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Dewatering of clay (11 replies)

Paul Morrow
10 months ago
Paul Morrow 10 months ago

What shall we do for dewatering a placer iron ore tail, which contains lots of clay?

We design a thickener (2*15) m at the first stage of dewatering. The thickener underflow solid percent is 50%. It is notable that we consider adding flocculant in the thickening stage. For more dewatering of thickener underflow we wanna to use a chamber filter press, but the tests have showed that the filter cake moister reaches to 30%. this moister content, in addition to losing a considerable amount of water, causes many problems in filter cake handling by conveyor.

Carmen Ibanz
10 months ago
Carmen Ibanz 10 months ago

High clay content tails have long been a problem. Settling ponds can take years to reach a semi-stable condition and still have problems. But to use dry stacking with belt conveyors you will need under 15% moisture as a minimum. Standard filters also have trouble reaching anything below 30% moisture. Pressure filters (belt presses) can reach reach 20% on a good day. Pressure plates usually can get below 20%, but you would probably need a lot of them and they are expensive. You will get the water back gfor reuse (may need some treatment) and the product will usually be conveyable.

Another solution would be regular filters followed by thermal drying using rotating disk dryers. This arrangement can achieve a fairly dry product, but again at a cost. Also you will not recover the last part of the water as it will go off as steam.

Victor Bergman
10 months ago
Victor Bergman 10 months ago

If the grain size is above 150 microns then you may try rotating pan filter with vacuum pump in combination with hydro cyclone. However it depends on the quantity you want to process

Bill Fraser
10 months ago
Bill Fraser 10 months ago

Points may clarify the issue:

  • however the d80 of the tail is 300 microns, but more than 50% is finer than 45 microns, indicating the clay content
  • we have ordered two filter presses fits with the tail capacity.
  • The prepared filter press is a chamber one with 1200*1200 mm plates and the proposed cake thickness is 40 mm.
  • as mentioned before, in addition to losing a part of water, problems with filter cake handling by conveyor is our critical solicitude.
  • We think there may be some solutions:
  • more pressure in feeding and cake blowing, in addition to some restrictions
  • changing the plate, so that the filter cake thickness decrease to 20 mm, however the filtering capacity will diminish
  • using a filter cloth with higher air permeability. The filtrate quality for turbidity is not critical, and the filtered water pumps back to the thickener

what mentioned solutions will be more effective, and/or is it any more solution?

Carmen Ibanz
10 months ago
Carmen Ibanz 10 months ago

It was not clear if your system operating yet? If it is and you are still having trouble making conveyable material, one concept that I have seen work is to add some coarser tails to filter press feed. This provides some increased content for the fines to build upon.

Bill Fraser
10 months ago
Bill Fraser 10 months ago

The system will start in a month. But laboratory tests have shown a semi flowing filter cake, which seems to have some problems with handling.

Our tail top size is 3mm, but by using a dewatering screen the press feed decreases to 700 micron (d80=300 and d50=45 microns). It means the tail divided to two fractions (0-700 microns and 700 microns to 3 mm). Do you think feeding the whole tail (0-3 mm) to filter press be more effective than a (0-700) microns press feed?

Marshal Dienes
10 months ago
Marshal Dienes 10 months ago

I may be a little late to the party, but have you been able to establish the K value - 10-7m/sec? This could then point towards further alternatives to the drainage and reducing of moisture content, without the artificial pressure created by presses. In some cases that I have seen, the pressure can cause the clay to stop internal moisture from escaping by forming an impervious coating with fines 'trapped' inside. The less outside pressure, the better as this product will naturally be very slow to drain, but it is very possible.

Helena Russell
10 months ago
Helena Russell 10 months ago

I would like to add a word of caution about the filtrate quality: if too much clay recirculates back to the clarifier, it will come back in the filters and the problems will increase daily until they stabilize.Have you tested coagulants in small amounts? Those are effective with small particles, if you select the right one. Do not solely test the polymers. The inorganic coagulants are sometimes very effective.

Sending the whole flow to your filters might give a better solid, but you will need more filters and the total operating cost will soar. You will have to find the best balance between operation and costs.

Zander Barcalow
10 months ago
Zander Barcalow 10 months ago

Did you ever consider sending the cake of the filter press through a centrifuging system?

Your dewatering system may look like this:

  1. Thickening
  2. Filter press
  3. Centrifuging

maybe an expensive exercise but the process may be of help to your current situation.

Tony Verdeschi
10 months ago
Tony Verdeschi 10 months ago

Ever consider screw conveyors to handle your clay cake?

Carl Jenkins
10 months ago
Carl Jenkins 10 months ago

I may be late to join here, but our iron ore mine have the same issue. Our mine soil is too sticky like clay as well, and made our quality drop

10 months ago
David 10 months ago

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