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Iron

Iron. WQT 134 Aquatic Chemistry II Standard Methods 20 th ed #3500 Iron (#110) Applied Water and Spent water Manual Chapter 38 Lecture 6. Week 6 Objectives . Reading assignment:

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Iron

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  1. Iron WQT 134 Aquatic Chemistry II Standard Methods 20th ed #3500 Iron (#110) Applied Water and Spent water Manual Chapter 38 Lecture 6

  2. Week 6 Objectives Reading assignment: American Public Health Association (APHA), American Water Works Association (AWWA) & Water Environment Federation (WEF). 1999.  Standard Methods for the Examination of Water and Wastewater, 20th edition Jackson. 1993. Applied Water and Spentwater Manual. 1. Understand the role and function of Iron in water treatment. 2. Understand how to measure Iron (SM #3500, #110) 3. Comprehend iron concentrations in nature.

  3. Iron #3500, #110 Total Iron: The amount of ferrous (Fe+2) and ferric iron (Fe+3) in a sample. Determined using a colorimeter. • Measure 50 ml of your sample into 125 ml erlenmeyer flask • Add 2 ml concentrated HCl (use pipette) • Add 2 ml hydroxylamine hydrochloride solution • Add a few glass beads and boil • Cool to room temperature and pour 38 ml into 100 ml volumetric flask Digestion Process • Add 10 ml ammonium acetate buffer • Add 2 ml phenanthroline solution • Dilute to mark with water Color Development

  4. Iron #3500, #110 Beer’s Law : (physical chemistry) The law which states that the absorption of light by a solution changes exponentially with the concentration, all else remaining the same.

  5. Iron #3500, #110 Factoids • Iron (Fe) is the first element in Group VIII of the periodic table • atomic number of 26, atomic weight of 55.85 • Common valences of 2 and 3; solubility of ferrous ion (Fe2+) is controlled by the carbonate concentration. • Average Fe in the earth’s crust is 6.22% • Soils Fe ranges from 0.5 to 4.3% • Streams averages ~0.7 mg/L • Groundwater averages 0.1 to 10 mg/L. Iron • Minerals hematite, magnetite, taconite, and pyrite.

  6. Iron #3500, #110 Factoids • Ferrous ion (Fe2+) is soluble form in nature • On exposure to air or addition of oxidants, ferrous iron is oxidized to the ferric state (Fe3+) and may hydrolyze to form red, insoluble hydrated ferric oxide

  7. Pipe Corrosion/Fe staining/Fe in GW ~20,000 gpd

  8. Iron #3500, #110 Day 1 Day 2 Day 4 Day 16 flow direction

  9. Iron #3500, #110 BC Column Final Pore Water goethite low magnetite medium Fe(II)aq siderite high inhibitors green rust Flow Direction dark Zachara et al., (2001) proposed that dissolved Fe(II) concentrations control secondary solid phase products of Fe oxide reduction. orange

  10. Iron #3500, #110

  11. Iron #3500, #110 • What is Iron? • Iron occurs in the minerals hematite(Fe2O3), magnetite (Fe3O4), ferrihydrite (FeOOH), aresenopyrite (FeAsS), siderite (FeCO3), aluminosilicates, and pyrite (FeS). It is widely used in steel, alloys, as well as for environmental remediation of nitrates and arsenic. • Why do we care? • Iron in residual waters after treatment can cause laundry and fixture staining, corrosion, rust, odor and aesthetic taste problems and iron bacterial blooms in drinking water.

  12. Iron #3500, #110 • How is it done? • Iron is brought into solution, reduced to the ferrous state by boiling with acid and hydroxylamine, and treated with 1,10-phenanthroline at pH 3.2 to 3.3. Three molecules of phenanthroline chelate each atom of ferrous iron to form an orange-red complex. • The colored solution obeys Beer’s law; its intensity is independent of pH from 3 to 9. Thus, sample is run at 510 nm on a colorimeter • A set of standards is run along with unknown sample and a blank to determine Fe concentration. • Plot absorbance or percent transmission (on the vertical or y-axis) vs. iron concentration (on the x or horizontal axis) in mg/l as a linear graph. • Determine unknown Fe concentration

  13. Iron #3500, #110 • What are advantages of the procedure? • Accuracy of dissolved or total concentrations of iron as low as 10 μg/L can be determined with a spectrophotometer using cells with a 5 cm or longer light path. • No pretreatment necessary for well or potable water samples

  14. Iron #3500, #110 • What are disadvantages of the procedure? • Preliminary treatment is a must for waste or organic rich stream water • Cyanide, nitrite, and phosphates (polyphosphates more so than orthophosphate), chromium, zinc in concentrations exceeding 10 times that of iron, cobalt and copper in excess of 5 mg/L, and nickel in excess of 2 mg/L. • Bismuth, cadmium, mercury, molybdate, and silver precipitate phenanthroline. • Color or organic matter may necessitate digestion before use of the extraction procedure.

  15. Iron #3500, #110 • What are typical values in nature? • The United Nations Food and Agriculture Organization recommended level for irrigation waters is 5 mg/L. • The U.S. EPA secondary drinking H2O MCL is 0.3 mg/L.

  16. Iron #3500, #110 • What are the units and conversions? • Fe in mg/l Calculations and Formulas? mg/L as Fe = mg/l as read from standard curve mg/L as Fe = (curve value)(dilution factor)

  17. Iron #3500, #110 Example Problem? If 25 ml of sample has been diluted to 100 ml, and then 50 ml of this solution was used for analysis, the dilution factor to multiply times the curve value (which is in terms of concentration- would be 4.0) Suppose the diluted sample produced an absorbance equivalent to 0.145 mg/L then the actual concentration would be: mg/l as Fe = (0.145)(4)= 0.580 mg/l as Fe

  18. Iron #3500, #110 • Tips and Suggestions? • If It says Fume Hood….. Keep it in the Fume Hood!! • 36 N Sulfuric acid will burn on contact, wear gloves!!! • Let spectrophotometer warm up a bit to 510 nm • Run all samples in succession • Take your time and try to learn/play with making a graph in Excel; its a great tool to have.

  19. Water containing high iron is objectionable in a public water supply because: a. excess iron will scale pipes b. excess iron will stain plumbing fixtures c. excess iron causes “baby blue” syndrome d. iron content has no effect on the water supply

  20. Red water may be caused by iron concentrations above: a. 0.01 mg/L b. 0.03 mg/L c. 0.1 mg/L d. 0.3 mg/L

  21. Dissolved iron in excessive amounts results in consumer complaints about: a. hardness b. corrosion c. smell d. turbidity

  22. Which of the following chemicals will most likely keep iron in suspension? a. chlorine b. lime c. polyphosphate d. potassium permanganate

  23. Before iron, manganese, and hydrogen sulfide can be removed by filtration they must first be converted to: • Insoluble precipitates through oxidation • Gases through flash mixing • An odor free state through settling • Gases through adequate detention time

  24. Unlike most surface waters, ground waters may need to have these materials removed • Iron and manganese • Copper and manganese • Iron and copper • Softening agents

  25. Iron and manganese may be removed from source waters by oxidation. The following chemicals are often used to precipitate iron. Check all that apply • Chlorine • Potassium permanganate • Alum • Sodium hydroxide • 1 and 2 only

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