Dewatering: Thickening, Filtering, CCD, Water Treatment & Tailings Disposal

Dewatering: Thickening, Filtering, CCD, Water Treatment & Tailings Disposal 2017-03-23T09:42:05+00:00
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​Re-pulping filter cake (14 replies and 1 comment)

Alan Carter
1 year ago
Alan Carter 1 year ago

Hi, I am looking at what's the best way to re-pulp the filter cake post a plate and frame filter press? Typically flter cakes are dropped into a bunker and taken away by front end loader or onto a conveyor for stockpiling or further processing but I need it to end up in an agitated tank as a slurry to enable further chemical traetment. The issues I'm trying to design around are the competent nature of the cakes, the batch wise production of the cake versus a continuous downstream process and limited head room and footprint.

I'm looking at Pug mill or screening options and want to know what experience other members have?

Bill Fraser
1 year ago
Bill Fraser 1 year ago

You could use a log washer, low head trommel scrubber or even attrition cells to repulp the cake.

JohnnyD
1 year ago
JohnnyD 1 year ago

In addition, I've seen people use monitors to wash the cake into a floor sump and then pump it to where it needs to go. I've seen mineral sands miners do this with fresh feed (admittedly a little easier than a finer filter cake) but also people treating gold tailings dumps. For specifics you may even find some info on OneMine about how some of the South African Gold Tails reclaim operations did this.

David Kano
1 year ago
David Kano 1 year ago

A question to better define your desired process:

  • Do you want to maintain a very high density/%solids slurry?
  • or are you using alot of liquid to re-pulp to a slurry?
  • What is the final desired %solids? and also what is the particle PSD or P80?
Victor Bergman
1 year ago
Victor Bergman 1 year ago

Yes and keep the pulp density up. Cake in water is like a dot of wasabi in a lot soy sauce. Impossible to mix. Add a few drops of soy first and you can use the viscosity to get it into a thin paste before diluting further.

Alan Carter
1 year ago
Alan Carter 1 year ago

I'm looking at log washers/pug mills/cake cutters at the moment. Trying to balance the batch production of cake with the size of the machine as I'm trying to avoid having a feed hopper due to the height issues. 

I thought about monitoring but I want it to be an automatic process so not sure how to make sure the monitors are always working efficiently. I am also repulping with a bleed of cyanide solution so some OHS issues with high pressure sprays. 

Yes, the next stage (detox) operates at 30% solids so we have some fluid to play with. P80 is 38 um. 

Hi Victor, good point on not dropping the cake into a tank of fluid and expecting it too mix. So I need to bleed in the cake and solution to keep the density up.

Tony Verdeschi
1 year ago
Tony Verdeschi 1 year ago

It seems a bit odd that once the solid dewatered as filter cake say with 10 % moisture again has to be diluted. There must be some reason for it. However we , for our on going project repulp or make slurry the bulk solids with pulp density at about 30 % by conveying the cake / dry solids and feeding to agitated tank with water addition.

Let the cake be dropped into a repulping tank where you add any process liquor to the required extent and agitate it to make a slurry of the desired solids consistency. Then pump it to the subsequent stage of operation.

John Koenig
1 year ago
John Koenig 1 year ago

How often do you empty the plate and frame press? If once an hour the solution would be different than once a day. How much manpower can you assign to this task? 

On first blush, I would think a log washer with slow solution addition at bottom of tank until mix is flowing easily then dump to the next step with a flus that would bring the mix to the desired density.

Helena Russell
1 year ago
Helena Russell 1 year ago

The filtration section of the old gold plants dropped a filter cake (10 - 15% moisture) into what was known as a "puddler" ahead of pumping to a storage tank for tailings disposal. These operations had the advantage of wash water going onto the belt thereby adding a bit more moisture. The water addition was via level control in the puddler. 

The mixing units had usually had offset twin horizontal arms with vertical blades to create a macerating type action, also had a fair amount of power going in. p80 was generally around 75 micron.

Maya Rothman
1 year ago
Maya Rothman 1 year ago

Depends on the friable nature of the cakes, which is a function of the PSD and shape. Coarse stuff will generally fall apart and slurry easily while fine bricks take considerably more energy. Hence for some, dropping into a reslurry tank works fine while for others, a pug mill may be needed. Stringing cables under the filter press discharge can help break up the slabs.

Bill Fraser
1 year ago
Bill Fraser 1 year ago

To maintain high density and do it safely, the best option would be attrition scrubber type of agitator tanks, at least two in series with an overflow between them. Two tanks for residence time and the overflow will act as a classifier will keep your head low. Then just balance solution and cake feed to maintain density. The more the cake can be broken up before mixing the better, so a good drop past some cake breakers (cables strung under filter) onto a conveyor followed by a few transfer points will help. Difficult to say what kind of power densities you will need or residence time but 15kw/m3 is the norm and a little lab/pilot work should put you in the ball park.

Tony Verdeschi
1 year ago
Tony Verdeschi 1 year ago

We do this by the hundreds of thousands of tons a year and have the added complication of frozen filter cake in Minnesota. Almost all of the stored iron ore concentrate filter cake generated by pellet plant outages or production mismatches is repulped and filtered again to control moisture for balling.

There are several tricks to make this work.

  • Repulp into an agitator of some kind. This breaks up fhe clods of filter cake. The agitators can be a vertical agitator in a sump, a mixing vessel like a pug mill, log washer, or blunger, or even a ball mill sized just large enough to break up the cake without regrinding the particles.
  • If density control is necessary we recirculate slurry while continuing to add cake until the density is right. Then two knife gate valves at a T flip and send the slurry to where it is going, usually a slurry storage tank.
  • When slurry is being drawn off, new water is added to the slurrying device and repulping continues. When slurry density falls off, the valves flip back, the new water is shut off, and slurry is again recirculated. Just make sure that when flow stops the pipes drain either back to the repulping tank or on to their destination.
  • If there are large competent chunks of filter cake, like our frost chunks, we often include a mechanical breaker like a Stamler Feeder Breaker ahead of the repulper to pre break the chunks to a managable size.
Bill Fraser
1 year ago

​I like your comment.

Victor Bergman
1 year ago
Victor Bergman 1 year ago

Eirich (Germany) make a "D" series mixer for this type of duty. They have been used for re-pulping (dispersing) kaolin clay which is extremely sticky and hard-to-mix after filter pressing.

The D series machines are a horizontal type, not inclined like their other mixers (R series).

But, without details of the process, why de-water a slurry to then make it into a slurry again. Why not take the slurry prior to the presses and if too concentrated then dilute, if not concentrated enough then look at making it more concentrated. It's years since I have operated presses, used in the coal industry to dewater flotation tailings before disposal, and what we did was to gradually eliminate them from our plants.

JohnnyD
1 year ago
JohnnyD 1 year ago

It would help to specify dry slurry SG and P80 screen analysis for a better understanding of the challenges you need addressing. I operated one plant where the filter cake density was over 4.0 SG, the screen analysis was minus 20 micron and the cake was visibly solid but contained approximately 40% solids or more. This is a total different situation than mentioned earlier with 10 - 30% solids range.

Maya Rothman
1 year ago
Maya Rothman 1 year ago

I AGREE the cake can run along a sluice trough , pushed along with process liquor to a filter press cake tank, add more process liquor if required to the tank. You can pump as a slurry from the tank underflow to where ever you want and dewater is need be.

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