Development of a process for producing high-purity calcium carbonate (CaCO3) from waste cement using pressurized CO2
✍ Scribed by Katsuyama, Yasuro ;Yamasaki, Akihiro ;Iizuka, Atsushi ;Fujii, Minoru ;Kumagai, Kazukiyo ;Yanagisawa, Yukio
- Publisher
- American Institute of Chemical Engineers
- Year
- 2005
- Tongue
- English
- Weight
- 161 KB
- Volume
- 24
- Category
- Article
- ISSN
- 0278-4491
- DOI
- 10.1002/ep.10080
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✦ Synopsis
Abstract
A new type of process for producing high‐purity calcium carbonate from waste cement powder was developed. The process consists of two main reactions; extraction of calcium in the form of calcium ions from waste cement powder in a water slurry by pressurized CO~2~ (typically at several MPa), and precipitation of calcium carbonate (CaCO~3~) from the extracted solution by reduction of the CO~2~ pressure. The process can be recognized as the emission reduction process of CO~2~ as well. Laboratory‐scale experimental studies were conducted for both the extraction reaction and the precipitation reaction, to examine the feasibility of the process. The extraction process was found to proceed at a relatively high rate, especially during the initial 10 min. The concentration of calcium ions exceeded the thermodynamic solubility of CaCO~3~ (supersaturation) when abundant waste cement was available. After filtration of the residues, CaCO~3~ particles with >98% purity were obtained by depressurizing the CO~2~. The dependency of the reaction rates on the operating conditions, such as the ratio of waste cement to water, CO~2~ pressure, and particle size of waste cement particles, was investigated. A process design was carried out based on the experimental results, assuming that the present process is applied to two types of CaCO~3~ production process: flue gas desulfurization and production of ultrahigh‐purity CaCO~3~. The estimated costs per 1 metric ton of CaCO~3~ were USD 136 for desulfurization and USD 323 for high‐purity CaCO~3~. © 2005 American Institute of Chemical Engineers Environ Prog, 2005