ES2394979A1 - Method for the production of alkali cements from industrial and urban waste glass - Google Patents

Abstract

The invention relates to a method for the production of alkali cements, characterised in that it comprises mixing an alkaline solution having a pH greater than 13 and selected from an NaOH solution or an NaOH and Na2C03 solution, with at least one alumino-silicate material that can be alkali-activated and at least one waste glass selected from urban waste glass, industrial waste glass or any of the mixtures of same, in which the percentage by weight of waste glass in the alkali cement is between 20% and 80%. The invention also relates to the resulting cement and to the use thereof in the production of concrete and/or prefabricates.

Description

Procedure for the manufacture of alkaline cements from urban and industrial vitreous waste.

Field of the Invention

The present invention relates to the field of construction, and more specifically, to the manufacturing sector of cement, concrete and prefabricated. 5

Background of the invention

In the last year (2010), the world production of Portland cement exceeded 2,000 million tons, which represents more than 300 kg per inhabitant of the planet; being the second product, after water, more consumed by man; In addition to being the essential component of the concrete used in construction. The development of these Portland cement concretes has been one of the fundamental pillars in the progress achieved in Western countries during the 10th century.

The manufacture of Portland cement implies an important consumption of thermal and electrical energy, since very high temperatures are required (~ 1500 ° C) so that all the chemical reactions that lead to the formation of the Portland cement clinker are completed; as well as the grinding processes of raw materials and final cement components. Due to the improvements introduced in the factories, the specific energy required has been significantly reduced 15 in recent years. Between 1973 and 1988 the specific energy needed to produce clinker decreased from 4750 MJ / t clinker to 3750 MJ / t. Since then, the specific energy has remained more or less constant. Additionally, the cement industry is also a highly polluting industry, as it exploits natural resources (quarries) and emits a large amount of polluting gases into the atmosphere (CO2, SO2, NOx). CO2 emissions are mainly associated with the decarbonation of limestones, which is the majority constituent of cement crude 20 (exceeding 60% of the total emission). The remaining pollutant gases are emitted during the combustion of fossil fuels used in cement plants. Worldwide, between 5-7% of CO2 emissions are due to the cement sector. If the growth of world cement production remains at current rates, it is estimated that in the first quarter of the 21st century CO2 emissions from the cement industry could reach 3,500 million tons, a value similar to the total amount that It is currently broadcast in Europe (including transport, 25 energy industry, etc.).

Therefore, the study and development of alternative construction materials to traditional Portland cements, in whose manufacture no polluting gases are emitted and an appreciable energy saving is obtained, constitutes a research line of great scientific and technological interest worldwide. Among these alternative materials are those that come from the alkaline activation of industrial by-products such as blast furnace slags and / or the 30 fly ash. These cements are obtained by mixing said residues and alkaline solutions. These new cements are characterized by low hydration heats, high mechanical performance, and good durability against different aggressive chemicals (acidic, sulphate, etc.), and do not require the high energy consumption that are inherent to the process of elaboration. Portland cement manufacturing.

However, the alkaline activators that favor the formation of materials with greater mechanical resistance and better durable behavior are hydrated alkali silicates (Me2O • mSiO2 • nH2O; Me = Na or K), called "waterglass", which are synthetic materials, obtained through economically expensive and highly polluting processes. One way to improve the economic and ecological balance of the alkaline cements would be to find substitutes (total or partial) of these alkaline activators, and in this line the present invention is framed, in which it is demonstrated that urban and industrial vitreous waste can be substitutes valid of these alkaline solutions of "waterglass" 40 as activators in the preparation of alkaline cements. This is because vitreous wastes, due to their chemical composition based primarily on SiO2 (65-75%) and Na2O (12-15%), are potential alkaline activators of the waterglass family.

Urban vitreous waste collected in Spanish and European cities is not 100% recycled. Between 40-60% of the waste is not reused, either because these are covered with other ceramic and / or metallic materials; well 45 because they are very fine granulometric fractions; due to inadequate chemical composition, or due to problems associated with the color of the glass, etc. These rejections occur because these anomalies can alter the conventional glass manufacturing processes. However, these wastes would be suitable for incorporation into the final composition of the new alkaline cements; enabling its reuse.

The collection and management of glass waste is an environmental policy with an increasing implementation in the 50 developed countries. In the United States, 12.5 million tons of vitreous waste are generated annually, of which only 20% is recycled. In 2008, around 1 million tons of glass were collected in Spain, of which 60% were recycled. However, although it tends to collect and classify urban and industrial vitreous waste according to its type, the truth is that these residues contain glass with various chemical compositions (flat glass, with and without color, with ceramic or metal coatings, etc.) , which makes reuse difficult, when mixed, in the 55

conventional technological processes. In the European Union between 2-6% of vitreous waste is in this form of mixing, and in Russia it amounts to 6-10%.

All existing technologies for recycling mixed glass waste include a crushing operation. The fragments obtained (fraction 1-8 mm) can be used as additional components (aggregates) in the preparation of mortars and concrete. However, this practice is limited since in the opinion of some authors (CD Johnston 5 (2000), Journal of Testing and Evaluation, 2 (85), pp. 344-350) alkali-silica reaction processes can occur that can decrease the dimensional stability of concrete, affecting its resistance and durability very negatively. However, some authors (M. Jin, et al. (2000), ACI Structural Journal, 97 (2), pp. 208-213) openly disagree with this interpretation; and even other researchers have shown that the replacement of 20% of the cement with vitreous residues in the preparation of concrete induces improvements in the mechanical properties and durability of concrete 10 (chloride permeability and ice-thaw cycles). In a very recent work C. Shi (C. Shi (2009), Journal of Materials in Civil Engineering, 21 (10), pp. 529-534) demonstrates that the expansion in concretes with vitreous aggregates is due to the formation of a Hydrated calcium-sodium silicate (NCSH) expansive around the glass particles, from the dissolution and precipitation in basic medium of the sodium-calcium glasses themselves, and not to the interaction between the glass particles and the cement alkalis. fifteen

 The mixed glass waste, in powder form (hardly reusable in glass manufacturing processes) can be reused in the construction sector, through the following applications:

1. Pozzolanic additions in the preparation of Portland cements (C. Shi, et al. (2005), Cement and Concrete Research, 35 (5), pp. 987-993);

2. Preparation of vitroceramic composites together with other industrial waste or by-products, such as fly ash and slag, ceramic waste, etc. In this case the sintering takes place between 850-1100ºC (F. Andreola, et al. (2008), Ceramics International 34, pp. 1289-1295);

3. Preparation of polymer matrix composites (pavements for vehicles and pedestrians) (W.H. Chester (1992), Utilization of Waste Materials in Civil Engineering Construction, pp. 296-307);

4. Main component for the production of foamed glass in the production of thermo-insulating materials. This process requires temperatures between 630 and 850 ° C (A.V. Gorokhovski, et al. (2005), Waste Management 25, pp. 733-736);

5. Raw material to synthesize solid sodium silicates and / or purified silica.

In the patent literature, US 6344081 describes a concrete comprising cement and recycled glass particles. On the other hand, US2005 / 0055069 describes a process of producing concrete from recycled glass, wherein said concrete comprises 25-79% by weight of glass; 8-35% by weight of cement and up to 22% by weight of an inhibitor of the alkali-silicon dioxide reaction.

These applications have some important problems in practice. On the one hand, the industries involved (cement and concrete preparation) must change their conventional process by introducing new raw materials, and in some cases these changes are not valued positively (applications 1 and 3). Applications 2 and 4 imply high energy consumption, which increases production costs. In addition, the manufacturing process of foamed glass entails an important emission of CO2 into the atmosphere.

On the other hand, there is currently a great interest in the construction sector to develop new cements and construction materials, whose manufacture implies lower energy consumption and lower emissions of pollutant gases into the atmosphere (mainly CO2), than the manufacture of Portland cement conventional. One of the 40 lines of research is to obtain new cements that lack clinker. These cements are obtained by mixing amorphous silico-aluminates such as blast furnace slags, fly ash, metacaolin or volcanic rocks, or binary and ternary mixtures of these, with strongly alkaline solutions (NaOH, Na2CO3 or hydrated alkali silicates) (F. Doors (1995), Building Materials, vol. 45 (239), pp. 53-66). Numerous works have confirmed the good mechanical properties (A. Fernández-Jiménez, F. Puertas, JG Palomo (1999), Cement and Concrete Research, vol. 29, pp. 593-604) and 45 durable (F. Puertas, et al . (2009), Cement and Concrete Composites, vol. 31, pp. 277-284) that present these cements, mortars and alkaline concretes, as well as their high thermal resistance (C. Shi (2003), Advances in Cement Research, vol 15 (2), pp. 77-81), being in many cases superior to that of conventional Portland cement.

KR 2010037889 describes a cement manufacturing process comprising the use of recycled glass particles and fly ash, as well as an activating agent that can consist of NaOH, where the mixture is subsequently subjected to a curing process. Also, GB 2362643 describes a "green" cement formed from a mixture of pulp ashes of paper waste (60-70% weight) and glass waste (30-40% weight).

Studies on these alkaline cements and concretes (A. Fernández-Jiménez, F. Puertas, J.G. Palomo

(1999), Cement and Concrete Research, vol. 29, pp. 593-604) have shown that the most determining factor, from the resistant point of view, is the nature of the alkaline activator; being the solutions of hydrated sodium silicate ("waterglass") those that give the cementitious material the greatest mechanical resistance. Taking into account that urban vitreous wastes are amorphous materials with a chemical composition based on SiO2 (65-75%), CaO (6-12%), Na2O (12-15%), Al2O3 (0.5-5%) and Fe2O3 (0.1-3%), one might think that these materials could be potential alkaline activators (of the "waterglass" family) of glass furnace slag and / or fly ash or other aluminosilicates.

Description of the invention

A first object of the invention is a process for the manufacture of alkaline cements from urban and industrial vitreous wastes, among other components. These components may consist of glass furnace slag, 10 fly ash or other silico-aluminous materials capable of being alkaline activated. In addition, alkaline solutions of the NaOH and / or NaOH + Na2CO3 type are also to be used.

Likewise, it is a further object of the invention to use said alkaline cements to prepare the corresponding concretes.

Thus, the invention relates to a new process for the manufacture of alkaline cements based on the use of new raw materials (vitreous residues). Likewise, said procedure has the advantage, compared to other processes of the state of the art, of being carried out from an activation system not only chemical, but also mechanical-chemical. Said mechanical-chemical activation system is especially advantageous, since it is a much more effective system from the point of view of the resistant development of cement and concrete pastes.

Therefore, as a consequence of the use of vitreous residues as the raw material of the process, it is possible to replace 20 solutions of hydrated sodium silicate (called "waterglass") commonly used in the art; solutions that give cements and alkaline concrete the greatest resistance, but are obtained through costly and ecologically costly processes. In this way, the present invention is capable of providing obvious economic and ecological advantages associated with the final product, but also related to the recovery or recovery of a waste (urban or industrial vitreous waste) not reusable in conventional glass manufacturing processes. 25

Brief description of the figures

FIG. 1a shows the results of compressive strength as a function of the vitreous residue / glass slag ratio of blast furnace subjected to chemical activation with a NaOH / Na2CO3 solution for 7 days;

  FIG. 1b shows the results of flexural strength as a function of the vitreous residue / glass slag ratio of blast furnace subjected to chemical activation with a NaOH / Na2CO3 solution for 7 days; 30

FIG. 1c shows the results of compressive strength as a function of the vitreous residue / glass slag ratio of blast furnace subjected to chemical activation with a NaOH / Na2CO3 solution for 90 days;

 FIG. 1d shows the results of flexural strength as a function of the vitreous residue / glass slag ratio of blast furnace subjected to chemical activation with a NaOH / Na2CO3 solution for 90 days;

FIG. 2a shows the results of compressive strength as a function of the vitreous residue / glass slag ratio of a blast furnace subjected to mechanochemical activation with a NaOH / Na2CO3 solution for 7 days;

  FIG. 2b shows the results of flexural strength as a function of the vitreous residue / glass slag ratio of blast furnace subjected to mechanochemical activation with a NaOH / Na2CO3 solution for 7 days;

FIG. 2c shows the results of compressive strength as a function of the vitreous residue / glass slag ratio of blast furnace subjected to mechanochemical activation with a NaOH / Na2CO3 solution for 90 days; 40

 FIG. 2d shows the results of flexural strength as a function of the vitreous residue / glass slag ratio of blast furnace subjected to mechanochemical activation with a NaOH / Na2CO3 solution for 90 days.

Detailed description of the invention

It is therefore a first object of the invention a process for the manufacture of alkaline cements by reusing urban and / or industrial vitreous waste in its composition. Four. Five

Cement preparation conditions are described below:

It is called M: Material or mixture of materials capable of being activated alkaline (preferably selected from blast furnace slags, fly ash, metacaolin, or any other natural or artificial material of silico-aluminous composition), D: Alkaline solution (preferably selected from NaOH or NaOH and Na2CO3); V:

Vitreous residue and A: Aggregates.

Although the composition of these vitreous residues may vary according to the origin and type of vitreous residue selected, in general, the composition of the vitreous residues may comprise SiO2 (65-75%), CaO (6-12%), Na2O ( 12-15%), Al2O3 (0.5-5%) and Fe2O3 (0.1-3%).

In a particular embodiment, said composition may comprise SiO2 (72.04%), Al2O3 (1.62%), Fe2O3 (0.27%), MgO 5 (3.39%), CaO (8.19%), Na2O (12.11%), K2O (2.32% ), TiO2 (0.04%), P2O5 (0.02%), Cr (179 ppm), Ba (67 ppm) and Pb (6 ppm).

Thus, the process object of the invention is characterized in that it comprises mixing at least one silico-aluminous material capable of being alkaline activated and at least one alkaline activator consisting of at least one vitreous residue selected from urban vitreous waste and vitreous waste industrial, or any of its mixtures, where the percentage by weight of vitreous residue in alkaline cement is between 20% and 80%, and more preferably between 50% and 80%. Additionally, at least one alkaline solution of pH greater than 13 is added to the mixture, wherein said solution is preferably selected from a solution of NaOH and a solution of NaOH and Na2CO3.

In a particular embodiment of the invention, the mixing and homogenization of the silico-aluminous material capable of being alkalinely activated (M) and the vitreous residue (V) can be carried out mechanically (for example, by means of a turbo), 15 for at least 2 hours.

Also, in a particular embodiment of the invention, once the mixture has been homogenized, it can be chemically activated. This chemical activation can be carried out by direct addition to the mixture of the silico-aluminous material capable of being alkalinely activated (M) and the vitreous residue (V) of at least one alkaline solution (D), preferably selected from a solution of NaOH (preferably a strongly basic solution with a pH greater than 13, and more preferably pH = 13.19) and a NaOH / Na2CO3 solution (in the same way, with a pH preferably greater than 13, and more preferably pH = 13.29) in an equivalent concentration preferably comprised between 3% and 20% Na2O over 100% of the silico-aluminous material capable of being alkaline activated (M). In each case, it will be necessary to determine the optimum liquid / solid ratio to achieve adequate runoff or consistency. 25

After the chemical activation of the mixture, it can proceed to cure it. The temperature at which said curing stage is carried out depends on the nature of the material capable of being alkaline activated, and may vary between room temperature (20 ° C-25 ° C) or a higher temperature, preferably between 65 ° C and 85 ° C. The first case is preferably carried out when the silico-aluminous material comprises calcium-rich silico-aluminates (such as high furnace glass slags) and the second, when it comprises calcium-poor silico-aluminates 30 (such as, Fly ash). The mortar preparation of these cements can be carried out, preferably, under equal conditions to those described in the European cement standard EN 197-1.

In another particular embodiment of the invention, prior to the preparation of the mixture of the silico-aluminous material capable of being alkaline activated (M) and the vitreous residue (V), the vitreous residue (V) can be subjected to a process grinding, preferably in ball mill. Said milling can be carried out in such a way that for each gram 35 of vitreous residue (V) between 5 ml and 20 ml of at least one alkaline solution (D) is added, preferably selected from a NaOH solution (preferably of higher pH at 13, and more preferably of pH = 13.19) and a solution of NaOH / Na2CO3 (preferably of pH greater than 13, and more preferably of pH = 13.29) in an equivalent concentration preferably comprised between 3% and 20% of Na2O over the 100% of the silico-aluminous material capable of being alkaline activated (M). The grinding times can preferably vary between 2 and 6 h, until reaching an average final particle size preferably less than 90 μm. In this case, therefore, the activation of the mixture consists of a mechanochemical activation (as opposed to the chemical activation of the previous embodiment).

In this particular embodiment of mechanochemical activation, once a vitreous residue suspension (V) -alkaline solution (D) is obtained, the material capable of being alkalinely activated (M) is added (preferably, a mixture of silico- aluminates) to form mixtures with the corresponding proportions. As in the case of chemical activation, the ratio silico-aluminous material / vitreous residue in said mixtures is between 80/20 and 20/80, and more preferably between 70/30 and 30/70.

 Subsequently, the process of kneading, compacting and curing the specimens can be carried out under equal conditions to those described in the chemical activation, that is, under equal conditions to those described for the European cement standard EN 197-1. fifty

In a further particular embodiment of the invention, the process may also comprise the addition of siliceous or calcareous aggregates (A), preferably in an A / M ratio between 1/1 and 4/1. Thus, the use of the cements described for the preparation of the corresponding concretes is a further object of the invention. The manufacture of these concretes can be carried out following the recommendations of the regulations and prescriptions of each country; in the case of Spain, following EHE-08. 55

In all the processes described above, special care must be taken with the handling of vitreous residues, as well as with the strongly alkaline solutions.

  Examples

A series of examples are given below by way of illustration and with no limitation of the present invention:

Example 1 5

 In this first example, an alkaline cement was prepared according to the process object of the invention, as previously described.

 For this purpose, different vitreous residue / glass furnace slag (BFS) mixtures (from 30/70 to 100/0) were prepared, with the following chemical composition (in percentage by weight):

 Table 1. Chemical composition of the blast furnace glass slag (BFS (% by weight) 10

 SiO2

 35.34 Na2O 0.01

 Al2O3

 13.65 SO3- 0.06

 Fe2O3

 0.39 S2-1.91

 MgO

 4.11 L.O.I. 2.72

 CaO

 41.00 I.R. 0.64

Table 2. Vitreous chemical residue composition (% by weight)

 SiO2

 72.04 K2O 2.32

 Al2O3

 1.62 TiO2 0.04

 Fe2O3

 0.27 P2O5 0.02

 MgO

 3.39 Cr (ppm)

 CaO

 8.19 Ba (ppm)

 Na2O

 12.11 Pb (ppm)

 Subsequently, an alkaline NaOH / Na2CO3 solution of pH = 13.29 was added directly to said mixtures, at a concentration equivalent to 5% Na2O over 100% slag in the mixture. The liquid / solid ratio remained constant at 0.4. The preparation of the pastes was done manually and the paste obtained was poured into 1x1x6 cm molds. The samples were cured in a humidity chamber at 22 ± 2 ° C and a relative humidity of 99%. The mechanical behavior of the mixtures at 7 and 90 days of curing is shown in Fig. 1. As a reference medium, a mixture of glass furnace slag (without ceramic residue) activated with the same activating solution at the same concentration was used, and with equal conditions of preparation and curing of pasta. twenty

 In Fig. 1, the 0/100 mixture is the paste without vitreous residue. As can be seen, comparable resistance is obtained when the slag content is 60 or 80%.

Example 2

 In this second example, prior to preparing the vitreous residue / glass furnace slag mixtures, this residue was subjected to a milling process in a ball mill. This grinding was carried out in such a way that for every 25 grams of waste there were 100 g of balls in the ground, with differentiated granulometry. In addition, for each gram of vitreous residue, 10 ml of the alkaline solution (NaOH / Na2CO3 pH = 13.29, 5% Na2O per slag mass) was added, with the same concentration as described above. In all cases the particle size of the vitreous residue was always less than 45 µm. The grinding times were: 10 min, 2h, 4h and 6h.

 With the resulting alkaline glass-solution suspensions, at each grinding time, the high furnace slag 30 was added to form the mixtures with the corresponding proportions (30/70 to 100/0). The liquid / solid ratio is

kept constant at 0.4. Subsequently, the process of kneading, compacting and curing the specimens was carried out under equal conditions to those described in the chemical activation.

 In all cases, the mechanical resistance to bending and compression was determined at 7 and 90 days of curing.

 The results show that 50/50 mixtures develop greater compressive strengths than those without vitreous residues (0/100 mixtures). 5

Claims (15)

1. Process for the manufacture of alkaline cements characterized in that it comprises mixing an alkaline solution of pH greater than 13, where said solution is selected from a solution of NaOH and a solution of NaOH and Na2CO3, with at least one susceptible silico-aluminous material if it is activated alkaline and at least one vitreous residue selected from urban vitreous and industrial vitreous wastes, or any of their mixtures, where the 5 percent by weight of vitreous residue in the alkaline cement is between 20% and 80%. 2. Method according to claim 1, wherein the alkaline solution of pH greater than 13 is added directly on a homogeneous mixture of the silico-aluminous material and the vitreous residue, resulting in a chemical activation of the mixture. 3. Method according to claim 1 or 2, wherein after chemical activation, a curing step of the mixture is carried out. 4. Method according to claim 3, wherein said curing is carried out at room temperature between 20 ° C and 25 ° C, or at a temperature between 65 ° C and 85 ° C. 5. Method according to claim 1, wherein prior to the mixing of the silico-aluminous material capable of being alkaline activated and of the vitreous residue, a step of grinding the vitreous residue is carried out with the alkaline solution of pH greater than 13, followed by the subsequent mixing of the vitreous residue and the alkaline solution of pH greater than 13 with the silico-aluminous material capable of being activated alkaline, resulting in a mechanochemical activation of the mixture. 6. Method according to claim 5, wherein for each gram of vitreous residue, between 5 ml and 20 ml of the alkaline solution with a pH greater than 13 is added. 7. Method according to claim 5 or 6, wherein the grinding is carried out for a time between 2 h and 6 h, until an average final particle size of the vitreous residue of less than 90 μm is reached. 8. Method according to any one of the preceding claims, wherein the alkaline solution is used in an equivalent concentration between 3% and 20% Na2O over 100% of the silico-aluminous material capable of being alkaline activated. 25 9. Method according to any one of the preceding claims, wherein the vitreous residue comprises, in weight percentage, between 65% and 75% SiO2, between 6% and 12% CaO, between 12% and 15% of Na2O, between 0.5% and 5% of Al2O3 and between 0.1% and 3% of Fe2O3. 10. Method, according to any one of the preceding claims, wherein the silico-aluminous material is selected from a group consisting of glass furnace slags, fly ash and metacaolin, as well as any 30 of their combinations. 11. Method according to any one of the preceding claims, characterized in that it comprises a subsequent step of adding aggregates. 12. Method, according to claim 11, wherein said aggregates are selected from siliceous aggregates and calcareous aggregates and wherein said aggregates are added in an aggregate / silico-aluminous material ratio capable of being alkalinely activated between 1/1 and 4 /one. 13. Alkaline cement obtainable from a process according to any one of the preceding claims. 14. Use of an alkaline cement according to claim 13 for the manufacture of concrete and / or prefabricated.