Silicon and Sodium removal

[aspearin1]

Silicon and Sodium are pervasive ions in our system. Removal by ion exchange resins have not been effective enough for our purposes. We're less worried about the Sodium, but are stumped with the Silicon removal. It comes from an upstream zeolite filter. It is likely in oxidized form. Any takers?

 

[tr6]

"Silicon" or "Silica"?

My guess is Silica. If you have determined that the silica is coming from an upstream zeolite filter then most likely it is coming from the support bed. Most filters use layers of graded gravel - large rocks on the bottom with progressively smaller particles until you reach the size of sand, and then the filtering media. Gravel (quartz) is made up of silicon dioxide. While the suppliers for the filter gravel say that it will not leach silica, the fact is that it does. Water treatment equipment manufacuters used to use the gravel at the bottom of their demineralizers instead of screening the laterals because of the cost. And then everybody would wonder where the silica in the system was coming from. It was discovered that silica was being leached from the quartz support beds. Now, all of the demineralizers that I have seen are designed with screened laterals and no gravel.

The removal of the silica is accomplished with a strong anion base resin that is regenerated using a 120^F 4% NaOH solution over a period of 60-90 minutes at a flow rate of around .25 GPM per cu ft of resin. Depending on the desired silica leakage, if you looking for less than 1 ppm then counterflow regeneration is the answer.

If silica removal is critical then sodium removal becomes critical as high sodium leakage will have a tendency to increase the silica leakage - NaOH. The removal of sodium is best accomplished with a counterflow strong acid cation.

Hope this helps.