Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction

Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction 2017-04-04T06:57:36+00:00
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Residual Gold after Filtration Leach (8 replies)

Rahil Khan
1 year ago
Rahil Khan 1 year ago

I am using a drum filter after high pressure refractory gold leach. My problem: the final product, filter cake, always contains high gold content even when the spray water is opened what could be the cause of this?

Paul Morrow
1 year ago
Paul Morrow 1 year ago

There could be a number of reasons. The following questions should be answered;

What is the vacuum reading on the filter?
Is the wash water running full across the filter and running down almost to the pulp in the filter boot?
Are there many, or any, cracks in the filter cake?
Is the cake relatively dry just before release?
Are the connections to the head of the filter good and not leaking?
Can you measure the amount of filtrate you are producing per filter?

You need to ensure there is plenty of wash over the filter and that the filter cake is not cracking. If you are getting any cracks then the filtering process is compromised.

Sturmbann
1 year ago
Sturmbann 1 year ago

Alternatively, if you have sulphides in the pressure leach, you could be forming ferric iron that will become some form of iron hydroxide or basic ferric sulphate (BFS) when you neutralize the pressure leach discharge. These hydroxides are notoriously difficult to settle or filter.

You might need to implement a "hot cure" process step where the pressure leach discharge is kept at a high temperature during neutralization. This will favor the precipitation of hematite rather than iron oxides.

Rahil Khan
1 year ago
Rahil Khan 1 year ago

The vacuum ranges from 67-68 kpa
The wash water is running full across the filter length
There are no cracks on the filter cake
No
No
Not necessarily because after the filter the cake is fed into a thermo-ventury drier, what are reported there are the actual tons of concentrate bag after drying. Measuring the filtrate after vacuum drier is not immediately possible because the conveyor used does not have weight-o-meter.

Will it help if I wash the filter cloth with hydrochloric acid?

Marshal Dienes
1 year ago
Marshal Dienes 1 year ago

The golden rule is points of reference:

What is the drum speed? have it as slow as possible but also watch out for a too thick cake which inhibits the cake rinse
What is the feed density of the slurry?- too thick a cake will result with a soluble entrainment that does not wash through- if the density is too high speed up slowly or dilute with water.
Cloth permeability is a big thing what is the cake moisture content on blow off? this needs to be less than about 18% vacuum should be about 23.5 inches at 5000ft above sea level - keep the pan as full as possible install a ball valve of the feed line to the pan
A good measure of the permeability is if you have spray flow meter and a filtrate flow meter, the difference will be the solution sucked in from the slurry and pan; this number should always be high. Acid wash the cloth regularly, a clogged or scaled cloth shows immediately as the duty drops off and dry lines occur on the canvass
What is the gold value in the spray water? most important- this has to be as little as possible- as mentioned, make sure the cloth / cake is totally covered with water, but don't flood the pan as it will dilute the density too low this will result in a thin cake and a thin cake is renowned to carry over excessive spray water if there is loss of vacuum
Filter sprays work a lot better than the OLD launder feed overflow

Sturmbann
1 year ago
Sturmbann 1 year ago

Also check your vacuum pump cooling water temperature. This needs to be well below 20C otherwise efficiency will drop off rapidly at higher temperatures.

David Kano
1 year ago
David Kano 1 year ago

In addition to comments I suggest that a filtering test should be done on the solids in order to more clarify the cake filterability, if the procedures mentioned above are not successful. My experiences with washing on drum filters are that they do not perform so well compared with the horizontal belt filters.

Rahil Khan
1 year ago
Rahil Khan 1 year ago

Thank you very much, through your expert advice I have discovered the following:

The vacuum pumps turned out to be a major issue this I discovered when looking at the filter cake moisture (22%), also the drum on the discharge side did not have cracks at all
Under normal operation the Knelson concentrator is always online for free gold, when this problem was picked up, gravity section was offline and a lot of gold reported to the concentrate which is leached under pressure to recover refractory gold, this lead to a very rich leach liquor that required the filter cake to be washed twice this lead to the following last point
Previously the section had two filter drums in series (1st cake was re-pulped and fed to the second filter drum), at present only one is online thus resulting in high gold reporting to the dried concentrate when gravity is offline.

Hauptsturm
1 year ago
Hauptsturm 1 year ago

Once before we had experts out to check every part of this process, we had filter drum header valve Teflon replaced and re-faced, filter drum pipes were replaced, we acid treated the filter cloths twice a week, but still had solution losses to filtered cake, particle size played a big role in the efficiency of filtration, two drum filters in series with re-pulping of the first filter cake reduced solution losses.


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