulation Consumption

(g/cm³) temperature (°C) time (mins)

(kWh)^a

1 0.859 1000 2 0.216

2 0.873 1100 15 2.994

3 1.005 1100 15 3.198

1 0.535 1050 2 0.362

2 0.572 1200 15 3.568

3 0.603 1200 15 3.817

Note:

a: all energy consumption is for 5 g balls (before sintering)

[00148] Example 2: Thermal Insulative Panel

[00149] Foam glass (0.15 g/cm³ to 0.3 g/cm³) and foam ceramic (0.3 g/cm³ to 0.5 g/cm³) are popular inorganic thermal insulative materials in the current market, which can be used in building construction and industries (FIG. 11). The prices of the valuable foam glass and foam ceramic in the market are around S$ 200 to 400 per m³. The high cost may partially be attributed to the high raw material costs, which are usually not recycled glass or ceramics due to the complex and costly sorting process of recycling glass and ceramics. Thermal conductivity is the key property of high quality foam glass, foam ceramic and lightweight aggregate. Low density, high closed pore content and low water absorption in foam materials constitute to low thermal conductivity. The thermal conductivity of foam materials, cement paste and concrete are 0.034-0.17, 0.57 and 1.15-1.44 W/m°K, respectively. Use of the thermal insulative panel may substantially reduce the energy consumption/lost and hence the carbon dioxide footprint. The foam materials can also be used in industries, such as oil and gas industry and power stations, as thermal insulator to reduce energy lost.

[00150] By changing the formulation and process, thermal insulative panel may be produced using solid wastes (incineration ash or marine clay or mud or their mixture) as main raw materials. The thermal insulative panel prototype is shown in FIG. 12, which exhibits low density (0.2 g/cm³ to 0.3 g/cm³), low water adsorption rate (less than 2 %), high compressive strength (0.8 MPa to 2.0 MPa) and high thermal stability (greater than 800 °C). To the best of the inventors' knowledge, recycling of incineration ash or marine clay or mud or their mixture to thermal insulative panel has not been previously reported.

[00151] The methodology of the production of thermal insulative panel (shown in FIG. 13) is similar to that of the production of lightweight aggregate. Solid wastes, including incineration ash, marine clay, mud and waste glass, are the main raw materials. Firstly, two or three types of solid wastes are mixed at various ratios. Then appropriate amount of foaming agent and additives are added in the solid waste mixture. The foaming agent and additives can be SiC, CaC0₃, borax, sodium dihydrogen phosphate and sodium metasilicate. After that, the mixture is ball milled at speed of 350 rpm for 10 min. Then appropriate amount of binder, aqueous alkaline solution of sodium silicate, is mixed with the fine mixture uniformly. Subsequently, the powder is put in a steel mould and pressed at pressure of 5 MPa to 10 MPa for 1 min using a hydraulic presser. Then the sample sintered at 1000 °C to 1150 °C for 10 min to 15 min. The thermal insulative panel is obtained after being cooled down to room temperature.

[00152] Example 3: Lightweight Partition Wall

[00153] Lightweight partition wall is another green building material, which is currently in high demand due to its inherent merits, such as easy to build, thermal insulation, sound proof and low dead load. The inventors have developed the technology to convert solid waste (incineration ash or marine clay or their mixture) to porous material with high open porosity, low density and high mechanical strength. A lightweight partition wall (FIG. 14) with sandwich structure has been developed and the properties are shown in TABLE 5. The developed lightweight partition wall exhibits some other advantages, such as high thermal stability (greater than 800 °C), non-toxic, rodent, bacterial and insect resistant and UV stable.

[00154] TABLE 5: Properties of the lightweight partition wall.

[00155] Example 4: Lightweight Brick [00156] A brick is a block or a single unit of a ceramic material used in masonry construction. Nowadays, huge amount of bricks are used in building construction. Traditionally, brick is made from clay which is non-renewable natural resource. In China, 800 billion pieces of standard bricks are produced annually, which consume 333 square kilometer of land. Hence, the government has prohibited the production and use of traditional clay brick (red brick). However, most of the buildings in Singapore are still using the traditional clay brick (red brick) (FIG. 15).

[00157] The thermal conductivity of clay brick is around 0.81 W/m°K, which is more than 3 times higher than that of lightweight concrete. In a hot country like Singapore, the use of clay brick will lead to higher temperatures in the rooms and higher energy consumption (aircon). If thermal insulative materials are used to replace clay brick, the temperatures in the rooms will be lower and the energy consumption of using aircon also will be lower.

[00158] It is necessary to develop new materials to replace the traditional clay brick. Lightweight, energy and resource saving, environmental friendly bricks have attracted strong interests. Lightweight concrete is one of the most popular lightweight brick available in China and it is widely used to replace traditional brick in building construction, which is due to its advantages, such as lightweight (0.3 g/cm³ to 1.0 g/cm³), low thermal conductivity (0.09 W/m°K to 0.27 W/m°K), non-flammable and low cost (S$ 50 to 60 per m³). However, the lightweight concrete has some drawbacks, such as high water adsorption rate, low mechanical strength, easy to cause cracks and high thermal conductivity after adsorbing water.

[00159] The inventors have developed the technology to convert solid waste (incineration ash or marine clay or their mixture) to lightweight brick with high porosity, low density, low thermal conductivity, high sound adsorption coefficient and high mechanical strength. The lightweight brick prototype is shown in FIG. 16 and the properties are listed in TABLE 6.

[00160] TABLE 6: Properties of lightweight brick

[00161] Example 5: Heavy metal leaching test [00162] In a leaching study of the current lightweight materials using UK Environment Agency EA NEN 7375: 2004 Leaching characteristics of moulded or monolithic building and waste materials, "Tank Test", the materials show non-detectable heavy metal leaching (TABLE 7). Our preliminary results thus indicate strong potential of the current work.

[00163] TABLE 7: Determination of leaching of inorganic components with the diffusion test.

^Cumu ative after 64 days.

[00164] Various embodiments disclosed herein describe a technology that converts incineration ashes, marine clay and mud into green building materials through a less energy intensive process. The novelty of this technology includes:

^■ A new formulation for the production of high quality lightweight aggregates with low density (0.25 g/cm³ to 0.8 g/cm³) and low water adsorption rate (less than 2 %) using high content (greater than 95 %) of solid wastes as raw materials (mixture of incineration ash or/and marine clay or/and mud or/and waste glass).

^■ This new formulation consists of sodium metasilicate which has the unique ability to create tighter closed cellular structure in the lightweight aggregate at lower temperature (Compare results from Examples 1.1, 1.2 and 1.3). The sodium metasilicate is suggested to act as a binder of the solid granular materials while lowering the sintering temperature. It enables the mixture of various solid wastes to be used as the main raw material.

^■ This new formulation enables the reduction of the foaming temperature of incineration ash and/or marine clay and/or mud to 1000 °C to 1100 °C with a low holding time of less than 2 minutes, obtaining significant energy savings (see TABLE 2 for comparison with existing technologies).

^■ This technology allows the conversion of a variety combination of solid waste materials, including incineration ash, marine clay and mud, to green building materials, i.e. thermal insulative panel, lightweight partition wall and lightweight bricks. The recycling of incineration ash, marine clay and mud to these green building materials has not been reported in the opening publications. [00165] The current technology has the potential to recycle a large amount of incineration ash and marine clay, hence significantly reducing the amount of solid waste being disposed in landfill, which will help Singapore to truly realize its 'zero landfill' goal in the near future. In addition, the applications of the green and lightweight materials in building construction and industries can save a tremendous amount of non-renewable natural resource and reduce the energy consumption of air-con and the energy loss, respectively. In Singapore, there is a drive towards green buildings construction by the award of Green Mark Points, and the current green lightweight materials has tremendous potential for green building construction after certification under Singapore Green Label Scheme. The impact of this research on Singapore's economy and its "green metropolis" image will be very significant towards its aim to be a global city with innovative sustainable technologies.

[00166] This technology is able to derive significant energy savings due to a lower foaming temperature and shorter holding time of the lightweight aggregate production process compared with other works (TABLE 2). Thus, the energy consumption of lightweight aggregate production using this technology is lower than that of the reported lightweight aggregate production process in publications. Additionally, this technology is also comparable with other technology of treating contaminated marine clay. NewEarth Pte Ltd, a Singapore company specializes in waste reclamation, has quoted a treatment cost for contaminated marine clay of $100 per ton, its high cost mainly attributed to an energy intensive process. However, for the production of LA using the technology disclosed herein, the total cost is estimated to be S$45 per ton of LA, which is lower than that of quoted from NewEarth.

[00167] The cost of incineration ash disposal to landfill is S$100-130 per ton. An approximate 500,000 tons of incineration ash is generated annually and 100% of it goes to landfill. If 100% of the incineration ash can be recycled, this means it can save S$50-65 million annually, aside environmental benefits. The green building materials, including lightweight aggregate, lightweight partition wall, thermal insulative panel and lightweight brick, are valuable materials, which are widely used in building construction and industries. Due to continuous growth in construction and increasing energy costs, the demand for thermal insulation materials will continue to expand at a healthy pace. According to the reports from Freedonia Group Inc., the market of insulation materials in China in 2013 is around 3.75 billion US dollars and the global market in 2014 is around 31.3 billion US dollars. In addition, the Chinese Ministry of Finance has announced that China will allocate around 270 million US dollars to support the construction energy efficiency programs in the country under its 12th five-year plan, and thermal insulation materials are anticipated to be an important part in this effort.

[00168] Overall, this technology will usher in a huge transformation of waste management industry, with new industry players finding new niches in business by leveraging on the new technology and products developed.

[00169] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Claims

A method of manufacturing a lightweight material, the method comprising

c) curing the mixture to obtain the lightweight material.

The method according to claim 1, wherein the solid waste comprises mud, ash obtained from incineration of waste, and waste glass in a weight ratio in the range of about 0:3:2 to about 5:3:2.

The method according to claim 1 or 2, wherein the solid waste comprises one or more contaminants.

The method according to claim 3, wherein the one or more contaminants is selected from the group consisting of a heavy metal, chalcogens, lead, bismuth, arsenic, aluminum, cyanides, sulfates, phosphates, and combinations thereof.

The method according to any one of claims 1 to 4, wherein the solid waste is subjected to a ball milling process prior to dispersing the solid waste in the aqueous reagent.

The method according to claim 5, wherein the ball milling is carried out for a time period sufficient to reduce particle size of the mixture to an average particle size of about 500 μιη or less.

The method according to any one of claims 1 to 6, wherein the foaming agent is selected from the group consisting of silicon carbide, ferric oxide, calcium sulfate, calcium carbonate, sodium carbonate, carbon black, and combinations thereof.

8. The method according to any one of claims 1 to 7, wherein amount of the foaming agent in the mixture is in the range of about 0.1 wt% to about 2 wt% of the mixture.

9. The method according to any one of claims 1 to 8, wherein the metal silicate is a water-soluble metal silicate.

10. The method according to any one of claims 1 to 9, wherein the metal silicate comprises or consists of an alkali metal silicate.

11. The method according to any one of claims 1 to 10, wherein the metal silicate is selected from the group consisting of sodium metasilicate, calcium silicate, aluminum silicate, and mixtures thereof.

12. The method according to any one of claims 1 to 11, wherein the metal silicate is sodium metasilicate.

13. The method according to any one of claims 1 to 12, wherein amount of the metal silicate in the mixture is in the range of about 1 wt% to about 10 wt% of the mixture.

14. The method according to any one of claims 1 to 13, wherein the additive comprises a fluxing agent.

15. The method according to claim 14, wherein the fluxing agent is selected from the group comprising sodium borate, boric acid, sodium carbonate, potassium carbonate, coke, lime, and combinations thereof.

16. The method according to claim 14 or 15, wherein amount of the fluxing agent in the mixture is about 5 wt% or less.

17. The method according to any one of claims 1 to 16, wherein the additive comprises a binder.

18. The method according to claim 17, wherein the binder comprises S1O2 and/or a silicate, and a hydroxide selected from the group consisting of an alkali-metal hydroxide, an alkaline earth metal hydroxide, ammonium hydroxide, and combinations thereof.

19. The method according to claim 17 or 18, wherein the binder comprises an aqueous alkaline solution of sodium silicate.

20. The method according to any one of claims 17 to 19, wherein amount of the binder in the mixture is about 5 wt% or less.

21. The method according to any one of claims 1 to 20, wherein mixing the dispersion with the additive comprises agglomerating the mixture to obtain one or more aggregates of the mixture.

22. The method according to claim 21, wherein the one or more aggregates has an average size in the range of about 0.5 cm to about 5 cm.

23. The method according to claim 21 or 22, wherein a second binder is added to the mixture while agglomerating the mixture.

24. The method according to claim 23, wherein the second binder comprises a silicate and a hydroxide selected from the group consisting an alkali-metal hydroxide, an alkaline earth metal hydroxide, ammonium hydroxide, and combinations thereof.

25. The method according to claim 23 or 24, wherein the second binder comprises an aqueous alkaline solution of sodium silicate.

26. The method according to any one of claims 23 to 25, wherein amount of the second binder in the mixture is about 5 wt% or less.

27. The method according to any one of claims 1 to 26, wherein the mixture is compressed and/or molded prior to curing.

28. The method according to claim 27, wherein the mixture is compressed at a pressure in the range of about 5 MPa to about 20 MPa.

29. The method according to claim 27 or 28, wherein the mixture is compressed for a time period in the range of about 1 minute to about 10 minutes.

30. The method according to any one of claims 1 to 29, wherein curing the mixture to obtain the lightweight material is carried out at a temperature in the range of about 1000 °C to about 1150 °C.

31. The method according to any one of claims 1 to 30, wherein curing the mixture to obtain the lightweight material is carried out at a temperature in the range of about

1100 °C to about 1125 °C.

32. The method according to any one of claims 1 to 31, wherein curing the mixture to obtain the lightweight material is carried out for a time period in the range of about 1 minute to about 15 minutes.

33. The method according to any one of claims 1 to 32, wherein curing the mixture to obtain the lightweight material is carried out by heating the mixture to a temperature in the range of about 1100 °C to about 1125 °C, holding the mixture at the temperature for about 1 minute to about 2 minutes, and thereafter cooling the mixture to room temperature.

34. A lightweight material manufactured by a method according to any one of claims 1 to 33. Use of a method according to any one of claims 1 to 33 in the manufacture of a lightweight aggregate, a thermal insulative panel, a lightweight partition wall, or a lightweight brick.