WO2015135954A1

WO2015135954A1 - Lime water composition

Info

Publication number: WO2015135954A1
Application number: PCT/EP2015/054988
Authority: WO
Inventors: Luis Alfredo Diaz Chavez; Robert Sebastian GÄRTNER; Xavier PETTIAU
Original assignee: Lhoist Recherche Et Developpement Sa
Priority date: 2014-03-11
Filing date: 2015-03-10
Publication date: 2015-09-17
Also published as: FR3018518A1; FR3018518B1

Abstract

The invention relates to a lime water composition containing slaked lime particles suspended in an aqueous phase. Said composition is characterized in that said slaked lime particles consist of over 60 wt%, preferably over 80 wt%, and more preferably over 90 wt% slaked lime particles relative to the total weight. The invention also relates to slaked lime particles that have a particle size described by a unimodal particle size distribution profile. The invention further relates to the method for manufacturing said composition.

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 (see for example EP 943 590 for producing calcium silicates, in a multitude of applications, in particular civil engineering, more particularly soil treatment, preferably soil stabilization, treatment, in particular conditioning and hygienization, of mineral or organic sludge (in particular manure or similar organic residues) or precipitation processes , where saturation control is critical, in pH adjustment, mineralization of drinking water, neutralization of chemical reactions and aerobic or anaerobic wastewater treatment.

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. Known milks of lime are described in US2004 / 0258612, WO2005 / 014483, FR2687396, US4464353.

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 , representing globally a few dozen grams per kilogram. Nevertheless, 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 0 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 extinction, 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. Moreover, in the context 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. 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 the quicklime, that is to say the reaction rate 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 t ₈₀ , the time required to reach 80% of the maximum temperature increase generated by the addition of 150 g of quicklime in a volume of water of 600 cm ³ initially to 20 ° C. According to this standard, the reactivity of quicklime can also be characterized by t ₆₀ , the time required to reach 60 ° C for a water volume of 600 cm ³ initially at 20 ° C, from the addition of 150 g of quicklime, the value of which is often similar to that of t ₈₀ .

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 drinking water softening ^" , MWM van Eekeren, JAM van Paassen, CWAM Merks, KIWA NV Research and Consultancy, Nieuwegein, September 1993 "produced and distributed by the KIWA, Royal Netherlands Institute of 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 it remains stable having thus reaches a maximum value. The time to reach this maximum conductivity since the beginning of the measurement is noted t ₁₀₀ . ₉₀ is defined as the time required to reach 90% of the maximum conductivity. It is this value t ₉₀ obtained which is considered to represent the reactivity of 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 milks of lime will be low if the quantity t ₉₀ 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 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.

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, advantageously 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 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 size distribution profile of Multimodal particles can comprise a significant population that is between 0.1 and 30 μιτι as well as several populations of coarser agglomerates. Populations between 0.1 and 30 μηη 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 bright / slaked lime particles which did not necessarily find 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.

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 due to 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 size greater than ₁₀ of particles or equal to 10 μηη, preferably greater than or equal to 15 μηη, a size greater than ₅₀ of particles or equal to 20 μηη, preferably greater than or equal to 50 μηη plus preferably greater than or equal to 100 μηη, in particular greater than or equal to 200 μηη, a particle size d ₉₀ greater than or equal to 200 μηη, preferably greater than or equal to 300 μηη, a particle size d ₉₀ less than or equal to 1 mm as measured by laser diffraction. The notation d _x represents a diameter, expressed in μηη, with respect to which X% by volume of the particles or grains measured are smaller.

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, based on 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 milk of lime, comprising the following steps:

a) an extinction of a quicklime by an aqueous phase of extinction by applying a proportion by weight of quicklime to the aqueous phase of extinction greater than 1 for 8, in particular 1 for 6, and less than 1 for 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, possibly diluted, obtaining at least a first fraction and a second fraction,

c) obtaining said milk of lime, 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 obtained lime but makes it more homogeneous and / or also a cut in order to eliminate only the fine particles to keep them for another application and thus enhance 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 d-value ₅₀ , 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 in weight of slaked lime particles, based on 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 of extinction, before or during said extinction, or to 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 chosen from the group consisting of sulphates having at least less a moderate solubility in water greater than or equal to 0.1 g / dm ³ , sulphites having at least a moderate solubility in water greater than or equal to 0.05 g / dm ³ , phosphates having at least one moderate solubility in water greater than or equal to 0.1 g / dm ³ , phosphites having at least moderate solubility in water greater than or equal to 0.1 g / dm ³ , inorganic carbonates having at least one solubility moderate in water greater than or equal to 0.1 g / dm ³ , 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 S0 ₄ (thenardite), Na ₂ SO ₄ .10H ₂ O ( mirabilite), CaSO ₄ (anhydrite),

CaS0 ₄ ^ -. L ₂ 0 (hemihydrate) of CaS0 ₄ .2H ₂ 0 (gypsum), of MgS0 _4, of MgS0 ₄ .7H ₂ 0 (epsomite) and mixtures thereof.

According to a preferred embodiment of the present invention, said sulfites are selected from the group consisting of Na ₂ S0 _3, NaHS0 ₃ of of CaS0 _3, K ₂ S0 _3, KHS0 ₃ and the mixtures thereof.

In an advantageous embodiment, said phosphates are salts of phosphates chosen from the group consisting of alkaline salts of phosphates, in particular Na ₂ HPO ₄ , NaH ₂ PO ₄ (nahpoite), K ₂ HPO ₄ (archerite), KH ₂ P0 ₄ 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 (HC0 ₃ ) ₂ , Mg (HC0 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. Said granulometric cutting step is a particle size cutting step of at most 500 μηη, said first fraction being formed of particles having a particle size of less than 500 μηη and said second fraction being formed of particles having a particle size of more than 500 μηη.

In a particular variant of the present invention, said granulometric cutting step is a granulometric cutting step at at most 400 μηη, said first fraction being formed of particles having a particle size of less than 400 μηη and said second fraction being formed of particles having a particle size of more than 400 μηη.

In a particular variant of the present invention, said granulometric cutting step is a granulometric cutting step at at most 250 μηη, said first fraction being formed of particles having a particle size of less than 250 μηη and said second fraction being formed of particles having a particle size of more than 250 μηη.

In a particular variant of the present invention, said granulometric cutting step is a granulometric cutting step of at most 200 μηη, said first fraction being formed of particles having a particle size of less than 200 μηη and said second fraction being formed of particles having a particle size of more than 200 μηη.

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 μηη, said first fraction being formed of particles having a particle size of more than 10 μηη and said second fraction being formed of particles having a particle size of less than 10 μηη.

Preferably, said granulometric cutting step is a granulometric cutting step of at least 20 μηη, said first fraction being formed of particles having a particle size of more than 20 μηη and said second fraction being formed of particles having a particle size of less than 20 μηη.

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

Advantageously, said granulometric cutting step is a granulometric cutting step of at least 100 μηη, said first fraction being formed of particles having a particle size of more than 100 μηη and said second fraction being formed of particles having a particle size of less than 100 μηη.

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 granulometric cutting step is a granulometric cutting step at at most 500 μηη, said first fraction being formed of particles having a particle size of less than 500 μηη.

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

Advantageously, said first granulometric cutting step is a granulometric cutting step at at most 250 μηη, said first fraction being formed of particles having a particle size of less than 250 μηη.

Preferably, said first granulometric cutting step is a granulometric breaking step of at most 200 μηη, said first fraction being formed of particles having a particle size of less than 200 μηη.

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

According to a preferred embodiment of the present invention, said second granulometric cutting step is a granulometric cutting step of at least 10 μηη, said first fraction being formed of particles having a particle size greater than 10 μηη. Advantageously, said second granulometric cutting step is a granulometric cutting step of at least 20 μηη, said first fraction being formed of particles having a particle size greater than 20 μηη.

More preferably, said second granulometric cutting step is a granulometric cutting step of at least 50 μηη, said first fraction being formed particles having a particle size greater than 50 μηη.

In a preferred variant, said second granulometric cutting step is a granulometric cutting step of at least 100 μηη, said first fraction being formed of particles having a particle size greater than 100 μηη.

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

According to an advantageous embodiment of the present invention, said first fraction is formed of particles having a particle size of less than 500 μηη, preferably less than 400 μηη, preferably less than 250 μηη and in particular less than 200 μηη and having a particle size greater than 10 μηη, preferably greater than 20 μηη, preferably greater than 50 μηη, in particular greater than 100 μηη by any breaking means such as sieving or hydrocycloning.

Preferably, the granulometric cutting step to at least 10 μηη, preferably at least 20 μηη, more preferably at least 50 μηη, is carried out by a hydrocycloning step.

In a variant of the present invention, said quicklime is a quicklime having a reactivity t ₈₀ 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 t ₈₀ 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 the treatment of aerobic or anaerobic wastewater.

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 gets, optionally after dilution, a lime milk 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. Indeed, the method also makes it possible to use different sources of extinguishing water in contrast to the typically known techniques 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 SiO ₂ has a water reactivity t _{80 of} less than 2 minutes, determined according to the procedure described in standard EN459. 2.

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 μηη of the suspension of whitewash 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, with the particles having a size of less than 500 μm.

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 di ₀ of 47 μηη, a d ₅₀ of 244 μηη, a d ₉₀ of 494 μηη and a d ₂₅ of 152 μηη, a solubility index t ₉₀ , determined according to the EN12485 standard, greater than 60 seconds and a viscosity of less than 10 mPa.s at 20% by weight of solid material measured by Brookfield standard DV-III rheometer at a rotation speed 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 allows to form quicklime having a water reactivity t ₈₀ greater than 5 minutes, determined according to the 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 μηη is performed on the suspension of whitewash and the particles smaller than 500 μηη in the suspension are then diluted to a solids content of 20%, relative to 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 μηη would make it possible to obtain such a focus of the majority populations mentioned above, which would thus have a size greater than 20 μηη.

The milk of lime obtained is characterized by a di ₀ of 10 μηη, a d ₅₀ of 247 μηη, a d ₂₅ of 140 μηη, a solubility index t ₉₀ , determined according to the EN12485 standard, greater than 60 seconds and a lower viscosity. at 10 mPa.s for a quantity of solid matter of 20% weight, measured by standard Brookfield DV-III rheometer at a rotational speed of 100 rpm.

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

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 size greater than ₁₀ of particles or equal to 10 μηη, preferably greater than or equal to 15 μηη, a size greater than ₅₀ of particles or equal to 20 μηη, preferably greater than or equal to 50 μηη, more preferably greater than or equal to 100 μηη, in particular greater than or equal to 200 μηη, a particle size d _{90 of} greater than or equal to 200 μηη, preferably greater than or equal to 300 μηη, a particles d ₉₀ less than or equal to 1 mm as measured by laser diffraction.

3. A composition according to claim 1 or claim 2, 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%, advantageously greater than or equal to 10%, of preferentially 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.

4. Composition according to any one of claims 1 to 3, having a dissolution rate in water distilled, 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.

5. Composition according to any one of claims 1 to 4, 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.

6. A process for producing milk of lime, comprising consecutively:

a) a step of quenching a quicklime with an aqueous quenching phase by applying a proportion by weight 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 step of granulometric cutting of said suspension of lime, possibly diluted, obtaining at least a first fraction and a second fraction,

c) a step of obtaining said milk of lime, possibly after a dilution step, containing said first fraction.

The method of claim 6, wherein said additive is added to the aqueous quenching phase, prior to or during said quenching, or to quicklime.

The process according to claim 6 or claim 7, 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. / dm ³ , sulphites having at least moderate water solubility greater than or equal to 0.05 g / dm ³ , phosphates having at least moderate water solubility greater than or equal to 0.1 g / dm ³ , phosphites having at least a moderate solubility in water greater than or equal to 0.1 g / dm ³ , inorganic carbonates having at least a moderate solubility in water greater than or equal to 0.1 g / dm ³ sulfuric, sulfurous, phosphoric, phosphorous, and carbonic acids, and mixtures thereof.

The process according to claim 8, wherein said sulfates are sulfate salts selected from the group consisting of alkali sulfates and alkaline earth sulfates and mixtures thereof, particularly Na ₂ SO ₄ (thenardite), Na ₂ SO ₄ · 10H ₂ O (mirabilite), CaSO ₄ (anhydrite), CaSO ₄ · H ₂ 0 (hemihydrate), CaSO ₄ · 2H ₂ O (gypsum), MgSO ₄ , MgSO ₄ · 7H ₂ 0 (epsomite) and their mixtures.

10. The method of claim 8 or claim 9, wherein said sulfites are selected from the group consisting of Na ₂ S0 _3, NaHS0 ₃ of of CaS0 _3, K ₂ S0 _3, KHS0 ₃ and the mixtures thereof.

The process according to any of claims 8 to 10, wherein said phosphates are phosphate salts selected from the group consisting of alkaline salts of phosphates, particularly Na ₂ HPO _{4 /} NaH ₂ PO ₄ (nahpoite), K ₂ HPO ₄ (archerite), KH ₂ PO ₄ and mixtures thereof.

12. Process according to any one of claims 8 to

11, wherein said inorganic carbonates are selected from the group consisting of alkali carbonates and alkaline earth carbonates and mixtures thereof, in particular Ca (HC0 ₃ ) _{2 /} Mg (HC0 ₃ ) _{2 /} NaHCO ₃ (nahcolite ), Na ₂ CO ₃ (sodium hydroxide or natrite), Na ₂ CO ₃ .H ₂ O (thermonatrite), Na ₂ CO ₃ .10H ₂ O (natron) and mixtures thereof.

The method according to any one of claims 6 to 12, wherein said granulometric cutting step is a granulometric breaking step of at most 500 μηη, said first fraction being formed of particles having a particle size of less than 500 μηη. and said second fraction being formed of particles having a particle size of more than 500 μηη.

14. Process according to any one of claims 6 to

12, wherein said granulometric cutting step is a grain size cutting step of at most 400 μηη, said first fraction being formed of particles having a particle size of less than 400 μηη and said second fraction being formed of particles having a particle size of particles of more than 400 μηη.

15. A method according to any one of claims 6 to 12, wherein said granulometric cutting step is a particle size cutting step to at most 250 μηη, said first fraction being formed of particles having a particle size of less than 250 μηη. and said second fraction being formed of particles having a particle size of more than 250 μηη.

The method according to any one of claims 6 to 12, wherein said granulometric cutting step is a particle size cutting step of at most 200 μηη, said first fraction being formed of particles having a particle size of less than 200 μηη. and said second fraction being formed of particles having a particle size of more than 200 μηη.

17. A method according to any one of claims 6 to 12, wherein said granulometric cutting step is a granulometric cutting step of at least 10 μηη, said first fraction being formed of particles having a particle size of more than 10 μηη. and said second fraction being formed of particles having a particle size of less than 10 μηη.

18. A method according to any one of claims 6 to 12, wherein said granulometric cutting step is a granulometric cutting step of at least 20 μηη, said first fraction being formed of particles having a particle size of more than 20 μηη and said second fraction being formed of particles having a particle size of less than 20 μηη.

19. A method according to any one of claims 6 to 12, wherein said granulometric cutting step is a granulometric breaking step at least 50 μηη, said first fraction being formed of particles having a particle size of more than 50 μηη and said second fraction being formed of particles having a particle size of less than 50 μηη.

20. Process according to any one of claims 6 to

12, wherein said granulometric cutting step is a granulometric cutting step of at least 100 μηη, said first fraction being formed of particles having a particle size of more than 100 μηη and said second fraction being formed of particles having a particle size of less than 100 μηη.

21. The method according to any of claims 6 to 12, wherein said at least one granulometric cut comprises first and second grain size cuts to obtain said first fraction, said second fraction and a third fraction.

22. The method of claim 21, wherein said first granulometric cutting step is a particle size cutting step to at most 500 μηη, said first fraction being formed particles having a particle size of less than 500 μηη.

23. The method of claim 21, wherein said first granulometric cutting step is a granulometric breaking step to at most 400 μηη, said first fraction being formed particles having a particle size of less than 400 μηη.

24. The method of claim 21, wherein said first granulometric cutting step is a particle size cutting step to at most 250 μηη, said first fraction being formed particles having a particle size less than 250 μηη.

25. The method according to claim 21, wherein said first granulometric cutting step is a particle size cutting step of at most 200 μηη, said first fraction being formed of particles having a particle size of less than 200 μηη.

26. The process according to claim 21 to 25, the second or third fraction is formed of particles having a particle size greater than 500 μηη, preferably greater than 400 μηη and preferably greater than 250 μηη, in particular greater than 200 μιτι.

27. A method according to any one of claims 21 to 26, wherein said second granulometric cutting step is a granulometric cutting step of at least 10 μηη, said first fraction being formed particles having a particle size greater than 10 μηη .

28. A method according to any one of claims 21 to 26, wherein said second granulometric cutting step is a granulometric cutting step of at least 20 μηη, said first fraction being formed particles having a particle size greater than 20 μηη .

29. A method according to any one of claims 21 to 26, wherein said second granulometric cutting step is a granulometric breaking step at least 50 μηη, said first fraction being formed particles having a particle size greater than 50 μηη .

30. A method according to any one of claims 21 to 26, wherein said second granulometric cutting step is a granulometric cutting step of at least 100 μηη, said first fraction being formed particles having a particle size greater than 100 μηη .

31. A process according to any one of claims 21 to 30, wherein said first fraction is formed of particles having a particle size of less than 500 μηη, preferably less than 400 μηη, preferably less than 250 μηη and in particular less than 200 μηη and having a particle size greater than 10 μηη, preferably greater than 20 μηη, preferably greater than 50 μηη, preferably greater than 100 μιτι.

32. The method of claim 31, wherein the granulometric cutting step at least 10 μηη, preferably at least 20 μηη, more preferably at least 50 μηη is performed by a hydrocycloning step.

33. Process according to any one of claims 6 to

32, wherein said quicklime is a quicklime having a reactivity t _80; 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 less than 10 minutes, preferably less than 5 minutes.

34. Process according to any one of claims 6 to

33, in which quenching is carried out with water, for example process water at a temperature of less than or equal to 20 ° C, preferably

15 ° C, more preferably at 10 ° C, and more particularly at 5 ° C.

35. Process according to any one of claims 6 to

34, wherein said extinguishing is carried out in a lime paste extinguisher.

36. Process according to any one of the preceding claims 6 to 35, 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.

37. Use of the milk lime composition according to claims 1 to 5 in the treatment of aerobic or anaerobic wastewater.

38. Use of the milk lime composition according to claims 1 to 5, in the treatment, in particular the conditioning and sanitization of mineral or organic sludge or in precipitation processes.

39. Use of the milk lime composition according to claims 1 to 5 in biochemical reactors, more particularly in biochemical reactors of organic acid type.