IRON & MANGANESE
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Transcript IRON & MANGANESE
IRON
&
MANGANESE
ENVE 201
Dr. Aslıhan Kerç
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IRON & MANGANESE
Problems in groundwater, surface water
certain seasons.
Some underground waters are free of Fe, Mn, but
some have
Biochemical changes effect Fe, Mn content
Changes in environmental condition brought by
biological reactions effect Fe, Mn content.
IRON & MANGANESE
Fe,Mn insoluble form in soil how converted
to soluble?
Fe is found in soils and minerals as :
insoluble ferric oxide
Mainly
ironsulfide (pyrite)
(slightly soluble) Ferrous carbonate (siderite)
Mn in soil as manganese dioxide (insoluble) in water
containing CO2
Under anaerobic cond. : oxidation state changes
ΙV ΙΙ
These changes occur due to biological rxns:
1) G.W. containing Fe, Mn low D.O high CO2
in the form Fe2+ , Mn2+
High CO2 bacterial oxidation of organic matter.
Absence of D.O anaerobic cond.
2) Wells producing good water change to poor
quality in time. What is the reason?
Organic wastes discharge aroundanaerobic
conditions occur in soil.
3) In surface waters (reservoirs) anaerobic conditions
occur in hypolimnion.
Fe,Mn released from bottom mud. Distributed to the
whole lake during fall overturn.
4) Mn (IV) , Fe (III) stable oxidation states for aerobic.
Reduced to soluble Mn(II) , Fe(II) under highly
anaerobic conditions.
G.W. contain CO2
FeCO3 + CO2 + H2O Fe2+ + 2HCO3-
like dissolution of calcium and magnesium carbonates
More problems w/ insoluble ferric compounds.
Under anaerobic (reducing) condition :
Fe3+ Fe2+
(ferric) (ferrous)
5) Certain bacteria use Fe (III) and Mn(IV) as electron
acceptor. (?)
When O2 containing water injected into G.W for
recharge soluble Fe content may increase.
O2 consumed by pyrite FeS2 leading to anaerobic
conditions again
2FeS2 + 7O2 + 2H2O 2Fe2+ + 42SO42- + 4H+
Environmental Significance
No harmful affect in drinking water
When exposed to air become turbid, form colloidal
precipitants
unaccepted aestheticaly
oxidation rate not rapid
Form stable complexes with humic substances more
resistant to oxidation
Interfere with laundering.
Environmental Significance
Difficulties in distribution sys. growth of iron bacteria
Imparts taste to water
Fe: 0.3 mg/L
SMCL
Mn: 0.05 mg/L
Measurement of Iron
(Phenanthroline Method)
Interferences : Phosphate
Heavy metals
1,10 phenonthroline combines with Fe2+ to form
complex ion orange in red color
Color produced confirms Beer’s Law
Visual
Photometric comparison
Phenanthroline Method
Sample exposed to atmospfere contains Fe2+ , Fe3+ , ppt of
ferric hydroxide.
All iron must be in soluble form
HCl is used
Fe(OH)3 + 3 H+ Fe3+ + 3 H2O
1,10 phenonthroline specific for measuring Fe(II)
Fe3+ is reduced to Fe2+
Hydroxylamine is used as reducing agent
4Fe(III) + 2 NH2OH 4Fe(II) + N2O + H2O + 4 H+
3 molecules of 1,10 phenantrhroline complex with each
Fe2+
Manganese measurement
method depend upon oxidation of
Mn to VII
forms highly colored permanganete ion
Obeys Beer’s Law
Visual or photometric comparison
Colorimetric
AAS
ICP
Manganese measurement
(Persulphate Method)
Ammonium persulphate oxidizing agent
Cl- interference: Because of reducing action in acid medium.
use Hg2+ for interference. HgCl2 complex is formed
Ag2+ is used as catalyst
Oxidation of Mn in lower valence to permanganete by persulfate.
Ag+
2Mn2++5S2O82- +8H2O 2MnO4- +10SO42- +16H+
(permanganete colored)