Journal of Membrane Science & Technology

Abstract

Insight in to the Initial Stages of Silica Scaling Employing a Scanning Electron and Atomic Force Microscopy Approach

Bogdan C Donose, Greg Birkett and Steven Pratt

The performance of reverse osmosis (RO) desalination can be limited by membrane scaling. Of particular concern is silica scale, which once deposited on the membrane is extremely difficult to remove. In this work, the deposition of silica-rich nanoparticles was considered. A novel in situ sample preparation method was developed for a microscopy investigation into the deposition and adhesion of the silica-rich nanoparticles. The method involves placing a clean silica wafer in agitated brine to collect particles to simulate initial stages of scaling. The ?scaled? surfaces were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Model brines, with varying nanoparticle, cation, and organic composition and concentration were tested, as well as reject brine from a full-scale operational water treatment facility. Microscopy revealed that silica-rich nanoparticles were deposited from all waters, with smaller nanoparticles more readily attaching to the wafer compared to larger ones. The presence of organics increased nanoparticle adhesion whereas divalent cations (Ca2+ and Mg2+) decreased nanoparticle adhesion. These results have implications for the evaluation, selection and operation of RO pre-treatment processes and chemical dosing strategies, particularly the requirement for weak acid cation ion exchange (WAC-IX) and anti-scalant chemicals, respectively.