(433d) CO2 Fixation through Carbonation of Waste Cement and Concrete

Authors: 
Yamasaki, A., Seikei University
Iizuka, A., Tohoku University
Inoue, M., Seikei University
Noguchi, M., Seikei University

CO2 capturing and fixation processes with waste concrete via mineral carbonation reactions have been developed. The waste concrete is either waste concrete generated from demolished concrete buildings (waste concrete, hereafter) or concrete sludge. Waste concrete is composed of aggregates and waste (hydrated) cement, and waste cement powder of which the diameter is under about 100 μm would be separated in the recycling process of aggregates. The concrete sludge is waste fresh concrete in the form of slurry generated at the concrete using sites. Both concrete wastes are alkaline containing calcium that could be used as a capturing and fixation material for CO2 via carbonation reaction. Several options are considered as the CO2 fixation process with these waste concrete, and process feasibility has been evaluated based on the laboratory experimental studies. The followings are the options examined in this study.

(1) Direct fixation of CO2 with concrete sludge

     This option is a direct fixation process of CO2 with waste concrete sludge. Flue gas is introduced to the slurry of concrete sludge, and CO2 will react with hydrating cement components, mainly calcium hydroxide, to form calcium carbonate.  The effect of hydration reaction time, gas flow rate, water content, CO2 concentrations on the CO2 fixation performances were examined in a small-scale laboratory experiments.

(2) Indirect multistep fixation of CO2 with waste cement powder

      This option is four-step process composed of (i) dissolution of calcium ions into an acid, (ii) CO2 capture with an alkaline solution, (iii) formation of calcium carbonate by mixing the above two solutions, and (iv) regeneration of the acid and the alkaline solutions via electrodialysis. Parameters affecting the process performances were examined for each step in laboratory experimental studies. 

Based on the experimental studies, the feasibilities of these processes have been evaluated in views of the process power consumption as well as the cost.

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