Development of a slow-release CO2 absorbent material for alkaline activation of persulfate oxidation of TCE and CO2 capture

Control of carbon dioxide (CO2) emission during chemical oxidation processes of organic-chemical contaminated sites has become a challenge. In this study, a novel slow-release CO2 absorbent material (SCAM) was developed for a slow release of Ca2+ and OH–, which were used for CO2 capture, pH adjustment, and alkaline activation of persulfate (PS) oxidation for trichloroethylene (TCE) degradation. The SCAM was produced using basic oxygen furnace slag (BOFs) and calcium sulfate hemihydrate (CSH) as the components for granulation and modification. Batch experiments were conducted to determine the optimal mass ratio of BOFs to CSH and evaluate CO2 capture capacity and SCAM performance. An increase in BOFs proportion led to a higher CO2 capture capacity, with the maximum capture amount reaching 156 g CO2/kg SCAM. An excessive addition of BOFs resulted in an overly alkaline pH value (pH = 12.4), causing the diminished PS oxidation efficiency. The optimal mass ratio of BOFs to CSH (1 to 1) could capture produced CO2 after TCE oxidation without inhibiting PS oxidation. The SCAM could serve as the catalyst and activate PS oxidation, resulting in 93.1 % of TCE oxidation (initial TCE concentration = 2.32 mM) and 95.4 % of CO2 emission reduction due to the formation of CaCO3 precipitates under alkaline conditions. Produced sulfate and hydroxyl radicals confirmed the PS oxidation of TCE using SCAM as an activator. The developed SCAM is a green catalyst for PS oxidation and it is also an effective CO2 absorbent. SCAM can reduce CO2 emission due to the formation of CaCO3 precipitates under alkaline conditions. The released OH– could also prevent the acidification problem caused by the production of sulfuric acid through PS decomposition.