Gold Prospecting Forums - General => Tech Talk => Topic started by: GollyMrScience on March 22, 2009, 03:01:39 PM

Title: Water Column Separators
Post by: GollyMrScience on March 22, 2009, 03:01:39 PM
This item is a very simple separator that has real potential if used properly.
I can see that I am gonna have to get some pics to help but I hope this written description will work to start.

Chick could you post the pic of your unit? I know that will help a lot!

In practice these would be better termed a super concentrator as it can be real hard to get clean gold.
Also called an Elutriation Column.

The principle is that a gently rising current of water is introduced into the bottom of a vertical clear tube.
The rising water is controlled so that the light material rises to the top and stays in suspension while the heavies sink to the bottom.

By carefully controlling the flow an operator can keep everything in suspension and the material sorts itself by specific gravity.

The lower heavies are barely liquid while the lighter material forms successively fluffier layers as you go higher in the column.

If you run the unit strong enough to blow the lightest sand over the top the heavies will fluff up more but you run the risk of blowing fine flaky gold out.

There are several commercial units that have been made. The Osterberg "Quick Gold" is well known by people familiar with the principle.

There is a fine screen at the bottom of the column and water is introduced through a valved inlet on the side at the bottom.

This screen helps break up the water flow and keeps material from sinking too low in the flow.

Since this unit relies on a finely tuned water flow the operator can help by doing a few things.

First and foremost is careful classification.

The closer the grains are to the same size the easier it is to adjust the flow. A wide range of sizes will work against you so screening on several narrow margin screens is important.

To really control flow the operator needs to have a dependable source of pressure and volume.
If operating from house tap the flow and pressure are pretty consistent but from a pump the fluctuating volumes and pressures can goo things up.

Even on house flow you may find that you cannot turn the flow rate down enough as the house pressure never changes. If your local pressure is 30 PSI you may find that you cannot keep a stable bed.

Ideally it would be great if you could control both pressure and flow.

After fighting with those variables in a camp situation I finally decided to use a stand pipe. Very easy to construct a stand pipe is another vertical column set beside the Water Column.  Imagine a four inch piece of PVC pipe set on its end vertical like the water column. Start with one about three feet long.  It has a valved outlet at the bottom that is linked to the water column and at intervals up the four inch pipe (mine was every two inches) I had another valve.
The stand pipe will operate like a bypass pressure regulator.

Water is pumped into the stand pipe from the top and by opening and closing valves you control how high the column of water gets in the stand pipe. When the water reaches the desired level and therefore pressure, it cannot get any higher as the open valve lets it out to flow back to your reservoir. As long as you feed it enough water to overflow at the bypass  everything will stay constant and WAY easier to work with.

Your stand pipe will control pressure and the valve on the standpipe and the water column will control water volume.

For most of the work I have done I found that filling the stand pipe to about ¼ to ½ higher than the height of my water column separator gave me optimum pressure to lift material into suspension without blowing holes in the material in suspension. Water under pressure will seek the easiest path and if there is a thin part in the stack of suspended material and not a good, even column of rising water with little over pressure, the water will blow through the thin spot and the material will sort of collapse – losing its nice stratified sorting.

This gets particularly noticeable the more heavies you get in the column. They begin to create a layer of  resistance that makes it harder and harder to get good even flow through without it turning into a seething mass of little geysers as the water pops through that layer in different places.

For best results water should be re-circulated and a wetting agent added to the water especially if working with really fine gold.

You should also be sure that the material you are running is pre-wetted to help eliminate the possibility of floating gold off the top.

Remember you are adding the material to the water level on the top of the column.  The water is constantly flowing over the edge of the column and dry material will have very little time to be wetted before it gets to the edge. For real security you can put a ring of plastic in the centre of the column such that the top of the ring sticks up above the water and its bottom edge sticks down below the surface of the water. Add material though that ring. That way no material can ever get out of the column on the surface tension of the water. It HAS to go under the water.

Add material slowly and let the system establish the stratification before you add more material.

Some people run their unit strong enough to lift light sand over the edge and out. I prefer to run it so that only the dirty water goes over cleaning the material so I can see better but not rejecting any real sand over the side.

The water is strong enough to just barely lift the heaviest material and it will give major fluff to the lighter sand.

What you will see is that there will be a very dark band of material in the lowest part of the column and then a thicker band of dark brown over that and then a very thick layer of light coloured material from the top of the darker brown to the top of the column getting lighter and lighter the higher in the column you go.
After awhile you will notice that material has built up enough to start interfering with the action.

Let the unit run for a few minutes without adding anything to let everything in the column get sorted as best as it ever will.

At that point you keep things running and carefully suck the upper layers out of the unit.

Careful here, as the amount of water and material being sucked out should be the same volume as being added.

You don’t want to get ahead of the water being added.

Once you have sucked out as much upper level light weight material out as you dare, you can pour the unit out into a tub to catch the super concentrate. The tub should be big enough that the dump of water and material does not overflow the tub. You can leave the unit running and wash the rest of the material out – controlling the water with the valve.

Save the stuff you suck out to check for gold loses in case you got a little carried away.

While people use these units to clean up black sands from placer work they are often frustrated because they can’t seem to get any real progress towards clean gold. Often they are already at very heavy black sand placer cons and it is difficult to get to a clean gold split or to even get any meaningful  upgrading.

As I mentioned these units are perhaps better called super concentrators as they rarely can be used to produce a clean gold product.

Nevertheless they are simple to run and the average person can build a workable unit easy enough.

Well this post is getting long. I will add more later.
Time for Chick’s two cents.
Title: Re: Water Column Separators
Post by: ClickTheYellowChick on March 22, 2009, 04:46:49 PM
Again, a very good job, Mr. Golly.

Here's the photo you asked for.  That will be 1 cent, please.   <-laugh->

Title: Re: Water Column Separators
Post by: GollyMrScience on March 22, 2009, 06:23:05 PM
Garnet can be a real pain sometimes. It is very disturbing to see large flakes of gold "floating" on a layer of garnet in a pan. wheel or table like a rock star crowd surfing.
You know the gold is heavier it SHOULD be on the bottom - under the garnet, but sometimes garnet sets up a bed that resists that to the point that gold is obviously getting away. Garnet can be worse than magnetite in this regard.
Title: Re: Water Column Separators
Post by: Woodspirit on March 23, 2009, 05:20:16 AM
Excellent description and advise, MrScience. I tip my hat.

In operating your "Quick Gold" are you using water supplied from your house tap?
Do you know the average water pressure/flow this unit takes for cons with black sand vs garnet material.
In certain locations of the Eastern US we have heavy blond sands as well. This blond sand can really be a pain to separate.

I love this forum!!!!

Title: Re: Water Column Separators
Post by: GollyMrScience on March 23, 2009, 08:41:28 AM
Woodspirit - if your blond sands are heavy then you may be dealing with something like zircon.
Zircon is very heavy and looks like quartz sand in your pan but just will not pan out.
It will drive ya nuts!
It usually isn't an issue till you start dealing with cons. Panning right to black sand in the field and then back panning and snuffing up the gold will rarely give you any hint of zircon.
When you get to cons though the zircon percentage is upped to the point that it becomes a serious pain.
With a specific gravity of 4.6 or so it is heavier than garnet and for that matter much of your black sand.
It is refractory and can be just icky as heck if you try to do a melt with it in the gold con.
Take a look at the blond sands under magnification and see if the crystals look like little quartz crystals with many of them having points at both ends. Often shorter and stubbier than regular quartz crytals and under magnification look brownish to dark brown though some can be pretty clear. Its weight (Specific Gravity) is the biggest hint though.
If you backwash some con and then feather the pan to see the gold line you will see this brownish trail liping along between the blacksand/garnet and the gold.
In western Canada there is a lot of zircon and one interesting thing is that it is very flourescent - it will glow a beautiful gold yellow under black light.
Very pretty but a pain nevertheless.
It would be interesting to check out Chicks anti garnet system to see if you can get a cleaner split.
Title: Re: Water Column Separators
Post by: Greg in BC on March 23, 2009, 09:47:01 AM
 [-1st-] Amazing and fantastically clear information.  Thank you very much Mr Science and Chick for sharing.

I like the idea of a stand pipe to help regulate flow and pressure - great idea and description.

Any thoughts on where to get large clear plastic pipe for the tower portion?

Chick, I think I have seen you mention elsewhere that you use a little suction device to pull off the heavies from below the lights - is that correct?  Do you then dump of the lights or do you keep running with the lights stacked in the tube?

Awesome thread - thanks for sharing.
Greg in BC
Title: Re: Water Column Separators
Post by: GollyMrScience on March 23, 2009, 10:10:25 AM
When I was running this unit in my lab I used a tap venturi device.
A simple plastic tube that was screwed onto a kitchen tap.
When you turn on the tap it creates a vacuum like a suction dredge does through venturi action.
I used this device to create a vacuum in a standard flask with a two hole rubber stopper in it.
So what I had was the venturi vacuum device on the tap with water running through it and a port on the side of that tube.
Off the port a rubber hose to one hole of the rubber stopper.
The stopper stuck in the flask and another tube coming out of the second hole that was my vacuum inlet.
By creating vacuum in the flask I could suck up material from the column and into the flask.
Worked slick.
The suck was immediate and was not hampered by small chunks as long as my tubes were bigger than the biggest stuff to be vacuumed and by using a pinch valve on the inlet ruber tube I could turn the suck on and off at will.
The original purpose of the venturi tube was to create vacuum as an alternative to more expensive and powerful vacuum pumps for lab filtration.

The folks at Action Mining have a slick arrangement using a baby wet dry vac to pull cons off their vibrating table.

What are you using in your system Chick?

As a complete divergence for a sec does anyone else think the word "vacuum" is one of the weirdest works we got?  <-thinking->
Title: Re: Water Column Separators
Post by: GoldFever on March 27, 2009, 04:22:05 PM
Interesting, and so simple.

Is this the same type of idea as the gold rocket on the Rotapan site?  but without the bells and whistles? (
Title: Re: Water Column Separators
Post by: ClickTheYellowChick on March 27, 2009, 05:30:40 PM
Excellent description and advise, MrScience. I tip my hat.

In operating your "Quick Gold" are you using water supplied from your house tap?

Do you know the average water pressure/flow this unit takes for cons with black sand vs garnet material.
RESPONSE:  No, sorry, I don't...I just tweak the velocity with an inline ball valve until I see it working right.

Title: Re: Water Column Separators
Post by: ClickTheYellowChick on March 27, 2009, 05:40:20 PM
Chick, I think I have seen you mention elsewhere that you use a little suction device to pull off the heavies from below the lights - is that correct?

Title: Re: Water Column Separators
Post by: ClickTheYellowChick on March 27, 2009, 05:50:44 PM
Interesting, and so simple.

Is this the same type of idea as the gold rocket on the Rotapan site?  but without the bells and whistles? (

Well, I swan.  I've been looking at that contraption for over 2 years now, and wondered what the heck it was. 

It wasn't until tonight when I watched the "new video prior to shipping to Indonesia" on that rocket URL you provided that I heard the word, elutriation, and understood what I was looking at.

Can't say a whole bunch for the pulsating water sourcing in that upper bowl as demonstrated in the video'd functionality test.  But maybe that was just a camera jiggle.  However, I'd swear I HEARD pulsating water in that drinking fountain looking upper bowl.

Thanks for bringing that up, GoldFever.  I sure like my under a $100 unit better than his $2500 priced unit...and in Aussie $$ no less. :o  'Course, I don't claim a 1/2 ton per day throughput either. [email protected]*

Thanks for that URL and the opportunity to learn about that "rotapan rocket" device.  I like the Rota-Pan unit, and have one.
Title: Re: Water Column Separators
Post by: Greg in BC on April 01, 2009, 12:39:32 AM

 Do you then dump of the lights or do you keep running with the lights stacked in the tube?
RESPONSE:  Well, since I'm a curious creature, I can't stand not checking between batches.  <-yahoo_> Doesn't take much gold to make me feel like queen of the anthill, so, I usually dump in my awaiting goldpan,
and dump in the next batch in a 1/3 to 1/2 cup increment. 

Megan, am I reading this wrong - does your unit hold 1/3 to 1/2 cup of material in total at a time or is that just the most efficient amount you add until it is full? In my mind I had pictured it holding something like 1/2 gallon of material in each batch.
Title: Re: Water Column Separators
Post by: GollyMrScience on April 01, 2009, 10:46:28 AM
I think mine holds about 6 cups by volume but it isn't the volume it holds its the gold it keeps. As a displacement system you can keep adding material until the system starts to have problems with keeping gold. As with any displacement system - including a sluice the system will hold the same volume of material whether you run it for five minutes or five hours - the concentration ratio just gets higher and higher. More gold in the same volume. As with any displacement system however there will be a point where the system can't deal with the build up of heavies and at that point the system must be cleaned out in some way or another. With this elutriation column you can suck out the cons from the bottom periodically and not have to shut it down or you can suck the obvious light weight material off the top and then dump out the cons - if you do that then the light weight material you sucked off the top will be the first stuff fed into the system at next startup to make sure you get all the gold. You can also just pour the entire thing into a container and deal with the lower concentration ratio.
Title: Re: Water Column Separators
Post by: Traveller on September 05, 2010, 06:18:10 PM
I joined this site recently after discovering there was discussion about e-towers here. I have long sought one but with no success.
There is another device that was marketed by Action Mining Services in the late 1980's and possibly early 1990's. It was called the Hydrostatic Vertical Table and was, I believe, a variation on the e-tower principle.  It was a rather flat device and consisted of a vertical column of water maybe 15 cm wide and 2-3 mm thick and 30 cm tall. It was all made of plastic and the face was clear, allowing the operator to see particles in the column. Water was regulated and introduced close to the bottom and black sand/ gold concentrate was metered through a slit at the top. The operator watched the black sand and gold particles falling through the flat column of water and gently opened the flow of water until the black sand particles stood still in suspension and the gold particles fell. Further opening of the valve moved the black sand particles up the column, past the infeed slit and to a waste portal. There was no chance of overloading the infeed water with gold as the gold particles dropped below the water infeed portal to a catch cup below it.
This device, according to Action Mining Services, had the distinction of being a gold separator and not a gold super concentrator.
Action Mining Services discontinued this unit many years ago in favor of a range of shaker tables they now market. I offered to purchase a set of plans from them for the HVT but had no success.
Does anyone recall this machine and possibly know where to purchase a used one? I would even attempt making one if someone had the specs.
Title: Re: Water Column Separators
Post by: GollyMrScience on September 05, 2010, 08:13:58 PM
I remember the Action Mining unit. Played with one for awhile but needed to classify on very narrow splits to get the action right.
The e-towers need careful classification as well to get optimum performance. Ultimately many people fond that a Miller type table will do a good enough job and not be as picky on classification - though it does need some. This is based on small scale operation. Larger scale heads for vibrating tables of some sort as an alternative.
Title: Re: Water Column Separators
Post by: Traveller on September 05, 2010, 11:10:12 PM
Hello MrScience
Thank you for responding. You are one of a handful of people who actually remember the Hydrostatic Vertical Table.
The HVT was definitely made for small scale operations. I can't recall the actual per hour throughput volume but I know it was not very much. However, this suited me just fine as the placer deposit I am working with is a very rich concentrate and not much material has to be processed. It is a beach placer deposited during storms. Very rich but also very VERY fine gold that just happens to be of a flaky nature as well. Hence, my interest in e-towers, as little else seems to work in gold this fine and quantities so small.
You mentioned a Miller table. I don't think I am familiar with this unit. Does it actually separate gold from black sand? Can you provide me with a link to a site for it?
Title: Re: Water Column Separators
Post by: GollyMrScience on September 06, 2010, 08:56:13 AM
Bob the e-towers are/were one of those ideas that just seemed so logical on paper but in application did not fare so well. Adding gold to the top of a column of lifting water creats float gold potential like crazy, the bed ends up puffing and channelling and gold keeps getting thrown to the upper layers and a host of other technical challenges. If it were just silica sand and gold life would be easier but the black sands in there add a variable that really gums things up.

In a related technolgy you might investigate inclined plate clairifiers. The application of the lamella design with the enhanced settling might get closer to merging the ideas of the e-tower and the hydrostatic table ideas. Something for the winter project lists.

If you do a search on this site there should piles of ideas on the miller table. There is also the commercially made version. For primary concentration they are way too slow. Meant to get the gold out of high grade cons.

How much material do you want to run at a time? Hand shovel? Just skimming the concentrate zones along the beach?
How portable do you need the equipment to be?
Do you have a rough idea on the size of the gold on average?
Title: Re: Water Column Separators
Post by: drpop on September 06, 2010, 09:54:23 PM
will vibrating or stirring help stop the puffing?

Would this start being a simple jig?

Title: Re: Water Column Separators
Post by: bakergeol on September 06, 2010, 10:15:09 PM
Excellent post GollyMrscience

I remember Lashley of ASAT (since passed away) did a lot of work on
on these separation towers back in the 80's.
 One problem  with getting a clean separation was that the water velocity was different
around the sides of the tube versus the center of the tube. You could have the correct
water velocity to remove the black sand in the center but not at the sides. Didn't he suggest
subdividing the column into many smaller columns to correct this or is my memory and old
age showing?
In addition,  the flatness factor  of gold versus the level of classification was always a problem.

Title: Re: Water Column Separators
Post by: nuggetsucker on September 06, 2010, 10:39:40 PM
I've built and used 3 E towers so far .As Golly says they're more of a super concentrater than clean gold getter.
In my mind they are'nt worth the effort even doing close screening on fine gold .I would use either a shaking table
as first choice and most expensive or a miller table as the simplist and least expensive useing the KISS principle.
Title: Re: Water Column Separators
Post by: GollyMrScience on September 07, 2010, 07:37:08 AM
Yes Walter (Lashley) and I spent may an hour on the phone discussing things like the e-towers.
There was some discussion about the tower within a tower idea. Using the drag of the water against the sides of the tower to advantage. In the end though it was becoming more work than it was worth.
The incline plate clarifier that I mentioned uses that drag to advantage but to get specific gravity seperation on gold and black sand it would be a pain to get it balanced.
As Nugget suggests a vibrating table on the high side and a Miller to the low side.
All a balancing act of economy over convienience all underpinned with the understanding that one should not spend an ounce of gold to get half an ounce.
For a primary concentrator on the high side would be centrifuges - low side sandard sluice. In the upper high side Jigs and on the upper low side a rocker like the type that Chuck is developing.
Title: Re: Water Column Separators
Post by: Traveller on September 07, 2010, 11:02:39 AM
Hello MrScience
Thank you again for your reply.
Your post led me to a site showing an Australian machine called the Reflux Classifier. It appears to be an e-tower with the addition of the lamella plates you mentioned. Although a very intriguing concept, it seems any production plans they have are for machines capable of many tonnes/ hour; hardly the portable small scale unit I had in mind. I did, however, e-mail the company regarding the possibility of them making a portable unit. I will share any reply I receive with this forum.
I should share a bit more info regarding the placer I am pursuing. As I stated earlier, it is a beach placer deposited by the violent Pacific storms we receive here in the winter months.  Often, lenses 25 cm. thick and 6 metres wide will be deposited for many miles of beach. The beach in question, though, is very remote and accessible only by quad, foot or horseback.
Back when Au assays only cost $10, I had two assays done on samples taken 150 metres apart on the beach. One came back with no Au values at all in it and the other came back at .32 oz. Au/ton. Given that this sample was taken from the upper side of the lens and was mostly magnetite (next down being hematite (purple) and the lower part of the lens was garnet (red)), it can be assumed that the specific gravity of that sample was well over 5. This would mean that, if there were .32 oz. Au/ton, a cubic metre of this material would have easily over 1.5 oz. Au. It would also, sadly, weigh in the neighbourhood of 5-6,000 kg. and would break the back of any animal or machine attempting to haul any sizeable amount of blacksand out over the rough beach.
For this reason, plus the facts that placer claims are not allowed on this material (any work is restricted to recreational mining involving only hand tools) and the difficulty of separating the very fine gold, there has been little success in recovering gold from this placer over the years. Mercury is frowned upon and is actually quite useless in a salt environment due to rapid oxidation of both the mercury and impurities in the gold.
Quite recently, I had a revelation which may change everything here. Remember how I said the one assay came back with no values for Au at all? I was puzzled by this as there was no physical difference between the two sample sites. I asked a few people here, who were supposedly in the know, what became of the gold and was told it had been washed out of the placer by the waves of the following tide. It seemed to make sense at the time but, the more research I did, the less sense it made. It was only after reading an article by a beach miner in Oregon that the real reason for no gold in the black sand became apparent. In his words, one had to "sneak up on a beach placer" as the wet environment, the high s.p. of gold and the flaky nature of beach gold all made it very easy for merely the vibration from one's footsteps to cause the gold to slip downwards below the lens of black sand.
This may seem like a bad thing but there is more to it. There is a layer of hardpan (marine clay) only a few feet below the surface of the beach. As these deposits seem to always occur on an eroding section of beach, the toe of the sand and gravel beach always has a flat section of clay protruding from the toe of the beach.
So, I think one could assume that each incoming wave during a storm may make any gold from previous waves sink down through black sand and gravel to the clay. Assuming there to be several thousand waves during a storm, this could equate to a sizeable deposit on the hardpan of fine gold from just one storm. Each winter, there are a few dozen of these storms. Also, by my calculations, in one area it has taken roughly twenty years for enough erosion to take place to transform what was the high tide mark into the toe of the beach. Therefore, multiply the few dozen storms by twenty and the possible value of the upper hardpan layer (under the toe of the beach) could be, quite literally, staggering. Who knows, a metre by metre by 3 mm thick section of hardpan may be loaded with gold.
Armed with this knowledge, I am now forced to await the arrival of a couple of good winter storms, likely in October, to re-deposit the black sand lenses which are mostly lost during the summer months. This will, of course, identify areas where it will be most likely that there are deposits on the hardpan. I will ride in on horseback and procure a sample for assaying.
One other thing I didn't mention about this placer. Everything in the black sand will pass through a 100 mesh screen and a goodly portion of it will pass through a 150 mesh screen. I don't know how this would affect the particle size of flakey gold but I would assume it would have to be even smaller.