Solving silica scaling is one of the most challenging issues in water treatment. In fact, silica has become the major limitation in the push for higher-recovery RO plants and Minimal Liquid Discharge (MLD)/Zero Liquid Discharge (ZLD) systems.

Silica Formation Mechanisms

Unlike other types of scale, silica forms through a polymerization process, where silicic acid polymerizes into small colloidal particles. Depending on the conditions, these particles can foul membranes as colloidal deposits or condense into a dense, glassy layer. Due to the extreme insolubility of these silica polymers, removing glassy silica scale is particularly difficult.

Silica Cleaning

This study demonstrates the effectiveness of AWC C-219 Silica Dissolver in removing severe silica scaling. The membrane in question, sourced from a mining site, exhibited a combination of biological and silica fouling on the lead elements, and the tail elements were coated with an extreme layer of glassy silica. The scaling was so severe that the membrane surface felt like 600-grit sandpaper.

We adopted a multi-step cleaning protocol to solve this problem:

1. C-227 was used to remove biological fouling and organic coatings.
2. Citric acid was applied to dissolve inorganic deposits.
3. C-219 was then introduced to break down the remaining silica scale.

The C-219 is a unique membrane cleaner that depolymerises and dissolves the silica without the use of the dangerous ammonium bifluoride (ABF) or hydrofluoric acid (HF).

After cleaning, the membrane was noticeably smoother to the touch. However to assess the improvement properly, we examined it under an electron microscope. The results were remarkable—only a few small colloidal silica particles remained. A second cleaning may be necessary to remove the last traces of biofouling and silica, but this approach presents a far more cost-effective solution than replacing the entire membrane train.

Conclusion

Silica scale is a common scale in high recovery RO systems and while the scale formation can normally be controlled with a high quality anti-scalant, once polymerization starts it can be exceedingly difficult to remove without using dangerous chemicals like HF. However, we now have the C-219 Silica Dissolver that can effectively remove both colloidal and polymerized glassy silica.

Do you have a unsolved scale problem? Contact us today to discuss how we can help make this a reality.