METHOD FOR MANUFACTURING SUPPLEMENTARY CEMENTITIOUS MATERIAL

Abstract

A method for producing a pozzolanic product by hydrothermal treatment of a feedstock including silicate, aluminate, and/or aluminosilicate materials, and a source of calcium ions, wherein the feedstock has a molar ratio of Ca:(Si+Al) from 0.4 to 1.2 and a maximum content of hydrated cement paste of 10 wt.-%, to provide a hydrate product, and subsequent carbonation of the hydrate product to provide a pozzolanic product including calcium carbonate and silica gel, alumina gel and/or silica-alumina gel. A pozzolanic product is obtainable by the method. The pozzolanic product is used as a supplementary cementitious material for manufacturing a composite cement including the pozzolanic product and a hydraulic cement.

Claims

1. A method for manufacturing a pozzolanic product comprising: hydrothermal treatment of a feedstock comprising silicate, aluminate, and/or aluminosilicate materials, and a source of calcium ions providing a hydrate product, wherein the feedstock has a molar ratio of Ca:(Si+Al) from 0.4 to 1.2 and a maximum content of hydrated cement paste of 10 wt.-%, wherein a water: solids weight ratio during hydrothermal treatment is at least 0.3, and subsequent carbonation of the hydrate product, wherein a concentration of CO.sub.2 during carbonation ranges from 1 Vol.-% to 99 Vol.-%, providing the pozzolanic product comprising calcium carbonate and silica gel, alumina gel and/or silica-alumina gel.

2. The method according to claim 1, wherein the molar ratio of Ca:(Si+Al) in the feedstock ranges from 0.6 to 1.0, and/or a molar ratio Al/Si in the feedstock is lower than 0.5.

3. The method according to claim 1, wherein the maximum content of hydrated cement paste in the feedstock is 5 wt.-%.

4. The method according to claim 1, wherein the silicate, aluminate and/or aluminosilicate material is selected from the group consisting of natural minerals, waste products, by-products, and mixtures thereof.

5. The method according to claim 4, wherein the natural mineral is selected from the group consisting of granite, rhyolite, quartz, feldspar, and minerals containing them; and/or the waste product or by-product is selected from the group consisting of quarry dust, calcined clay not achieving the required specification of EN 197-1:2011 or ASTM C618, ash, and slag.

6. The method according to claim 5, wherein, with respect to the total amount of silicate, aluminate and/or aluminosilicate material, an amount of Si, Al, or Si and Al in the silicate, aluminate and/or aluminosilicate material is at least 50 wt.-%, and/or the content of calcium is lower than 25 wt.-%, all calculated as oxides, i.e. as SiO.sub.2, Al.sub.2O.sub.3, Fe.sub.2O.sub.3, and CaO, respectively, and on a loss on ignition free basis.

7. The method according to claim 1, wherein the source of calcium ions is selected from cement kiln dust, process dust from clinker grinding, calcium rich fly ash or bottom ash, slag, calcium carbide residues, and mixtures of two or more thereof.

8. The method according to one of claim 7, wherein the amount of calcium ions is at least 30 wt.-%, with respect to the total amount of the source of calcium ions, and/or 60 wt.-%, of the calcium ions are not bound in carbonated phases or glass, and/or the waste or by-product as source of calcium ions have a molar ratio Ca/(Si+Al)>0.9.

9. The method according to claim 8, wherein a water: solids weight ratio during hydrothermal treatment is adjusted to range from 0.3 to 10, and/or a temperature range from 105 to 300 C.

10. The method according to claim 1, wherein during carbonation a pressure ranges from ambient to 25 bars, and/or a temperature ranges from ambient.

11. (canceled)

12. The method according to claim 1, wherein the pozzolanic product is subjected to a thermal treatment at a temperature ranging from 120 to 350 C.

13. A pozzolanic product comprising calcium carbonate and silica gel or alumina gel or silica-alumina gel obtained by hydrothermal treatment of a feedstock comprising silicate, aluminate, and/or aluminosilicate materials, and a source of calcium ions providing a hydrate product, wherein the feedstock has a molar ratio of Ca:(Si+Al) from 0.4 to 1.2 and a maximum content of hydrated cement paste of 10 wt.-%, wherein a water: solids weight ratio during hydrothermal treatment is at least 0.3, and subsequent carbonation of the hydrate product, wherein a concentration of CO2 during carbonation ranges from 1 Vol.-% to 99 Vol.-%, providing the pozzolanic product comprising calcium carbonate and silica gel, alumina gel and/or silica-alumina gel.

14. (canceled)

15. A method for manufacturing composite cements comprising: hydrothermal treatment of a feedstock comprising silicate, aluminate, and/or aluminosilicate materials, and a source of calcium ions, to provide a hydrate product, wherein the feedstock has a molar ratio of Ca:(Si+Al) from 0.4 to 1.2 and a maximum content of hydrated cement paste of 10 wt.-%, wherein a water: solids weight ratio during hydrothermal treatment is at least 0.3, and subsequent carbonation of the hydrate product, wherein a concentration of CO.sub.2 during carbonation ranges from 1 Vol.-% to 99 Vol.-%, to provide a pozzolanic product comprising calcium carbonate and silica gel, alumina gel and/or silica-alumina gel, and mixing the pozzolanic product with an hydraulic cement.

16. The method according to claim 15, wherein the hydraulic cement is selected from the group consisting of Portland cement, and cement based on Portland clinker, alite based cement, belitic cement, cement based on calcium aluminate clinker, cement based on calcium sulfoaluminate clinker, cement based on calcium sulfoaluminate-belite clinker, cement based on calcium ferrite clinker, and mixtures of them.

17. The method according to claim 15, wherein the composite cement comprises from 1 to 90 wt.-% of pozzolanic product.

18. The composite cement obtained by the method according to claim 15, wherein the composite cement comprises from 1 to 90 wt.-% of pozzolanic product.

19. The composite cement according to claim 18, additionally comprising one or more of admixtures, additives, and other supplementary cementitious materials.

20. The pozzolanic product according to claim 13, wherein the silicate, aluminate and/or aluminosilicate material is selected from the group consisting of granite, rhyolite, quartz, feldspar, natural minerals containing granite, natural minerals containing rhyolite, natural minerals containing quartz, natural minerals containing feldspar, quarry dust, calcined clay not achieving the required specification of EN 197-1:2011 or ASTM C618, ash, slag, and mixtures thereof.

21. The pozzolanic product according to claim 13, wherein the source of calcium ions is selected from cement kiln dust, process dust from clinker grinding, calcium rich fly ash or bottom ash, slag, calcium carbide residues, and mixtures of two or more thereof.

22. The pozzolanic product according to claim 13, wherein a water: solids weight ratio during hydrothermal treatment is adjusted to range from 0.3 to 10, and/or a temperature ranges from 105 to 300 C.

23. The method according to claim 1, wherein the molar ratio of Ca:(Si+Al) in the feedstock ranges from 0.7 to 0.9, and/or a molar ratio Al/Si in the feedstock is lower than 0.4.

24. The method according to claim 1, wherein the maximum content of hydrated cement paste in the feedstock is 2 wt.-%.

25. The method according to claim 2, wherein, with respect to the total amount of silicate, aluminate and/or aluminosilicate material, an amount of Si, Al, or Si and Al in the silicate, aluminate and/or aluminosilicate material is at least 70 wt.-%, and/or the content of calcium is lower than 15 wt.-%, all calculated as oxides, i.e. as SiO.sub.2, Al.sub.2O.sub.3, Fe.sub.2O.sub.3, and CaO, respectively, and on a loss on ignition free basis.

26. The method according to claim 1, wherein a water: solids weight ratio during hydrothermal treatment is adjusted to range from 0.4 to 3, and/or a temperature ranges from 120 to 200 C.

27. The method according to claim 1, wherein during carbonation a pressure ranges from ambient to 25 bars, and/or a temperature ranges from ambient to 80 C.

28. The method according to claim 1, wherein the pozzolanic product is subjected to a thermal treatment at a temperature ranging from 150 to 300 C. until constant mass.

29. The method according to claim 5, wherein the source of calcium ions is selected from cement kiln dust, process dust from clinker grinding, calcium rich fly ash or bottom ash, slag, calcium carbide residues, and mixtures of two or more thereof.

30. The method according to claim 29, wherein a water: solids weight ratio during hydrothermal treatment is adjusted to range from 0.3 to 10, and/or a temperature ranges from 105 to 300 C.

31. The method according to claim 30, wherein during carbonation a pressure ranges from ambient to 25 bars, and/or a temperature ranges from ambient to 99 C.

32. The method according to claim 9, wherein during carbonation a pressure ranges from ambient to 25 bars, and/or a temperature ranges from ambient to 99 C.

Description

EXAMPLE 1

[0064] A cement plant equipped with Leilac technology is producing lime (100% CaO is assumed, see also table 1 below) as an intermediate product and clinker (65% CaO, 21% SiO.sub.2, 7% Al.sub.2O.sub.3, rest others). Such clinker has process emissions of 510 kg CO.sub.2/t clinker considering all CaO provided by CaCO.sub.3. At the plant, high quality calcined clay (composed of 75% metakaolin and 25% quartz) and limestone (pure CaCO.sub.3) are also available. They are used to produce a comparison composite cement CC3 with 30% calcined clay and 20% limestone with process emissions of 255 kg CO.sub.2/t cement. Such cement also contains about 23 wt.-% of pozzolanic aluminosilicates (metakaolin).

[0065] According to the invention, the lime produced is blended with quartz (1 t of lime+3.76 t quartz) and autoclaved. Hydrothermal C-S-H with C/S of about 0.8 is produced. The C-S-H is carbonated, binding 1.21 t of CO.sub.2 and producing about 9 t of pozzolanic product 1 composed of about 42 wt.-% silica gel (dry basis) and 58 wt.-% CaCO.sub.3. This SCM is used to produce a composite cement CC1 according to the invention. CC1 is composed of 50 wt.-% clinker and 50 wt.-% of the pozzolanic product 1 as SCM. The process emissions of such cement are 255 kg CO.sub.2/t cement, calcium carbonate content is 29 wt.-% and the content of reactive pozzolanic silicates is 21 wt.-%.

[0066] Alternatively, clinker is used as calcium source for manufacturing the pozzolanic product. For this, 1 t of clinker is blended with 0.64 t of ground quartz, autoclaved and carbonated (0.4 t CO.sub.2 is mineralized). The obtained pozzolanic product 2 is used to produce a second composite cement CC2 according to the invention. CC2 contains 50 wt.-% clinker and 50 wt.-% the pozzolanic product 2 as SCM. Process emissions of such cement are 255 kg CO.sub.2/t cement, calcium carbonate content 27 wt.-% and the content of reactive pozzolanic silicates is also 21 wt.-%.

[0067] Table 1 summarizes the composition of the materials in the example. In table 2 the compositions of the cements and the carbon dioxide emission associated with their production are listed and compared with a conventional Portland-Limestone cement CEM I.

TABLE-US-00001 TABLE 1 Lime- Calcined pozzolanic pozzolanic Material stone Lime Clinker clay product 1 product 2 CaO 56% 100% 65% 32% 30% SiO.sub.2 21% 66% 42% 40% Al.sub.2O.sub.3 7% 34% 3% CO.sub.2 44% 65% 25% 24% Others 7% 3% Process 0 0.785 0.51 0 0 0 emissions (t CO.sub.2/t material) Pozzolanic 75% 42% 43% SiO.sub.2 + Al.sub.2O.sub.3

TABLE-US-00002 TABLE 2 Cement CC1 CC2 CC3 CEM I clinker 50% 50% 50% 95% Limestone 20% 5% Calcined clay 30% pozzolanic product 1 50% pozzolanic product 2 50% Process emissions 0.255 0.255 0.255 0.485 (t CO.sub.2/t cement) Pozzolanic 21% 21% 23% 0 SiO.sub.2 + Al.sub.2O.sub.3 Calcium carbonate 29% 27% 30% 5%

[0068] As can be seen, composite cements CC1 and CC2 according to the invention contain significantly less clinker than CEM I, saving substantial amounts of carbon dioxide for clinker production. Nonetheless, their strength development is comparable to that of the composite cement CC3 containing a known reactive calcined SCM, namely clay, and limestone.

EXAMPLE 2

[0069] FIG. 1 illustrates an exemplary device for carrying out the method according to the invention as continuous process. In the shown embodiment the hydrothermal treatment takes place in the first tube 1 and the carbonation in the second tube 2, arranged around the first tube 1. A feedstock from alumino-silicate material unsuitable as pozzolan and calcium rich fly ash is mixed with water and the formed slurry s with a solids content of e.g. 20 Vol.-% is introduced into the first tube 1 at its top. The slurry s has ambient temperature, e.g. 20 C., or a bit higher, e.g. 40 C. from using the recycled liquid phase as water, and is under ambient pressure, 1 bar, when entering the first tube 1. Due to the force of gravity, the slurry sinks inside the first tube 1, e.g. with a volume flow of 0.009 m.sup.3/second. Thereby, in a device with e.g. 40 m height, 1 m inner diameter and 1.4 m outer diameter, a pressure of more than 4 bar is reached at the bottom of first tube 1. There, the slurry s is heated, e.g. with a burner or microwave device or electric resistance heating, to a temperature of e.g. 150 C. The heated slurry passes into the second tube 2 in which it rises to the top, due to the slurry being continuously fed at the top of the first tube 1 and assisted by the heating. Carbon dioxide CO.sub.2 is added into the second tube 2. Suitable are e.g. gaseous carbon dioxide like exhaust gas or concentrated exhaust gas, as well as aqueous solutions of carbon dioxide. During rising in the second tube 2, the hydrate product in the slurry s is carbonated. At the top of the second tube 2, the slurry is withdrawn and separated into pozzolanic product SCM and a liquid phase I. The liquid phase I is recycled into the device e.g. as mixing water to provide the slurry s. Alternatively, and not shown, all or a part of it can be used to provide a solution to scrub carbon dioxide from an exhaust gas in e.g. a spray scrubber and form a carbon dioxide rich solution to be added into the second tube 2. A residence time of slurry s in the device, i.e. from entering at the top of first tube 1 to withdrawal at the top of second tube 2, of 60-120 minutes is usually sufficient to accomplish the hydrothermal treatment and the carbonation.

LIST OF REFERENCE SIGNS

[0070] 1 first tube [0071] 2 second tube [0072] s slurry from water and feedstock comprising silicate/aluminate/silicate -aluminate material and calcium ions [0073] h heat provided e.g. by a burner, microwaves, electric heater, . . . [0074] SCM pozzolanic product [0075] CO.sub.2 carbon dioxide, e.g. gas or liquid containing CO.sub.2 [0076] I liquid after separation from pozzolanic product