Communications Project

Document Type:Dissertation
Name:Harry Richard Diz
Degree:Doctor of Philosophy
Department:Civil Engineering
Committee Chair: John T. Novak
Committee Members:
Keywords:iron biooxidation, iron precipitation, iron removal technology, acid mine drainage
Date of defense:August 11, 1997
Availability:Release the entire work for Virginia Tech access only.
After one year release worldwide only with written permission of the student and the advisory committee chair.


This dissertation reports the design of a process (patent pending) to remove iron from acid mine drainage (AMD) without the formation of metal hydroxide sludge. The system includes the oxidation of ferrous iron in a packed bed bioreactor, the precipitation of iron within a fluidized bed, the removal of manganese and heavy metals (Cu, Ni, Zn) in a trickling filter at high (>9) pH, with final neutralization in a carbonate bed. The technique avoided the generation of iron oxyhydroxide sludge. In the packed bed bioreactor, maximum substrate oxidation rate (R,max) was 1500 mg L-1 h-1 at dilution rates of 2 h-1, with oxidation efficiency at 98%. The half-saturation constant (similar to a Ks) was 6 mg L-1. The oxidation rate was affected by dissolved oxygen below 2 mg L-1, with a Monod-type Ko for DO of 0.33 mg L-1. Temperature had a significant effect on oxidation rate, but pH (2.0 to 3.25) and supplemental CO2 did not affect oxidation rates. Iron hydroxide precipitation was not instantaneous when base was added at a OH/Fe ratio of less than 3. Induction time was found to be a function of pH, sulfate concentration and iron concentration, with a multiple R2 of 0.84. Aqueous [Al (III)] and [Mn (II)] did not significantly (a = 0.05) affect induction time over the range of concentrations investigated. When specific loading to the fluidized bed reactor exceeded 0.20 mg Fe m-2 h-1, dispersed iron particulates formed leading to a turbid effluent. Reactor pH determined the minimum iron concentration in the effluent, with an optimal at pH 3.5. Total iron removals of 98% were achieved in the fluidized bed with effluent [Fe] below 10 mg L-1. Further iron removal occurred within the calcium carbonate bed. Heavy metals were removed both in the fluidized bed reactor as well as in the trickling filter. Oxidation at pH >9 caused manganese to precipitate (96% removal); removals of copper, nickel, and zinc were due primarily to sorption onto oxide surfaces. Removals averaged 97% for copper, 70% for nickel and 94% for zinc. The treatment strategy produced an effluent relatively free of iron (< 3 mg/L), without the formation of iron sludge and may be suitable for AMD seeps, drainage from acidic tailings ponds, active mine effluent, and acidic iron-rich industrial wastewater.

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