CHEMICAL AND BIOLOGICAL TREATMENT OF ACID MINE DRAINAGE FOR THE REMOVAL OF HEAVY METALS AND ACIDITY

Type of Document Dissertation
Author Diz, Harry Richard
Author's Email Address hrdiz@vt.edu
URN etd-81697-135443
Title CHEMICAL AND BIOLOGICAL TREATMENT OF ACID MINE DRAINAGE FOR THE REMOVAL OF HEAVY METALS AND ACIDITY
Degree Doctor of Philosophy
Department Civil Engineering
Advisory Committee
Advisor Name Title
John T. Novak Committee Chair
Donald S. Cherry none
J. Donald Rimstidt none
Nancy G. Love none
William R. Knocke none
Keywords

* iron biooxidation
* iron precipitation
* iron removal technology
* acid mine drainage

Date of Defense 1997-08-11
Availability unrestricted
Abstract

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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