A Method of Producing an Expanded Material

Abstract

A method of producing an expanded clay material, comprising providing a clay material and mixing it with digestate to form a mixture, shaping the mixture into a plurality of material pieces, and firin

Description

FIELD The present teachings relate to a method of producing an expanded clay material, and a mixture composition of a material. BACKGROUND Expanded clay, sometimes referred as lightweight expanded clay aggregate, is a manufactured and artificial lightweight aggregate. After heating in a kiln, the clay is expanded to several times its original size. Expanded clay has been heated to a semiplastic condition and expanded to several times its original volume by the formation of a vitrified surface and internal gas. During the heating process, gases are produced which form bubbles within the clay to expand the clay. The result is a hard, honeycombed lightweight structure that provides good strength and insulating properties. Lightweight expanded clay aggregate can be manufactured using certain raw clays with specific properties, and these will expand when heated in a kiln. Other types of clays can be made to expand by the addition of additives, and additives of various sorts are mixed with non-bloating or poorly bloating clays to cause these nonexpanding or poorly expanding clays to expand. In the construction industry, expanded clay is often used in the production of lightweight concrete, blocks, and precast structural elements such as panels, partitions, bricks and lightweight tiles. The increase in the popularity of using environmentally friendly, low cost and lightweight construction materials in the building industry brings the need for searching more innovative, flexible and versatile materials for a variety of applications. The present teachings seek to provide an environmentally friendly expanded material. SUMMARY According to a first aspect there is provided a method of producing an expanded clay material, the method comprising the steps of: providing a clay material; forming a material mixture by mixing the clay material with digestate; shaping the mixture into a plurality of material pieces; and firing the material pieces. The material may be a building material. The term "building material" or "expanded material" as used herein is intended to mean a material for use in construction and / or non-construction applications. The material may contain natural materials, synthetic or non-natural materials, or a mixture thereof. The expanded clay material may be considered to be a lightweight expanded clay aggregate. The term "lightweight aggregate" as used herein is intended to take it usual meaning in the art in accordance with the standard BS EN 13055:2016 - Lightweight Aggregates. BS EN 13055 encompasses lightweight aggregates (LWA) of mineral origin having particle densities not exceeding 2000 kg / m3 (2,000 Mg / m3) or loose bulk densities not exceeding 1200 kg / m3 (1,200 Mg / m3) including natural LWA, LWA manufactured from natural materials, LWA manufactured from by-products of industrial processes or from recycled source materials, and LWA as by-products of industrial processes. Biosolids are solid organic matter recovered from a sewage treatment process. Biosolids are frequently used as fertilizer and spread over agricultural lands; however this practice has polluted soils with microplastics, nanoplastics, synthetics, heavy metals, pharmaceuticals and engineered nanoparticles. In an attempt to control the pollutants regulators are attempting to limit the pollution from the practice of spreading the biosolids. A form of biosolids is digestate. Digestate is a biosolid comprising solid-liquid organic matter produced as the result of mesophilic anaerobic digestion of biodegradable feedstock, for example sewage sludge, industrial sludge, municipal waste or a mixture thereof. Anaerobic digestion of the biosolid produces two main products: digestate and biogas. The digestate is a solid-liquid by-product. The digestate may be a sewage sludge digestate. The term "sewage sludge" as used herein is intended to mean the residual, semisolid (i.e. liquid-solid) material that is produced as a by-product during sewage treatment of industrial or municipal wastewater. Including waste materials such as sewage sludge digestate as a raw material in the manufacture of expanded materials advantageously combines the recycling of the waste materials with the sustainable handling of environmental pollution. Moreover, through the use of the digestate (i.e. the sewage sludge digestate) in the manufacture of ceramics there is considerable evidence that pollutants are considerably contained or captured. Accordingly, using digestate in the manufacture of expanded clay materials means that harmful pollutants in the digestate are immobilised and prevented from contaminating soils. In some instances, the harmful elements may be rendered inert due to the processing of the material. The use of digestate in the manufacture of expanded materials also removes biosolids from the human food chain. This invention uses the digestate in a thermal process by adding it to the clay alone or with other components to produce a lightweight aggregate. This process utilises the treated sewage sludge digestate as an additive to enable non-bloating or poorly bloating clays to cause these non-expanding or poorly expanding clays to expand. The lightweight aggregate to be used in construction will lead to improved building insulation and less raw material being used, leading to a net overall reduction in carbon dioxide emissions for the sustainable building process. The use of materials that are lighter in weight will also lead to reduced handling and transportation costs across the supply chain. This invention uses the digestate in a thermal process by adding it to the clay alone or with other components to produce a lightweight aggregate. The lightweight aggregate to be used in construction will lead to improved building insulation and a reduction in the overall quantity of raw material used, leading to a net overall reduction in carbon dioxide emissions for the sustainable building process. Lightweight expanded clay aggregates typically have particle densities of 0.4 to 1.0 kg / m3. Use of these expanded clay aggregates allow for lightweight concrete to be produced that have a low density. The digestate may be a solid-liquid digestate. The removal of the liquid content of the digestate and / or the mixture is expensive and energy intensive. In one embodiment, wet digestate is combined with the clay. The liquid present in the digestate may modify the plasticity of the mixture. The moisture content of the digestate facilitates the necessary plasticity of the mixture for enabling the mixture to be shaped before entering a kiln to be fired. In this way, the use of the digestate is selected so as to optimise the energy required to produce the expanded material. The mixing at the forming stage of wet digestate to create the optimum plasticity with the lowest moisture content to minimise energy usage during the firing of the mixture. The method may comprise the step of adjusting the water / liquid content of the digestate prior to mixing with the clay. This adjustment of the water / liquid content of the digestate may comprise the addition and / or removal of liquid / water. Removal of the liquid from the digestate may be achieved via evaporation or any other suitable means. The digestate may comprise a liquid content of up to about 50 wt.%, or about 60 wt.% or about 70 wt.%, or about 80 wt.%. Preferably the digestate may comprise a liquid content of up to about 75 wt.%. The digestate may comprise a solid content of at least about 5 wt.% or about 10 wt. % or about 20 wt.% or about 30 wt.%. Preferably, the digestate may comprise a solid content of at least about 25 wt. %. Mixing the clay material with digestate may comprise mixing about 5 to about 25 wt.% dry digestate with the clay material. Preferably about 5 to about 20 wt.%, or about 5 to about 15 wt.%, more preferably about 8 to about 12 wt.% dry digestate is mixed with the clay material. Alternatively, about 5 wt.%, or about 6 wt.%, or about 7 wt.%, or about 8 wt.%, or about 9 wt.%, or about 10 wt.%, or about 11 wt.%, or about 12 wt.%, or about 13 wt.%, or about 14 wt.%, or about 15 wt.% dry digestate is mixed with the clay material. Preferably, about 10 wt.% dry digestate is mixed with the clay material. The mixture may comprise water in an amount of about 10 to about 34 wt. %, preferably about 12 to about 32 wt. %, or about 15 to about 29 wt. %, more preferably about 17 to about 27 wt. %. Alternatively, the mixture may comprise about 15 wt.%, or about 16 wt.%, or about 17 wt.%, or about 18 wt.%, or about 19 wt.%, or about 20 wt.%, or about 21 wt.%, or about 22 wt.%, or about 23 wt.%, or about 24 wt.%, or about 25 wt.%, or about 26 wt.%, or about 27 wt.%, or about 28 wt.%, or about 29 wt.%. Providing a water content in these ranges has been found to provide the optimum level of plasticity of the mixture for shaping of the mixture, whilst reducing the energy required to remove the water from the mixture during the firing process. The digestate may comprise at least about 15 wt.% of carbon, for example at least about 20 wt.%. A naturally bloating clay may be mixed with the digestate and the clay material. As used herein the term "naturally bloating clay" is intended to mean clays that will expand when heated in a kiln without the presence of an additive. Examples of such naturally bloating clays include but are not limited to clays from the Jurassic period or glacial clays. The naturally bloating clay may be added to the digestate and clay material in an amount of about 5 wt.% to about 50 wt.%, or about 10 wt.% to about 40 wt.%, or about 20 wt.% to about 20 wt.%. Alternatively, the naturally bloating clay may be added to the digestate and clay material in an amount of about 0.5 wt.%, or about 5 wt.%, or about 10 wt.%, or about 15 wt.%, or about 20 wt.%, or about 25 wt.%, or about 30 wt.%, or about 35 wt.%, or about 40 wt.%, or about 45 wt.%, or about 50 wt.%. The advantage of adding a naturally bloating clay is that can aid the expansion of the clay material and digestate. The presence of a naturally bloating clay may also help to smooth any geological variation in the clay material. Without being bound by theory, it is also believed that including a naturally bloating clay may improve properties such as strength and plasticity of the clay material. This effect can vary between clay types. The method may comprise the step of grinding the clay material prior to mixing with the digestate. The method may comprise the step of grinding the clay material such that 95% of the ground clay material passes through a 1000 pm filter. The firing process leads to the clay expanding. The material pieces may be referred to as expandable material pieces, material pellets, or expandable material pellets. The step of firing the material pieces may comprise heating said material pieces in a kiln. The kiln may be an electrically powered kiln, or a gas fired rotary kiln. Both electrically powered and gas fired rotary kiln trials have shown that digestate and various clays in appropriate proportions can produce expanded clays. The method may comprise the step of cooling the fired material. Subsequent to firing and cooling of the material, the expanded clay material may then be graded into fractions for use in many applications. The fractions may be size fractions or density fractions or strength grades or combinations thereof. The method may comprise the step of heating the material pieces to a temperature of about 1100 °C to about 1250 °C, or about 1120 °C to about 1220 °C, or about 1140 °C to about 1200 °C, or about 1150 °C to about 1190 °C, or about 1160 °C to about 1180 °C. Alternatively, the method may comprise the step of heating the material pieces to a temperature of about 1100 °C, or about 1110 °C, or about 1120 °C, or about 1130 °C, or about 1140 °C, or about 1150 °C, or about 1160 °C, or about 1170 °C, or about 1180 °C, or about 1190 °C, or about 1200 °C. The method may comprise the step of heating the material pieces for at least about 10 minutes, optionally for at least about 15 minutes, optionally, for at least about 30 minutes, optionally for at least about 60 minutes. The method may comprise the step of shaping the mixture into material pieces by extruding the mixture into elongate strand or tube. The elongate strand or tube may comprise a diameter in the range of about 2mm to about 18mm, for example in the range of about 4mm to about 16 mm. The method may comprise the step of cutting the elongate strange or tube into a plurality of discrete material pieces. The method may comprise the step of coating the material pieces with a coating material. The addition of a various coatings to the pellets can produce different properties of the expanded clay pellets. The method may comprise the step of coating the material pieces with materials such as, but not limited to sand, calcium hydroxide, clay, calcium carbonate or dust from the manufacturing process or combinations thereof. The use of a sand coating material helps to prevent clumping of the pellets in the production process, during the transportation of the wet pellets, and in the thermal treatment of the pellets. The coating also helps to reduce the chance to the pellets clumping together in both the wet stage of the pellets and in the thermal processing. The term "clumping" as used herein is intended to take its normal meaning in the art, referring to the pellets sticking together, causing them to agglomerate. It will be understood that the lightweight expanded clay may be used for a range of different purposes, for example lightweight concrete, underfloor insulation, soil replacement, for water treatment or any other suitable purpose. According to a second aspect, there is provided a material mixture for forming an expanded clay material, the mixture comprising: a clay material; and digestate. The material may be an aggregate material. The digestate may comprise a liquid content of up to about 50 wt.%, or about 60 wt.% or about 70 wt.%, or about 80 wt.%. Preferably the digestate may comprise a liquid content of up to about 75 wt.%. The digestate may comprise a solid content of at least about 5 wt.% or about 10 wt. % or about 20 wt.% or about 30 wt.%. Preferably, the digestate may comprise a solid content of at least about 25 wt. %. Mixing the clay material with digestate may comprise mixing about 5 to about 25 wt.% dry digestate with the clay material. Preferably about 5 to about 20 wt.%, or about 5 to about 15 wt.%, more preferably about 8 to about 12 wt.% dry digestate is mixed with the clay material. Alternatively, about 5 wt.%, or about 6 wt.%, or about 7 wt.%, or about 8 wt.%, or about 9 wt.%, or about 10 wt.%, or about 11 wt.%, or about 12 wt.%, or about 13 wt.%, or about 14 wt.%, or about 15 wt.% dry digestate is mixed with the clay material. Preferably, about 10 wt.% dry digestate is mixed with the clay material. The mixture may comprise water in an amount of about 10 to about 34 wt. %, preferably about 12 to about 32 wt. %, or about 15 to about 29 wt. %, more preferably about 17 to about 27 wt. %. Alternatively, the mixture may comprise about 15 wt.%, or about 16 wt.%, or about 17 wt.%, or about 18 wt.%, or about 19 wt.%, or about 20 wt.%, or about 21 wt.%, or about 22 wt.%, or about 23 wt.%, or about 24 wt.%, or about 25 wt.%, or about 26 wt.%, or about 27 wt.%, or about 28 wt.%, or about 29 wt.%. The digestate may comprise at least about 15 wt.% of carbon, for example at least about 20 wt.%. A naturally bloating clay may be mixed with the digestate and the clay material. As used herein the term "naturally bloating clay" is intended to mean clays that will expand when heated in a kiln without the presence of an additive. Examples of such naturally bloating clays include but are not limited to clays from the Jurassic period or glacial clays. The naturally bloating clay may be added to the digestate and clay material in an amount of about 5 wt.% to about 50 wt.%, or about 10 wt.% to about 40 wt.%, or about 20 wt.% to about 20 wt.%. Alternatively, the naturally bloating clay may be added to the digestate and clay material in an amount of about 0.5 wt.%, or about 5 wt.%, or about 10 wt.%, or about 15 wt.%, or about 20 wt.%, or about 25 wt.%, or about 30 wt.%, or about 35 wt.%, or about 40 wt.%, or about 45 wt.%, or about 50 wt.%. The advantage of adding a naturally bloating clay is that can aid the expansion of the clay material and digestate. The presence of a naturally bloating clay may also help to smooth any geological variation in the clay material. Without being bound by theory, it is also believed that including a naturally bloating clay may improve properties such as strength and plasticity of the clay material. This effect can vary between clay types. The digestate may be a sewage sludge digestate. The term "sewage sludge" as used herein is intended to mean the residual, semisolid (i.e. liquid-solid) material that is produced as a by-product during sewage treatment of industrial or municipal wastewater. According to a third aspect, there is provided a method of forming a building article using expanded clay material produced via the first aspect. Examples of building articles that may be formed from the expanded clay material are concrete, concrete blocks, concrete slabs etc. EXAMPLES Example 1 - Rotary gas kiln trials 5 Clay samples with digestate (Samples A and B) were heated in a propane rotary kiln under the conditions shown in Table 1. A control sample (Sample C) with no digestate was also heated. The results are shown in Table 1. Table 1 Sample A Sample B Sample C Clay / digestate mix 92% non-bloating clay + 8% dry weight digestate 92% non-bloating clay + 8% dry weight digestate 100% nonbloating clay Coating 0.75% Lime 0.75% Lime 0.75% Sand Temperature (°C) 1130 1140 130 Residence time 22 min 23 min 22 min Feed rate 20 Kg / hr 21 Kg / hr 21 Kg / hr Bulk Density (kg / m3) 0.502 0.473 1.158 Particle density (kg / m3) 0.92 0.82 1.92 Strength (kg / F) 37.92 105.41 10 As shown in Table 1 above, the samples containing digestate, i.e., Samples A and B have particle densities of 0.92 and 0.82 respectively. These values fall within the range of 0.4 to 1.0 kg / m3 for lightweight aggregates. However, Sample C which contains no digestate has a particle dentistry of 1.92 kg / m3 which is too high to be considered as a lightweight aggregate. 15 The bulk density values for Samples A and B also fall within the range for lightweight aggregates, whereas the bulk density value for Sample C does not. Accordingly, the results of table 1 show that the addition of digestate to the clay mixture allows the clays to expand and form lightweight expanded clay materials. Example 2 - Diaestate addition trials Different amounts of dry digestate were added to clay mixtures to measure the 5 particle density of the resulting product. The non-bloating clay is not naturally prone to bloating or expanding. The naturally bloating clay was included to smooth any geological variation in the clay material and to facilitate the bloating of clays less prone to bloating or non-bloating clays. Naturally bloating clays can also aid the digestate in the formation of a lightweight expanded clay with a particle density 10 within the desired range. The mixtures were heated in an electric rotary kiln. The results of the trials are shown in Table 2. Table 2 Entry Clay / digestate mix Temperature Residence Particle (°C) time density (kg / m3) 1 100% non-bloating 1180 15 min soak 1.85 clay 2 80% non-bloating 1180 15 min soak 0.83 clay + 20% naturally bloating clay + 10% dry digestate 3 80% non-bloating 1180 15 min soak 0.95 clay + 20% naturally bloating clay + 6.7% dry digestate 4 80% non-bloating 1180 15 min soak 0.86 clay + 20% naturally bloating clay + 10% dry digestate 5 80% non-bloating clay + 20% naturally bloating clay + 10% dry digestate 1180 15 min soak 0.82 6 80% non-bloating clay + 20% naturally bloating clay + 10% dry digestate 1180 15 min soak 0.82 7 80% non-bloating clay + 20% naturally bloating clay + 10% dry digestate 1180 15 min soak 0.65 8 80% non-bloating clay + 20% dry digestate 1180 15 min soak 1.00 Table 2 shows that using a non-bloating clay alone (entry 1) provides a clay with a particle density outside of the acceptable range for lightweight aggregate clays (i.e. 0.4 to 1.0 kg / m3). Entry 3 shows that adding 6.7% digestate provides a lightweight 5 aggregate clay with a particle density inside the acceptable range but close to the upper limit, i.e., 0.95 kg / m3. Entry 8 shows that adding 20% dry digestate provides a lightweight aggregate clay with a particle density at the upper limit of the acceptable range i.e., 1.0 kg / m3. Entries 2 and 4-7 show that the addition of 10% dry digestate is the optimum amount for forming a lightweight aggregate clay from 10 the tested clay mixtures. Example 3 - Clay mix trials Applicants have found that for certain clays that do not bloat naturally, adding a combination of digestate and a naturally bloating clay can be advantageous. The particle density of clay mixtures with 10% dry digestate and a varying amount of 15 naturally bloating clay was tested. The mixtures were heated in an electric rotary kiln. The results are provided in table 3 below. Entry Clay / digestate mix Temperature Residence time Particle density (kg / m3) 1 60% non-bloating clay + 40% naturally bloating clay + 10% dry digestate 1180 15 min soak 0.72 2 70% non-bloating clay + 30% naturally bloating clay + 10% dry digestate 1180 15 min soak 0.73 3 75% non-bloating clay + 25% naturally bloating clay + 10% dry digestate 1180 15 min soak 0.75 4 80% non-bloating clay + 20% naturally bloating clay + 10% dry digestate 1180 15 min soak 0.81 5 90% non-bloating clay + 10% naturally bloating clay + 10% dry digestate 1180 15 min soak 0.92 The results of Table 3 show that when a combination of digestate and naturally bloating clay is added to a clay that does not naturally bloat, an expanded 5 lightweight aggregate can be produced with a particle density within the desired range. The results show that decreasing the amount of naturally bloating clay in the mixture increase the particle density. All samples tested were within the range for lightweight aggregates Although the teachings have been described above with reference to one or more 5 preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope as defined in the appended claims.

Claims

1. A method of producing an expanded clay material, the method comprising the steps of:providing a clay material;forming a mixture by mixing the clay material with digestate;shaping the mixture into a plurality of material pieces; andfiring the material pieces at a temperature of 1100 °C to 1250 °C to produce an expanded clay material,wherein the digestate is a biosolid,wherein the digestate comprises a liquid content of at least 10 wt.%, wherein the mixture comprises water in an amount of 10 to 34 wt. %,wherein the method further comprises the step of coating the material pieces with sand.

2. The method according to claim 1, wherein the digestate comprises a solid content of at least 20 wt.%.

3. The method according to claim 1 or claim 2, wherein the digestate comprises a liquid content of at least 15 wt.%.

4. The method according to any preceding claim, wherein 5 to 25 wt.% of dry digestate is mixed with the clay material5. The method according to any preceding claim, wherein the mixture comprises water in an amount of 12 to 32 wt. %.

6. The method according to any preceding claim, wherein the digestate comprises at least 15 wt.% of carbon.

7. The method according to any preceding claim, comprising grinding the clay material prior to mixing with the digestate.

8. The method according to any preceding claim, comprising mixing a naturally bloating clay with the digestate and the clay material.

9. The method according to any preceding claim, wherein firing the material pieces comprises heating said material pieces in a kiln.

10. The method according to claim 1, comprising heating the material pieces to a temperature of 1120 °C to 1220 °C.

11. The method according to any preceding claim, wherein shaping the mixture into material pieces comprises extruding the mixture into elongate strand or tube.5 12. The method according to claim 11, comprising cutting the elongate strandor tube into a plurality of discrete material pieces or pellets.

13. The method according to any preceding claim, wherein the digestate is a sewage sludge digestate.

14. The method according to any preceding claim, wherein the digestate is 10 produced from mesophilic anaerobic digestion of biodegradable feedstock.