Physical aspects of membrane scaling

Crystallisation processes are well understood from the thermodynamic point of view. But all desalination processes, such as reverse osmosis, are kinetically limited, and thus the kinetics of the crystallisation is of particular interest. The kinetics of scale formation, especially together with impurities like antiscalants, is poorly understood. Here a physical model of the scaling process is described which focuses on the kinetics and thus can explain a wide variety of phenomena (for example, induction time) which play a major role in module scaling.

Classical theory categorises antiscalants into two groups: nucleation inhibitors and growth inhibitors. In the case of the nucleation inhibitors this explanation is unphysical, because stochastic processes cannot be inhibited; only forced. For the growth inhibitors static surface adsorption has been proposed as the major impact on the induction time, but this is only a valid assumption at low supersaturation, e.g. for barium sulphates in oil wells. The classical theory could not cope with the large variety of scaling phenomena because the path-dependent kinetic aspects during the scaling process were neglected to simplify the approach. The necessity and possibility to optimise antiscalants for specific processes implies a model approach of higher complexity which includes the system state and its dynamics to determine the mechanism of scaling and scale preventing processes. Our novel approach reduces the system complexity to six physical aspects and their