A study on the occurrence modes and distribution characteristics of sulfur and mercury in coal gasification slag

Abstract

Although coal gasification is recognized as a core technology for clean coal utilization, S and Hg can migrate to gas, wastewater, and slag during the gasification process, causing environmental pollution. It is well known that S and Hg have a strong affinity. Therefore, the interaction between S and Hg during the gasification process warrants further investigation. In this study, the occurrence modes and distribution characteristics of S and Hg in gasification slag were systematically investigated using multiple treatments and various characterization techniques. The results showed that sulfur in the gasification slag exists predominantly as organic sulfur, while mercury mainly exists as HgS/silicate-bound Hg. Although the relative enrichment index of Hg (RE < 0.7) indicates its high volatility, a more pronounced enrichment effect for mercury of fine slag was indicated by its much higher RE than coarse slag. When exploring the relationship among the contents of C, S, and Hg and specific surface area in gasification slag, it was found that the correlation between S and Hg content in fine slag was the strongest, with a correlation coefficient (R2) of 0.96, indicating a significant influence of sulfur content in fine slag on mercury content. Additionally, it was observed that the S and Hg contents in gasification slag increased with the decrease of particle size and density. These results provide an important understanding of the distribution, migration, and transformation behavior of S and Hg during coal gasification, as well as a certain theoretical support and technical basis for the resource utilization of gasification slag.