pH modification for silica control

ABSTRACT

Lowering solution pH slows the polymerization of silica and formation of silica scale. In batch systems, lowering the pH of approximately 200 ppm silica solutions prevents scale formation for over 300 h. Silica scale forms most quickly near pH 8. Solutions with pH 3.6–3.7 can maintain silica levels of 1,000–3,000 ppm for roughly 90 h. Bench-scale membrane testing showed that silica scale formation lag times of approximately 72 h were achievable after lowering the pH to 4.5–4.7, which might allow flushing of silica-laden solutions through, for example, flow reversal, before scale formation occurs during water treatment.

Keywords:

• Silica
• Scale formation
• Nanofiltration

Acknowledgments

We greatly appreciate the efforts of the Editor, Miriam Balaban, and the reviewers. This study was funded by the US Department of Energy’s National Energy Technology Laboratory (DOE/NETL). The NETL sponsors for this project were Isaac “Andy” Aurelio and Andrea McNemar, Project Managers, and Jared Ciferno, Technology Manager for the Existing Plants, Emissions and Capture Program. The authors also acknowledge the contributions of DOE/NETL colleague Lynn Brickett. This NETL management team provided guidance and technical oversight for this study. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.