Restricted membrane electrochemical reactor and its applications in water hardness removal

Electrochemical descaling technology is focused by many researchers because of its convenient to use and environmental compatibility. However, the problems of serious backmixing and low current efficiency limit its applications. In this work, a novel restricted membrane (RM) electrochemical descaling reactor are constructed, and the descaling process is improved by stewing cathode discharge. When the membrane porosity decreased from 100 % to 42 %, the current efficiency increased from 11.7 % to 23.1 %. Under all current densities, the current efficiency of the processes < 30 % without stewing. After stewing cathode discharge (15 min), the current efficiency of the processes > 30 %. Furthermore, the current efficiency significantly increased from 20 %∼22 % (hydraulic retention time (HRT) 32 s) to 35∼40 % (HRT 8 s) after stewing 15 min. Prolonging HRT leads to a generalized high pH in the cathode side region. In this case, calcium carbonate will crystallize in solution rather than on the cathode surface. The microstructural characterization of the scale show that the scale precipitated on the cathode surface is ellipsoidal, while the scale obtained by stewing is typical calcite morphology.