Proceedings of the 4th International Conference on Accelerated Carbonation for Environmental and Materials Engineering pages:357-367
ACEME 2013 location:Leuven, Belgium date:9-12 April 2013
A two-stage process was devised to transform blast furnace slag (BFS) symbiotically into two valuable products: precipitated calcium carbonate (PCC) and zeolitic sorbents. Calcium is first selectively extracted by leaching with organic acids, followed by carbonation of the leachate to precipitate CaCO3. In parallel, the hydrothermal conversion of the extracted solid residues in alkaline solution induces the dissolution/precipitation mechanism that leads to the formation of micro- and meso-porous materials. Two organic acids were trialled: succinic and acetic acids. Both acids satisfactorily prevented the leaching of aluminium, required for the subsequent synthesis of zeolites. However, while the leaching performance of succinic acid was superior, carbonation of its leachate did not result in the production of PCC, but rather the precipitation of calcium succinate. In contrast, carbonation of the acetic acid leachate resulted in the production of PCC of mainly calcite mineralogy. The hydrothermal conversion stage successfully resulted in the formation of two zeolitic phases, ferrierite (Na2Mg(Si15Al3)O36•9H2O) and gmelinite (Na4(Si8Al4)O24•11H2O), along with tobermorite (Ca5(OH)2Si6O16•4H2O), due to the incomplete removal of calcium in the leaching stage.