Silica Break Through of Demineralizers

SILICA
A Parameter for Continuous Analysis of Demineralizer

When exchangers approach their end point, silica usually is the first impurity to "break through" into the effluent. For this reason, silica is a critical quality control parameter in demineralized / ultrapure water treatment. Conductivity measurements, long used as a measure of water purity, are unreliable in detecting resin bed exhaustion because silica breakthrough does not increase conductance appreciably. For high pressure boiler operators, semiconductor manufacturers and chemical processors, continuous silica analyzers provide dependable monitoring of demineralizer performance and guard against introduction of silica into pure water reservoirs and systems downstream.

[Figure] Two stages of a strongly basic exchange column show anion layering as column nears exhaustion. Silica is the first impurity to break through the exhausted resin. Research data indicate slug concentrations of silicates slipping off the exhausted column can be four or more times higher than that of incoming raw water.

Figure: A typical demineralizer exhaustion cycle,
left early in cycle, right near exhaustion

Source: Water analysis handbook - Hach