Efficient leaching and separation of iron, aluminum, and calcium from carbon-rich components in coal gasification fine slag using organic acids

The efficient extraction and separation of valuable metal elements from coal gasification fine slag (CGFS) are crucial for the comprehensive high-value utilization of its constituents. This study focused on the carbon-rich components of CGFS (CGFS-H) and systematically investigates the selective leaching behavior of Fe3+, Al3+ and Ca2+ using three organic acid extractants, i.e., citric acid, tartaric acid, and tetrasodium iminodisuccinate. Additionally, the stepwise leaching of iron, aluminum and calcium from CGFS-H is explored. The selective dissolution mechanisms of these metals by different organic acids are elucidated through X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM) analyses. The results indicate that tetrasodium iminodisuccinate exhibits the highest leaching selectivity for Fe3+, while tartaric acid demonstrateds a comparable affinity for both Fe3+ and Al3+. In contrast citric acid shows superior selectivity toward Ca2+. The leaching yield of Fe3+, Al3+ and Ca2+ after sequential leaching with the three organic acids were 79.8%, 65.08% and 78.6%, respectively. These findings confirm that effective and selective separation of Fe3+, Al3+ and Ca2+ from CGFS-H can be achieved via optimized organic acid-based leaching strategies. This advancement provides a critical foundation for developing Ca/Fe/Al hydrotalcite materials using CGFS-H as a sustainable feedstock, thereby facilitating the transformation of waste residue into high-value functional materials and promoting resource-efficient utilization of coal gasification fine slag.