Method for Producing a Carbonate Bonded, Compacted Article

Abstract

The method for producing a carbonate bonded, compacted article, which method comprises the steps of providing a particulate, carbonatable material; compacting the particulate material to form a compact; and carbonating said compact. The carbonation of the compact is started and subsequently continued for at least 1 hour with a low partial carbon dioxide pressure in the carbonation gas which is lower than 0.5 bars, after which carbonation of the compact is continued for at least 8 hours with a high partial carbon dioxide pressure in the carbonation gas which is higher than 0.5 bars. By carbonating in two phases with a low and a high partial carbon dioxide pressure, a higher compressive strength of the carbonated compacts can be achieved within a predetermined carbonation time, in particular within a carbonation time of about 24 hours so that every day new compacts can be carbonated.

Claims

1. A method for producing a carbonate bonded, compacted article, which method comprises the steps of: providing a particulate carbonatable material; compacting the particulate material to form a compact; and carbonating said compact for a predetermined period of time with a gas which contains carbon dioxide to produce carbonates thus transforming the compact into said carbonate bonded, compacted article, wherein carbonation of said compact is started and subsequently continued for at least 1 hour with a low partial carbon dioxide pressure in said gas, after which carbonation of said compact is continued for at least 8 hours with a high partial carbon dioxide pressure in said gas, said low partial carbon dioxide pressure being lower than 0.5 bars and said high partial carbon dioxide pressure being equal to or higher than 0.5 bars.

2. A method according to claim 1, wherein subsequently to having started the carbonation of said compact, the carbonation thereof is continued for at least 1.5 hours with said low partial carbon dioxide pressure in said gas.

3. A method according to claim 1, wherein subsequently to having started the carbonation of said compact, the carbonation of said compact is continued for less than 16 hours, with said low partial carbon dioxide pressure in said gas.

4. A method according to claim 1, wherein carbonation of said compact is continued for at least 12 hours, with said high partial carbon dioxide pressure in said gas.

5. A method according to claim 1, wherein said gas having said low partial carbon dioxide pressure is at a pressure which is lower than 5 bars, said pressure being equal to or higher than the atmospheric pressure.

6. A method according to claim 1, wherein said gas having said high partial carbon dioxide pressure is at a pressure which is lower than 5 bars, said pressure being equal to or higher than the atmospheric pressure.

7. A method according to claim 1, wherein said low partial carbon dioxide pressure is lower than 0.45 bars.

8. A method according to claim 1, wherein said low partial carbon dioxide pressure is higher than 0.05 bars.

9. A method according to claim 1, wherein said high partial carbon dioxide pressure is higher than 0.6 bars.

10. A method according to claim 1, wherein said predetermined period of time comprises less than 32 hours.

11. A method according to claim 1, wherein said predetermined period of time comprises more than 16 hours.

12. A method according to claim 1, wherein carbonation of said compact is started with said gas having a temperature lower than 50° C.

13. A method according to claim 1, wherein carbonation of said compact is started with said gas having a temperature higher than 20° C.

14. A method according to claim 1, wherein during the carbonation of said compact the temperature of said gas is increased to a temperature higher than 50° C.

15. A method according to claim 1, wherein said particulate material comprises carbonatable slag from a metal production process, slag from the production of phosphorus, bottom ash and/or fly ash, the particulate material comprises steel slag.

Description

EXAMPLES

Example 1

[0066] A stainless steel slag material was crushed to a particle size of between 0 and 35 mm and was separated in a 10 to 35 mm fraction and a 0 to 10 mm fraction. The 0 to 10 mm fraction was separated in a 0 to 2 mm fraction and in a 2 to 10 mm fraction.

[0067] From the 0 to 2 mm fraction, the steel particles were removed and the fraction was separated in a coarse sand fraction of 0.5 to 2 mm and in a fine sand fraction of 0 to 0.5 mm.

[0068] The fine sand fraction was dried and the moisture content thereof (expressed in percent by total weight) was adjusted to the values indicated in Table 1. Compacts were made with a compaction pressure of 0.4 MPa using 100% of the fine sand fraction. Carbonation was carried out at atmospheric pressure, i.e. at about 1 bar absolute pressure. The gas used to carbonate the compact is a mixture of gasses obtained by enriching air with CO.sub.2. The CO.sub.2 content of the gas (enriched air) used to carbonate the compacts is indicated in volume percent. Since the total pressure of the gas used to carbonate the compacts is equal to the sum of the partial pressures of the different gasses contained in this gas (in this case mainly CO.sub.2, N.sub.2 and O.sub.2), the partial carbon dioxide pressure in this gas can easily be determined and is equal to the volume percent of CO.sub.2 in that gas multiplied by the total pressure of the gas. In the present examples, the total pressure of the gas used to carbonate the compacts was equal to about 1 bar, so that when this gas contained 40 vol. % of CO.sub.2 (in the first carbonation phase) the partial carbon dioxide in this gas was equal to about 0.4 bar whilst when this gas contained 80 vol. % CO.sub.2 (in the second carbonation phase) the partial carbon dioxide in this gas was equal to about 0.8 bar.

TABLE-US-00001 TABLE 1 Carbonation parameters and resulting compressive strengths of the carbonated compact produced in Example 1 First carbonation Second carbonation Moisture phase phase Compressive content Duration Vol. Duration Vol. strength (wt. %) (hours) % CO.sub.2 (hours) % CO.sub.2 (MPa) 5.66 2 40 18 80 51.8 7.22 2 40 18 80 54.7 9.15 2 40 18 80 46.9

[0069] Due to the relatively high reactivity of the fine sand fraction, a high compressive strength was obtained after a total carbonation time of 20 hours. These compressive strengths were much higher than the compressive strength obtained in the Example “Sample Building Product 1” of US 2017/0073270. Notwithstanding the fact that in this Example also a reactive steel slag binder was used and a similar water content, whilst a much higher compaction pressure of 12 MPa was applied, which should normally lead to higher compressive strengths due to the reduced porosity, the obtained carbonated construction block only had a compressive strength of 22.8 MPa.

Example 2

[0070] In this example a same 0 to 0.5 mm fine sand fraction was used as in Example 1 together with the 0.5 to 2 mm sand fraction and a 2 to 6 mm fraction sieved out from the 2 to 10 mm fraction.

TABLE-US-00002 TABLE 2 Carbonation parameters and resulting compressive strengths of the carbonated compacts Comparative example Example 2 Parts 0/0.5 sand 50 50 Parts 0.5/2 sand 35 50 Parts 2/6 sand 15 — Moisture content 7.4 5.3 (wt. %) Compaction 2 2 pressure (MPa) First carbonation Duration (hours) 24 2 phase Vol. % CO.sub.2 100 40 Total pressure 1.5 atmospheric (bars) Second carbonation Duration (hours) — 18 phase Vol. % CO.sub.2 — 80 Total pressure — atmospheric (bars) Compressive 10.7 16.1 strength (MPa)

[0071] It can be seen that a higher compressive strength was obtained with the two phase carbonation process, notwithstanding the fact that in the comparative example pure CO.sub.2 gas was used, at a higher pressure of 1.5 bars and for a longer duration, namely for 24 hours instead of only 20 hours.

Example 3

[0072] In this example a same 0 to 0.5 mm fine sand fraction was used as in Example 1 together with the 0.5 to 2 mm sand fraction.

TABLE-US-00003 TABLE 3 Carbonation parameters and resulting compressive strengths of the carbonated compacts Comparative example Example 2 Parts 0/0.5 sand 60 60 Parts 0.5/2 sand 50 50 Parts 2/6 sand — — Moisture content 9.5 9.6 (wt. %) Compaction 4 4 pressure (MPa) First carbonation Duration (hours) 24 2 phase Vol. % CO.sub.2 100 40 Total pressure 1.5 atmospheric (bars) Second carbonation Duration (hours) — 20 phase Vol. % CO.sub.2 — 80 Total pressure — atmospheric (bars) Compressive 13.8 19.5 strength (MPa)

[0073] It can be seen that a higher compressive strength was obtained with the two phase carbonation process, notwithstanding the fact that in the comparative example pure CO.sub.2 gas was used, at a higher pressure of 1.5 bars and for a longer duration, namely for 24 hours instead of only 22 hours.