Dolphin Centrifuge

Can a centrifuge separate salt from water?

A centrifuge cannot separate salt from water. Centrifuges use the force of gravity to affect the separation of solids from liquids. Salt dissolves in water to form a solution. The centrifugal force exerted by a centrifuge separates immiscible phases such as sand from water but not miscible phases such as salt in water.

Why can’t a centrifuge separate salt from water?

A centrifuge cannot separate salt from water because salt dissolves in water. The dissolution of salt in water is a chemical process wherein the salt molecules form a chemical bond with the water molecules forming a cohesive liquid.

A centrifuge works by acting on the different specific gravities of fluids in a mixture. Since a solution such as salt and water does not have phases with different specific gravities, a centrifuge cannot separate them.

Are there any cases where a centrifuge cannot separate immiscible solids from liquids?

Yes, under certain conditions, a centrifuge cannot separate immiscible solids from liquids. Since the centrifuge uses differential sedimentation to separate solids from liquids, it requires the solids to be denser or heavier than the liquid.

When the solid particles are light and minuscule, the centrifugal force is not adequate to push the particles out of the liquid. In such cases, the solid particles remain suspended in the liquid without separating.

An example of this failure of centrifugal separation is the carbon particles in used engine oil. These particles are sub-micron level and are predominantly combustion byproducts such as ash. The relatively low specific gravity combined with the tiny particle size makes it impossible for a centrifuge to separate these particles.

Also, these particles are the cause of the black color of used engine oil. And therefore, processing used engine oil through a centrifuge does not change the color of the oil, and the oil remains black post centrifugation.

Examples of other mixes that a centrifuge cannot separate.

There are multiple examples of solids solutions with liquids and liquid with liquids that one cannot separate with a centrifuge. Some examples of such solutions are listed below.

  • Sugar and Water
  • Ink in Water
  • Diesel and Gasoline
  • Diesel and Lube Oil
  • Water and Glycol (Anti-Freeze)
  • Used Oil and Diesel Fuel
  • Alcohol and Water
  • Chicken Fat and Vegetable Oil
  • Emulsified Oil and Water

Examples of liquid mixes that a centrifuge can separate

The following is a list of standard liquid/liquid and liquid/solid mixes that a centrifuge can separate.

  • Milk from Milk Fat
  • Oil from Water
  • Diesel from Water
  • Sludge from Oil
  • Waste Oil from Water and Sludge
  • Fine Sediment from Lube Oil
  • Water from Lube Oil
  • Algae Cells from Water
  • Clarified Butter from Butter Solids
  • Vegetable Oil from Gums
  • Fruit Juice from Pulp
  • Wine from Grape Skin
  • Beer from Yeast

Methods to separate salt from water

As explained above, a centrifuge cannot separate dissolved solids from liquids. So the obvious question is - how to separate dissolved solids from liquids?

The most common method of separating dissolved solids from liquids is evaporation or distillation. The evaporation process involves transforming a liquid into its vapor form through higher temperatures (boiling) or reducing the pressure below vapor pressure (distillation).

In either case, the carrier liquid changes state to a gaseous form while the dissolved solids remain. The most common example of this process is the production of salt from seawater.

Salt production involves the evaporation of seawater in large lagoons. The water evaporates due to the heat from sunlight leaving behind the dissolved salt in crystals of sea salt.

Methods to separate dissolved solids from liquids using centrifuges

In some instances, chemicals in the form of polymers or precipitants aid the separation of dissolved solids from liquids using mechanical separation devices such as centrifuges.

For example, heavy metal compounds dissolved in water precipitate into solid particles in the presence of catalysts or through a chemical reaction with precipitation agents.

Conclusion

It is clear from the above article that centrifuges cannot separate salt from water or any solid that is dissolved in a liquid.


This article is based on our 40 years of disc centrifuge experience. To know more about us, visit the About Us page.

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