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Extracting magnetite from sand using electromagnets--design help :-)

Extracting magnetite from sand using electromagnets--design help :-)

Extracting magnetite from sand using electromagnets--design help :-)


I am trying to extract Magnetite from ordinary sand using a somewhat unique design involving electromagnets.  I don't have much experience with magnetic engineering--so I thought you guys could help me out.

Here's the gist of the process:  (I also put this online here for better viewing)


- Two electromagnets with metal plates are fixed apart with a gap between.
- The electromagnets are powered by a car battery and controlled through a relay by a laptop (over the lpt port).
- The laptop can then independantly turn each on and off.


- Magnetite laden sand (5-10%) is poured in a steady stream between the electromagnet plates while both plates are activated.
- Almost all magnetite will cling to either face, and the rest of the sand will be collected.
- The magnetite extracted will only be about 75% pure--other sands will be swept up in the processes and become attached to the plates.
- To remove this sand, the laptop turns on and off the two electromagnets in quick alternating pulses.
- The excess-sand should be shaken out and the remaining magnetite will be purified as the magnetite is thrown between the two plates.
- The excess sand will be discarded and the magnetite will be released into another container by turning off both electromagnets.

My questions:
* How should the electromagnets be designed? I need them optimized for a strong force over the entire face of the plates. Number of turns, gauge of wire, length of pole, pole face area, are all variables.  I would like to wind my own.

* What power source should I use? --car battery? 12V, 350W Computer power supply?

* Do you think this will work?

Thanks for your help!

RE: Extracting magnetite from sand using electromagnets--design help :-)


The electromagnets dstart their alternating pulsing after the sand stops pouring.  

ie, there will be these stages:

1.) Pour sand (electromagnets ON)
2.) Stop Sand (electromagnets ON)

3.) Alternate electromagnets (EM 1 on while EM 2 off, then EM 2 on while EM 1 off, etc...)

4.) Collect sand than is shaken out.
5.) Stop Pulsing magnets (both ON)
6.) Change collection containers
7.) Drop magnetite (both OFF)

RE: Extracting magnetite from sand using electromagnets--design help :-)

Hello wazer,

Let me answer your third question ("Do you think this will work?") first: This will not work very well as shown.  The secret to separating magnetic particles from a stream is gradient magnetic fields.  The design as shown will produce a relatively uniform field between the poles and that won't attract a lot of ferrous particles.  The few that do get caught will be near the edges of the poles (where the gradient is located), while the central portion of the pole face will remain clear of particles.  In addition, as the particles collect on the edges, they'll reduce the gradient which will reduces the holding power for subsequent particles.

One good way to get a gradient field is to have the stream move by an alternating magnetic field pattern (North-South-North-South) and the particles will be attracted more strongly to the transitions between North & South.  In addition, there will be more areas for attracting the particles, thus increasing the yield.

You emphasized that you want to wind your own electromagnet for this, but it is a relatively complicated structure you are looking for, especially if you want an optimized separator.  It is not something I'd recommend designing if you are not experienced with magnetics.  There are companies that specialize in electromagnet separators and they even have standard products (do a search for Magnetic separators).  You might find something that is cost-effective.

BTW: This is a pretty trivial thing to do with permanent magnets, if you are open to a non-electromagnet application.

RE: Extracting magnetite from sand using electromagnets--design help :-)

A better approach would be to have a belt running around a magnetic pulley. The belt would be parallel to the ground. Continously place magnetite sand on belt. When the magnetite and sand get to the pulley, the sand will fall to the ground, the magnetite will continue on the belt until gravity is greater than the magnetic pull of the pulley.
This approach has been used for many years and undoubtly there is something on the WWW about it.
Sounds like a fun project.
Good Luck
Carl Pugh

RE: Extracting magnetite from sand using electromagnets--design help :-)

Thanks CarlPugh,

I have heard of those belt seperators, but I am guessing that, at least for sand, the result will not be very pure.  Lots of sand tends to bind in with the magnetite and get carried along  at least in my experiences with this.  I will have to give it some more thought though.

I am trying to get the Magnetite to about 99.5% purity.

Thanks for all your answers!

RE: Extracting magnetite from sand using electromagnets--design help :-)

The technique used to purify coarse sand like magnetite is high speed permanent magnetic drum separators. These are 3 feet in diameter with surface speed of 1000 to 1500 fpm. The centrifugal force throws the non-magnetic sand off quite nicely. Capacities range from 1 or 2 ton per hour per foot of width to over 100 tph.

I've done this successfully on material as fine as flyash. However at that fine particle size wet separation is better.

On a very small scale basis of say a few hundred pounds an hour wazer's technique could be modified with one pole to pick up the magnetite. And as CarlPugh suggests having a belt running around the magnet to clean it. This is what was known as the 'Hope Cross Belt' separator. Typically not used for magnetite because of it's low capacity for the capital costs.

Wazer if you could tell us more of your goals and needs we might be of better help. An older mining engineering or minerals processing text will have ref's that should be reviewed for the HCB.

Completely describe the ore you are working with. Minerals and particle sizes.

Describe your goal. You have mentioned 99.5% purity. % on what basis.

Describe your capacity needs. 1 pound and you are done or 100 TPH. It makes a difference in what makes sense to do as a process.

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