On-line viscometer monitors dense media

An XL7 on-line viscometer from Hydramotion has proved "more than capable" of accurately monitoring the dense media used in the separation of mineral ores by a world leader in exploration and mining

Viscosity is an important factor in the process of "dense media separation" ("DMS"), because if the medium is too viscous the particle settling rate will fall and the efficiency of the separation will be reduced.

In the process, crushed ore from the company's mines is wet screened to size it into different fractions then introduced into a conical or cylindrical separator in which the constituent minerals are separated in a "sink-float" process.

A vortex is created within the separator, causing denser particles to migrate to the bottom (the underflow) while less dense particles migrate to the top (the overflow).

Separation is more effective if a heavy fluid or "medium" is used rather than plain water, since material with densities up to 2.6 g/cc can then be made to float.

Suitable artificial media can be made by suspending dense powders such as ferrosilicon (FeSi) or medium-grade magnetite (ferrous-ferric oxide) in water.

The mining company attempted to monitor viscosity off-line using a rotational-type viscometer but found that, because the shear rate in their pipeline was significantly higher than the 150 per sec obtainable with the off-line instrument, the results did not reflect the rheology of the material in practice.

Other viscometers also failed for a variety of other reasons, including calibration problems, plant vibration and high wear rates.

Looking for a robust and reliable instrument that could deliver continuous real-time viscosity measurement at higher shear rates, the company turned to Hydramotion, and were immediately impressed.

The Hydramotion XL7 on-line viscometer was easy and quick to install, required no on-site calibration or set-up and began delivering accurate viscosity measurement as soon as the power was connected.

"The main objective here was to find an on-line unit that gives a realistic representation of the rheology characteristics of in-circuit media in order to correlate recovery performance with viscosity," commented the engineer in charge of the project.

"I think that the XL7 viscometer is more than capable of fulfilling this objective.

It has shown itself to be a reliable process instrument for DMS".

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