Crushing, Screening & Conveying

Crushing, Screening & Conveying2017-04-04T06:57:13-04:00
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Trommel Screen and Vibrating screen (5 replies and 3 comments)

HotelBravo
11 months ago
HotelBravo 11 months ago

Hello
I am helping a alluvial mine in South America with their transformation to mercury free mining. They have an input of 208t/h of relatively fine particles (-0.25 inch particles make 55% of the total initial weight, -10 Mesh [2mm] particles make 30% of the total initial weight) and the wanted gold particles are smaller than Mesh 35 (0.5mm). How to I concentrate down effectively to the size of the gold particles as cheap as possible and without sluiceboxes (because I want to use them afterwards)? My idea would be a trommel screen followed by vibrating screen with screen sizes of Mesh 10 and Mesh 35 respectively. I am wondering now, if this is practically feasible to create a small trommel screen and vibrating screen having a such a high throughput (208t/h)? What are your experiences, suggetions, critics?
Thank you very much for your help!

 

Todd H
11 months ago
Todd H 11 months ago

Concentrating gold via screening will only be effective in reducing the mass of the total feed as you have no gravity differential step.  At the rate you suggest you are not talking about a small trommel further, as the particle size gets smaller the required area for the trommel and the screen gets larger. Screening the 12 mm material with a trommel will be possible with significant wash water and you can screen the other sizes on a vibrating screen again with significant wash water. Then you will have a size separation but a lot of water to deal with.

Do you have gold assays by size fraction?  Why don't you want to use a gravity method like a sluice or an Icon machine (centrifugal)?  You can build sluices fairly easily even for this size of operation.

Regards

 

Todd Harvey - Global Resource Engineering http://www.global-resource-eng.com

HotelBravo
11 months ago

Thank you very much for your answer!
For the moment they are using only sluices and amalgamation, but at a rather poor efficiency (I estimate at around 50-70% only for the sluices). The mine wants to increase the recovery rate but do not know how and I, environmental engineer without any mining experience, should help them out with technical inputs.
One way would be to improve the sluices, but I doubt the achievement of a significant recovery rate increase without knowing precise information about the raw material (specific gravity, granulometry, etc.). Or do you know a tool/manual to design a highly efficient sluicebox without many precise information necessary?
Now I know from an older scientific study that, approx. 1% by weight of the gold particles are larger than 1mm (mesh 18) and approx. 84% by weight are smaller than 0.3 mm (mesh 50). Hence, as you said, I want to reduce a fair amount of the mass of the total feed in order to have the smallest weight share of the initial input material as possible for the concentration step. In the concentration step I want to convince the local miners to change gradually from sluicebox to iCONS 350. “Gradually”, because they are sceptic towards new technologies and because they probably cannot afford to buy directly 3 or 4 concentrators (for approximately 40-50 t/h) in one step. After the centrifugal concentrators I suggest a shaking table and then directly smelting (so, no mercury).
To come back to your question, I have planned gravity methods, but I want to reduce primarily the total feed to the “interesting” particles sizes, reducing the number of new necessary pieces with gravity methods (concentrator and shaking tables). **I hope my expressions are understandable and you get roughly my intentions** So I thought of trommel screens or vibrating screens to do this job but down to the intended sizes is rather difficult (or even impossible with wet screens due to adsorbance) or expensive, as I have read on the internet and as you indicated.
Another solution might be jigs, but this is a even more unknown technology (and difficult to maintain) for the miners and therefore questionable..
What would you suggest and why?

Thank you very much for your or any help!

Regards

Gene Cheeseman
11 months ago

Hello HB,

You are definitely on the right track with your plan to screen off the coarse barren material and treat the fine fractions with centrifugal concentrators->table->smelt.

With the fine nature of your gold a centrifuge will likely be far more effective than a sluice.

Screening at 0.5" would not be a problem using vibratory screens or a trommel. Screening at 10M (2 mm) would be best achieved with a vibrating screen and as others have mentioned, lots of water. Screening at 35M (0.5 mm) is possible but probably not feasible in this application.

Treating the -10M with the i350 concentrators would be the best process method. The -0.5" / +2 mm fraction would be ideal to feed to your sluice to recover any coarser gold.

If your material has a high clay content a scrubber prior to feeding the material to your vibrating screen would be appropriate. As you are already interested in the iCON concentrator I recommend you look at the iCON website to check out the modular plants.

https://www.911metallurgist.com/equipment/gold-washplant/

The IGR3000 includes the process described above.

jaimecarmonaa@gmail.com
11 months ago

Hi.

It is very important to know if the matrix in which the fraction of gold is embedded is clayey or not; also to know if the clay is plastic or not.

In principle the trommels were designed to process alluvial material with very low clay content (Alaska case), if the presence of these occurs, large amounts of water must be used to make the washing efficient and it is clear that the subsequent handling of This is an additional problem to deal with, if this were the case, the design of the trommen should have a particular configuration in the scrubber section to achieve a good wash.

Now, it is very important to know what will be the gravimetric concentration method that will be used for the recovery of the gold fraction.

If you need advice, do not hesitate to contact me, I am in Colombia and I have extensive experience in alluvial operations.

You can contact me at my email: jaimecarmonaa@gmail.com or my mobile phone: (+57) 3106220353

Regards

HotelBravo
11 months ago
HotelBravo 11 months ago

Hello Everybody,

Thank you for all your comments and advices. I will follow probably your suggestion, Gene Cheeseman, with one vibratory screen at 2mm apertures and feed as much as possible of the underflow to the concentrators (6 Icons350 are probably a bit too expensive in one step for the mine).

is 5% clay a high content or not? Anyway, a scrubber or a trommel screen will probably added in a later step.

Thanks again for your help, I really appreciated it!

Regards

Gene Cheeseman
11 months ago

5% clay isn't high but eventually getting a scrubber or trommel would likely improve your screening efficiency.

Here are a few videos of a screen, sluice, iCON setup as well as an IGR3000 plant.

https://www.youtube.com/watch?v=USBEqiqZIY4

https://www.youtube.com/watch?v=64_79DAkW_o

Best of luck

Masterkap
11 months ago
Masterkap 11 months ago

Hello guys.,

Personally, I think a trommel is the better solution for this kind of prospection.

I like to use those moss mats to guarantee more and bigger nuggets. It's necessary although to use a vinyl mat at least 15 mm thick, solid back, right color (generally royal blue), and check how you like the thickness also on the fibers. I recommend the mats from Masterkap because they manufacture as I want.

What do you guys think about that solution?

 

Mike R
7 months ago
Mike R 7 months ago

You may have solved these problems by now. If not then....

You have a screening and sizing problem, but you did not say what was being done now for those issues, and how. Gradual financial changes as you suggested, depends upon where your start from.  For example how do they get rid of the 45% +0.25" material? What size range were they feeding to what size sluices? With how much water flow?  Any sluice has to be designed for certain quantity and size of feed and matched with the water flow. There are modern mats that are more efficient for fines than just fibrous type mats. Test the end of the sluice: if your losing values, change the system. So more info would help the starting position to recommend certain changes.

One idea might be to see how much loss of Au would occur if dry screening were used to get to the ~1/2" or 1/4" size. If you are digging wet sand then obviously this does not apply.  I work with a lot of dry placer sand where all my gold is -1/8" and so this is an easy and efficient task IF the dig is not too deep each day where it has not had time to dry out, even in our desert SW area of the USA. My sand and gravel bars do not have much clay content either and thus size down easily and efficiently. So I typically can run sized -1/4" through a drywasher(s).

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