Size and Zeta Potential of Oxidized Iron and Manganese in Water Treatment: Influence of pH, Ionic Strength, and Hardness

Abstract

© 2016 American Society of Civil Engineers.Iron and manganese are commonly found in natural waters, particularly in groundwater. Because of the importance of particle size distribution (PSD) on the performance of removal processes, this research focuses on understanding the PSD andζ-potentials of oxidized iron/manganese in water, as a function of pH, ionic strength, and hardness. After rapid oxidation of dissolved iron/manganese, laser diffraction (LD), dynamic light scattering (DLS), and fractionation through serial membrane filtration techniques were used to define the PSD. For manganese dioxide, theζ-potential was found to decrease as the pH decreased and as the ionic strength and hardness increased, resulting in a higher aggregate size. The aggregation rate of manganese dioxide strongly increased with hardness. On the other hand, ferric hydroxide PSD was not significantly altered by ionic strength or hardness at pH values relevant to typical natural waters. A combination of several techniques was found to be essential for providing a complete picture of the PSD. The DLS and LD techniques were generally well adapted for nano-scale and micron-scale particles, respectively. The serial membrane filtration technique was suggested for water practitioners working toward the selection of an appropriate process for iron/manganese control in drinking waters.