FR2841895A1 - Lime-based material, useful as a binder material, water absorber and/or energy source, comprises partially hydrated calcium oxide - Google Patents

Abstract

Lime-based material comprising pre-hydrated calcium oxide in which its complete conversion to calcium hydroxide on contact with water is delayed by at least 20 minutes. Independent claims are also included for the preparation of the material, its uses and articles manufactured from a mixture containing the material.

Description

MY LIME BASE COMPOSED OF CaO PARTIALLY

  HYDRATE, PREPARATION PROCESS AND USE THEREOF

  THAT BINDER, WATER SENSOR AND / OR SOURCE OF ENERGY

FIELD OF THE INVENTION

  The present invention relates to (i) a lime-based material consisting of CaO partially hydrated with Ca (OH) 2, as a new industrial product, (ii) its process of preparation and (iii) its use as binder, water sensor and / or energy source, in particular in the production of articles or lime

  acts as a binding agent, water suppressant and / or energy source.

ARTANTERIEUR

  We know that the reaction: CaO + H2O -> Ca (OH) 2 (1) is exothermic, immediate and complete. It is energized as soon as

  that calcium oxide is in contact with water, and ends very quickly.

  In practice, with the CaO currently available on the market, the kinetics of reaction 1 is very high: there is a duration less than or equal to 3 minutes between the

  contacting CaO and H20 and the transformation of all CaO into Ca (OH) 2.

  Thus with the CaO produced by straight or rotary lime kilns, this duration is generally less than 5 minutes. However, in certain cases, the hydration of CaO produced in coke ovens may have a slower kinetics: the reaction is initiated without delay when contacting CaO and

  H2O then ends in no more than 15 minutes after said contacting.

PURPOSE OF THE INVENTION

  It turns out that there is an interest in delaying reaction 1 after contacting CaO and H20, that is to better shape the article where the lime will act as a binder, water sensor and / or source. energy, on the one hand, or

  still to better protect the environment, on the other hand.

  Reaction 1 carried out in restricted confinement (in particular a small reactor) can be explosive. CaO spread on plants

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  destroys them. When CaO comes into contact with an eye, it is necessary in less than 2-3 minutes to treat this eye with water buffered to pH 5 and physiologically

acceptable to save it.

  According to the invention, it is proposed to provide a new technical solution for delaying the initiation of reaction 1, without using a

  significant amount of a mineral filler serving as a solid CaO diluent.

OBJECT OF THE INVENTION

  The new technical solution which is recommended to solve the problem of the delay in triggering said reaction I is based on the use of a lime-based material consisting of CaO partially hydrated with

previous Ca (OH) 2.

  We have a surprisingly discovered effect that partially CaO

  hydrated, reacted with H2O, reacts only after a certain lag time.

  According to a first aspect of the invention, a lime-based material is provided, characterized in that it consists of calcium oxide partially hydrated beforehand, and in that it exhibits after being brought into contact with water triggering of reaction 1: CaO + H20 -> Ca (OH) 2 (1)

delayed by at least 20 minutes.

  According to a second aspect of the invention, a method is provided for preparing said lime-based material, said method being characterized in that an excess of CaO is reacted, according to reaction 1, with stirring.

stoichiometric conditions.

  According to a third aspect of the invention, use is provided of said

  material as a binder, water sensor and / or energy source.

SHORT DESCRIPTION OF THE DRAWING

  In FIG. 1 of the appended drawing, the curves relating to the development of reaction 1 have been represented in the system (Y, t) to illustrate the kinetics of said reaction 1 depending on whether or not calcium oxide has been previously partially hydrated. Y represents the percentage by weight of Ca (OH) 2, formed during the reaction (i.e. the percentage of CaO which has been hydrated), as a function of the reaction time t expressed in minutes. FIG. 1 represents the kinetics of a CaO produced in the usual way; curve 2 represents the kinetics of a material according to the invention consisting of CaO before and partially

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  hydrated [here having a Ca (OH) 2 content of 10% by weight and a CaO content

90%].

  DETAILED DESCRIPTION OF THE INVENTION

  From a practical point of view, the lime-based material according to the invention will have a hydration capacity less than or equal to 95% of that of a lime with conventional reactivity. In other words, the material according to the invention will contain at least 5% by weight of Ca (OH) 2; with such a material, the delay in hydration in the presence of water will be adjustable in an interval ranging from 20 minutes to more than 2 hours. Advantageously, the lime-based material according to the invention will consist of calcium oxide (90 to 95% by weight) before and partially

  hydrated with calcium hydroxide (10 to 5% by weight).

  Advantageously, the delay in hydration can be adjusted in an interval ranging from 20 minutes to more than 2 h, in particular by choosing the initial content of Ca (OH) 2 in the CaO partially hydrated beforehand. This initial content will be greater than or equal to 5% by weight. The delay in hydration

  increases with the initial Ca (OH) 2 content in partially hydrated CaO.

  Conveniently, the process of the invention will include the reaction of CaO with H2O with stirring, where CaO is in excess relative to the stoichiometric conditions. For example, by reacting 1000 parts by weight of CaO divided with 100 parts by weight of H2O, the temperature of the reaction medium (in movement by means of a rotary agitator providing a suitable shear force) rises quickly and volatilizes a significant part of the water supplied. After cooling, there remains calcium oxide (approximately 90%

  by weight) partially hydrated with Ca (OH) 2 (approximately 10% by weight of Ca (OH) 2).

  When this calcium oxide is brought into contact with water, it remains substantially inert in reaction until hydration

is growing rapidly.

  Thanks to this inertia, the lime-based material according to the invention is useful for the preparation of a formable article in which the lime acts as a binder and / or water suppressant. Indeed, as long as the hydration does not develop quickly, there is the possibility of handling and shaping the product

  that we want to consolidate by implementing reaction 1.

  With this material, it is in particular possible to manufacture any article requiring water for its shaping (in particular earth, clay or cement). Such an article can be molded without difficulty, the water used for its preparation being eliminated by evaporation, on the one hand, and captured in the formation of Ca (OH) 2,

on the other hand.

  This material can also be used for the production of plasters and coverings requiring drying or allowing drying of the surfaces thus covered. In particular, an article containing lime is recommended, characterized in that it is produced from a mixture comprising: (a) a material based on lime consisting of CaO partially hydrated beforehand with Ca (OH) 2 and which is in divided form (in particular powder or aggregate), (b) water to complete reaction 1, and (c) where appropriate, an inorganic or organic filler in divided form (in particular powder or granulate or even liquid), then hardened by reaction 1, said mixture being formable for at least 20

minutes before hardening.

  As an example of a mineral filler (c), mention may especially be made of earth, clay, cement. As an example of an organic filler (c), it is possible in particular

  cite superplasticizers and organic paints.

  According to a particular mode of implementation, the composition (a) + (b) + (c) can be liquid, in particular in the case of a whitewash having a hydration capacity due to the presence of CaO. Unlike traditional lime milk where all the CaO present has been transformed into hydrated form Ca (OH) 2, here we have a substantially inert liquid during the lag time (ie delay in hydration) and still containing CaO useful for enforce

reaction 1.

  As an "active" lime milk (ie containing CaO), an article containing lime and produced from a mixture comprising: (a) a lime-based material consisting of CaO partially hydrated beforehand is recommended as Ca (OH) 2 and which is in divided form, (b) water in sufficient quantity for suspension, and (c) an organic filler which is a superplasticizer, this mixture, which is in the form of a suspension , being stable during

minus 20 minutes.

  This "active" lime milk, which can be homogenized, can be used in particular to harden the sludge, by reacting (having regard to the CaO that it contains) with the water they contain. Overall this "active" lime milk absorbs water

sludge and hardens said sludge.

  Other advantages and characteristics of the invention will be better understood on reading the following examples of embodiments which are in no way limiting but which are provided by way of illustration.

EXAMPLE I

  Use is made of 1 kg of lime (CaO) divided (powder or aggregate) having a hydration capacity of 100% and having, according to reaction 1, a total reaction time of less than 5 minutes between contacting CaO with H 2 O and completion of said reaction. This lime has kinetics represented by the

curve 1 of figure 1.

  0.1 kg of water is poured into this lime, stirred by means of a rotary agitator. The reaction starts spontaneously. A portion of the water is evaporated by the heat produced, the remaining portion serving for the hydration of CaO to Ca (OH) 2. Calcium oxide is obtained having a hydration capacity of%, that is to say CaO (approximately 90% by weight) partially hydrated

  as Ca (OH) 2 (approximately 10% by weight).

  The lime-based material thus obtained, when it is brought into contact with H2O, exhibits a hydration delay equal to or greater than 20 minutes (see

  curve 2 of said figure 1) and adjustable beyond, if necessary.

  EXAMPLE 2 (Comparative) For comparison, the hydration kinetics of a mixture obtained by incorporation with stirring of 10% by weight of Ca (OH) 2 and 90% were studied.

by weight of CaO.

  This mixture, when it is brought into contact with H2O, spontaneously transforms, without delay in hydration, into Ca (OH) 2 in less than 5 minutes. From the kinetic point of view, we obtain a curve similar to curve 1 in Figure 1, with the difference that it starts from the value Y = 10 instead of Y = 0, due to the

  initial content of 10% by weight of Ca (OH) 2.

EXAMPLE 3

  A mixture is prepared from 100 parts by weight of the material of Example 1 divided, 80 parts by weight of water and 450 parts by weight of divided clay, under kneading. This mixture is distributed in molds where reaction 1 takes place, the heat released driving off the excess water. The lime material according to

  the invention intervenes here, as a reagent and source of energy.

  The implementation of the method of Example 3 makes it possible to facilitate, or even eliminate, the drying which is essential before the baking of the molded article.

thus obtained.

EXAMPLE 4

  A milk of lime is prepared from the material obtained in Example 1, a superplasticizer and an amount of water sufficient for suspension, this water being introduced last into the mixture of the material of Example 1

with the superplasticizer.

  Such milk has a hydration capacity less than or equal to 95%

  that of a CaO with conventional reactivity.

EXAMPLE 5

  The milk of lime obtained in Example 4 is mixed with an industrial slurry during the standby time according to the invention, which is greater than 20 minutes. At the end of the latency time, the hydration of the CaO present ensures the

solidification of the mud.

Claims (10)

  1. Lime-based material, characterized in that it consists of calcium oxide partially hydrated beforehand, and in that it exhibits, after contact with water, triggering of reaction 1: CaO + H2O - Ca (OH) 2 (1) delayed by at least 20 minutes.   2. Material according to claim 1, characterized in that the calcium oxide contains at least 5% by weight of Ca (OH) 2, advantageously said material can in particular contain 90 to 95% by weight of calcium oxide and 10 to% by weight of calcium hydroxide. 3. Material according to claim 2, characterized in that it has a   trigger of reaction 1 delayed from 20 minutes to more than two hours.   4. Method for preparing a lime-based material according to one   any one of claims 1 to 3, said method being characterized in that one   reacts, according to reaction 1, and with stirring, an excess of CaO relative to under stoichiometric conditions.   5. Method according to claim 4, characterized in that 1 kg of CaO is reacted with 0.1 kg of H2O to obtain a calcium oxide containing   approximately 10% by weight of Ca (OH) 2.   6. Use of a material according to any one of claims 1 to   3, characterized in that said material is used as a binder, sensor of water and / or energy source.   7. Use according to claim 6, for the preparation of a formable article, in which the lime acts as a binding agent, suppressor. of water and / or energy source.   8. An article containing lime, characterized in that it is produced from a mixture comprising:   (a) a material according to any one of claims 1 to 3, which is   in divided form, (b) water to complete reaction 1, and (c) if necessary, an inorganic or organic filler in divided form, then hardened by reaction 1, said mixture being capable of being shaped for at least 20 minutes before hardening.   9. An article containing lime, characterized in that it is produced from a mixture comprising:   (a) a material according to any one of claims 1 to 3, which is   in divided form, (b) water for suspension, and (d) an organic filler which is a superplasticizer, this mixture, which is in the form of a suspension being stable during minus 20 minutes.   10. Article according to claim 9, characterized in that it is in the form of a lime milk containing CaO, and is in particular usable for harden the sludge.