【Daily Question】Chemical Engineering Principles 337: Sedimentation of Colloids in Water (March 9)

Answer: 1. Since colloids of the same type carry like charges, there is an electrical repulsion between them, causing them to push each other away when they come into contact. 2. Due to solvation (the ions on the surface of the colloid combining with water molecules to form a hydrated layer), a layer of water molecules surrounds the surface of the colloid, preventing contact between the colloid particles.

Colloidal particles in water are tiny particles with sizes ranging from 10-4 to 10-10 mm; they are very stable in water and do not settle easily. Its natural settling rate is only 0.154×10-6 mm per second; it takes 200 years to settle by 1 meter. This is because colloidal particles are generally formed when insoluble substances precipitate from aqueous solutions. When many ions or molecules gather together in sufficient quantities, the surface of these particles develops an adsorptive capacity, allowing them to absorb various ions from water. Alternatively, ionization at the particle surface can also result in the formation of ions, endowing the particle surface with electrical charge. Thus: (1) Colloids of the same type carry like charges, which results in like-charge repulsion; this prevents the colloidal particles from coming into contact with each other or sticking together, allowing them to remain in a particulate state and stay suspended in water ； (2) The surface of the colloidal particles is also tightly surrounded by a layer of water molecules; this hydration layer prevents and isolates contact between the colloidal particles, allowing them to maintain their particle form even during thermal motion, so that they do not stick together and remain suspended in water. For the above two reasons, alternating particles in water do not settle naturally easily.

Colloidal particles in water are particles with sizes ranging from 10-4 to 10-6 mm; they are very stable in water and do not settle easily

1. Colloids carry like charges that repel each other, making it difficult for them to settle. 2. The colloid is surrounded by a thin layer of water molecules that act as a protective layer; this hydrated layer also prevents and isolates the contact between the colloid particles, allowing them to maintain their particle form even during thermal motion, so that they do not stick together and remain suspended in water

Colloidal particles in water refer to particles with a particle size of 0.001μm–0.1μm; they are very stable in water and do not settle easily.

Colloidal particles in water are tiny particles with sizes ranging from 10-4 to 10-10 mm; they are very stable in water and do not settle easily. Its natural settling speed is only 0.154×10-6 mm per second; it takes 200 years to settle by 1 meter. This is because colloidal particles are generally formed when insoluble substances precipitate from aqueous solutions. When many ions or molecules gather together in sufficient quantities, the surface of these particles develops an adsorptive capacity, allowing them to absorb various ions from water. Alternatively, ionization at the particle surface can generate additional ions, endowing the particle surface with electrical charge. Thus: (1) Colloids of the same type carry like charges, which results in like-charge repulsion; this prevents the colloidal particles from coming into contact with each other or sticking together, allowing them to remain in a particulate state and stay suspended in water ； (2) The surface of the colloidal particles is also tightly surrounded by a layer of water molecules; this hydration layer prevents and isolates contact between the colloidal particles, allowing them to maintain their particle form even during thermal motion, so that they do not stick together and remain suspended in water. For the above two reasons, alternating particles in water do not settle naturally easily.

Why don’t colloids in water settle easily? Colloidal particles in water refer to particles with a particle size of 0.001μm–0.1μm; they are very stable in water and do not settle easily. Its natural settling rate is only 0.154×10-3 μm per second, so it takes about 200 years to settle 1 meter. This is because colloidal particles are generally formed when insoluble substances precipitate from aqueous solutions; when many ions or molecules aggregate to a certain amount, the surface of these particles develops an adsorptive capacity, allowing them to adsorb many ions from water. Or, due to the ionization of the particle surface, many ions are generated, endowing the particle surface with electrical charge. Thus: (1) Colloids of the same type carry like charges, which results in repulsion between them; this prevents the colloidal particles from coming into contact or sticking together, allowing them to remain in a particle form and stay suspended in water ； (2) The surface of the colloidal particles is also tightly surrounded by a layer of water molecules; this hydration layer prevents and isolates contact between the colloidal particles, allowing them to maintain their particle form even during thermal motion, so that they do not stick together and remain suspended in water. For these two reasons, colloidal particles in water remain suspended and do not settle naturally.

Because the colloid is charged and water molecules are polar, they are attracted in a directed manner to the vicinity of the colloid particles, forming a hydration layer. The hydration layer has a structurally ordered arrangement; when the colloidal particles come close to each other, this hydration layer is compressed and deformed. Due to its tendency to restore its original ordered structure, the hydration layer exhibits elasticity, which acts as a resistance force when the particles get close to one another, preventing them from aggregating and settling together.

Why don’t colloids in water settle easily? Colloidal particles in water refer to particles with a particle size of 0.001μm–0.1μm; they are very stable in water and do not settle easily. Its natural settling rate is only 0.154×10-3 μm per second, so it takes about 200 years to settle 1 meter. This is because colloidal particles are generally formed when insoluble substances precipitate from aqueous solutions; when many ions or molecules aggregate to a certain amount, the surface of these particles develops an adsorptive capacity, allowing them to adsorb many ions from water. Or, due to the ionization of the particle surface, many ions are generated, endowing the particle surface with electrical charge. Thus: (1) Colloids of the same type carry like charges, which results in repulsion between them; this prevents the colloidal particles from coming into contact or sticking together, allowing them to remain in a particle form and stay suspended in water ； (2) The surface of the colloidal particles is also tightly surrounded by a layer of water molecules; this hydration layer prevents and isolates contact between the colloidal particles, allowing them to maintain their particle form even during thermal motion, so that they do not stick together and remain suspended in water. For these two reasons, colloidal particles in water remain suspended and do not settle naturally