Cross-Reference to Related Applications

This patent appl ication is related to Italian Patent Application No . 102022000012584 fi led on June 14 , 2023 , the entire disclosure of which is incorporated herein by reference .

Technical Field

The present invention refers to an agglomerated product for use in a steelmaking process , especially for use in a process for the production of steel in an electric arc furnace ( EAF) .

State of the Art

Steelmaking processes are processes well known in the art , through which iron and ferrous alloys , such as cast iron and steel , are produced starting from ores or from scrap, by-products and ferrous-based waste . In the steel sector, the production of steel in the EAF furnace is one of the steel production technologies with the lowest environmental impact , as it uses scrap, by-products and postconsumer ferrous waste as a starting ferrous material .

The cycle of production of the steel in the EAF furnace (EAF cycle ) essentially involves the following steps : ( i ) loading the ferrous material to be melted into the EAF furnace ; ( ii ) melting the charge by means of an electric arc that is sparked between the electrodes of the furnace and the charge itsel f ; ( iii ) refining of the molten metal bath to obtain the steel with the desired chemical composition . The liquid steel obtained at the end of the refining step is subsequently processed to obtain the final solid products .

At di f ferent times of the EAF cycle it is required to introduce further materials or compounds into the furnace , such as carbonaceous materials , gaseous oxygen, quicklime , alloying compounds , etc .

The most commonly used carbonaceous materials (hereinafter also referred to as "carbon sources" ) are materials of fossil origin and derivatives therefrom, such as anthracite and coke . These carbon sources are mainly used as chemical energy sources ( fuels ) , reducing agents to recover iron oxides that are formed during melting and to control the content of carbon in steel or as foaming slag forming agents . Typically, the above carbonaceous materials are employed in an amount of about 10 - 15 kg/ 1 of steel produced .

The carbon sources are generally fed into the furnace in coarse si ze , when they are charged together with the starting ferrous material ( so-called "charge carbon" ) . When introduced during the step of melting or refining, instead, the carbon sources are generally in powdered form (pulveri zed carbon) and are inj ected directly into the liquid metal bath or into the floating slag above the bath, for example by means of lances using a gaseous flow as a carrier agent ( so- called " inj ected carbon" ) .

To limit the consumption of materials of fossil origin and compensate for the carbon dioxide emissions generated by them, in the EAF cycle it is known to use alternative " sustainable" or non- fossil carbon sources , in at least partial replacement of the charged and inj ected carbon . The alternative carbon sources include mainly thermoplastic materials and biomass products , such as woody biomasses and carbonaceous materials of biogenic origin ( so-called "biochar" ) .

The thermoplastic materials used in the steel industry and, in particular, in the EAF cycle , generally consist of residues from the recycling processes of the plastic materials , in particular those deriving from the separate collection of municipal waste ( e . g . polyolefin materials used for packaging, such as bottles , containers , fi lms , etc . ) and industrial waste from the production processes of plastic products . The residues of the recycling processes of the elastomeric materials , in particular the elastomers deriving from the recycling of tyres , are also used .

The thermoplastic materials represent an important alternative carbon source to the conventional fossil carbon sources due to the chemical composition of the polymers of which they are composed, the latter being mainly constituted by chains of carbon and hydrogen atoms . The thermoplastic materials also have the advantage of being widely available in every industriali zed area of the world .

The use of the thermoplastic materials in the steelmaking processes , however, has several drawbacks .

Firstly, due to their low density, the thermoplastic materials in addition to having di f ficulty in penetrating the metal bath tend to be easily entrained and captured by the flue gas suction system of the furnace ( carryover) , without entering into contact with the molten metal bath or the slag . The dosed thermoplastic material , therefore , has a limited ef fectiveness of use .

To overcome the aforesaid problem, the thermoplastic materials can be subj ected beforehand to dens if ication processes which give the material a form and density more suitable for use in a steel furnace ( e . g . granules or pellets ) . The known densi f ication processes , however, are based on hot extrusion of the thermoplastic material , at temperatures of about 200 ° C - 300 ° C, and are generally characteri zed by high energy consumption and a low production yield . An example of a densi f ication process of the prior art is described in W02020230177A1 .

The thermoplastic materials also have a very high reactivity to the conditions of use in the metallurgical furnaces . Therefore, when introduced into the furnace , they are subj ect to a rapid combustion, which prevents the material from entering into contact with the liquid metal bath or the slag with consequent material dosage problems and ignition risks .

The use of the thermoplastic materials according to the prior art also has drawbacks during the operations of conveying and dos ing of the materials to the furnace , which are typically carried out by means of pneumatic systems . In the pneumatic systems , in fact , the heat generated by the friction of the thermoplastic material against the walls of the conveying pipelines can induce locali zed melting of the same with consequent formation of agglomerates , which prevent the correct functioning of the conveying systems and of the devices for the inj ection of the material in the furnace . The aforesaid problems can also occur in the case of the use of carbonized biogenic materials (biochar) obtained from thermochemical conversion processes of biomass as well as non-carbonized biogenic materials (e.g. lignocellulosic biomasses, etc.) .

In the state of the art it is also known to use recycled plastic as a binding material for the preparation of agglomerates by means of which the conventional additives used in the metallurgical processes (e.g. carbon sources, such as coke and anthracite) in pre-dosed form or the scraps or waste of a steelmaking process (e.g. fume abatement dust containing iron oxides, etc.) are fed into the furnace. In these agglomerates, the recycled plastic is present in modest quantities, having essentially the function of keeping the other materials, generally present in a more or less finely divided form, bound together and therefore does not substantially produce any effect as a carbon source alternative to the conventional fossil carbon sources neither give any significant contribution to the chemical energy .

An example of use of recycled plastics as binding material for the production of agglomerates for steel furnaces is described in US7105114B2, which shows the preparation of quicklime briquettes containing 0.5% - 5% by weight of recycled plastics as binder.

Summary of the invention

Considering the aforementioned state of the art, the Applicant has set itself the primary objective of providing a product in agglomerated form capable of overcoming the drawbacks highlighted by the agglomerated products and by the uses of the substances as an alternative carbon source which are known in the state of the art .

In particular, a speci fic aim of the present invention is to provide an agglomerated product that allows to use the carbonaceous materials , especially thermoplastic materials deriving from the recycling of by-products and waste , in a steelmaking process more ef fectively than the products of the prior art .

A second aim of the present invention is to provide an agglomerated product in which it i s possible to control the reactivity and the volatility of the carbonaceous material , so as to avoid phenomena of early combustion or of material loss during use and consequently improve the ef fectiveness of their dosage .

A third aim of the present invention is to provide an agglomerated product that allows to overcome the drawbacks associated with the operations of transport and inj ection of the carbonaceous materials to the furnace according to the prior art .

A further aim of the present invention is to provide an agglomerated product that allows feeding in a metallurgical furnace , in addition to the carbonaceous materials , also other additives useful for the process , without however adding inert or in any case undesired materials for the purposes of the metallurgical process .

The Applicant has found that this aim and others , which will be better illustrated hereinafter, can be achieved by agglomerating the carbonaceous materials with air quicklime , so as to form an agglomerated product having a substantial concentration of carbonaceous material as well as optimal density, volume and si ze for use in a steelmaking process , especially a process for the production of steel in an EAF furnace .

The agglomerated product according to a preferred embodiment has an apparent density from 1 g/cm ³ to 3 g/cm ³ , preferably from 1 . 1 g/cm ³ to 2 . 8 g/cm ³ , more preferably from 1 . 2 g/cm ³ to 2 . 5 g/cm ³ .

It has in fact been observed that it is possible to obtain an agglomerated product having a shape , si ze and density suitable for use in a steel furnace by mechanical compaction of a mixture containing air quicklime and at least one carbonaceous material , both in finely divided form . The compaction process of the mixture of the two materials can be carried out at ambient temperature or by moderately heating the mixture of materials to be compacted to a temperature that is suf ficient to soften or at least partially melt the carbonaceous material ( e . g . polymeric material , high lignin content material , etc . ) , so as to favour the cohesion of the particles that form the agglomerate and therefore its mechanical strength . The process can be carried out with the techniques and the equipment known for the production of lime agglomerates and is therefore simpler and cheaper to be carried out compared to the processes of densi f ication of the plastics of the prior art generally implemented by extrusion, as well as compared to the processes of densi f ication of the biomass materials usually obtained through processes of extrusion, micro-pelletization/pelletization and briquetting optionally using specific binding agents.

The formulation of the carbonaceous material as an agglomerated product together with air quicklime also allows an adequate control of the reactivity and of the volatility of the carbonaceous material, reducing the phenomena of early combustion and of material loss which are caused by the fume collection system and, consequently, making the dosage of the carbonaceous material and of the air quicklime more effective .

The use of an agglomerated product based on air quicklime also has the advantage of introducing into the furnace, in addition to the carbonaceous material, a second material of great utility in the steelmaking processes, such as air quicklime. For example, in the EAF production cycle the air quicklime is used in large quantities (e.g. 28 - 50 kg/ t of steel produced) as a fluxing and purifying agent to favour the melting and the formation of a basic slag, characterized by a balanced chemistry and a correct viscosity and foaming, able to remove impurities (e.g. sulphur, phosphorus, etc.) , operate the correction of the content of other elements (e.g. silicon, manganese, etc.) , safeguard the refractory linings of the furnace and ensure adequate coverage of the electric arc in addition to insulating the metal bath protecting it from oxidation and from hydrogen absorption and optimizing the thermal efficiency of the furnace .

In one embodiment, the agglomerated product may contain biomass materials, such as lignocellulosic biomasses and biochar, as an alternative to thermoplastic polymeric materials . The introduction of these materials in the agglomerated product has the particular advantage of solving the problems of high reactivity, volatility and dosage , which af fect the use of these carbon sources in steelmaking processes in a similar way to what is required for the thermoplastic materials . Furthermore , by appropriately choosing the weight ratios between air quicklime , carbonaceous material and any additional materials , it is possible to introduce the aforesaid components into the steel furnace simultaneously through a single dosing operation . This makes it possible to simpli fy the production system, as it avoids introducing these materials separately into the furnace through a plurality of distinct lances or noz zles .

The agglomerated product , which thanks to the presence of quicklime is characteri zed by high stability for the benefit of management safety ( smaller reaction surface to the air of the carbonaceous component dispersed in the inert matrix of quicklime ) , is also characteri zed by a degree of flowability that is suf ficient to prevent the formation o f agglomerates within the pipes of the pneumatic conveying and inj ection systems , thus overcoming the drawbacks of the prior art associated with the polymeric nature of the thermoplastic materials .

The present invention therefore concerns an agglomerated product according to what is defined in Claim 1 . The present invention further concerns a process for the production of the agglomerated product according to what is defined in Claim 12 and the use of the agglomerated product as defined in Claim 15.

Further features and advantages of the present invention will be more evident from the following detailed description .

Detailed description of the invention

The agglomerated product for use in a steelmaking process according to the present invention comprises: a carbonaceous material selected from the group consisting of thermoplastic polymeric recycled materials, biogenic materials obtained from the thermochemical conversion of biomasses, non-carbonized biogenic materials and mixtures thereof; and

- air quicklime in an amount from 50.0% to 90.0% by weight with respect to the total weight of the product.

The thermoplastic material usable for the purposes of the present invention is preferably a material comprising a thermoplastic polymer or a mixture of thermoplastic polymers. In one embodiment, the thermoplastic material comprises polyolefin polymers, elastomers or mixtures thereof .

Preferably, the thermoplastic material comprises at least one polymer selected from: polyethylene (PE) , polypropylene (PP) , polyethylene terephthalate (PET) , polystyrene (PS) , polyvinyl chloride (PVC) , natural rubber (NR) , styrene-butadiene rubber (SBR) , acrylonitrile- butadiene-styrene (ABS) and mixtures thereof.

Although the thermoplastic material may be a virgin material, it is preferably a recycled material, i.e. a material deriving from the recycling of post-consumer or post-industrial thermoplastic by-products and/or waste.

In one embodiment, the thermoplastic material is the material that is the residue from the recycling processes of the plastics, such as the plastics deriving from the separate collection of municipal waste (e.g. packaging in polyolefin material, such as bottles, containers, films, etc.) and of industrial waste from the production processes of plastic products, and from the recycling processes of the elastomeric materials, the elastomers deriving from the recycling of tyres .

Preferably, the thermoplastic material has a content of carbon equal to or greater than 70% by weight with respect to the dry weight of the thermoplastic material, preferably equal to or greater than 75% by weight, even more preferably equal to or greater than 80% by weight, even more preferably equal to or greater than 85% by weight.

The melting temperature and thus the softening temperature of the thermoplastic materials is lower than 280°C, preferably lower than 200°C, more preferably lower than 180°C and even more preferably lower than 130°C.

The biogenic materials can be obtained from the thermochemical conversion of lignocellulosic biomasses or they can be biochar.

As regards biochar resulting from the processes of pyrolysis and/or gasification of biomasses, this must have a high content of carbon greater than 65%, preferably greater than 75% and even more preferably greater than 85%. The moisture content of the biochar must be modest (lower than 5%, preferably lower than 2% and even more preferably lower than 1%) as well as it must have a low content of ash (lower than 7%, preferably lower than 5% and even more preferably lower than 3%) and of volatile matter (lower than 10%, preferably lower than 7%, more preferably lower than 5% and even more preferably lower than 3%) , the former being inert and possible carrier of undesired elements from the point of view of steel applications and the latter being susceptible to devolatilization phenomena during use.

As far as the use of non-carbonized biogenic materials is concerned, these may preferably comprise residual biomasses deriving from the recovery of the coppiced waste or as by-products from wood processing (shavings, sawdust and wood powders) and agro-industrial residues (husks and shells of hazelnut, walnut, coconut, almond, olive pits, fruit kernels, etc.) preferably characterized by a high lignin content or by a high value of the C/N ratio which must be greater than 30, preferably greater than 40 and even more preferably greater than 45. Such biomasses must be characterized by a low moisture content and a content of carbon on dry basis of at least equal to 40%, preferably greater than 45% and even more preferably greater than 50%. The melting temperature and thus the softening temperature of the non-carbonized biogenic materials must be lower than 250°C, preferably lower than 200°C, more preferably lower than 180°C and even more preferably lower than 130°C, as well as the glass transition temperature is preferably of the order of 100-150°C.

Furthermore, the non-carbonized biogenic materials can be derived substances such as fats, pomaces and vegetable oils (e.g. sunflower, soybean, pomace, palm, olive, etc.) .

The air quicklime (hereinafter also referred to as "quicklime" for simplicity's sake) usable for the purposes of the present invention is a mixed oxide composed predominantly of calcium oxide (CaO) and a minor amount of magnesium oxide (MgO) .

Preferably, the quicklime comprises calcium and magnesium, expressed as CaO and MgO, in a total amount CaO+MgO equal to or greater than 80% by weight.

The chemical composition of quicklime, in particular the content of CaO, MgO, CO2 and SO3, is intended to be determined in accordance with the standard EN 459-2:2021.

Based on the content of MgO, the quicklime usable for the purposes of the present invention is classified into:

- calcium quicklime, if the content of MgO is equal to or lower than 5% by weight;

- magnesium quicklime, if the content of MgO is greater than 5% by weight and lower than 30% by weight;

- dolomitic quicklime, if the content of MgO is equal to or greater than 30% by weight and, preferably, equal to or lower than 42% by weight.

Preferably, the quicklime used in the present invention is selected from: calcium quicklime, magnesium quicklime, dolomitic quicklime and mixtures thereof.

The quicklime, in addition to Ca, Mg and 0, may also comprise impurities of other elements (e.g. sulphur, silicon, iron, aluminium) , preferably in a total amount (expressed in terms of the sum of the amounts of the corresponding oxides SO3, SiC>2, Fe2C>3 and AI2O3) not greater than 1.0%, more preferably lower than 0.5% and even more preferably lower than 0.2% by weight.

The quicklime may comprise a residual fraction of inorganic carbon expressed as CO2 not greater than 6%, preferably lower than 4%, more preferably lower than 2% and even more preferably lower than 1%.

In a preferred embodiment, the air quicklime comprises calcium and magnesium, expressed as CaO and MgO, in a total amount CaO+MgO equal to or greater than 80% by weight. More preferably, the quicklime is selected from calcium quicklime type CL90-Q (having, content of calcium and magnesium in terms of the summation CaO+MgO > 90%, content of magnesium expressed as MgO < 5% and residual CO2 content < 4% and content of sulphur in terms of SO3 d 2%) , magnesium quicklime type DL90-5-Q (having, content of calcium and magnesium in terms of summation CaO+MgO > 90%, content of magnesium expressed as MgO > 5% and residual CO2 content < 6% and content of sulphur in terms of SO3 d 2%) and dolomitic quicklime type DL90-30-Q (having, content of calcium and magnesium in terms of the summation CaO+MgO > 90%, content of magnesium expressed as MgO > 30% and residual CO2 content < 6% and content of sulphur in terms of SO3 d 2%) , the aforesaid types of lime being defined in the standard EN 459-1:2015.

In a preferred embodiment, the powdered quicklime used for the generation of the agglomerates according to the present invention is a dolomitic quicklime wherein the Mg/Ca ratio in weight is ranging from 0.36 to 0.62, more preferably from 0.52 to 0.62 and/or the Mg/ (Ca+Mg) ratio is in the range 0.27 - 0.38, more preferably in the range 0.34 - 0.38.

In another preferred embodiment, the powdered quicklime used for the generation of the agglomerates according to the present invention is a calcium quicklime wherein the Mg/Ca ratio in weight is ranging from 0.002 to 0.04, preferably from 0.01 to 0.02, and/or the Mg/ (Ca+Mg) ratio is in the range 0.002 - 0.04, more preferably in the range 0.01 - 0.02.

In a further preferred embodiment, the powdered quicklime used for the generation of the agglomerates according to the present invention is a magnesium quicklime wherein the Mg/Ca ratio in weight is ranging from 0.05 to 0.35, more preferably from 0.06 to 0.25, and/or the Mg/ (Ca+Mg) ratio is in the range 0.05 - 0.26, preferably in the range 0.06 - 0.20.

In particular, the chemical composition of the airquicklime to be preferably used in the agglomerated product for use in the processes in EAF electric arc furnace provides for a high content of CaO and/or of CaO+MgO with low content of residual carbonate fractions (CO2) , silica (SiO2) , sulphur (S) as well as hydrated fractions. The presence of residual carbonate fractions leads in fact to a greater energy expenditure by the process with local effects of cooling of the slag and of increase in the viscosity of the latter; moreover, the formation of CO2 macrobubbles deriving from the calcination of the aforesaid carbonate fractions produces a rapid evolution from the liquid bath which, although it generates a certain (beneficial) turbulence in the bath, is not as beneficial as the formation of CO microbubbles which, by evolving from the liquid bath in a uni formly distributed manner, tend instead to remain longer in the slag favouring optimal foaming . Any hydrated fractions , although present in moderate quantity, contribute to introducing water into the melting furnace with a consequent increase in the thermal consumption of the melting process and an increase in the risk of hydrogen inclusions in the steel that can give rise to embrittlement phenomena . The presence of s ilica generally results in the slowdown of the dissociation process of lime into the slag, in addition to the decrease in the available active lime content since Si02 combines three times its weight with CaO and in certain cases , given precisely the greater af finity for calcium, can cause regressive reactions with release of impurities in the metal bath ( e . g . phosphorus ) ; likewise , the possible input of sulphur associated as impurity to quicklime reduces the ability to remove sulphur by the slag following the inhibition of the correct metal/ slag partition .

The particle si ze distribution ( PSD) of the quicklime used for the preparation of the aggregates is intended to be determined by dry-sieving by shaking in accordance with the standard EN 459-2 : 2021 according to the standard method EN 933- 1 : 2012 in test sieves with square-shaped mesh opening as reported in the standard EN 933-2 : 2020 .

In a preferred embodiment , the powdered quicklime to be used for the production of the agglomerated product according to the present invention has a nominal particle si ze distribution of 0-3 mm or, considering the ISO 3310 sieves , is for at least for 90% by weight , preferably at least for 95% by weight , even more preferably at least for 98 % by weight , even more preferably for 100% by weight passing through the sieve with square mesh openings equal to 3 . 15 mm . The result is that at least for 90% by weight , preferably at least for 95% by weight and more preferably at least for 98 % by weight passes through the sieve with a net mesh opening si ze equal to 4 mm and in any case for 100% by weight passes through the sieve with square mesh openings equal to 5 mm .

In another preferred embodiment the powdered quickl ime to be used for the production of the agglomerates according to the present invention has a nominal particle si ze distribution of 0- 1 mm that is , considering the ISO 3310 sieves , is for at least 92 % by weight , preferably at least for 95% by weight and even more preferably at least for 98 % by weight , even more preferably for 100% by weight passing through the sieve with square mesh openings equal to 1 mm . The result is that at least for 97 % by weight and preferably at least for 99% by weight passes through the sieve with a net mesh opening si ze equal to 2 mm and in any case for 100% by weight passes through the sieve with square mesh openings equal to 3 . 15 mm .

The assortment and the gradation of the particl e si ze distribution must be such as to ensure a correct balance between the coarsest particle fractions and the finest particle fractions so that during the compaction process at high pressure it is possible to optimise the mutual proximity of the particles and achieve the best possible interpenetration in relation to obtaining a final agglomerated product characteri zed by good mechanical strength characteristics.

Preferably, the PSD of the quicklime 0-1 mm and of the quicklime 0-3 mm used for the purposes of the present invention is characterized by a value of the index Dio as follows .

Quicklime 0-1 mm:

Dio ranging from 0.006 mm to 0.015 mm, preferably from 0.007 mm to 0.012 mm and more preferably from 0.008 mm to 0.010 mm.

Quicklime 0-3 mm:

Dio ranging from 0.007 mm to 0.030 mm, preferably from 0.010 mm to 0.025 mm and more preferably from 0.013 mm to 0.020 mm.

Preferably, the PSD of the quicklime 0-1 mm and of the quicklime 0-3 mm used for the purposes of the present invention is characterized by a value of the index Dso as follows .

Quicklime 0-1 mm:

D50 ranging from 0.030 mm to 0.065 mm, preferably from 0.035 mm to 0.050 mm and more preferably from 0.038 mm to 0.045 mm.

Quicklime 0-3 mm:

D50 ranging from 0.04 mm to 1.60 mm, preferably from 0.10 mm to 1.20 mm and more preferably from 0.40 mm to 0.85 mm.

Preferably, the PSD of the quicklime 0-1 mm and of the quicklime 0-3 mm used for the purposes of the present invention is characterized by a value of the index D90 as follows . Quicklime 0-1 mm:

D90 ranging from 0.25 mm to 0.85 mm, preferably from 0.35 mm to 0.65 mm and more preferably from 0.38 mm to 0.55 mm.

Quicklime 0-3 mm:

D90 ranging from 1.60 mm to 4.00 mm, preferably from 1.90 mm to 3.50 mm and more preferably from 2.10 mm to 2.85 mm.

The values of the indices Dio, D50 and D90 are calculated from the cumulative particle size distribution curve and correspond, respectively, to the size of the powdered quicklime particles to be used for the production of the agglomerates according to the present invention whereby 10%, 50% and 90% by weight have a size smaller than the value of Dio, D50 and D90. Other indices "D _x ", where x is a number between 0 and 100, can be determined in the same way, so that for a given value of D _x it results that x% by weight of the material has a size equal to or lower than the value D _x .

Preferably, the PSD of the quicklime 0-1 mm and of the quicklime 0-3 mm used for the purposes of the present invention is characterized by a value of the gradation index, given by the sum of the ratio of the indices Doi (characteristic size of the coarsest part of the particle size distribution) and D50 (median value of the particle size distribution) and of the ratio of the indices D50 and Dis (characteristic size of the finest part of the particle size distribution) divided by two, as follows.

Quicklime 0-1 mm: gradation index ranging from 3 to 8, preferably from 4 to 7 and more preferably from 4.5 to 6.5.

Quicklime 0-3 mm: gradation index ranging from 9 to 24, preferably from 12 to 21 and more preferably from 13.5 to 19.5.

Advantageously, the quicklime powder for producing the agglomerated products subject-matter of the present invention may comprise or consist of the fraction of residual fine powders that are generated in the different steps of the quicklime production cycle, such as for example the quicklime powders generated in the operation of the lime kilns or the fractions of the residual undersize powders from the comminution and screening processes of the quicklime in lumps for the production of granular products, the quicklime powders captured by the environmental protection systems present on the production plants, such as the systems used for the comminution and particle size separation processes or at silo unloading and vehicle loading points.

The reactivity with water of the quicklime, measured according to what is prescribed by the standard EN 459-2:2021 is generally considered in the state of the art an indirect index of the ability of the quicklime to be used in a steelmaking process. For example, the reactivity in water is considered an index of the rate and of the dissolution efficiency of the quicklime in the floating slag on a molten metal bath, in the EAF furnace.

The reactivity test, normally made explicit in a timetemperature graph in which the so-called reactivity curve is plotted, involves slaking the quicklime (150 g) in distilled water in a water/lime mass ratio equal to 4:1, under adiabatic conditions inside a Dewar vessel in which the water/ lime system is kept under stirring ( 300 rpm) , and by recording the evolution over time of the temperature starting from the initial value of 20 ° C and until the completion of the reaction ( the reaction is considered as completed when the temperature of the sample reaches the maximum value T ' max and stabilises on this , without increasing further ) . The measurements of temperature ( in ° C ) and time therefore allow to define a reactivity curve from which it is possible to obtain the indices tso and tso, corresponding to the time required to reach the temperature of , respectively, 50 ° C and 60 ° C . For the purposes of the present invention, the value tso is used to characteri ze the reactivity of the quicklime having a content of MgO greater than 5 % by weight , while the value tso is used to characteri ze the reactivity of the quicklime having a content of MgO lower than or equal to 5 % by weight .

Preferably, the quicklime used for the purposes of the present invention has the following reactivity in water :

- when the concentration of MgO in the quicklime is greater than 5% by weight , the slaking time tso in water is equal to or lower than 20 minutes , preferably equal to or lower than 10 minutes , more preferably equal to or lower than 5 minutes , even more preferably equal to or lower than 3 minutes and, even better, equal to or lower than 2 minutes ;

- when the concentration of MgO is equal to or lower than 5% by weight, the slaking time tso in water is equal to or lower than 10 minutes , preferably equal to or lower than 8 minutes , more preferably equal to or lower than 4 minutes , even more preferably equal to or lower than 2 minutes and more preferably equal to or lower than 1 minute.

Another index that is used to outline the rapidity of the slaking reaction of the quicklime in water is represented by the time required to complete the reaction at 80% (t _u ) corresponding to the value of temperature (T _u ) , expressed in degrees Celsius, at which the reaction is 80% completed which can be calculated according to the relation T _u = [ (0.8 x T ' max ) + (0.2 x To) ] , To being the initial temperature (in degrees Celsius) and T'm x the maximum temperature (in degrees Celsius) reached by the water/lime system.

The air quicklime is present in the agglomerated product in a variable amount in the range 50.0% - 90.0% by weight referred to the overall weight of the agglomerated composition, preferably in the range 55.0% - 85.0%, more preferably in the range 61.5% - 80.0% and even more preferably in the range 65.0% - 75.0%, the complementary fraction being made up of carbon source materials and/or mixtures thereof.

The agglomerated product according to the present invention is preferably in the form of briquettes of uniform size in the typical regular three-dimensional "pillow" shape, granules of uniform size and regular lenticular- spheroidal shape or calibrated flakes.

The briquettes have size expressed in terms of equivalent spherical diameter, defined as the diameter of the equivalent circle having the same surface area as the surface projected perpendicularly to the support plane by the briquette in its position of greatest stability, ranging from 15 mm to 60 mm, preferably ranging from 20 mm to 50 mm, more preferably ranging from 25 mm to 45 mm and even more preferably ranging from 30 mm to 40 mm.

The lenticular-spheroidal shaped granules have an equivalent spherical diameter falling within the particle size range ranging from 2 mm (lower particle size limit) to 15 mm (upper particle size limit) , preferably from 2.5 mm to 12.5 mm and even more preferably from 3 mm to 10 mm.

The calibrated flakes have an equivalent spherical diameter falling within the particle size range ranging from 2 mm (lower particle size limit) to 15 mm (upper particle size limit) , preferably from 2.5 mm to 12.5 mm and even more preferably from 3 mm to 10 mm.

Compared to the products in lumps obtained by calcination (decarbonation) of limestone (CaCCt) or dolomitic rock (CaCOs .MgCOs) and to the granular and powdered products deriving from their comminution at various levels and particle size classification treatments, the use of agglomerated products composed of quicklime in powdered form, allows to benefit from the advantage of a densified but highly reactive product, easy to disperse and with an optimized solubilization rate into the slag, which at the same time guarantees the containment of the dustiness in handling; a further advantage in the use of agglomerated fine products, by limiting the surface exposed to the atmosphere, is to limit the presence of hydrated or recarbonated fractions that can also be substantial in the case of products in a properly powdery form because of the high surfaces of exposure to air. The process to produce the agglomerated product according to the invention comprises the following steps.

First, a composition is mixed comprising at least:

- a carbonaceous material selected from the group consisting of thermoplastic polymeric recycled materials, biogenic materials obtained from the thermochemical conversion of biomasses, non-carbonized biogenic materials and mixtures thereof; and

- air quicklime in an amount from 50.0% to 90.0% by weight with respect to the total weight of the composition, preferably having a nominal particle size distribution of 0-3 mm or of 0-1 mm.

Subsequently the above composition is mechanically compacted at high pressure. The high-pressure mechanical compaction takes place in a dry process, by effect of the action of external forces acting on the mass of particles maintained under completely or at least partially confined conditions. This process provides that the composition to be agglomerated is de-aerated and the particles themselves undergo a spatial rearrangement and are brought to the minimum mutual distance, and therefore are pressed and plastically deformed so as, also inducing a partial fragmentation of the particles themselves, to increase their contact points and enhance the individual interactions between them (e.g. mechanical forces, electrostatic forces, van der Waals forces, formation of solid bridges and joints, recombination bonds between particle surfaces, etc.) to obtain the desired compact.

In one embodiment, the high-pressure mechanical compaction process aimed at the production of the agglomerated product according to the invention can be operated by using a roller press , being a widely established technology for the processes of compaction and manufacture of agglomerated l ime-based products . The operating principle is simple : the material to be agglomerated, beforehand mixed, is fed between two rollers of identical dimensions , counterrotating and operating synchronous ly, both provided with an external ring ( defined as forming ring) suitably shaped according to a more or less accentuated alveolar conformation that defines the shape and the si ze of the agglomerate . The material to be compacted is introduced into the interstice comprised between the two rollers , one of which is usually kept in a fixed position and the other able to float with a movement perpendicular to its own axis to cause precisely the correct interstitial opening, by gravity or as a preferential option by means of a feeding system that generally consists of a compacting auger operating perpendicularly to the axis of rotation of the rollers capable of producing a certain degree of de-aeration and pre-compaction of the mass of the particle material before its entry into the machine . The material is forced to pass through the nip between the rollers within the alveolar space so that , in relation to the si ze of the latter, it is compacted and formed into briquettes of uni form si ze and shape or into a compact tablet having typically the surfaces shaped like bosses that trace spheroidal-lenticular-shaped granules obtainable following a crushing and screening process , or again into a compact ribbon, i . e . a sheet in which both parts are smooth ( or corrugated) or one part is smooth ( or corrugated) and the other has a bossed surface which, following speci fic crushing and screening processes , leads to obtain aggregates of more irregular shape as flakes having calibrated si ze .

In all the aforesaid cases , the agglomerates exceeding the desired si ze or the fractions of material having a si ze smaller than desired are separated, optionally milled and recycled to the process .

Generally the linear pressing force , i . e . the speci fic force per centimetre of "active" width of the roller to be applied to the aforesaid composition for the formation of agglomerates is ranging from 40 kN/cm to 170 kN/cm, preferably ranging from 60 kN/cm to 160 kN/cm, more preferably ranging from 70 kN/cm to 140 kN/cm and even more preferably from 80 kN/cm to 125 kN/cm . "High pressure" therefore means the aforesaid ranges of linear pressing force , this being the characteristic parameter of the operation of the roller press .

Irregularly shaped aggregates of calibrated flakes can also be obtained from briquette crushing and screening processes .

In a preferred embodiment the aforesaid composition is cold compacted, the mixture of material to be agglomerated, consisting of quicklime and one or more carbon source materials , being supplied to the high-pressure compaction process at ambient temperature . The frictions that develop internally to the mass to be agglomerated deriving from the high-pressure compaction process , especially in the case of non-carbonized carbon source materials with a content of high lignin and recovered thermoplastic materials, generating temperature increases are able to locally favour melting or softening that, following a morphological transition, allow to obtain a good cross-linking and to improve the solid bridges between the particles of the agglomerate increasing their mechanical strengths.

The process preferably also comprises a step of heating the composition from 90°C to 250°C, preferably from 95°C to 180°C, more preferably from 100°C to 160°C, even more preferably from 110°C to 130°C, the step of heating being before, at the same time or after the step of compacting.

Advantageously the thermal energy necessary to heat the composition to be agglomerated before, during or after the compacting process is provided by recovering the heat of the exhaust gases emitted from a lime kiln for the production of quicklime .

Preferably, the step of heating is after the step of compacting .

The process preferably also comprises a preliminary step of drying the carbonaceous material or the mixtures thereof, bringing such components to a maximum moisture content lower than 10% by weight, preferably lower than 5% by weight, more preferably lower than 2.5% by weight and even more preferably lower than 1% by weight.

The carbonaceous material or the mixtures thereof must have a fine powdery form and a particle size distribution congruent with that of the quicklime constituting the matrix of the agglomerate, preferably being for 100% by weight passing through the sieve with square mesh openings equal to 2 mm, preferably passing through for 100% by weight the sieve with square mesh openings equal to 1 mm and more preferably passing through for 100% by weight the sieve with square mesh openings equal to 0.5 mm. As a rule, since biochar is intrinsically a material that easily tends to decay into powder or is in a fine powdery form, it does not require dedicated milling operations, while in the case of residual thermoplastic materials downstream of plastics recycling processes, operations of milling (optionally under cryogenic conditions) or co-milling together with quicklime may be necessary. Even the non-carbonized biogenic materials in solid form such as the lignocellulosic biomasses may have to undergo dedicated processes of particle size reduction or co-milling together with quicklime.

The step of mixing and homogenization preferably also provides for the addition of a lubricating additive (for example calcium stearate) in a percentage amount ranging in the order of 0.1% and 0.5% by weight with respect to the total mass of material to be agglomerated, preferably from 0.15% to 0.4% by weight with respect to the total mass of material to be agglomerated and even more preferably from 0.18% to 0.35% by weight with respect to the total mass of material to be agglomerated.

Subsequent to the step of mixing and homogenization of the components, the mixture to be agglomerated is fed to the high-pressure compaction process.

Further auxiliary processes downstream of the high- pressure compaction process consist, in relation to the type of final agglomerated product , only in a step of screening in which the fractions of material having a si ze smaller than desired are separated, optionally milled and recycled to the process , or in a double crushing and screening process to produce calibrated granules and wherein the agglomerates exceeding the desired si ze are sent again to the crushing process while the fractions of material having a si ze smaller than desired are separated, optionally milled and recycled again to the entire process at step of mixing and homogeni zation . In some cases , in this case with regard to the densi fied products having regular spheroidal-lenticular shape , it may be necessary, upstream of the screening phase , to resort to a surface post-treatment to improve the circularity of the agglomerates by eliminating any sharp edges and surface irregularities .

With regard to the production of the agglomerate in the form of briquettes , the process according to the present invention provides a cold high-pressure compaction process ; in this case the mixture of material to be agglomerated, consisting of quicklime and one or more carbonaceous materials , is fed to the high-pressure compaction process at ambient temperature . The frictions that develop internally to the mass to be agglomerated deriving from the high- pressure compaction process , especially in the case of noncarboni zed carbon source materials with a content of high lignin and recovered thermoplastic materials , generating temperature increases are able to locally favour melting or softening that , following a morphological transition, allow to obtain a good cross-linking and to improve the solid bridges between the particles of the agglomerate increasing their mechanical strength .

A further preferred embodiment involves the production of agglomerates according to the present invention by a high- pressure compaction process in order to obtain cold-bonded briquettes , subsequently subj ected to a thermal posttreatment process by heating to the temperature values speci fied above .

In another preferred embodiment , the production of agglomerates according to the present invention involves a high-pressure compaction process in order to obtain hot- bonded briquettes after heating the mixture to be agglomerated to the temperatures speci fied above .

Heating the mixture of materials being fed to the high- pressure compaction process at temperatures higher than ambient temperature may be necessary so that the carbon source materials , especially recovered thermoplastic materials and the non-carboni zed biogenic materials with a high lignin content , achieve an appropriate mal leability capable of improving the solid bridges between the particles when they reach their own glass transition being able to more easily give rise to the correct formation of agglomerates with good mechanical strength .

In another preferred embodiment , the production of agglomerates according to the present invention provides a high-pressure compaction process for the production of cold- densi fied products of regular spheroidal-lenticular shape , obtained following a crushing and screening process of a compact tablet typically having the shaped surfaces with bulges that trace the aforesaid spheroidal-lenticular shaped granules . In this case the mixture of material to be agglomerated, consisting of quicklime and one or more carbon source materials , is fed to the high-pressure compaction process at ambient temperature . Like for the production of briquettes , alternative forms of production involve heating the mixture before , during or after compaction .

In another preferred embodiment , the production of agglomerates according to the present invention involves a high-pressure compaction process carried out in cold mode or with heating before , during or after compaction, in order to obtain a compact ribbon, i . e . a sheet from which irregularly shaped aggregates of calibrated chips or flakes are obtained by subsequent crushing and screening operations . In a further preferred embodiment , the production of agglomerates according to the present invention involves speci fic crushing and screening processes in order to obtain irregularly shaped aggregates of calibrated chips or flakes starting from briquettes deriving from a cold or hot high- pressure compaction process .

The agglomerated product according to the present invention is advantageously used in a process for the production of steel in an electric arc furnace .

The following embodiment examples are provided merely to show the present invention and should not be construed in a sense that would limit the scope of protection de fined by the appended Claims .

EXAMPLES

Ten samples of agglomerates ( Samples A-J) , having cylindrical conformation, based on air calcium quicklime and in admixture with substances as synthetic (polyethylene) or natural (woody biomass) carbon sources, were prepared at the laboratory scale; for each sample three series of fifty agglomerates each were generated.

The aforementioned agglomerates were obtained by means of a high-pressure compaction process according to what is reported below.

Materials

The air quicklime used for the generation of the aforesaid agglomerates is a calcium quicklime of standard industrial production, classified, according to the designation reported in the standard EN 459-1:2015, as CL90- Q having the following composition: content of calcium and magnesium in terms of the summation CaO+MgO > 90%; content of magnesium in terms of MgO < 5%; content of sulphur in terms of SO3 2%; residual CO2 content d 4%; the aforesaid percentages being percentages by weight referred to the weight of the material.

Calcium quicklime has a nominal particle size distribution of 0-3 mm and is characterized by the following characteristic diameters Dio=O.O2 mm, Dso=O.47 mm and Dgo=2.53 mm, indicating respectively the particle size corresponding to 10%, to 50% (median) and to 90% of the cumulative particle size distribution curve, with an average diameter D _a ve=0.88 mm. The summary data were derived from the cumulative particle size distribution curve obtained from the air jet sieving test in compliance with what is reported in the standards EN 459-2:2021, EN 932-2:2000 and EN 933-10:2009: the test was carried out with a series of ISO 3310 sieves having mesh openings size equal to 0.032 mm, 0.045 mm, 0.063 mm, 0.090 mm, 0.125 mm, 0.200 mm, 0.250 mm, 0.500 mm, 1 mm, 2 mm, 3.15 mm, 4 mm and 5 mm.

The bulk density of air calcium quicklime, determined in accordance with the standard EN 459-2:2021 and the standard EN 932-2:2000, is equal to 0.98 kg/dm ³ .

The calcium quicklime has reactivity, measurable in terms of slaking time in water tso in accordance with what is prescribed by the standard EN 459-2:2021, equal to 1.9 minutes .

The polyethylene (PE) used for the generation of the aforesaid agglomerates based on air quicklime is a low density polyethylene (LDPE) characterized by a true density equal to 0.919 g/cm ³ , has a content of carbon of 84.9%, a content of ash equal to 0.8% and has softening and melting temperature values equal to 95°C and 115°C, respectively. The low density polyethylene used for the generation of quicklime-based agglomerates has a fine powdery form with a particle size distribution characterized by the following characteristic diameters Dio=O.Ol mm, Dso=O.19 mm, Dgo=O.62 mm, D _aV e= 0.27 mm and has a bulk density equal to 0.29 kg/dm ³ .

The woody biomass used for the generation of the aforesaid aerial quicklime-based agglomerates is a byproduct of wood processing (shavings, sawdust, chips, cutting residues of wood, chipboard and veneers) , characterized by a content of carbon on a dry basis of 49.2% (of which 99.6% of biogenic origin) and by a content of ash equal to 1.8%. The woody biomass used for the generation of quicklime-based agglomerates has a fine powdery form with a particle size distribution characterized by the following characteristic diameters Dio=O.Ol mm, Dso=O.O4 mm, Dgo=O.17 mm, D _aV e= 0.11 mm and has a bulk density equal to 0.22 kg/dm ³ .

High-pressure compaction process

The high-pressure compaction process was carried out with the aid of a manually operated laboratory hydraulic press, consisting of a pump block in which the hydraulic fluid (oil) is pressurized through the pumping action, exerted by means of a hand lever, in a manner such as to allow the lifting of a piston and therefore of a pressing plate arranged above it; on the pressing plate there is disposed an evacuable cylindrical mould in stainless steel, provided on the bottom with an air vent hole, inside which the charge of the material to be compacted is introduced enclosed between two polished and ground stainless steel discs, the upper one being placed in contact with a cylindrical pressing plunger in polished and ground stainless steel tightened by means of a threaded lead screw. The compaction action is therefore promoted by the lifting that the pressing plate exerts on the system consisting of the cylindrical mould and of the pressing plunger against the tightening lead screw of the latter: the compressive load on the sample is given by the resistance provided by the system.

Each agglomerate, having a cylindrical shape, was produced by loading into the evaluable cylindrical mould a quantity by weight of the mixture of the starting materials equal to 15 ± 0.1 grams and exerting a compressive load equal to 12.5 tonnes for a forming time of the order of 3 minutes following the complete de-aeration of the mixture to be compacted .

The ten samples of agglomerates consist respectively of air quicklime (Sample A) and of a mixture of quicklime and low density polyethylene (Samples B-G) and of a mixture of quicklime and woody biomass (Samples H-J) in such a proportion as to maintain a predetermined lime/carbon ratio in which the content by weight of lime is respectively equal to 3 times, 4 times and 5 times the content of carbon by weight : quicklime 0-3 mm; quicklime 0-3 mm and 28.2% polyethylene ;

S amp 1 e C: 77.3% quicklime 0-3 mm and 22.7% polyethylene ; polyethylene ; quicklime 0-3 mm and 28.2% polyethylene ;

S amp 1 e F: 77.3% quicklime 0-3 mm and 22.7% polyethylene ; polyethylene ; woody b i oma s s ; woody b i oma s s ;

10 ) Sample J : 71 . 1 % quicklime 0-3 mm and 28 . 9% woody biomass .

The raw materials were previously mixed and homogeni zed in a laboratory planetary mixer for a time equal to 10 minutes ; the total weight of the mixture of mixed and homogeni zed raw materials for the generation of each series of fi fty agglomerates was equal to 800 grams .

The step of mixing and homogeni zation also provided for the addition of calcium stearate as a lubricating agent in an amount equal to 0 . 2 % by weight with respect to the total weight of the mixture .

Sample A was prepared in accordance with the method described above by operating the high-pressure compaction process completely in cold mode .

Samples B-D were prepared in accordance with the method described above by providing, prior to the high-pressure compaction process , the homogeneous and uni form heating of the mixture to be agglomerated in a thermostatic sand bath at temperature values maintained in the range 125- 130 ° C for a time equal to 1 hour .

Samples E-G were prepared in accordance with the method described above by operating the high-pressure compaction process completely in cold mode and then providing a thermal post-treatment process of the agglomerates obtained by heating in a laboratory stove at temperature values maintained in the range 125- 130 ° C for a time equal to 1 hour .

Samples H-J were prepared in accordance with the method described above by operating the high-pressure compaction process completely in cold mode .

Dimensional analysis of the agglomerates

The dimensional characteristics of the agglomerates based on air calcium quicklime and in admixture with substances as carbon sources were measured directly on the individual cylindrical agglomerates produced by using a centesimal vernier caliper reading with a comparator having a measuring precision of 0 . 01 mm .

The average values characteri zing the dimensions of the aggregates of the samples produced are reported in Table 1 .

Determination of the mechanical durability of the agglomerates

The cylindrical agglomerates based on air calcium quicklime and in admixture with substances as carbon sources were subj ected to mechanical strength analysis and to wear resistance analysis deriving from dynamic stresses such as abrasion and impact fracture .

The mechanical strength of the cylindrical agglomerates based on air calcium quicklime and in admixture with substances as carbon sources was determined by means of a structure analyser consisting of a high-precision dynamometer operating in compression provided with a piston terminating in a wedge-shaped chisel tip that imparts to the cylindrical agglomerate , arranged on a test support in its position of greatest stability, an increasing compressive load up to the complete penetration of the tip inside the cylindrical agglomerate and to the breaking thereof by recording the peak stress : the mechanical strength is expressed as an average value obtained from fi fteen measurements carried out on fi fteen agglomerates of each series of each sample for a total of forty- five measurements of the same sample of agglomerates . The results of the determination of the mechanical strength are reported in Table 1 .

Resistance to abrasion and to breakage following dynamic stresses of the cylindrical agglomerates based on calcium aerial quicklime and in admixture with substances as carbon sources was determined through " shatter test" which assume that a test sample consisting of five agglomerates is loaded into a cylindrical container in plastic material with a closure cap ( outer diameter equal to 75 mm and length equal to 130 mm) having a containment volume equal to 500 cm ³ , in turn inserted into a cylindrical steel container ( inner diameter equal to 78 mm and length equal to 690 mm) , fitted with closures at both ends and kept under rotation around a pin fixed on the outer surface of the container at the median cross-section . The cylindrical container was kept under rotation at a rotation speed equal to 15 rpm for a number of complete rotations in total equal to 75 : in this way the agglomerates constituting the test sample were subj ected to a series of controlled impacts and to a state of wear by abrasion caused by the rubbing and by the collision of the ones with the others and against the walls of the containment container left free to move inside the rotating cylindrical container .

The result of the shatter test is given by the percentage by weight of the agglomerates of the test sample that remain intact following mechanical treatment with respect to the total weight of the test sample agglomerates before the shatter test .

Within the scope of this characteri zation, the percentage by weight of particles retained in the 12 . 5 mm- sided square mesh sieve following the shatter test , designated in this description by the " shatter test index" ( 1ST ) , is defined quantitatively .

The extent of the 1ST shatter test index provides an indication of the resistance to abrasion and to breakage of the agglomerates based on air calcium quicklime and in admixture with substances as carbon sources .

The results of the determination of the 1ST shatter test index, expressed as an average value obtained from three shatter tests performed on fi fteen agglomerates of each series of each sample for a total of nine measurements of the same sample of agglomerates , are reported in Table 1 .

Reactivity in water

The wet slaking test for the determination of the reactivity in water of the agglomerates based on air calcium quicklime and in admixture with substances as carbon sources was carried out according to what is prescribed by the standard EN 459-2 : 2021 .

The reactivity test was carried out on a test sample obtained by first subj ecting twenty agglomerates based on air calcium quicklime and in admixture with substances as carbon sources of each series of the ten samples produced ( Samples A-J) to a combustion treatment operated in a laboratory muf fle furnace at a temperature of 1000 ° C in an oxidi zing environment for a maximum time equal to 30 minutes in order to ensure complete thermal degradation of the carbon source, followed by a process of particle size reduction to values < 0.2 mm and of homogenization after having been cooled in a laboratory dryer: such test sample, net of the residual ash contained in the substances as carbon sources, is entirely composed of quicklime.

In the wet slaking test, the following were determined: a) the index too corresponding to the slaking time, i.e. to the time elapsing between the start of the hydration reaction between quicklime and distilled water in the ratio 150:600 grams, starting from an initial temperature value To=2O°C and the moment in which the temperature of the lime/water mixture, kept under stirring (300 rpm) under adiabatic conditions inside a Dewar vessel, reaches 60°C; b) the temperature T'max corresponding to the maximum temperature, expressed in degrees Celsius, reached by the lime/water mixture while performing the wet slaking test: the slaking reaction of the quicklime is considered to be 100% completed when the maximum temperature value T'max is reached; c) the index t _u corresponding to the time elapsing between the start of the hydration reaction of the quicklime in water and 80% of the completion of the lime slaking reaction, corresponding to the temperature value (T _u ) , expressed in degrees Celsius, at which the reaction is 80% completed calculable according to the relation T _u = [ (0.8 x T ' max ) + (0.2 x To) ] , To being the initial temperature (To=2O°C) and T'max being the maximum temperature (in degrees Celsius) reached by the water/lime system. The results of the tests of reactivity in water, expressed as an average value obtained from a total of three tests carried out for each sample of agglomerates , are reported in Table 1 . TABLE 1 - Characteri zation of the agglomerates based on calcium quicklime and in admixture with substances as carbon sources ( the results are expressed as the average value o f the values determined on the three series of agglomerates constituting each the samples of agglomerates A - J .

The characteri zation results show that the agglomerates based on air calcium quicklime in admixture with substances as carbon sources according to the present invention possess good mechanical durability, resulting in both the mechanical resistance to penetration of a wedge-shaped chisel tip and the resistance to wear due to abrasion and to breakage following dynamic stresses ( 1ST shatter test index ) higher than those of the agglomerates based on air calcium quicklime .

The data from the wet slaking test show that the reactivity in water of the quicklime contained in the formulation of the agglomerates based on air calcium quicklime in admixture with substances as carbon sources according to the present invention remains substantially of the same order as that of the quicklime constituting the agglomerates based on air calcium quicklime , net of the ef fects due to the input of residual ash contained in the substances as carbon sources that remain in the quicklime sample following the combustion process .