School of Chemical Engineering and Technology, China University of Mining and Technology, Xuzhou 221116, China; National Engineering Research Center of Coal Preparation and Purification, China University of Mining and Technology, Xuzhou 221116, China.
National Engineering Research Center of Coal Preparation and Purification, China University of Mining and Technology, Xuzhou 221116, China; Shandong Xuanyuan Scientific Engineering and Industrial Technology Research Institute Co., Ltd., Heze 274918, China.
Sci Total Environ. 2022 Jul 20;831:154726. doi: 10.1016/j.scitotenv.2022.154726. Epub 2022 Mar 22.
The coal gasification fine slag (CGFS) from the entrained-flow coal gasification unit faces the challenge of safe disposal and clean utilization in the Ningdong region, China. This study aims to provide complete and thorough understanding of the distribution features, chemical speciation, environmental impact, and leaching behavior of typical heavy metals (i.e., V, Cr, Mn, Ni, Cu, Zn, Ba, and Pb) in the CGFS with different size fractions. The results show that the distribution of selected heavy metals in the CGFS has evident particle size dependence. Except for Zn, the other heavy metals in different size fractions mainly exist in chemical speciation of residual form with the ratio of 50.11-86.69 wt%. Moreover, it is found that the heavy metals in the different-sized CGFS show different RAC (risk assessment code) environmental risk levels and TCLP (Toxicity Characteristic Leaching Procedure) leaching concentrations. Especially, Zn in SGFS-C and SGFS-D posed a high-risk level to the environment, while the heavy metal elements of Cr, Mn, Ni, Zn, and Ba in other size fractions are classified as a medium environmental risk. In addition, the TCLP test results indicate that the leaching concentration of Cr, Mn, Ni, Zn, Ba, and Pb exceeds the groundwater-related regulatory limit in China. The pH-dependent leaching experiments suggest that Pb shows the amphoteric behavior, while the leaching mode of other heavy metals seems to be the cationic pattern. Furthermore, the leachability of the selected heavy metals in small-size fractions of the CGFS should be given more consideration at both acid and alkaline pH ranges. The leaching kinetic results demonstrate that the most effective mechanism to describe the leaching process of Cr, Ni, Zn, and Pb in different CGFS size fractions is the diffusion-controlled theory, which is supported by the different morphological traits of spherical mineral particles and carbon particles in the CGFS.
中国宁东地区气流床煤气化细渣（CGFS）的安全处置和清洁利用面临挑战。本研究旨在全面深入地了解不同粒径 CGFS 中典型重金属（V、Cr、Mn、Ni、Cu、Zn、Ba 和 Pb）的分布特征、化学形态、环境影响和浸出行为。结果表明，所选重金属在 CGFS 中的分布具有明显的粒径依赖性。除 Zn 外，不同粒径分选中的其他重金属主要以残渣态的化学形态存在，比例为 50.11-86.69wt%。此外，发现不同粒径 CGFS 中的重金属具有不同的 RAC（风险评估代码）环境风险水平和 TCLP（毒性特征浸出程序）浸出浓度。特别是 SGFS-C 和 SGFS-D 中的 Zn 对环境构成高风险，而其他粒径分选中的 Cr、Mn、Ni、Zn 和 Ba 重金属元素则被归类为中等环境风险。此外，TCLP 测试结果表明，Cr、Mn、Ni、Zn、Ba 和 Pb 的浸出浓度超过了中国与地下水相关的监管限值。pH 依赖性浸出实验表明，Pb 表现出两性行为，而其他重金属的浸出模式似乎是阳离子模式。此外，应在酸性和碱性 pH 范围内更关注 CGFS 小粒径分选中选定重金属的浸出性。浸出动力学结果表明，描述不同 CGFS 粒径分选中 Cr、Ni、Zn 和 Pb 浸出过程的最有效机制是扩散控制理论，这得到了 CGFS 中球形矿物颗粒和碳颗粒不同形态特征的支持。
