The iodine distils off and can be collected on a cooled surface. It may be purified by sublimation in vacuo.
This reaction is also used on a large scale,to obtain iodine from seaweed. The ash from burnt seaweed (kelp) is extracted with water,concentrated,and the salts other than iodides (sulphates and chlorides)crystallise out. The more soluble iodides remain and the liquor is mixed with sulphuric acid and mangenese dioxide added;the evolved iodine distils off and is condensed.
Most iodine produced commercially comes from the sodium iodate(V) remaining after sodium nitrate has been crystallised from Chile saltpetre. The iodate(V) is first reduced to iodide by blowing sulphur dioxide into the solution (or by addition of sodium sulphite).