Bench-Scale Studies on Capture of Mercury on Mineral Non-carbon Based Sorbents

Abstract

A new high-temperature, mineral non-carbon based dispersed sorbent derived from paper recycling products has been shown to capture mercury at high temperatures in excess of 600 °C. The sorbent is consisted of kaolinite/calcite/lime mixtures. Experiments have been conducted on chemi-sorption of elemental mercury in air on a packed bed. The sorption occurs at temperatures between 600 and 1,100 °C and requires activation of the minerals contained within the sorbents. Mercury capture is dominated by temperature and capture on sorbents over long time scales. The capture shows a maximum effectiveness at 1,000 °C and increases monotonically with temperature. The presence of oxygen is also the required. Freshly activated sorbent is the most effective, and deactivation of sorbents occurs at high temperatures with long pre-exposure times. This activation is suspected to involve a solid-solid reaction between intimately mixed calcium oxide and silica that are both contained within the sorbent. Deactivation occurs at temperatures higher than 1,000 °C, and this is due to melting of the substrate and pore closure. The situation in packed beds is complicated because the bed also shrinks, thus allowing channeling and by-passing, and consequent ambiguities in determining sorbent saturation. Sorbent A had significantly greater capacity for mercury sorption than did Sorbent B, for all temperatures and exposure time examined. The effect of SiO₂ on poor Sorbent B is much larger than sorbent A.