Effect of polyvinyl alcohol on the CO2 uptake of carbonated steel slag

Recycled by-products that capture CO2 are seen as a potential solution to reduce global greenhouse gas emissions produced by the construction industry. Steel slag has been used as an alternative binder to cement in the last decade and was most recently investigated as a CO2 sequestration material. However, the production of construction materials from steel slag is accompanied by the release of CO2. In order to achieve carbon-negative or -neutral production, it is necessary to increase the carbon capture capacity of steel slag. In this study, experiments were carried out to determine the degree of carbon sequestration by steel slag when treated with an environmentally friendly solution of polyvinyl alcohol (PVA). The modification of steel slag with PVA treatment before and after carbonation was investigated using the mass gain method, X-ray diffraction, thermogravimetric analysis (TG), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The mass gain method showed that after carbonation, steel slag with a PVA content of 1.0% showed a 7% increased uptake of CO2 compared to 4% for the untreated steel slag. Analysis of the endothermic peaks and weight loss from TG thermograms demonstrates an increase in CaCO3 content by PVA treatment. According to the calculation of the mass loss from the decomposition of CaCO3, PVA contributes to an increase in CO2 absorption from 2.8 to 5.9% compared to untreated steel slag. The results reveal that carbon dioxide uptake by steel slag in the presence of PVA was mainly due to the increased formation of calcium carbonate, the reaction result between CO2, CaO, and Ca(OH)2. The results found by SEM show that after the carbonation PVA formed a porous structure in the pore space of the steel slag, covered its particles with a thin film, and formed a structure of polymer-bridge bound particles. The use of PVA as an activator of the process of CO2 uptake with the formation of carbonates and a stable microstructure offers prospects for processing steel slag into a green non-structure component.