Integrated Carbon Mineralization and Air Pollutant Emission Reduction Via a High-Gravity Process Using Alkaline Wastes

The application of a high-gravity rotating packed bed (RPB) for accelerated carbonation coupled with alkaline wastes including fly ash (FA) from paper mill boiler was investigated for carbon dioxide (CO₂) fixation and air emission reduction (i.e., SO₂, NO_x and particle matters (PM) ) under the key operating factors of on-site experiment, i.e., gas flow rate and rotating speed. The experiment was conducted (i) indirect carbonation: using pH-swing method for FA leaching process before carbonation and (ii) direct carbonation: the carbonation with FA slurry. After carbonation, the concentration of CO₂, SO₂ and NOx were monitored immediately by air pollutants analyzer while the total suspended particulates (TSP) were collected by a filter cartridge. The results indicated that the maximal removal efficiencies of CO₂, SO₂, NO_x and TSP were respectively achieved 96.3%, 99.4%, 95.9% and 83.4% using FA leachate at rotating speed of 600 rpm, with a capture capacity of 0.51 of CO₂ tons per day. In addition, the fresh and leached FA were used as supplementary cementitious materials in blended cement at different substitution ratio (i.e., 0%, 5% and 10%). The performance of the blended cement mortar including flow test, sulfate resistance, drying shrinkage and compressive strength, was evaluated. The results indicated that the mortar of leached and carbonated FA exhibited a greater workability, durability and compressive strength than pure Portland cement mortar at a substitution ratio of 10 w.t.%. Furthermore, the various operation conditions were holistically evaluated by the 3E (environmental, economic and engineering) analysis and the results indicated that the optimal conditions were obtained at gas flow rate of 4.23 m³/min, rotating speed of 600 rpm; and liquid-to-solid ratio of 40ml-tap water/g-fly ash. The environmental and economic analyses represented that the high-gravity process could not only reduce the environmental impact by carbon fixation and air emission reduction but increase the economic benefits by air pollution fee saving, carbon credits profits and alkaline wastes reclamation.

Key words: High gravity technology; carbon mineralization; air pollution reduction; cement substitution; 3E analysis