Difference Between Flocculent and Coagulant

Flocculent vs Coagulant

Mixture is a collection of different substances, which are physically combined, but do not join chemically. Mixtures show different physical or chemical properties than the individual substances. Solid, gaseous, or liquid substances are mixed in different ratios, in these mixtures. The state of the particles in these mixtures may vary and, depending on that, there are different types of mixtures as solutions, colloids, etc. Coagulation and flocculation are two methods to separate out the suspended particles in a solution. Coagulants and flocculants are formed to assist these processes. Though coagulation and flocculation are used interchangeably, they are two distinct processes.


Colloidal solution is seen as a homogeneous mixture, but it can be heterogeneous as well (e.g. milk, fog). The particles in colloidal solutions are of intermediate size (larger than molecules) compared to particles in solutions and suspensions. However, as the particles are in solutions, they are invisible to the naked eye and cannot be filtered using a filter paper. The particles in a colloid are termed as dispersed material, and the dispersing medium is analogous to the solvent in a solution. The particles are distributed within the colloidal medium, and do not settle down if it is left still. Colloidal solutions are translucent or opaque. Sometimes particles in a colloid can be separated out by centrifugation or coagulation.

Coagulation means a process where the dispersed colloidal particles agglomerate. The suspended particles are usually very small in size, and they may have electrical charges on them or between particles. Usually these are negative charges, which cause them to repel each other. Coagulants are used to neutralize these charges. They neutralize the repulsive electrical charges between the small particles by surrounding them. This allows the particles to come together and form larger clumps. Cationic coagulants are largely used for this. After coagulants are added, the mixture should be rapidly mixed in order to disperse the coagulants throughout the liquid. Coagulants can be metallic salts (e.g. alum) or polymers. Polymers can be cationic, anionic or nonionic.


Flocculants are also added to facilitate the settling of suspended particles in a solution. Flocculants facilitate the agglomeration and, therefore, make larger floccules. These tend to settle down due to gravitational force. Flocculants try to bridge the molecules forming clumps. For example, an anionic flocculent will react with a positively charge polymer and will adsorb those particles. This may cause destabilization due to charge neutralization or bridging. In flocculation, flocculants are added slowly and mixed gently. Therefore, small flocs can agglomerate into larger particles.


What is the difference between Flocculent and Coagulant?

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