Aqueous mixture, spongy marble obtained therefrom and relative preparation method

Abstract

An aqueous mixture comprises a solid material, which in turn comprises hydrolysed keratin and marble sand, and water. The weight ratio between hydrolysed keratin and marble sand is comprised between 1 :0.2 and 1 : 180. The weight ratio between hydrolysed keratin and water is comprised between 1 :0.03 and 1 :60.

Description

[0001] TITLE: "Aqueous mixture, spongy marble obtained therefrom and relative preparation method"

[0002] DESCRIPTION

[0003] Technical Field

[0004] The present invention relates to an aqueous mixture. More particularly, the present invention finds useful application for the production of spongy marble. In particular, the spongy marble obtained by the present invention is applicable in various fields. In particular, spongy marble can be used as an insulating panel or for multilayer panels, in the construction sector, as a packaging material or as a biocompatible scaffold.

[0005] Description of the prior art

[0006] In the construction sector, marble is widely used, for example to make flooring, wall coverings or pillars. The marble is extracted from quarries. The most common method for extraction is cutting it with diamond wire.

[0007] Document CN 107082613 A describes an insulating, microporous, permeable and self-cleaning material made of a blend comprising water and marble sand.

[0008] Problem of the prior art

[0009] The extraction of marble from quarries is a process that generates a considerable amount of waste material, called "quarry waste", which means a material that is particularly homogeneous by chemical composition (mainly CaCCh), but extremely heterogeneous in size. In particular, the waste comprises both rocks of considerable size and ultrafine and nanometric powders.

[0010] Particulate matter with a size of less than 60 pm, called marble slurry, is an environmental problem. In fact, this debris is easily transported by atmospheric agents into waterways. The marble slurry is deposited in the riverbeds and banks of rivers, blocking the airways of fish and invertebrates, and burying the flora and algae, which are at the base of the food chain of aquatic life forms.

[0011] The marble slurry can be separated by decanting the washing water of a small portion of the quarry waste generated. The product thus generated is still considered waste and destined for landfill.

[0012] SUMMARY OF THE INVENTION

[0013] In this context, the technical task underlying the present invention is to propose an aqueous mixture comprising waste materials.

[0014] In particular, it is an object of the present invention to provide an aqueous mixture for spongy marble which is more eco-sustainable.

[0015] The technical task mentioned and the objects stated are substantially achieved by an aqueous mixture comprising the technical features set out in one or more of the appended claims.

[0016] The present invention allows to provide an aqueous mixture for reconstructed marble that allows to recover the waste material coming from the production of marble, in particular marble slurry.

[0017] Advantageously, it is possible to obtain an aqueous mixture using valuable materials such as marble and at the same time reducing the number of wastes released into the environment.

[0018] DETAILED DESCRIPTION

[0019] An aqueous mixture, in accordance with the present invention, comprises a solid material and water. The solid material in turn comprises hydrolysed keratin and marble sand.

[0020] Keratin is an animal protein and is the main element of mammalian epidermis and fur, bird plumage and reptile armour. Keratin-rich materials appear as waste at the end of numerous industrial processes, in particular from the slaughtering and production of textile material of animal origin, for example wool.

[0021] Keratin acts as a foaming agent, favouring the stabilization of air bubbles in the aqueous mixture. In addition, keratin has an effect of stabilizing the finished product, i.e. spongy marble, described in the following description. In the context of the present invention, spongy marble means the porous material that constitutes the finished product. In fact, the hydrolysed keratin has the effect of producing a more homogeneous distribution of pores in the spongy / porous marble obtained.

[0022] Preferably, the marble sand has a variable granulometry. The granulometry is determined through a characteristic size, for example the diameter. Preferably, the marble sand has variable fractions of ultra-fine marble particles, with a characteristic size of less than 60 pm. Even more preferably, the marble sand in use for making the aqueous mixture has a characteristic size of less than 20 pm.

[0023] The weight ratio between hydrolysed keratin and marble sand is comprised between 1 :0.2 and 1 : 180.

[0024] The weight ratio between hydrolysed keratin and water is comprised between 1 :0.03 and 1 :60.

[0025] Preferably, the aqueous mixture comprises sodium bicarbonate. The weight ratio between hydrolysed keratin and sodium bicarbonate is comprised between 1 : 10 and 1 :0.3.

[0026] Advantageously sodium bicarbonate allows the generation of carbon dioxide CO2, both by acid-base reaction and by thermal decomposition in the presence of water for T above 50° C. The gas generated allows the formation of a stable foam.

[0027] Preferably, the aqueous mixture comprises sodium percarbonate. The weight ratio between hydrolysed keratin and sodium percarbonate is comprised between 1 : 10 and 1 :0.3.

[0028] Advantageously, sodium percarbonate has the function of an oxidizing agent, allowing the stabilization of the keratin polymer chain by oxidation of the disulfide bridges.

[0029] Preferably, the aqueous mixture comprises glycerol. The weight ratio between hydrolysed keratin and glycerol is comprised between 1 :30 and 1 : 1.

[0030] Advantageously, glycerol acts as a plasticizing agent, making the compound more elastic and able to absorb kinetic energy in the form of compression of the material.

[0031] Preferably, the aqueous mixture comprises hexamethylene diisocyanate. The weight ratio between hydrolysed keratin and hexamethylene diisocyanate is comprised between 1 : 10 and 1 :0.3.

[0032] Advantageously, the hexamethyl diisocyanate allows to increase the polymerisation of the keratin polymer chains making the material resistant to solubilization by water.

[0033] Preferably, the aqueous mixture comprises polydiglycidyl ether. The weight ratio between hydrolysed keratin and polydiglycidyl ether is comprised between 1 : 10 and 1 :0.3.

[0034] Advantageously, the polydiglycidyl ether allows to increase the polymerisation of the keratin polymer chains making the material resistant to solubilisation by water.

[0035] The aqueous mixture according to the present invention is used to obtain spongy marble.

[0036] According to a first embodiment, the spongy marble is obtained by pouring the aqueous mixture into moulds and firing at a temperature comprised between 60°C and 90°C, preferably at a temperature equal to 70°C, for a time interval comprised between 30 minutes and 4 hours, preferably equal to one hour.

[0037] Preferably, the moulds are rectangular. Still preferably, the moulds are preformed with the shape of the object to be protected. Preferably, the aqueous mixture is poured on a conveyor belt. Preferably, the poured aqueous mixture is fired until plates, slabs or spongy marble fragments are formed. Advantageously, in accordance with this first embodiment, the aqueous mixture, after pouring and before firing, can be coupled with knitted fibres and / or cardboard and / or aluminium. In this way, it is possible to obtain slabs or plates for applications in the construction field.

[0038] In accordance with a second embodiment, the spongy marble is obtained by pouring the aqueous mixture into moulds and pressing the poured aqueous mixture and drying at a temperature comprised between 15 and 45°C, preferably between 20°C and 25°C, for a time interval comprised between 4 and 72 hours.

[0039] Preferably, the poured aqueous mixture is pressed with a pressure comprised between 100 kg / cm2and 400 kg / cm2, preferably with a pressure greater than 300 kg / cm2. Preferably, the drying time interval is chosen as a function of the thickness of the pressed aqueous mixture.

[0040] Preferably, a first method for preparing spongy marble comprises a first step of preparing the aqueous mixture. The first method for preparing spongy marble comprises a second step of pouring the aqueous mixture into a mould. The first method includes a third step of firing the aqueous mixture at a temperature comprised between 60°C and 90°C, for a time interval comprised between 30 minutes and 4 hours, preferably equal to one hour.

[0041] Preferably, a second method for preparing spongy marble comprises a first step of preparing the aqueous mixture. The second method for preparing spongy marble includes a second step of pouring the aqueous mixture into a mould. The method for preparing spongy marble includes a third step of pressing the aqueous mixture into the mould. The method for preparing spongy marble includes a fourth step of exposing the pressed aqueous mixture to a temperature comprised between 15°C and 45°C, preferably between 20°C and 25°C, for a time interval comprised between 4 and 72 hours.

[0042] Preferably, the step of preparing the aqueous mixture comprises a first sub step of providing a solid material comprising hydrolysed keratin, marble sand, sodium bicarbonate and sodium percarbonate.

[0043] Preferably, according to a first embodiment, the step of preparing the aqueous mixture comprises a first substep of blending the hydrolysed keratin and the marble sand. Preferably, the first substep is performed until a homogeneous blend of hydrolysed keratin and marble sand is obtained.

[0044] Preferably, the step of preparing the aqueous mixture comprises a second substep of providing water.

[0045] Preferably, the step of preparing the aqueous mixture comprises a third subsequent substep of adding water to the blend of hydrolysed keratin and marble sand. Still preferably, the blend with water is heated to a temperature of 40°C. Still preferably, the blend with water is mechanically stirred until a homogeneous blend is obtained.

[0046] Preferably, the step of preparing the aqueous mixture comprises a fourth sub step of adding sodium bicarbonate to the blend with water. Still preferably, the blend with sodium bicarbonate is mechanically stirred.

[0047] Preferably, the step of preparing the aqueous mixture comprises a fifth sub step of adding sodium percarbonate to the solution with solid bicarbonate. Still preferably, the blend with sodium percarbonate is mechanically stirred.

[0048] Preferably, in accordance with a second embodiment, the step of preparing the aqueous mixture comprises a first step of providing a solid material comprising hydrolysed keratin and marble sand.

[0049] Preferably, the step of preparing the aqueous mixture comprises a second substep of blending the hydrolysed keratin and the marble sand. Still preferably, the substep of blending the hydrolysed keratin and the marble sand is performed until a homogeneous blend is obtained.

[0050] Preferably, the step of preparing the aqueous mixture comprises a third sub step of providing water. Preferably, the step of preparing the aqueous mixture comprises a fourth step of adding water to the blend of keratin and marble sand. Still preferably, the fourth substep is performed under blending.

[0051] Preferably, in accordance with a third and a fourth embodiment, the step of preparing the aqueous mixture comprises a first substep of providing a solid material comprising hydrolysed keratin, marble sand, sodium bicarbonate, sodium percarbonate, glycerol, polydiglycidyl ether or hexamethylene diisocyanate.

[0052] Preferably, the step of preparing the aqueous mixture comprises a second substep of blending the hydrolysed keratin with glycerol. Preferably, the second substep comprises a further substep of heating the hydrolysed keratin blended with the glycerol to a temperature of 40°C.

[0053] Preferably, the step of preparing the aqueous mixture comprises a third sub step of adding marble sand to the blend of hydrolysed keratin and glycerol.

[0054] Preferably, the step of preparing the aqueous mixture comprises a fourth sub step of providing water.

[0055] Preferably, the step of preparing the aqueous mixture comprises a fifth sub step of adding water to the blend with marble sand.

[0056] Preferably, the step of preparing the aqueous mixture comprises a sixth sub step of adding the sodium bicarbonate to the blend with water.

[0057] Preferably, the step of preparing the aqueous mixture comprises a seventh step of adding the sodium percarbonate to the blend with sodium bicarbonate.

[0058] Still preferably, the seventh substep of adding the sodium percarbonate comprises a further substep of heating the blend with water up to 45°C. Still preferably, the seventh substep comprises a subsequent substep of cooling the blend with sodium bicarbonate and percarbonate to 35 °C when the blend with sodium bicarbonate and percarbonate is homogeneous.

[0059] Preferably, the step of preparing the aqueous mixture comprises an eighth substep of adding polydiglycidyl ether or hexamethylene diisocyanate to the solution with sodium bicarbonate and percarbonate.

[0060] According to a first embodiment, the aqueous mixture comprises a solid material and water. The solid material in turn comprises hydrolysed keratin, marble sand, sodium bicarbonate and sodium percarbonate.

[0061] According to this first example, the weight ratio between hydrolysed keratin and marble sand is equal to 1 : 18.

[0062] The weight ratio between hydrolysed keratin and sodium bicarbonate is equal to 1 :0.4.

[0063] The weight ratio between hydrolysed keratin and sodium percarbonate is equal to 1 :0.4.

[0064] In addition, the weight ratio between hydrolysed keratin and water is equal to 1 :2.

[0065] According to this first example, the aqueous mixture thus obtained is used to obtain spongy marble.

[0066] According to a first embodiment, the spongy marble is obtained by pouring the aqueous mixture into moulds and firing at a temperature comprised between 60°C and 90°C, preferably at a temperature of 70°C, for a time interval comprised between 30 minutes and 4 hours.

[0067] Preferably, the moulds are rectangular.

[0068] Preferably, the aqueous mixture is poured on a conveyor belt.

[0069] Preferably, the poured aqueous mixture is fired until spongy marble plates or slabs are formed.

[0070] In accordance with one embodiment, the aqueous mixture, after pouring and before firing, can be coupled with knitted fibres and / or cardboard and / or aluminium. In this way, it is possible to obtain slabs or plates for applications in the construction field.

[0071] A method for preparing spongy marble, in accordance with the first example, will now be described.

[0072] The method includes a first step of preparing the aqueous mixture.

[0073] This step includes further substeps. In particular, the method includes a first substep of providing a solid material comprising hydrolysed keratin, marble sand, sodium bicarbonate and sodium percarbonate.

[0074] The step of preparing the aqueous mixture comprises a second substep of blending the hydrolysed keratin and the marble sand. This second substep is performed until a homogeneous blend of hydrolysed keratin and marble sand is obtained.

[0075] The step of preparing the aqueous mixture comprises a third substep of providing water.

[0076] The step of preparing the aqueous mixture comprises a fourth sub step of adding water to the blend of hydrolysed keratin and marble sand. The water is added under mechanical stirring. In addition, the blend with water is heated to 40°C.

[0077] The step of preparing the aqueous mixture comprises a fifth sub step of adding sodium bicarbonate to the blend with water. Sodium bicarbonate is added to the blend with water under stirring.

[0078] The step of preparing the aqueous mixture comprises a sixth sub step of adding sodium percarbonate to the solution with solid bicarbonate. Sodium percarbonate is added to the blend with water under stirring.

[0079] The method for preparing spongy marble includes further steps.

[0080] In the first embodiment, the method comprises a second step of pouring the aqueous mixture into a mould. In accordance with an alternative embodiment, the method comprises a second step of pouring the aqueous mixture on a conveyor belt.

[0081] The method includes a subsequent step of firing the pressed aqueous mixture at a temperature comprised between 60°C and 90°C. Preferably, the aqueous mixture is fired at 70°C until the slabs or plates are formed.

[0082] In accordance with a second embodiment, the aqueous mixture comprises a solid material and water. The solid material in turn comprises hydrolysed keratin and marble sand.

[0083] According to this second example, the weight ratio between hydrolysed keratin and marble sand is equal to 1 : 11.25.

[0084] The weight ratio between hydrolysed keratin and water is equal to 1 :0.25.

[0085] In addition, the weight ratio between hydrolysed keratin and water is equal to 1 :0.25.

[0086] According to this second example, the aqueous mixture thus obtained is used to obtain spongy marble. According to a second embodiment, the spongy marble is obtained by pouring the aqueous mixture into moulds, pressing the poured aqueous mixture and drying at a temperature comprised between 15 and 45°C for a time interval comprised between 4 and 72 hours.

[0087] In accordance with this second embodiment, the aqueous mixture is pressed with a pressure equal to 400 kg / cm2. In accordance with this second embodiment, the aqueous mixture is left to dry at a temperature comprised between 20°C and 25°C. In accordance with this second embodiment, the aqueous mixture is left to dry for a time interval depending on the thickness of the pressed aqueous mixture.

[0088] A method for preparing spongy marble in accordance with the second example will now be described.

[0089] The method includes a first step of preparing the aqueous mixture.

[0090] The first step of preparing the aqueous mixture comprises a first substep of providing a solid material comprising hydrolysed keratin and marble sand.

[0091] The first step of preparing the aqueous mixture comprises a second substep of blending the hydrolysed keratin and the marble sand.

[0092] The first step of preparing the aqueous mixture comprises a third substep of providing water.

[0093] The step of preparing the aqueous mixture comprises a fourth step of adding water to the blend with keratin and marble sand. Preferably, during the fourth substep, the water is added by continuing to blend the blend with keratin and marble sand.

[0094] The method for preparing spongy marble includes further steps.

[0095] In the second embodiment, the method comprises a second step of pouring the aqueous mixture into a mould.

[0096] In accordance with the second embodiment, the method comprises a third step of pressing the poured aqueous mixture. During the third step, the aqueous mixture is pressed with a pressure of 400 kg / cm2.

[0097] The method includes a fourth drying step at a temperature comprised between 15 and 45°C, preferably between 20°C and 25°C, for a time interval comprised between 4 and 72 hours. Note that the drying time interval is chosen according to the thickness of the pressed aqueous mixture.

[0098] In accordance with a third embodiment, the aqueous mixture comprises a solid material and water. The solid material in turn comprises hydrolysed keratin, marble sand, sodium bicarbonate and percarbonate, glycerol and hexamethylene diisocyanate.

[0099] The weight ratio between hydrolysed keratin and marble sand is equal to 1 :5.

[0100] The weight ratio between hydrolysed keratin and sodium bicarbonate is equal to 1 :0.2.

[0101] The weight ratio between hydrolysed keratin and sodium percarbonate is equal to 1 :0.2.

[0102] The weight ratio between hydrolysed keratin and glycerol is equal to 1 :1.

[0103] The weight ratio between hydrolysed keratin and hexamethylene diisocyanate is equal to 0.2.

[0104] In addition, the weight ratio between hydrolysed keratin and water is equal to 1 : 1.

[0105] According to this third example, the aqueous mixture thus obtained is used to obtain spongy marble. The spongy marble is obtained by pouring the aqueous mixture in moulds and firing at a temperature comprised between 60°C and 90°C for a time interval comprised between 30 minutes and 4 hours.

[0106] In accordance with the third example, the poured aqueous mixture is fired at a temperature of 70°C.

[0107] In the preferred embodiment, the poured aqueous mixture is fired in flat furnaces. In the preferred embodiment, the poured aqueous mixture is fired for a time interval equal to one hour.

[0108] A method for preparing spongy marble in accordance with the third example will now be described.

[0109] The method includes a first step of preparing the aqueous mixture.

[0110] In accordance with the third example, the step of preparing the aqueous mixture comprises a first substep of providing a solid material comprising hydrolysed keratin, marble sand, glycerol and hexamethylene diisocyanate.

[0111] The step of preparing the aqueous mixture comprises a second substep of blending the hydrolysed keratin with glycerol. In the preferred embodiment, the second step is carried out at a temperature of 40°C.

[0112] The step of preparing the aqueous mixture comprises a third sub step of adding marble sand to the blend of hydrolysed keratin and glycerol.

[0113] The step of preparing the aqueous mixture comprises a fourth substep of providing water.

[0114] The step of preparing the aqueous mixture comprises a fifth sub step of adding water to the blend of hydrolysed keratin, glycerol and marble sand.

[0115] The step of preparing the aqueous mixture comprises a sixth sub step of adding the sodium bicarbonate to the blend with water.

[0116] The step of preparing the aqueous mixture comprises a seventh step of adding the sodium percarbonate to the blend with sodium bicarbonate.

[0117] In the preferred embodiment, the compound is heated up to a temperature of 45°C.

[0118] In the preferred embodiment, the seventh step comprises a substep of cooling the blend with sodium percarbonate to a temperature of 35°C when the blend with sodium percarbonate is homogeneous.

[0119] The step of preparing the aqueous mixture comprises an eighth substep of adding hexamethylene diisocyanate to the blend with sodium percarbonate.

[0120] The method for preparing spongy marble includes further steps.

[0121] In the third embodiment, the method comprises a second step of pouring the aqueous mixture into a mould. In an alternative embodiment, the aqueous mixture is poured on conveyor belts.

[0122] The method for preparing spongy marble comprises a third step of firing the poured aqueous mixture at a temperature comprised between 60°C and 90°C for a time interval comprised between 30 minutes and 4 hours. In the preferred embodiment, the poured aqueous mixture is fired at 70°C for one hour. In the preferred embodiment, the third firing step is carried out in flat furnaces. In the preferred embodiment, the poured aqueous mixture is fired for a time interval equal to one hour.

[0123] In accordance with a fourth embodiment, the aqueous mixture comprises a solid material and water. The solid material in turn comprises hydrolysed keratin, marble sand, sodium bicarbonate, sodium percarbonate, glycerol and polyglycidyl ether.

[0124] The weight ratio between hydrolysed keratin and marble sand is equal to 1 :5.

[0125] The weight ratio between hydrolysed keratin and sodium bicarbonate is equal to 1 :0.2.

[0126] The ratio between hydrolysed keratin and sodium percarbonate is equal to 1 :0.2.

[0127] The weight ratio between hydrolysed keratin and glycerol is equal to 1 :1.

[0128] The weight ratio between hydrolysed keratin to polyglycidyl ether is equal to 0.2.

[0129] In addition, the weight ratio between hydrolysed keratin and water is equal to 1 : 1.

[0130] According to this fourth example, the aqueous mixture thus obtained is used to obtain spongy marble. The spongy marble is obtained by pouring the aqueous mixture in moulds and firing at a temperature comprised between 60°C and 90°C for a time interval comprised between 30 minutes and 4 hours.

[0131] In accordance with the fourth example, the poured aqueous mixture is fired at a temperature of 70°C. In the preferred embodiment, the poured aqueous mixture is fired in flat furnaces. In the preferred embodiment, the poured aqueous mixture is fired for a time interval equal to one hour.

[0132] A method for preparing spongy marble in accordance with the fourth example will now be described.

[0133] The method includes a first step of preparing the aqueous mixture.

[0134] In accordance with the fourth example, the step of preparing the aqueous mixture comprises a first substep of providing a solid material comprising hydrolysed keratin, marble sand, sodium bicarbonate, sodium percarbonate, glycerol and polyglycidyl ether.

[0135] The step of preparing the aqueous mixture comprises a second substep of blending the hydrolysed keratin with glycerol. In the preferred embodiment, the second step is carried out at a temperature of 40°C.

[0136] The step of preparing the aqueous mixture comprises a third sub step of adding marble sand to the blend of hydrolysed keratin and glycerol.

[0137] The step of preparing the aqueous mixture comprises a fourth substep of providing water.

[0138] The step of preparing the aqueous mixture comprises a fifth sub step of adding water to the blend of hydrolysed keratin, glycerol and marble sand.

[0139] The step of preparing the aqueous mixture comprises a sixth sub step of adding the sodium bicarbonate to the blend with water. The step of preparing the aqueous mixture comprises a seventh step of adding the sodium percarbonate to the blend with sodium bicarbonate. In the preferred embodiment, the compound is heated up to a temperature of 45°C.

[0140] In the preferred embodiment, the seventh step comprises a substep of cooling the blend with sodium percarbonate to a temperature of 35°C when the blend with sodium percarbonate is homogeneous.

[0141] The step of preparing the aqueous mixture comprises an eighth substep of adding polyglycidyl ether to the blend with sodium percarbonate.

[0142] The method for preparing spongy marble includes further steps. In the third embodiment, the method comprises a second step of pouring the aqueous mixture into a mould. In an alternative embodiment, the aqueous mixture is poured on conveyor belts.

[0143] The method for preparing spongy marble comprises a third step of firing the poured aqueous mixture at a temperature comprised between 60°C and 90°C for a time interval comprised between 30 minutes and 4 hours. In the preferred embodiment, the poured aqueous mixture is fired at 70°C for one hour. In the preferred embodiment, the third firing step is carried out in flat furnaces. In the preferred embodiment, the poured aqueous mixture is fired for a time interval equal to one hour.

Claims

CLAIMS1. Aqueous mixture comprising: a) a solid material, in turn comprising:• hydrolysed keratin,• marble sand, b) water, wherein- the weight ratio between hydrolysed keratin and marble sand is comprised between 1 :0.2 and 1 : 180,- the weight ratio between hydrolysed keratin and water is comprised between 1 :0.03 and 1 :60.

2. Aqueous mixture, according to claim 1 comprising:- sodium bicarbonate, the weight ratio between hydrolysed keratin and sodium bicarbonate being comprised between 1 : 10 and 1 :0.3.- sodium percarbonate, the weight ratio between hydrolysed keratin and sodium percarbonate being comprised between 1 : 10 and 1 :0.3.

3. Aqueous mixture, according to claim 1 or 2 comprising:- glycerol, the weight ratio between hydrolysed keratin and glycerol being comprised between 1 :30 and 1 : 1,- hexamethylene diisocyanate, the weight ratio between hydrolysed keratin and hexamethylene diisocyanate being comprised between 1 : 10 and 1 :0.3.

4. Aqueous mixture, according to claim 1 or 2, comprising- glycerol, the weight ratio between hydrolysed keratin and glycerol being comprised between 1 :30 and 1 : 1,- polydiglycidyl ether, the weight ratio between the hydrolysed keratin and the polydiglycidyl ether being comprised between 1 : 10 and 1 :0.3.

5. Spongy marble obtained by pouring into moulds the aqueous mixture, according to claim 1, pressing the poured aqueous mixture and drying at a temperature comprised between 15 and 45°C for a time interval comprised between 4 and 72 hours.

6. Spongy marble obtained by pouring into moulds the aqueous mixture according to claims 2 or 3 or 4, and firing at a temperature comprised between 60°C and 90°C for a time interval comprised between 30 minutes and 4 hours.

7. Method for preparing spongy marble, comprising the steps of:- preparing the aqueous mixture according to claim 2 or 3 or 4,- pouring the aqueous mixture into a mould,- firing the pressed aqueous mixture at a temperature comprised between 60°C and 90°C for a time interval comprised between 30 minutes and 4 hours.

8. Method for preparing spongy marble, according to claim 7, wherein the step of preparing the aqueous mixture comprises the following substeps:- blending the hydrolysed keratin and the marble sand,- adding water to the blend of hydrolysed keratin and marble sand obtained from the previous step,- adding sodium bicarbonate to the blend with water obtained from the previous step,- adding sodium percarbonate to the blend with solid bicarbonate obtained from the previous step.

9. Method for preparing spongy marble, according to claim 7, wherein the step of preparing the aqueous mixture comprises the following substeps:- mixing the hydrolysed keratin with glycerol,- adding marble sand to the blend of hydrolysed keratin and glycerol obtained from the previous step,- adding water to the blend with marble sand obtained from the previous step,- adding sodium bicarbonate to the blend with water obtained from the previous step,- adding sodium percarbonate to the blend with water obtained from the previous step,- adding polydiglycidyl ether or hexamethylene diisocyanate to the blend with sodium percarbonate obtained from the previous step.

10. Method for preparing spongy marble, comprising the steps of:- preparing the aqueous mixture according to claim 1,- pouring the aqueous mixture into a mould,- pressing the aqueous mixture in the mould,- exposing the pressed aqueous mixture to a temperature comprised between 15°C and 45°C for a time interval comprised between 4 and 72 hours.

11. Method for preparing spongy marble, according to claim 10, wherein the step of preparing the aqueous mixture comprises the following substeps:- mixing the hydrolysed keratin and the marble sand,- adding water to the blend with hydrolysed keratin and marble sand obtained from the previous step.