Laboratory Testing & General Mineral Processing Engineering

Laboratory Testing & General Mineral Processing Engineering 2017-04-04T06:57:51+00:00
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Sonic Sieves like Gilson Ultrasiever (5 replies)

Tony Verdeschi
2 years ago
Tony Verdeschi 2 years ago

Can anybody share their experience with sonic sieves? Something like the Gilson Ultrasiever, but there is other manufacturers - principle of operation appears the same though Thanks

Maya Rothman
2 years ago
Maya Rothman 2 years ago

One must be patient as it takes about 4-6 hours to sieve ~2 g @ 10 um bottom of the stack (the finest I ever used). Ideally should have no more than 0.5 g per sieve.
The top and bottom parts (latex) last about 4-6 months - it depends how much acid fumes are in circulation in the laboratory atmosphere, along with exposure to sun light.
The material to sieve must be bone dry, otherwise it clogs the sieves quite rapidly and even the side taps becomes useless.

Other than that, pretty much like conventional sieving.

Conventional sieves as fine as 25 um (500 mesh) and I think 20 um (600 mesh) can be obtained. Preferred is to use double sieves - the top one being 38 or 45 um and really an inexpensive sacrificial sieve.

JohnnyD
2 years ago
JohnnyD 2 years ago

The Blue Coast Group has developed a method with home made filter bags and an ultrasonic bath - works quite well and only takes 30 minutes per size fraction for sub 20 micron stuff.

Bob Mathias
2 years ago
Bob Mathias 2 years ago

Attempts to do this dry on the Gilsonic are hugely dependent on particle size & propensity to agglomeration. As a general rule, it does not work (like the flour industry applications) and various folk have resorted to either wet screening (try modifying the Gilsonic to wet operation!) or variations of the 10 or 25 micron nylon screening with alternate mechanisms. There are some clever applications that folk use, ranging from use of alcohols where water soluble minerals are around, to modifications such as Dave likely alludes to above. I use a 2-stage method which employs a customised pre-screen removing a significant proportion of a slime from a pulped aliquot before it goes into the ultrasonic bath to reduce blinding and improve efficacy. Hint: get an ultrasonic bath with an exit tap!

Maya Rothman
2 years ago
Maya Rothman 2 years ago

From my experience, your comment that, as a general rule, sonic sifting does not work is too sweeping. It does work and one needs to set things up properly and be patient.

There are some circumstances that one does not want to expose the sample to water as in wet sieving. On such circumstances is if the sample is to be used for investigation of surface charge phenomena - there is a significant difference in the PZC if the sample was prepared dry or through a wet process. For this, sonic sifting is the only way for small samples - unless one has an Infrasizer in a back closet (air classifier similar to a Cyclosizer in its principle of operation).

With respect to agglomeration, it can often be dealt with by grounding the stack - notably the finest sieve.

With respect to screen blinding, ensuring the sample is truly dry often helps. Also, there are variations on the design - with gentle regular tapping of the sides of the sieves.

Having said that, if it is only desired to size the sample for assaying or mineralogy, one can do quite well with wet sieving down to 20 um (after a precautionary 38 um wet scalping). I also concur that using an ultrasonic bath for the finest sieve would do nicely.

Bob Mathias
2 years ago
Bob Mathias 2 years ago

You're right it was too sweeping a statement. In our mineral world where there is often complex mineralogy and many differently charged materials together, is what I should have said. In a mono-mineralic or mono-phase system (like flour & pure or near- systems) it works just fine.

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