Fe & Mn Removal
Content
Fe & Mn Removal
The filter is the most important piece of treatment equipment in an iron and manganese plant. 13 Chlorine should never be fed ahead of the polyphosphate, because it will oxidize the Fe and Mn (causing insoluble precipitates to form too soon). 3 Polyphosphate treatment to control Fe and Mn is usually the most effective when the poly is added upstream from the Cl2, but they can be fed together. 3 Fe and Mn can be removed by ion exchange, if the water contains no dissolved oxygen. If it contains D.O., the resin becomes fouled with rust or MnO2. 4 Fe can be oxidized by aeration to from insoluble ferric hydroxide Fe(OH)3. This can be accelerated by an increase in pH. 5 Do not use high doses of Cl2 if the water contains a high level of organic color, due to TTHM formation. 6 When Fe and Mn are oxidized by aeration, chlorination or permanganate to insoluble forms, the process is usually followed by filtration to remove the insoluble material. 7 If oxidation is by either aeration or chlorination, a Cl2 residual must be maintained in the filter influent to prevent the insoluble ferric form from returning to it’s soluble state and passing through the filter. 7 “Red water” or “dirty water” problems can be caused by corrosive water or iron bacteria in the distribution system. 8 Slime growths can be controlled by maintaining a free chlorine residual in the distribution system. 8 If water produced by the well contains D.O. along with Fe and Mn, this is an indication that the water is being drawn from more than one aquifer, since D.O. reacts with both elements to from insoluble compounds. It is also highly probable that the Fe or Mn bearing water is from deeper aquifers. 9
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Fe and Mn may be the cause of consumer complaints (red or black water). 11 Growth of bacteria is controlled by chlorination. 10 KMnO4 is often used with manganese zeolite or manganese greensand. After the greensand has been treated with KMnO4, it can oxidize both Fe and Mn to their insoluble states. 12 A lot of “iron complaints” in drinking water are caused by old steel or cast iron water mains. A possible solution to this problem is to inject polyphosphates directly into the distribution mains. 14 Acceptable limits: 10 Fe – 0.3 mg/L Mn – 0.05 mg/L Definitions Acidified – Addition of an acid (usually nitric or sulfuric) to a sample to lower the pH below 2.0. Its purpose is to “fix” a sample so it won’t change until it is analyzed. 15 Greensand – A mineral (glauconite) that looks like ordinary filter sand except that it’s green in color. Natural ion exchange material, capable of softening water. Greensand treated with KMnO4 is called “manganese greensand”, which is used to remove Fe, Mn and H2S from groundwater. 15 Polyphosphates – corrosion control and scaling inhibitor. Potassium Permanganate – (KMnO4) strong oxidant. Sodium hexametaphosphate – prevents scaling of Ca(SO4)2 on RO membranes 1 and is used in corrosion control. 2 Zeolite – Type of ion exchange material. 16 1. Natural – Silica compound which removes Ca and Mg and replaces them with Na.
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2. Synthetic (or organic) – removes Ca and Mg and replaces them with either Na or H. 3. Manganese – removes Fe and Mn. Footnotes 1. II, 173; 16.42 2. I; 375; 8.44 3. II, 9; 12.21 4. II; 11; 12.22 5. II; 12: 12.23 6. II; 13: 12.24 7. II; 14; 12.26 8. II; 21; 12.5 9. II; 9; 12.20 10.II; 6; 12.0 11.I; 30; 2.22 12.II; 13: 12.25 13.II; 17; 12.30 14.II; 15; 12.29 15.II; 4 16.II; 5
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The filter is the most important piece of treatment equipment in an iron and manganese plant. 13 Chlorine should never be fed ahead of the polyphosphate, because it will oxidize the Fe and Mn (causing insoluble precipitates to form too soon). 3 Polyphosphate treatment to control Fe and Mn is usually the most effective when the poly is added upstream from the Cl2, but they can be fed together. 3 Fe and Mn can be removed by ion exchange, if the water contains no dissolved oxygen. If it contains D.O., the resin becomes fouled with rust or MnO2. 4 Fe can be oxidized by aeration to from insoluble ferric hydroxide Fe(OH)3. This can be accelerated by an increase in pH. 5 Do not use high doses of Cl2 if the water contains a high level of organic color, due to TTHM formation. 6 When Fe and Mn are oxidized by aeration, chlorination or permanganate to insoluble forms, the process is usually followed by filtration to remove the insoluble material. 7 If oxidation is by either aeration or chlorination, a Cl2 residual must be maintained in the filter influent to prevent the insoluble ferric form from returning to it’s soluble state and passing through the filter. 7 “Red water” or “dirty water” problems can be caused by corrosive water or iron bacteria in the distribution system. 8 Slime growths can be controlled by maintaining a free chlorine residual in the distribution system. 8 If water produced by the well contains D.O. along with Fe and Mn, this is an indication that the water is being drawn from more than one aquifer, since D.O. reacts with both elements to from insoluble compounds. It is also highly probable that the Fe or Mn bearing water is from deeper aquifers. 9
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Fe and Mn may be the cause of consumer complaints (red or black water). 11 Growth of bacteria is controlled by chlorination. 10 KMnO4 is often used with manganese zeolite or manganese greensand. After the greensand has been treated with KMnO4, it can oxidize both Fe and Mn to their insoluble states. 12 A lot of “iron complaints” in drinking water are caused by old steel or cast iron water mains. A possible solution to this problem is to inject polyphosphates directly into the distribution mains. 14 Acceptable limits: 10 Fe – 0.3 mg/L Mn – 0.05 mg/L Definitions Acidified – Addition of an acid (usually nitric or sulfuric) to a sample to lower the pH below 2.0. Its purpose is to “fix” a sample so it won’t change until it is analyzed. 15 Greensand – A mineral (glauconite) that looks like ordinary filter sand except that it’s green in color. Natural ion exchange material, capable of softening water. Greensand treated with KMnO4 is called “manganese greensand”, which is used to remove Fe, Mn and H2S from groundwater. 15 Polyphosphates – corrosion control and scaling inhibitor. Potassium Permanganate – (KMnO4) strong oxidant. Sodium hexametaphosphate – prevents scaling of Ca(SO4)2 on RO membranes 1 and is used in corrosion control. 2 Zeolite – Type of ion exchange material. 16 1. Natural – Silica compound which removes Ca and Mg and replaces them with Na.
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2. Synthetic (or organic) – removes Ca and Mg and replaces them with either Na or H. 3. Manganese – removes Fe and Mn. Footnotes 1. II, 173; 16.42 2. I; 375; 8.44 3. II, 9; 12.21 4. II; 11; 12.22 5. II; 12: 12.23 6. II; 13: 12.24 7. II; 14; 12.26 8. II; 21; 12.5 9. II; 9; 12.20 10.II; 6; 12.0 11.I; 30; 2.22 12.II; 13: 12.25 13.II; 17; 12.30 14.II; 15; 12.29 15.II; 4 16.II; 5
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