Preparation of High-Purity Calcium Carbonate by Mineral Carbonation Using Concrete Sludge

Abstract

A new type of mineral carbonation process for concrete sludge, a waste of fresh concrete under hydration, was developed, and the carbonation performances of the process were examined by laboratory-scale experiments. The process is composed of two steps; filtration of concrete sludge and bubbling of CO 2 into the filtrate to form calcium carbonate. Model concrete sludge, a mixture of cement and water, was filtered through a cellulose filter after hydration for 24 h to obtain a solution containing dissolved calcium ions. Then, the model flue gas containing CO 2 (10%) was bubbled through the filtrate solution, and calcium carbonate was precipitated by the carbonation reaction. About 3% of calcium in the concrete sludge could be extracted into the filtrate in a single filtration step, and more than 95% of dissolved calcium was recovered as calcium carbonate by the bubbling of CO 2 . The obtained calcium carbonate was calcite with a high purity (>95%) and 5–10 μm. The solid residue (concrete sludge) after filtration was mixed with fresh water and filtered through a cellulose filter. Then, the model flue gas was bubbled into the filtrate solution for carbonation. This filtration–bubbling step was repeated 5 times, and 10.8% of calcium in the feed cement was extracted into the filtrates in total. More than 95% of the extracted calcium could be recovered as calcium carbonate with high purity (>97%), and the overall conversion of calcium in the feed cement to calcium carbonate was 10.1%. The purity of calcium carbonate and the calcium conversion were much higher than those for the direct bubbling method, where the model flue gas is bubbled into concrete sludge.

Thermal Insulation Properties and Simulation Analysis of Foam Concrete Regulated by Mechanical and Chemical Foaming

“…However, the use of organic insulation materials in underground spaces is restricted due to their high susceptibility to fire hazards. Inorganic insulation materials, particularly foam concrete materials, are gaining significant interest among researchers due to their noncombustibility and thermal insulation properties. − A review of the literature indicates that foam concrete is predominantly prepared using mechanical foaming methods − or chemical foaming techniques. , He et al produced alkali-activated slag foamed concrete with a dry density of 600–800 kg/m 3 using mechanical foaming, and it was observed that as the foam content increased, the thermal conductivity of the foamed concrete gradually decreased . However, the addition of preformed foam to concrete slurry through mechanical foaming results in compromised foam durability due to the mixing and pouring processes.…”

“…Inorganic insulation materials, particularly foam concrete materials, are gaining significant interest among researchers due to their noncombustibility and thermal insulation properties. 24 − 32 A review of the literature indicates that foam concrete is predominantly prepared using mechanical foaming methods 33 − 35 or chemical foaming techniques. 36 , 37 He et al produced alkali-activated slag foamed concrete with a dry density of 600–800 kg/m 3 using mechanical foaming, and it was observed that as the foam content increased, the thermal conductivity of the foamed concrete gradually decreased.…”