Patent ID: 7279103

Claim:
A method for removing at least one of metals and sulfates from acidic wastewaters, for recovering metals and for producing water suitable for discharge, comprising: (a) precipitating each metal in the wastewater in a separate stage comprising maintaining the Eh and adding an aqueous solution of a hydroxide to maintain the pH in a range for effective formation of precipitates sequentially in the following order of removal: copper, ferric iron, zinc, aluminum, ferrous iron and manganese; (b) introducing gas containing hydrogen sulfide into the wastewater into the stages in which copper, zinc, ferrous iron and manganese are removed; (c) adding an aqueous solution of a hydroxide at a suitable concentration to precipitate ferric hydroxide and aluminum hydroxide in their appropriate order; (d) recovering the metal precipitated at each stage individually or as mixtures as a precipitate selected from the group consisting of cupric sulfide, ferric hydroxide, zinc sulfide, aluminum hydroxide, ferrous sulfide, and manganese sulfide, to produce a metal-free sulfate containing water; (e) treating the ferrous sulfide with an oxidizing agent to convert the ferrous sulfide to iron products selected from the group consisting of goethite, magnetite, hematite, lipidocrocite, and feroxyhyte; (f) treating the metal-free sulfate-containing water in a hydrogen utilizing sulfate reducing bacteria (SRB) bioreactor to convert the sulfate to hydrogen sulfide, and removing and recovering the hydrogen sulfide for re-use in the metal precipitation stages, wherein excess hydrogen sulfide is recovered.