EP2571805A1

EP2571805A1 - A process for the production of hydrogen, the sequestration of carbon dioxide and the production of building materials starting from slags and/or industrial ashes

Info

Publication number: EP2571805A1
Application number: EP11729711A
Authority: EP
Inventors: Paolo Plescia; Enrico Barbarese; Maurizio Pinna
Original assignee: Asiu SpA
Current assignee: Asiu SpA
Priority date: 2010-05-20
Filing date: 2011-05-20
Publication date: 2013-03-27
Also published as: WO2011145080A1; IT1400139B1; ITPI20100058A1

Abstract

The present invention refers to a process for the production of hydrogen and the contemporaneous sequestration of carbon dioxide starting from slags and/or industrial ashes. In particular, said process allows to produce a gas substantially composed of hydrogen and, at the same time, allows to prepare materials having the characteristics of being avid carbon dioxide sequestrators and of being advantageously usable as inert materials for preparing hydraulic mixtures with lime and/or cement.

Description

TITLE

A PROCESS FOR THE PRODUCTION OF HYDROGEN, THE SEQUESTRATION OF CARBON DIOXIDE AND THE PRODUCTION OF BUILDING MATERIALS STARTING FROM SLAGS AND/OR

INDUSTRIAL ASHES

Technical Field

The present invention refers to a process for the production of hydrogen and the sequestration of carbon dioxide starting from slags and/or industrial ashes (such as steelworks waste, incineration waste, energy production processes waste), in which said slags and/or ashes result, preferably, from blast furnace iron metallurgy, from oxygen converters and/or electric furnaces, from incineration (for example, from grill furnaces, fluidized bed furnaces, plasma furnaces) , from pyrolysis and gasification plants, from energy production facilities, from fossil fuels and from biomasses, as also from all the dusts (from now on called "light dusts") and the light ashes (from now on called "fly ashes") that are generated in said processes. In particular, the process of the invention allows to produce a gas substantially composed of hydrogen and, at the same time, allows to prepare materials having the characteristics of being avid sequestrants of carbon dioxide (C0₂) and of being advantageously usable as inert materials for preparing hydraulic mixtures with lime and/or cement.

Therefore, the present invention refers to a process for the production of hydrogen (and therefore, of energy) and the sequestration of carbon dioxide (of any origin and/or provenance) , and also for the eventual preparation and/or recovery of inert materials of any type to be employed in the production of hydraulic mortars and/or concretes, using iron metallurgy slags and/or ashes, thermodestruction slags and/or ashes and any other type of industrial solid slag having a composition similar to the mentioned ones.

Background Art

The slags resulting from the metallurgy industry are one of the most popular waste matters in the industrialized countries and they have been used/recycled in the building industry for over a hundred years. Just as a way of example, for each cast iron and steel ton produced, 200 to 400 kg of slag are produced. These materials have substantially a silicon calcium or ferro calcium composition, but there exist also materials that are richer in magnesium or in other elements and/or in highly toxic metallic waste. Due to the rigid European and national regulations, the slags are now subjected to rigid controls and to specific rules about their recovery/recycle, mainly created for the preparation of inert materials for road foundations, cement mixtures and other products with cement. The first experiences of recovery/recycle of iron metallurgy and thermodestruction slags date back to the end of the XIX century in Germany, where the use of vitrified slags started (the so-called heavy slags) as raw material for the production of inerts for the construction of roads. The patents and the experiences known in the field of recovery of said slags are really many. Most of them include the use of quite sophisticated techniques to produce their grinding, subdivision/classification into granulometric classes, separation of the residue metal fractions and their use as inert materials or in mixtures ad hoc. Among the many documents of the background art, we can mention, just to illustrate but absolutely not to limit, Italian patent application IT2000MI02294 and European patent EP 1328488 Bl, in which the use of slag mixtures, inert materials (also resulting from demolition and building rubble) , and a number of so-called "catalizators" , based on alkaline or alkaline earth solutions is described, to obtain hydraulic mixtures suitable for producing building materials. The only aim of said documents is that of taking advantage of the pozzolanxc characteristic of the slags to dispose of the greatest possible amount of them as base material, mixing them with demolition and building inerts, together or in substitution of the quarry inerts. A further Italian patent application, IT2008CO0003, extends such a concept of recovery of the slags to their use as road inerts, but does not introduce any material change with respect to the technology already described in the preceding documents. In any case, the authors of the present invention know that neither the patents mentioned above nor the other documents of the background art related to the use of slags for the production of inert or mixed materials or of catalyzed hydraulic mortars, are contemporaneously aimed also at the production of energy, preferably, at the production of hydrogen, and at the contemporaneous sequestration of carbon dioxide, of any origin and/or provenance .

On the contrary, it would be really very useful to be able to have at our disposal a simple process that allows to use the metallurgy and thermodestruction slags to produce hydrogen, that is energy, in an advantageous and economical manner, and, at the same time, to sequestrate carbon dioxide and also to further obtain inert and non-toxic materials to be able, for example, to dispose of and/or use them in the production of hydraulic mortars and/or concretes.

The authors of the present invention realize that none of the existing patents describe the use of metallurgy slags to reduce water at a low temperature. For example, patent US2009220410 Al uses the slags only at high temperature, that is at temperatures higher than 1500 °C, at which the water molecule turns into hydrogen and oxygen and the presence of reducing agents like carbon and/or metallic iron does not permit the recombination of such gases. Such a process, however, cannot be used on thermodestruction slags, since they are formed at too low temperatures (on average comprised between 900 °C and 1200 °C) to be able to resolve the water molecule.

As for the capture of the carbon dioxide, there exists in the background art a number of documents, but all of them describe only this single specific use and only with reference to a restricted class of materials. The capture reactions of the C0₂ claimed are always the same, that is the following:

CaO + C0₂ -> CaC0₃

(Ca, g)Si0₃ + C0₂ ~> (Ca, Mg)C0₃ + Si0₂

In the first case, the classic carbonation reaction of calcium oxide to give calcium carbonate is obtained, by the passage in aqueous phase of the hydrate lime Ca(OH)₂. In the second case, the carbonation reaction of calcium and magnesium silicates to give calcium and magnesium carbonates is obtained, with the release of silicon dioxide. These two reactions are at the base of any carbonation process/patent of mineral phases containing oxides or silicates. Just as a way of example, patent US2007261947 Al describes the capture of carbon dioxide by means of the carbonation of calcium and magnesium silicates. The use of steelworks slags (as well as of heavy thermodestruction slags, carbon and liquid fuels flying ashes) , mixed with calcium oxide or with mixtures of oxides comprising calcium, is also known in the field to obtain the capture of carbon dioxide.

The carbon dioxide sequestered can derive from any source, for example from air and/or from any industrial process that produces it, including the extraction of gas and/or of liquids from the subsurface. Nevertheless, in these cases the documents of the background art just limit themselves to describe possible uses of the slags just as sequestering materials, without mentioning or much less making reference to other possible uses of them that are concurrent and/or combined. In particular, the authors of the present invention know that no patent or preceding document describes, or much less suggests, the possibility of achieving contemporaneously or, eventually, in combination between them, the production of hydrogen and the sequestration of carbon dioxide eventually followed by the production/recovery of useful inert and non-toxic materials starting from slags and/or industrial ashes resulting, for example, from thermodestruction, from thermal plants or from iron metallurgy.

Technical Problem

The need remains in the field to have at our disposal a simple and economical process that allows to produce in an advantageous manner energy, preferably hydrogen, and to sequestrate carbon dioxide and also, eventually, to obtain and/or recover useful inert, non-toxic and ecologically compatible materials, starting from discard and/or waste material containing amounts also significant of toxic residues.-

The aim of the present invention is to answer in an adequate manner to the above-mentioned technical need. Brief Description of the Invention

The applicant has now unexpectedly found that, by appropriately treating in an appropriate acidic environment and then in an appropriate basic environment and at non-high temperatures slags and/or industrial ashes, it is possible to give an adequate answer to the problem generated by the above-mentioned technical need. It is therefore the aim of the present invention to provide a process for the production of hydrogen and the sequestration of carbon dioxide by means of at least one treatment in an acidic environment of slags and/or industrial ashes and/or a mixture thereof, followed by at least one treatment in a basic environment of the activated products resulting from the preceding acid treatment mentioned above, as per the attached independent claim.

It is also another aim of the present invention to provide a process as described above further comprising the preparation and/or the recovery of environmentally compatible inert materials for their use in the building industry, as per the attached corresponding claim.

It is another aim of the present invention to provide a plant for carrying out the process of the present invention, as per the attached independent claim.

Other aims of the present invention are described in the other attached dependent claims.

Brief Description of the Figures

Attached Figure 1 illustrates, by means of a scheme, a particularly preferred embodiment (and omni comprehensive) of the process according to the present invention, as well as of the possible type of plant preferably usable for carrying out said process. In particular, of the said process the following are schematically indicated: the container (s) (for example, silos) for preliminary piling up and storing the waste (block (A) of the scheme) ; the leaching reactor/tank of waste with acid pH (block (B) of the scheme) , where hydrogen gas is substantially generated; the leaching reactor/tank of waste at basic pH and in the presence of C0₂ (block (C) of the scheme) , where hydrogen gas is generated and C0₂ is sequestered; the carbonation site/tank (block (D) of the scheme) where the carbonation of the exhausted scoriaceous waste is completed after the basic treatment; the mixing site/tank of all the different inert materials with cement and/or lime and/or additives and/or a mixture thereof (block (E) of the scheme) , where the inert, neutral and non-toxic mixtures advantageously usable in the building industry are prepared.

Detailed Description of the Invention

The present invention refers to a process for the production of hydrogen - and the sequestration, contemporaneous and/or combined, of carbon dioxide starting from slags and/or industrial ashes, comprising: at least one phase b) , preceding the following phase c) , of acidic leaching/maturation, in which said slags and/or industrial ashes and/or a mixture thereof are subjected, in a sealed reaction environment, to a treatment in an acid solution having a pH < 3,5, during which a gas substantially composed of hydrogen is produced and from the slags and/or ashes the hazardous metals are extracted under the form of soluble salts of nitrogen and/or sulphur, and/or chlorine and/or phosphorus and/or fluorine and/or acetic acid; and

at least one phase c) , following the above phase b) , of alkaline leaching/maturation, in which the slags and/or industrial ashes and/or preferably, a mixture thereof previously treated in above phase b) are subjected, in an appropriate sealed reaction environment and in the presence of C0₂, to a treatment in an alkaline solution having a pH > 8, during which a gas substantially composed of hydrogen is produced and the CO₂ present/added in the environment is sequestered.

Said slags and/or industrial ashes comprise, preferably: steelworks slags, both from blast furnaces and electric furnaces, and/.or slags from oxygen converters, and/or light dusts and/or ashes from iron metallurgy and/or other slags and/or solid waste from iron, aluminum and non-ferrous metals iron metallurgy and/or bottom ashes and/or filter ashes from thermal plants, from incineration of special and/or urban waste and/or from thermal and/or pyrolysis plants and/or from gasification and/or from energy production facilities and/or fossil fuels and/or from biomasses.

In a preferred embodiment of the invention, said slags/industrial ashes are preferably, but anyway not exclusively, selected from the group comprising:

metallurgical slags, both from electric furnace and from blast furnace;

- light dusts and/or fly ashes from metallurgy, both from electric furnace and from blast furnace;

light dusts from the abatement of the smokes from depulverization plants;

heavy and/or light slags from incineration of urban, hospital, special waste;

heavy and/or light slags from carbon and/or liquid fuels (or both) thermal or electric power plants, comprised ashes from biomasses ;

heavy and/or light slags from pyrolysis, gasification, plasma plants.

In a preferred embodiment of the invention, in said phase b) , the acid solution has preferably a pH ≤ 3, more preferably ≤ 2,5, even more preferably ≤ 2, even more preferably ≤ 1,5. Further, in said phase b) , the acid solution contains an effective amount of at least one acid, preferably selected from: nitric acid and/or sulphuric acid and/or acetic acid and/or hydrochloric acid and/or phosphoric acid and/or hydrofluoric acid and/or aqua regia or a mixture thereof. Further, in said phase b) , the reaction environment comprises at least one closed container/tank equipped with at least feeding means of said slags and/or ashes and/or, preferably, of a mixture thereof, agitation and control means, feeding means of the acid solution, extraction means of the generated gas, extraction means of the treated/exhausted material, extraction means of the resulting acid solution at the end of the treatment. Further, in said phase c) of said preferred embodiment, the C0₂ is added to the reaction environment by bubbling it, under the form of gas (for example, as such or as industrial gaseous waste that contains it) , in said alkaline solution or by bubbling air into said solution.

Moreover, in said phase c) , the alkaline solution has preferably a pH ≥ 9, more preferably ≥ 9,5, even more preferably ≥ 10,5, even more preferably ≥ 11,5.

Moreover, in said phase c) , the alkaline solution contains an effective amount of a least one alkali metal or alkaline earth metal oxide or hydroxide, preferably selected from the group comprising: NaO, K₂0, CaO, MgO, NaOH, KOH, Mg (OH) ₂, Ca (OH) ₂■

Moreover, in said phase c) , the reaction environment comprises at least one closed container/tank equipped with at least feeding means of said slags and/or ashes and/or, preferably, a mixture thereof, agitation and control means, CO₂ and/or air feeding means, feeding means of the alkaline solution, extraction means of the generated gas, extraction means of the treated/exhausted material, extraction means of the resulting alkaline solution at the end of the treatment.

In a particularly preferred embodiment, the process of the invention further comprising:

at least one phase d) , following the phase c) above, in which the exhausted material resulting from said phase c) , is subjected to exhaustive carbonation, preferably in a sealed environment containing C0₂, or also by exposing it to open air; said phase d) is followed by a phase e) , in which said exhaustively carbonated material resulting from said phase d) is mixed with an effective amount of inert materials and/or aggregates and with an effective amount of cement and/or lime and/or additives and/or a mixture thereof to give a final inert and non-toxic mixture advantageously usable for producing the inert, neutral and environmentally compatible products usable in the building industry.

In said phase d) , the C0₂ can, for example, be taken from the atmosphere or from industrial gaseous wastes that contain it, for example, those originated from thermal plants, as well as the C0₂/CO recovered from the mixture of the gases emitted from the basic leaching tank during the phase c) above.

In said phase e) , the inert materials and/or aggregates are preferably selected from the group comprising: inerts from quarry and/or demolition and/or building debris and/or plastic inerts, such as PVC (polyvinyl chloride) and/or HOPE (high density polyethylene) granules and/or other plastics, for example, high density ones, including, among them, pellets resulting from the recovery of tires for cars, inerts obtained by crushing the discharged and classified as non-hazardous railway ballast, inerts from the process of scarification of road asphalts and inerts from the pelletizing of light dusts from the abatement of non- hazardous smokes and sludges.

Once prepared, said inert non-toxic mixture usable for advantageously producing building products can be packaged and appropriately stored, in stand-by to be used, also for long periods of time, or is transported as such directly to the application site and added with the necessary amount of water, preferably at the time of use, to give the desired product for the building industry.

In a particularly preferred embodiment, the process of the invention comprises, in sequence, the following phases :

- one phase b) according to what has been described before and further exemplified in what follows of the description;

- one phase c) according to what has been described before and further exemplified in what follows of the description;

- one phase d) according to what has been described before and further exemplified in what follows of the description .

In a further particularly .preferred embodiment, the process of the invention comprises also one first phase a) in which the slags and/or ashes, previously treated, purified, grinded, selected by type and granulometry, are measured out and mixed together before being subjected to the subsequent treatments. Therefore, in this case, the process of the invention comprises, in sequence, the following phases: one first phase a) , according to what has been described before and further exemplified in what follows of the description;

one phase b) according to what has been described before and further exemplified in what follows of the description;

one phase -c) according to what has been described before and further exemplified in what follows of the description;

To sum up, the process of the present invention and the machineries that produce it allow to:

- produce at a low cost significant amounts of hydrogen (H₂) , to be employed in the generation of energy and, contemporaneously or in combination, sequestrate carbon dioxide (C0₂) , and therefore constitute a useful material for the "carbon trading" , and, preferably,

activate also the slags and the ashes, so that the pozzolanic properties present in them result enhanced, and use them as raw materials or quality products in the building industry, including the development of the eventual growth of zeolites and other secondary phases useful for the purpose.

The mixtures of scoriaceous materials (or, slags) can be constituted by slags of different origin (as already described above) and/or composition and/or property. For example, said slags contain, among others: silicon, calcium, magnesium, iron oxides and oxides of other metals, transition metals to the zero-valence or combined status and/or alkali and/or alkaline earth metals. Moreover, said slags show reactivity from pH 4,5 upwards, granulometric values comprised between 0 and 80 mm, preferably between 0 and 60 mm, more preferably between 0 and 40 mm, even more preferably between 0 and 30 mm. The flying ashes (or ashes) can be constituted by calcium, magnesium, sodium, potassium silicates, metal oxides; further, they can contain metals in combined or zero-valence form, unburnt fractions and chlorine_/ sulphur, fluorine, nitrate salts and complex salts.

The different raw materials used in the process of the invention are substantially selected from the group comprising :

aqueous acid solutions of hydrochloric acid and/or phosphoric acid and/or hydrofluoric acid and/or nitric acid and/or sulphuric acid and/or acetic acid and/or aqua regia at concentrations comprised between 0,01 and 5 M, preferably between 0,01 and 3,5 M, more preferably between 0,02 and 2 M; and/or

- aqueous solutions alkalinized with calcium oxide or calcium hydroxide or milk of lime, with minimum content of calcium hydroxide of 0,1 M, preferably 0,2 , more preferably of 0,3 M; and/or

alkali and/or alkaline earth metal oxides or hydroxides (potassium, sodium, etc.) in concentrations between 0,1 and 5 M, preferably between 0,1 and 3,5 , more preferably between 0,2 and 2 M; and/or

- cement in the forms 325, 425 or superior; and/or

- fluidificant additives commonly used in the industry; and/or

- exhausted catalysts of the oil and chemistry industry classified as non-hazardous.

Moreover, among the raw materials are also included inert materials and/or aggregates, which can derive from quarries (natural ones) or from demolition and building. As already indicated, among the possible inert materials are preferably included plastic inerts, including the PVC (polyvinyl chloride) , HDPE (high density polyethylene) granules or other plastics, preferably high density ones, including the granules resulting from the recovery of tires for cars. Description on a particularly preferred embodiment of the process of the invention

The various materials (slags, ashes, raw materials) are pre-treated, grinded, purified from useless or toxic waste, riddled and selected/subdivided by type and granulometry and stored in silos or tanks or deposits ad hoc or in another suitable protected environment to avoid, for example, the dispersion of the light dusts in the atmosphere and undesired reactivity (block (A) of the scheme of Figure 1) .

Slags and ashes are therefore measured out, with appropriate measurement systems known in the background art, on transporter tapes towards a first mixing apparatus. Said mixing apparatus mixes the various components and feeds them in the acidic leaching/maturation tank ( s ) /reactor ( s ) (block (B) of the scheme of Figure 1) containing an acid solution, preferably with pH < 2. Such tank(s) constitute ( s) the first reaction environment where the water reduction reaction takes place with relative emission of hydrogen and where the heavy metals present in the slags are contemporaneously solubilized and/or inertized. The tank(s) is (are) provided with an hermetic closure to capture the gas produced, substantially hydrogen-based, avoiding its dispersion in a hazardous way in the atmosphere. Such a gas is directed towards a cleaning and filtering circuit to be then stored and/or optimized in an ordinary energy recovery plant.

From the first tank(s) the scoriaceous material treated is directed towards one (or also more) basic maturation/leaching tank/reactor (a so-called "still pool"; schematized in block (C) of the scheme of Figure 1) where it is treated under agitation with high pH solutions, preferably ≥ 11,5. Here the residue soluble metallic phases inside the slags are first neutralized and then become insoluble hydroxides. Also in this phase significant emissions of hydrogen are generated, which are also directed towards the purification circuit and to the storage/use. In this phase carbon dioxide (C0₂) is also let in/pumped/bubbled in the basic solution (for example, taken from the atmosphere or from industrial gaseous wastes, as those generated from thermal plants) , which is captured by the complex alkaline hydroxides of the slags, and fixed as carbonates. The basic leaching liquid is then directed to a recovery circuit, where the insoluble sludges are separated, and the alkaline hydroxides are regenerated. As it has been described before, the leaching/maturation tanks are closed so that the hydrogen is not dispersed in the external environment, are preferably provided with a rotor that carries out the mixture and the agitation of the solid material and are also provided with appropriate control means, for example of the temperature and of the pH of the solutions employed. The gases generated by the chemical actions that are carried outside the reaction tanks are analysed continuously to verify the rate of hydrogen and in other eventual fuel gases and in residue carbon dioxide. Out from said tanks, the gas flow contains from 5 ppm to 40% in volume, preferably, from 10 ppm to 30% in volume, more preferably, from 20 ppm to 25% in volume, of hydrogen and other fuel gases and, after appropriate purification with methods and devices known in the background art, is directed to an idoneous collection and use system, while the CO₂/CO in excess is separated from the hydrogen and from the other gases usable and recycled into the stilling pool (block (C) of the scheme of Figure 1) or, preferably, recycled in the carbonation tank (block (D) of the scheme of Figure 1) as described below. Preferably, a traditional screw system carries away the washed and exhausted material, now inert and non-toxic, from the basic maturation tank(s) towards an appropriate storage site where said material will wait to become, for example, part of a concrete or of an hydraulic mortar. Said storage of said exhausted, inert and non-toxic material takes place preferably in an appropriate carbonation tank (block (D) of the scheme of Figure 1) or also into open air, for an appropriate period of time sufficient to complete the carbonation process. The verification of the exhaustion of the carbonation process is carried out by means of the use of the calcimetry or in XR diffratometry (that is, X-ray) or by means of another known idoneous measurement system of the crystalline phases. Finally, when the- material has to be used, it is for example measured out and loaded on a tape that transports it towards a second mixer (block (E) of the scheme of Figure 1), in which the necessary raw materials, appropriately measured out in the desired percentages on the basis of the type of mixture to produce, are merged: inerts, slags, cement and/or hydrate lime and/or additives in specific amounts. The material thus mixed is downloaded and, if necessary, immediately taken to the application site, where, last, the necessary water will be added, preferably at the time of use. The formation of the carbonates in the mixture does not limit but, on the contrary, enhance the inert function of the slags and also determines a reduction of the risk of swelling of the manufacture due to the subsequent formation of the carbonates, above all of the magnesium ones, at the same time giving the residue lime the possibility of activating the silicates.

Therefore, the acid and basic treatments, preferably combined among them, in the maturation tanks according to the process of the present invention, allow to obtain different significant advantages with respect to the technologies already known and commonly in use, such as, for example :

- the production of hydrogen, which allows to produce energy;

- the sequestration of C0₂, where the forced carbonation of the material causes, in addition, the annihilation of the magnesium and calcium oxide in excess, which normally determine swelling and splitting of the manufactures;

- the treatment of the slags and/or ashes eliminates the chlorine salts and the other soluble salts, in particular, of the heavy metals, and the organic materials in suspension;

- the forced leaching of the most pernicious metallic phases and their removal from the raw material;

- the formation and the enrichment of high capacity ionic exchange zeolitic phases in the slag so that the stability of the material itself is increased and the capacity of stabilization of the ammoniacal pollutants and of the metals in ionic form is increased and the use as an amender is also allowed.

Preferably, the maturation tanks are made of non- reactive materials, such as polypropylene, Teflon, polyethylene, carbon fibre, plastic reinforced by fiber glass. On average, the temperature of the process is maintained at a value not lower than 40°C, preferably, without the use of external energetic sources, due to the exothermicity of the hydration reaction. In the tanks control systems will be inserted, such as pH and measurement systems, and inlet means of the reagents and of the initial or recycles gases and of extraction of the gases generated and of the materials treated and of the exhausted solutions. The hydration water, including washing salts, will be recovered and treated in an appropriate water treatment plant.

In a particularly preferred embodiment of the invention, schematically the plant for carrying out the process of the invention, substantially comprising at least:

· one or more silos (A) for piling up the slags and the light dusts (block (A) of the scheme of Figure 1) , preferably provided with weights and with extraction systems, preferably remote controlled for measuring out the components; transporter tape(s) that carry the measured components towards a hopper;

a hopper that feeds said components into an acid leaching tank (B) ;

a closed acid leaching tank (B) (block (B) of the scheme of Figure 1), with water having an acid pH, as described before, where the product reacts with the acid solution, produces hydrogen and dissolves into the solution most of the metals soluble and available from the scoriaceous product; from the tank itself (B) the reaction gases rich in hydrogen are extracted and directed towards filtering, storage and/or immediate use systems to produce energy; moreover, from the same tank (B) the exhausted leaching liquid is then pumped and taken to a water treatment plant, where the metal salts are extracted and the liquid is regenerated at the right acidity, and is afterwards re-fed in the tank (B) ;

screws or countercurrent tapes for extracting the acid leached product from tank (B) and for directing it to an alkaline leaching tank (C) ;

a closed alkaline leaching tank (C) (block (C) of the scheme of Figure 1), with water having an alkaline pH, as described before, where the slag resulting from (B) undergoes a second chemical attack that causes the activation thereof; in fact, from the same tank (C) the reaction gases rich in hydrogen are extracted, while the slag sequestrates the C0₂ fed into the reaction environment; then, from the tank (C) the material is extracted with screws or countercurrent tapes and downloaded in a third closed tank (D) (block (D) of the scheme of Figure 1) , into which a gas enriched in carbon dioxide, or atmospheric air (with carbon dioxide) , or industrial gaseous wastes, are fed, including, preferably, the portion of CO₂/CO recovered from the mixture of gases emitted from tank (C) during the basic treatment, and in which the carbonation process of the exhausted slags is appropriately completed (it is reminded that, as described before, in another embodiment of the invention, said exhausted carbonation process can also be carried out by simply storing said exhausted treated slags into open air for an adequate period of time; from the tank (D) screws or tapes then the carbonated material and download it into open air, now inert and non-toxic; from the piles of said inert material are subsequently, or immediately, taken the necessary quantities to produce the cement mixtures, using

• a mixer (E) (block (E) of the scheme of Figure 1), in which all the inerts are mixed according to the method described before to give the cement mixtures useful for the preparation of environmentally compatible materials advantageously usable in the building industry.

The following experimental examples have the aim of illustrating at least some of the particularly preferred aspects of the invention and, for the technician of the field, they are not to be intended absolutely limiting of the wide applicative potential of it.

Example 1

An amount of about 100 g of LD blast furnace slag (that is slag resulting from an oxygen converter) has been riddled and put under agitation in a calibrated flask with 200 g of solution 1M of NaOH. The system has produced a total flow of about 0,04 litres of hydrogen (0,4 1/kg of slag) determined through the gas chromatographic analysis of the gases evolved, with an average amount around 120 ppm of ¾ . The carbon dioxide has been sequestered with a yield of about 0,29 kg/kg of slag. The use of the same amount of slag in solution 0,1 of Ca(OH)₂ has given nearly the same results. Example 2

An amount of 100 g of riddled blast furnace slag at a granulometry inferior to 1 mm has been put in a calibrated flask together with 200 g of solution 1 of NaOH. Also in this case, the production of hydrogen has been abundant, around 0,22 1/kg, determined through the analysis of the gases evolved by means of gas chromatography, while the carbonation has yielded about 0,23 kg of C0₂ sequestered per kg of slag.

Example 3

An amount of about 100 g of thermodestruction slag (mobile grill furnace) , quarted and sorted under the 3 mm, has been put in contact with a solution of Ca(OH)₂ 0,5 , in an amount of 250 cc. The boiling effect results evident and is vividly manifested, providing an amount of hydrogen superior to 10% in volume, determined through the analysis of the evolved gases, by means of gas chromatography. The carbon dioxide is sequestered quickly in the lime solution, with a yield of 0,16 kg/kg of slag.

Example 4

In a calibrated flask an amount of fly ashes from incinerator of urban waste equal to 120 g has been inserted. A lime solution 2 in an amount of 250 cc has then been added and the analysis of the evolved gases has been performed by means of gas chromatography, noticing a very vivid emission of hydrogen equal to about 1 litre/kg of ashes. The yield of absorption of the C0₂ has resulted on average of about 0,1 kg/kg of slag, while the reduction of the soluble chlorine salts has resulted significant, since said salts pass from the initial about 11% to 0,8% in weight.

Example 5

In a calibrated flask an amount of LD blast furnace slag (oxygen converter) has been inserted, in an amount equal to 250 g, together with a solution 0,5 M of nitric acid. The relation between LD slag and acid solution is of 500 g/litre. Immediately, the development of hydrogen gas is observed, in an amount comprised between 15% and 25% of the volume of the gases emitted, together with carbon dioxide and traces of carbon monoxide. The analysis performed in XR fluorescence of the final content of metals in the LD slag treated shows a consistent reduction of chrome, nickel and vanadium that have been solubilized.

Example 6

The residue of slag obtained after the treatment described in the preceding Example 5 is recovered, again placed in another calibrated flask and added of a solution 1M of NaOH in a ratio of 100 cc/g of slag waste. The subsequent elaboration is the same as the one described in the preceding Example 1. The system has produced a total flow of about 0,04 litres of hydrogen (0,4 1/kg of slag) determined through the gas chromatographic analysis of the evolved gases, with an average yield of around 120 ppm of ¾. The carbon dioxide has been sequestered with a yield of about 0,29 kg/kg of slag .

Example 7

The leached/exhausted slag obtained after the treatment described in the preceding Example 6 is recovered, washed in water having a neutral pH and riddled so as to select the fraction comprised between 2 and 30 mm. The product of the riddling is mixed with inerts from quarry, in turn riddled so as to provide an overall granulometric curve compliant to the prescriptions of Rule UNI8520. The mixture is weighed and mixed with cement 325. The percentages of the various components are: total inert (exhausted slag + quarry inert) = 75 %, cement 325 = 16, 5 %, water = 8%. A 0.5% of fluidificant is also added. The mixture is poured into the moulds, subjected to vibration to eliminate the air bubbles and therefore placed in maturation for 24 hours into open air, and, immediately afterwards, in a maturation tank. Such a mixture has given a Ck resistance equal to 230 Mpa after four days of maturation and has resulted perfectly suitable for the production of high resistance cement mixtures for road uses.

Claims

1. A process for the production of hydrogen and the sequestration of carbon dioxide starting from slags and/or industrial ashes, comprising:

at least one phase b) , preceding the following phase c) , of acidic leaching/maturation, in which said slags and/or industrial ashes and/or a mixture thereof are subjected, in a sealed reaction environment, to a treatment in an acid solution having a pH < 3,5, during which a gas substantially composed of hydrogen is produced and from the slags and/or ashes the hazardous metals are extracted under the form of soluble salts of nitrogen and/or sulphur, and/or chlorine and/or phosphorus and/or fluorine and/or acetic acid; and

at least one phase c) , following the above phase b) , of alkaline leaching/maturation, in which said slags and/or industrial ashes and/or a mixture thereof previously treated in above phase b) are subjected, in a sealed reaction environment and in the presence of C0₂, to a treatment in an alkaline solution having a pH > 8, during which a gas substantially composed of hydrogen is produced and the CC>2 present in the environment is sequestered.

2. The process according to claim 1, in which said slags and/or industrial ashes, preferably comprise:

steelworks slags, both from blast furnaces and electric furnaces, and/or slags from oxygen converters, and/or light dusts and/or ashes from iron metallurgy and/or other slags and/or solid waste from iron, aluminum and non-ferrous metals iron metallurgy and/or bottom ashes and/or filter ashes from thermal plants, from incineration of special and/or urban waste and/or from thermal and/or pyrolysis plants and/or from gasification and/or from energy production facilities and/or fossil fuels and/or from biomasses.

3. The process according to claim 1 or 2, in which, in said phase b) , said acid solution has a pH ≤ 3, preferably ≤ 2,5, more preferably ≤ 2, even more preferably ≤ 1,5.

4. The process according to anyone of claims from 1 to 3, in which, in said phase b) , said acid solution contains an effective amount of . at least one acid selected from: nitric acid and/or sulphuric acid and/or acetic acid and/or hydrochloric acid and/or phosphoric acid and/or hydrofluoric acid and/or aqua regia or mixtures thereof.

5. The process according to anyone of the preceding claims, in which, in said phase b) , said reaction environment comprises at least one closed container equipped with at least feeding means of said slags and/or ashes and/or of a mixture thereof, agitation and control means, feeding means of the acid solution, extraction means of the generated gas, extraction means of the treated/exhausted material, extraction means of the resulting acid solution at the end of the treatment.

6. The process according to anyone of the preceding claims, in which, in said phase c) , said CO₂ is added to the reaction environment by bubbling it, under the form of gas, in said alkaline solution or by bubbling air into said alkaline solution.

7. The process according to anyone of the preceding claims, in which, in said phase c) , said alkaline solution has a pH ≥ 9, preferably ≥ 9,5, more preferably ≥ 10,5, even more preferably ≥ 11,5.

8. The process according to anyone of the preceding claims, in which, in said phase c) , said alkaline solution contains an effective amount of at least one alkali metal or alkaline earth metal oxide or hydroxide; preferably, selected from the group comprising: NaO, K₂0, CaO, MgO, NaOH, KOH, Mg(OH)₂, Ca(OH)₂-

9. The process according to anyone of the preceding claims, in which, in said phase c) , said reaction environment comprises at least one closed container equipped with at least feeding means of said slags and/or ashes and/or a mixture thereof previously treated in phase b) , agitation and control means, C0₂ and/or air feeding means, feeding means of the alkaline solution, extraction means of the generated gas, extraction means of the treated/exhausted material, extraction means of the resulting alkaline solution at the end of the treatment .

10. The process according to anyone of the preceding claims, further comprising:

at least one phase d) , following said phase c) , in which the exhausted material, resulting from said phase c) , is subjected to exhaustive carbonation, more preferably, in an environment containing C0₂, or by exposing it to open air; said phase d) is followed by a phase e) , in which said carbonated material from said phase d) is mixed with an effective amount of inert materials and/or aggregates and with an effective amount of cement and/or lime and/or additives and/or mixtures thereof to give a mixture usable for producing the inert, neutral and environmentally compatible products, usable in the building industry.

11. The process according to claim 10, in which said inert materials and/or aggregates are selected from the group comprising: inerts from quarry and/or demolition and/or building debris and/or plastic inerts, PVC and/or HDPE granules and/or high density plastics, including pellets resulting from the recovery of tires for cars, inerts obtained by crushing and grinding the discharged and classified as non-hazardous railway ballast, inerts from processes of pelletising light dusts from the abatement of industrial smokes and industrial sludges.

12. The process according to anyone of the preceding claims, comprising, in sequence, the following phases: one phase b) , according to claims 1 to 5;

one phase c) , according to claims 1 and 6 to 9;

one phase d) , followed by a phase e) , according to claims 10 to 11.

13. The process according to anyone of the preceding claims, further comprising one first phase a) , in which the slags and/or ashes are measured out and mixed together before being subjected to the subsequent treatments .

14. The process according to anyone of the preceding claims, comprising, in sequence, the following phases: one phase a) , according to claim 13;

one phase b) , according to claims 1 to 5;

one phase c) , according to claims 1 and 6 to 9; one phase d) , followed by a phase e) , according to claims 10 to 11.

15. A plant for carrying out the process according to anyone of the preceding claims, substantially comprising at least:

• one or more silos (A) for piling up slags and light dusts ;

• transporter tape(s) that carry the measured scoriaceous components towards a hopper;

· a hopper that feeds said components into an acid leaching tank (B) ;

• an acid leaching tank (B) with water having an acid pH according to claims 1 and 3 to 5, where the product reacts with the acid solution, produces hydrogen and dissolves into the solution most of the metals soluble and available from the product;

• screws or countercurrent tapes for extracting the acid leached product from tank (B) and for directing it to an alkaline leaching tank (C) ;

· a closed alkaline leaching tank (C) , with water having an alkaline pH according to claims 1 and 6 to 9, where the slag resulting from (B) undergoes a second chemical attack that causes the activation thereof to give a mixture of reaction gases rich in hydrogen and the sequestration of the C0₂ fed into the reaction environment;

screws or countercurrent tapes for extracting the alkaline leached product from tank (C) and for directing it to a carbonation tank (D) ;

a closed carbonation tank (D) into which a gas enriched in carbon dioxide, or atmospheric air, or industrial gaseous wastes, are fed, including, preferably, the portion of C0₂/CO recovered from the mixture of gases from tank (C) , to complete the carbonation process of the exhausted slags deriving from tank (C) ;

screws or tapes for extracting the carbonated material from tank (D) and for downloading it into open air and/or for directing it to a mixer (E) ; a mixer (E) , in which the inert materials are mixed according to claims 10 to 11 to give the cement mixtures useful for the preparation of environmentally compatible materials for the building industry.