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Thickening and Dewatering of Clay (14 replies)

Jean Rasczak
9 months ago
Jean Rasczak 9 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’s notable that we consider adding flocculant in the thickening stage. For more dewatering of thickener underflow we want to use a chamber filter press, but the tests have showed that the filter cake moister reaches to 30%. This moisture content, in addition to losing a considerable amount of water, causes many problems in filter cake handling by conveyor.

9 months ago
Gruppen 9 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 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 for 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.

Jean Rasczak
9 months ago
Jean Rasczak 9 months ago

Thanks for your comment. We plans to add PAM( POLYACRYLAMIDE) as an anionic flocculant, in the top of the thickener. Then is it possible to answer these questions?

  • How and where can we add the coagulant? In the thickener and/or in the baffled tanks before the filter-press?
  • How about ferric chloride (Fe (III)Cl3) as a cationic coagulant?

Points may clarify the issue more:

  • 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

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

9 months ago
Unterstarm 9 months ago

Here is a solution that may be worthwhile looking in to from a benchmarking point of view: The AQUARIUS-MudMaster is apparently used in Europe for dredging and sludge processing in the cleaning of waterways - the sludge processing part of that product may spark some ideas for you:

Zander Barcalow
9 months ago
Zander Barcalow 9 months ago

The USBM published reports on the dewatering of phosphate and coal slime streams using Polyethylene oxide (PEO). The dewatering was performed using a sieve bend. The coal slimes could be walked on in1week. I suggest you look up these reports.

John Koenig
9 months ago
John Koenig 9 months ago

If you tail content 50% -45 microns firstly is necessary cycloning (30-40 psi) of it. Then overflow product must go to two high tanks (20-25 meters each). In primary tank cake moisture will be 35-40%. In secondary tank 20-25%.

9 months ago
OberstGruppen 9 months ago

As far as you can try to avoid drying you should think about a possibility of further clay processing to some building materials production (e.g. LWA). Thus you will need separate "grain" part of the tailings (by hydro cyclones) and the rest clay slip could be processed in a rotary kiln plant.

Sugar Watkins
9 months ago
Sugar Watkins 9 months ago

You should analyse which pressure you are pump in and maybe use a membrane filter press technology. Do you also blow air in the cake after the filling and compacting phase?

9 months ago
Oberstorm 9 months ago

There possible way of getting a higher solid w/w in clay bearing tails. You may consider improving sedimentation by playing operating conditions of your thickener such that changing your floc addition do you have feed well system that.

Maya Rothman
9 months ago
Maya Rothman 9 months ago

Main problem in dewatering clay is water surface force. Need to reduce it. Need adding frother (oksal) before you press filter. To thickener need adding sodium alkaline (for pH = 8).

Carl Jenkins
9 months ago
Carl Jenkins 9 months ago


Number of perforated pipes shall be used (Victaulic pipes of 4" dia. shall be rappered with a ganny bags throughout the pipe length)

Precautionary measures shall be taken for less Stagnation of water where clay is duped or stoked.

To time Supervision are needed that the top most water shall be separated by a syphen method. Sludge should not be over flow (Water shall be separated by a syphen method of 1" and 1/2" number of hose pipes.

Carmen Ibanz
9 months ago
Carmen Ibanz 9 months ago

Thickening clay to 50% solids in a thickener is quite an achievement! On top of it you are currently not adding any flocculent. However it is highly unlikely that all the facts are on the table. The 50% underflow is most probably iron ore particles and I guess 5% to 10% iron ore ultra fines or maybe (mineralogy through XRD should prove that it is, in fact,) clay possibly even less than 5%.

The flocculation of clay is well researched and published. The coagulant and/or flocculent, process water composition, dosing points and the energy of mixing are important parameters to take into account. Of these parameters, the process water composition and energy of mixing probably have the most impact. Finer than 45 micron is no indication of clay content. It is not even an indication that any clay is present. Some silt might be present if the PSD indicate particles finer than 5 micron.

Clay is a mineral with specific surface and physical properties. A silt or rock flour is not clay and explain how you achieve the high underflow densities without flocculent.
If you had clay; the addition of coagulant and flocculent would not be optional but a definite requirement.
To reduce the water consumption you need to do a water balance over the total of two streams:
Split the stream into a fines and slimes fraction. Slimes could be the fraction finer than 20 micron. Use hydro-cyclones for the split. De-water the fines through filtering or similar means to a cake
Process the slimes in the thickeners at which stage flocculent would be required to achieve underflow densities of 50% or more (which should be achievable with the material you are processing).
The water balance will most probably indicate increased water return to the plant with more controllable process equipment.

9 months ago
Oberfuhrer 9 months ago

Much of this seems to be "silly" iron ore particles, as generally getting 50% slurry with just clay, without a flocculants and without a paste or deep cone thickener, would be quite incredible!

It would be interesting to know the true "clay" weight fraction – i.e. the fraction that actually needs significant treatment.

In truth, without more data, there are a lot of questions; even larger, macro questions:

Do you actually NEED to get so much water back? Why are you targeting such a high water recovery? Environmental reasons? Is it economical to target high moistures?

Is it economical to recover some of the iron fines? What is the grade like, by size fraction?

Would their possibly be sense in separating and treating the iron fines from the true clay fines? (E.g. the iron fines will settle or classify much more readily than the clays). You could possibly produce two separate streams that might be much more easily, effectively and economically treated by different methods?

Just some thoughts...

David Kano
9 months ago
David Kano 9 months ago

Agreed to the above comments and further to it please

Assuming that your are processing iron ore (probably) Haematite with silica and alumina clays. Making pellets which requires concentrate fe should be around 60-62 % and particle should be 65 to 75 percent passing 45 micron.

Following options maybe thought of in this case.

If your mineralogical and liberation studies support coarse liberation then it will be better to go for coarse grinding followed by separation and finally a fine ground to meet the concentrate specification.

If the optimum liberation is coarse, separation and de watering will be easy and economical but capital on two stage grinding will be increased.

Separation equipment like mineral spirals and magnetic separators will work with better efficiency.

Silica and clay will be separated post to the primary or first grind so over grinding of same will be reduced, supporting improved sedimentation and filtration characteristics of tailings.

Assuming your process is single stage grinding and generation of slimes can’t be reduced or avoided.

Need to study tailings by sizing on cyclo sizer to find the optimum size required for sedimentation (for settling rates with available flocculent) and filtration (for moisture content) from which we can ascertain de sliming cyclone cut point.

The de sliming cyclone underflow may be de watered in an HRT or paste thickener with the aid of flocculent, lime in thickener and finally filtered in pressure filters.

The de sliming cyclone overflow need to be processed in natural settling pond with available special chemicals from companies Like NALCO. These chemical accelerate water - particle disassociation.

The second option needs two stages settling i.e. a thickener and settling pond.
Option needs to evaluate on techno commercial basis, study focussed should result in continuous, trouble free, stable and economic operation. 

9 months ago
Obersturmbann 9 months ago

Please tell me more about your case? It is a research project or its industrial project? I am working with clay finer than 4 microns for more than 4 years! I think for solid liquid/separation it could be handled simply but keep in mind that when you should treat with clay; you should do especial processes not conventional thickening or pressure filtration; in this case the size of thickener or number of pressure membrane could be increased accordingly.

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