Utilization of waste concrete powder with different particle size as absorbents for SO2 reduction

Abstract Overexploitation of natural limestone used in wet flue gas desulfurization (WFGD) process has led to multiple ecological impacts. To reduce consumption of natural limestone, waste concrete powder (WCP) generated in waste concrete recycling plants were used as an alternative desulfurization absorbent for SO2 controlling. The SO2 absorbing performance of WCP with different particle size is evaluated in a stirred tank reactor with an fixed flat gas–liquid interface at 600 rpm, operated in gas-phase continuous operation mode. The results indicate that the slurry prepared as WCP dissolved in water is strongly alkaline and rich in Ca2+ species. The SO2 in flue gas was effectively removed by the WCP slurries, reaching a desulphurization efficiency of above 98%. Under acidic conditions produced upon dissolving SO2 in the slurry, the Ca2+ ions releasing process of WCP particles involves two stages: a primarily sharp increasing period and a following stable stage. Because of the Ca-rich cement hydrates concentrate in the finer parts of the WCP particles, the Ca2+ ions releasing capacity of WCP increases as its particle size decreases, resulting in a higher desulphurization capacity of finer WPC particles. The Ca2+ ions releasing process is well described by Fick's first law and pseudo-second order model. The Ca2+ ions released combine with SO42- to form insoluble gypsum. As the particle size of WPC decreases, the desulphurization capacity increases in the range of 0.44–0.73 (gSO2 /gWCP). The study provides new and efficient materials for SO2 controlling in waste flue gas and offers an innovative solution for the disposal of WCP also.