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Silica detection in the DI-line with Mi-Vision – But without a silicometer!

In this chapter you will see something we never expected: Measuring silicic acid without a silicometer!

The first evaluation projects already showed that Mi‑Vision is able to detect the breakthrough of weak acids through the anion exchanger (AN) in the DI-line with high sensitivity. The first "candidates" for breakthrough are naturally organic acids (a component of TOC), carbonic acid and silicic acid.

The breakthrough of the carbonic acid is the easiest to determine, because it always measurably changes the conductivity (first decreasing, then increasing).

The set of curves in the plot shows that the conductivity (blue) on the far right in the breakthrough does not react at all yet (i.e. no carbonic acid breakthrough), while the red online silicometer signal already shows clear deflections. For many experts it was very surprising that the green curve of the weak acids calculated by Mi‑Vision is obviously able to show the SiO2 breakthrough as well, although no HCO3- breakthrough is measurable at all yet.

SiO2- breakthrough detection of Mi‑Vision G1, parallelism with TOC measurement data
Surprising precision of SiO2 detection in Mi‑Vision G2

At the end of the loading, the green curve rises very clearly in sync with the silicometer (red) which was actually the surprising thing, since everyone - with good reason - says that SiO2 does not contribute to conductivity. Indeed, the conductivity (blue) does not increase at all, but the silicic acid content is still measurable which results in the green curve.

The scepticism of the experts towards this measurement of SiO2 breakthrough is quite justified. Therefore, we always speak cautiously of the breakthrough of weak acids and also the organic acids (component of TOC) remain a possible cause for the green signal. The large hump in the green curve at 2000 m3 throughput is such a TOC hump in the AN effluent.

The development of Mi‑Vision-Generation 2 was thus continued in the direction of optimising SiO2 detection and resulted in an extremely good signal-to-noise ratio of the measurement. The adjacent figure shows an example of a loading curve of our research DI-line with this G2 SiO2 measurement.

The achieved signal-to-noise ratio of the green Mi‑Vision-signal is almost in the range of the silicometer and in any case in the necessary range for a desalination line. The great result was well worth a patent application, which has already been assessed.

However, the fact that such results are not only achievable in research plants is shown by the example of a very large plant whose feed qualities vary extremely strongly within each run - a special challenge for the economic operation, but also for the Mi‑Vision technology!