Opposing scaling and fouling during electrodialysis of sodium fluoride solution in a membrane cell reactor

Electrodialysis of a sodium fluoride solution in a membrane cell reactor was studied as part of a process to bleed magnesium from process liquors of electrolytic zinc plants. Because, in industrial practice, the long-term stability of membranes is a must, performance of the membranes over a long time was studied. Scaling of one of the membranes occurred as a result of the specific composition requirements. Without opposing measures, this scaling causes the reactor voltage to increase continuously. Four effective measures could be identified to reduce the scaling. Creating a small pressure difference over the membrane, causing the membrane to bulge and the scaling to breakdown, was very effective as well as the addition of dilute acid pulses. Furthermore, creating a turbulent environment and brushing the membranes could be applied to reduce the scaling. One of the membranes also experienced fouling, although this fouling did not influence the selectivity of the membrane for at least 500 h.