Separation by physical means refers to the processes used to separate components of a mixture based on their physical properties, without altering the chemical composition of the substances involved. Here are some common methods of physical separation, along with the principles behind each:
1. Filtration
- Principle: This method separates solid particles from liquids or gases using a porous medium that allows fluid to pass through but retains the solid particles.
- Application: Used for separating sand from water or for purifying liquids by removing suspended particulates.
2. Distillation
- Principle: Distillation relies on differences in boiling points of liquids. By heating a liquid mixture to create vapors and then cooling those vapors, you can separate the components.
- Application: Used in the separation of alcohol from water or the refining of crude oil into gasoline, diesel, and other products.
3. Evaporation
- Principle: This method involves removing a liquid from a solution by heating it until the liquid changes to vapor, leaving behind the solid residue.
- Application: Commonly used to concentrate salt from seawater or to recover substances dissolved in a solvent.
4. Centrifugation
- Principle: In centrifugation, a mixture is spun at high speeds, causing denser substances to settle at the bottom due to centrifugal force.
- Application: Used in laboratories to separate blood components (red blood cells, plasma) or in the dairy industry to separate cream from milk.
5. Chromatography
- Principle: This technique separates components based on their movement through a stationary phase under the influence of a mobile phase. Different substances migrate at different rates.
- Application: Used extensively in analytical chemistry to separate and analyze complex mixtures like inks, dyes, or biological samples.
6. Magnetic Separation
- Principle: This method separates magnetic materials from non-magnetic ones using a magnetic field.
- Application: Used in recycling and mining to remove iron filings from mixtures or to separate certain ores from their impurities.
7. Sublimation
- Principle: Sublimation is the process where a substance changes directly from a solid to a gas without passing through a liquid phase. This can be used to separate sublimable substances from non-sublimable ones.
- Application: Used for purifying iodine or separating dry ice (solid CO₂) from other materials.
8. Decantation
- Principle: Decantation involves pouring off the liquid from a mixture, leaving solids or denser liquid behind. This method is based on the differences in density.
- Application: Used to separate oil from water or sediment from clear liquid.
9. Floatation
- Principle: This process separates different materials based on their densities by introducing air bubbles. Lighter materials can attach to the bubbles and float, while heavier materials sink.
- Application: Used in mineral processing to separate valuable minerals from ore.
10. Sieving
- Principle: Sieving separates particles of different sizes by passing the mixture through a series of screens or meshes.
- Application: Commonly used in cooking (to sift flour), construction, and mining operations.
Summary
These physical separation techniques leverage the inherent physical properties of materials, such as size, density, phase, solubility, and magnetic susceptibility, to isolate individual components from mixtures. This contrasts with chemical separation methods, which involve chemical reactions or changes to the substances being separated.