Abstract
We propose a new concrete recycling process via carbonic acid treatment. The proposed process consists of two main reactions. The first is the extraction of calcium ions (Ca2+) from waste cement particles in water slurry by pressurized carbon dioxide (several MPa pressure). The second is the precipitation of calcium carbonate (CaCO3). Ca2+ extracted from waste cement is deposited as CaCO3 when the pressure is reduced. In this paper, we considered to use the product, CaCO3 as a desulfurization agent. Experimental studies were carried out in a laboratory-scale experimental apparatus to examine the feasibility of the proposed process. It was found that the extraction process can be proceed with relatively high rates in the initial 10 minutes of the reaction time, where the concentration of calcium ions exceeded thermodynamic solubility (supersaturation). The dependencies of the extraction reaction rate on the ratio of waste cement to water, CO2 pressure, and the particle size of the raw waste cement particles were investigated experimentally with a laboratory-scale setup. Calcium carbonate with about 97 % purity was obtained in the precipitation process. A process simulation was conducted based on the experimental results, and energy consumption and the cost for a model process were estimated. The cost for the production of 1 metric-ton of CaCO3 for desulfurization of the 500 MW thermal power pliant is estimated to be about 13000Yen.
