 When water contaminated with cadmium ions comes into contact with sediment containing FeS, the cadmium displaces the iron according to Equation 3 and becomes tightly bound to the sulfide ion.Due to the large difference in Ksp values for the two metal sulfides, this reaction proceeds effectively to completion, meaning that until all the sulfide in a sediment is used up, all the cadmium in that sediment will be present in the solid CdS form.A number of other toxic heavy metals behave similarly, including lead, copper, zinc, mercury, and nickel.