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How does filtration separate crystals from a liquid?
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filtration
Tap water filtration system.
Filtration separates crystals from a liquid by utilizing a filter medium—such as filter paper, woven cloth, or a porous screen—that allows the liquid to pass through while retaining the solid crystals.123
The process relies on the following principles:
- Size Exclusion: The filter medium acts as a barrier with pores smaller than the crystals, effectively trapping the solid particles while the liquid (filtrate) flows through.124
- Driving Force: To overcome the resistance of the filter medium and accelerate the separation, a driving force is applied. This is commonly achieved through gravity, pressure, or a partial vacuum.134
- Industrial and Laboratory Application: In industrial settings, such as the crystallization of wax from oil, rotary filters use a vacuum to draw the liquid through a cloth, leaving the crystals on the surface to be scraped off. In laboratory settings, mixtures are often poured into a funnel lined with filter paper or a Büchner funnel, sometimes using vacuum filtration to increase the speed of the process.534
By effectively isolating the solid phase from the liquid, filtration allows for the recovery of either the clarified liquid, the solid crystals (filter cake), or both.13