Coal gasification slag (CGS), a byproduct of coal chemical processes, can be repurposed as functional materials through acid treatment to remove impurities such as Al, Ca, and Fe.This study investigates the acid-leaching behavior of these impurities by examining the slag’s mineralogical structure and elemental distribution. The process involved initial carbonash separation via physical sieving (0.85 mm), yielding a low-carbon slag (L-CS) with < 3% carbon content and a 48.33% yield, characterized by dense, lamellar aluminosilicate glass with uniformly dispersed and encapsulated Ca and Fe. The L-CS was subjected to heat treatment at varying temperatures, followed by hydrochloric acid leaching. Results revealed that heat treatment broke and rearranged the original Si-O-Si(Al) bonds, partially converting [AlO4] structural units into more stable [AlO6] and leading to the sequential formation of magnetite and esseneite phases. This structural reorganization significantly reduced the leaching rates of Al, Ca, and Fe. Kinetic analysis demonstrated that the leaching of Fe and Ca was governed by a combination of internal diffusion and interfacial chemical reactions, whereas Al leaching was controlled solely by interfacial reactions. The Ca and Fe components were leached more readily than Al. Under optimized conditions (70 °C, 180 min, 8% HCl, liquid-to-solid ratio 8:1), the leaching rates reached 74.17% for Al, 90.01% for Ca, and 83.34% for Fe. The acid-leached residue primarily retained amorphous aluminosilicate phases with minor quartz, exhibiting a more ordered structure than the precursor. Morphologically, the original dense structure was disrupted, forming fractured surfaces composed of 40–60 nm nanospheres. The residue possessed a specific surface area of 101.44 m²/g and an average pore diameter of 5.734 nm. These findings indicate that the acid-leached CGS residue has significant potential for direct application as a mesoporous adsorbent material or for uses requiring enhanced reactivity.

Characterization and kinetic analysis of acid leaching of low carbon fraction in coal gasification slag
    Abstract
    1 Introduction
    2 Experimental sections
        2.1 Materials
        2.2 Experiments
        2.3 Characterizations
    3 Results and discussion
        3.1 Separation of carbon and ash from CS
        3.2 Leaching behavior of impurity elements in L-CS
        3.3 Analysis of L-CS structural evolution after heat treatment
        3.4 Leaching process for L-CS-20
            3.4.1 Optimization of leaching process conditions
            3.4.2 Leaching reaction kinetics
    3.5 Characteristics of slag treated with a hydrochloric acid solution
        3.5.1 Structure and morphology
        3.5.2 BET analysis
    4 Conclusion
    References

• Yifan Chai(Key Laboratory of Green Extraction and Efficient Utilization of Light Rare-Earth Resources, Inner Mongolia University of Science and Technology, Baotou 014010, China)
• Shengli An(Key Laboratory of Green Extraction and Efficient Utilization of Light Rare-Earth Resources, Inner Mongolia University of Science and Technology, Baotou 014010, China, School of Materials Science and Engineering, Inner Mongolia University of Science and Technology, Baotou 014010, China) Corresponding author
• Yu Li(Key Laboratory of Green Extraction and Efficient Utilization of Light Rare-Earth Resources, Inner Mongolia University of Science and Technology, Baotou 014010, China, School of Materials Science and Engineering, Inner Mongolia University of Science and Technology, Baotou 014010, China, School of Chemical Engineering, Ordos Institute of Technology, Ordos 017010, China)
• Ruifeng Wang(School of Chemical Engineering, Ordos Institute of Technology, Ordos 017010, China)
• Hui Liu(Key Laboratory of Green Extraction and Efficient Utilization of Light Rare-Earth Resources, Inner Mongolia University of Science and Technology, Baotou 014010, China, School of Chemical Engineering, Ordos Institute of Technology, Ordos 017010, China, Inner Mongolia Environmental Governance Engineering Co., Ltd, Huhhot 010000, China)
• Zhanfeng Yang(Key Laboratory of Green Extraction and Efficient Utilization of Light Rare-Earth Resources, Inner Mongolia University of Science and Technology, Baotou 014010, China, State Key Laboratory of Balyunobo Rare Earth Resources and Comprehensive Utilization, Baotou 014010, China)