Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Need opinions on how to separate dust/silt from dirt...

  1. Aug 20, 2015 #1
    I work at an auto dismantler (wrecking yard) in CA and the regulations for storm water runoff are getting tighter and tighter. The owner of the business is probably farther ahead of most yards in the state when it comes to trying to do the right thing. Our biggest concern is the heavy metals washing from the soil and showing up in our storm water tests so the owner threw the question out to us of how we would go about separating the fine dust/silt from the dirt in the yard, the theory being that we would pick up the bad stuff before it can wash away. We have about 10 acres but would only be able to "clean" about one or two as far as surface area goes... main roadways, some asphalt and open areas that don't have a vehicle parked on it. Most of the loose dust is in the areas we can get to, or the areas that get driven on and broken up.

    Okay, that was a long setup for my question. Do any of you mechanical minded people know of a way to separate the dust/powder/silt from the dirt and gravel? The typical industrial vacuums don't seem to be the answer since they're designed more for trash, leaves, debris and things with more surface area to pick up and filter. I have my thoughts on a concept but thought I'd ask the question first...

    Thanks for reading and I'll add more detail as needed.

    Rocklin, CA
  2. jcsd
  3. Aug 20, 2015 #2


    User Avatar
    Education Advisor
    Gold Member

    Welcome to the forum.

    My suggestion is you contact the appropriately certified and licensed professional. There are lots of things you could try that would wind up making it much worse. And, depending on what is in the ground, lots of things that could wind up producing exposure to the individuals involved. Imagine, for example, you are trying to get rid of the lead (from welding or soldering or whatever) and you wind up disturbing and so releasing something that was already there.

    Depending on the exact material involved your options may include some kind of chemical treatment, some kind of stabilization in place, or removal to a permanent disposal site. All of these have significant risks and may be expensive.

    Especially seeing as it is California, you could also run afoul of a lot of environmental laws if you don't stay "inside the lines."

    So a licensed pro seems to be in order, at least for a consult.
  4. Aug 20, 2015 #3
    Thanks for the reply. Unfortunately, the "licensed professionals" are limited for this kind of thing. We get more of a water treatment perspective when getting professional help, like how to filter the stormwater, drainage plans, how to test the water, etc. We're doing those things and WAY ahead of most yards, but as far as trying to remove the sediment before it can get washed away... no one to ask.

    In my opinion, the dust is being disturbed all day long as the employees drive around in it in yard vehicles, tow trucks and transports unloading and loading vehicles in the dirt, etc. By trying to collect most of the fine dust/silt that gets created, it would seem that it would reduce the exposure to employees. The concern is the heavy metals in the dirt... zinc, nickel, and other metals related to automobiles. The oils and fluids are not a problem because its removed before putting the vehicles in the yard. We've never heard of anyone try to "clean" their dirt in the way we'd like to. Not excavate it, filter it and replace, but just try to remove the top layer of fine dust, which is what transports the heavy metals in stormwater.
  5. Aug 20, 2015 #4
    I worked as the plant mechanic at a concrete mixing and bagging plant and we had a similar issue with removing fine dust from the air. Fine, dry dust carries a static electrical charge and is naturally attracted to negatively charged anodes. I'd build a system of steel pipes that can be negatively charged mounted on wheels so it can be moved around an inch off the ground, cleaning is simply reversing the charge. However, the heavy metals in the dust sounds more like a symptom not the cause, again, if it was me, I'd find the source of the problem and build a way to capture the run-off so it could be cleaned of any pollutants. Maybe where they stored used batteries back in the old days?
  6. Aug 20, 2015 #5


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You, as an employee, are co-operating with the owner, who as a responsible citizen is trying to anticipate regulatory headaches --- great. We'll take for granted that you're not going to try anything without a "mother, may I" blessing from the state. Dry granular materials/powders are handled with pneumatic conveyors (vacuum cleaners), and separated using screens/sieves.
  7. Aug 20, 2015 #6
    Interesting idea about the "magnet", we have a strong magnet hanging on the bottom of our golf cart we drive around the yard, trying to pick up nails and screws that might puncture tires. The metals come from the vehicles stored in the yard, about 700 of them right now, but its only what would get washed off the vehicles in the rain and end up on the ground. There's more metals washing down the storm drains on the streets from vehicles using brakes, etc., but because we're the dreaded auto dismantler (junk yard) the watchdogs think we cause all the damage. Right now we wait until the storms come and wash what metals there are into the holding ponds, then when the water flows over the top of the pond we have to test it. Basically any water that leaves our property has to pass testing guidelines. There is no good way to stop the metals from getting in the dirt, except for paving ten acres.
  8. Aug 20, 2015 #7
    Yes, we're looking into vacuum cleaners but don't know anything about them or whether they'd work for what we need. Do you know of anyone using one to vacuum up the dirt/powder on top of hardpan/gravel? I thought it might have to be a specialized unit.
  9. Aug 20, 2015 #8


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    The only way to prevent contamination is to dismantle the cars in a controlled environment, a "clean room" if you will, where the metal dust never mixes with the soil.

    If you only dealt with magnetic material, like iron and steel, possibly the ferrous material could be separated from the soil using a magnet of some sort. But cars contain non-magnetic metals, like lead, aluminum, or other alloys, and recovering or separating this material is more difficult (and costly).

    I suspect that the ultimate solution to this problem will be one which disappoints many people: this industry will re-locate out of California to neighboring states, or more likely, to Mexico.
  10. Aug 20, 2015 #9
    With the help of the internet and new technology, this industry has already begun to move away from the regulated yards and into garages and backyards. An insurance salvage vehicle (insurance total) can be purchased by anyone at a computer, without a license and no regulation, have it delivered to their driveway, take the car apart with no oversight and then sell the parts on craigslist and ebay for much more profit than a regulated business. As the regulations get tighter and tighter, the "underground economy" in used auto parts grows. So yes, eventually the environmentalist will get what they want and the auto dismantling industry will go elsewhere. At least that's what it will look like to most people. The bottom line is, they regulate the yards, not the vehicles.

    Another way to put it... the storm water coming off of any Walmart parking lot has WAY more harmful materials than a regulated auto dismantler, yet our regulations continue to get tighter and tighter. Do I sound frustrated? ;-)
  11. Aug 20, 2015 #10
    no, no, no... not a vacuum cleaner, talk to someone in your area that deals in automotive paint booths, they use a static electric air filters and may be ableto shed some light on removing dust using static electricity
  12. Aug 22, 2015 #11


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

  13. Sep 4, 2015 #12
    Seems to me that you could talk to some dust collector companies like Torit and they could steer you in the right direction. Also talk to companies who make the equipment to sweep up the fines after a black-top road is ground down. You could maybe use the road-sweeper equipment to gather up the dirt/gravel/dust and the Torit to filter out the dust.
  14. Sep 6, 2015 #13


    User Avatar
    Science Advisor

    Do not stir up the dust. That will just cause more problems than it solves. There may be asbestos fibres from old brake systems or natural things like anthrax present in soil.

    I do not think you have a problem. You have several potential problems but they are chemically different. You first need to develop a base line and identify which metals might be a problem.

    First start with a survey. Put down some shallow wells with an auger to below the water table. Do the same with a neighbouring site with the same geology as a control. Take soil samples as you bore the hole, keep them in plastic bags. Put a PVC pipe into the hole to stop it collapsing. Cap the wells with a cover to keep out the rain and dust. Take a water sample from each well every month and put it aside in secure storage. That will give you a base line. It would be really silly to close the business and pay the fine for contaminating the soil if the 'contaminant' was naturally occurring in your area. If you are brave you can get an early water sample analysed which may quickly identify a problem, or confirm you have no problem.

    Unless your soil is acidic and anaerobic, that is it is wet with blue and green coloured clays, rather than red or yellow, you do not have a problem with aluminium. Al will oxidise immediately and become part of the soil. The same is true of iron and many other metals.

    Lead sulphate from spilled battery acid may be mobile, but if it oxidises it will not be in the ground water.
    Lead from old gasoline spills, pre-ULP, might be a problem.
    Zinc might be a problem but where does it come from? it is not usually a problem.

    So what metals do you fear?
  15. Sep 6, 2015 #14


    User Avatar
    Science Advisor
    Gold Member

    How about developing a walk around scanner device which both detects and analyses contaminants in your surface soil . Remedial action then could be manual brush up with suitable precautions or a portable clean and recycle machine .

    Would need lots of work to develop practical system but it is possible .

    Information about this subject on web is fragmented and scarce but I did find this

  16. Sep 6, 2015 #15


    User Avatar
    Science Advisor

    Handheld X-Ray Fluorescence is an answer. Used by geologists and in scrap metal yards to identify alloys.
    Search ebay for an ' XRF Analyzer '
    See also; https://en.wikipedia.org/wiki/X-ray_fluorescence

    About XRF Analyzer
    From sorting scrap to screening soil, from pricing precious metal to setting safety standards: An XRF analyzer is a multipurpose tool with a wide range of industrial applications. Working on the principle of exposing a sample to a beam of primary X-rays, an X-ray fluorescence analyzer is a proven way to test materials in a non-destructive manner. The atoms of the sample absorb energy from the X-rays, and then emit secondary X-rays at a unique energy, allowing for quick and easy identification. Use a handheld XRF spectrometer to test whether paint contains lead or other harmful substances, to sort various types of metal for recycling, or even to organize a collection of jewelry. In large-scale industries, the spectrometer is a simple way to screen materials to see if they adhere to safety standards, for preparing bulk loads of scrap material for sale, or for analyzing seams when mining. The sellers on eBay have a wide selection of tools for use at home and in the workplace, making it easy to find an XRF analyzer at a great price.
    Last edited: Sep 6, 2015
  17. Sep 10, 2015 #16
    A centrifuge and filter with corresponding sizes of desired debris to filter would do the job.
    I'll leave you the time for imagination to do the rest.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook