Retention of mercury by low-cost sorbents: Influence of flue gas composition and fly ash occurrence

The present study employs chars obtained from the gasification of different types of biomass as low cost sorbents of mercury at laboratory scale. The influence of gas composition and fly ash occurrence on mercury retention and oxidation by char samples was evaluated. Chars obtained from a mixture of paper and plastic waste showed mercury retention capacities similar to those obtained with a commercial activated carbon. Homogeneous mercury oxidation was mainly promoted by NO2 and, to a certain extend, by SO2 + O2. The highest heterogeneous mercury oxidation was observed in the chars with the highest mercury retention capacity suggesting that the sorption process also involves the capture of oxidized mercury species. The presence of fly ash particles clearly influenced heterogeneous oxidation but did not affect mercury retention by the char sorbents.

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► Chars from plastic-paper waste exhibit high mercury retention capacities.
► NO2 with/without O2 are the main factors responsible for homogeneous oxidation.
► Chars with the highest level of mercury retention show the highest heterogeneous oxidation.
► Mercury retention by the char samples is not affected by the fly ash particles.