Process for the recovery and stabilisation of incinerator SLAG, lightweight manufactured product for the construction trade and grinding device

Abstract

A process for recovering incinerator slag from which an aggregate is obtained for the production of concrete is disclosed. The aggregate, obtained from grinding and separation steps, among others, is characterised by a fineness of less than 2 mm for 98 99%. Also a lightweight manufactured product for the construction trade, made of concrete is disclosed. The concrete for producing said manufactured product comprises as aggregates the aggregates obtained from incinerator slag, from which metals have been separated, and ground down to a diameter of less than 2 mm, and said manufactured product is produced by means of a vibrocompression process. Lastly, a grinding device, suitable for grinding, in one or more passes, incinerator slag completely to a diameter of less than 2 mm is disclosed, which device is formed by a rod mill which exhibits an end peripheral discharge ( 7 ).

Description

[0001] PROCESS FOR THE RECOVERY AND STABILISATION OF INCINERATOR SLAG, LIGHTWEIGHT MANUFACTURED PRODUCT FOR THE CONSTRUCTION TRADE AND GRINDING DEVICE

[0002] DESCRIPTION

[0003] The present invention relates, in general, to a process for the recovery and stabilisation of incinerator slag, a lightweight manufactured product, normally for the construction trade and which can be obtained with the product of the process, as well as processing and grinding devices, to be used in the recovery process .

[0004] Industrialised society produces considerable quantities of waste, which should be disposed of in some way . In the past, when much less waste was produced and scientific knowledge was less advanced, waste dumping sites were especially found to be useful, which are places with the ground made impermeable to prevent seepage into the earth and into the water bearing strata, where the waste is deposited, covered with earth and left there over time . A more efficient method and which enables a considerable saving of space is incineration . In practice, incineration is in itself a very old technology, perhaps more so than waste dumping sites . However, for many years, it has been used very little (at least in Italy) .

[0005] On the other hand, the incineration of waste is a very desirable disposal technique in itself : the waste is reduced from large volumes to minimal volumes of ash (around 3% by volume and 20% by weight of the initial waste) , which can be disposed of in various ways, and when the combustion process is managed in the correct way, very low emissions can be achieved. Various factors have led in recent times to the resumption of the use of incinerators : the bias to very high temperatures - as has just been hinted at - eliminates the risk of producing dioxins and various other toxic substances; the high temperatures can lead to the reuse of the heat generated in the combustion for industrial and / or domestic uses, being able to convert it into electricalenergy or use it for district heating or as heat sources for industrial reactions .

[0006] As regards the ash that remains, it is made up partly of metallic material - the recovery of which has dedicated to it a vast amount of research in the sector - and partly of mineral material . Generally, it is quite easy to separate the ferromagnetic metallic material from the ash, even making use of the magnetism itself; unfortunately, the non-ferrous metallic material is instead separated from the mineral material in only small quantities . In particular, it is very difficult to separate "non-ferrous", i . e . non-f erromagnetic, metals of small sizes, such as for example aluminium present in considerable quantities in the waste of every source .

[0007] Aluminium, just as other metals, tends to oxidise in moist environments . The oxidation of aluminium, for example, gives rise to expansion phenomena, both through the formation of aluminates and due to giving rise to the release of hydrogen .

[0008] The mineral material - which forms 80-90% by weight on a dry base of the slag, and which has, among others, potentially, pozzolanic and / or geopolymeric properties - can be advantageously used in the production of concrete . It would be highly desirable to recover this majority fraction in the slag, extolling the pozzolanic and / or geopolymeric properties which it potentially already has as a result of the process from which it comes . However, the presence of aluminium and also of other metals, as well as the predominantly amorphous nature of the mineral fraction, give rise to some problems . The main problem regarding fresh concrete is that, when the material is added to the concrete, amphoteric metals (primarily aluminium) that are still present, since they are difficult to separate, come into contact with significant quantities of water, thus giving rise to the abovementioned oxidation reaction, with the formation of hydrogen involving the formation of gas bubbles form that can damage the concrete itself . On hardened concrete, moreover, pop-out phenomena arise, presumably due to both corrosion of the metals at highpotential, and to the "alkali-silica" or "alkali-aggregate" reaction, due to the amorphous nature of the mineral fraction .

[0009] For the purposes of the present description and accompanying claims, "dry grinding" is understood to mean grinding performed on material with a moisture content of normally less than about 12-15% by weight (therefore between 0% and about 12-15%) . In the specific case of incinerator slag, which is often quenched in water and for which forced drying would involve additional costs, "dry grinding" is understood in particular to mean grinding performed with a moisture content typically between around 2% and 12% by weight and preferably between 3% and 8% by weight . Such grinding is to be understood to be clearly distinct from "wet grinding", in which moisture contents are generally greater than 30% by weight and more often between 30% and 50% depending on the fineness sought . To achieve the typical granulometries of the present invention ( for example 0-2 mm) , wet grinding would involve in general moisture contents of an order of magnitude of around 35% . In the context of dry grinding, controlling the moisture content also has an operational function, since excessively low moisture can increase dust formation from the solids obtained, while excessively high moisture content can favour phenomena of packing and reduction in the efficiency of grinding and classification . The distinction between dry and wet grinding is important, since it directly affects energy consumption and the industrial management of the downstream phases (separation / drying) .

[0010] This problem has already been addressed by the inventor of the present invention . Indeed, EP 2 288 582 illustrated a method for removing and / or corroding in advance the metallic aluminium and other metals subjected to corrosion from the mineral fraction, subjecting the material to intensive wet grinding, suitably alternated with separation steps, and using for the successive processes very fine mineral fractions . Thus, the separation was highly intensive, eliminating or, in any case, substantially reducing the phenomenon of the formation of hydrogen with consequent swelling, thus fully exploiting the pozzolanic and / orgeopolymeric properties of the mineral part of the incineration ash, by virtue also of the alternating of the steps of separation and corrosion of the metals with the wet grinding. By virtue of the highly intensive grinding and the resulting high degree of fineness the pop-out phenomena were also non-existent .

[0011] However, this solution, although brilliant, leaves some significant unsolved drawbacks . First of all, the process is very complex, involving intensive grinding and the execution of steps of separation in aqueous suspension in a highly alkaline environment which gives rise to the formation of very significant quantities of hydrogen, which is highly explosive even in processes in aqueous suspension . Moreover, the use of water for the wet processes and the significant quantities of hydrogen which are formed, mainly due to the corrosion of the metallic aluminium, give rise to the formation of ternary mixtures, containing solids, liquids and, which are notoriously difficult to pump on an industrial scale, with the development, among other phenomena, of relatively high temperatures, also through the contribution of exothermic reactions, and the processes easily reach temperatures of between 40°C and 60 °C . At the end of these processes, water must then be eliminated, which could release hydrogen with the associated risk of explosion, this operation therefore also being rather complicated, in order to be able to obtain a mineral fraction in solid form and no longer in aqueous solution, and which involves considerable plant-engineering complexities and a high energy cost .

[0012] The intensive grinding of the ash hence involves costs for the energy required for this grinding. Even reducing the moisture is a process involving a high amount of energy, with associated costs .

[0013] The concrete obtained using the aggregates produced according to that patent requires a greater quantity of water than normal and includes a quantity of air that is also greater than normal; all this requires that superplasticisers and anti-foaming agents are added in large quantities, with a further increase in costs .The present invention is a considerable advancement over the previous one in that it promotes an industrial equilibrium between effectiveness of the treatment and simplicity / robustness of the process, avoiding wet, complex and energy-intensive processes . In particular, it was observed that a granulometry in which more than 98-99% of particles exhibit sizes of less than about 2 mm (and preferably less than 1. 6 mm, 1. 4 mm or 1.25 mm) represents a point of equilibrium particularly favourable between effectiveness of the treatment and industrial simplicity of the process . Indeed, at such granulometric sizes, pop-out phenomena are reduced to non-detectable levels, although avoiding excessively intensive grinding operations and therefore high energy consumptions .

[0014] Similar considerations can be made for CN 112 142 416, which describes a procedure that is very similar to EP 2 288 582. CN 112 142 416 describes a permeable concrete which comprises the following components (in parts by weight) : 1, 050-1, 250 parts of aggregate recycled from waste incinerator slag; 350-400 parts of cement; 14-16 parts of reinforcing material; water reducing agent : 1.5-2 parts ; 100-150 parts water . The reinforcing material is a combination of silica fume, fly ash and mineral powder; the sizes of the particles of the aggregate recycled from waste incinerator slag are 0.25-0.5 mm. As it is to see, municipal solid waste incinerator slag is used in large quantities (completely replacing natural aggregate) as constituents of cement slurry .

[0015] In this document, reference is made to the use of incinerator slag as aggregate and of preliminary treatments of the slag and of the particles with finer granulometry . Moreover, the industrial operational methods are not highly detailed. The patent teaches that the slag is subjected to washing, crushing, magnetic separation, roughing, sedimentation and further screening, neglecting various aspects that apply on an industrial scale . It further teaches that the mixture is poured (see paragraph

[0052] , where there is stated: "The slurry was filled into a lOOmmxlOOmmxlOOmm mold in two layers .") , therefore under conditions of highly plastic slurry . As can be understood therefrom, the crushing of the slag takes place under highmoisture conditions . However, in this document, no reference is made to vibropressed manufactured products, with moist earth texture . This patent does not clarify anything regarding the formation of hydrogen due to the corrosion of metallic aluminium and regarding the separation of the water from the granular fraction, at the end of the process . However, from the text and from the claims, it is clearly understood that the mineral fraction obtained from the incinerator slag and used for the final slurry is actually in dry form, which would involve very significant costs for drying it, downstream of washing processes . The pop-out problems or those related to surface defects which are created by using a massive amount of incinerator slag in vibropressed concrete blocks are not completely dealt with .

[0016] Moreover, this patent does not clarify the methods of crushing and, for the technician skilled in the art, it is clear that obtaining a fraction of between 0.25 mm and 0.5 mm involves the use of grinding machinery providing intensive grinding, with the production of a significant quantity of the <0.25 mm fraction, unless it is intended to obtain this fraction substantially through separation, therefore, using light grinding (in effect, the patent refers to "crushing" which is a process distinct from "grinding"; it seems therefore clear that with the term "crushing" the Chinese document indicates typically a primary or secondary crushing operation, not suitable in itself to ensure a narrow granulometric distribution as that claimed) which, however, involves the recovery of only a small fraction of incinerator slag, which, at precisely between 0.25 mm and 0.5 mm, could form a reduced share of the total (approximately a few percentage points, probably around 3% of the total of the slag) leaving the problem of the other 97% unresolved. In any case, it is very difficult to give an industrial sense to the invention claimed by CN 112 142 416.

[0017] The present invention is differentiated therefore by the aim of processing a significantly larger share of the slag by means of a process compatible with industrial conditions having low energy consumption and reduced water usage . In this context, thechoice of a granulometry in which almost all the particles are smaller than about 2 mm does not represent an arbitrary value, but rather the result of a technical and industrial assessment which provides for achieving a substantial elimination of the pop-out phenomena while maintaining an energetically sustainable and industrially simple treatment process .

[0018] Uses of the mineral fraction of the incinerator slag -although with the presence of non-ferrous metallic fractions which fail to be separated as stated above - according to the prior art, are briefly set out as follows . The slag (which at the end of the incineration processes has a typical granulometric distribution in which 20% to 25% has a diameter less than 2 mm, for 20% to 30% it is between 2 mm and 4 mm, for 30% to 45% it is between 4 mm and 10 mm, and 5% to 15% has a diameter greater than 10 mm) following known treatments (comprising steps of grinding, screening, various separations) , is in general collected in homogeneous fractions, for example, 0-2 mm, 2-4 mm, 0-4 mm and 0-10 mm, according to the intended uses . The intended uses are, for example, for the 0-2 fraction, the production of cement clinker (not blended cements, a point which, as will be seen, is essential) , bricks and bituminous concretes . The other fractions (0-4 mm, 2-4 mm and 0-10 mm) , apart from the aforementioned intended uses, are applied in the production of concrete mixtures and cementitious manufactured products . It is noted that, in known technologies, the 0-2 mm fraction is obtained predominantly as a by-product of the screening and granulometric classification operations, while in the present invention the granulometric reduction is deliberately pursued by means of controlled grinding, as part of the process described hereafter, in order to reduce or render harmless the expansion phenomena associated with the presence of residual metals and with alkali-aggregate reactions . However (excluding the uses in which the slag, which comes from incineration processes at around 1, 000-1, 200 °C, is again subjected to high temperature thermal processes - clinkerisation, production of ceramics and bricks, vitrification, etc - with associated emissions, environmental impacts and costs, and also excludinguse for the production of bituminous concrete mixtures, intended for the production of "binders" and "wearing courses", subjected to frequent repairs and wear, which appears in contrast with the control regarding dispersion into the environment) , in the case of use in a cementitious matrix, the problems, which have been described previously, have over time led to using these aggregates obtained from incinerator slag in significant percentage quantities in the production of cement mixes (where there are no quality issues, but seepage into the environment may be determined) and in very small percentage quantities (in general 5-7%) , so as to contain the amount of negative effects, in the production of concrete mixtures and cementitious manufactured products . Such modes of use have, over time, brought to light various limits and problems, a fact which, for example, has led to producing concretes which are almost exclusively intended for foundation works or for castings intended to remain hidden .

[0019] It will be noted that obtaining a granulometric fraction of between 0 mm and 2 mm represents in itself a known and widespread practice in the field of incinerator slag recovery, this fraction being commonly produced by means of separation and granulometric classification operations .

[0020] In the present invention however, this fraction is not obtained substantially by means of selection, but rather by means of a combination of selection and controlled grinding, aimed at reducing the share of particles of sizes greater than the preset limit, alternated with selection steps . The aim therefore is not to produce extremely fine particles, but to gradually remove the coarse fraction responsible for pop-out phenomena, while maintaining an industrially feasible and actually simple process with limited energy consumption, as better illustrated hereafter .

[0021] Delving a little deeper into the specifics, therefore, because it is impossible to completely separate the non-ferrous metals of smaller sizes (<2— 3 mm) , the addition of these aggregates in cementitious concretes and concrete mixtures (which have the advantage of being cold processes and of embedding these aggregates in a stable manner) , according to the technologiescurrently in use, fundamentally leads to two types of drawbacks . In the case of fluid concrete, as has already been seen, the aluminium in the plastic phase corrodes and hydrogen forms, with an increase in volume and loss of compactness and strength . Moreover, both alkali-aggregate or alkali-silica reactions, related to the amorphous nature of the ash, and corrosion of metals still present in the aggregate occur; these two reactions, following a few different mechanisms, lead to the occurrence of a phenomenon known as pop-out, i . e . the formation of surface microcraters : this is a very nasty phenomenon which can damage the aesthetics of a building. On the other hand, in the case of concrete with non-fluid consistency, similar to moist earth, because of having limited water quantity, phenomena of corrosion of aluminium in the plastic phase do not arise but later expansion phenomena do occur, after the concrete has hardened, due both to the alkali-alkali-aggregate-metal reaction and to the corrosion of the metals; even in this case, the abovementioned pop-out phenomenon arises .

[0022] The abovementioned problems can be limited (even if not eliminated) in how they arise, by turning to ageing the slag. However, even this solution is not without drawbacks : it requires large spaces, the slag must be kept moist and, to that end, moistened with complicated handling and water management . Moreover, it would become impossible to recover some metals since they would corrode . Lastly, the pozzolanic and / or geopolymeric potentials would be lost .

[0023] One of the most immediate ways to use concrete is in the production of concrete-based manufactured products to be used in construction . A particularly interesting method of obtaining such manufactured products is the vibrocompression technique : a slurry is prepared containing aggregates and cement with a rather low water / cement ratio, and is introduced into moulds, made to vibrate mechanically and, simultaneously, pressed hydraulically, and the manufactured products are removed from the moulds and then harden at room temperature . Some typical vibropressed manufacturedproducts are masonry blocks, interlocking block paving and road kerbs .

[0024] A disadvantage of masonry blocks thus obtained is their high density, of the order of 2 , 100-2 , 300 kg / m3. This high density, which can to date be reduced only by using very expensive aggregates, such as expanded clay, expanded glass and others, very much limits the possibility of using these blocks, confining their use to situations in which weight is not an issue : in the production of above-ground masonry for civil use or similar, these blocks are not used in practice, the lighter clay and aerated concrete blocks being preferred.

[0025] Recently, however, some facts have arisen to change their possibilities of use . Indeed, the increase in the costs of bricks and aerated concrete would make it desirable to use these vibrocompressed concrete blocks . However, it remains a problem that these blocks have insulating properties, from a thermal perspective, that are inferior to those of other materials and maintain too high a density .

[0026] Incinerator slag based aggregates have already been used for the production of vibrocompressed concrete blocks, but have never been pretreated to reduce the pop-out phenomenon until it is practically eliminated.

[0027] The problem underlying the invention is to propose a method for recovering incinerator slag which overcomes the drawbacks mentioned and by which, using simple operations and with a relatively low energy consumption, a lightweight manufactured product for the construction trade can be obtained, which enhances its recovery in an ecological manner . This aim, based on a first aspect, is achieved by a process for the recovery of incinerator slag for the use of this slag as aggregate for the production of concrete and / or blended cement and / or cementitious products, comprising steps of grinding the slag, demetallisation, separation and selection of said slag, characterised in that said grinding is executed with a moisture level of the slag of between 0% and 15% by weight and in that the particles that have, for 98-99%,particle sizes, determined granulometrically by sieving, of less than 2 mm are used as aggregate .

[0028] Based on a second aspect, the aim is achieved by a lightweight manufactured product for the construction trade, made of concrete, characterised in that the concrete for producing said manufactured product comprises aggregates having particle sizes, determined granulometrically by sieving, of less than 2 mm for 98-99% .

[0029] Lastly, based on a third aspect, the aim is achieved by a grinding device, suitable for grinding, in one or more passes, the incinerator slag completely to particle sizes of less than 2 mm, characterised in that it is formed by a rod mill .

[0030] Based on a preferred embodiment, said rod mill is a peripheral discharge rod mill .

[0031] Based on one embodiment, said peripheral discharge rod mill is an end peripheral discharge rod mill . Based on an alternative embodiment, said peripheral discharge rod mill is a central peripheral discharge rod mill .

[0032] The dependent claims describe preferred characteristics of the invention .

[0033] Based on one embodiment, the slag is processed by means of various processing steps : screening / classif ication, demetallisation, separation, grinding. The processing steps can be repeated with different sequences and can be suitably repeated before and after the other steps . For example, the removal of iron generally takes place both before and after the grinding, and the grinding, in the event that it is already carried out without arriving at the desired fineness, must be repeated until the desired fineness is achieved.

[0034] Based on one embodiment, the grinding is performed on two granulometric fractions .

[0035] Based on a preferred embodiment, the moisture level of the slag being ground is between 2% and 12% by weight .

[0036] Based on one embodiment, the aggregate obtained is formed by particles having particle sizes, determined granulometrically bymeans of sieving, of less than 0. 063 mm in a quantity of less than 30% by weight . Preferably, said particle fraction having particle sizes of less than 0. 063 mm is in a quantity of less than 25% by weight . More preferably, said fraction of particles having diameters of less than 0.063 mm is in a quantity of less than 20% by weight . Most preferably, said particle fraction having particle sizes of less than 0. 063 mm is in a quantity of less than 15% by weight .

[0037] Based on a preferred embodiment, more than 98%, preferably more than 99%, of the particles exhibit particle sizes of less than 1. 6 mm, and based on a more preferred embodiment they exhibit particle sizes of less than 1.4 mm and, in the most preferred embodiment, they exhibit particle sizes of less than 1.25 mm.

[0038] Based on one embodiment, the particle fraction having particle sizes of between 0.063 mm and 1 mm is greater than 40% by weight .

[0039] Based on one embodiment, the particles of the desired sizes are subjected to a maturation step, sending them to a storage facility, with an initial relative humidity of between 10% and 18% and preferably higher than 12%, more preferably between 12% and 16%, which with the passing of time is reduced, for a period longer than one week . Preferably, the maturation time is longer than two weeks, more preferably longer than three weeks .

[0040] Based on one embodiment, the particles which, after having exhausted one grinding cycle, still exhibit sizes larger than desired, are subjected to a maturation step, before being directed to another grinding cycle . Preferably, said maturation step takes place by sending the particles to maturation, such that the initial relative humidity of the maturation is between 7% and 18%, preferably higher than 9%, more preferably from 9% to 16% . In order to achieve this degree of moisture, which then reduces over time, it is appropriate to proceed with significant moistening while sending to the maturation phase, downstream of the grinding, screening and separating processes . This maturation step, in which the temperature, mainly due to the grinding and exothermichydration reactions, is generally higher than or equal to 40°C, is longer than one week, preferably longer than two weeks, more preferably longer than three weeks . In any case, the duration of the maturation, referred to in the previous points, can vary as a function of the granulometry and of the operational conditions, while remaining within the scope of the present invention .

[0041] Based on one embodiment, said desired particle sizes are smaller than 2 mm for more than 98%, preferably for more than 99% ; preferably said desired particle sizes are smaller than 1. 6 mm for more than 98%, preferably for more than 99%; more preferably smaller than 1.4 mm for more than 98%, preferably for more than 99%; most preferably smaller than 1.25 mm for more than 98% , preferably for more than 99% .

[0042] Based on a preferred embodiment, the particles obtained, of the desired sizes, before being put into use, undergo maturation, storing them with an initial relative humidity of between 10% and 18%, more preferably between 10% and 16%, for a period longer than one week; preferably, said period is longer than two weeks; more preferably it is longer than three weeks ; alternatively, said period is between one and four weeks . The relative humidity then reduces with the passing of the days and weeks .

[0043] Based on one embodiment, there is a maturation step for particles of sizes, for 98-99%, of less than 2 mm or of the desired sizes for a period longer than one week, with an initial relative humidity of between 10% and 18%, more preferably between 10% and 16% . Advantageously, said period is longer than two weeks ; more preferably, said period is longer than three weeks . Alternatively, said period is between one and four weeks . Preferably, there is a maturation step for particles, for 98-99%, of the desired sizes or of sizes less than 2 mm, before the desired product particles are obtained, for a period longer than one week, with an initial relative humidity of between 12% and 18%, preferably between 12% and 16% . Advantageously, said period is longer than two weeks; preferably said period is longer than three weeks . Alternatively, said period is between one and four weeks . In any case, the duration of the maturation, referred to in the previous points,can vary as a function of the granulometry ( for example, where finer granulometries are opted for such as those in which 98-99% of the particles are smaller than 1. 4 mm or 1.25 mm, the maturation period could be reduced to within one week) and of the operational conditions, while remaining within the scope of the present invention, it being understood that these variations must in any case maintain operational conditions suitable for achieving the substantial reduction of the pop-out phenomena in cementitious manufactured products produced using the aggregate obtained.

[0044] Based on one embodiment, the ground and demetallised particles, of sizes larger than the desired sizes or larger than 2 mm, are sent again to a grinding, screening and demetallisation step after an intermediate maturation step having a duration of more than one week, with an initial relative humidity of between 7% and 18%, preferably between 7% and 16% . Preferably, the ground and demetallised particles, of sizes larger than the desired sizes or larger than 2 mm, are sent again to a grinding, screening and demetallisation phase after an intermediate maturation step for a period longer than one week, with an initial relative humidity of between 9% and 18%, preferably between 9% and 16% . Preferably, said maturation period is longer than two weeks; more preferably, said maturation period is longer than three weeks . Alternatively, said maturation period is between one and four weeks .

[0045] Based on one embodiment, said grinding takes place in rod mills .

[0046] Based on one embodiment, said grinding takes place in end peripheral discharge rod mills . Indeed, it has been verified that, in the grinding of slag, which, as mentioned, still contains metals, the end peripheral discharge rod mills are much more efficient than axial discharge rod mills . The experiment illustrated later highlights the greater efficiency of an end peripheral discharge mill with covering of 50% of the openings by means of perforated plates, as compared with an axial discharge mill .Based on one embodiment, the grinding in rod mills takes place on two granulometric fractions, divided by means of screening upstream of the grinding :

[0047] • a finer fraction, intended for a first rod mill, containing material passing, as an indication, through an 8 mm to 25 mm hole or opening clearance screen; and

[0048] • a coarser fraction, intended for a second rod mill, passing through a 10-20 cm clearance screen; owed to the fact that the finer fraction (passing through the 8-25 mm clearance screen) is, in general, of much higher quantity than the coarse fraction, it is possible, in order to optimise the yields of the mills, to also direct a part of the intermediate fraction to the second rod mill suitable for the processing of the coarser fraction, which is possible, for example, by creating a certain number of simple openings in the screen .

[0049] Based on one embodiment, the end peripheral discharge rod mill, suitable for receiving the coarsest fraction, exhibits the following characteristics :

[0050] • through-bore diameter inside the bearing greater than 40 cm, preferably greater than 45 cm, more preferably greater than 50 cm, most preferably greater than 55 cm, more preferably greater than 60 cm;

[0051] • feeder with internal auger which rotates integrally with the mill and which auger continues in the section inside the bearing .

[0052] • outlet clearance of diameter equal to or greater (preferably 20-30% greater) than the openings of the upstream screen which selects the maximum sizes of the fraction intended for this mill;closure and / or covering, with perforated plates or grates, of the discharge openings of the end peripheral discharge rod mill such that the rod mill has a quantitatively much lower productivity than normal and, at the same time, a longer residence time for the fraction to be ground; such a flow rate correction, in practice, must be such that the end peripheral discharge rod mill, which normally has a flow rate of more than double that of an axial discharge mill of equal size, has a flow rate similar to an axial discharge mill; preferably the perforated plates or grates have holes with clearances of between 3 mm and 12 mm; more preferably between 5 mm and 9 mm.

[0053] Based on one embodiment, the end peripheral discharge rod mill, used for grinding the finest fractions, exhibits the following characteristics :

[0054] • through-bore diameter inside the bearing greater than 40 cm, preferably greater than 45 cm (which, moreover, is quite normal ) ;

[0055] • feeder with internal auger (or equivalent system which pushes the material towards the inside of the mill) which rotates integrally with the mill and which auger continues in the section inside the bearing.

[0056] • outlet openings which are closed and / or, preferably, covered with perforated plates or grates, such that the end peripheral discharge rod mill has a quantitatively much lower productivity than normal and, at the same time, a longer residence time for the fraction to be ground; such a flow rate correction, in practice, must be such that the end peripheral discharge rod mill, which normally has a flow rate of more than double that of an axial discharge mill of equal size, has a flow rate similar to an axial discharge mill; preferably the perforated plates or grates have holeswith clearances of between 3 mm and 12 mm; more preferably between 5 mm and 9 mm; these opening clearance sizes take account of the typically higher peripheral speed of a rod mill as compared with that of a trommel screen, which determines the effective screening yield.

[0057] Based on an alternative and preferred embodiment of the lightweight manufactured product for the construction trade, the concrete for producing said manufactured product comprises aggregates obtained from incinerator slag that is demetallised, within the limits of the available technologies, and ground, so as to have sizes of less than 2 mm for 98-99%, and said manufactured product is produced by means of a vibrocompression process .

[0058] Based on one embodiment, the lightweight manufactured product contains a quantity of aggregate obtained from incinerator slag that is greater than 30% by weight based on dry components .

[0059] Other features and advantages of the invention will become clearer from the following detailed description of a preferred embodiment, given purely by way of example and in a non-limiting manner, and illustrated in the appended drawings in which :

[0060] Figure 1 represents an embodiment of an end peripheral discharge rod mill, based on the third aspect of the present invention;

[0061] Figure 2 represents the form of an axial discharge rod mill according to the prior art, used for comparison with the mill of Figure 1 ;

[0062] and Figure 3 is a block diagram of an embodiment of the process according to the first aspect of the present invention .

[0063] For the grinding performed in the steps of the process according to the present invention, the preferred instrument is the rod mill, given that it enables the desired granulometry to be achieved with a reduced content of very fine particles (particle sizes <0.063 mm) .

[0064] Rod mills are particularly suitable because :• they produce a limited quantity of very fine particles (particle sizes of less than 0. 063 mm) and, at the same time, a high quantity of particles within the desired threshold (particle sizes of less than 2 mm) ;

[0065] • they carry out a quite selective grinding, i . e . not excessively heavy (as compared with other grinding machinery) , which provides for :

[0066] o grinding the mineral fraction very well; o preserving the integrity of the metallic fractions which, if they are excessively reduced in size, would become impossible to recover, would be highly oxidised and would lose value;

[0067] o separating the metals from the mineral fraction of the slag . Preferably, rod mills produce a limited quantity of very fine particles (particle sizes of less than 0.063 mm) and, at the same time, a high quantity of particles within the desired threshold (particle sizes of less than 1. 6 mm) ; more preferably, they produce a limited quantity of very fine particles (particle size of less than 0. 063 mm) and, at the same time, a high quantity of particles within the desired threshold (particle sizes of less than 1. 4 mm) ; most preferably, they produce a limited quantity of very fine particles (particle sizes of less than 0. 063 mm) and, at the same time, a high quantity of particles below the desired threshold (particle sizes of less than 1.25 mm) .

[0068] • Preferably, rod mills produce a limited quantity of very fine particles (particle sizes of less than 0. 063 mm) and, at the same time, a high quantity of particles within the desired threshold (particle sizes of less than 2 mm, preferably less than 1 . 6 mm) ; more preferably, they produce a limited quantity of very fine particles (particle sizes of less than 0.063 mm) and, at the same time, a high quantity of particles within the desired threshold (particle sizesof less than 1. 4 mm) ; most preferably, they produce a limited quantity of very fine particles (particle sizes of less than 0. 063 mm) and, at the same time, a high quantity of particles below the desired threshold (sizes of less than 1.25 mm) . As regards the separation of metals from the slag, it is considered that, when extinguishing the incinerator slag in water, following the incineration process during which a large part of the mineral fraction, as well as the low melting point metals, melts, the slag which congeals abruptly determines the fact that the metals and mineral fraction cling to one another . To this end, a sufficiently energetic mechanical action is required to achieve the separation of materials of different kinds : mineral or metallic . For this function, rod mills are optimal . Moreover, rod mills are capable of receiving and processing much coarser slag with respect to the granulometries which, in general, feed them.

[0069] The slag, after possible separation of the coarser fractions - for example larger than 8-20 cm, which are in very small quantities of 1-2% by weight and can be separated and reduced volumetrically , for example by means of grinding, in order to then be reintroduced into the main process - is screened and divided up by granulometric classes . The granulometric fractions obtained are allocated and processed in a differentiated manner . The fractions which are already of the desired sizes, after demetallisation, are sent to the final maturation storage facility . The other, coarser, fractions, after separation of metals and, where appropriate, of the lightweight fractions, are sent to appropriate rod mills according to their granulometric characteristics . The coarser fraction, generally containing pieces selected by 8 cm to 20 cm clearance screening, is processed in a rod mill, preferably characterised by the following :

[0070] • End peripheral discharge rod mill with :

[0071] o a large through-bore diameter inside the bearing, i . e . an internal diameter greater than 40 cm, preferably greater than 50 cm, more preferably greater than 55 cm, most preferably greater than 60 cm, and openings for the exiting of the material of sizesequal to or preferably greater than the maximum sizes selected for the feeding, which openings can be reduced in number and / or covered, at least in part, by means of perforated plates or grates, in order to increase the residence time for the material inside the mill; increasing the residence time can be achieved by limiting, at the construction stage of the mill, the number of openings or, preferably, by covering the openings or, more preferably, by covering a significant number of openings with perforated plates, grates or similar, with holes of suitable clearances (in general, with clearances of between 3 mm and 12 mm, preferably between 5 mm and 9 mm) ; such perforated plates or grates provide for a faster evacuation of fine material, notably improving the yield of the grinding; in particular, the presence of the perforated plates or the grates determines a granulometric classification simultaneously with the grinding, allowing the already sufficiently fine particles to quickly exit the mill, while the coarser particles remain for a longer time inside the grinding chamber .

[0072] o preferably the feed intake is equipped with a feeder which rotates integrally with the rod mill, since it is joined to it, and is equipped with an internal auger (or equivalent system which pushes the material towards the inside of the mill) which continues, even if in a reduced cross-section, inside the bearing until the grinding chamber and allows all the pieces, even the coarse ones, to be pushed into the mill, clearing the obligatory horizontal passage stretch inside the bearing; this is extremely useful, for example, for non-f erromagnetic metal pieces of particularly elongated shape ( for example stainless steel sections ) , not separated using magnetic separators, which can pass through the openings of the screen even though they are particularly sizeable lengthwise and which, in the absence of a rotating feeder with internal auger, would tend to easily clog up the feeding of the mill .

[0073] The less coarse fraction, in general passing through the 10-20 mm clearance screen, is sent to another rod mill, which also preferably has the following characteristics :• End peripheral discharge rod mill with :

[0074] o through-bore diameter inside the bearing greater than 35 cm, preferably greater than 40 cm, more preferably greater than 45 cm;

[0075] o a reduced number of openings for the exiting of the material, which can be achieved either by providing, at the construction stage, a reduced number of openings than usual or, preferably by closing or covering the openings or, more preferably, by covering a good number of the openings with perforated plates or grates, for example perforated plates, with suitably sized holes (in general, with clearances of between 3 mm and 12 mm, preferably between 5 mm e 9 mm) , bearing in mind that the peripheral speed of the mill is much higher than the peripheral speed of a screen, which affects the selection efficiency; the perforated plates or grates or similar provide for a faster evacuation of fine material, notably improving the yield of the grinding; in particular, the presence of the perforated plates or the grates determines a granulometric classification simultaneously with the grinding, allowing the already sufficiently fine particles to quickly exit the mill, while the coarser particles remain for a longer time inside the grinding chamber;

[0076] o preferably, there is fitted upstream of the inlet bearing a feeder which rotates integrally with the rod mill, since it is joined to it, equipped with an internal auger (or equivalent system which pushes the material towards the inside of the mill) which continues, even if in a reduced cross-section, inside the bearing until the grinding chamber and allows all the pieces to be pushed into the mill, clearing the obligatory horizontal passage stretch inside the bearing; this is extremely useful, for example, for materials such as stainless steel wires not separated using magnetic separators which, having diameters, forexample, of 3-6 mm, can pass through the 10-20 mm clearance screens, but can be very long ( for example, 20-30 cm) and therefore could easily clog up the feeding in the absence of an auger feeder .

[0077] In Figure 1, there is represented a rod mill 1 according to the present invention, preferably connected to a feeder 2 which pushes the material to pass through the hole 3, inside the bearing 4, to reach the grinding chamber 5, inside which there are the grinding rods 6.

[0078] This end peripheral discharge rod mill is equipped with openings 7 , some of which are covered with perforated plates 8, and an end support bearing 9.

[0079] Based on the present invention, with particular regard to the processing of the coarser fraction, the diameter of the hole 3 and the openings 7 are relatively large, in order to enable both the loading and discharging of pieces of slag even containing metallic scraps that are rather large and much larger than those occurring in common rod mills . Moreover, a large number of the openings 7 are covered with perforated plates, such as in 8, achieving :

[0080] • a faster evacuating of the already fine fractions, • a lengthening of the residence time in the mill for the coarser fractions .

[0081] In particular :

[0082] 1. in the case of the processing of the coarse fraction :

[0083] • it is preferred that the passage (3) inside the bearing (4 ) has a diameter greater than 40 cm, it is further preferred that it has a diameter greater than 45 cm and it is even more preferred that it is greater than 50 cm and most preferred a diameter greater than 60 cm .

[0084] • it is preferred that the openings 7 have sizes equal to or larger than the openings of the screen which feeds said mill and which selects the maximum sizes ; preferably, the openings ( 7 ) , with respect to the maximumsizes of the fractions at the inlet, have diameters of more than 20% larger, and more preferably more than 30% larger .

[0085] • it is preferred that, upstream of the mill 1, there is a feeder 2 equipped with a system suitable for pushing the material towards the inside of the grinding chamber 5, also passing through the hole 3.

[0086] Typically, the feeder 2 and hole 3 are equipped with an internal auger . The feeder 2, which preferably rotates integrally with the mill to which it is joined, is preferably equipped with an internal auger or feed screw or device performing the function (for example based on vanes ) , the direction of rotation of which pushes the slag towards the inside of the mill, according to the prior art .

[0087] In Figure 2, there is represented an axial peripheral discharge rod mill 10 according to the prior art, used for comparison purposes, connected to a feeder 11 which pushes the material through the hole 12 , inside the bearing 13, to reach the grinding chamber 14, inside which there are the grinding rods 15. The ground material therefore flows out from the opening 16 to the inside of the bearing 17 .

[0088] End peripheral discharge mills generally have flow rates much higher than axial discharge mills and produce lower quantities of fine particles . According to the present invention, for the purposes of the grinding of the slag, it is important to be able to benefit from the characteristics of the dynamics of the grinding of end peripheral discharge rod mills, limiting however the speed of transit and increasing the average residence time for the fraction to be ground inside the mill . With the openings being larger in size than usual, it is possible to achieve this by reducing the number of openings and / or, preferably, partially closing a certain number of openings by means of perforated plates or grates or similar, with 3 mm to 12 mm clearance perforations or openings, preferably 5 mm to 9 mm, which let the material that is already within a certain fineness to pass through, processing the coarser material for longer, bearing inmind that the peripheral speed of the mill is much higher than the peripheral speed of a screen, which affects the efficiency of the selection . As an indication, the flow rate of an end peripheral discharge rod mill thus modified is preferably reduced to values approximately equal to half the flow rate that is usual for this type of mill . In more general terms, the flow rate of the mill can be reduced to values of approximately between 25% and 75% of the nominal flow rate of the same mill operating without covering the discharge openings . The purpose of such a reduction in the flow rate is to increase the average residence time for material inside the mill, while maintaining the possibility of quickly evacuating the already sufficiently fine particles . It is noted that the same principles of functional modification of the mill, and in particular the limitation of the flow rate by means of reduction and / or covering of the material outlet openings, can be applied not only to end peripheral discharge rod mills but also to central peripheral discharge rod mills, achieving similar results in terms of control of the grinding and granulometric distribution . Therefore, reference to end peripheral discharge configurations must be understood as being preferred and not limiting .

[0089] It is appropriate to provide a second mill, intended to grind the granulometrically intermediate fraction between the coarse fraction and the fraction of the desired size, in general between 2 mm and 20 mm. A large part of the slag falls into this granulometric fraction . In this case, the passage of the hole 3, inside the bearing 4 , does not require particularly larger size than normal . Similarly, the openings 7 can have normal clearances, but it is appropriate that they are either limited in number or, more preferably, covered with perforated plates or grates or similar, with hole or opening clearances of between 3 mm and 12 mm, preferably between 5 mm and 9 mm, in order to limit the flow rate, in the same proportions already identified and to accelerate the evacuation of already relatively fine fractions . The number of openings to be closed with perforated plates or grates is normally adjusted empirically during the grinding. Alsoin this case, it is noted that the same principles of functional modification of the mill, and in particular the limitation of the flow rate by means of reduction and / or covering of the material outlet openings, can be applied not only to end peripheral discharge rod mills but also to central peripheral discharge rod mills, achieving similar results in terms of control of the grinding and granulometric distribution . Therefore, reference to end peripheral discharge configurations must be understood as being preferred and not limiting .

[0090] In both the abovementioned cases, the essential aspect does not lie in the specific geometric configuration of the discharge of the mill, but rather in the control of the flow rate and of the residence time for the material inside the mill . When processing incinerator slag, the behaviour of the rod mill differs significantly from that observed in the grinding of homogeneous mineral materials . Indeed, the slag contains a considerable quantity of metallic bodies which do not crush down during the grinding and which interfere with the typical grinding mechanism of rod mills .

[0091] In traditional grinding processes, such metallic bodies tend to reduce the efficiency of the process, since they impede the gradual reduction of spaces between the rods which normally allows the finer particles to advance and exit from the mill without being further ground.

[0092] In the present invention, this behaviour is exploited through a combined regulation of the flow rate of the mill and of the conditions of evacuation of the ground material . In particular, the reduction in the flow rate of the mill and the presence of openings covered by means of perforated plates or grates determine :

[0093] • a faster evacuation of already sufficiently fine particles ;

[0094] • an increase in the average residence time for the coarser fractions;

[0095] • a reduction in the damping effect exerted by the fine fractions on the grinding bed.This provides for achieving a more selective and energetically more efficient grinding as compared with traditional rod mills . In particular, this effect is particularly evident in the processing of slag containing uncrushable metallic bodies .

[0096] Unlike processes in which the desired granulometry is achieved predominantly by selection downstream of the crushing, in the present invention the control of the granulometric distribution is achieved mainly by regulating the flow rate and the residence time for the material inside the mill with simultaneous granulometric classification by means of perforated plates or grates . This approach provides for reducing the residence of the already sufficiently fine particles in the mill, preventing phenomena of excessive grinding and limiting the production of ultrafine fractions . The present invention is based on the technical principle of limiting, along the entire production process, the energy intake and the conditions that favour undesired reactions, preventing both an excessively intense grinding, and an excessive supply of water in the next phases of use . In general terms, the present invention is based on the technical principle according to which the stabilisation of the material is not achieved by extreme treatments, but rather by a balanced control of operational conditions along the whole process . The set of characteristics described here provides for achieving an overall technical effect, consisting of the possibility of using aggregates derived from incinerator slag in high percentages in the production of cementitious manufactured products, while maintaining the pop-out phenomena within non-detectable or in any case technically harmless levels, all this without resorting to high energy consuming wet treatment and grinding processes . In other words, the present invention provides for achieving an equilibrium between stability of the material, industrial simplicity of the process and cutting of energy consumption, which is not achievable by means of the known separation and intense grinding processes alone .

[0097] When it is desired to proceed with the incinerator slag recovery process according to the present invention, the slag,quenched after incineration, is collected and sent to the plants or to the slag recovery sections thereof . Initially, it is preserved for 2-4 weeks, to allow the moisture to reduce naturally, and it is then subjected to processing.

[0098] The slag 18, fed at the first processing step 19 in which the excessively coarse and / or undesired fractions are separated from the slag, may also comprise a first step for removing ferrous metals . This step 19 can be performed both by machinery, and, in part, manually, according to techniques and methods known in the art . Under step 19, the excessively coarse fractions, for example those that do not pass through screening with clearances in general of between 10 cm and 20 cm or equivalent size, if selected in a different way, for example manually, can also be reduced volumetrically , for example by means of a crusher, and reintroduced in the cycle .

[0099] Downstream of step 19, the slag is in general sent to a screening step 20 to be divided into granulometric classes .

[0100] In general, there are three granulometric classes for material intended to continue in the process : the material within the desired sizes, exiting from 21 (<2 mm) , the intermediate fraction, exiting from 22 (in general, smaller than 10-20 mm) and the coarse fraction exiting from 23 (in general, smaller than 10-20 cm) . It is however suitable to also provide an outlet for a fourth granulometric fraction 24 (the excessively coarse one, for example, larger than 10-20 cm) which, after possible preservation in a storage facility, is reintroduced into step 19, thus enabling in fact a second step against the risk that metallic fractions of elongated shape and particularly bulky ones continue in the process in the next steps, running the risk of becoming jammed.

[0101] Next, the process continues as follows .

[0102] • The granulometric fraction of the desired size 21 is demetallised, in particular removing the ferromagnetic metals, in step 25, and sent to the final maturation process in the storage facility 26 with the addition of water 27, preferably during handling and / or introduction; on this veryfine fraction, the technologies for separating non-ferrous metals have little effectiveness;

[0103] • The intermediate granulometric fraction 22, after a demetallisation step (in general, it is limited in this step to the separation of ferrous metals) and possible separation of lightweight fractions 28, is sent for grinding 29, preferably carried out using the end peripheral discharge rod mill 1 with characteristics suitable for the intermediate fraction;

[0104] • The coarse granulometric fraction 23, after a possible demetallisation step (in general, it is limited in this step to the separation of ferrous metals ) and possible separation of lightweight fractions 30, is sent for grinding 31, preferably carried out using the end peripheral discharge rod mill 1 with characteristics suitable for the coarse fraction;

[0105] • In the three cases set out above, the moisture of the particles being ground is less than 12-15% . In particular, this moisture is between 2% and 12% by weight, preferably between 3% and 8% by weight . Thus, there is neither an excess of dust nor a packing of the ground material .

[0106] Downstream of the grinding step 29 :

[0107] • the material is screened, exiting from 32 :

[0108] • the fraction 33, of the desired size, is demetallised 34 (as for the fraction 21, in general, it is limited to ferrous metals ) and sent for maturation 26 with the addition of water 27, preferably during handling and / or introduction;

[0109] • the material of intermediate size, exiting from 35, is demetallised in step 36 and sent to the intermediate maturation step 37 with the addition of water 43, preferably during handling and / or introduction;

[0110] • the coarse material, exiting from 38, formed in very large part by metals, is subjected to separation 45between ferrous and non-ferrous metals, subsequently destined for recovery / reuse in respective metallurgical sectors, and lightweight fractions .

[0111] Downstream of the grinding step 31 :

[0112] • the material is subjected a screening step 39 : the fraction exiting from 40, of the desired size, flows into the demetallisation stage 34 and, then, to the storage facility 26, together with the fraction 33 or by a similar route, with the associated addition of water 27 , preferably during handling and / or introduction;

[0113] • the fraction of the intermediate size, exiting from 41, is subjected to a demetallisation step 42 (naturally, the fractions 35 and 41 can also be brought together before carrying out only one demetallisation process ) and sent for intermediate maturation in the storage facility 37 with the addition of water 43, preferably during handling and / or introduction;

[0114] • the coarse material, exiting from 44, formed in very large part by metals, is subjected to being divided up 45 between ferrous and non-ferrous metals, subsequently destined for recovery / reuse in respective metallurgical sectors, and lightweight fractions .

[0115] Downstream of the intermediate maturation in the storage facility 37 , the material exiting from 46 can be reintroduced into the grinding cycle in the grinding step 29 or, alternatively, in step 19 or 20 or, alternatively, it can be processed in other parts of the plant, not indicated here, to be subjected to further grinding . A possible benefit of reintroducing it from step 19 or 20, rather than from step 29 is related to the opportunity of making available, when the plant is being fed and from step 19 or 20, a material which can usefully contribute to maintaining a moisture content within optimal intervals, and this can more easily be achieved by mixing fresh slag and materials that have already been partially processed.Regarding the separation of metals and lightweight fractions, the following is to be taken into consideration . The ferromagnetic metals are easily separated by magnets ; however, it is appropriate that this takes place gradually on fractions that are granulometrically as homogeneous as possible and, in large part, after the material has transited from the grinding, which brings about a detachment between the metal and the mineral fraction of the slag . Proceeding with the separation of metals for homogeneous fractions, for those which are much more difficult to be separated, applies also for non-ferrous metals, in general, separated by parasitic currents, but also using other technologies . The technologies for separating fractions of nonferrous metals of size of less than 2 mm are, at present, not very effective .

[0116] Still according to the prior art, the metals, both ferrous and non-ferrous, can also be separated simply by screening downstream of the grinding steps in which the minerals are crushed, while the metal, which is not crushed, is at most deformed, thus making a size-based separation downstream of the grinding effective . The metals thus recovered can be divided up and then directed, after possible further processing, to dedicated markets thereof, with considerable environmental and economic advantages . The separation of the lightweight fractions can, on the other hand, be carried out by means of air jets, according to the prior art .

[0117] Preferably, after the outlets 7 and 8, the slag being processed is subjected to screening, demetallisation and separation of the lightweight fractions .

[0118] Preferably, the screening takes place in several steps or levels, to prevent the screening clearances from clogging up . The aggregate of the desired size has particle size of less than 2 mm for 98-99%, preferably less than 1. 6 mm for 98-99%, more preferably less than 1. 4 mm for 98-99%, most preferably less than 1.25 mm for 98-99% . The figures indicated represent a particularly advantageous operational threshold, not necessarily unique . For clarity and to avoid any misunderstandings, it is noted that inEurope the EN standards relating to aggregates provide a classification thereof in which up to 10% by weight of oversize material is tolerated; therefore, a 0 / 2 mm classification could mean that only 90% of the particles is less than 2 mm. Now, such a tolerance may not bring about the desired results, with excessive pop-out phenomena . However, oversize material of 1% or 2% by weight is acceptable .

[0119] Although the optimal size is very small, as just indicated, it is worthwhile ensuring that there are not excessive quantities of particles of size smaller than 0.063 mm, otherwise the water requirement during concrete production would be excessive . By regulating the grinding, it is sought to have a content of very fine particles (i . e . with particle size smaller than 0.063 mm) of less than 30% by weight, preferably less than 25% by weight, more preferably less than 20% by weight, most preferably less than 15% by weight .

[0120] Ideally and consistently with the abovementioned limits, there should be a content of particles having particle size of between 0. 063 mm and 1 mm of more than 40% by weight, preferably more than 50% by weight, more preferably more than 60% by weight .

[0121] After each grinding, screening and separation phase in the chosen steps and sequences, the fractions collected are then sent to a maturation step .

[0122] The aggregate fraction which already has the desired size is sent, for maturation, to a storage facility, with an initial moisture level of between 10% and 18%, preferably higher than 12%, more preferably between 12% and 16%, for a period longer than one week, preferably longer than two weeks, more preferably longer than three weeks . Thus, there is :

[0123] o maturation, with loss of moisture,

[0124] o a certain degree of corrosion of the metallic residues that could not be separated from the mineral fraction,o the development of alkali-aggregate and alkali-silica reactions in a context in which they do not produce any damage .

[0125] This maturation contributes to reducing the pop-out phenomena in the manufactured products to negligible levels . Indeed, it is unnecessary to completely suppress the phenomenon but only to reduce it to a level that is difficult to detect (aesthetic reasons) and which does not lead to a worsening of the mechanical properties of the final manufactured product (technical reasons) .

[0126] The material fraction which does not yet have the desired size is sent, after demetallisation, for maturation in a storage facility, with an initial moisture level of between 7% and 18%, preferably higher than 9%, more preferably between 9% and 16%, for a period longer than one week, preferably longer than two weeks, more preferably longer than three weeks during which the temperature of the material is maintained at mostly above 40 °C . Thus, there is maturation, with loss of moisture and corrosion of metallic residues that could not be separated and possibly recovered, and the development of alkali-aggregate and alkalisilica reactions . Once the maturation is completed, the material is sent again to the processing steps described above, having to, where necessary, repeat them until the aggregates attain the desired size .

[0127] At the end of the processing, the pop-out phenomenon, which no longer occurs with significant effects , becomes negligible; the moisture in the slag, ground and moistened, is reduced; the temperature, due to the petering out of the exothermic reactions and dispersion into the environment, is reduced. In any case, before the aggregates obtained are used, a maturation phase is carried out, preserving them in a storage facility for a period of between one and four weeks, with an initial moisture content of between 10% and 18%, preferably higher than 12%, more preferably between 12% and 16% . Following this maturation, the aggregates can be used for concrete production .The set of characteristics described above must be understood to be collaborative in defining the technical principle of the present invention, being able however to be adopted with various intensities and combinations, as a function of the specific operational conditions and of the desired performance level .

[0128] The aggregates obtained according to the present invention can also be used in the production of ordinary concretes, of cementitious products or high-fluidity mortars (i . e . not of "moist earth" consistency) , or, particularly in a quantity of between 2% and 10% by weight, in the production of blended cements (use today limited by regulatory constraints which would require an update via an EAD-ETA route, at least in Europe) , the requirement still remaining, in these applications, to consider the occurrence of expansion phenomena, although contained by virtue of the processing according to the present invention, which are connected with the residual presence of metallic aluminium and / or of other reactive metals in the presence of a significant quantity of water actually available in the cementitious slurries . Therefore, in these uses, the slag-based aggregate is preferably used in small percentages and / or in combination with further approaches known to the person skilled in the art, while the heavy use of slagbased aggregate is particularly advantageous in the production of vibropressed concretes of "moist earth" consistency, in which the limited availability of water drastically reduces corrosion reactions in the plastic phase and, therefore, the occurrence of expansion phenomena . In such fluid applications, aggregate obtained from slag is generally used in small percentages, typically of the order of a few percentage points ( for example about 2-7% by weight of total aggregate or of the cement constituents ) , in order to contain possible expansion phenomena .

[0129] Therefore, by virtue of the present invention, it is possible to expand the use of the slag even to ordinary concretes, while recognising that the most advanced and cost-effective use is in water-based vibropressed processes .

[0130] The aggregates obtained can be used to produce vibrocompressed concrete, because of their notable pozzolanicand / or geopolymeric properties and the tendency to not exhibit the pop-out phenomenon, therefore providing for obtaining manufactured products and plasters and / or premixed products of high quality, both from an aesthetic and technical performance perspective .

[0131] A particular use of aggregates produced as described previously is in the production of manufactured products for the construction trade, and, in particular, masonry blocks . Based on the present invention, it is possible to obtain manufactured products and masonry blocks made of concrete, using as aggregate the particles obtained according to the previously described process . Preferably, these manufactured products and masonry blocks are produced using a quantity of aggregate, obtained according to the above process, of greater than 30% by weight based on dry components . More preferably, the aggregate content is greater than 40% by weight based on dry components . Even more preferably, the aggregate content is greater than 50% by weight based on dry components . More preferably, the aggregate content is greater than 60% by weight based on dry components . Most preferably, the aggregate content is greater than 70% by weight based on dry components . Particularly preferred is a lightweight manufactured product for the construction trade, made of concrete, characterised in that the concrete for producing said manufactured product comprises aggregates obtained from incinerator slag from which the ferrous and non-ferrous metals and lightweight fractions have been separated, within the limits of technical possibilities, and all ground down to sizes of less than 2 mm for more than 98-99%, preferably less than 1. 6 mm, more preferably less than 1. 4 mm, most preferably less than 1.25 mm, and in that said manufactured product is produced by means of a vibrocompression process .

[0132] Based on one embodiment of the present invention, the manufactured products for the construction trade and / or masonry blocks are produced from vibrocompressed concrete . During preparation, the cementitious mixture, because of the high fineness of the aggregates used, it is preferable to provide awater / cement ratio greater than 0.55, more preferably greater than 0. 60 and most preferably greater than 0. 65. With these quantities of water, a particularly lightweight manufactured product is obtained (dry density of 1, 400-1, 900 kg / m3, preferably 1, 400-1, 800 kg / m3, more preferably 1, 500-1, 750 kg / m3, most preferably 1, 550-1, 750 kg / m3, and a porosity greater than 15%, but sometimes greater than 20% or greater than even 30%) . The high porosity of the manufactured product obtained contributes to determining optimal properties of thermal insulation . The vibrocompressed concrete masonry blocks obtained according to the present invention are also advantageously very breathable .

[0133] When preparing the concrete, additives can also, appropriately, be used as follows :

[0134] • polyacrylate- or polycarboxylate-based additives, in dosage, with respect to the weight of the cement - expressed as dry on dry, even though they are used in aqueous dispersion - of greater than 0.2% by weight, preferably greater than 0.25% by weight, more preferably greater than 0.3% by weight, most preferably greater than 0.35% by weight; these additives provide clear improvements to the performance of the present invention;

[0135] • naphthalene sulfonate-based additives, also in dosage, with respect to the weight of the cement - expressed as dry on dry, even though they are used in aqueous dispersion - in a quantity of greater than 0.4% by weight, preferably greater than 0.5% by weight, more preferably greater than 0. 6% by weight, most preferably greater than 0.7% by weight; these dosages have never been used in the past and lead to notably improved results ;

[0136] • hydrophobic or water-repellent additives, such as stearate-based products, also in dosage, with respect to the weight of the cement - expressed as dry on dry, even though they are used in aqueous dispersion - in a quantity of between 0.5% and 2% by weight of the cement; stearate-based additives can be obtained from other kinds of waste, by suitable regeneration processes .In addition to the characteristics of lightness and robustness - which allow them to be handled easily, even by hand - the manufactured products and masonry blocks according to the present invention do not exhibit the pop-out phenomenon to an appreciable extent, in any case to a harmless degree .

[0137] The present invention provides for reusing waste incinerator slag, with a device suitable for grinding it into a size such that the concrete into which it is introduced as aggregate is given pozzolanic and / or geopolymeric properties, without exhibiting the pop-out phenomenon, also enabling extremely lightweight vibrocompressed concrete masonry blocks to be produced. The present invention does not require slag washing steps and the absence of such operations for washing ground slag is an enormous advantage from an industrial point of view, since these operations are very expensive .

[0138] The technical effect sought by the present invention is generally achieved by a combination of process approaches which collaborate with each other . In particular, the reduction of the pop-out phenomena to non-detectable levels, in any case harmless levels in practice, can be encouraged by one or more of the following factors : 1 ) granulometric selection, 2 ) dry grinding, 3) controlled moistening, 4 ) maturation, 5) control of temperature and residence times and maturation . How much depends on these factors may depend on the final granulometry and on the actual operational conditions, although not departing from the present invention and from its claims . The approach described and claimed provides for obtaining, in a simple way from an industrial point of view and with relatively low energy consumption, aggregates suitable for producing cementitious manufactured products of high quality, minimising the formation of surface phenomena such as pop-outs . The operational conditions just mentioned are to be understood as an element cooperating with the process, some of them able to influence the result of the process . Therefore, it is not necessary for all the operational approaches to be present at the same time, nor for them to be present with the same intensity .EXAMPLES

[0139] The following examples relate to the effectiveness achieved in terms of minimising pop-out phenomena using screens, with specific clearances in the screening surfaces, and maturation methods .

[0140] Example 1

[0141] A process according to the present invention was implemented. Particles of desired fineness were selected by trommel screens, with 3 mm clearance screening meshes . At the end of the processing, about 99% of the particles were <2 mm and only 1. 1% >2 mm. The granulometry thus obtained was subjected to successive wet maturation steps, with initial moisture of approximately 13.5% which, over the course of two weeks, was reduced to approximately 10% .

[0142] The outcome of this preparation was that vibropressed manufactured products were produced (in the form of masonry blocks ) containing approximately 80% (referring to dry on dry content) of aggregate obtained from incinerator slag, and the results were good in the sense that only a very small quantity of pop-out phenomena and of very small size was visually detected.

[0143] To verify the mechanical properties, the vibropressed concrete samples were subjected to compressive strength tests after 7 days, 28 days, 90 days and after steam curing cycles at 60 °C for 72 hours .

[0144] From these tests, repeated a high number of times, the result was that :

[0145] - between 7 days and 28 days, an average increase in mechanical strength of 20% occurred, similar to that for type I and type II cements ;

[0146] - between 28 days and 90 days, a further average increase in mechanical strength of 20% occurred, similar to that for type III, type IV and type V cements, thus confirming good pozzolanic and / or geopolymeric reactivity;- the steam curing cycles, suitable for activating any alkali-silica or alkali-aggregate reaction phenomena and pop-out phenomena, did not bring to light a reduction in mechanical strengths with respect to the strengths at 90 days, with very small and hardly visible surface pop- out phenomena .

[0147] Example 2

[0148] It was proceeded as in Example 1, but with the difference of using 2.5 mm clearance screening meshes . The screening resulted in 99% of the particles <1. 6 mm and only 1. 1% >1. 6 mm. In the subsequent use of the aggregate for the production of vibropressed manufactured products, downstream also of wet maturation phases, identical to those of the previous experiment and indicated above, pop-out phenomena that are normally visually perceivable did not arise .

[0149] To verify the mechanical properties, the procedure exactly as illustrated above was carried out, obtaining the same results :

[0150] - between 7 days and 28 days, an average increase in mechanical strength of 20% occurred, similar to that for type I and type II cements ;

[0151] - between 28 days and 90 days, a further average increase in mechanical strength of 20% occurred, similar to that for type III, type IV and type V cements, thus confirming good pozzolanic and / or geopolymeric reactivity;

[0152] - the steam curing cycles, suitable for activating any alkali-silica or alkali-aggregate reaction phenomena and pop-out phenomena, did not bring to light a reduction in mechanical strengths with respect to the strengths at 90 days, with very small and hardly visible surface pop-out phenomena .

[0153] Therefore, a fully satisfactory result . It is considered however that further enhancements in terms of fineness, <1.25 mm, may provide for working with wider safety margins and operating in a "comfort zone" .From these examples, it is clear that it is necessary to take into account the effective efficiency of the screening, influenced also by the moisture : using a trommel screen with 3 mm and 2 .5 mm clearance holes, almost all the particles (around 99%) were smaller than 2 mm and 1. 6 mm respectively .

[0154] Example 3

[0155] In order to verify the efficiency of the grinding of end peripheral discharge rod mills according to the present invention as compared with axial discharge rod mills, the following experiment was conducted:

[0156] Inside the same incinerator slag processing plant, the following were present :

[0157] • an end peripheral discharge rod mill, intended for grinding the coarser fraction (passing through the 9 cm clearance screen) , which mill had been modified according to the present invention, i . e . , in particular, with 20 outlet openings 7 , having circular cross-sections with 9 cm diameters, 10 of which were covered as in 8 with perforated plates having 8 mm clearance . The machine details are as follows :

[0158] o machine weight without rods : 23, 100 kg;

[0159] o rod load: 11, 000 kg;

[0160] o motor power : 90 kW;

[0161] o average power consumption : 38 kWh approx

[0162] • an axial discharge rod mill intended for grinding the intermediate fraction (2 mm - 15 mm) :

[0163] o machine weight without rods : 39, 000 kg;

[0164] o rod load: 17 , 000 kg;

[0165] o motor power : 200 kW;

[0166] o average power consumption : 80 kWh approx The performance comparison between the end peripheral discharge rod mill and the axial discharge rod mill was as follows :

[0167] With the same flow rates, of about 7 t / h and despite the axial discharge mill consumption (80 kWh) being more than double that of the end peripheral discharge mill (38 kWh) , the endperipheral discharge mill was capable of much better grinding than the axial discharge mill as can be deduced from the following table :

[0168] End peripheral discharge

[0169] rod mill according to the

[0170] present invention Axial discharge rod mill

[0171] retained through through retained through through Screen at sieve 2 mm 1 mm at sieve 2 mm 1 mm clearance of screen screen of screen screen mm clearance clearance

[0172] 5 . 6 0 0. 1

[0173] 4 0.5 0.2

[0174] 2 7 . 8 19.3

[0175] 1 25.5 36. 7

[0176] 0.5 21.5 19. 1

[0177] 0.25 14 . 9 10. 8

[0178] 91. 7 80 . 4

[0179] 0 . 125 11.3 66.2 7 . 3 43 . 7 0 .063 9. 1 3. 9

[0180] bottom 9. 4 2 . 6

[0181] total 100 100

[0182]

[0183] This indicates a very significant difference in yield, which can be summarised in the capacity to produce particles of granulometry passing through the 2 mm sieve, related to the energy consumption, as follows :

[0184] • end peripheral discharge rod mill modified according to the present invention : 6 kWh / t

[0185] • axial discharge rod mill : 14 kWh / t,

[0186] which means that consumption has more than halved.If the above comparison is made in relation to the particles passing through the 1 mm sieve, this results in an even greater macroscopic difference, as follows :

[0187] • end peripheral discharge rod mill modified according to the present invention : 8.2 kWh / t

[0188] • axial discharge rod mill : 22.3 kWh / t, which means consumption of 37% approx, i . e . a reduction in consumption of 63% approx .

[0189] The experimental results show that the technical effect achieved cannot be attributed solely to the reduction in the flow rate of the mill, but to the combination of limiting the flow rate and the selective evacuation of the fine fractions through the covered openings .

[0190] It is understood that the invention must not be considered to be limited to the particular arrangement illustrated above, which forms only one example embodiment thereof, but that various variants are possible, all within the capabilities of a technician skilled in the art, without thereby departing from the scope of protection of said invention, which scope is defined in the claims that follow.LIST OF REFERENCE SYMBOLS

[0191] 1 rod mill

[0192] 2 feeder (of 1 )

[0193] 3 hole (of 4 )

[0194] 4 feed bearing (of 1 )

[0195] 5 grinding chamber (of 1 )

[0196] 6 grinding rods (of 1)

[0197] 7 outlet openings (of 5)

[0198] 8 perforated plates (of 7 )

[0199] 9 bearing (of 1)

[0200] 10 axial discharge rod mill

[0201] 11 feeder (of 10)

[0202] 12 internal hole (of 13 )

[0203] 13 feed-end bearing (of 10)

[0204] 14 grinding chamber (of 10)

[0205] 15 grinding rods (of 10 )

[0206] 16 discharge opening (of 10 )

[0207] 17 bearing (of 10 )

[0208] 18 slag feeding

[0209] 19 first slag processing step

[0210] 20 screening

[0211] 21 exit of desired-size material fraction ( from 20) 22 exit of intermediate fraction (from 20 )

[0212] 23 exit of coarse fraction (from 20 )

[0213] 24 exit of excessively coarse fraction (from 20 ) 25 demetallisation26 maturation storage for the desired-size material (from 21 )

[0214] 27 addition of water

[0215] 28 demetallisation and separation of lightweights ( from 22 )

[0216] 29 grinding

[0217] 30 demetallisation and separation of lightweights ( from 23 )

[0218] 31 grinding

[0219] 32 screening (from 29)

[0220] 33 exit of desired-size fraction (from 32 )

[0221] 34 demetallisation (from 33 and 40)

[0222] 35 exit of intermediate fraction (from 32 )

[0223] 36 demetallisation (from 35 )

[0224] 37 intermediate maturation step

[0225] 38 exit of coarse fraction (from 32 )

[0226] 39 screening step ( from 31)

[0227] 40 exit of desired-size fraction (from 39)

[0228] 41 exit of intermediate fraction (from 39)

[0229] 42 demetallisation and separation of lightweight fractions (of 41 )

[0230] 43 addition of water

[0231] 44 exit of coarse fraction (from 39)

[0232] 45 separation of ferrous and non-ferrous metals, and lightweight fractions (of 44 )

[0233] 46 exit of material ( from 37 )

Claims

CLAIMS1) Process for the recovery of incinerator slag for the use of this slag as aggregate for the production of concrete and / or blended cement and / or cementitious products, comprising steps of grinding the slag, demetallisation, separation and selection of said slag, characterised in that said grinding is performed with a moisture level of the slag of between 0% and 15% by weight and in that the particles that have, for 98-99%, particle size, determined granulometrically by sieving, of less than 2 mm are used as aggregate .2 ) Process according to Claim 1, characterised in that the grinding is performed with a moisture level of between 2% and 12% by weight .3) Process according to Claim 1 or Claim 2, characterised in that the aggregate is characterised by a particle content, for particles of size less than 0.063 mm of less than 30% .4 ) Process according to any one of Claims 1 to 3, characterised in that the fraction of particles having size of between 0.063 mm and 1 mm is greater than 40% by weight .5) Process according to any one of Claims 1 to 4, characterised in that said grinding takes place in one or more rod mills ( 1 ) .6) Process according to any one of the preceding claims, in which the particles of the desired size are subjected to a maturation step, preserving them in a storage facility, characterised in that the moisture level, when introduced, is between 10% and 18%, for a period of longer than one week .7 ) Process according to any one of Claims 1 to 6, characterised in that two maturation steps (26; 37 ) are provided on the fractions obtained by processing the slag, for a duration of longer than one week, preferably longer than two weeks, more preferably longer than three weeks, one (26) on the fraction of the desired fineness, intended for use, in which the relative humidity when introduced varies from 10% to 18%, the other (37 ) on the fraction of particles of diameter greater than the desiredthreshold, in which the relative humidity when introduced varies from 7% to 18% .8) Process according to Claim 7, characterised in that the maturation step (26) on the fraction of aggregate intended for use takes place with a relative humidity when introduced of between 12% and 18%, while the other maturation step (37 ) takes place with a relative humidity when introduced of between 9% and 18% .9) Lightweight manufactured product for the construction trade, made of concrete, characterised in that the concrete for producing said manufactured product comprises aggregates having particle size, determined granulometrically by sieving, of less than 2 mm for 98-99% .10 ) Lightweight manufactured product for the construction trade, made of concrete, characterised in that the concrete for producing said manufactured product comprises as aggregates materials obtained from incinerator slag, all ground down to particle sizes of less than 2 mm for 98-99%, and in that said manufactured product is produced by means of a vibrocompression process .11 ) Manufactured product according to Claim 9 or Claim 10, characterised in that said aggregates, obtained from incinerator slag, have a particle content, for particles of size less than 0.063 mm of less than 30%, and, for particle size between 0. 063 mm and 1 mm, of greater than 40% .12 ) Manufactured product according to any one of Claims 9 to 11, characterised in that it contains a quantity of aggregate greater than 30% by weight based on dry components .13 ) Manufactured product according to any one of Claims 9 to 12, characterised in that the solid matrix has a dry density of between 1, 400 kg / m3and 1, 900 kg / m3and a porosity greater than 15% .14 ) Manufactured product according to in any one of Claims 9 to 13, characterised in that the concrete for producing said manufactured product also comprises one or more chosen from among the following additives : polyacrylate- or polycarboxylate-basedadditives (in dosage, with respect to the weight of the cement -expressed as dry on dry - of greater than 0.2% by weight) , naphthalene sulfonate-based additives (in dosage, with respect to the weight of the cement - expressed as dry on dry - of greater than 0. 4% by weight ) , stearate-based additives (in dosage, with respect to the weight of the cement - expressed as dry on dry -of between 0.5% and 2% by weight) .15 ) Grinding device, suitable for grinding, in one or more passes, incinerator slag completely down to a size of less than 2 mm, comprising a rod mill (1 ) with peripheral discharge, characterised in that the material outlet openings are at least partly covered by means of granulometric classification elements and in that said granulometric classification elements are perforated plates ( 8) or grates .16) Grinding device according to Claim 14 , characterised in that said peripheral discharge rod mill exhibits an end peripheral discharge .17 ) Grinding device according to Claim 14 , characterised in that said peripheral discharge rod mill exhibits a central peripheral discharge .18 ) Grinding device according to Claim 17 , characterised in that the covering of the openings is such that the flow rate of the peripheral discharge rod mill is reduced to values of between 25% and 75% of the nominal flow rate of the same mill operating without the covering.19) Grinding device (1 ) according to Claim 17 or Claim 18, characterised in that the clearance of the covering plates is between 3 mm and 12 mm, preferably between 5 mm and 9 mm.

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