Study on Mercury Adsorption and Desorption on Different Modified Biochars

Area of Science:

• Environmental Science
• Materials Science
• Chemistry

Background:

• Mercury (Hg) contamination in aqueous solutions poses significant environmental and health risks.
• Biochar-based adsorbents are explored for efficient removal of heavy metals.
• Surface modification of biochar can enhance its adsorption properties for target pollutants.

Purpose of the Study:

• To evaluate the adsorption performance of various modified biochars for mercury (Hg(II) and methylmercury).
• To investigate the impact of different functional groups (amino, epoxy, ethoxy, hydrosulfuryl, selenium, chitosan) on biochar's mercury adsorption capacity and rate.
• To assess the stability of mercury adsorption on modified biochars.

Main Methods:

• Synthesis and characterization of untreated (BC-CK) and six modified biochars (BC-NH, BC-C2H2O, BC-C2H5O, BC-SH, BC-Se, BC-Chitosan).
• Simulated adsorption experiments to determine adsorption capacity and rate for Hg(II) and MeHg.
• Mercury desorption experiments to evaluate adsorption stability.

Main Results:

• Hydrosulfuryl (BC-SH) and selenium (BC-Se) modified biochars exhibited significantly improved mercury adsorption capacities (1.26 and 1.51 times BC-CK, respectively), attributed to stable -SH-Hg and Hg-Se complex formation.
• Some modified biochars (BC-NH, BC-C2H2O, BC-C2H5O, BC-Chitosan) showed reduced adsorption capacity, potentially due to decreased specific surface area and pore volume.
• All biochars demonstrated very low mercury desorption, indicating high adsorption stability. BC-Chitosan showed the highest adsorption speed.

Conclusions:

• Biochar modification strategies, particularly using hydrosulfuryl and selenium groups, can substantially enhance mercury adsorption performance.
• Chitosan modification offers rapid mercury adsorption kinetics.
• The study provides critical insights into the effectiveness of modified biochars for mercury removal in aqueous solutions, guiding practical applications.