Comparative study of chemical speciation and leaching feature of typical heavy metals in coarse and fine slags from the entrained-flow coal gasification

ABSTRACT

The dissimilarity in chemical speciation and release properties of heavy metals will result in varying levels of environmental hazards and potential applications of coal gasification coarse and fine slags. The distribution, chemical speciation, leaching features, and potential environmental risks of heavy metals (Cr, Cu, Cd, Zn, Pb, and Mn) in coarse and fine slags from different coal gasification processes were revealed and compared by the sequential chemical extraction method, Horizontal vibration method, and pH-dependent leaching experiments. The results show that Cr (516.78 mg/kg) in coarse slag, Zn (348.50 mg/kg) and Pb (214.78 mg/kg) in fine slag are highly enriched and the content exceeds the screening value, indicating the need for better management during stockpiling and landfilling. The distribution of Cr, Cu, Pb, and Mn in residual state, Zn in Fe-Mn oxide bound state, and Cd in unstable bound state is the highest in both coarse slag and fine slag. The leaching toxicity of heavy metals (HMs) does not exceed the standard, but the leachate is classified as Level V surface water or groundwater quality due to the leaching concentration of Pb exceeding 0.1 mg/L. Furthermore, leaching of Cr, Zn, Cd, and Pb in fine slag is much more dependent on pH compared to coarse slag, and the concentrations of Zn and Pb exceed emission standards at pH < 3.0. The high concentration of heavy metals caught on the surface of fine slag is more harmful to the environment. The properties of HMs in the slags and pH of the application environment must be comprehensively considered before coal gasification slag disposal, especially fine slag.

KEYWORDS:

• Entrained-flow coal gasification
• coarse slag
• fine slag
• heavy metals
• chemical speciation
• leaching feature

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the national key research and development program of China [2019YFC1904304]; the Natural Science Foundation of China [51974323].

Notes on contributors

Feiyong Lyu

Feiyong Lyu: experimental design, experimental execution, data analysis and manuscript.

Mo Chu

Mo Chu: experimental design and manuscript check.

Xingbo Sun

Xingbo Sun: chemical speciation analysis experiment and partial data analysis.

Shengjun Cao

Shengjun Cao: experimental execution.

Jianfei Dong

Jianfei Dong: investigation.

Shengnan Liu

Shengnan Liu: investgation.