A mechanical mixture is one that can be separated through mechanical means, such as a magnet or a centrifuge. Mechanical mixtures are not chemically bonded.
While mechanical mixtures may be attracted to each other, there is no permanent gain or loss of electrons; they do not form different molecules.
One example of a mechanical mixture is iron filings in flour. No matter how thoroughly they are mixed, the iron filings can always be separated from the flour using a magnet. Water with microscopic particles in it is a mechanical mixture, as these particles can be removed through filtration. Oil floating on water is a mechanical mixture because oil and water do not combine. Even blood can be separated into its components, as red cells are heavier than plasma. However, salt water is not a mechanical mixture because the ions in salt are bonded to the water molecules. The salt cannot be extracted without, for example, the application of heat to cause a chemical change.
Mechanical mixtures are often created in recycling. Magnets, filtration and other methods are used to separate each recyclable component, as they have different physical properties. Given the lack of chemical bonds, it is also possible to apply chemicals that only affect one component of the mixture.