How To Separate Rock From Wood Products

Classifier with bath (float tank)

Companies who are involved in wood recycling, cleaning up old mill sites, wood yards or log yard debris, often encounter the problem of how to separate rock and dirt from wood products. Although numerous size trommel screens, vibratory screens or finger screens can be used for prescreening wood waste and to complete this process, the cost often begins to outweigh the benefits.

That’s where the water bath classifier or stationery trommel with water bath (float tank) comes in (see photo above).

The brand we’ve used is a Wittco stationary screening plant with a 6000 gallon water bath. As shown in the photograph, the process begins at the hopper.

A mix of wood and rock (dirty material) is loaded into the hopper. A conveyor, or feed belt then carries the product into a 28 foot long trommel screen which rotates. Different size screens can be installed into the trommel and the screens which are located at the bottom of the trommel determine the size of the product that is produced. As the wood, dirt and/or rock products pass over the screens, that which is small enough drops through, and the large pieces of wood and rock are carried through the trommel and drop into a 6000 gallon water bath (float tank).

Wood belt on classifierThe water bath which is attached to the trommel encompasses two conveyor belts which are partially positioned beneath the surface of the water. The wood will float, be picked up by the upper conveyor (wood belt -see photo on left), carried out of the bath and disposed of in front of the classifier. rock_belt_on_classifier_with_float_tank.JPGThe rock and/or heavily saturated wood products will sink to the bottom of the bath and will be carried out by the lower belt (rock belt -see photo on right) and dispensed to the rear of the classifier (behind the bath).

The wood which is expelled from the bath can then be picked up with a piece of heavy equipment, taken back to the tub or horizontal grinder and be reground into wood chips. The rock can often be reused in other parts of the recycling operation, or be sold.

The classifier runs on either a diesel or electric powered engine. The controls for the trommel are located in a tower directly across the bath in line with the trommel. In the event any product gets hung up inside of the trommel, the classifier operator can stop the trommel with the flip of a switch.

The classifier can also be used for blending products such as compost and topsoil, creating a topsoil blend enriched with nutrients. It’s perfect for resizing bark products, as well.

In our wood recycling operation, learning how to separate wood from rock involved a lot of experimentation until we purchased the stationary classifier with trommel and water bath (float tank). Not only did our production increase, but we were able to reduce labor and heavy equipment costs, plus eliminated all other screening equipment.

6 Comments Post a Comment
  1. Linda says:

    WOW! what a process! Isn’t experimentation fun? It really brings out the ideas.

    Linda┬┤s last blog post..How About Bitublock ?

  2. BSwafford says:

    Hi Linda – Yes, before we got the right piece of equipment we spent tons of time and money trying to separate the rock from the dirt. You name it, we tried it. It was a great learning experience that taught us, sometimes there are no shortcuts.

  3. Mike Kosyk says:

    I’m intersted in more information. We have a Woodyard that we clean-up every year by scraping the debris with a grader, but of course a layer of rock is removed as well. Eventaully the grade needs to be restored.

  4. BSwafford says:

    Hi Mike,

    Thank you for your comment and interest. I’ll send you an email so we can discuss this further.

  5. Alan says:

    looking for a waterbath to separate ferrous and non ferrous. Had one in last palce but cannot get make. Can you help

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