IRON FILINGS: PROPERTIES, HOW THEY ARE MADE, TOXICITY, USES - CHEMISTRY - 2025

The iron filings is a material consisting of small particles of metallic iron. The particles are small enough to look like black sand, which exhibits very interesting properties in response to their interaction with a magnetic field.

Also, this sand or filing is often mixed with other substances to create what is called a ferromagnetic fluid. This behaves as if it were a porcupine or black hedgehog; or, on the other hand, if it is covered with a polymer, it gives the impression that the mass formed takes on a life of its own under the stimuli of the magnets.

Iron filings on a magnet. Source: Aney via Commons Wikimedia.

The image above shows an agglomerate product of the attraction felt by iron filings towards a magnet. This property has served him to be used since time immemorial in the academy as a manifesto of magnetism; either in elementary school and in college.

Iron filing should be treated or viewed as another physical way to arrange the metal. Therefore, you can expect your applications to orbit around small particles, such as pollutants, in small spaces or large surfaces.

Properties of iron filings

The properties of iron filings, coming from larger pieces of iron, are precisely the same as for metal. Some of those properties are as follows:

-It is a magnetic solid with metallic and grayish glints.

-Insoluble in water and organic solvents that do not present acidity.

-It is sensitive to oxidation if it is exposed too long to air and water.

-Due to its larger surface area, it can easily catch fire if it comes into contact with high temperatures.

-Its melting and boiling points are 1535 and 3000ºC, respectively.

-The density of these filings is 7.86 g / mL.

-Although it is not a physical property, the size of its particles varies depending on the method with which they are produced and how they are processed.

How are they made?

To make or create iron filings follow a series of relatively simple steps.

cut

It begins with a piece of iron from which its particles will be obtained. If said piece is tubular, a milling cutter is used; and if it is flat, a radial to sand the surface, like a sheet of wood that gives off sawdust.

Sieving

The particles obtained by any of the techniques or tools used in metal cutting can be of very different sizes. It is desired that the filings have only the smallest particles; therefore, they are sieved to separate the powder from larger pieces or crystals.

The more refined the sieve, the smaller the particles and the finer the filings. However, for learning purposes, a typical kitchen strainer is sufficient.

Washed

Finally, the iron filings are washed.

One method consists of immersing them in water and, at the bottom of the container, placing a magnet to separate the impurities from the filings so that the former remain suspended; and thus, decant with the rest of the water. This procedure is repeated several times until the filings are considered to be sufficiently greyish in color.

The disadvantage of the previous method is that the water favors the oxidation of the filings in rust.

Another method, unlike the first, uses mineral oil or glycerin. The oil helps remove rust or oxide from filings by mechanical agitation. The suspension is allowed to stand so that the filings settle to the bottom. Once this is done, the dirty oil is decanted and the procedure is repeated several times until the filings are clean.

The advantage of using oil is that greater resistance to oxidation is guaranteed. It is also a suitable means of keeping filings in storage. When they are going to be used, they are put on absorbent paper as many times as necessary until they do not stain it.

Toxicity

Iron filings do not represent any danger to the body; at least, not in normal situations, and in the absence of high temperatures or chemicals that react violently with iron.

Because they are so small, they can easily slip through the nostrils or eyes, causing irritation. However, iron filings do not have a strong absorption into the skin, so no possible negative effects have been reported.

Applications

Magnetic field lines experiment

Iron filings are very sensitive to the magnetic field of magnets. Each iron particle behaves like a small magnet that lines up for or against the north and south poles of the central magnet.

Thus, one iron particle attracts and repels the other, which gives rise to characteristic circular (on paper) or spherical (in fluids such as water and oil) patterns. In the image below, for example, you can see how iron filings are aligned in the resulting magnetic field over the two poles of a magnet.

Iron filings interacting with the magnetic field of a magnet. Source: Newton Henry Black.

Even more interesting is to develop the experiment with filings (also called shavings) immersed in a fluid. The magnet seems to have the power to give them a life of their own and the patterns obtained are more surprising.

Adsorbent

Iron filings can have an affinity for certain compounds, which interact electronically with their metallic surface.

In this way they are able to retain, for example, phosphorus and calcium alginate biopolymers. This is done for the purpose of purifying a medium, such as a lake, of specific compounds.

Coprecipitation and iron source

Iron filings represent a different source of iron than its salts, rusts, sulfides, and other minerals. They also have the advantage of a greater surface area, which is proportional to its reactivity or addition; the latter process can be carried out, for example, by co-precipitation of iron.

A polymer can exhibit ferromagnetism or some other property if it manages to incorporate metallic iron into its structure from filings. However, iron nanoparticles, still thousands of times smaller than filings, can easily meet this same goal.

References

1. Wikipedia. (2019). Iron fillings. Recovered from: en.wikipedia.org
2. Mirko Pafundi. (2016, August 11). Iron filings in the water. Supermagnete. Recovered from: supermagnete.de
3. Industrial Research Inc. (2016). Iron fillings MSDS. Recovered from: iron-filing.com
4. State of Victoria. (sf). Separating iron fillings, salt and sand. Recovered from: primaryconnections.org.au
5. Natarajan P, Gulliver J., Arnold B. (2016).Iron Filings Application to Reduce Internal Phosphorus Loading in Lakes. Department of Civil, Environmental, and Geo-Engineering
6. University of Minnesota, Minneapolis.
7. AN Bezbaruah et al. (2009). Entrapment of iron nanoparticles in calcium alginate beads for groundwater remediation applications. Journal of Hazardous Materials 166. 1339-1343.