Investigation of blast furnace slag reuse and recycling properties
Creators: name: Yasipourtehrani, Sara
Publisher: name: Macquarie University
Year: 2023
Subjects: classificationCode: 399999
subject: Other education not elsewhere classified

description: Metal extraction, as a part of the industrialization and urbanization, impacts the environment through extraction and waste generation. Blast Furnace Slag (BFS) is the main by-product of the iron making industry produced in significant amounts worldwide every year. This by-product is typically reused as a part of cement and concrete production or as a road base material. This study tries to consider the importance of the chemical composition of BFS to investigate the other aspects ofrecycling of this waste material in an environmentally friendly way while considering the economic benefits. To improve energy use, it is necessary to understand the thermal behaviour of slags under differing compositions at varying temperatures. This study determined the thermal properties and behaviour of selected slag samples using several experimental techniques, including high temperature Hot Stage Scanning Electron Microscopy (HS-SEM), and Computer Aided Thermal Analysis (CATA). Further methods, such as Energy Dispersive Spectroscopy (EDS) and Fourier Transfer Infrared Spectroscopy (FTIR) were applied to determine the chemical content and nature of the studied BFS samples. According to the results, the chemical composition of BFS has an effect of thermal behaviour of molten slag. Comparing the chemical composition of the slags and their thermal behaviour, the effect of magnesium oxide and aluminium oxide was evident on the crystallisation and fluidity of the molten slag. Additionally, the content of silicon dioxide had an effect on the crystallisation temperature and network strength. Treatment of wastewater becomes an important task due to increased population while the chemical and physical properties of BFS show potential for reuse in this field. In this work, BFS was used to investigate the phosphate removal ability in wastewater. BFS has the required concentrations of surface calcium to potentially precipitate phosphate from wastewater. Removal of phosphate from wastewater depends on variety of conditions, such as the size of BFS particles, adsorbent dose, contact time and pH. The conditions responsible for phosphate removal from wastewater with BFS were analysed and the phosphate removal capacity optimised according to the BFS chemical content. The analysis of the chemical composition of BFS demonstrated that the high basicity (CaO/Si0<sub>2</sub>) of the BFS reduces the capability of phosphate removal from the wastewater. BFS composition before and after phosphate removal was determined with Energy Dispersive Spectroscopy (EDS), Fourier Transfer Infrared Spectroscopy (FTIR) and UV-Vis spectrophotometry. The results revealed that the slag samples added varying concentrations of trace metals Al, Cd, Co and Hg into the treated water, which will need to be further conditioned by dilution with unpolluted water or other treatments before disposal or re-use. BFS has potential to be integrated in dye removal from wastewater. BFS has a large porous surface area and distribution of particles that increase the ability of dye removal from wastewater. Dye removal from wastewater, similar to the phosphate removal, depends on a variety of conditions, such as the size of BFS particles, adsorbent dose, contact time and pH. The conditions responsible for dye removal from wastewater with BFS were analysed and the removal capacity was optimized according to the BFS chemical content. In addition, BFS composition before and after dye removal was determined with Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), and Fourier Transfer Infrared Spectroscopy (FTIR). Higher BFS basicity showed higher ability for dye removal of acidic dyes (in the small concentration) and basic dyes (in high concentration). For removing the dye, the physical properties of the BFS are important where BFS samples with compact morphology and nanoparticles remove dye more efficiently. CO<sub>2</sub> is the most important greenhouse gas with significant increase in emissions, especially after the rapid industrialization. This study investigated the use of the calcium in BFS as a CaO-based sorbent to capture the CO<sub>2</sub> by calcium looping (CaL). CaO-based CaL materials received wide applications in thermochemical CO<sub>2</sub> capture and energy storage technologies, as well as CO<sub>2</sub>-related energy conversion processes. BFS has about 40% calcium that makes it potentially valuable for recycling as a CaO-based sorbent. High purity CaO-based sorbents were prepared with acid leaching of BFS using two types of acids, acetic acid and nitric acid. The study concluded that BFS is a promising feedstock to prepare robust CaO-based sorbents for CO<sub>2</sub> capture in high-temperature calcium looping cycles. BFS properties make this by-product valuable for reusing and recycling in a number of applications. Overall, the obtained finding demonstrated the potential of this by-product for reusing in the wastewater treatment for phosphate and dye removal, and capturing the CO<sub>2</sub> by preparing CaO-based sorbent from the BFS. The study further outlined the environmental benefits for higher level of reuse of BFS benchmarked against its reuse in the cement industry.