Carbonation of alkaline paper mill waste to reduce CO 2 greenhouse gas 1 emissions into the atmosphere

16 17 The global warming of Earth's near-surface, air and oceans in recent decades is a direct 18 consequence of anthropogenic emission of greenhouse gases into the atmosphere such as CO2, 19 CH4, N2O and CFCs. The CO2 emissions contribute approximately 60% to this climate change. 20 This study investigates experimentally the aqueous carbonation mechanisms of an alkaline paper 21 mill waste containing about 55 wt% of portlandite (Ca(OH)2) as a possible mineralogical carbon 22 dioxide sequestration process. The overall carbonation reaction includes the following steps: (1) 23 Ca release from the portlandite dissolution, (2) CO2 dissolution in water and (3) calcium 24 carbonate precipitation. This CO2 sequestration mechanism was supported by geochemical 25 modelling of final solutions using PHREEQC software, and observations of scanning electron 26 microscope and X-ray diffraction of final reaction products. According to our experimental 27 protocol, the system proposed would favour the total capture of approx. 218 kg of CO2 into stable 28 calcite per every ton of paper waste, independently of initial CO2 pressure. The final product 29 from carbonation process is a calcite (ca. 100 wt%)-water dispersion. Indeed, the total captured 30 CO2 mineralized as calcite could easily be stored in soils or in the ocean without any significant 31 environmental negative impact. This result demonstrates the possibility to use the alkaline liquid32 solid waste for CO2 mitigation and reduction of greenhouse effect gases into the atmosphere. 33 34