USE OF A CLAY IN THE PREPARATION OF A GEOPOLYMER PRECURSOR

Abstract

A method for the use of a clay including: less than 30% of kaolinite; and at least 20% of muscovite and/or illite; from 1% to 20% of smectite; the muscovite and/or illite/kaolinite weight ratio being greater than 1; for the preparation of a geopolymer precursor.

Claims

1. A method comprising adding a clay comprising: less than 30% of kaolinite; and at least 20% of muscovite and/or illite; from 1% to 20% of smectite; the muscovite and/or illite/kaolinite weight ratio being greater than 1; when preparing a geopolymer precursor.

2. The method according to claim 1, wherein the clay contains less than 25% of kaolinite.

3. The method according to claim 2, wherein the clay contains less than 20% of kaolinite.

4. The method according to claim 1, wherein the clay contains at least 25% of muscovite and/or illite.

5. The method according to claim 4, wherein the clay contains from 25% to 50% of muscovite and/or illite.

6. The method according to claim 1, wherein the muscovite and/or illite/kaolinite weight ratio in the used clay is greater than 2.

7. The method according to claim 1, wherein the clay contains from 2% to 17% of smectite.

8. The method according to claim 7, wherein the clay contains from 3% to 15% of smectite.

9. The method according to claim 1, wherein the clay further contains at least 1% of calcite.

10. The method according to claim 1, wherein the clay contains from 15% to 55% of an amorphous phase containing silica, alumina and/or calcium.

11. The method according to claim 9, wherein the clay contains from 20% to 50% of an amorphous phase containing silica, alumina and/or calcium.

12. The method according to claim 1, wherein the clay further contains chlorite, quartz, dolomite, microcline and/or hematite.

13. A method for preparing a geopolymer precursor comprising the following steps: possible drying and then possible milling of the clay according to claim 1; calcination of the obtained material at a temperature comprised between 650° C. and 900° C.; and possible deagglomeration of the obtained calcined clay until reaching a median diameter from 10 μm to 20 μm.

Description

EXAMPLE 1

Calcination of the Clay

[0056] 1.1—Composition of the Clay

[0057] A raw clay having the mineralogical composition reported in the following Table 1 is used.

TABLE-US-00001 TABLE 1 Mineralogical composition of the clay before calcination Category Phase % (w/w) Clays Muscovite/Illite 39.8 Kaolinite 14.9 Chlorite 5.6 Smectite 7.9 Carbonates Calcite 4.1 Dolomite 5.4 Others Quartz 12.2 Hematite 1 Albite 0.4 Anatase 2.1 Microcline 2.3 Amorphous phase 4.3

[0058] The clay hereinabove has the chemical composition (in % (w/w)) reported in the following Table 2.

TABLE-US-00002 TABLE 2 □ Chemical composition of the clay before calcination Loss on SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO SO.sub.3 K.sub.2O Na.sub.2O SrO TiO.sub.2 P.sub.2O.sub.5 MnO ignition 47.79 20.94 6.16 4.24 2.90 0.08 2.75 0.26 0.02 0.99 0.08 0.04 13.83

[0059] The used clay further has the physical characteristics reported in the following Table 3.

TABLE-US-00003 TABLE 3 Physical characteristics of the clay before calcination Density (in g/cm.sup.3) 2.6 Specific surface Blaine (in cm.sup.2/g) 2300 BET (in m.sup.2/g) 43.9

[0060] 1.2—Calcination of the Clay

[0061] 1.2.1□In the Laboratory Furnace

[0062] The above-described clay is dried for 12 hours at 105° C. and then milled in a ring mill until reaching a median diameter from 30 to 40 μm. The powder prepared in this manner is baked in a laboratory furnace by batches of 200 g at 800° C. for 1 h 00 with hot loading and unloading. Afterwards, the calcined clay obtained in this manner (calcined clay AC-1) is milled again slightly in a planetary mill (15 seconds, 700 rpm) to deagglomerate it and obtain a median diameter of 20 μm.

[0063] 1.2.2 □In the Flash Calciner

[0064] The above-described clay is dried for 72 hours at 105° C. and then crushed in a jaw crusher until obtaining 100% passage through a 2 mm sieve. Afterwards, the powder obtained in this manner is calcined in a flash calciner at 625° C. (calcined clay ACF-1), 780° C. (calcined clay ACF-2), 870° C. (calcined clay ACF-3) or 875° C. in a reducing atmosphere (calcined clay ACF-4) with an average stay time from 1 to 2 seconds. Afterwards, the calcined clay obtained in this manner is milled again in a vertical mill to deagglomerate it and obtain a median diameter of 10-11 μm.

[0065] The calcined clays obtained in this manner are analyzed. The mineralogical composition (in % (w/w)) of the latter is reported in the following Table 4.

TABLE-US-00004 TABLE 4 Mineralogical composition of the calcined clays ACF-1 to ACF-4 Category Phase ACF-1 ACF-2 ACF-3 ACF-4 Clays Muscovite/Illite 26.4 24.8 17.6 17.2 Kaolinite 5.8 2.5 — — Chlorite 3.1 — — — Carbonates Calcite 3.3 3 1.7 2.1 Dolomite 1.1 0.2 — — Others Quartz 10.7 11.8 12.1 11.9 Hematite 1.7 1.8 1.9 1.6 Microcline 4.2 3.5 2.3 2.3 Free lime — 0.5 0.5 0.4 Periclase — 0.5 0.4 0.4 Amorphous phase 43.8 51.3 63.4 64

EXAMPLE 2

Mortar Composition

[0066] Preparation of the Mortars 1 to 10

[0067] In this example, the geopolymer precursor is the calcined clay ACF-3.

[0068] A reference mortar (hereinafter the Mortar 1) is prepared from a cement Portland CEM II 32.5 according to the standard EN 196-1. The composition of the mortar 1 is as follows: [0069] 450 g of cement CEM II 32.5; [0070] 1350 g of standard sand; and [0071] 225 g of water.

[0072] In turn, the mortars 2 to 10 have been prepared from 506 to 570 ml of a geopolymer binder and 1350 g of a standard sand, the composition of the geopolymer binder being as follows: [0073] 561 ml-54% of ACF-3/9% of SiO.sub.2/8% Na.sub.2O/29% water (mortar 2); [0074] 523 ml-51% of ACF-3/9% of SiO.sub.2/7% Na.sub.2O/33% water (mortar 3); [0075] 506 ml-49% of ACF-3/11% of SiO.sub.2/10% Na.sub.2O/31% water (mortar 4); [0076] 566 ml-53% of ACF-3/7% of SiO.sub.2/9% Na.sub.2O/31% water (mortar 5); [0077] 547 ml-56% of ACF-3/6% of SiO.sub.2/8% Na.sub.2O/30% water (mortar 6); [0078] 558 ml-57% of ACF-3/8% of SiO.sub.2/5% Na.sub.2O/30% water (mortar 7); [0079] 570 ml-52% of ACF-3/11% of SiO.sub.2/8% Na.sub.2O/28% water (mortar 8); [0080] 554 ml-55% of ACF-3/8% of SiO.sub.2/8% Na.sub.2O/29% water (mortar 9); and [0081] 557 ml-56% of ACF-3/10% of SiO.sub.2/6% Na.sub.2O/29% water (mortar 10).

[0082] Mechanical Strength

[0083] The mechanical strength of the mortars is measured in accordance with the standard EN 196-1 on 4×4×16 cm.sup.3 prismatic test specimens of the mortars prepared at 20° C.

[0084] The results of the measurements of the compressive strength (Rc) at 7 days are reported in the following Table 5.

TABLE-US-00005 TABLE 5 Compressive strengths Mortar Compressive Strength at 7 days (in MPa)  1 (reference) 30  2 20.6  3 18  4 10  5 12.3  6 19.3  7 20.4  8 18.6  9 18.1 10 28.7

[0085] It comes out that the mortars prepared from a geopolymer obtained from a sufficient amount of calcined clay (mortars 2, 3, 6, 7, 8, 9 and 10) have a mechanical strength at 28 days that is comparable with that of the mortar prepared from the Portland cement alone (mortar 1) and comparable with that of the mortar prepared from a Portland cement.

EXAMPLE 3

Mortar Composition

[0086] Preparation of the Mortars 11 to 16

[0087] In this example, the geopolymer precursor is a mixture of calcined clay ACF-3 and metakaolin (MK) in the following proportions: [0088] 55% of ACF-3; and [0089] 45% of metakaolin.

[0090] The mortars 11 to 16 have been prepared from 506 to 598 ml of a geopolymer binder and 1350 g of a standard sand, the composition of the geopolymer binder being as follows: [0091] 598 ml-51% of MK/7% of SiO.sub.2/9% Na.sub.2O/33% water (mortar 11—reference); [0092] 563 ml-54% of MK+ACF-3/9% of SiO.sub.2/8% Na.sub.2O/29% water (mortar 12); [0093] 506 ml-52% of MK+ACF-3/9% of SiO.sub.2/7% Na.sub.2O/31% water (mortar 13); [0094] 570 ml-52% of MK+ACF-3/12% of SiO.sub.2/8% Na.sub.2O/29% water (mortar 14); [0095] 553 ml-55% of MK+ACF-3/8% of SiO.sub.2/8% Na.sub.2O/29% water (mortar 15); and [0096] 566 ml-56% of MK+ACF-3/10% of SiO.sub.2/6% Na.sub.2O/29% water (mortar 16).

[0097] Mechanical Strength

[0098] The mechanical strength of the mortars is measured on 4×4×16 cm.sup.3 prismatic test specimens of the mortars prepared at 20° C. according to the standard EN 196-1.

[0099] The results of the measurements of the compressive strength (Rc) are reported in the following Table 6.

TABLE-US-00006 TABLE 6 Compressive strengths Mortar Compressive Strength at 7 days (in MPa) 11 (reference) 41.2 12 48.4 13 43.3 14 50.0 15 43.5 16 39.8

[0100] It comes out that the mortars prepared from a geopolymer obtained from a mixture of metakaolin and calcined clay (mortars 12 to 16) have a mechanical strength at 7 days that is higher than that of a mortar prepared from a geopolymer obtained from the metakaolin alone (mortar 11).

EXAMPLE 4

Comparative Tests

[0101] A raw clay having the mineralogical composition reported in the following Table 7 is used.

TABLE-US-00007 TABLE 7 Mineralogical composition of the clay before calcination Category Phase % (w/w) Clays Muscovite/Illite 60.2 Kaolinite 16.2 Chlorite 0 Smectite 0 Carbonates Calcite 5.4 Dolomite 0.2 Others Quartz 1.9 Hematite 0 Albite 0.8 Anatase 0.1 Microcline 15.2 Amorphous phase 0

[0102] Hence, this clay does not contain smectite.

[0103] This clay is calcined under the conditions described for the clay ACF-3 (cf. Example 1—item 1.2). The calcined clay ACF-5 is thus obtained.

[0104] The mortars 17 to 19 have been prepared from 506 to 598 ml of a geopolymer binder and 1350 g of a standard sand, the composition of the geopolymer binder being as follows: [0105] 563 ml-54% of ACF-5/9% of SiO.sub.2/8% Na.sub.2O/29% water (mortar 17); [0106] 506 ml-52% of ACF-5/9% of SiO.sub.2/7% Na.sub.2O/31% water (mortar 18); and [0107] 570 ml-52% of ACF-5/12% of SiO.sub.2/8% Na.sub.2O/29% water (mortar 19).

[0108] Mechanical Strength

[0109] The mechanical strength of the mortars is measured on 4×4×16 cm.sup.3 prismatic test specimens of the mortars prepared at 20° C. according to the standard EN 196-1.

[0110] The results of the measurements of the compressive strength (Rc) are reported in the following Table 8.

TABLE-US-00008 TABLE 8 Compressive strengths Mortar Compressive Strength at 7 days (in MPa) 17 <3.0 18 <3.0 19 <3.0

[0111] It comes out that the mortars prepared rom a geopolymer obtained from the calcined clay ACF-5 (mortars 17 to 19) have very low mechanical strengths. These mechanical strengths are lower than the detection threshold of the press. These strengths are much lower than those obtained on a mortar composed by the clay ACF-3.