CARBONATION OF CALCIUM SULFATE CONTAINING MATERIALS
A method for sequestering carbon dioxide includes providing a starting material having calcium ions, sulfate and/or sulfite ions, and alkali metal ions with a molar ratio Σ Alk:Σ SO3>2.00, reacting the starting material with carbon dioxide at a pressure in the range from ambient up to 3.5 bar overpressure and/or a temperature in the range from 10 to 145° C. to obtain a carbonated product comprising calcium carbonate and alkali sulfate. The obtained product is used as a set regulator or accelerator for cement and/or as a minor or main cement component.
1 . A method for sequestering carbon dioxide comprising
providing a starting material comprising calcium ions, sulfate and/or sulfite ions, and alkali metal ions with a molar ratio Σ Alk:Σ SO 3 ≥2.00,
reacting the starting material with carbon dioxide at ambient pressure or at up to 3.5 bar overpressure and/or at a temperature in the range from 10 to 145° C. either in an aqueous liquid at a water:solids weight ratio from 1 to 100 or in a gas-solid reactor at a relative humidity from 75 to 100%, and
obtaining a carbonated product comprising finely precipitated calcium carbonate and alkali sulfate.
2 . The method according to claim 1 , wherein the starting material is reacted with carbon dioxide at ambient pressure or at an overpressure of up to 1 bar and/or at a temperature in the range from 20 to 90° C.
3 . The method according to claim 1 , wherein the starting material is provided by mixing a material comprising calcium sulfate and a material comprising alkali metal ions, wherein the material comprising calcium sulfate is selected from the group consisting of gypsum, anhydrite, hemihydrate, phosphogypsum, waste concrete, slags, red and brown muds, bottom ashes, and mixtures thereof to provide calcium sulfate and the material comprising alkali metal ions is selected from the group consisting of dusts collected during cement and clinker production, especially bypass dust, clinker kiln dust, electro-static precipitator dust; paper ash; wood ash; biomass ash; and mixtures thereof to provide alkali metal ions.
4 . The method according to claim 1 , wherein the molar ratio Σ Alk:Σ SO 3 in the starting material ranges from 2.00 to 5.00.
5 . The method according to claim 1 , wherein sulfite and/or sulfide present in the starting material is oxidized to sulfate prior to carbonation and/or sulfite and/or sulfide present in a material used to provide the starting material is oxidized to sulfate.
6 . The method according to claim 1 , wherein a particle size of the starting material and/or a material used to provide the starting material is optimized by grinding or co-grinding and/or classifying.
7 . The method according to claim 1 , wherein exhaust gas from a cement kiln, lime kiln, waste incineration, coal fired power plant, gas fired power plant or exhaust gases combined from two or more of them is used as the carbon dioxide.
8 . The method according to claim 1 , wherein the reaction time ranges from 1 to 100 minutes.
9 . The method according to claim 1 , wherein carbonation is carried out in aqueous suspension, by bubbling the carbon dioxide in gaseous form through the aqueous suspension.
10 . The method according to claim 9 , wherein a solid product comprising calcium carbonate is separated from the aqueous suspension by precipitation.
11 . The method according to claim 1 , wherein carbonation is carried out in a gas-solid reactor.
12 . The method according to claim 11 , wherein calcium carbonate is separated from alkali sulfate by suspending the carbonated product in water and precipitating the calcium carbonate.
13 . The method according to claim 1 , wherein the obtained carbonated product comprising calcium carbonate and alkali sulfate is used as set regulator or as cement component.
14 . The method according to claim 13 , wherein the starting material contains at least 15 wt.-% sulfate and/or sulfite calculated as calcium sulfate to provide the set regulator or the cement component being an activator.
15 . The method according to claim 13 , wherein the starting material contains from 0.1 to 25 wt.-% sulfate and/or sulfite calculated as calcium sulfate and/or the alkali sulfate is removed from the carbonated product for use as minor or main cement component.
16 . The method according to claim 2 , wherein the molar ratio Σ Alk:Σ SO 3 in the starting material ranges from 2.00 to 4.00.
17 . The method according to claim 3 , wherein the molar ratio Σ Alk:Σ SO 3 in the starting material ranges from 2.00 to 3.00.
18 . The method according to claim 6 , wherein the particle size is adjusted to range from 0.01 μm to 200 μm or from 0.01 μm to 100 μm or from 0.01 μm to 50 μm.
19 . The method according to claim 11 , wherein the gas-solid reactor is a mill and calcium carbonate is separated from alkali sulfate by suspending the carbonated product in water and precipitating the calcium carbonate.
20 . The method according to claim 14 , wherein the starting material contains at least 50 wt.-% sulfate and/or sulfite calculated as calcium sulfate.