What mixtures can be separated by decantation?

Suspensions.

In colloids and , the particles are evenly mixed around so you won't be able to pour the away from them during decantation.

However, in a suspension, the particles settle to the bottom, leaving the liquid on the top, which can then be poured off.

Decanting is just allowing a mixture of solid and liquid or two immiscible liquids to settle and separate by gravity.

Once the solid has settled, you carefully pour off the supernatant ("swimming above") liquid.

You can also use decantation to separate two immiscible liquids, like oil and water.

You pour the mixture into a separatory funnel. After the layers have separated, you can carefully remove the denser lower layer through the stopcock.

OK.