Potassium Permanganate
5. POTASSIUM PERMANGANATE
Potassium permanganate (KMnO4) is used primarily to control taste and odors, remove color, control biological growth in treatment plants, and remove iron and manganese. In a secondary role, potassium permanganate may be useful in controlling the formation of THMs and other DBPs by oxidizing precursors and reducing the demand for other disinfectants (Hazen and Sawyer, 1992). The mechanism of reduced DBPs may be as simple as moving the point of chlorine application further downstream in the treatment train using potassium permanganate to control taste and odors, color, algae, etc. instead of chlorine. Although potassium permanganate has many potential uses as an oxidant, it is a poor disinfectant.
5.1 Potassium Permanganate Chemistry
5.1.1 Oxidation Potential
Potassium permanganate is highly reactive under conditions found in the water industry. It will oxidize a wide variety of inorganic and organic substances. Potassium permanganate (Mn 7+) is reduced to manganese dioxide (MnO2) (Mn 4+) which precipitates out of solution (Hazen and Sawyer, 1992). All reactions are exothermic. Under acidic conditions the oxidation half-reactions are (CRC, 1990): MnO4- + 4H+ + 3e- à MnO2 + 2H2O MnO4- + 8H+ + 5e-à Mn2+ + 4H2O Under alkaline conditions, the half-reaction is (CRC, 1990): MnO4- + 2H2O + 3e- à MnO2 + 4OHEo = 0.60V Eo = 1.68V Eo = 1.51V
Reaction rates for the oxidation of constituents found in natural waters are relatively fast and depend on temperature, pH, and dosage.
5.1.2 Ability To Form a Residual
It is not desirable to maintain a residual of KMnO4 because of its tendency to give water a pink color.
5.2 Generation
Potassium permanganate is only supplied in dry form. A concentrated KMnO4 solution (typically 1 to 4 percent) is generated on-site for water treatment applications; the solution is pink or purple in color. KMnO4 has a bulk density of approximately 100 lb/ft3 and its solubility in water is 6.4 g/mL at 20ºC.
April
Potassium permanganate (KMnO4) is used primarily to control taste and odors, remove color, control biological growth in treatment plants, and remove iron and manganese. In a secondary role, potassium permanganate may be useful in controlling the formation of THMs and other DBPs by oxidizing precursors and reducing the demand for other disinfectants (Hazen and Sawyer, 1992). The mechanism of reduced DBPs may be as simple as moving the point of chlorine application further downstream in the treatment train using potassium permanganate to control taste and odors, color, algae, etc. instead of chlorine. Although potassium permanganate has many potential uses as an oxidant, it is a poor disinfectant.
5.1 Potassium Permanganate Chemistry
5.1.1 Oxidation Potential
Potassium permanganate is highly reactive under conditions found in the water industry. It will oxidize a wide variety of inorganic and organic substances. Potassium permanganate (Mn 7+) is reduced to manganese dioxide (MnO2) (Mn 4+) which precipitates out of solution (Hazen and Sawyer, 1992). All reactions are exothermic. Under acidic conditions the oxidation half-reactions are (CRC, 1990): MnO4- + 4H+ + 3e- à MnO2 + 2H2O MnO4- + 8H+ + 5e-à Mn2+ + 4H2O Under alkaline conditions, the half-reaction is (CRC, 1990): MnO4- + 2H2O + 3e- à MnO2 + 4OHEo = 0.60V Eo = 1.68V Eo = 1.51V
Reaction rates for the oxidation of constituents found in natural waters are relatively fast and depend on temperature, pH, and dosage.
5.1.2 Ability To Form a Residual
It is not desirable to maintain a residual of KMnO4 because of its tendency to give water a pink color.
5.2 Generation
Potassium permanganate is only supplied in dry form. A concentrated KMnO4 solution (typically 1 to 4 percent) is generated on-site for water treatment applications; the solution is pink or purple in color. KMnO4 has a bulk density of approximately 100 lb/ft3 and its solubility in water is 6.4 g/mL at 20ºC.
April