BE1022069B1 - LIME MILK COMPOSITION - Google Patents

Abstract

Milk of lime composition comprising particles of slaked lime suspended in an aqueous phase, characterized in that said particles of slaked lime consist of more than 60% by weight, preferably more than 80% by weight, more preferential of more than 90% by weight of slaked lime particles, relative to the total weight of slaked lime particles, which have a particle size described by a monomodal particle size distribution profile.

Description

"COMPOSITION OF LIME MILK"

The present invention relates to a lime milk composition comprising slaked lime particles suspended in an aqueous phase, to its manufacturing process and to its use.

Suspensions of slaked lime particles sometimes also called lime milk, lime cream or lime slurry are used industrially as reagents, in a multitude of applications, including civil engineering, especially soil treatment, preferably the soil stabilization, treatment, particularly conditioning and hygienization, of mineral or organic sludge (including manure or similar organic residues) or precipitation processes, where saturation control is critical, in the adjustment pH, the mineralization of drinking water, the neutralization of chemical reactions and the treatment of waste water aerobically or anaerobically.

Such suspensions of slaked lime particles or lime milks are commonly obtained by slaking quicklime in the presence of water or by suspending pulverulent slaked lime. The particles obtained are predominantly composed of calcium hydroxide.

This slaked lime or calcium hydroxide can obviously contain impurities, namely phases derived from SiO 2, Al 2 O 3, Fe 2 O 3, MnO, P 2 O 5, K 2 O and / or SO 3, generally representing a few tens of grams per kilogram. However, the sum of these impurities, expressed in the form of the aforementioned oxides, does not exceed 8% by weight, preferably 5%, preferably 3% or even 2% of the weight of the slaked lime according to the invention. In particular, the slaked lime advantageously contains less than 1.5% by weight of Fe 2 O 3, preferably less than 1% and preferably less than 0.5%.

This slaked lime may also contain calcium oxide that would not have been hydrated during the quench, just as it may contain CaCO 3 calcium carbonate. This calcium carbonate can come either from the initial limestone which is derived from the slaked lime according to the invention (incuits), or from a partial carbonation reaction of the slaked lime in contact with the air. The calcium oxide content in the slaked lime in the context of the present invention is generally less than 3% by weight, preferably less than 2% and advantageously less than 1% of the weight of the slaked lime according to the invention. invention. That of calcium carbonate is less than 10% by weight, preferably less than 6% and advantageously less than 4%, even more advantageously less than 3%.

This slaked lime may also contain MgO magnesium oxide or Mg (OH) 2 or MgCO 3 type derived phases, generally representing a few tens of grams per kilogram. Nevertheless, the sum of these impurities, expressed in the form of MgO, advantageously does not exceed 8% by weight, preferably 5%, preferably 3% or even 2% of the weight of the slaked lime according to the invention.

One of the factors limiting the use of milk milks with respect to other potential reagents generally lies in their rate of reaction or neutralization in the reaction medium of the application.

Of course a low reaction rate is sought as soon as it allows the implementation of slower processes and therefore longer residence times. This has the advantage of being able to have calcium hydroxide for a sufficiently long time, which makes the reactions involved effective in the aforementioned fields of application.

The slow but continuous release of calcium hydroxide allows, based on a single addition of reagent, a pH increase spread over a long period of time. This phenomenon is advantageously used in many applications requiring a slow increase in pH, especially in the treatment, in particular the conditioning and sanitization, of mineral or organic sludge (in particular manure or similar organic residues). In the context of the hygienization of manure or similar organic residues in particular, the use of lime milks with a low reaction rate makes it possible both to maintain a constant pH but also to prevent biological growth. As part of biochemical processes, it has been found that effects of unintentional pH changes occur within biochemical reactors. These pH changes in the reaction medium are harmful to the bacteria / yeasts that are present in the reactor.

In view of the above, it is clear that there is a real need to provide a low reactivity milk of lime whose rate of dissolution can be controlled reproducibly. In this way, a homogeneous reactivity of the milk of lime can be envisaged over a long period of time and it does not matter the source of the milk of lime.

Another problem, this time related to the use of fine lime milks, comes from too much viscosity reducing their workability or requiring dilution of these milks of lime and thus limiting their use in certain fields, in particular in civil engineering and more particularly in soil treatment.

Indeed, the treatment of soil on site is complicated because the supply of raw material is limited because of the difficulty and / or the distance of access to the site. The use of conventional milks of lime sufficiently manageable that can require a large amount of water, the treatment of the soil directly on site by means of these is unfavorable.

There is therefore a real need to develop milks of lime requiring smaller amounts of water, in other words more concentrated milks of lime which are however easy to handle.

In the context of the present invention, it is necessary to distinguish the reactivity of the lime milk which represents the dissolution rate of the hydrated lime particles of the reactivity of your quicklime, that is to say the rate of reaction of the lime live with water to produce slaked lime and thus for example a whitewash.

Indeed, the reactivity of quicklime is generally characterized and measured by the procedure disclosed in the European standard EN459-2. This standard defines the reactivity of quicklime by the t8o, time necessary to reach 80% of the maximum temperature increase generated by the addition of 150 g of quicklime in a water volume of 600 cm3 initially at 20 ° vs. According to this standard, the reactivity of quicklime can also be characterized by the t6o, time required to reach 60 ° C for a volume of water of 600 cm3 initially at 20 ° C, from the addition of 150 g of quicklime, which is often similar in value to t8o.

The reactivity of milk milks is in turn characterized in the sense of the present invention according to the work of van Eekeren et al. disclosed in the document "lmproved milk-of-lime for softening of drinking water", M.W.M. van Eekeren, J.A.M. van Paassen, C.W.A.M. Merks, KIWA Research and Consultancy NV, Nieuwegein, September 1993 "produced and distributed by the KIWA, Royal Netherlands Institute for Water Analysis (KIWA NV Research and Consultancy, Groningenhaven 7, PO Box 1072, 3430BB Nieuwegein).

For the purposes of the present invention, the described procedure has been refined in order to improve the accuracy and reproducibility of the results and has been tested on several different formulations of lime milks.

According to the present invention, the rate of dissolution of slaked lime in deionized water is measured as an increase in the electrical conductivity of the solution, under conditions at which the solution remains below the saturation threshold relative to with calcium hydroxide. For this purpose, 0.1 g of hydrated lime is added to 700 g of water at 25 ° C., which makes it possible to remain well below the solubility threshold of the calcium hydroxide which is approximately 1.5 g. per liter of solution at 25 ° C (see, for example, "Solubilities of Inorganic & Metalorganic Compounds - Volume 2", A. Seidell, WF Linke, 1953, van Nostrand (publ.), 631).

To achieve this precise and reproducible measurement, prepare 500 g of suspension containing 2% by weight of slaked lime to be characterized, namely 10 g of slaked lime in 490 g of water. This suspension and 700 g of deionized water are thermostated at 25 ° C. precisely. A response time conductivity cell of 0.05 s or less is used to automatically record, using a datalogger, the sample conductivity of 700 g of deionized water that is vigorously stirred throughout. of the measurement, for example at a speed of 450 rpm with a propeller stirrer of 30 mm diameter.

At the beginning of the measurement, 5 cm 3 of the 500 g suspension is injected into the sample of 700 g of deionized water and the conductivity value is recorded over time until the latter remains stable, thus having reaches a maximum value. The time to reach this maximum conductivity since the beginning of the measurement is noted ti00. Analogously, tg0 is defined as the time required to reach 90% of the maximum conductivity. It is this value t90 obtained which is considered to represent the reactivity of the milk of lime. More details on the procedure for measuring this reactivity of milk milks are available in § 6.11. "Determination of the solubility index by conductivity" of EN 12485: 2010.

It is therefore considered according to the present invention that the reactivity of the milk of lime will be low if the size tgo is at least equal to 15 s.

Bright lime of different reactivities and of different origins would commonly produce, even under identical quenching conditions, lime milks with different rheological properties and reaction properties. In addition, since the reactivity of quicklime is generally dependent on the type of furnace used to calcine lime in quicklime, the type of oven also plays a role in the properties of lime milk, in addition to the influence of the origin. limestone. The invention aims to overcome many of the disadvantages of the state of the art by providing a milk of lime that can use any source of quicklime and which will be applicable in many areas. This lime milk then advantageously has a reaction behavior (reactivity) that can be homogeneous, controlled and predictable so that it can be used effectively as a reagent in multiple fields of application, in particular in civil engineering (soil treatment), in the treatment, in particular conditioning and sanitizing, of mineral or organic sludge (in particular manure or similar organic residues) and in biochemical reactors.

To solve this problem, it is provided according to the invention, a lime milk composition as indicated at the beginning, characterized in that said slaked lime particles consist of more than 60% by weight, preferably more than 80% by weight. % by weight, preferably more than 85% by weight, more preferably more than 90% by weight, in particular more than 95% by weight of slaked lime particles, based on the total weight of the slaked lime particles , which have a particle size described by a monomodal particle size distribution profile.

The milk of lime according to the invention having a monomodal particle size distribution profile means that a population of particles is very predominantly present in the milk of lime. This population therefore comprises relatively similar particle sizes and therefore react substantially at the same speed. In this way, a single particle population is evidenced to prevent intermediate populations from interfering when a reaction is carried out in the presence of lime milk. Thus, the lime milk of the present invention has a monomodal particle size distribution that can counteract the problems associated with the use of conventional lime milks.

Thus each grain of lime milk has a dissolution rate similar to other grains which promotes a homogeneous and controlled reaction behavior.

In fact, conventional lime milks typically have a particle size distribution profile that is multimodal (having several peaks) and thus comprises several populations of slaked lime particles. These different particle populations will typically be composed of fine fractions with increased reactivity and coarser fractions with reduced reactivity. In addition, other intermediate fractions may be present, depending on the patterns of the particle size distribution pattern observed. For example, the multimodal particle size distribution profile may include a significant population of between 0.1 and 30 μm as well as several populations of coarser agglomerates. Populations between 0.1 and 30 μm have a rapid dissolution rate compared to populations in a higher particle size range. The intermediate fractions therefore react at different speeds. Therefore, this distribution of the reactive behavior due to the various reaction rates results in a reaction behavior (reactivity) of the non-homogeneous lime milk, which is problematic for many applications, as mentioned above. Applications dependent on the dissolution rate of milk of lime are for example, but not limited to, the treatment, in particular the conditioning and the sanitization, of mineral or organic sludge (in particular manure or similar organic residues) or biochemical processes.

In addition, the lime milk having a multimodal particle size distribution profile is accompanied by the aforementioned drawbacks, namely that the lime milk exhibits a reaction behavior that is neither homogeneous nor controlled. This does not allow a slow and continuous supply of basic agent (such as calcium hydroxide) in biochemical reactors to avoid unwanted pH variations.

The lime milk of the present invention therefore not only makes it possible to provide a lime milk having a monomodal particle size profile but also with a low reactivity. This makes it possible to provide a milk of lime that can be used in targeted applications that require slow reactions such as in biochemical reactors. What is more, this lime milk can be obtained from particles of quicklime that could not be found. inevitably their utility in the majority of applications of lime milks as they disrupted the homogeneity of the reaction of conventional lime milks or were discarded. It is therefore particularly advantageous to be able to provide a milk of lime whose rate of dissolution is such that calcium hydroxide intake can be assured and supported during the treatment in question.

In the specific case of biochemical reactors, the lime milk according to the present invention makes it possible to effectively and reliably limit any undesirable pH variation within the reactor.

Moreover, the application of lime milk according to the present invention is made favorable in civil engineering and more particularly in the treatment of soils where it is essential to be able to supply the site to be treated as few times as possible in amount of water. Thanks to the lime milk of the present invention, the viscosity of the milk of lime is such that it can do without a large presence of water for the reaction to be favorable.

The lime milk with a monomodal particle size distribution profile according to the present invention does not have a distribution of the reaction rate. In contrast, the milk-lime composition according to the present invention reacts homogeneously because of the homogeneous distribution of the slaked lime particles in the reaction medium, which is due to the monomodal particle size distribution profile and therefore to the homogeneity of particle size.

Advantageously, said particles have a dio particle size greater than or equal to 10 μm, preferably greater than or equal to 15 μm, a particle size d 50 greater than or equal to 20 μm, preferably greater than or equal to 50 μm, and more preferably greater than or equal to 50 μm. or equal to 100 pm, in particular greater than or equal to 200 pm, a particle size d90 greater than or equal to 200 pm, preferably greater than or equal to 300 pm, a particle size d90 of less than or equal to 1 mm as measured by laser diffraction.

As can be seen from the particle size values given above, the particles are coarse, in addition to having a monomodal particle size distribution profile.

In a particular embodiment, the slaked lime composition according to the present invention has a viscosity of less than 300 mPa.s, preferably less than 150 mPa.s, and more preferably less than 50 mPa.s, in particular less than 25 mPa.s as measured by Brookfield standard DV-III rheometer at a rotational speed of 100 rpm.

Preferably, the composition is a suspension of slaked lime in the form of milk of lime having a solid content greater than or equal to 5%, advantageously greater than or equal to 10%, preferably greater than or equal to 25%, in particular greater than or equal to 30%, particularly preferably greater than or equal to 40%, relative to the total weight of the suspension.

In a particularly advantageous embodiment according to the invention, the slaked lime particles have a dissolution rate in distilled water, as measured in the EN12485 standard, such that 90% of the slaked lime particles are dissolved after more than 15 seconds, preferably after more than 40 seconds and more preferably after more than 60 seconds.

Advantageously, the composition according to the invention has a total content of sulfur, phosphorus, sodium and potassium in the range from 0.05 to 2% by weight, preferably from 0.15 to 1% by weight, relative to the total weight of the slaked lime.

Even more preferably, the composition according to the invention is a low reactivity milk of lime composition. Other embodiments of the slaked lime composition according to the invention are indicated in the appended claims. The subject of the invention is also a process for producing lime milk, comprising the following steps: a) an extinction of a quicklime by an aqueous phase of extinction by applying a proportion of quicklime to the aqueous phase of extinguishing greater than 1 to 8, in particular 1 to 6, and less than 1 to 3 to form a suspension of lime, said extinguishing being carried out in the presence of a water-soluble additive, b) at least one particle size cut of said suspension of lime, optionally diluted, obtaining at least a first fraction and a second fraction, c) obtaining said lime milk, possibly after dilution, containing said first fraction.

The process according to the present invention has the great advantage of being able to use any type of industrial lime with a chemistry and a reactivity quite standard, without having to resort to lime of high purity at the base, to produce a suspension lime which is easily granulometrically cut. The granulometric cutting step may advantageously be a simple removal of a very coarse fraction which may contain calcium carbonate in the form of incuit or any insoluble inorganic impurity, such as, for example, silicates or aluminates, which does not affect the reactivity of the milk of lime obtained but makes it more homogeneous and / or also a cut in order to eliminate only the fine particles to preserve them for another application and thus valorize the coarser fraction to make a monomodal lime milk according to the present invention. The steps of the process according to the invention make it possible to provide a lime milk, in particular of low reactivity, which has a monomodal particle size distribution profile and which will have a particularly suitable reactivity for particular applications as mentioned above. Thus, the process developed makes it possible to provide lime milks, in particular those with a low reactivity, in a reliable, reproducible and controlled manner, and which uses "cheap" particles in that the process according to the invention makes it possible to obtain a valued composition. particles typically little or not used.

The method according to the present invention thus makes it possible, by virtue of the combined action of the additive and the granulometric cut, to produce a milk of lime, in particular with a low reactivity compared with conventional lime milks, the reaction behavior of which is homogeneous and controlled. during the treatment and for a wide range of applications, as mentioned above, since the milk of lime has a monomodal particle size distribution profile, the additive making it possible to better control the size of the particles and of keep it over time.

The term "monomodal" in this context means that the measured differential particle size distribution obtained by conventional measurement methods described above shows either only one mode or peak, preferably evenly distributed around the d50 value, or a particle size distribution profile dominated by a particle mode, this mode containing more than 60% by weight, preferably more than 80% by weight, advantageously more than 85% by weight, more preferably more than 90% by weight , in particular more than 95% by weight of slaked lime particles, relative to the total weight of the slaked lime particles.

It has been found that the presence of the additive advantageously makes it possible, as a result of the granulometric cutting, to provide a milk of lime which does not have the disadvantages of conventional lime milks. In fact, the initial coarse fraction is larger and, after granulometric cutting, comprises particle sizes whose distribution profile is monomodal. Thus, the reaction behavior of the milk of lime is homogeneous because the particles react substantially at the same speed.

Advantageously, said additive is added to the aqueous phase extinction, before or during said extinction or quicklime.

Practically, three cases can occur. In the first case, the aqueous phase is formed of water when the additive is added to quicklime, either as a solid powder or as a solution sprayed on quicklime. In the second case, the aqueous phase consists of a solution containing the additive in water when the additive is added before extinction in water. Finally, depending on the solubility rate of the additive, the aqueous phase may comprise a solution of the additive when the latter is added during the quenching to the aqueous phase.

Preferably, said additive, preferably of mineral origin, is selected from the group consisting of sulphates having at least a moderate solubility in water greater than or equal to 0.1 g / dm3, sulphites having at least moderate solubility in water greater than or equal to 0.05 g / dm3, phosphates having at least moderate solubility in water greater than or equal to 0.1 g / dm3, phosphites having at least moderate solubility in the upper water or 0.1 g / dm3, inorganic carbonates having at least a moderate solubility in water greater than or equal to 0.1 g / dm3, sulfuric, sulfurous, phosphoric, phosphorous and carbonic acids, and mixtures thereof.

More preferably, said sulphates are sulphate salts selected from the group consisting of alkaline sulphates and alkaline earth sulphates and mixtures thereof, in particular Na 2 SO 4 (thenardite), Na 2 SO 4 .10H 2 O (mirabilite), CaSO 4 (anhydrite) , CaSO 4 .H 2 O (hemihydrate), CaSO 4 .2H 2 O (gypsum), MgSO 4,

MgSO4.7H2O (epsomite) and mixtures thereof.

According to a preferred embodiment of the present invention, said sulfites are selected from the group consisting of Na 2 SO 3, NaHSO 3, CaSO 3, K 2 SO 3, KHSO 3 and mixtures thereof.

In an advantageous embodiment, said phosphates are salts of phosphates chosen from the group consisting of alkaline salts of phosphates, in particular Na2HPO4, NaH2PO4 (nahpoite), K2HPO4 (archerite), KH2PO4 and mixtures thereof.

In another advantageous embodiment of the present invention, said inorganic carbonates are selected from the group consisting of alkaline carbonates and alkaline earth carbonates and mixtures thereof, in particular Ca (HCO 3) 2, Mg (HCO 3) 2, NaHCO 3 (nahcolite), Na 2 CO 3 (sodium or natrite), Na 2 CO 3 .H 2 O (thermonatrite), Na 2 CO 3 · 10H 2 O (natron) and mixtures thereof.

In an alternative according to the invention, a particle size cut is carried out in order to eliminate the very coarse fractions containing, in particular, the incuits or any insoluble organic impurity. The particle size cutoff is a particle size cutoff of at most 500 μm, said first fraction being formed of particles having a particle size of less than 500 μm and said second fraction being formed of particles having a particle size of more than 500 μm.

In a particular variant of the present invention, said particle size cutoff is a grain size cutoff of at most 400 μm, said first fraction being formed of particles having a particle size of less than 400 μm and said second fraction being formed of particles having a size of particles larger than 400 μm.

In a particular variant of the present invention, said particle size cut is a grain size cutoff of at most 250 μm, said first fraction being formed of particles having a particle size of less than 250 μm and said second fraction being formed of particles having a size of particles larger than 250 μm.

In a particular variant of the present invention, said particle size cutoff is a grain size cutoff of at most 200 μm, said first fraction being formed of particles having a particle size of less than 200 μm and said second fraction being formed of particles having a size of particles larger than 200 μm.

In another variant of the invention, a particle size cut is carried out to remove the fine particles. Said particle size cutoff is a particle size cutoff of at least 10 μm, said first fraction being formed of particles having a particle size of more than 10 μm and said second fraction being formed of particles having a particle size of less than 10 μm.

Preferably, said particle size cutoff is a particle size cutoff of at least 20 μm, said first fraction being formed of particles having a particle size of more than 20 μm and said second fraction being formed of particles having a particle size of less than 20 μm. .

More preferably, said particle size cutoff is a particle size cutoff of at least 50 μm, said first fraction being formed of particles having a particle size of more than 50 μm and said second fraction being formed of particles having a particle size of less than 50 μm. .

Advantageously, said granulometric cut-off is a particle size cutoff of at least 100 μm, said first fraction being formed of particles having a particle size of more than 100 μm and said second fraction being formed of particles having a particle size of less than 100 μm. .

In another variant according to the invention, said at least one granulometric cut comprises first and second grain size cuts with obtaining said first fraction, said second fraction and a third fraction.

In another variant according to the invention, said first particle size cutoff is a grain size cutoff of at most 500 μm, said first fraction being formed of particles having a particle size of less than 500 μm.

In yet another variant according to the invention, said first particle size cutoff is a particle size cutoff of at most 400 μm, said first fraction being formed of particles having a particle size of less than 400 μm.

Advantageously, said first particle size cutoff is a particle size cutoff of at most 250 μm, said first fraction being formed of particles having a particle size of less than 250 μm.

Preferably, said first particle size cutoff is a grain size cutoff of at most 200 μm, said first fraction being formed of particles having a particle size of less than 200 μm.

Particularly advantageously, the second or the third fraction is formed of particles having a particle size greater than 500 μm, preferably greater than 400 μm and preferably greater than 250 μm, in particular greater than 200 μm.

According to a preferred embodiment of the present invention, said second particle size cutoff is a particle size cutoff of at least 10 μm, said first fraction being formed of particles having a particle size greater than 10 μm.

Advantageously, said second particle size cut is a particle size cutoff of at least 20 μm, said first fraction being formed of particles having a particle size greater than 20 μm.

More preferably, said second particle size cutoff is a particle size cutoff of at least 50 μm, said first fraction being formed of particles having a particle size greater than 50 μm.

In a preferred variant, said second particle size cutoff is a particle size cutoff of at least 100 μm, said first fraction being formed of particles having a particle size greater than 100 μm.

Advantageously, the second or the third fraction is formed of particles having a particle size of less than 100 μm, preferably less than 50 μm, more preferably less than 20 μm, in particular less than 10 μm.

According to an advantageous embodiment of the present invention, said first fraction is formed of particles having a particle size of less than 500 μm, preferably less than 400 μm, preferably less than 250 μm and in particular less than 200 μm, and having a particle size greater than 10 μm, preferably greater than 20 μm, preferably greater than 50 μm, in particular greater than 100 μm.

Preferably, the granulometric cutting step at least 10 μm, preferably at least 20 μm, more preferably at least 50 μm, is performed by a hydrocycloning step.

In a variant of the present invention, said quicklime is a quicklime having a reactivity t8o measured according to the reactivity test described in the EN459-2 standard of between 0.5 and 20 minutes, preferably greater than 1 minute; in particular t8o is less than 10 minutes, preferably less than 5 minutes.

In another variant according to the present invention, the quenching is carried out with a water, for example a process water at a temperature of less than or equal to 20 ° C., preferably at 15 ° C., more preferably at 10 ° C., and more particularly at 5 ° C.

Advantageously, said extinction is carried out in a lime paste extinguisher.

More preferably, the additive is added in an amount of between 0.1 and 2.5% by weight, preferably between 0.1 and 1% by weight, relative to the total weight of quicklime. Other embodiments of the process according to the invention are indicated in the appended claims.

The present invention also relates to the use of the milk lime composition according to the invention in civil engineering, particularly in the treatment of soil, more preferably in the soil stabilization treatment.

Advantageously, the milk lime composition according to the invention is used in the treatment of wastewater aerobically or anaerobically.

Preferably, the lime milk composition according to the present invention is used in the treatment, in particular the conditioning and sanitizing, of mineral or organic sludge (especially manure or similar organic residues) or in precipitation processes.

According to a preferred embodiment, the milk lime composition according to the present invention is used in biochemical reactors, more particularly in biochemical reactors of organic acid type. Other embodiments of the use of the lime milk composition according to the invention are indicated in the appended claims. Other features, details and advantages of the invention will become apparent from the description given below, without limitation and with reference to the accompanying drawings.

Figure 1 is a graph showing an example of monomodal particle size distribution of a lime milk according to the invention.

Figure 2 is a graph illustrating a preferred example of monomodal particle size distribution of a lime milk according to the invention in the presence of MgO.

The present invention thus relates to a process for producing a lime milk in three stages which makes it possible to produce a lime milk in which the size distribution profile of the particles is monomodal and concerns coarse particles.

The first step is to extinguish quicklime in a dough extinguisher in the presence of a water-soluble additive to produce an aqueous suspension of lime. The second step consists of a granulometric cutting operation, also called granulometric screening, which makes it possible, among other things, to remove inert particles and impurities, such as silica or limestone, from the lime suspension, which may be diluted. The third step makes it possible to obtain, possibly after dilution, a milk of lime whose particle size distribution profile is monomodal and whose content of inert particles is reduced.

This particular distribution of the size of the monomodal particles makes it possible to obtain a milk of lime homogeneous in particle sizes and whose reactivity is also homogeneous.

The choice of extinction conditions and grain size cutoff largely depends on the characteristics of the lime milk resulting from the source of quicklime. The object of the invention is to produce, independently of the characteristics or qualities of the lime source, a lime milk composition whose particle size distribution profile is monomodal. The flexibility provided by the process according to the invention as for the source of lime is not the only advantage. In fact, the method also makes it possible to use different sources of extinguishing water, unlike earlier documents in which it had to be of high purity. Advantageously, a cold water will be preferred to achieve the extinction which allows to form coarser size particles compared to an extinction performed in the presence of water at room temperature.

The lime milk according to the present invention having said monomodal particle size distribution profile makes it particularly suitable for use in long residence time applications, such as the treatment, in particular the conditioning and the sanitization, of mineral sludge or organic (including manure or similar organic residues), biochemical reactors, and precipitation processes. EXAMPLES EXAMPLE 1

A quicklime obtained by calcination of a limestone sample A comprising less than 1% by weight of MgO and SiO2 has a water reactivity t8o less than 2 minutes, determined according to the procedure described in the EN459-2 standard.

1 g of technical grade Na 2 SO 4 is dissolved in 600 g of deionized water at 15 ° C to form an aqueous solution. 150 g of high reactivity quicklime are then reacted with the aqueous solution for a residence time of 30 minutes to obtain a slurry of milk of lime. A granulometric cut at 500 μm of the suspension of lime milk is carried out. The suspension thus obtained is diluted in order to obtain a solids content of 20%, relative to the total weight of the suspension.

Figure 1 illustrates the particle size distribution of the milk of lime obtained in this example.

Thus, the milk of lime obtained by the above-mentioned treatment method is characterized by a d10 of 47 μm, a d50 of 244 μm, a d90 of 494 μm and a d25 of 152 μm, a solubility index t 90 determined according to the standard. EN12485, greater than 60 seconds and a viscosity of less than 10 mPa.s for 20% by weight of solid material measured by Brookfield standard DV-III rheometer at a rate of. rotation of 100 revolutions per minute. EXAMPLE 2

A calcination of a sample of lime B which contains less than 1% by weight of MgO and SiO 2 is carried out and makes it possible to form quicklime having a reactivity with water greater than 5 minutes, determined according to EN459-2 standard.

15% by weight of dolomite is added to quicklime to obtain a mixture of lime having a MgO content of 3-5% by weight. Then, 0.5 g of Na 2 SO 4 was dissolved in 600 g of deionized water at 15 ° C to form an aqueous solution.

150 g of the lime mixture comprising dolomite is mixed with the aqueous solution and the reaction is allowed to continue for a residence time of 30 minutes to form a low reactivity slurry of lime.

A particle size cut at 500 μm is performed on the suspension of lime milk, which is then diluted to a solids content of 20%, based on the total weight of the suspension.

Figure 2 illustrates the particle size distribution of the obtained milk lime slurry. In Figure 2, it can be seen that the particle size distribution profile is not perfectly monomodal. The presence of a majority population in the suspension of whitewash can be isolated to achieve a monomodal particle size distribution profile. For example, a granulometric cut at 20 pm would make it possible to obtain such a focus of the majority populations mentioned above.

The milk of lime obtained is characterized by a d10 of 10 μm, a d50 of 247 μm, a d25 of 140 μm, a solubility index t 90, determined according to the EN12485 standard, greater than 60 seconds and a viscosity of less than 10 mPa. s for a quantity of solid material of 20% by weight, measured by Brookfield standard DV-III rheometer at a rotation speed of 100 revolutions per minute.

It is understood that the present invention is in no way limited to the embodiments described above and that many modifications can be made without departing from the scope of the appended claims.

Claims (41)

A lime milk composition comprising slaked lime particles suspended in an aqueous phase, characterized in that said slaked lime particles consist of more than 60% by weight, preferably more than 80% by weight, of more preferably more than 90% by weight of slaked lime particles, based on the total weight of the slaked lime particles, which have a particle size described by a monomodal particle size distribution profile. 2. Composition according to claim 1, wherein said particles have a particle size di0 greater than or equal to 10 μm, preferably greater than or equal to 15 μm, a particle size d50 greater than or equal to 20 μm, preferably greater than or equal to 20 μm. equal to 50 pm, more preferably greater than or equal to 100 pm, in particular greater than or equal to 200 pm, a particle size d90 greater than or equal to 200 pm, preferably greater than or equal to 300 pm, a lower particle size d90 or 1 mm as measured by laser diffraction. 3. A composition according to claim 1 or claim 2 having a viscosity of less than 300 mPa.s, preferably less than 150 mPa.s, and more preferably less than 50 mPa.s, especially less than of 25 mPa.s, as measured by Brookfield standard DV-III rheometer at a rotational speed of 100 rpm. 4. Composition according to any one of claims 1 to 3, wherein the composition is a suspension of slaked lime in the form of milk of lime having a solids content greater than or equal to 5%, preferably greater than or equal to 10% , preferably greater than or equal to 25%, in particular greater than or equal to 30%, particularly preferably greater than or equal to 40%, relative to the total weight of the suspension. 5. Composition according to any one of claims 1 to 4, having a dissolution rate in distilled water, as measured in EN12485, such that 90% of the slaked lime particles are dissolved after more than 15 seconds, preferably after more than 40 seconds and more preferably after more than 60 seconds. 6. Composition according to any one of claims 1 to 5, having a total content of sulfur, phosphorus, sodium and potassium in the range of 0.05 to 2% by weight, preferably 0.15. at 1% by weight, based on the total weight of the slaked lime. A method for producing lime milk, comprising the following steps: a) quenching a quicklime with an aqueous quenching phase by applying a proportion of quicklime to the aqueous quenching phase greater than 1 to 8 , in particular 1 to 6, and less than 1 to 3 to form a suspension of lime, said extinction being carried out in the presence of a water-soluble additive, b) at least one granulometric cut of said suspension of lime, optionally diluted, with obtaining at least a first fraction and a second fraction, c) obtaining said milk of lime, possibly after dilution, containing said first fraction. The method of claim 7, wherein said additive is added to the aqueous quenching phase, prior to or during said quenching, or to quicklime. 9. The method of claim 7 or claim 8, wherein said additive, preferably of mineral origin, is selected from the group consisting of sulphates having at least a moderate solubility in water greater than or equal to 0.1 g. / dm3, sulphites with at least moderate water solubility greater than or equal to 0.05 g / dm3, phosphates with at least moderate water solubility greater than or equal to 0.1 g / dm3, phosphites having at least a moderate solubility in water greater than or equal to 0.1 g / dm3, inorganic carbonates having at least a moderate solubility in water greater than or equal to 0.1 g / dm3, sulfuric acids, sulfurous, phosphoric, phosphorous, carbonic, and mixtures thereof. The process according to claim 9, wherein said sulfates are sulfate salts selected from the group consisting of alkali sulfates and alkaline earth sulfates and mixtures thereof, especially Na 2 SO 4 (thenardite), Na 2 SO 4 .10H 2 O (mirabilite ), CaSO4 (anhydrite), CaSO4.1H20 (hemihydrate), CaSO4.2H2O (gypsum), MgSO4, MgSO4.7H2O (epsomite) and mixtures thereof. The process of claim 9 or claim 10 wherein said sulfites are selected from the group consisting of Na 2 SO 3, NaHSO 3, CaSO 3, K 2 SO 3, KHSO 3 and mixtures thereof. The process according to any one of claims 9 to 11, wherein said phosphates are phosphate salts selected from the group consisting of alkaline salts of phosphates, particularly Na2HPO4, NaH2PO4 (nahpoite), K2HPO4 (archerite) , KH2PO4 and mixtures thereof. The process according to any one of claims 9 to 12, wherein said inorganic carbonates are selected from the group consisting of alkaline carbonates and alkaline earth carbonates and mixtures thereof, in particular Ca (HCO 3) 2, Mg (HC03) 2, NaHCO 3 (nahcolite), Na 2 CO 3 (sodium or natrite), Na 2 CO 3 .H 2 O (thermonatrite), Na 2 CO 3 · 10H 2 O (natron) and mixtures thereof. The process according to any one of claims 9 to 13, wherein said particle size cut is a particle size cutoff of at most 500 μm, said first fraction being formed of particles having a particle size of less than 500 μm and said second fraction being formed of particles having a particle size of more than 500 μm. The method of any one of claims 9 to 13, wherein said particle size cut is a particle size cut to not more than 400 μm, said first fraction being formed of particles having a particle size of less than 400 μm and said second fraction being formed of particles having a particle size of more than 400 μm. The process according to any one of claims 9 to 13, wherein said particle size cut is a particle size cut to not more than 250 μm, said first fraction being formed of particles having a particle size of less than 250 μm and said second fraction being formed of particles having a particle size of more than 250 μm. The process according to any one of claims 9 to 13, wherein said particle size cut is a particle size cutoff of at most 200 μm, said first fraction being formed of particles having a particle size of less than 200 μm and said second fraction being formed of particles having a particle size of more than 200 μm. 18. A method according to any one of claims 9 to 13, wherein said particle size cut is a particle size cut to at least 10 μm, said first fraction being formed of particles having a particle size of more than 10 μm and said second fraction being formed of particles having a particle size of less than 10 μm. The method of any one of claims 9 to 13, wherein said particle size cut is a particle size cut to at least 20 μm, said first fraction being formed of particles having a particle size of more than 20 μm and said second fraction being formed of particles having a particle size of less than 20 μm. The method of any one of claims 9 to 13, wherein said particle size cut is a particle size cut to at least 50 μm, said first fraction being formed of particles having a particle size of more than 50 μm and said second fraction being formed of particles having a particle size of less than 50 μm. The method of any one of claims 9 to 13, wherein said particle size cut is a particle size cut to at least 100 μm, said first fraction being formed of particles having a particle size of greater than 100 μm and said second fraction being formed of particles having a particle size of less than 100 μm. 22. A method according to any one of claims 9 to 13, wherein said at least one granulometric break comprises first and second grain size cuts to obtain said first fraction, said second fraction and a third fraction. The method of claim 22, wherein said first particle size cutoff is a particle size cutoff of at most 500 μm, said first fraction being formed of particles having a particle size of less than 500 μm. 24. The method of claim 22, wherein said first particle size cut is a grain size cut to not more than 400 μm, said first fraction being particles having a particle size of less than 400 μm. 25. The method according to claim 22, wherein said first particle size cutoff is a particle size cutoff of at most 250 μιτι, said first fraction being formed of particles having a particle size of less than 250 μm. The method of claim 22, wherein said first particle size cut is a particle size cut to not more than 200 μm, said first fraction being particles having a particle size of less than 200 μm. 27. The method of claim 22 to 26, the second or the third fraction is formed of particles having a particle size greater than 500 pm, preferably greater than 400 pm and preferably greater than 250 pm, in particular greater than 200 pm. The method of any one of claims 23 to 27, wherein said second particle size cut is a particle size cut to at least 10 μm, said first fraction being particles having a particle size of greater than 10 μm. The method of any one of claims 23 to 27, wherein said second particle size cut is a particle size cutoff of at least 20 μm, said first fraction being particles having a particle size greater than 20 μm. The method of any one of claims 23 to 27, wherein said second particle size cutoff is a particle size cutoff of at least 50 μm, said first fraction being formed of particles having a particle size of greater than 50 μm. 31. A process according to any one of claims 23 to 27, wherein said second particle size cut is a particle size cutoff of at least 100 μm, said first fraction being particles having a particle size greater than 100 μm. 32. A process according to any one of claims 23 to 31, wherein said first fraction is formed of particles having a particle size of less than 500 μm, preferably less than 400 μm, preferably less than 250 μm and in particular less than 200 μm and having a particle size greater than 10 μm, preferably greater than 20 μm, preferably greater than 50 μm, preferably greater than 100 μm. 33. The process according to claim 32, wherein the granulometric cutting step of at least 10 μm, preferably at least 20 μm, more preferably at least 50 μm, is carried out by a hydrocycling step. 34. A method according to any one of claims 7 to 33, wherein said quicklime is a quicklime having a t8o reactivity, measured according to the reactivity test described in EN459-2 between 0.5 and 20 minutes, preferably greater than 1 minute; in particular less than 10 minutes, preferably less than 5 minutes. Process according to any one of claims 7 to 34, wherein the quenching is carried out with water, for example process water at a temperature of less than or equal to 20 ° C, preferably at 15 ° C, plus preferably at 10 ° C, and more particularly at 5 ° C. 36. The method according to any one of claims 7 to 35, wherein said extinction is carried out in a limestone extinguisher. 37. Process according to any one of the preceding claims 7 to 36, in which the additive is added in an amount of between 0.1 and 2.5% by weight, preferably between 0.1 and 1% by weight. relative to the total weight of quicklime. 38. Use of the composition of lime milk according to claims 1 to 6 in the civil engineering, particularly in the treatment of soil, more preferably in the soil stabilization treatment. 39. Use of the milk lime composition according to claims 1 to 6, in the treatment of aerobic or anaerobic wastewater. 40. Use of the milk lime composition according to claims 1 to 6 in the treatment, in particular the conditioning and sanitization of mineral or organic sludge or in precipitation processes. 41. Use of the milk lime composition according to claims 1 to 6, in biochemical reactors, more particularly in biochemical reactors of organic acid type.