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Guru

Join Date: Nov 2007
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How to separate clay, silt and sand from heavy clay subsoil?

01/25/2008 12:09 AM

I make cob which is clay sand and straw mixed together. It hardens into a fairly decent building material. My soil contains clay and sand which is good (the clay binds the sand particles together but also silt which has no binding qualitys. How can i separate out the clay and sand and leave the silt? Ideally, I want to separate all three, to have a clay pile, a sand pile and a silt pile. I presume I can do this in a water based separation process. Any suggestions?

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Guru

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#1

Re: How to separate clay, silt and sand from heavy clay subsoil?

01/25/2008 10:54 PM

Getting the sand separated is a simple washing job. Have no knowledgeable suggestion for the soil. Would try a small amount to see if there is enough difference in density for the clay to settle out and the soil wash away.

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#2
In reply to #1

Re: How to separate clay, silt and sand from heavy clay subsoil?

01/26/2008 1:06 AM

Yes, I plan to make a small pond. and simply wash a pile of the subsoil into the pond. and recirculate the water back around. I have also heard of all kinds of vertex devices that spin out the bigger particles. But perhaps they need lots of power? As far as I know, sand drops really quickly, in seconds (I know this for sure) silt drops next (perhaps in 4 or 5 minutes) and the clay can take a day or 3. I am happy if I can get the sand/silt separated from the clay. I am really happy if I can separate all 3 components! I do not care if the process is slow. I plan to power it with a solar panel and a 12 volt bilge pump, that pumps to a maximum of 6 ft high. If it takes all day to sort a wheelbarrow of subsoil, thats fine. I can have 3 sections to the pond, for the sand that settles first, for the silt and a final larger one for the clay. Years ago, I washed sand and powered the washing process with a pulser pump. At that time all I wanted was coarse masonry sand. This time i want it all! Brian

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Commentator

Join Date: Jul 2007
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#5
In reply to #2

Re: How to separate clay, silt and sand from heavy clay subsoil?

01/26/2008 12:18 PM

what you outline is exactly what I came here to suggest. You can shorten the time by carefully titrating the water in the mix so that it's just enough to suspend all three components, run it into a small collecting pond where you can stand with a shovel digging out the sand. The size of the subsequent ponds would be directly related to the length of time it takes for the desired suspension to settle out. Or you could just let the mix run down a long, long trough where the sand would settle out first then taper off into the silt, and finally the clay. You would need the water running constantly because stagnant water would settle out all three in the same location all along the ditch. So you need a ditch long enough that three or four days later, it is still running down at the very end of the ditch, now clear of all soil elements, where it can be recycled into the beginning of the process. You could do this with hundreds of parallel switchbacks. Doesn't sound practical to me.

Let's consider a pool with a screen suspended a bit above the bottom so that any turbulence toward the surface would be dampened close to the screen and virtually eliminated below the screen. This would allow you to run a conveyor belt through the bottom of the pool, slowly lifting its product out and depositing it in a pile for final drying. If you do a bit of experimentation, you should be able to come up with pretty accurate length of time it takes for all the sand, silt, and clay to settle out.

You could have the dirty water in the pond one for the hour or two it takes for the sand to settle out, run the conveyor to remove the sand, remix the water with a paddle or an outboard motor to return the silt and clay to even distribution, let it settle for the silt-settling period of time, run the conveyor to remove the silt. No need for a remix. let it sit for the clay-settling period of time. Run the conveyor. The water should be ready to be remixed with another load of dirt. I suppose there are chemicals that could be added to the water that would make it less conducive to supporting clay or other particulates.

You could dry the material completely using the sun and black sheets of plastic, constantly raking through it, breaking up clods, until it no longer clings together due to latent moisture (I think this is what you're breaking down with the water bath, anyway). Pull out a screen that is fine enough to let silt and clay through, but not sand. Work it with a board and rake. It won't get rid of all the silt and clay, but it is the clay you're interested in and sand contaminated with silt and clay won't ruin your project. You will now have a screened box full of small stones, lost jewelry, and sand. Dump it in your sand pile. Under this, have a screen roughly twice as fine, being worked with a board and a rake to further break down the mix to let the clay through but not the silt. You won't get rid of all the clay, but it doesn't matter if your silt is contaminated a little bit by clay.

The bottom wouldn't have a screen but a solid bottom where the clay would collect. You're going to have a lot of dust (mostly clay) so there will be losses, but the clay should be pretty nearly pure clay. I think you can see why this method might be less efficient in terms of quantities (the water method would probably end up pulling virtually all the clay out of the suspension) but in terms of time, if you have four or five assistants, this method would process a big pile of homogenous dirt much quicker and without need for any external energy supply. You can use your photovoltaic array to power your XM radio and a small fridge full of beer.

Consider air and venturi tubes. Blast your dry mix into the intake of a venturi tube with an air hose. Inside the venturi tube, a high-pressure air stream would spin the air column at thousands of revolutions per second. within an inch or two of the air input nozzle, all of the sand will be centrifuged out. You'll need to invent some sort of device that waits for sand to collect in a small hopper inside the tube, then opens a baffle to let it out as it accumulates. You can't leave it open because it would interfere with the venturi magick, letting the entire mixture excape. Another inch or two up the tube, a similar device for removing the silt as it accumulates. The air and clay would blow out the end of the tube. Blow it out into a series of dampers over a hopper that would slow the air down and let the clay fall out.

Venturis are really, really cool. In fact, once you have a source of high pressure air, you can use it to heat or cool the work space. A venturi tube spins the denser, cooler air toward the outside and concentrates the less dense, hotter air toward the center of the air column. By selecting the air vented into the room, you can use the same air to heat or cool.

Isn't clay pretty much the same thing as very, very fine sand? I may be wrong, but an alternate solution is to grind and grind the sand and silt until they are claylike. How would you go about grinding sand? Industrial diamonds embedded in rollers, rolling the sand between them with a weak fan blowing through the material coming out the bottom. The protoclay would be blown into one hopper and the sand would be allowed to drop directly into another hopper. Recycle the sand from the lower sand hopper to the top (or have a series of diamond rollers) until everything is ground to dust.

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#7
In reply to #5

Re: How to separate clay, silt and sand from heavy clay subsoil?

01/26/2008 12:35 PM

(from wikipedia) Clay is composed primarily of fine-grained phyllosilicate minerals typically formed over long periods of time by the gradual chemical weathering of rocks (usually silicate-bearing) by low concentrations of carbonic acid and other diluted solvents. Some clay minerals are formed by hydrothermal activity. Clay deposits may be formed in place as residual deposits, but thick deposits usually are formed as the result of a secondary sedimentary deposition process after they have been eroded and transported from their original location of formation. Clay deposits are typically associated with very low energy depositional environments such as large lake and marine deposits. Clays are distinguished from other fine-grained soils by composistion. Silts, which are fine-grained soils which do not include clay minerals, tend to have larger particle sizes than clays, clays being finer, silts being coarser. Sedimentologists often use 4-5 μm, and colloid chemists use 1 μm. Geotechnical engineers distinguish between silts and clays based on the plasticity properties of the soil, as measured by the soils' Atterberg Limits.

sand particles range in diameter from 0.0625 (or 116 mm) to 2 millimeters

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Guru

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#8
In reply to #5

Re: How to separate clay, silt and sand from heavy clay subsoil?

01/27/2008 4:54 AM

I was thinking just about separation in water. The 3 settling ponds seems good, i just got to have the right flow rates. And the venturi tubes? I was thinking also of an entirely water system. perhaps you could swirl the mixture in a vortex through the right pipe set up to get rid of the sand more reliably? Maybe sand and silt both. Like the cyclones in feed mills except that the fluid is water not air. Really I am only interested in the clay. If I can get rid of the sand and silt together in one quick device, and let the clay settle in a big settling tank, that is fine. When I washed sand before, it went into a big 40 gallon barrel. it went down a 3 inch pipe into the barrel and a slow countercurrent kept the silt out. I got coarse sand ideal for rock wall masonry. I emptyed the barrel by opening a "bag closer clip" that sealed off a rubber 1 inch piece of bicycle tyre at the bottom. As soon as i opened it the sandy water mix always started to gush out. It never blocked, because i guess the coarseness was right. If I had let the silt down, I bet it would have blocked. I think my bilge pump is 60 gallon per hour and does not lift more than about 5 ft. I plan to spray it onto a pile of clay mix, and let it wash down into the cyclone or pond system. Previousy, I found an irregular spraying system was best. If you just set up a hose to spray on a pile of subsoil, it will not do a good job of moving it. It will move rellly quickly at first and then slow down a lot. My old system had the water going up to a tank and another pipe leading from the tank down to the dirty sand pile. The pipe down to the dirty sand sucked air and squirted and spluttered onto the sand pile. I had the spluttering output just above the height of the "stream" going to my big barrel. This was good because an avalanch or sudden sump of the sand blocked the spluttering for a while (a simple effective speed regulator). A regular feed of sand to be washed was better than sudden overloads which would be improperly washed. I actually still have the splutter nozel somewhere in my house about 15 years later!

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#3

Re: How to separate clay, silt and sand from heavy clay subsoil?

01/26/2008 1:11 AM

Liberally apply lime to the surface then flood or keep wet to perc through soil layers 8-10 days ussually separates clay from sand.

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#4

Re: How to separate clay, silt and sand from heavy clay subsoil?

01/26/2008 2:41 AM

Sand will settle readily.

Silt will take some time.

Clay takes ages to settle in water mix.

Once Sand and silt are "Classified in 2 tandem chambers from the fluid stream- you get clay in water.

There is where you ElectroCoagulate( Google it).

And you get clay settling in minutes-not days!!

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#6

Re: How to separate clay, silt and sand from heavy clay subsoil?

01/26/2008 12:28 PM

Right you are MUKUL... It can be done also by screening. Clays are simply classified as those passing the #200 seive. But I am sure you do not want to screen them out. That would work good for a small sample. It would me nearly impossible to get the sand to be suspended in a pond. It will be at the head of the first pond. The silt will settle in the first day or so. the muddy water will have all of you clay.

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#9

Re: How to separate clay, silt and sand from heavy clay subsoil?

01/27/2008 9:45 PM

Since your material is mix of clay, silt and sand I would like to suggest a combination of washing pond and sand classifier. First, as suggested by many, wash the mix to seperate out clay as it is easily dissolved in water. The remaining part can be treated through sand classifier which is nothing but an inclined screw conveyor. in the classifier, the mix will be fed at lower end. The sand will come out from higher end while the silt will be disposed off through lower end with water. This can be collected into a pit or pond.

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#10

Re: How to separate clay, silt and sand from heavy clay subsoil?

01/28/2008 10:55 AM

I wrote this before, but it seems to have disappeared.

Consider winnowing--the most ancient method of separating dry mixes of different densities. First thoroughly dry the mix, then begin tossing it into the air in front of a fan turned on low. The sand and silt will fall straight down. The clay will billow away as dust. Next, place a "sail" made of burlap or some other coarse material wind will readily blow through. Most of the dust will cling to the sail. Periodically, turn off the fan, let the air settle, and beat the burlap with a rug beater or a tennis racquet or something similar. The dust in the burlap will come free and gently fall to earth where you can gather it. Each of these processes can be done by hand or automated. I think you'll find that the sand in the first pile will become purified as a secondary pile of silt develops a short distance away.

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#11

Re: How to separate clay, silt and sand from heavy clay subsoil?

01/28/2008 1:57 PM

Wash the clay and silt from the sand. Then filter the silt from the clay. A finer filter can be used to remove the water from the clay.

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#12

Re: How to separate clay, silt and sand from heavy clay subsoil?

02/13/2008 3:39 PM

I'm wondering if you could use the soil as is by adding a binder such as sodium silicate http://en.wikipedia.org/wiki/Sodium_silicate or an organic polymer such as a furan type http://www.freepatentsonline.com/6391942.html.

By adding a binder you might avioid the labor intensive filtration/separation requirement and could possibly end up with a superior product.

Adobe is made from native soil using hay, weeds and even horse manure for effective binders. In the southwestern US many adobe structures have lasted for hundreds of years. Although I don't suggest you use manure for you binder perhaps a little google research will yield other binders with a (ahem) more acceptable odor.

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#13
In reply to #12

Re: How to separate clay, silt and sand from heavy clay subsoil?

08/03/2008 1:02 PM

couldnt you just mix the dirt with water... let it soak for awhile if there's larger chunks of clay. then agitate the hell out of the water... the sand will settle quickly. The silt will settle next... then siphon the muddy water into another container. Let the water settle and then siphon the water off the top of the clay that collects at the bottom.

shouldn't that work?

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#15
In reply to #13

Re: How to separate clay, silt and sand from heavy clay subsoil?

09/06/2010 3:16 PM

shouldn't that work? Might work on the sand but...

Clay and silt are too small in size of the particles for screens to be effective. I would suspend the clay and silt in water and then Electrocoagulate the clay as suggested by MUKULMAHANT in Post #4.

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#14

Re: How to separate clay, silt and sand from heavy clay subsoil?

09/06/2010 2:43 PM

You can also use a screen sieve sets to sort the different types of soil.

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