WO2020173906A1

WO2020173906A1 - A composite

Info

Publication number: WO2020173906A1
Application number: PCT/EP2020/054841
Authority: WO
Inventors: Arno Keulen; Diego A. Santamaria Razo; Frans Temmermans; Olof TROMP
Original assignee: Calduran Kalkzandsteen BV; CRH Nederland BV
Current assignee: Calduran Kalkzandsteen BV; CRH Nederland BV
Priority date: 2019-02-26
Filing date: 2020-02-25
Publication date: 2020-09-03
Anticipated expiration: 2021-08-26
Also published as: EP3930932A1

Abstract

The invention relates to a process of producing a composite comprising: a) providing a particulate material, b) providing an organic waste material, c) mixing the particulate material and the organic waste material to form a mixture, and d) carbonating the mixture in the presence of carbon dioxide, wherein the particulate material comprises calcium oxide, calcium hydroxide, calcium silicate or combinations of two or more thereof.

Description

A COMPOSITE

The present invention relates to a composite, a process for producing a composite and uses of a composite. Further, the present invention relates to the manufacture of cement or lime.

BACKGROUND TO THE INVENTION

The environmental impact of carbon dioxide and waste materials is a cause for concern. Carbon dioxide is often produced as a by-product from industry, such as in the production of cement and lime. Existing EU legislation seeks to reduce the amount of carbon dioxide released into the atmosphere using a cap and trade principle which limits the amount of carbon dioxide that can be produced and allows companies to trade emissions allowances.

The environmental impact of sending particulate waste to landfill is also a cause for concern. Particulate waste from a variety of sources is sent to landfill which prevents the waste being reused. In addition, there are environmental concerns regarding dumping particulate waste in landfill in terms of the space used and the potential for undesirable components leaching into groundwater. Particulate waste may be a by-product of industry, such as air pollution control residue, fines, slag and ash. Further, it may be dusts or filter cakes.

Organic waste material such as sewage sludge and contaminated soil can be difficult and costly to process due to their water content. This also applies to industrial sludges. Further, they can be can be difficult and costly to process due to their contaminant content. Further, sending this waste to landfill and can be harmful to the environment, leaching undesirable components into the groundwater. It is possible to incinerate such waste, but this is costly due to the increased thermal input needed to handle the excess water in the waste and it results in the production of carbon dioxide and ash which then require separate processing to mitigate their environmental impact.

There is a need for a process to reduce carbon dioxide emissions. There is a need for a process that captures carbon dioxide to reduce emissions. There is a need for a process to recycle carbon dioxide to reduce emissions. There is a need for a carbon neutral process in industry, such as in the production of lime and cement. There is a need for improved methods of process waste, such as waste from industries like cement and lime production. Further, there is a need for improved processes of handing organic waste material. There is also a need for a product to capture carbon dioxide and waste materials to enable the raw materials to be further used. Further there is a need to reduce the amount of fuel such as coal or coke used in industry, such as in the production of cement and lime. Further there is a need to reduce the amount of fuels such as gas or oil used in industry, such as in the production of cement and lime. Further there is a need to reduce the amount of limestone from a quarry which is used in industry, such as in the production of cement and lime. Further there is a need to reduce the amount of limestone from a quarry which is used in industry, such as in the production of aggregate in building material production.

It is, therefore, an object of the present invention to seek to alleviate the above identified problems.

SUMMARY OF THE INVENTION

In a first aspect of the invention, there is provided a process of producing a composite comprising:

a) providing a particulate material,

b) providing an organic waste material,

c) mixing the particulate material and the organic waste material to form a mixture, and

d) carbonating the mixture in the presence of carbon dioxide,

wherein the particulate material comprises calcium oxide, calcium hydroxide, a calcium silicate or a combination of two or more thereof.

In a second aspect of the invention, there is provided a composite produced by the method of the first aspect of the invention.

In a third aspect of the invention, there is provided a composite comprising organic waste material and a calcium carbonate binder.

In a fourth aspect of the invention, there is provided the use of a composite as a fuel, wherein the composite is produced according to the first aspect of the invention or the composite is according to the second aspect or third aspect of the invention.

In a fifth aspect of the invention, there is provided the use of a composite as a secondary aggregate for building or for producing concrete, wherein the composite is produced according to the first aspect of the invention or the composite is according to the second aspect or third aspect of the invention.

In a sixth aspect of the invention, there is provided a method of recycling cement kiln dust or lime kiln dust comprising using cement kiln dust or lime kiln dust as the particulate material in a process according to the first aspect of the invention to form a composite, and using the composite in a method of manufacturing cement or lime, wherein the composite provides both fuel to the method and starting materials for the production of cement or lime.

In a seventh aspect of the invention, there is provided a method of capturing carbon dioxide, comprising using carbon dioxide in a process according to the first aspect of the invention.

In an eighth aspect of the invention, there is provided a method of manufacturing lime comprising:

i. providing limestone,

ii. providing a fuel,

iii. adding the limestone and the fuel to a kiln, and

iv. heating the kiln to produce lime, carbon dioxide and lime kiln dust, wherein the carbon dioxide/and or the lime kiln dust are used in a process according to the first aspect of the invention.

In a ninth aspect of the invention, there is provided a method of manufacturing cement comprising:

i. providing limestone,

ii. providing a silicate,

iii. providing a fuel,

iv. adding the limestone, the silicate and the fuel to a kiln, and v. heating the kiln to produce cement, carbon dioxide and cement kiln dust,

wherein the carbon dioxide/and or the cement kiln dust are used in a process according to the first aspect of the invention.

In a tenth aspect of the invention, there is provided a carbon neutral process of producing cement or lime, wherein carbon dioxide produced in the method of producing cement or lime is used in a process according to the first aspect of the invention.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows a method of manufacturing lime.

Figure 2 shows a method of manufacturing cement.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process of producing a composite comprising: a) providing a particulate material,

b) providing an organic waste material,

d) carbonating the mixture in the presence of carbon dioxide,

wherein the particulate material comprises calcium oxide, calcium hydroxide, calcium silicate or combination of two or more thereof.

Calcium silicate has varying proportions of calcium as calcium oxide, and silicon as silicon dioxide. Calcium silicates may be anhydrous or hydrated. Calcium silicate may also comprise other constituents such as magnesium ions, aluminium ions, iron ions and fluoride ions. Preferably calcium silicate may comprise other constituents such as magnesium ions, aluminium ions, and fluoride ions.

Preferably calcium silicate is formed of varying proportions of calcium as calcium oxide, and silicon as silicon dioxide and optionally water.

Preferred calcium silicates include calcium orthosilicate - Ca₂Si0₄, wollastonite - CaSi0₃ bellite - 2CaO S1O2 and tricalcium silicate - 3CaO S1O2.

An advantage of the process is that carbon dioxide emissions are reduced by capturing carbon dioxide in the composite such as shown by the following reaction schemes.

Calcium oxide:

CaO + CO2 ^® CaCCh

Calcium hydroxide:

Ca(OH)₂ + C0₂ ® CaCOs +HzO

Tricalcium silicate:

2Ca₃Si0₅ + 7H₂0 ® 3Ca0-SiO₂-4H₂O + 3Ca(OH)₂

Ca(OH)₂ + C0₂ ® CaCOs +HzO

Bellite -

2 Ca₂Si0₄ + 4 H₂0 3 CaO 2 Si0₂ 3 H₂0 + Ca(OH)₂

Ca(OH)₂ + C0₂ ® CaCOs +HzO As shown above, calcium silicates may react directly with carbon dioxide, or may react first with water to produce calcium hydroxide. Calcium hydroxide may further react with carbon dioxide to form calcium carbonate. It will be appreciated that other calcium silicates will have different reaction schemes which will result in the formation of calcium carbonate.

Preferably, the carbonation step results in the formulation of calcium carbonate. Calcium carbonate is a suitable binder to hold the composite together. It provides structural rigidity to the composite. Further carbonates may be produced to act as a binder to provide additional structural rigidity, such as magnesium carbonate or potassium carbonate.

Further, the optional formation of aluminium silicate hydrates may also act as a binder. Such aluminium silicate hydrates are well known in cement production.

The formation of calcium carbonate, and optionally magnesium carbonate and/or potassium can help expel water as the composite is formed. Further, applying pressure during the formation of the composite can also expel water as the composite is formed. Further, the application of heat can help evaporate water from the composite, such as by applying hot air. Heat may advantageously be supplied from a kiln.

Preferably, the particulate material comprises calcium oxide or calcium hydroxide, most preferably the particulate material comprises calcium oxide.

Preferably, about 10% to about 100% by weight of the particulate material is selected from calcium oxide, calcium hydroxide, calcium silicate, or a combination of two or more thereof, more preferably about 25% to about 95% by weight of the particulate material is selected from calcium oxide, calcium hydroxide, calcium silicate, or a combination of two or more thereof, more preferably about 30% to about 85% by weight of the particulate material is selected from calcium oxide, calcium hydroxide, calcium silicate, or a combination of two or more thereof, more preferably about 40% to about 70% by weight of the particulate material is selected from calcium oxide, calcium hydroxide, calcium silicate, or a combination of two or more thereof. Such proportions of calcium oxide, calcium hydroxide, calcium silicate, or a combination of two or more thereof are suitable to react to form a calcium carbonate binder to hold the composite together.

Preferably, about 10% to about 100% by weight of the particulate material is selected from calcium oxide, calcium hydroxide, or a combination thereof, more preferably about 25% to about 95% by weight of the particulate material is selected from calcium oxide, calcium hydroxide, or a combination thereof, more preferably about 30% to about 85% by weight of the particulate material is selected from calcium oxide, calcium hydroxide, or a combination thereof, more preferably about 40% to about 70% by weight of the particulate material is selected from calcium oxide, calcium hydroxide, or a combination thereof. Such proportions of calcium oxide, calcium hydroxide, or a combination thereof are suitable to react to form a calcium carbonate binder to hold the composite together. Calcium oxide and calcium hydroxide are particularly preferred as they can react directly with carbon dioxide to form calcium carbonate.

Preferably, about 10% to about 100% by weight of the particulate material is calcium oxide, more preferably about 25% to about 95% by weight of the particulate material is calcium oxide, more preferably about 30% to about 85% by weight of the particulate material is calcium oxide, more preferably about 40% to about 70% by weight of the particulate material is calcium oxide.

Such proportions of calcium oxide are suitable to react to form a calcium carbonate binder to hold the composite together. Calcium oxide is particularly preferred because it reacts directly with carbon dioxide to form calcium carbonate, without producing any by-products, such as water. This makes the process more efficient as excess water does not need to be removed or incorporated into the composite.

Preferably, the particulate material has an average particle size of about 1 pm to about 30 mm, preferably about 10 pm to about 5 mm, most preferably about 1 mm to about 5 mm.

The particulate material may be in the form of a fine powder with an average particle size of about 1 pm to about 3 mm, preferably about 1 pm to about 1 mm, preferably about 10 pm to about 500 pm. An advantage of using particles of this size is that they have a relatively large surface area which maximises the efficiency of the carbonation reaction. Further, it is an advantage of the present invention that such fine powders can be used as a starting material and incorporated into a larger final composite for further use.

Alternatively, the particulate material may be in the form of a granule with an average particle size of about 1 mm to about 300 mm, preferably about 1 mm to about 30 mm, preferably about 1 mm to about 10 mm, most preferably about 1 mm to about 5 mm. Such particle sizes have the advantage of not requiring specialist equipment to handle them as they are of a relatively large size.

The average particle size may be measured by laser diffraction or sieving, preferably by laser diffraction. The average particle size of the particulate material may be reduced, such as by grinding, or crushing. Further, the particulate material may be made from a larger piece or pieces of material such as by grinding or crushing.

Preferably, the particulate material further comprises aluminium oxide, silicon dioxide, iron oxide, an iron silicate, an aluminium silicate, magnesium oxide, magnesium hydroxide, a magnesium silicate, a sodium silicate, a potassium silicate, magnesium sulphate, calcium sulphate, potassium sulphate, sodium sulphate or a combination of two or more thereof. Preferably, the particulate material further comprises aluminium oxide, silicon dioxide, iron oxide, an iron silicate, an aluminium silicate, magnesium oxide, magnesium hydroxide, a magnesium silicate, a sodium silicate, or a combination of two or more thereof. An advantage of including further constituents is that they too may react to help harden the composite. This may be by a hydration reaction, a carbonation reaction, or a further reaction. These further reactions improve the strength of the resulting carbonate, in particular the composite.

Preferably the sulphur dioxide is present in step d). Sulphur dioxide is typically present in flue gases, and it is an advantage of the invention that it is not necessary to separate the sulphur dioxide from the flue gas. Further sulphur dioxide may react with substituents in the mixture, particularly with sodium or potassium containing compounds to form sodium sulphite, sodium sulphate, potassium sulphite, potassium sulphate, or a combination of two or more of. This has the dual advantage of capturing sulphur dioxide, and hardening the composite.

Preferably, the particulate material comprises, air pollution control residue, Portland cement, Portland clinker, rock fines, concrete fines, slag, fly ash, bottom ash, paper ash, oil shale ash or a combination of two or more thereof. The present invention provides a way to divert such waste materials from landfill.

Preferably, the particulate material comprises, air pollution control residue, Portland cement, Portland clinker, rock fines, concrete fines, slag, fly ash, bottom ash, dusts, paper ash, oil shale ash, bleaching earth material or a combination of two or more thereof. The present invention provides a way to divert such waste materials from landfill.

Preferably, the particulate material comprises, air pollution control residue, Portland cement, Portland clinker, rock fines, concrete fines, slag, fly ash, bottom ash, dusts, paper ash, oil shale ash, bleaching earth material, synthetic slag or a combination of two or more thereof. Preferably, the particulate material comprises synthetic slag. Synthetic slag is preferably produced from a mixture of primary or secondary oxides, preferably CaO, S1O₂ and AI₂O₃. Synthetic slag has similar physicochemical properties to that of granulated blast furnace slag. An advantage of using synthetic slag is that a known composition of particulate material is used. Further, synthetic slag it is preferably made from waste materials and it is an advantage of the invention to reuse waste materials.

Preferably the Portland cement, or Portland clinker are out of date. This means that the best before date for these has been passed.

Preferably, the fly ash and bottom ash is from burning coal, biomass, manure or waste, such as household waste, or is produced by industries such as glass production, oil and gas refinement.

Preferably, the fly ash and bottom ash is from burning coal, biomass, manure or waste, such as household waste.

Preferably, the slag is from metal production, such as the production of metal smelts, iron, stainless steel, copper, lead, nickel or zinc.

Preferably, the slag is from metal production, such as the production of iron, copper, lead, nickel or zinc.

Preferably, the bleaching earth material is from industry, producing natural oil such as palm oil, preferably the bleaching earth material is bleaching earth filtrate material.

Preferably, the particulate material comprises air pollution control residue from cement production, lime production, steel and metal production, incineration or from industry, bleaching earth from industry or a combination of two or more thereof, more preferably the particulate material comprises cement kiln dust or lime kiln dust, most preferably wherein the particulate material comprises cement kiln dust. Preferably the particulate material has an average particle size of about 1 pm to about 3 mm, preferably about 10 pm to about 500 pm.

Preferably cement kiln dust includes cement kiln bypass dust. Preferably lime kiln dust includes lime kiln bypass dust. Preferably, the particulate material comprises air pollution control residue from cement production, lime production, steel and metal production, incineration, or a combination of two or more thereof, more preferably the particulate material comprises cement kiln dust or lime kiln dust, most preferably wherein the particulate material comprises cement kiln dust. Preferably the particulate material has an average particle size of about 1 pm to about 1 mm, preferably about 10 pm to about 500 pm.

It will be appreciated that air pollution control residue has a known meaning in the art, and is a by-product of industry. Air pollution control residue is typically a mixture of ash, carbon and lime. It may comprise further components.

Preferably at least about 80 wt% on a dry weight basis of the particulate is used to form the composite, more preferably at least about 90 wt%, more preferably at least about 95 wt%, more preferably at least about 99 wt%, most preferably all of the particulate material, on a dry weight basis is used to form the composite. This allows for efficient use of the starting materials and reduces waste.

Preferably, the process comprises washing the particulate material with water, preferably washing the particulate material with water prior to mixing step (c). An advantage of washing the particulate material is that water soluble salts are removed, such as sodium chloride, potassium chloride and magnesium chloride. These salts can then be used for other processes, such as after they have been recovered by evaporation. It is advantageous to remove such water soluble salts because they are undesirable impurities. For example, in processes such as the manufacture of cement, the amount of salt needs to be carefully controlled. The presence of such salt may weaken the strength and reduce the durability of any resulting concrete, particularly steel reinforced concrete.

A further advantage of washing the particulate material is that water soluble heavy metals are removed, such as cationic and anionic metal species. These metals can then be used for other processes, such as after they have been recovered by evaporation. It is advantageous to remove such water soluble heavy metals because they are undesirable impurities. For example, in processes such as the manufacture of cement, the amount of water soluble heavy metals needs to be carefully controlled. The presence of such metals may weaken the strength and reduce the durability of any resulting concrete, particularly steel reinforced concrete. A further advantage of washing the particulate material is that the presence of water can start a curing process of the particulate material. In particular, calcium oxide can react with water to form calcium hydroxide. Further, calcium silicates can react with water to form calcium silicate hydrates which act as an additional binder for the composite.

The washing step is particularly advantageous when the particulate material comprises cement kiln dust or lime kiln dust as these materials typically contain unwanted salts. Further, the composition of these materials means that they start to cure in the presence of water.

After the washing step has been carried out, the particulate material may be pressed, filtered or processed under vacuum to remove excess water. This has the advantage of removing salts dissolved in the water from the particulate material and removing excess water. This has the further advantage of removing heavy metals dissolved in the water from the particulate material.

Preferably, the free water content of the particulate material, is about 2 to about 50 wt%, preferably about 10 to about 40 wt %, more preferably about 15 to about 30 wt%. Preferably, this is the free water content of the particulate material in step (c). Such water contents are suitable for starting a hydration reaction, while minimising the amount of water in the process.

Free water is water that is not bound to another component. Free water does not include water which forms a hydrate.

The organic waste material may be washed with water, and/or pressed to remove any salts and excess water. An advantage of this washing and/or pressing step is the removal of excess water and salts. A further advantage of this washing and/or pressing step is the removal of water soluble heavy metals.

Preferably, the organic waste material has a free water content of about 2 to about 60 wt%, preferably about 10 to about 40 wt %, preferably about 10 to about 35%, more preferably about 15 to about 30 wt%. Preferably, this is the free water content of the organic waste material in step (c). An advantage of this process is that it is not necessary to remove excess free water from an organic waste material prior to this process. This has an environmental advantage as energy does not need to be expended to heat or press the organic waste material to remove excess free water. Preferably, the organic waste material has a calorific value of about 5 to about 40 kJ/g on a dry basis, preferably wherein the organic waste material has a calorific value of about 10 to about 30 kJ/g on a dry basis. The calorific value may be measured using a calorimeter. An advantage of such a calorific value is that the resulting composite can then act as a fuel, for example in a lime or cement kiln. This provides a convenient way to utilise the calorific content of the organic waste material and to divert it from landfill. It helps take an undesirable waste product and use it in order to minimise the environmental impact of the waste and is much more efficient and useful than sending the organic waste material to landfill.

Preferably the organic waste material has a carbon content of at least about 10 wt% on a dry weight basis, such as about 10 wt% to about 60 wt%, preferably about 20 wt % to about 60 wt%, preferably about 30 wt% to about 60 wt%, preferably 10 wt% to about 50 wt%, preferably about 20 wt % to about 50 wt%, preferably about 30 wt% to about 50 wt%. Preferably carbon content refers to bound and unbound carbon.

Preferably the waste organic material has an organic matter content of at least 10% on a dry weight basis, such as about 10 wt% to about 60 wt%, preferably about 15 wt % to about 50 wt%, preferably about 20 wt% to about 40 wt%.

An advantage of the present invention is that it allows waste organic materials to be recycled into a composite. It is not necessary to pretreat the organic waste material as it may be directly mixed with the particulate material. Contaminants in the organic waste material can then be contained within the calcium carbonate binder formed. This will result in an inert composite that can be used for a variety of purposes.

Preferably, the organic waste material comprises biomass, soil, coal, sludge, organic wet fraction, plastic, oil and gas well drilling sludge, or a combination of two or more thereof, preferably comprises biomass, soil, sludge, plastic, or a combination of two or more thereof. Preferably, the organic waste material comprises biomass, oil and gas well drilling sludge, sewage sludge, plastic, wastes or a combination of two or more thereof, preferably sewage sludge, soils or plastic.

Preferably, the organic waste material comprises biomass, soil, sludge, organic wet fraction, plastic, or a combination of two or more thereof, preferably comprises biomass, soil, sludge, plastic, or a combination of two or more thereof. Preferably, the organic waste material comprises biomass, sewage sludge, plastic, or a combination of two or more thereof, preferably sewage sludge or plastic. Preferably the organic waste material is not ash. Ash is not an organic waste material and does not provide a high enough calorific value to be used as an organic waste material in the present invention. Ash may be used as a particulate material as defined above.

Preferably the organic waste material is not biomass ash.

Biomass is waste material from plants or animals that is not used for food or feed. It is an advantage of the invention that this waste material can be reused.

Sludge is a semi-solid slurry comprising organic matter, preferably sewage sludge, dredging sludge, organic sludge from soil cleaning, oil well drilling or petroleum sludge, preferably sewage sludge, dredging sludge, organic sludge from soil cleaning or petroleum sludge. It is an advantage of the invention that this waste material can be reused.

Oil and gas well drilling sludge/ soils are produced as part of oil and gas well drilling.

Soil is preferably clay soil, sandy soil, organic soil or oil and gas well drilling soil or a combination of two or more thereof, preferably clay soil, sandy soil, organic soil or a combination of two or more thereof. It is an advantage of the invention that soil can be used as it is readily available.

Plastic is preferably organic polymers, refuse derived fuel (RDF), solid recovered fuel (SRF), plastic residue from waste streams or combinations of two or more thereof. RDF may be produced by shredding domestic and business waste after removing non-combustible materials such as metals and glass. SRF is a higher quality fuel than RDF and may be derived from, plastic, paper, textiles, wood.

Organic wet fraction is produced as part of waste streams, particularly residential waste streams.

Preferably, the organic waste material comprises biomass, soil, sludge or a combination of two or more thereof, more preferably the organic waste material comprises sewage sludge, dredging sludge, organic sludge from soil cleaning, petroleum sludge, contaminated soil, natural soil or contaminated bleaching earth or a combination of two or more thereof, more preferably, the organic waste material comprises sewage sludge. Preferably, the organic waste material comprises biomass, soil, sludge or a combination of two or more thereof, more preferably the organic waste material comprises sewage sludge, dredging sludge, organic sludge from soil cleaning, oil and gas well drilling sludge/ soils, petroleum sludge, contaminated soil, natural soil or contaminated bleaching earth or a combination of two or more thereof, more preferably, the organic waste material comprises sewage sludge, soil and sludge.

Preferably, the organic waste material comprises plastic residue from waste streams, refuse derived fuel, solid recovered fuel, or a combination of two or more thereof, preferably refuse derived fuel.

Preferably, contaminated means that it contains undesirable components, such as man-made chemicals, including hydrocarbons and heavy metals. Further, undesirable components include radioactive nuclides. A heavy metal may have a density of greater than about 5 g/cm³. It is an advantage of the invention that contaminated organic waste materials can be recycled.

Preferably at least about 80 wt% on a dry weight basis of the organic waste material are used to form the composite, more preferably at least about 90 wt%, more preferably at least about 95 wt%, more preferably at least about 99 wt%, most preferably all of the organic waste material, on a dry weight basis is used to form the composite. This allows for efficient use of the starting materials and reduces waste.

Preferably the dry weight ratio of the particulate material to the organic waste material is about 1 : 10 to about 10:1 , preferably wherein the dry weight ratio of the particulate material to the organic waste material is about 1 :5 to about 5: 1 , preferably wherein the dry weight ratio of the particulate material to the organic waste material is about 1 :2 to about 2:1. Such ratios balance the need for the resulting composite to have a useful calorific content and the need for sufficient calcium carbonate to be formed to bind the composite together.

Preferably the particulate material and the organic waste material are mixed such that both are present throughout the mixture, preferably the mixture is substantially homogeneous. This helps to produce a uniform product, with a known composition.

Preferably the mixture comprises at least 5% on a dry weight basis of organic waste material. Preferably the mixture comprises 5% to 60 % on a dry weight basis of organic waste material, preferably 10% to 50%, preferably 15% to 40%, such as more than 35% on a dry weight basis. Such amounts are suitable for providing calorific content to the resulting composite. Preferably the mixture comprises 5% to 95% on a dry weight basis of particulate material. Preferably the mixture comprises 5% to 60 % on a dry weight basis of particulate material, preferably 10% to 50%, preferably 15% to 40%, such as more than 35% on a dry weight basis. Such amounts are suitable for providing sufficient calcium carbonate in the resulting composite.

Preferably, waste water can be added during step (c). This has the advantage of using another waste product in the present invention. The waste water preferably comprises organic complexes, inorganic complexes, metals and combinations thereof. The waste water may further help cure the mixture.

In step (d), the concentration of carbon dioxide may be that of air at standard atmospheric pressure. This has the advantage of not requiring additional carbon dioxide in the process. Standard atmospheric pressure is defined as 101325 Pa (1.01325 bar). The concentration of carbon dioxide in air may be about 300 ppm to about 500 ppm, such as about 410 ppm. Preferably, when carbon dioxide is used at the concentration of air at standard pressure, the particulate material further comprises aluminium oxide, silicon dioxide, iron oxide, an iron silicate, an aluminium silicate, magnesium oxide, magnesium hydroxide, a magnesium silicate, a sodium silicate, a potassium silicate, magnesium sulphate, calcium sulphate, potassium sulphate, sodium sulphate or a combination of two or more thereof. Preferably, the particulate material further comprises aluminium oxide, silicon dioxide, iron oxide, an iron silicate, an aluminium silicate, magnesium oxide, magnesium hydroxide, a magnesium silicate, a sodium silicate, or a combination of two or more thereof. An advantage of including further constituents is that they too may react to help harden the composite. This may be by a hydration reaction, a carbonation reaction, or a further reaction. These further reactions improve the strength of the resulting composite.

Preferably, in step (d), the concentration of carbon dioxide is about 5% to about 100% by volume, preferably the concentration of carbon dioxide is about 10% to about 100% by volume, preferably the concentration of carbon dioxide is about 30% to about 100% by volume, preferably the concentration of carbon dioxide is about 70% to about 100% by volume. Preferably, in step (d), the concentration of carbon dioxide is about 10% to about 95% by volume, preferably about 20% to about 90% by volume, preferably about 30% to about 80% by volume. Such concentrations have the advantage of using excess carbon dioxide, such as that produced in industry, such as during lime or cement production or incineration. Capturing excess carbon dioxide in this way has environmental benefits. Further, increasing the concentration of carbon dioxide will speed up the carbonation process as more carbon dioxide is available to react to form calcium carbonate. In some situations, it is desirable to have a concentration of about 100% by volume carbon dioxide. In other situations, it can be desirable to have less than about 90%, or about 80% or about 70% or about 10% by volume carbon dioxide to control the rate of the reaction.

Carbonation may occur over a period of about 20 minutes up to about 3 weeks, preferably about 1 hour to about 2 weeks, more preferably about 2 hours to about 1 day.

Preferably, the carbon dioxide in step (d) comprises carbon dioxide that is a by-product from industry, preferably from a cement kiln or lime kiln. Preferably the carbon dioxide in step (d) is from the flue gas of a cement kiln or a lime kiln. An advantage of using carbon dioxide in this way is that it reduces the carbon footprint of an industrial process by capturing carbon dioxide produced in that process. It is a particular advantage to use carbon dioxide from a cement kiln or a lime kiln because the resulting composite can be used in a cement kiln or a lime kiln to act as a fuel and to provide starting materials for cement or lime production. This allows the production of cement or lime to have a reduced carbon footprint, and even become carbon neutral as carbon dioxide produced in a kiln is reused to make a starting material. Further, if the composite is used as a building material, the carbon dioxide has been captured and is not released into the atmosphere.

Carbon dioxide may be provided in gaseous form, or in liquid form. Where carbon dioxide is in a gaseous form, it is preferably provided from a flue gas. An advantage of providing carbon dioxide in gaseous form is that it can be piped, such as from a flue into the reaction of the present invention. An advantage of providing carbon dioxide in liquid form, is that it can be transported from one location to another with reduced volume. Further, liquid carbon dioxide may be mixed in with the particulate material and waste organic material to increase the rate of reaction by bringing an increased amount of carbon dioxide in contact with the particulate material and waste organic material.

The mixture can be formed into a desired shape, before, during or after carbonation.

Preferably the composite is formed into an aggregate, a monolithic product or a paving slab, preferably an aggregate or a monolithic product, preferably an aggregate.

Preferably, the composite is formed by granulating, grinding, crushing, pelletization, extrusion, batch mixing or a combination of two or more thereof. These are suitable methods for producing composites of a desired size. The mixture may be formed into a monolithic product, such as with a volume of about 0.5 m³ to about 3 m³, preferably about 1 m³ to about 2 m³. Such monolithic products are convenient to form and store. Preferably the carbonation process starts during the mixing process, and continues after the mixture has been formed into the desired shape. It is convenient to supply carbon dioxide to the mixture in liquid or gaseous form to allow even mixing of the particulate material, organic waste material and carbon dioxide.

Preferably, the monolithic product is subsequently reduced in size by grinding or crushing to produce an aggregate. The crushing or grinding step may be carried out immediately after carbonation. Alternatively, the crushing or grinding step can be carried out at a later point, such as prior to use, such as use to produce lime or cement in a kiln. It may be easier to transport a monolithic product, rather than an aggregate.

The carbonation step may continue after the composite has been formed into the desired shape, such as by batch mixing, cold pressing, granulating, pelletization or extrusion, preferably granulating, pelletization or extrusion, in order to allow the mixture to be shaped and then hardened. The mixture may be partially carbonated prior to being shaped, such as by pelletization or extrusion. Alternatively, the carbonation step may substantially begin after the mixture has been shaped, such as by pelletization or extrusion. Preferably, where the mixture is shaped, such as by granulating, pelletization or extrusion, preferably by pelletization or extrusion the mixture is partially carbonated before it is shaped, and the carbonisation step then continues. This allows the mixture to be sufficiently flowable to be shaped, and then hardened into the desired composite. Preferably the composite material is shaped into an aggregate.

Preferably, liquid carbon dioxide is provided in step c) and is mixed with the particulate material and organic waste material and carbonation occurs. Preferably, gaseous carbon dioxide is provided in step c) and is mixed with the particulate material and organic waste material and carbonation occurs. Preferably, the resulting mixture is formed into the desired shape, such as by cold pressing, extrusion or pelletization, preferably extrusion or pelletization, and then treated with liquid or gaseous carbon dioxide, preferably gaseous carbon dioxide to continue the carbonation process, preferably wherein the amount of carbon dioxide present is defined above. Preferably, the shaped mixture is treated with carbon dioxide for about 5 minutes to about 2 hours, preferably about 10 minutes to about 1 hour, preferably about 15 minutes to about 30 minutes. After the carbon dioxide treatment, the resulting composite may be stored in air to continue the carbonation process and harden the composite. Preferably the composite continues to harden in air for at least about 1 day, such as about 1 day to about 6 months, preferably about 2 days to about 3 months, preferably about 1 week to about 1 month.

Preferably, the process of the invention is a continuous process. This allows a steady input of the particulate material, the organic waste material and the carbon dioxide, and a steady output of the composite material. This is particularly useful when the process is in line with another process, such as the manufacture of cement or lime.

Alternatively, the process may be a batch process. This has the advantage of a known input of starting materials and a known output of composite. A batch process is preferred when producing a monolithic product.

Excess water can be removed at any stage of the process, such as by heating. If the process is used in line with an exothermic method, such as a method for the production of cement or lime, the heat, for example from the kiln, can be used to evaporate water from the process or resulting composite. Further, such heat can be used to evaporate water removed in any washing steps to produce a solid residue for further use.

Preferably the process is carried out at a temperature of about 10 °C to about 250 °C. Such temperatures are suitable for carrying out the present invention.

Preferably the process is carried out at a temperature of less than about 80 °C, preferably less than about 70 °C, preferably less than about 60 °C, preferably less than about 50 °C, such as about 10°C to about 90 °C, preferably about 20 °C to about 80 °C. It is not necessary for high temperatures to be used to produce the composite of the present invention.

Preferably the process is carried out at a temperature of about 100°C to about 250 °C, preferably about 100 °C to about 200 °C. Such temperatures are particularly suitable when the carbon dioxide supplied is a flue gas as it can be used directly in the process of the invention.

Preferably oxygen may be present during the process. This makes the process easier to manage as it is not necessary to exclude oxygen.

The present invention relates to a composite produced by the method of producing a composite described herein. The present invention relates to a composite comprising organic waste material and a calcium carbonate binder.

Preferably the composite comprises a calcium carbonate binder and a calcium silicate binder. Including two binders increases the strength of the composite.

Preferably the composite is man-made.

Preferably, the organic waste material is as described above.

Preferably, the composite is an aggregate and preferably has an average particle size of about 1 pm to about 100 mm, preferably about 500 pm to about 60 mm, preferably about 1 mm to about 60 mm, preferably about 5 mm to about 60 mm. A particle size of at least 1 mm, preferably at least 5 mm is preferred for ease of handling the composite and for use as a fuel in the production of cement or lime.

Preferably, the aggregate is substantially spherical or substantially cylindrical.

Preferably, at least about 80% of the aggregate and the aggregate produced by the process described herein are substantially spherical or substantially cylindrical, preferably at least about 85%, preferably at least about 90%, preferably at least about 95%, preferably at least about 97%, preferably at least about 99%, preferably all of the aggregate.

Within this specification, substantially spherical means having a sphericity of about 0.5 to about 1 , preferably about 0.6 to about 0.95, preferably about 0.7 to about 0.9. These sphericities are suitable for use as a secondary aggregate as they resemble the shape of primary aggregates, such as gravel. Further such shaped aggregates may be used in a method of production of cement or lime.

Wthin this specification, substantially cylindrical means having a deviation of less than about 20% by volume from a theoretical cylinder, preferably at less than about 10% by volume from a theoretical cylinder, preferably less than about 5% by volume of a theoretical cylinder preferably less than about 2% by volume of a theoretical cylinder, preferably less than about 1 % by volume of a theoretical cylinder, preferably no deviation from the volume of a theoretical cylinder. The volume of the theoretical cylinder is calculated by measuring the widest diameter and then the longest perpendicular length of the composite. These tolerances are suitable for use as a secondary aggregate. Substantially cylindrical composites are preferably made by pellitization or extrusion, or combinations thereof.

Preferably, substantially spherical or substantially cylindrical means spherical or cylindrical.

Preferably the composite is a monolithic product, such as with a volume of about 0.5 m³ to about 3 m³, preferably about 1 m³ to about 2 m³ Such monolithic products are convenient to form and store. The monolithic product may be crushed or ground to form an aggregate as described herein.

Preferably the composite is a paving slab. Preferably the mixture is moulded into a paving slab, and then the composite is hardened by carbonation, preferably in the presence of carbon dioxide as described herein. Preferably the mixture is compacted in a mould to form the shape of the paving slab. Preferably a paving slab has a height of about 5 to about 50 cm and a length and a width each individually selected from about 20 cm to about 1 m, preferably a paving slab has a height of about 10 to about 40 cm and a length and a width each individually selected from about 40 cm to about 80 cm. It is an advantage of the present invention that the composite can be directly formed into a paving slab.

The composite of the present invention is preferably a solid. This gives the composite the structural rigidity to be used as an aggregate or as a fuel.

Preferably, the composite has a density of about 500 kg/m³ to about 3000 kg/m³, preferably about 1000 kg/m³ to about 2000 kg/m³. Such densities are suitable for use as a secondary aggregate such as for making concrete.

Preferably, the composite has a calorific value of about 5 kJ/g to about 35 kJ/g on a dry basis, preferably about 10 kJ/g to about 25 kJ/g. Such calorific values are useful when the composite is used as a fuel in the production of cement or lime.

Preferably, the composite has a free water content of about 0 to about 30 wt%, preferably about 1 to about 20 wt %, more preferably about 5 to about 15 wt%. It is not necessary to remove all the free water in the composite, prior to using it as a building material, to produce concrete or as a fuel for a cement kiln or a lime kiln.

The present invention relates to the use of a composite as a fuel, wherein the composite is produced as described herein or the composite is as described herein, preferably as a fuel in cement production or lime production. It is an advantage that the composite can be used as a fuel, thus utilising the waste products to produce heat. Furthermore, it is a particular advantage to use the composite as a fuel in a cement production or lime production because the composite provides both calorific value and starting materials for the production of cement or lime.

It is an advantage of the invention, that the composite does not need to be fully carbonated or hardened prior to use as a fuel, such as in a cement kiln or a lime kiln. This is because it is not necessary for the composite to have a strength such as required when it is used as an aggregate, because it will be burnt as a fuel. Further, this means that the process for making the composite can be carried out on a reduced timescale.

Cement as described herein is a binder that sets, hardens and adheres to other materials to bind them together. Cement preferably comprises Ordinary Portland Cement, Portland Pozzolana Cement, rapid hardening cement, quick setting cement, low heat cement, sulphates resisting cement, high alumina cement, white cement, coloured cement, blast furnace slag cement, air entraining cement, hydrographic cement, expansive cement, or a combination of two or more thereof, more preferably Ordinary Portland Cement or Portland Pozzolana Cement, preferably Ordinary Portland Cement.

The present invention relates to the use of a composite as a secondary aggregate for building or for producing concrete, wherein the composite is produced as described herein or the composite is as described herein.

Such a secondary aggregate may be used in the production of asphalt or in road base construction. This has the advantage that the carbon dioxide used in the process of manufacture of the composite is captured and removed from the atmosphere. The carbon dioxide is contained in the secondary aggregate.

A secondary aggregate is a man-made particulate material. A primary aggregate is a naturally occurring particulate material, such as rocks. The use of the composite of the invention in building or in concrete means that the carbon dioxide captured in the composite is not released into the atmosphere but remains within the composite material. Furthermore, the composite is made of waste products, which means that rather than the particulate material and organic waste material being sent to landfill, they are turned into a useful product, and can be used instead of natural resources such as rock. This has the dual environmental impact of reducing landfill and reducing the need to use naturally occurring rocks. Concrete may be made in accordance with normal practice by combining fine and course aggregate and cement.

The present invention relates to the use of a composite as a paving slab wherein the composite is produced as described herein or the composite is as described herein. This has the advantage that the carbon dioxide used in the process of manufacture of the composite is captured and removed from the atmosphere. The carbon dioxide is contained in the paving slab.

The present invention relates to a method of recycling cement kiln dust or lime kiln dust comprising using cement kiln dust or lime kiln dust as the particulate material in a process described herein to form a composite, and using the composite in a method of manufacturing cement or lime, wherein the composite provides both fuel to the method and starting materials for the production of cement or lime.

The present invention relates to a method of capturing carbon dioxide, comprising using carbon dioxide in a process as described herein, preferably wherein the carbon dioxide is from a cement kiln or from a lime kiln.

The present invention relates to a method of manufacturing lime comprising:

i. providing limestone,

ii. providing a fuel,

iii. adding the limestone and the fuel to a kiln, and

iv. heating the kiln to produce lime, carbon dioxide and lime kiln dust, wherein the carbon dioxide/and or the lime kiln dust are used in a process as described herein.

Preferably the limestone has an average particle size of less than about 50 mm. Larger pieces of limestone may be crushed or ground to reach the desired average particle size.

Preferably the kiln is heated to at least about 900°C.

Such a method allows the carbon footprint of a lime kiln to be reduced by capturing carbon dioxide. It will be appreciated that the method may be repeated such that excess carbon dioxide and lime kiln dust are recycled to make a composite of the present invention, which is then used as a fuel in the production of lime. Preferably, the fuel comprises a composite as described herein. It will be appreciated that the composite used as a fuel will provide both calorific value and starting materials for lime production.

The present invention relates to a method of manufacturing cement comprising:

i. providing limestone,

ii. providing a silicate,

iii. providing a fuel,

wherein the carbon dioxide/and or the cement kiln dust are used in a process as described herein.

Preferably the kiln is heated to at least about 1200°C, preferably at least about 1400°C.

Preferably the silicate is an aluminosilicate, preferably clay.

Preferably an aluminium source, and/or an iron source and/or a sulphate source are added to the kiln in step iv.

Preferably the kiln produces clinker, such as Portland clinker which is then ground or crushed, optionally with gypsum, to form cement, such as Portland Cement, preferably Ordinary Portland Cement.

Such a method allows the carbon footprint of a cement kiln to be reduced by capturing carbon dioxide. It will be appreciated that the method may be repeated such that excess carbon dioxide and cement kiln dust are recycled to make a composite of the present invention, which is then used as a fuel in the production of cement.

Preferably, the fuel comprises a composite as described herein. It will be appreciated that the composite used as a fuel will provide both calorific value and starting materials for cement production. The present invention relates to a carbon neutral process of producing cement or lime, wherein carbon dioxide produced in the method of producing cement or lime is used in a process of producing a composite as described herein.

A process is carbon neutral if there is a net zero carbon emissions by balancing a measured amount of carbon dioxide released with an equivalent amount sequestered or offset. It is the aim of the present invention to prevent the release of carbon dioxide by reusing it to make a composite material.

DETAILED DESCRIPTION OF THE FIGURES

Figure 1 shows a method of manufacturing lime. Limestone 1 , such as from a quarry, and fuel 3, are added to a kiln 5. The limestone can be optionally crushed, such as to an average particle size of less than 50 mm, prior to addition to the kiln. The kiln 5 is heated, such as to at least about 900°C to produce lime 7, carbon dioxide 9 and lime kiln dust 1 1. It will be appreciated that this is a standard method of manufacturing lime and that the skilled person can vary the reaction conditions that are required to produce lime without departing from the essence of the invention. The lime 7 can then be used as required.

The lime kiln dust 1 1 is traditionally a waste product. In the present invention however, it may be reused. The lime kiln dust 11 can optionally be washed in water as described herein to produce washed lime kiln dust 13. The washing step has the dual function of removing water soluble salts, such as sodium chloride, potassium chloride and magnesium chloride. These salts can then be used for other processes, such as after they have been recovered by evaporation. In particular, the heat of the kiln can be used in this evaporation step. A further advantage of washing the lime kiln dust is that the presence of water can start a curing process of the particulate material. In particular, calcium oxide can react with water to form calcium hydroxide.

The lime kiln dust 1 1 or the washed lime kiln dust 13 is then mixed with organic waste material 15. Preferably carbon dioxide 9 is also used during and after the mixing step to allow carbonation to occur. Alternatively, carbon dioxide from an external source 19 can be used. Alternatively, no excess carbon dioxide is used but this is less preferred as the carbonation reaction will be slower.

A composite 21 is formed. The composite may be granulated, ground, crushed, pelletized, extruded, or a combination of two or more thereof to produce a composite of the desired shape and size such as an aggregate or a monolithic product. The composite 21 , in the form of an aggregate, may then be used as a secondary aggregate 23, for building or for the production of concrete, such as asphalt or road base construction.

Preferably the composite 21 is reused as a fuel 3 in the method of manufacture of lime.

The present invention allows the waste products of lime production, namely carbon dioxide 9 and lime kiln dust 11 to be recycled into a fuel for use in a method of manufacture of lime and further to provide starting materials for the manufacture of lime. This means that carbon dioxide is not released into the atmosphere and lime kiln dust is not sent to landfill. Further, organic waste material 15 can be recycled and used to divert it from landfill. Further there is a reduction in the amount of fuel required from other sources, such as coal or coke, as the composite 21 provides calorific value and acts as a fuel. Further less limestone 1 is required as the calcium carbonate in the composite acts as a starting material in the method. Further, carbon dioxide from an external source can be used. Further, the composite can be used as a secondary aggregate and therefore the carbon dioxide is captured.

Figure 2 shows a method of manufacturing cement. Limestone 30, such as from a quarry, a silicate 32 and a fuel 34 are added to a kiln 38. The limestone can be optionally crushed, such as to an average particle size of less than 50 mm, prior to addition to the kiln. The kiln 38 is heated, such as to at least about 1200°C, preferably at least 1400°C to produce cement 40, carbon dioxide 42 and cement kiln dust 44. It will be appreciated that this is a standard method of manufacturing cement and that the skilled person can vary the reaction conditions that are required to produce cement without departing from the essence of the invention. The cement 44 can then be used as required. Preferably the kiln produces clinker, such as Portland clinker which is then ground or crushed, optionally with gypsum, to form cement, such as Portland Cement, preferably Ordinary Portland Cement.

The cement kiln dust 44 is traditionally a waste product. In the present invention however, it may be reused. The cement kiln dust 44 can optionally be washed in water as described herein to produce washed cement kiln dust 46. The washing step has the dual function of removing water soluble salts, such as sodium chloride, potassium chloride and magnesium chloride. These salts can then be used for other processes, such as after they have been recovered by evaporation. In particular, the heat of the kiln can be used in this evaporation step. A further advantage of washing the cement kiln dust is that the presence of water can start a curing process of the particulate material. In particular, calcium oxide can react with water to form calcium hydroxide. The cement kiln dust 44 or the washed cement kiln dust 46 is then mixed with organic waste material 50. Preferably carbon dioxide 42 is also used during and after the mixing step to allow carbonation to occur. Alternatively, carbon dioxide from an external source 49 can be used. Alternatively, no excess carbon dioxide is used but this is less preferred as the carbonation reaction will be slower.

A composite 52 is formed. The composite may be granulated, ground, crushed, pelletized, extruded, or a combination of two or more thereof to produce a composite of the desired shape and size such as an aggregate or a monolithic product.

The composite 52, in the form of an aggregate, may then be used as a secondary aggregate 54, for building or for the production of concrete, such as asphalt or road base construction.

Preferably the composite 52 is reused as a fuel 34 in the method of manufacture of lime.

The present invention allows the waste products of cement production, namely carbon dioxide 42 and cement kiln dust 44 to be recycled into a fuel for use in a method of manufacture of cement and further to provide starting materials for the manufacture of cement. This means that carbon dioxide is not released into the atmosphere and cement kiln dust is not sent to landfill. Further, organic waste material 50 can be recycled and used to divert it from landfill. Further there is a reduction in the amount of fuel required from other sources, such as coal or coke, as the composite 52 provides calorific value and acts as a fuel. Further less limestone 30 is required as the calcium carbonate in the composite acts as a starting material in the method. Further, carbon dioxide from an external source can be used. Further, the composite can be used as a secondary aggregate and therefore the carbon dioxide is captured.

Within this specification embodiments have been described in a way which enables a clear and concise specification to be written, but it is intended and will be appreciated that embodiments may be variously combined or separated without parting from the invention. For example, it will be appreciated that all preferred features described herein are applicable to all aspects of the invention described herein and vice versa.

Wthin this specification, the term "about" means plus or minus 20%, more preferably plus or minus 10%, even more preferably plus or minus 5%, most preferably plus or minus 2%. Within this specification, the term "substantially" means a deviation of plus or minus 20%, more preferably plus or minus 10%, even more preferably plus or minus 5%, most preferably plus or minus 2%. It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications are covered by the appended claims.

Claims

1. A process of producing a composite comprising:

a) providing a particulate material,

b) providing an organic waste material,

d) carbonating the mixture in the presence of carbon dioxide,

wherein the particulate material comprises calcium oxide, calcium hydroxide, calcium silicate or combinations of two or more thereof.

2. A process according to claim 1 , wherein the particulate material has an average particle size of about 1 pm to about 30 mm, preferably about 10 pm to about 5 mm, most preferably about 1 mm to about 5 mm, and/or

wherein the particulate material has an average particle size of about 1 pm to about 1 mm, preferably about 10 pm to about 500 pm and/or

wherein the particulate material further comprises aluminium oxide, silicon dioxide, iron oxide, an iron silicate, an aluminium silicate, magnesium oxide, magnesium hydroxide, a magnesium silicate, a sodium silicate, a potassium silicate, magnesium sulphate, calcium sulphate, potassium sulphate, sodium sulphate or a combination of two or more thereof and/or

wherein the particulate material comprises air pollution control residue, Portland cement, Portland clinker, rock fines, concrete fines, slag, fly ash, bottom ash, dusts, paper ash, oil shale ash, bleaching earth material, synthetic slag or a combination of two or more thereof, preferably wherein the particulate material comprises air pollution control residue from cement production, lime production, steel and metal production, incineration, or a combination of two or more thereof, more preferably wherein the particulate material comprises cement kiln dust or lime kiln dust, most preferably wherein the particulate material comprises cement kiln dust, and/or

wherein the particulate material comprises calcium oxide or calcium hydroxide, most preferably the particulate material comprises calcium oxide, and/or

wherein at least about 80 wt% on a dry weight basis of the particulate is used to form the composite, more preferably at least about 90 wt%, more preferably at least about 95 wt%, more preferably at least about 99 wt%, most preferably all of the particulate material, on a dry weight basis is used to form the composite.

3. A process according to any preceding claim, comprising washing the particulate material with water, preferably washing the particulate material with water prior to mixing step (c), and/or wherein the particulate material has a free water content of about 2 to about 50 wt%, preferably about 10 to about 40 wt %, more preferably about 15 to about 30 wt%.

4. A process according to any preceding claim wherein the organic waste material has a free water content of about 2 to about 60 wt%, preferably about 10 to about 40 wt %, more preferably about 15 to about 30 wt%, and/or

wherein the organic waste material has a calorific value of about 5 to about 40 kJ/g on a dry basis, preferably wherein the organic waste material has a calorific value of about 10 to about 30 kJ/g on a dry basis, and/or

wherein the organic waste material comprises biomass, soil, sludge, organic wet fraction, plastic, or a combination of two or more thereof, preferably wherein the organic waste material comprises sewage sludge, dredging sludge, organic sludge from soil cleaning, petroleum sludge, contaminated soil, natural soil or contaminated bleaching earth or combinations of two or more thereof, more preferably wherein the organic waste material comprises sewage sludge, and/or

wherein the organic waste material comprises organic polymers, refuse derived fuel (RDF), solid recovered fuel (SRF), plastic residue from waste streams or combinations of two or more thereof, preferably refuse derived fuel or solid recovered fuel, preferably refuse derived fuel, and/or

wherein the organic waste material has a carbon content of at least about 10 wt% on a dry weight basis, such as about 10 wt% to about 60 wt%, preferably about 20 wt % to about 60 wt%, preferably about 30 wt% to about 60 wt%, preferably 10 wt% to about 50 wt%, preferably about 20 wt % to about 50 wt%, preferably about 30 wt% to about 50 wt%, and/or

wherein the waste organic material has an organic matter content of at least 10% on a dry weight basis, such as about 10 wt% to about 60 wt%, preferably about 15 wt % to about 50 wt%, preferably about 20 wt% to about 40 wt%, and/or

wherein at least about 80 wt% on a dry weight basis of the organic waste material are used to form the composite, more preferably at least about 90 wt%, more preferably at least about 95 wt%, more preferably at least about 99 wt%, most preferably all of the organic waste material, on a dry weight basis is used to form the composite.

5. A process according to any preceding claim, wherein the dry weight ratio of the particulate material to the organic waste material is about 1 : 10 to about 10:1 , preferably wherein the dry weight ratio of the particulate material to the organic waste material is about 1 :5 to about 5:1 , preferably wherein the dry weight ratio of the particulate material to the organic waste material is about 1 :2 to about 2:1 , and/or

wherein in step (d), the concentration of carbon dioxide is about 5% to about 100% by volume, preferably wherein the concentration of carbon dioxide is about 30% to about 100% by volume, preferably wherein the concentration of carbon dioxide is about 70% to about 100% by volume, and/or

wherein the carbon dioxide in step (d) comprises carbon dioxide that is a by-product from industry, preferably from a cement kiln or lime kiln, preferably flue gas from a cement kiln or lime kiln and/or

wherein the composite is formed into an aggregate or a monolithic product, preferably by granulating, grinding, crushing, pelletization, pressing, compacting and extrusion, batch mixing or a combination of two or more thereof, and/or

wherein the mixture comprises at least 5% on a dry weight basis of organic waste material, preferably 5% to 60 % on a dry weight basis of organic waste material, preferably 10% to 50%, preferably 15% to 40%, such as more than 35% on a dry weight basis, and/or

wherein the mixture comprises 5% to 95 % on a dry weight basis of particulate material, preferably 5% to 60%, preferably 10% to 50%, preferably 15% to 40%, such as more than 35% on a dry weight basis, and/or

wherein waste water can be added during step (c), and/or

wherein the process is carried out at a temperature of less than about 80 °C, preferably less than about 70 °C, preferably less than about 60 °C, preferably less than about 50 °C, such as about 10°C to about 90 °C, preferably about 20 °C to about 80 °C.

6. A composite produced by the process of any of claims 1 to 5.

7. A composite comprising organic waste material and a calcium carbonate binder, preferably a calcium carbonate binder and a calcium silicate binder.

8. A composite according to claim 6 or claim 7, wherein the composite has an average particle size of about 1 pm to about 100 mm, preferably about 500 pm to about 60 mm, preferably about 1 mm to about 60 mm, preferably about 5 mm to about 60 mm and/or wherein the composite has a density of about 500 kg/m³ to about 3000 kg/m³, preferably about 1000 kg/m³ to about 3000 kg/m³, and/or

wherein the composite has a calorific value of about 5 to about 35 kJ/g on a dry basis, and/or

wherein the composite has a free water content of about 0 to about 30 wt%, preferably about 1 to about 20 wt %, more preferably about 5 to about 15 wt%.

9. Use of a composite as a fuel, wherein the composite is produced according to any of claims 1 to 5 or the composite is according to any of claims 6 to 8, preferably as a fuel in cement production or lime production.

10. Use of a composite as a secondary aggregate for building or for producing concrete, wherein the composite is produced according to any of claims 1 to 5 or the composite is according to any of claims 6 to 8.

11. A method of recycling cement kiln dust or lime kiln dust comprising using cement kiln dust or lime kiln dust as the particulate material in a process according to any of claims 1 to 5 to form a composite, and using the composite in a method of manufacturing cement or lime, wherein the composite provides both fuel to the method and starting materials for the production of cement or lime.

12. A method of capturing carbon dioxide, comprising using carbon dioxide in a process according to any of claims 1 to 5, preferably wherein the carbon dioxide is from a cement kiln or from a lime kiln.

13. A method of manufacturing lime comprising:

i. providing limestone,

ii. providing a fuel,

iii. adding the limestone and the fuel to a kiln, and

iv. heating the kiln to produce lime, carbon dioxide and lime kiln dust, wherein the carbon dioxide/and or the lime kiln dust are used in a process according to any of claims 1 to 5, preferably wherein the fuel comprises the composite produced by the process of any of claims 1 to 5, or the composite according to any of claims 6 to 8.

14. A method of manufacturing cement comprising:

i. providing limestone,

ii. providing a silicate,

iii. providing a fuel,

wherein the carbon dioxide/and or the cement kiln dust are used in a process according to any of claims 1 to 5, preferably wherein the fuel comprises the composite produced by the process of any of claims 1 to 5, or the composite according to any of claims 6 to 8.

15. A carbon neutral process of producing cement or lime, wherein carbon dioxide produced in the method of producing cement or lime is used in a process according to any of claims 1 to 5.