| Mineral carbonation is the most promising method for carbon sequestration because it is excellent carbon sequestration capacity and sequestration time. In addition, the strength of carbonate binder is mainly derived from mineral carbonation. So, it is important for researching in mineral carbonation. Generally, Mineral carbonation has divided into two states:one is liquid state (liquid to solid ratio>1) and another is solid state (liquid to solid ratio<1). The main role of liquid carbonation is to prepare calcium carbonate or to sequestrate carbon dioxide. However, the purpose of this study is to use carbonation method for the preparation of building materials. So, the second method has been chose, i. e. solid carbonation. In this study, influences of compaction pressure, CO2gas pressure and foreign ions (Mg2+and β-CD) on the carbonation properties of calcium hydroxide have been investigated. The main parameters are mass gain degree, compressive strength, free water content and morphology of carbonated products. In the end, the new carbonation process has been presented. The main work and results are as follows:(1) For different compaction pressures, results showed that the carbonation degree of calcium hydroxide increased at first (0-8MPa) and decreased in the later (10-14MPa) and the low compaction pressure was in favor of early carbonation but adverse to the later stages of carbonation. For the morphology of carbonation products, low compaction pressure was tend to form typical crystal morphology of calcite (rhombohedral), while it would change to ellipsoid-like when compaction pressure reached8MPa. Moreover, the bonding between the products became more densification under high compaction pressure, and it could increase the compressive strength of carbonated compact.(2) For different CO2gas pressures, results showed that the mass gain degree of compacts was increased with the CO2gas pressure increased (0.05MPa-0.20MPa) and decreased with the gas pressure continued to increase (0.30MPa-0.50MPa).The compressive strength was increased with the gas pressure increased. TGA result also showed that the0.20MPa was the optimal CO2gas pressure.(3) Under the influence of Mg2+. the CO2mass gain degree increased at first, reached the maximum, and then decreased with the increasing C/M ratio. The C/M ratio of that CO2mass gain degree reached the maximum was5. SEM photographs showed that the morphology of carbonated products changed by different compaction pressures and content of magnesium hydroxide. On the other hand, the β-CD inhibited the carbonation of calcium hydroxide at initial carbonation stage, but improved at later stage. SEM photographs showed that the morphology of carbonated products changed from rhombohedron to hollow cone tube-like structure, thus the compressive strength of what was improved.(4) In the end, the new carbonation process of calcium hydroxide has been presented. It was diffused from the outside into the inside as the carbonation time prolongation and the boundary of carbonated layer and uncarbonated layer was very distinctive through comparing the images of cross-section of compacts. However, at the later stage of carbonation, the carbonation degree of inner is higher than the outside. So, it can introduce a new carbonation process of calcium hydroxide according to its carbonation degree in different position of compacts.In this study, XRD and TGA results showed that the carbonation products were calcite and few amorphous calcium carbonate.The results of this study can provide theoretical basis and reliable parameters for the mineral carbonation and the requirement of carbonation condition is low. So it is suitable for large-scale application. |
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