An Introduction to Environmental Chemistry

eqn. 5.15

followed by the oxidation of ferrous iron (Fe(II)) to ferric iron (Fe(III)):

eqn. 5.16

Oxidation happens very slowly at the low pH values found in acid mine waters.

However, below pH 3.5 iron oxidation is catalysed (see Box 4.4) by the iron

bacterium Thiobacillus thiooxidans. At pH 3.5–4.5 oxidation is catalysed by

Metallogenium. Ferric iron may react further with pyrite:

41 Fe^2 O22l 048 H O Fe OH 3 H

Fe II Fe III

()aq g s aq

+

++() () ()()+ +()

()() ()()

158 Chapter Five

25

50

10

25

New York

Atlantic

Ocean

Gulf of

Mexico

Miami

10

50

Chicago

(b)^25

km

0 300

N

25

Fig. 5.7Cont.