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The Oxidation of Divalent Manganese Under Conditions Present in Tile Lines as Related to Temperature, Solid Surfaces, Microorganisms, and Solution Chemical Composition¹

ABSTRACT

The oxidation and precipitation of Mn was measured in the laboratory under conditions similar to those present in tile lines. The presence of microorganisms capable of oxidizing Mn²⁺ was the most important factor controlling oxidation of Mn. These microorganisms were intimately associated with MnO₂ collected from tile lines and could not be separated from the MnO₂ particles. Hence, oxidation of Mn in the presence of microorganisms without the MnO₂ could not be studied. Surfaces of sand or clay did not catalyze the oxidation. An increase in temperature from 20 to 30C increased the oxidation only slightly.

The effects of dissolved oxygen, soluble organic carbon, total salt content, pH, and bicarbonate over the concentration ranges occurring in tile lines were determined using solutions containing manganese oxidizing microorganisms. Soluble organic carbon and total salt content have no significant effect on manganese oxidation. The percent oxygen in the gas mixture did not affect the oxidation rate when it was varied between 1 and 21%. When nitrogen was flushed through the cylinders, the zero oxygen resulted in solution of Mn²⁺ from the manganese dioxide. When the bicarbonate level was raised to 9.0 meq/liter (4% CO₂), the oxidation rate was 3 times the rate at the 5.3 meq/liter level of bicarbonate.

¹ Contribution from the Western Region, Soil, Water, and Air Sciences, ARS, USDA, Brawley, Calif., and the Univ. of California, Riverside.

² Soil Scientist, Imperial Valley Conserv. Res. Cent., 4151 Hwy 86, Brawley, Calif. 92227; Associate Professor and Professor of Soil Science, Univ. of California, Riverside, Calif., respectively.

Received for publication January 2, 1973. Accepted for publication April 9, 1973.