ES2804064B2 - Procedure for obtaining an ultralight aggregate and aggregate thus obtained - Google Patents

Description

DESCRIPTION

Procedure for obtaining an ultralight aggregate and aggregate thus obtained

field of invention

The present invention falls within the general field of chemical engineering and development of new materials and in particular refers to a very low density porous aggregate manufactured by sintering from clayey sludge rich in iron and cork waste, as well as to its potential use in concrete structures and pieces, geotechnical engineering, floriculture and horticulture, among others.

State of the art

Generally, aggregates are obtained through the direct exploitation of light natural resources (for example, volcanic glass or vermiculite) or they are manufactured industrially through a thermal transformation process starting from raw materials that are also natural (mainly clay, schist and slate). or from industrial by-products. In this area, the production of light aggregates has been studied with different raw materials, including clay and/or the addition of residues such as fly ash, bottom ash, sewage sludge ash, municipal solid waste combustion ash, slag. blast furnace, recycled glass, mining waste, heavy metal sludge or contaminated soil, among others. However, in no case has the production of expanded ultralight aggregates been investigated with the residues detailed in the present invention, and the obtaining of a material of lower density than all those already existing on the market or reported in the scientific literature is also noteworthy.

Thermal expansion is the most widespread method for manufacturing lightweight, high-porosity aggregates on an industrial scale. The raw materials are first crushed to a suitable particle size. After this, the material is mixed with a suitable water content and pelletized in the form of small granules (normally 4-10 mm approximately). Once dry, the material undergoes a relatively rapid heat treatment at high temperatures (normally between 1000-1300°C), during which the particle softens and undergoes an expansion caused by a gas release inside. Upon cooling, the particles harden while retaining the porosity caused by gas bubbles.

In relation to these materials, for example, document ES2085831 describes a porous and hydrophilic substrate from sewage sludge.

It is necessary to develop new ultralight aggregates that start from different raw materials and obtain low-density characteristics that provide advantages as an ultralight material.

Brief description of the invention

The present invention shows a highly porous and very low density granular product (artificial light aggregate) made from two technological nutrients that are currently managed as waste or by-products, with the consequent expense for the production company and for the environment, without detriment of being able to use natural materials that adjust to the desired characteristics. The dominant residue in the mixture is a clayey sludge rich in iron and of an intense red color, whose origin may be the pigmentation industry or other chemical, mining or other industries, while cork dust from the industrial processing of said material. After heat treatment, an ultralight expanded aggregate is obtained with a high porosity, both closed and interconnected, whose density is significantly lower than those of the products on the market and/or reported in the scientific literature. Secondarily, this would translate into: lower bearing load of the structures that contain it, lower transport and commissioning costs, greater conductivity and water retention, greater thermal and acoustic insulation, lower carbon footprint and, ultimately, greater possibilities of application than those of products currently used for the same uses.

On the other hand, as it is manufactured from different industrial waste, it has the advantage of reusing waste products, therefore, assuming an improvement for the environment.

Therefore, a first aspect of the invention relates to a process for the manufacturing an expanded ultralight aggregate comprising the following stages:

a) drying of a clayey sludge comprising an iron oxide content of 15-30 % by weight,

b) grinding and sieving of the clayey sludge from stage a),

c) mixing the product of step b) with cork waste in powder form and mixing with water,

d) extrusion and pelletization of the material from step c),

e) drying of the pelletized granular material from step d)

f) cooking in a rotary tubular kiln of the granular material obtained in e) according to the following sequence: preheating in the first section of the tube at a temperature of about 400-800°C for about 1.5-10 minutes; sintering of the granular material in the central zone of the tube at about 1150-1250°C for 2-30 minutes; rapid cooling of the sintered granular material, first in the last section of the tube, and finally outside, until it reaches room temperature.

In the present invention, "aggregate" is understood as the granular material that is added as a dispersed phase to obtain mainly construction materials, such as concrete, mortar and pavements, generally consisting of crushed rocks. In the case of the ' "light aggregates" are usually highly porous materials of natural origin or artificially manufactured.This high porosity would be responsible for the low density, resistance to frost and high thermal and acoustic insulating power of the products in which they are constituents.

In the present invention, "ultralight aggregate" is understood as an aggregate that has an apparent density equal to or less than 200 kg/m3. Preferably between 30kg/m3 and 180 kg/m3.

In a particular embodiment, the weight percentage of the starting materials with respect to the total weight percentage is:

95-99% by weight of clayey sludge rich in iron oxide,

1-5% by weight of cork powder.

In a more particular embodiment, the clay sludge has kaolinite and quartz as major phases, while the minority phases would be hematite, goethite and illite, which translates into an iron oxide content of 15-30 % by weight, silicon oxide of 40-50 % by weight, aluminum oxide of 10-25% by weight and other oxides, such as titanium, potassium, magnesium, calcium or sodium between 0.1-5% by weight. The mass loss on ignition of the clay sludge of the present invention would comprise values of 5-15% by weight.

In another particular embodiment, the iron-rich clayey sludge has medium to high plasticity, with a plasticity index/liquid limit ratio greater than 0.3.

In another particular embodiment, the cork powder residues that form part of the ultralight expanded aggregate of the present invention comprise 55-70% by weight of carbon, 6-10% by weight of hydrogen, 25-35% by weight of oxygen, 0.1-1% by weight of nitrogen, 0.01-0.1% by weight of sulfur, and a loss on ignition of 98-100% by weight.

In a particular embodiment, the cork dust residues of the present invention comprise a lower heating value of 6300-6700 cal/g.

In a more particular embodiment, the drying of the sludge from stage a) is carried out at a temperature between 60-120°C, preferably at a temperature of 105°C.

In another particular embodiment, the grinding of the elements of stage b) is carried out until reaching a grain size of 0.1-2 mm, preferably 0.2 mm.

In another particular embodiment, the percentage of water added to the mixture of stage c) corresponds to that in which the paste obtained is plastic without becoming sticky, preferably corresponding between 30% and 60% by weight with respect to to the total weight of raw materials.

In another particular embodiment, the size of the pellet formed in step d) will comprise diameters between 1 mm and 25 mm, preferably 4-10 mm.

In another particular embodiment, the drying of the granular material in stage e) is would be carried out between 60-120°C, preferably at a temperature of 105°C.

Another aspect of the invention refers to an ultralight aggregate obtained by the process defined in any of the embodiments or aspects defined above.

Another aspect of the invention refers to the expanded ultralight aggregate, which comprises an expansion index of 50-70%, a loose apparent density of 0.15-0.25 g/cm3, a particle density of 0.30-0.40 g/cm3, an absorption of water after 24 hours soaking of 25-35% and an average resistance to crushing of the individual grain of 0.1-2 MPa.

In another aspect, the present invention relates to the use of the iron-rich clayey red sludge and the cork dust residues of the present invention for the manufacture of lightweight aggregates.

In another aspect, the present invention relates to the use of expanded ultralight aggregate in lightweight concrete, mortar, pavements or other construction elements.

In another aspect, the present invention relates to the use of ultralight expanded aggregate in geotechnical and civil engineering applications.

In another aspect, the present invention relates to the use of ultralight expanded aggregate in artificial wetlands and other applications in environmental engineering.

In another aspect, the present invention relates to the use of the ultralight expanded aggregate of the present invention in crops.

In another aspect, the present invention relates to the use of the expanded ultralight aggregate of the present invention in landscaping and green roofs.

In the present invention, "green roof" means any structure applied to a façade, mainly but not limited to roofs, which is covered with vegetation. The term green indicates its ecological value and is not limited solely to the color of the vegetation.

Description of the figures

Figure 1. Ultralight aggregate presented in this patent. From left to right: external appearance; core of a split specimen; detail of the internal porosity in the shell-core zone.

Figure 2. Ultralight aggregates of this patent floating in water, thus demonstrating its high lightness.

Figure 3. Detail of the porosity in the crust-core zone of the developed aggregate. Image obtained by scanning electron microscopy.

Detailed description of the invention

The product detailed in the present invention has already been developed on a laboratory scale, according to the following specific steps:

- Oven drying of the red mud at 105°C for 24 h. The cork powder did not require drying as it is already supplied dry.

- Dry disintegration of red mud by mechanical grinding to a particle size of less than 0.2 mm. The cork powder did not require grinding because it already has a suitable individual particle size.

- Preparation of a homogeneous mixture consisting of 97.5% red mud and 2.5% cork powder (percentages by weight).

- Addition of 40.5% water. Subsequent maceration for 24 hours in hermetic conditions to favor the complete distribution of water throughout the paste.

- Mechanical extrusion of the wet material, pelletizing it into granules of about 9-10 mm in diameter and drying them for 24 hours in the air and at least another 24 hours in an oven at 105°C until completely dry.

- Firing in a laboratory-scale rotary tube kiln at a rotational speed of 2.5 rpm. Preheat the pellets at 400-800°C for 1.5 min in the tube inlet area, to avoid bursting. After this, the pellets are introduced into the central area of the rotary kiln where the maximum temperature is reached. In this case, the temperatures tested with a high degree of satisfaction have been 1200-1225°C. After 4 minutes of permanence in the zone of maximum temperature, the pellets are redirected outside, where rapid cooling is favored.

The product obtained is an artificial light aggregate made from waste with the following main characteristics:

-Expansion rate: 59.5%.

- Loose bulk density 180 kg/m3

-Saturated particle density with dry surface 350 kg/m3

-Water absorption after 24 hours according to UNE-EN-1097-6: 30.6%

-Mechanical resistance to individual aggregate crushing: 0.4 MPa. (Yashima et al., 1987; Li et al., 2000):

The expansion index is measured according to the document; Fakhfakh E, Hajjaji W, Medhioub M, Rocha F, Lopez-Galindo A, Setti M, Kooli F, Zargouni F, Jamoussi F, 2007. Effects of sand addition on production of lightweight aggregates from Tunisian smectite-rich clayey rocks. App. Clay Sci. 35, 228-237. doi:10.1016/j.clay.2006.09.006.

Loose apparent density according to UNE-EN-1097-3, 1999. Tests to determine the mechanical and physical properties of aggregates. Part 3: Determination of bulk density and porosity. Spanish Association for Standardization and Certification AENOR Spanish standard.

Saturated particle density and water absorption after 24 hours according to UNE-EN-1097-6, 2000. Tests to determine the mechanical and physical properties of aggregates. Part 6: Determination of particle density and water absorption. Spanish Association for Standardization and Certification AENOR Spanish standard.

The mechanical resistance to individual aggregate crushing according to Yashima, S., Kanda, Y., Sano, S., 1987. Relationship between particle size and fracture energy or impact velocity required to fracture as estimated from single particle crushing. Powder Technol. 51, 277-282 and Li, Y., Wu, D., Zhang, J., Chang, L., Fang, Z., Shi, Y., 2000. Measurement and statistics of single pellet mechanical strength of differently shaped catalysts . Powder Technol. 113(1-2), 176-184. doi:10.1016/S0032-5910(00)00231-X.

Claims (15)

1. Procedure for manufacturing an expanded ultralight aggregate comprising the following stages: a) drying of a clayey sludge comprising an iron oxide content of 15-30 % by weight, b) grinding and sieving of the clayey sludge from stage a), c) mixing the product of step b) with cork waste in powder form and mixing with water, d) extrusion and pelletization of the material from step c), e) drying of the pelletized granular material from step d) f) firing in a rotary tubular kiln of the granular material obtained in e) according to the following sequence: preheating in the first section of the tube at a temperature of about 400-800°C for about 1.5-10 minutes; sintering of the granular material in the central zone of the tube at about 1150-1250°C for 2-30 minutes; rapid cooling of the sintered granular material, first in the last section of the tube, and finally outside, until it reaches room temperature. 2. Method according to claim 1, characterized in that the clayey sludge from stage a) represents 95-99% by weight with respect to the sum of the weight of the sludge and the weight of cork powder. 3. Process according to any of the preceding claims, characterized in that the clayey sludge comprises an iron oxide content of 15-30% by weight, silicon oxide of 40-50% by weight, aluminum oxide of 10-25% by weight. weight and other oxides, such as titanium, potassium, magnesium, calcium or sodium between 0.1-5% by weight, with a loss of mass on ignition of 5-15% by weight. 4. Process according to any of the preceding claims, characterized in that cork powder comprises 55-70% by weight of carbon, 6-10% by weight of hydrogen, 25-35% by weight of oxygen, 0.1-1% by weight of nitrogen, 0.01-0.1% by weight of sulfur, and a loss on calcination of 98-100% by weight. 5. Process according to any one of the preceding claims, characterized in that the drying of the sludge from stage a) is carried out at a temperature between 60-120°C. 6. Procedure according to any one of the preceding claims, characterized in that the grinding of the elements of stage b) is carried out until reaching a grain size of 0.1-2 mm. 7. Method according to any one of the preceding claims, characterized in that the size of the pellet formed in step d) will comprise diameters between 1mm and 25mm. 8. Process according to any one of the preceding claims, characterized in that the drying of the granular material in step e) would be carried out between 60-120°C. 9. Ultralight aggregate obtained by the process defined in any of claims 1 to 8. 10. Expanded ultralight aggregate, characterized in that it comprises an expansion index of 50-70%, a loose bulk density of 0.15-0.25 g/cm3, a particle density of 0.30-0.40 g/cm3, water absorption after 24 hours soaking of 25-35% and an average crushing strength of the individual grain of 0.1-2 MPa. 11. Use of the expanded ultralight aggregate according to any of claims 9-10 in lightweight concrete, mortars, pavements or other construction elements. 12. Use of the expanded ultralight aggregate according to any of claims 9-10 in geotechnical and civil engineering applications. 13. Use of the expanded ultralight aggregate according to any of claims 9-10 in artificial wetlands and other applications in environmental engineering. 14. Use of the expanded ultralight aggregate according to any of claims 9-10 in crops or gardening. 15. Use of the expanded ultralight aggregate according to any of claims 9-10 for the construction of green roofs.