MadSci Network: Chemistry

Re: Can dissolved substances in water be removed magnetically?

Date: Thu May 12 10:02:05 2005
Posted By: Tony Gaglierd, Assistant Professor , Natural Science and Engineering Technology
Area of science: Chemistry
ID: 1115131012.Ch

You Asked. Can dissolved substances in water be removed magnetically?

If one could pull salt out of water with the appropriate combination of low-power electric and magnetic fields it would not be necessary to remove salt from water by the incredibly costly process of boiling away and then recondensing, as is done in Saudi Arabia where oil is cheap and fresh (drinking) water dear.

From a more general point of view, the removal of dissolved salts from water is vital to the reclamation of irrigation water in the West and to pollution control everywhere. Thus the subject of your investigation is of enormous practical importance.

You are dealing with two different forces the Lorentz and Coulomb Forces.

Charges interact under all conditions via the Coulomb force, which states like charges repel and unlike attract.

When charges are moving, they also interact via the Lorentz force, which states that the paths of moving like charges bend toward each other, and the paths of moving unlike charges bend apart.

The ions in your salt solution are also moving, but in short bursts of motion in random directions as they knock around against the water molecules.

Although the Lorentz force from your magnet bends each short little path, and affects sodium and chlorine ions oppositely, the paths are randomly changed so often by collisions with water molecules that no large-scale separation of the ions can result.

A process of magnetic separation has been developed for removing small amounts of dissolved contaminating substances from aqueous liquids.

The process operates in two steps. Magnetic absorbents are mixed with the substance to be treated. The mixture of liquid and absorbent is then allowed to flow through a magnetic trap removing the absorber with any contaminant that has been picked up from the liquid.

An effective trapping arrangement consists of a matrix of coated steel balls in a magnetic field. This gives a close packing arrangement where 50% of the matrix is void. As the magnetic field is greater on the ball surface, trapped absorbent will form layers on the ball leaving pathways through the matrix for more fluid to penetrate.

Using suitable conditions of field strength and flow rate, the absorbent will not build up the layer but move through the matrix column and cover other ball surfaces.

Trapped absorbent has to be discharged at intervals by removing the magnetic field and diverting the released absorber into a receiver.


Magnetic absorbents are prepared in a finely divided state incorporating a magnetic constituent.

A sulphide absorber can help remove heavy metal ions including copper, lead, cadmium, zinc, mercury, manganese, nickel, cobalt and gold. It is also a good absorber of gamma ray emmiting radioactive nuclides present in waste discharges from nuclear processing plant.

The absorber will also work in the presence of salts of the lighter elements that are normally present in ground water, such as magnesium and calcium.

Another absorber will remove cesium which is the major component of radioactive fall-out. Specific absorbers for radioactivity such as zirconium phosphate, hydrous titanium oxide and nickel hexacyanoferrate have been shown in their magnetic form to be slightly more effective absorbers.

You were on the right track. As you see you can use magnetic forces to remove small amounts of dissolved contaminating substances from aqueous liquids. Itís just the application of the principle.

The world needs young men like you who are willing to think outside the box.

Good luck in your future career what ever it may be. Thinking outside the box isnít just useful in science.

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