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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Flocculants Blinding Filter Cloth (14 replies)

Zander Barcalow
1 year ago
Zander Barcalow 1 year ago

What's the best way to break down flocculants that when in use, blinds up filter clothes? Heat or agitation or both? How do I stop filter cloth blinding by flocculant?

Alan Carter
1 year ago
Alan Carter 1 year ago

Try backing down on your floc dosing a bit. As I see it if your filter belts/cloths are getting blinded there is an overdose issue as in normal situations the floc does not blind the cloths.

I would think your thickener would give you some indication of what is happening with the floc.

Being a lead operator you would probably already thought of that.

Are you sure it is the floc doing the blinding and not fine particles blocking you cloths.

Zander Barcalow
1 year ago
Zander Barcalow 1 year ago

Thanks for your input it just might be the fines and the floc both causes the issues. Passing the information to the operator having the problems!

Gruppen
1 year ago
Gruppen 1 year ago

I agree with you about the flocculent overdosing. Are you adding the flocculent just for the thickening operation? Are you re-trimming the flocculent into the head tank for use as a filter production booster?

If you want to break it up, agitation is the way to go. It may be easier to add just a little bit of flocculent into the line coming from the distributor to re-form a floc. Typically less than 0.1 # /ton.

Alan Carter
1 year ago
Alan Carter 1 year ago

Just to reinforce what he has said, agitation will break the floc down by destroying the floc chains, but this is a huge waste of flocculent, as you would be reversing what the floc is supposed to do.

Floc works best if it is distributed into the flow stream into the thickener, preferably in more than one place in the flow stream. This will give it time to do its thing and be suitably mixed in the thickener. The thickener should tell you if you are overdosing by an increase in torque and a "Jelly belly" in the cone of the thickener.

Carmen Ibanz
1 year ago
Carmen Ibanz 1 year ago

Bad dissolution of flocculent can be one of the reasons behind cloth blinding. Flocculent is usually diluted in two stages, first to a concentration of 0.1-0.5% and then further to 10/20 times thinner solution to 0.01-0.05% concentrations. If one of the dilutions is inefficient, it can leave nods within the liquor.

First dissolution is pretty easy to test from the storage tank - look for the solution consistency while it's flowing from the mixing tap (like in a pancake batter, there should be no nods, it should flow continuously). Second dilution is rarely the issue if the first step is done correctly.

One more thing though - water quality for both flocculent dilutions and within the thickener:

•Usually hot or warm water is used for first dissolution of flocculent. Or an active spraying system at the same dissolution moment. If one of those is missing, there might be nods in the flocculent solution after first dissolution step.

•If pH of water is too high (pH more than 8) during second dissolution, it will start the flocculation action too early, which can also lead to the nods in the solution (quality easy to check from the flocculent pipe incoming into thickener feed well, not so easy if it comes directly to thickener feed pipe). By the way, flocculation action takes place primarily because flocculent is first dissolved into a pH neutral solution and then pH changes dramatically, usually to basic (pH more than 7), inside the thickener.

•If slurry pH is too high (over 11.5) and the mixing in the thickener feed well is inadequate, the flocculation action might be too quick, which again leads to nod formation, but now in the slurry. At the thickener bottom, there is usually some sort of emergency exit pipe, where you can test the viscosity of the slurry itself. It should form a nice cone.

Other issues which can lead to clogging of filter cloth include fine particles and clays in the process feed as mentioned before.

Sandeep Bisht
1 year ago
Sandeep Bisht 1 year ago

A strong oxidizing agent such as sodium hypochlorite will chemically break down flocculent solution.

Zander Barcalow
1 year ago
Zander Barcalow 1 year ago

Thanks to all. I will be passing the information to my coworker that's having the issues. And thanks for taking the time to post your knowledge.

Oberstorm
1 year ago
Oberstorm 1 year ago

Under-mixing can also be the root problem sometimes.

Assuming your flocculent is anionic (negatively charged), then a cationic coagulant or flocculent (normally polymer types) can neutralize the flocculent and reduce the viscosity and blinding issues associated with "high" residuals of flocculent.

However, the problems with floc and/or coag residuals in filter applications is often due to over-dosing (poor control) and/or under-mixing (which often results in the "need" for more chemical).; further, over-mixing can also result in the "need" for more floc.

What sort of filter is it?

Zander Barcalow
1 year ago
Zander Barcalow 1 year ago

The floc is added to a sump underground to settle out fines, the fines are then pumped into a filter feed tank along with Rougher tails from a thickener which also floc has been added. The slurry is filtered by a Disc Filter as a process to make paste for underground filling.

Sturmbann
1 year ago
Sturmbann 1 year ago

You need to provide "rough flocculation". Please if possible specify for filter feed tank:

•pH

•Solids/liquid ratio

•Flocculent dosage

•% of -5 mkm particles

•Operation temperature

•Type of ore

•Type of filter (ceramic or what else)

•What kind of reagents in rougher flotation?

Zander Barcalow
1 year ago
Zander Barcalow 1 year ago

There were no issues with the current flow and reagents until the floc was added to the sump area underground. Type of filer media is cloth over urethane sectors.

Maya Rothman
1 year ago
Maya Rothman 1 year ago

As mentioned by a few already, the mixing of flocculent and slurry needs to be looked at to make sure the flocculation mixing is correct good, check that the flocculent is well hydrated (2 minimum - 4hrs) and isn't hydrating further after dosing leading to an overdosing situation. Cut back that floc addition to a minimum that gives you the overflow you require. Get your flocculent supplier to do some tests on a floc that gives you both good clarity (that what you aim is) and good filtration without cloth blinding. And as last measures don’t be shy to give it a good shear using a shear loop and a centrifugal pump unless of course you need the flocculent for the filtration.

Oberstorm
1 year ago
Oberstorm 1 year ago

Some further, more basic questions include the following:

•Is the raw flocculent a liquid or powder? Or, is it perhaps supplied as a solution?

•Are you adding the flocculent as a solution (i.e. as a liquid or powder made down into a solution)?

•How are you making-down the raw flocculent into a solution (by hand? machinery?)

•What concentration are you making down the solution to (from raw)?

•What concentration are you dosing the solution as into the process?

Kumar Choudhry
1 year ago
Kumar Choudhry 1 year ago

Try washing them with hot water and the floc should dissolve. This has always worked for me when trying to remove floc build up.

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