Methods of Separation of Mixtures

Introduction

Any physical combinations in chemistry are two identical or variable compounds. These combinations are mixed to form a solution, suspension, or colloids. Such compounds are called a mixture, and the compounds’ properties are easily retained. Colloids are a specific type of mixture in which the particles involved with the dimensions of 1 to 1000 nanometers approximately. The particles form colloids that can be separated through particular methods of separating mixtures. These particles contain specific molecules and clumps which frequently have opaque appearances. The colloids usually form a heterogeneous mixture where the particles are efficient enough to appear in scattered light. Milk and fog are some common examples of colloids.

Colloids: Definition

These are the types of mixture where one insoluble comprises a microscopic appearance suspended by another substance in the methods of separation of mixtures. This substance in which the particles are dispersed can be aerosols, gels, or in any liquified form. The particles in the colloids appear scattered with light because of the Tyndall effect, while the other ones have a murky or dull appearance. This is because the disperse phase in colloids occurs with the suspended particles, whereas the medium of suspensions carries a continuous phase.

Types of Colloids

There are mainly two types of colloids useful in our daily lives. The colloids can be distinguished based on their properties and the types of particles involved. All these particles attain different physical appearances and chemical properties. It changes the complete colloidal solution with appearance, and methods of separation of mixtures will also be other for the types.

Here is the classification based on the nature of particles involved in the colloids:

• Hydrophilic colloids: When mixed with water, these colloids form a colloidal solution that cannot be easily destabilised. It is a solution like soap and water.
• Hydrophobic colloids: Hydrophobic colloids contain highly insoluble particles like metals oxide, clay, and similar non-hydrated substances. All these particles can quickly destabilise due to their unstable nature.

Separation Method of Colloids

The separation methods of mixtures of colloids include various modes to separate the microscopic insoluble particles from the colloids. The small solid particles in colloids contain a negative electrostatic charge and are around 1 to 100 nanometre in size. All the particles attain a similar electric control (negative). An electric force keeps all the charged particles separate in the colloids with an insoluble state, making it a suspension of small particles.

The particle stabilisation in colloids is determined by the Zeta potential (Zp). If the zeta potential is high in the particles, the repulsion forces between the particles will be higher. It will provide the colloid with a more robust suspension state with a high stability ratio. With high zeta potential, electrostatic repulsion is more potent, and lower values of Zp aggregate the particles present in colloids, resulting in an unstable system.

To separate a colloidal solution, destabilisation is necessary for the mixture. With this process, the particles form a heavy flock conveniently separated for the colloidal solution. For separating these flocks, any conventional method can be applied. To make the flock of the microscopic particles, three effective methodologies are necessary:

• Coagulation
• Flocculation
• Sedimentation

Coagulation

It is the process where the negative charge of the particles is either decreased or neutralised, where the suspended particles attain the zeta potential. With this process, the zeta potential (Zp) decreases, and thus the particles are aggregated and form several micro flocks. This process usually uses Van der De waals force to charge the aggregated particles to develop the micro flocks quickly.

Flocculation

It is the bridging action to take the particles in large accumulations, bringing them together and mixing them physically as a long-chain polymer system. This bridging action makes the high molecular weight particles attached to a negatively charged surface. This process usually takes around 10 to 30 minutes to bridge the negatively charged particles, depending on the particles’ water quality and molecular arrangement. 

Sedimentation

This final separation method of mixtures separates the last flock to settle down. The settled particles are easily extracted from the clarified water. The retention duration of this process is approximately 4 to 6 hours.

Centrifugation

It is a highly used process to separate any heterogeneous mixture on a practical platform. As colloids are also heterogeneous mixtures, they get separated through this method. Here the suspended solid and microscopic particles are separated through a centrifuge. This apparatus includes a tube-like holder, which is known as a rotary. Here, the separation process depends upon the viscosity, chemical properties, and density of the particles present in the colloids. Some common examples are –

• Cream from the milk
• Blood plasma and cells from blood

Conclusion

All the particles present in the colloids attain a high negative charge which creates an electrostatic repulsion between the particles. Separation of this mixture occurs by decreasing the potential repulsion charge between these particles. It is a stepwise procedure with a variation of state in particles and their charge and chemical properties.