Calcium carbonate scale inhibition of a cathode surface under polarization by 2-phosphonobutane-1,2,4-tricarboxylic acid

Scale formation on the cathode surface of an electrocatalytic oxidation equipment restricts the effective operation of the equipment. The scaling mechanism on a cathode surface and the scale inhibition performance of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) under cathodic polarization were studied by gravimetric, solution, and surface analysis methods. The results showed that the amount of scaling on the cathode surface increased as the polarization potential shifted negatively. The scale inhibition performance of PBTCA was enhanced with the increase of PBTCA concentration. However, when the polarization potential was negatively shifted to -1.3 V and below, the addition of PBTCA at lower concentrations promoted scaling on cathode surface. The CaCO3 crystals formed in the blank solution were mainly calcite, with some vaterite possibly caused by electric field. In contrast, all the CaCO3 crystals formed on cathode surface in solution containing PBTCA were calcite. The addition of PBTCA increased the Ca2+ concentration and pH in solution near the cathode surface. The promotion of scaling with lower concentration PBTCA was mainly attributed to the higher pH of the solution and the weak solubilization of the scale inhibitor.