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Filtration is the operation through which solid particles are separated from fluids (liquids or gases) by passing the impure fluid through a filter or some other separation body, which allows the fluid to pass while stopping the solid residue.

Types of filtration

Cold filtration

Used for removing a desired compound which is very soluble in the filtrate.

Hot filtration

Mainly used to separate impurities from a hot, supersaturated solution, where the desired material is dissolved in the filtrate.


Used for removing almost all the traces of liquid from a precipitate. Büchner funnels are generally employed.

Filter media

Filter paper

Widely used due to simplicity.

Fritted glass

Encountered in Büchner funnels and similar devices, is commonly used for filtering corrosive solutions.

Filter bed

Used in combination with a fritted filter, it is commonly used for removing extremely fine impurities from a solution. The fine precipitate is almost never recovered from filter bed, as it's not worth the effort. Common materials used in the filter bed are silica gel (usually crystalline), diatomaceous earth, perlite, or rarely powdered cellulose.

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