The most common contaminants are:[1] Industrial oils are purified through sedimentation, filtration, centrifugation, vacuum treatment and adsorption purification.
[citation needed] Sedimentation is precipitation of solid particles and water to the bottom of oil tanks under gravity.
[citation needed] Filtration is a partial removal of solid particles through filter medium.
[3] Adsorption purification, in contrast to the methods mentioned above, does not remove solid particles and gases, but it shows good results at removing water, oil sludge and aging products.
This process uses adsorbents of natural or artificial origin: bleaching clays, synthetic aluminosilicates, silica gels, zeolites, etc.