Effectiveness of mossy tin filters to remove mercury from aqueous solution by Hg(II) reduction and Hg(0) amalgamation

Reduction of bivalent mercury (Hg(II)) by mossy tin combined with Hg(0) air stripping has been recently proposed as a method to remove Hg from groundwater. We investigated the effectiveness of mossy tin to remove Hg(II) from aqueous solution at different flow rates and determined the retention of Hg through the formation of HgSn amalgams. Results show that mossy tin layers of only 2 cm thickness can reduce 100% of 800 μg Hg(II) 1−1 at a flow rate of about 1 volume of drainable porosity min−1 (Vol min−1), and even 100% of 5000 μg l−1 at 0.125 Vol min−1, 89% and 97% of the Hg(0) were retained in the filter through amalgamation. No Hg was remobilized from the loaded tin filters by chloride (10–50 mg Cl− l−1) or dissolved organic carbon DOC (0.5–6 mg DOC l−1). The capacity of mossy tin to adsorb Hg was found to be at least 5–6% of the weight of the filter. The study shows that mossy tin has a high capacity to remove Hg effectively from aqueous solution. Disadvantages arise from the release of tin from the filters exceeding legal limits of 20 μg l−1 in most cases but occurred as mostly insoluble tin particles or Sn hydroxide.