Electrophoretic mobility of magnetite particles in high temperature water

Magnetite (Fe 3O 4) is one of the most common oxides forming deposits and particulate phases in industrial high temperature water circuits. Its colloidal characteristics play a principal role in the mechanism of deposit formation and can be used as controlling factors to prevent or minimize deposit formation and damage of industrial pipelines due to under-deposit corrosion. In this study, a high temperature particle electrophoresis technique was employed to measure the zeta potential at the magnetite/water interface—the parameter that controls colloidal stability of particles, their aggregation, and deposition. The measurements were made at temperatures up to 200 °C over a wide range of pH. The isoelectric points of magnetite, at which the deposition of particles is increased, were determined at pH 6.35, 6.00, 5.25, and 5.05 for temperatures 25, 100, 150, and 200 °C, respectively. The observed temperature dependence of zeta potential and the isoelectric pH point of magnetite can help to explain the extent of interactions between the colloidal particles and the steel wall surfaces under hydrothermal conditions, and indicate methods for controlling and mitigating oxide deposition in high temperature water cycles. ► We measured electrophoretic mobility of magnetite at temperatures up to 200 °C over a wide range of pH. ► We estimated the isoelectric points of magnetite as 6.35, 6.00, 5.25, and 5.05 at temperatures 25, 100, 150, and 200 °C, respectively. ► We calculated zeta potential at the magnetite/water interface. ► We experimentally found that magnetite surface would maintain a negative charge in typical high temperature power plant water.