An Adsorption Process for Metal Recovery from Acid Mine Waste: The Berkeley Pit Problem

An adsorption process comprised of inorganic chemically active adsorbents (ICAAs) has been developed for recovery of Fe(III), Cu(II), Zn(II), Cd (II) and Pb(II) from acid mine drainage solutions similar to the Berkeley Pit near Butte, Montana. ICAAs are prepared by immobilization of chelating agents on the ceramic supports. The detailed laboratory-scale studies are executed to determine selectivity and operating conditions of each ICAA for individual metal ions. This paper presents results of separation studies using several ICAAs materials with simulated acid mine drainage solutions similar to the Berkeley Pit. Three most suitable ICAA materials have the potential to remove and recover desired metal ions from acidic streams without neutralization. Accordingly, an integrated adsorption process with three independently operating stages can be devised. Three fixed-bed adsorbers, comprised of ICAA(A), ICAA(C), and ICAA(D), selectively removed Fe(III), Cu(II), and Zn(II) Cd(II) and Pb(II) respectively, from the acidic stream. In addition, the last bed, comprised of ICAA(D), acts as an acid scavenger and increases the pH of the effluent to greater than 7, which can then be discharged in an environmentally safe manner. The adsorbed metal ions can be recovered as pure metal salts by stripping with sulfuric acid, and the regenerated bed can then be used for future cycles.