Claus process and Frasch process are the most used sulphur producing processes. But, sulphur produced through these processes is not absolutely pure because of the presence of suspended material, sulphur dioxide, moisture, sulphur acids, hydrogen sulfide, carbonaceous material, oxygen and dissolved nitrogen in small amount.
The high purity of sulphur is required as impurities affect many of sulphur's properties like- carbonaceous material which greatly affect the viscosity of sulphur and other properties. That's why there are lots of purification processes published and used in the world. Although there are some selective ones which are used most often because of their easiness.
There are very simple methods used for removal of some impurities as given below-
Moisture can be removed by heating the sulphur.
Suspended material are removed from sulphur by filtering it through a filtering medium in a heated funnel.
The most useful method of removing Acid from sulphur is- mixing the molten sulphur with any alkaline material like lime. Thereafter filtering it through filtering medium.
Other impurities/materials are not that easy to remove from the sulphur in order to purify it.