Sustainable removal of gaseous Hg⁰ using sulfur functionalized biochar: Adsorption experiment and life cycle...

Maximizing the sorption capacity of gaseous Hg⁰ by sulfur-functionalized biochar can lead to increased energy consumption and the production of secondary environmental pollutants such as greenhouse gases. This study evaluates the environmental impact of producing sulfurized biochar through a life cycle assessment (LCA), weighing these impacts against the benefits of enhanced Hg removal efficiencies. The biochar's Hg⁰ adsorption capacity, which ranges between 3 and 22 μg-Hg⁰/g-biochar, is influenced by several factors: it increases with higher sulfur loading (0-15 %), higher O₂ levels (0-21 %), and longer pyrolysis times (1-5 h). However, it also decreases with increased pyrolysis temperature (100-500 °C). XPS and FT-IR analysis confirm that the sulfur in the biochar primarily exists as elemental sulfur, but each sulfurization condition also resulted in the formation of sulfate, organic sulfur, and sulfone. LCA results indicate that using biochar as a sorbent for Hg⁰ is carbon-negative when the biochar is disposed of in landfills. Sensitivity analysis showed that increasing mercury adsorption capacity through excessive investment in energy and resources does not necessarily reduce the overall environmental impact. Consequently, when selecting an adsorbent for mercury removal, it is crucial to consider both sorption capacity and environmental impact.