LU83139A1 - BINDERS BASED ON RESIDUAL GYPSUM AND SYNTHETIC ANHYDRITE - Google Patents

Description

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The present invention relates to new binders obtained by simple mixing of residual gypsum from the chemical industry or from thermal power stations with a synthetic anhydrite. Up to now, the recovery of gypsum by-products of the chemical industry, such as phosphogypsum, or gypsum resulting from the desulfurization of combustion gases from thermal power plants, 'has not found a solution. "... absolutely satisfactory, 10 The processes aimed at obtaining from these by-products a calcium sulphate hemihydrate, usable as a binder in the building industry, have the disadvantage of requiring both purification of the residual gypsum and a calcination operation, It has also been proposed in European patent application n ° 0 007 610 to mix the gypsum resulting from the desulfurization of the combustion gases from thermal power stations, after partial or total dehydration, with a natural gypsum dehydrated, where to dehydrate simultaneously the mixture of residual gypsum and natural gypsum. This process also involves A costly dehydration step in energy,

The Applicant has discovered quite unexpectedly that one can obtain very good quality binder binders by simply mixing residual gypsum of chemical origin or coming from the desulfurization of gas! * I thermal power plants with a synthetic anhydrite binder, | without any purification or calcination, i, <; The term “synthetic anhydrite binder” is intended to mean a binder in accordance with the German standard DIN 4208, obtained from fluorarihydrite, by-product of the manufacture of fluorhydriqua acid, or from phosphoanhydrite, obtained for example according to the process. French patent no. 2 423 463 I of the applicant, Natural anhydrite is not usable in the preparation of the binders according to the invention,.

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Residual gypsum from the chemical industry, like phosphogypsum, which can be used according to the invention, contains at least 90 £, and preferably at least 95% of calcium sulphate dihydrate Ca50 t 2 H2D. They are contaminated with various impurities, such as calcium fluoride, silica, iron oxides, alumina, phosphates, etc. ”.

Their maximum particle size is generally less than 0.3 mm, the average particle size being of the order of 30 to 40 μm. The residual gypsum from thermal power stations, also usable according to the invention, is obtained during the course. desulfurization of the combustion gases, of these plants by washing with an aqueous lime solution. First a mixture of neutral sulfite and calcium acid sulfite is formed, which is oxidized by air to calcium sulfate dihydrate. This raw gypsum cohtient at least 90 £ in weight of CaSQ ^, 2 ^ 0 * It is contaminated by very many impurities, like sulfites, chlorides, carbonates, silica, alumina, magnesia, oxides of iron, etc.

Its maximum particle size is generally less than 0.2 mm, the average particle size being of the order of 30 to 40 μm.

The respective proportions of residual gypsum and synthetic anhydrite in the mixtures constituting the 25 new binders according to the invention can vary quite widely between 90 - 10% and 10 - 90 From an economic point of view, it is advantageous to introduce in mixtures the greatest possible quantity of inexpensive residual gypsum; from the point of view of technical performance, the melans rich in synthetic anhydrite are the most interesting.

The best compromise is obtained by equal-mixtures ”. , xaux of residual gypsum and synthetic anhydrite.

It is also possible according to the invention to use several residual gypsum from different origins in /. . ....

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The new binders. Scion 1 * invention can be used in pure paste or Dtre associated with aggregates to obtain mortars or concretes. Additives can be added to pure pastes, mortars or concretes to modify the properties of the mixing mass before setting or the properties of the material after hardening.

The applications relate to all materials used in the building industry. One can in particular realize, V by fluidization, self-leveling screeds in pure paste, '· '10 or in mortar. Oh can also make cellular materials by expanding pure paste or mortars, for example using aluminum powder.

In the two examples given below to illustrate the invention, pure doughs were prepared, by adjusting the mixing water so that the spreading diameter of the dough, determined according to German standard DIN 1164, i.e. 150 * 5 mm. The beginning and the end of setting are measured according to the same standard DIN 1164. The breaking stress in tension by bending and the breaking stress in compression are measured on test pieces of 4 x 4 x 16 cm according to standard NF P 15-451, “EXAMPLE 1

A phosphogyp- • having the following characteristics * is used as the residual gypsum: a) particle size: between 0.7 and 200 μm; average · ϊ 33 pm, b) chemical analysis:

CaSO ^ j, 2 H2O ·· “· * ······ * ·····. ·· 95.5 5o

CbF2 ........................ 2.0% 305i02 .................. .......... 0.8%

Fe203 ........................ 0.2% A12ü3 .................... ....... 0.3 ^ P2® $ soluble in water .. ··. ···· 0.1 5o *. ·. · • · ''. . ·.-4.

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000 g of this phosphogypsum are mixed with BDO g of fluoroonhydrite, in accordance with the German standard DIN 4208, and 176 g of water. The start and end times for setting, as well as the mechanical strengths after 7 and 28 days are indicated in the table given after example 2.

EXAMPLE 2

A residual gypsum from a thermal power station is used, having the following characteristics: a) particle size, determined by sieving on a product dried at 100 ° C.

Refus sieve mesh opening (pm) (p by weight); 37 68 74 ‘10 ‘15 90 1.4 100 0 b) chemical analysis:

CaS04, 2 H20 .................... 95.5 £ ‘

SiO ^, .............. 0.5 # 20 S0., “······ * · ♦ ················ ···· 0.3 ^ • c “fe2Ô3 ..... * ........ · * ........... 0.1% V * • MgO * .. .......................... 0.1% C02 ............ 0.1% H20 .. ........ 3.4% * φ - 25 800 g of this desulphurization gypsum are mixed with 800 g of fluoroanhydrite, in accordance with German standard DIN 4208, and 168 g of water. The start and end times for setting, as well as the mechanical resistance after 7 and 28 days are recorded in the table below ï / "·" '· i / ♦. .

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TABLE ". Α 'ί Resistance to n,.,.,' Start End’ ^ tensile volume by Resistance to

Examples of (g / cm3) bending compression grip taken (bars) (bars / 7 days 20 days 7 days 23 days 7 days 23 days v 1 '> 6 h> 12 h 1.6B 1.66 26 52 115 220 2 65 min 105 mr 1f7B 1.76 74 76 27D 275 ή • · •, * * · ψ% · /

Claims (6)

1. Binders characterized in that they consist of mixtures of residual gypsum and synthetic anhydrite, 2. Binders according to claim 1, characterized in that the residual gypsum is phosphogypsum, y 3 -'Binders according to claim 1, characterized in that the residual gypsum comes from the desulfurization of · combustion gases from thermal power stations, j 4. Binders according to claim 1 # characterized in that the synthetic anhydrite is a fluoroanhydrite. 5. Binders according to claim 1, characterized in that · the synthetic anhydrite is a phosphoanhydritc, 6. Binders according to any one of claims 1 to 5, characterized in that the proportion of residual gypsum is 10 to 90% by weight, 7- Binders according to any of claims 1, 4 \ 5 and 6, characterized in that several gypsum residues of different origins are used, • 8 - binders according to any one of claims 1, 2, 3, 20 6, 7, characterized in that one uses several synthetic anhydrides of different origins, " 9. Building materials obtained using the binders according to claims 1 to 8, 'U .... /