Inhibition of calcium carbonate scaling in reverse osmosis by Zn++ using pure calco-carbonic solutions and the membrane CO2 degassing method

This study evaluates the inhibition mechanisms of CaCO 3 scaling in reverse osmosis using Zn ++ which has been superficially investigated in RO, with only three papers published. In order to do that a novel experimental approach was used; this approach involved a synthetic calco-carbonic solution, with an initial hardness of 60 °F (240 mg/l Ca++) and saturated with CO 2 , The CO 2 leakage through the RO membrane allowed the interfacial pH to increase and, thus, accelerated the scaling occurrence. The condition for CaCO 3 precipitation is the solubility product verification: (Ca ++ )* (CO 3 = ) ≥ K S . In saturation pH, the CO 3 = concentration remained at ppm level; masking the CO 3 = ligand by Zn ++ , for scaling prevention, was the main research hypothesis. This approach is very different from conventional kinetic and crystallographic theories. Furthermore, the synthetic solution was desalted in batch mode using various Zn ++ concentrations (0–1.5 ppm); the results showed a 288 minutes induction time without Zn ++ and 402 mn with Zn ++ at 1.5 ppm, the saturation pH increased from 7.33 to 8.18, confirming the Zn ++ efficiency. Also, the pH–time, conductivity–time, [Ca ++ ]–time and turbidity–time plotting allowed scaling detection in the fluid bulk; their comparison showed a good correlation. SEM and EDS spectro were used.