Silica gels believed to be grafted with dithioacetal derivatives were recently used for Hg(II) extraction, and were found to selectively remove 94–100% of Hg 2+ ions from metal ion mixtures. The current studies with one derivative suggest that the functional group in the Hg(II) removal is the mercapto (SH) ligand. The dithioacetal group in (ClCOCH 2 S) 2 CHPh (2) was hydrolyzed during its reaction with amine (O) 3 Si(CH 2 ) 3 NH 2 (3) grafted on silica gel to give the mercapto ligand (O) 3 Si(CH 2 ) 3 NHCOCH 2 SH (4). The silica gel grafted with the mercapto ligand 4 selectively removed Hg 2+ ions with reported high capacities.