Silica removal to prevent silica scaling in reverse osmosis membranes

“Reverse osmosis membranes are increasingly used in drinking water treatment. However, the production of a
concentrate stream is the main disadvantage of its application. Increasing the recovery of the membranes in
order to have the smallest amount of concentrate possible is an attractive approach. In the absence of bivalent
cations in the feedwater, silica and silica-derived precipitants are limiting factors in high-recovery reverse osmosis
operations. The removal of silica in a separate pretreatment process might be the solution. Several methods
were tested to remove silica. Precipitation of silica with Fe(OH)3, Al(OH)3 and silica gel was investigated, and
also the removal of silica using a strongly basic anion (SBA) exchange resin.
Al(OH)3 was the most effective precipitant for silica, removing nearly all of the molecularly dissolved silica.
However, a residual amount of aluminum remained in solution, and aluminosilicate colloids were not removed.
The use of the SBA exchange resin also showed a good performance, removing up to 94% of the silica. However,
further investigations, such as checking whether the residual small amounts of silica and aluminum can still
cause scaling in the membrane, need to be conducted.”
© 2014 Elsevier B.V. All rights reserved.
(Citaat: Salvador Cob, S., Hofs, B., et al. Silica removal to prevent silica scaling in reverse osmosis membranes – Desalination 344(2014), p.137-143)