Grinding & Classification Circuits

Grinding & Classification Circuits 2017-03-23T09:46:37+00:00
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Screening or Cycloning in Ball Mill Circuit (11 replies)

Bob Mathias
1 year ago
Bob Mathias 1 year ago

What will be the better option in a Ball Mill Grinding Circuit: Screening or Cycloning?

The separation is 500 micron and the feed is 100 TPH

John Koenig
1 year ago
John Koenig 1 year ago

It depends. What size are you grinding to and what is your feed rate?

If you are grinding to a top size of 0.15 mm or finer, the screen area needed is quite large and require a large area and the feed and collection piping gets complicated. The same occurs at high feed rates.

The efficiency of cylcones is not as good, especially with current practice to operate at very high concentrations (~50 % by weight).

At low feed rates (say under 500 t/hr) or coarser grinds (>0.5 mm), screens become more practicle.

Another option is a combined circuit using cyclones to make the primary separation and then putting the overflow over screens with a coarser opening to take out large misplaced material.

Helena Russell
1 year ago
Helena Russell 1 year ago

Yes it does depend on what size you want and I suspect that is dependent on what beneficiation you are doing downstream jigging or hydraulic classification etc. It would not be uncommon to screen for iron ore however depends what you are going to do next.

Bob Mathias
1 year ago
Bob Mathias 1 year ago

It means desliming with cyclone for -100 micron and the underflow to screen!

John Koenig
1 year ago
John Koenig 1 year ago

Making a 500 micron split on a screen at 100 t/hr is doable, probably using either sieve bends or high efficiency screens (similar to Derrick). Running the material through a cyclone to deslime at 100 microns (or even slightly coarser) then running across the screen would work.

Running the cyclones at even a coarser cut (say 1000 microns and then running the overflow across the screen to make the 500 micron cut would give you an even sharper cut.

Bill Fraser
1 year ago
Bill Fraser 1 year ago

Why not consider a spiral classifier?

For classification at a coarse size like 500 micron and processing a dense mineral this can be an ideal solution for a low cost operation. With the correct design the spiral classifier can elevate the coarse solids back up to the feed of the mill to be recycled. This removes the need for pumps, cyclones and screens!

It is old technology that has been used in thousands of applications.

John Koenig
1 year ago
John Koenig 1 year ago

Spiral classifiers would work fine (surprised I didn't think of that). This is the right size and feed rate for them to operate. Much sharper separation than cyclones, and simpler than cyclones and screens. Also low power consumption. Depending on layout the standard way would be to have the mill overflow go directly into the spiral and the coarse discharge go right back into the mill feed (run in parallel).

Alan Carter
1 year ago
Alan Carter 1 year ago

Some iron ore circuits in Canada use Hydrosizer up current classifiers in their grind circuits. They give a sharp cut in the 200 to 500 micron range, and wear is low

Victor Bergman
1 year ago
Victor Bergman 1 year ago

Depending on the mineralogy, spirals have high wear rate particularly with coarser sizes. The flight edges (shoes) should be of high manganese steel or so called "white iron" 

One hundred TPH should be doable with a 12'X12' mill with 3 inch balls if feed is less than 1/2 inch.

David Kano
1 year ago
David Kano 1 year ago

Spiral classifiers work great and generally aren't a maintenance problem. The main problem is that most mills have outgrown them for direct use in closed circuits. The best bet would be to pump the mill discharge to the classifier and flow the sands by gravity back into the mill if direct feed can't be arranged.

For wear, we've found urethane flight faces and shoes to be much longer lasting than ni-hard (white metal) for taconite up to 3/8" (9 mm) for these applications. Urethane is also quicker and easier to replace than ni-hard castings.

Hydrosizers need clean water to operate effectively. Any organics like grass, wood, plastic sheet from explosives in the pit, or fish in the water will plug up the sprays. Clean water like this can be a rare commodity in a processing plant. Don't even think small filters will help, they plug up even quicker and no one has time to clean them.

Plastic sheet from explosives bags and hole liners is the worst, it plugs filters quickly, doesn't deteriorate, and floats in the tailings thickener. It doesn't disintegrate in the explosion, it just gets ripped into small pieces that come in with the ore.

Care also has to be taken in the water circuit design to prevent slurry from being drawn back into the water system and plugging it up when the water pumps are shut off.

Tony Verdeschi
1 year ago
Tony Verdeschi 1 year ago

We have to be aware when we are comparing screens with cyclones in performance;the first one separates based on particle size and shape while cyclones separate particles based on size and shape in addition to specific gravity of each particle.
After noting the above, we have to consider the capacities we are talking about and the space available.Then comes the capital cost and maintenance.
Take all these factors and then decide.

John Koenig
1 year ago
John Koenig 1 year ago

Yes the capacities need to be considered, but also the percent solids being feed to the system. With recent trends being to feed cyclones at high solids, there separating efficency is decreased, As to hydrosizers, they are an excellent choice if high efficiency is desired, but in addition to the water consumption they do take up verticle clearance. Meaning that both a cyclone/screen circuit and a hydrosizer circuit would require pumping. In addition the product from a hydrosizer will be more dilute (more wate) than other circuits.

As to ball mill spiral circuits, I remember being in the old Metcalf mill and seeing a long b row of mills with spirals and no pumps (flotation was a level below.)

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