The production of artificial aggregates with flue gas desulfurization ash: Development of a novel carbonation route

Abstract

Using solid waste to absorb CO2 in the production of aggregates is an efficient approach, which can reduce CO2 emissions and improve the recycling of solid waste. However, a challenge lies in addressing the cracking issues of aggregates prepared by the calcium oxide (CaO) system, particularly those containing flue gas desulfurizati ash (FGDA), during the direct carbonation process. This study presents a novel carbonation route combining air curing (AC) and CO2 curing (CC) under industrial flue gas conditions that effectively resolves the cracking problem of FGDA. The results show that under the optimized conditions (6 % CaO, 2 % Na2SO4, 3 days of AC, and 12 h of CC), the FGDA can be used to produce the flue gas desulfurization ash artificial aggregate (FGDAA), with pellet strength and water absorption of 3.11 MPa and 16.87 %, respectively. The CaCO3 forms during the carbonation, which improves pellet strength and decreases water absorption, except for the high CaO content (8 %) or AC age over 3 days. This shows that this method has clear requirements for the CaO content in solid waste. By developing a low-cost and energy-efficient carbonation process, FGDAA offers significant advantages in the construction field. With a production cost of only $5.14 per ton and a shorter curing time, it is environmentally sustainable and has a low global warming potential of 52.68 kg CO2-Eq. Although its compressive strength of 32.52 MPa is slightly lower than some conventional aggregates, FGDAA is still suited for applications such as road construction and mine backfill.