Abstract: A technique is presented for the sequential extraction of nearly pure metal sulfides from solutions containing a mixture of metals, such as acid mine drainage. The technique is based on analysis of naturally occurring biofilms that selectively concentrate zinc, in zinc-sulfide, from a complex natural groundwater solution associated with a subsurface metal-sulfide mine. It was predicted and shown experimentally that release of sulfide ions, due to the activity of sulfate reducing bacteria, leads to sequential precipitation of pure metal sulfide phases from a solution of mixed metal ions, so long as the rate of production of sulfide ions does not exceed the rate of supply of the metal ions. This observation makes possible the design of biochemical processes to harness sulfate-reducing bacteria to separate and recover metals from mixed-metal waste streams.