How to screen/separate gravel from weed?

[FB100-Backhoe]

Hi guys,

I´m looking for a clever method to separate a mixture of top soil, gravel and weed. I own some squaremeters of land here in spain, and for preventing wildfire I use a brushcutter from time to time to remove the weed/grass/undergrows. Sometimes I also use my backhoe with a cleaning bucket, resulting this faster but with a larger amount of debris.

The "problem" starts when I rake the cutten stuff, because there is a nice top layer of natural gravel on my land and with the rake and the cleaning bucket I recollect a large amount of this gravel I would like to conserve or to screen from the rest of the organic material.

Anybody can give me a hint on how to separate this stuff? The fastest and most effective would be burning down the mixture and then screen the ashes for the gravel, but I can´t use this option. I´m sure that a gravel-tolerant shredder with a cyclone separator would do the job, but this is too oversized.

I thought about excavating a type of pond, fill it with water and put the stuff in, maybe organic debris floats and gravel and earth can be removed from ground and the organic debris float on the top?

Any idea for me? Thank you in advance!

 

[DMiller]

Commercial screens are stepped, take the bigger rocks out conveyor to another smaller screen take out the next smaller etc etc. Is really difficult to get clean material in one pass screening. How much material are you working, what sized machines and how long do you plan to do this?

 

[FB100-Backhoe]

Sure that a comercial solution can be developed to do this task, but I think that this will be complete (financial!) overkill
I´m talking of, at this time collected over the past years some 20 cubic meters, maybe 25 tons of material. Every year, depending on how I cut/recollect the new grown weed/brushes there will be some two to three 20 cubic meters more.
I own a TBL, and think that I will have to do this job at least 6 to 8 years more, until I have designed/built a nice garden/park/swimming pond etc.

I thought of doing something like producing a strong air stream with a big blower and throw the mixture in, the lighter parts will be blown away with the air, the heavier stones will fall down. Don´t know if my neighbours would like this solution ;-)

 

[DMiller]

There are loader tractor buckets available one may consider copying as to a portable small scale and convenience screen. Varieties from Skid steer size to large machine. Look up Flip Screen or Screening Buckets. As to removal of weed seeds I dare say that may not be a level of screening achievable.

 

[funwithfuel]

A simple screen wouldn't be a bad idea. Screen size dependent on gravel size. You would end up with dirt/sand/gravel but should effectively remove weed material. Then you could screen the dirt/sand from the gravel.
Take a look at what doublewide and his father in law have put together. Very simple, very clean, very efficient.
Good luck

 

[Tinkerer]

I think you are waiting too long between brush cutting intervals. Do it more often so there isn't so much material. Better yet get the growth short enough so you could mow it.
Or spray it with vegetation killer if it is available and permitted to use in your area.

 

[DMiller]

I built a simple screen for separating larger rock from dried beef manure, works somewhat but need to be vibratory to actually work better. Screen lifts off frame so will not be so hard to rig out. Used 3/4" (19mm) mesh, should have used 1" and heavier wire as well a angle iron Pre Screen set above this to slip the bigger rock away, ^^^^^^^^^^

 

[hosspuller]

My former industry used screeners in the process. Electric powered vibrators for screeners work well. But for home-made... a couple of choices come to mind. a rotating weight eccentrically mounted or a crank mounted to the flat inclined screen. The screen has to be held either with springs, cables, chain, torsion bars to allow the screen to move.
Search "rotex screener"

A trommel is an inclined screen barrel that rotates. As the material is feed into the upper end, it separates the material by size. Some are stepped so the larger sizes come out first then progressively smaller to the lower end. https://en.wikipedia.org/wiki/Trommel_screen

Last and most simple is a grizzly. see here … https://www.rocktough.com/light-duty-adjustable-bar

 

[Vetech63]

I have neighbors that will buy all the weed you ca...……………...oh wait...……….

 

[thepumpguysc]

Lol.. I "was gonna" say something along those lines..lol

 

[thepumpguysc]

I like the trommel idea.. stones outta 1 end & dirt on the other..
The grass might come out w/ the stones but that could be burned off or wait till it died & Bob's your uncle.

 

[kshansen]

Not sure about the volume of material we are talking but could you get access to a old fashioned cement mixer? Load the mixture into the mixer and let it run while filling with water hose. The vegetable matter should float and as the water overflows was out the material.

Something on this style:

Now if we are talking several yards of material at a time that would not work.

The pond idea might work if you can have it so water can overflow at one end to carry away the material that floats.

 

[Ronsii]

I have neighbors that will buy all the weed you ca...……………...oh wait...……….

Every time I see this thread that's what I thought LOL!!!


I like the trommel idea, maybe with an air knife kinda setup???

 

[Tinkerer]

I put thousands of yards of dirty topsoil thru a vibratory screed with a 973. Big problem was small tree branches and fragments of railroad ties. The dam things would go vertically to the underneath screen and jam it up like you wouldn't believe. sometimes we would spend more time scratchin and pulling that stuff than we did feeding the dam thing.
It was was similar to the one in the picture but it was on a steel frame to elevate it so that a big pile of clean stuff could accumulate.
We were clearing a 130 acre abandoned railroad yard that was being converted to an intermodal yard.
.

 

[hosspuller]

A correction: in a trommel... the small stuff comes out first, then the larger. Just like any multi size screener. Opposite of my post description above. A senior moment …

 

[John C.]

There was a company out here between McCleary and Olympia who made a separator that was used a lot in the Aberdeen and Hoquiam sort yards separating wood debris out of the rock used as a base for the yards. It was basically a rectangular tank filled with water that had a chain flight conveyor that went to the bottom. The vegetation floated and was skimmed off the water at one end while the rock sank and was picked up by the flight conveyor and dumped in a pile off to the side.
Coal screening plants worked on the same principle.

 

[Ronsii]

There was a company out here between McCleary and Olympia who made a separator that was used a lot in the Aberdeen and Hoquiam sort yards separating wood debris out of the rock used as a base for the yards. It was basically a rectangular tank filled with water that had a chain flight conveyor that went to the bottom. The vegetation floated and was skimmed off the water at one end while the rock sank and was picked up by the flight conveyor and dumped in a pile off to the side.
Coal screening plants worked on the same principle.

Yeah, there is a sawmill operation down here that used to use that setup but mainly for removing bark from the gravel they run on, but from what I hear they quit doing it ten or so years back as it just didn't pay for itself in trying to split the two.

 

[FB100-Backhoe]

Thank you a lot for thinking about this issue and for all your answers.
I built a simple screening bucket for my TBL four years ago, it did it fast, with available material and without engineering to much, this was the result:

Although the form was not ideal, it worked fine for screening aprox. 100 cubic meters of soil, "filtered" out all big stones. During the work with this bucket I thought about all the things I would do better in a second one. So I sold this bucked, and because I´m still thinking about "perfectionating" the new one, I converted a 55cm-bucket in a temporal solution with smaller "mesh", cutting the bucket´s base plate and welding some rebars in.


The new one I think to build includes a elastic suspension for the bucket part and a hydraulic-motor with excentric mass, like some commercial available solutions.

I tried both buckets with the soil-gravel-weed (I know, "weed" also is the name for a special type of plant but I don´t know any english word that better describes what I want to get off from the gravel - maybe anybody of you can give me a hint?) and obviously large pieces are "filtered", but the small ones fall through the sieve (and even bigger ones if the "stand up"). Exactly what tinkerer describes in his post. And while moving (shaking) the bucket, larger brush pieces are beeing crushed by the stones/gravel and fall through.

So I think that a standard or grizzly type of screener will always end up with a mixture of organic residue in gravel, not perfect for road paving or for compacting.

Chemical vegetation killer is a no-go, but I started to cut the growth more frecuently, but this also produces smaller debris - acting as organic fertilizer, with the result that the weed grows faster.

The trommel sounds interesting, I know this type of screens and its industrial applications, I thought about it time ago, but it seems more difficult to built especially the trommel. In some way this is similar to the cement mixer. I have one with 200l capacity, but surely I will be working the rest of my life feeding it with material ;-)

Exactly what John C. describes is what I think will be one of the best solution. Maybe I can find a second-hand rubble skip (right name?), fill it with water (and pumping in water continuously), throw the mixture in, organic material spills out with excess of water and gravel/soil sinks to ground. From time to time I dig it out and start the procedure again.

But: What to do with the water/organic material mixture? Hmm, I think I will start a new thread

 

[Ct Farmer]

Without the use of chemicals it is going to be near impossible to get and keep anything weed free. Even if you clear it all out seed will always remain and or blown in. You need a pre-emergent to keep the seed from germinating. Without chemicals there is no way we could keeps miles of fence line and crop areas clear. We don’t overuse or just hose everything but it is the only real choice at this point.

Short of that you need to till, rake or otherwise disturb the surface very often. Propane burners work good too but obviously you need to be careful.

For cleaning the mixture a grizzly type screen will work ok if you add a shaker to it. We built one with with 3/4 inch mesh that one the right slope with dry material screens well under 3/4”. But we consider the rock and organic matter to be waste that just get piled for future road/fill so it doesn’t matter if they are mixed. When piled most of the organic rots and goes away rapidly. Water wash helps clean the rock. Topsoil goes to the fields.

The idea of an air curtain sounds interesting but the material would need to be really dry. Pond might work but you will still have weed seed as many viable seeds don't float.

There are some natural/organic/green weed killing options that do work if you have time and keep up with the spraying.

 

[FB100-Backhoe]

@Ct Farmer: Thanks for your answer and information.
There is no doubt that keeping the land totally free of weed without use of chemicals (or bushfire from time to time ;-) ) will be impossible; but this is not necessary. At this moment I´m removing the weed/brushes that have grown over the last ten to twenty years; once donde this I will try to keep the weed more controlled, using the brushcutter three of four times the year.

What I want to do, once removed manually all the big brushes/weed, is pass the cleaning bucket with my backhoe to leave a smooth surfuce without at least bigger stones and, if possible, even without gravel on the surface, what will makes a lot more easier the recollection of the cutted weed with a rake.

I´ve tested my "pond-method" in a smaller scale, but I´m not satisfied with the result: Most part of organic material flows out with water, but in the remaining sump there are still a lot of almonds (the land was a former almond plantation) and other organic material not swimming up. And it needs _very_ much water.

I found a air-curtain-type solution, mixed with high-performance electronics: The mixed material is beeing scanned with cameras while falling from a conveyor belt, each particle classified for size, color, material and then, before landing on a lower conveyor belt, blown out by discrete air streams from high-speed nozzels controlled by the computer. With this method they achieve to clean 20 tons of topsoil per hour, removing any stones, plastic and other debris. Or, in larger scale, sorting different stone types in quarries, up to 200 tons/hour. Impressive but maybe some overkill for my task.

I will do some test with separation by mass and density, first accelerating the material mix and "throw" it of the belt´s end and then see if it is possible to separate by "flight path/distance". And if this one will not work, it will try with a cyclonic separator. At this moment the material is all very dry, due to lack of rain in the last 4 months.