Investigation of the Scaling Mechanism in Membrane Modules and the Influence of Antiscalants on This Process

Abstract

Knowledge of the mechanism of deposition of sparingly soluble salts (scaling) in reverse osmosis membrane devices is extremely important for the selection of means of controlling the scaling and increasing the recovery. This study has made it possible to take a fresh look at the mechanism of scaling and the role of antiscalants in the inhibition of this process. The development of the experimental procedure is based on the idea that the first phase of crystallization—nucleation—is homogeneous; that is, it occurs in the “dead” areas in the bulk of the concentrate at high values of calcium carbonate supersaturation. After formation, the crystals are removed from the “dead” areas and deposited on the membrane surface, like other suspended particles contained in the feed water. The paper also presents the results of a study of the adsorption of polymeric antiscalants on crystal surfaces during nucleation and crystal growth on the membrane. The experimentally revealed relations of the adsorption rates of antiscalants to the antiscalant dose, the calcium carbonate formation rate, the nucleation rate, and the total surface of the seed crystals formed are presented. An experimental procedure is described that makes it possible to determine the concentration of dissolved salts in the dead areas and calculate the supersaturation values corresponding to the onset of crystallization from antiscalant-free water and water in the presence of scale inhibitors in various amounts.