Evaluation of Two Sulfur Impregnation Methods on Activated Carbon and Bentonite for the Production of Elemental Mercury Sorbents

Abstract

ABSTRACT

Adsorption of vapor-phase elemental mercury by virgin and modified bentonite and activated carbon was evaluated at 140°C, empty-bed contact time in a fixed-bed adsorber of 0.011 s, and influent mercury concentration of 55 μg/m³. Acid-treated bentonite had somewhat higher capacity than the virgin bentonite due to higher surface area and perhaps some active surface sites created by acid treatment. Sulfur impregnation through hydrogen sulfide oxidation enhanced mercury removal efficiency over the nonimpregnated bentonite. However, mercury removal efficiency was promoted to a limited extent, due to predominance of nonreactive sulfur allotropes and significant reduction in surface area. Sulfur impregnation of bituminous coal-based carbon (BPL) was performed using thermal deposition of elemental sulfur (BPL_S) at high temperature (600°C) or hydrogen sulfide oxidation (BPL_HS) at low temperature (150°C). Both BPL_S and BPL_HS performed significantly better than virgin BPL carbon. Although sulfur content of BPL_HS increased with an increase in impregnation time, impregnation for 0.25 h produced the most effective sorbent (BPL_HS-0.25). Although BPL_S and BPL_HS-0.25 had similar sulfur content, BPL_S performed significantly better due to greater surface area and predominance of more reactive sulfur allotropes. However, application of BPL_HS sorbents for mercury control may be justified by the pollution prevention efforts for a number of industrial processes that generate H₂S waste streams.

Key words:

mercury; activated carbon; bentonite; adsorption; sulfur impregnation; hydrogen sulfide