This paper describes a ＇＇magnetic feedback chemostat＇＇ for decontaminating various heavy metal solutions, from industrial sources, with direct precipitation as metallic sulphides or with bacterially-produced FeS magnetic adsorbents. The proposal has implications for dramatically improving the economics of this biomagnetic separation process. Variations in magnetic susceptibility of FeS in the region of compositional interest, on the S-rich of 50-50 atomic %, can reduce the cost of heavy metal extraction by a factor of 50-fold. Appreciable variations in the magnetic properties of the bacterial-FeS occur and this leads to a variability of the overall process rate through the magnetic separator which affects the cost. The problem is that under a particular set of conditions produced by the solution to be treated, the bacteria which produce the most magnetic product are outgrown by those with a less magnetic product. To select the desired bacteria which produce a strongly magnetic adsorbent, the method proposed is to grow, at various dilution rates, a mixed culture of sulphate reducing bacteria (SRB) in the solution to be treated in a chemostat. This will be used to treat an influent df heavy metals and other compounds from polluted industrial sources. Nutrient plus sufficient Fe will be added to the influent for the growth of the SRB together with the production of the FeS adsorbent. The overflow from the chemostat will go to a Vortex magnetic separator in which the magnetic FeS and the associated SRB are retuned to the chemostat. The bacteria producing the required magnetic product will therefore be selected and preferentially multiplied in the chemostat, This method will yield SRB producing the desired product starting from inocula obtained from various natural sources, In this way different bacterial consortia will be selected, appropriate to each industrial requirement.