The H2xMnxSn3-xS6 (x 0.11-0.25) is a new solid acid with a layered hydrogen metal sulfide (LHMS). It derives from K2xMnxSn3-xS6 (x 0.5.....0.95) (KMS-1) upon treating it with highly acidic: solutions. We demonstrate that LHMS-1 has enormous affinity for the very soft metal ions such as Hg 2+ and Ag+ which occurs via a rapid ion exchange process. The tremendous affinity of LHMS-1 for Hg2+ is reflected in very high distribution coefficient KdHg values(>106 mL g-1). The large affinity and selectivity of LHMS-1 for Hg 2+ persists in a very wide pH range (from less than zero to nine} and even in the presence of highly concentrated HCI and HNO3 acids. LHMS-1 is significantly more selective for Hg2+ and Ag+ than for the less soft cations Pb2+ and Cd2+. The Hg 2+ ions are immobilized in octahedral sites between the sulfide layers of the materials via Hg-S bonds as suggested by pair distribution function (PDF) analysis. LHMS-1 could decrease trace concentrations of Hg 2+ (e.g.<100 ppb) to well below the acceptable limits for the drinking water in less than two min. Hg-laden LHMS-1 shows a remarkable hydrothermal stability and resistance in 6 M HCI solutions. LHMS-1 could be regenerated by treating Hg-loaded samples with 12 M HCI and reused without loss of its initial exchange capacity.