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Author Topic: Fine gold project or has anyone used wedge wire for screening?  (Read 6625 times)

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Offline bakergeol

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I am designing a 4"  land dredge which will incorporate secondary recovery for  my fines. Being from Colorado ultra fine gold is the norm here.   Very little of the bank run  microscopic gold  we are seeing on my small wave table is being seen in our sluice cons. Although a popandson sluice would do for a high banker with controlled feed and low water useage( 40gpm?), it is not something one would consider for a dredge with  a 175gpm water useage and 3 inch rocks tumbling down the box. I am not interested in building a triple or an over and under sluice as punch plate does a pretty poor job in classification and gold recovery in high water useage sluice boxes  http://ygsftp.gov.yk.ca/publications//tech/placerrecovery.pdf .

What I wanted to do was to run a grizzy(size?) and than a short Le Trap for coarse gold. Then incorporate 20 mesh? wedge wire screen(DMS) to capture all the water and mesh sizes below 40 mesh( 1/2 the size for wedge wire). Wedge wire is different than regular screens as they are mounted perpendicular to the water flow and openings are wedge shaped and supposedly do not clog up. The material would then be dewatered through a couple of small  hydrocyclones and run over my Utech table or a popandson sluice.

My question would be- How effective is wedge wire(DMS- other name sieve bend) for particle classification. Has anyone used this type of screen before? Do they clog up?  How long will they last? I have not priced them yet but I imagine big bucks for the screens.

Thanks
George




 

Offline GollyMrScience

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Re: Fine gold project or has anyone used wedge wire for screening?
« Reply #1 on: June 30, 2010, 01:35:00 PM »
Wedge wire can be used in a sieve bend configuration or like regular wire. Because the narrowest opening is at first contact and then the wedge shape opens out they offer accruate sizing and less clog potential for some applications.
When you turn a screen like that crossways to the flow in a sieve bend configuration it goes from being an exact size screen to an averaging screen and depending on the angle the average size particle likely to drop through can be controlled.
As the simplest approach a linear screen or grizzly at 45 degrees set crossways to flow would average particles that are half the diameter as the width of the opening.
Notice I said average. You get some that get close to the maximum size of the opening too and depending on several factors that can vary.
They are pretty good at resisting clogging or blinding as long as you don't overfeed them. Under certain overfeed situations not only will the screen blind out but the hold back on the screen will cause larger particles to be deflected through the screen and your average particle passing being half the width rule goes out the window.
Many sieve bend screens have a special curve to them that enhances their action but for the rough and ready application you are considering you could lkely get away with flat screen on steep angle. Heck even square opening screen could work at that steep an angle though blinding and clogging are a greater concern.
How you introduce the flow to the screen is as important as angle. For many applications standard slot wire screen will work though perhaps not as tight a spec.
If you plan on taking all minus 40 mesh and the cyclones are only for dewater the UTech will not be able to keep up.
Something you might consider as a super simple though less efficient perhaps system that could keep up is taking the minus 40 mesh and all of the water that goes with it as a sieve bend is excellent for grabbing the water too and running it through a properly sized and designed fine gold sluice. As long as your average gold isn't below 100 mesh you can make excellent recoveries with carefully controlled sluice technology -especially considering that a dredge has sluggy feed that can vary considerably which many more efficient systems really have trouble with. The cons would then work fine on the UTech.
One thing to check though is the recovery of the Le Trap. Given 1/2 inch minus to a highbanker the Le Traps do very well on gold considered to be pretty fine on average. 50 to 100 mesh does pretty good. A dredge though could be problematic. Varying waterflow and feed can be hard on most recovery systems.
What the heck - lets just keep mixin' stuff together till it blows up or smells REALLY bad!

Offline bakergeol

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Re: Fine gold project or has anyone used wedge wire for screening?
« Reply #2 on: June 30, 2010, 03:37:18 PM »
Thanks GollyMrScience for your input.

You have given me some points to consider. Over feeding the screen is one, Le Trap may not handle the rigorous useage- perhaps regular steel hungarian riffle would be best . The most interesting point is introducing the flow to the wedge wire screen by the use of slotted screens.

What size of slotted screen would you recommend?

Unfortunately, this has to be a ultra fine gold sluice as a high percentage of the gold is actually below 100 mesh. Not surprising as  a lot of this ultra fine gold has already been through a sluice box before.


Again, thanks for your input
George

Offline Chuxgold

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Re: Fine gold project or has anyone used wedge wire for screening?
« Reply #3 on: June 30, 2010, 09:31:42 PM »
I have been doing a post on my fine gold panning method.  It is the only way I have found to work below 400 mesh gold free.
So many do not even know its there.
Even with the right tools you still must be able to work a pan. To even glimpse it from a slues.
Glad to see some one not trying to push a mountain thru there’s. A slow steady feed will get twice the gold as pushing to much material at ones.
Even when catching nuggets. In the pursuit of catching the coarser by pumping ground thru the box. All the fine gold is lost. And only the gold with significant specific weight will lodge.
Here in Washington we have a 1' by 3' foot restriction on slues size. That limits the volume you can run efficiently. And is a lot slower than most think it should be. If wanting the finer gold to stick
Even if you do slow down you still need to be able to pan your cons out. And if you do not have a table or rocker to assist you.
As Mr. science mentions about the braking in half the demotions of your material first. If used to panning coarser black sands mixed in with the finer. As it is simple and gets most all the coarser gold. But flushes most of the fines in doing so.
It works the same on down in varying sizes. It must be broke in half. Even if trying for below 800 mesh cons. Witch you have to have to gathered with a rocker or other specific gravity devise to have a significant amount  of it in your cons from a large volume of material.
The gold’s there in those sizes. And gets even much smaller than that. But no screens to break it down below 40 mesh that can work a volume of material that mite count for somthing
Chuck.
Give self, to gain wisdom,

Offline bakergeol

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Re: Fine gold project or has anyone used wedge wire for screening?
« Reply #4 on: July 01, 2010, 07:26:35 AM »
Thanks for your reply Chuck

I agree with you than there is a lot of ultra fines out there. The question is will it be profitable in the long haul for a ultra fine gold sluice in the first place?

An interesting question is indeed the amount of volume that is going to be run over my sluice. In contract to regular 4 "  water dredges I will be using it only on the bank with a Hydroforce 4" nozzle. The sands and gravels I am aiming at are usually well compacted with 3 and 4" cobbles well represented.- a pickaxe is required for highbanking. Considering the amount of time required to loosen or flush the gravels with the Hydroforce nozzle before dredging out the material, the volume I am expecting is no way near what a 4" stream dredge will do. I am still hoping to use my Utech table as it supposedly can run 700 lbs an hour. My Utech table will be used just as a black sand catcher only.  I hope to use the table as a sampling tool. Put a pan under the cons outlet, dredge some material and check the cons for gold content. The black sands will be taken back and run on my small wave table for better concentration.

Indeed the problem with secondary fine gold recovery is effective classification and effective secondary fine gold recovery. Perhaps for folks who live in coarse gold country, it is best that one believes that our  own dredge does an excellent job in fine gold recovery and leave it at that.

To be honest I do not feel a sluice box will ever be a good  secondary ultra fine gold recovery device for a dredge. Just a matter of high water useage over the ultra fines. Less water useage the better. I like the idea of using just 8gpm(Utech table) to process my -40 mesh material instead of 40gpm or 100gpm.

The solution I felt was simply to dewater the material after effective classification and then run it on a good fine gold recovery device. De watering dredge water I feel is more of a cost issue than a technology issue. One could install  four 4" classifying hydrocyclones to dewater 200gpm but the cost of those hydrocyclones would be outrageous. A hydrocyclone is a simple cone but put a "mining" or "oil industry label in front of it and the cost skyrockets. I had to look under agriculture dewatering hydrocyclones to find some with a reasonable price.
There is also the issue of how effective a classifying hydrocyclone would be in capturing all of the ultra fine gold.  Fine material collected in catch tubs from  the hydrocyclone overflow would have to looked at for any fine gold loss.

Although I am 60 years  of age, I am still looking and learning.

George





Offline GollyMrScience

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Re: Fine gold project or has anyone used wedge wire for screening?
« Reply #5 on: July 01, 2010, 08:23:40 AM »
As Chuck suggests George there is a real need to determine how much effort should be put in what part of the recovery process.
The secondary pumping of the fines to the cyclones may be a pain -to work best you need to maintian proper slurry ratio and pressures.
If I read correctly you are considering this as more a dredge fed highbanker.
In that case you might consider a centrifuge. As a jack of all trades recovery system they are pretty darn good.
A well run centrifuge can handle a lot of material or a little material and do fine. It can get good recovery down to 400 mesh and excellent recovery in the minus 100 plus 250. To get that you can often get away with only screening on an 8 to 20 mesh screen.
The centrifuge required would not be big and a non water injected would be a good option.
Since they create their own gravity they are not too fussy about being level and their gyroscope effect means they don't shake stuff up or need to be anchored.
Heck your screening system could even be a shrt trommel. Don't need a lot of length in a suction dredge trommel as the dredge has broken stuff up well and there is plenty of water to get stuff washed well before it even hits the screen.
I have used dredge fed centrifuges in both dry land and floating platforms with every satisfaction except cost.  <-laugh->
The non water injected centrifuge that Will was working on would be the ticket.
What the heck - lets just keep mixin' stuff together till it blows up or smells REALLY bad!

Offline bakergeol

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Re: Fine gold project or has anyone used wedge wire for screening?
« Reply #6 on: July 01, 2010, 10:53:08 AM »
Yes GollyMcScience Will's centrifuge looks pretty good and yes I am looking at building a dredge/highbanker without the sluicebox as the main fine gold recovery system.


I have considered centrifuges in the past(actually have built a couple of Butler centrifuges). However, the following is the problems I see with these.
1. Cost - mega bucks for these
2, Portability- I am a one man band- occasionally with my partner. I want a light weight unit that I  can transport around easily.
3   Dewatering? How  much water can your centrifuge handle? If your centrifuge can't handle large volumes of    water, I suppose one could have a sump for fines retention. After classification, the fines from the sump  would be  pumped to the centrifuge. But How much fine gold will be washed away out of the sump with  175gpm dredge water. Is there a sump out there that doesn't have considerable fines loss with high water useage? A dewatering mechanism would be needed if you wanted to process all the water.

 A question would be- Is there a dewatering system out there that is effective, inexpensive(well ?) and  lightweight besides hydrocyclones? They may be a pain to operate (I own 2) but what else is there?

4. Effectiveness of fine gold capture. A lot of people may say these are very effective for fine gold but you are going to have to show me. I am skeptical about low G force centrifuges- centrifuges that operate at low G force and do not have a mechanism to prevent packing. I remember one project I was on that we  examined the tailing of a popular low G force bowl. We were pretty shocked at the fine gold loss we were seeing. Heard enough horror stories about these bowls to make me wary. I always figured that high G force centrifuges were better because at high Gs gold's natural poor shape does not play a negative effect on it's recovery. Probably the main reason why low G force concentrating hydrocyclones have such poor fine gold recovery.

I was very interested in Will's thread about his centrifuge and await further word on his work. Now if he can just keep it lightweight and affordable I would love to run some of my material over one.

George

Offline Chuxgold

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Re: Fine gold project or has anyone used wedge wire for screening?
« Reply #7 on: July 01, 2010, 11:52:16 PM »
You should try your hand at building a rocker box.
Sounds like you have plenty of the right skills.
There is no classification beyond what the design of the apron can handle.
Mine have a half inch drop from the top of the pool. So only one half inch material and smaller will displace in it. Regardless of varying sizes.
I would not say its going to beat the production of you other equipment in a end value. but will show what a bigger or automated version can do.
I would say buy one of mine. But I have as yet to find a way to guarantee something that first requires there is gold. and secondly that the one buying can cope with working fines in a pan. Patients is the big obsical.
I can work around one but first there has to be gold.
But hew really knows if there is a amount worth working if you do not at least try to look by making your own.
I will be trying again! But this time I am going for the full wash plant. That is aimed at already existing gold.
First one is the last one and there is nothing in-between now. I can't make a better one. And I have reached the end of the science. Just trying to apply all what I know now into one single sale.
Tried the other end first. But was against to much. So much so, that it is a bigger story. Why are so many against the idea that fine gold has a value? Was a time when it was already proven. What happened? I should not have had to try so hard. Bad enough to design from only glimpses of other peoples ideas. Compiling a working concept that I must have some idea what I was doing by then? I did not want thousands of dollars then. But I will now. Because what I will offering is a guaranteed paying job that no price could be put on that would be realistic to what it can do even in a month.
I am sorry about how I must approach the subject. But I can't just pass it by. Ground like you describe. If any one has similar.  Its a once a day with a good rocker box. And ones you realize this. Building one is nothing. Even if its to study the viability of buying mine to work even more, or catch more below 400 mesh.
A 400 mesh peace. Is a nugget to my design. I am more worried about 800 and smaller now. And am finding ways to ease even that from my mind. 
In the end. Witch I hope is not the end of me too. Because I will have it all. In all ways. Ones I prove I have broke the ceiling on how fine gold can be concentrated out of one specifically classified size. And unconcentrated material.
It finds and collects the fine gold by collecting and concentrating the sands that a slues can't even hold. First. Second, is it can separate it. Third would have to be. It looses no gold do to displacement. Well placer anyways. I am working on the Au in the black sand.
And only lack money to search for application of my ideas on what I mite do different to get that final edge of this idea of a shovel right.
As The shovel dug the old timers into the old gold rushes. Being the first to hit the loads.
I am dead certain there is another one in what they missed. Mite not be able to ever find more than a few ounces a day. But that is what you will find tomorrow and the next.
Its not a road to riches. Just a job that you can't be fired from. And there is as guaranteed pay check, as long as you are willing to do the work.
I have come to believe it is all opposites. Nuggets to flower. Were one only has guesses and doubts. Based on odds and chance. To having certainty and confidence that it is were you know it is, and it is going to be there when ever you want some of it. Just one already has a way to be got. If you can find it. The other is working what everyone knows is there. but can't catch it. I'm working on the other. Every day. Until it kills me or drives me completely nuts knowing what I know about it.
Chuck.
Give self, to gain wisdom,

 


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