 When dissolved in water, sulfide has a high affinity for numerous heavy metal ions.That is, the solubility-product constants (Ksp) for the sulfides of these metals are very small, meaning they will precipitate as solids when a heavy metal ion and sulfide ion come into contact, as in Equation 2, where M2+ is a generic metal in the +2 oxidation state.In anoxic sediments uncontaminated by heavy metals, the associated metal (M in equation 2) is usually iron (Fe) or manganese (Mn).