IRON & MANGANESE ENVE 201 Dr. Aslıhan Kerç /marmaraengineer/

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  insoluble ferric oxide  ironsulfide (pyrite) (slightly soluble) Ferrous carbonate (siderite) (slightly soluble) Ferrous carbonate (siderite) Mainly

Mn  in soil as manganese dioxide (insoluble) in water containing CO 2 Under anaerobic cond. : oxidation state changes ΙV  ΙΙ ΙV  ΙΙ These changes  occur due to biological rxns: 1) G.W. containing Fe, Mn  low D.O high CO 2 in the form Fe 2+, Mn 2+ High CO 2  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 around  anaerobic 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. 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 CO 2 FeCO 3 + CO 2 + H 2 O  Fe HCO 3 - like dissolution of calcium and magnesium carbonates More problems w/ insoluble ferric compounds. Under anaerobic (reducing) condition : Fe 3+  Fe 2+ Fe 3+  Fe 2+ (ferric) (ferrous) (ferric) (ferrous)

5) Certain bacteria use Fe (III) and Mn(IV) as electron acceptor. (?) When O 2 containing water injected into G.W for recharge  soluble Fe content may increase. O 2 consumed by pyrite FeS 2  leading to anaerobic conditions again 2FeS 2 + 7O 2 + 2H 2 O  2Fe SO H +

Environmental Significance  No harmful affect in drinking water  When exposed to air  become turbid, form colloidal precipitants unaccepted aestheticaly unaccepted aestheticaly oxidation rate  not rapid 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 Fe: 0.3 mg/L SMCL SMCL Mn: 0.05 mg/L Mn: 0.05 mg/L

Measurement of Iron (Phenanthroline Method) Interferences : Phosphate Heavy metals Heavy metals 1,10 phenonthroline combines with Fe 2+ to form complex ion orange in red color Color produced confirms Beer’s Law Visual Visual Photometric comparison Photometric comparison

Phenanthroline Method Sample exposed to atmospfere contains Fe 2+, Fe 3+, ppt of ferric hydroxide. All iron  must be in soluble form HCl is used HCl is used Fe(OH) H +  Fe H 2 O Fe(OH) H +  Fe H 2 O 1,10 phenonthroline  specific for measuring Fe(II) Fe 3+ is reduced to  Fe 2+ Hydroxylamine is used as reducing agent 4Fe(III) + 2 NH 2 OH  4Fe(II) + N 2 O + H 2 O + 4 H + 3 molecules of 1,10 phenantrhroline  complex with each Fe 2+

Manganese measurement  Colorimetric method  depend upon oxidation of Mn to  VII forms highly colored permanganete ion forms highly colored permanganete ion Obeys Beer’s Law Visual or photometric comparison  AAS  ICP

Manganese measurement (Persulphate Method) Ammonium persulphate  oxidizing agent Cl - interference: Because of reducing action in acid medium. use Hg 2+ for interference. HgCl 2 complex is formed Ag 2+ is used as catalyst Oxidation of Mn in lower valence to permanganete by persulfate. Ag + Ag + 2Mn 2+ +5S 2 O H 2 O  2MnO SO H + (permanganete colored) (permanganete colored)