Role of zinc in bulk precipitation from the steaming process of potable water

Abstract

Water chemistry plays an important role in fouling kinetics and morphology. This work investigates the influence of zinc cations in potable water, specifically the kinetics of crystallisation and their effect on the fouling layer during the operation of a batch steam generator system and a once-through flow system. The kinetics of precipitation in the batch crystalliser were examined based on the change in concentration of the foulants, while the fouling resistance approach was used in the flow system. In addition, morphological testing was carried out using Scanning Electron Microscopy, Powder X-ray Diffraction, and Energy dispersive X-ray. The findings showed that the precipitation rate of calcium carbonate decreases with the increase in zinc ions until reaching the zinc carbonate supersaturation in the water due to water evaporation. Regarding morphology, co-precipitation of zinc carbonate was observed at high zinc concentrations. As a result, a double effect was observed where zinc both retarded and enhanced fouling over time. The fouling rate in the flow system decreased as the zinc concentration increased. Zinc ions were found to influence the morphology of deposit minerals significantly. Moreover, the surface deposition of zinc salts increased with the solution content of zinc.