Synthesis, characterization, and application of pyrite for removal of mercury

• Near nano-scale pyrite was formed by iron chloride and sodium hydrosulfide with microwave.
• Fast removal kinetic and high removal capacity of pyrite.
• Mercury is removed by adsorption and complex surface reactions.
• HgS was formed on pyrite surface.

Pyrite has been demonstrated to be an excellent adsorbent for removing mercury in many studies. But most of them used natural pyrites that were grinded to micro-scale size or even larger. This study investigated methods to produce near nano-scale pyrite particles. Iron (III) chloride and sodium hydrosulfide were used as the source chemicals to synthesize pyrite. Several aging methods, including hydrothermal, ultrasonic and microwave irradiation, were studied in order to reduce the pyrite particle size. SEM/EDS and TEM/EDS analysis showed that microwave irradiation was the most effective way to produce small pyrite crystals close to the nano-scale. Results of batch kinetic experiments revealed that 0.1 g/L pyrite was able to remove about 90% Hg(II) in the first 5 min and all Hg(II) has been removed after 12 h, although some release of mercury to the solution was observed after 5 min. The release could be due to the formation of soluble Hg complexes or by other reactions that tended to increase pH. The mercury loading batch tests showed that the capacity of pyrite for adsorption of Hg(II) could reach 900 μmol Hg(II)/g FeS2. The presence of salts (0.01 M sodium sulfate and sodium nitrate) decreased the removal efficiency.

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