What is difference between flocculation and precipitation?

Answer 1

Precipitaion

Lets take protein in water as a solution as an example. Protein consists of hydrophobic amino acids and hydrophilic amino acids. Hydrophobic amino acids are usually seen in the protein core and hydrophilic aminoacids forms hydrogen bond with water molecules. When an organic solvent, or salt is added to the solution water molecules which are in hydrogen bond with the hydrophilic amino acids break the bond and binds with the salt or solvent. Thus protein protein interaction becomes stronger than protein -water interaction. So due to partial dipole interaction and electrostatic force of attraction protein molecules aggregate and precipitate.

Flocculation

Consider a solution of proteins. If the solution is agitated continuously the protein molecules come together. If the agitation is that stronger effect to overcome the electrostatic force of repulsion between the protein molecules, they will cling together and forms floc. Another method is adding chemicals called flocculants. By adding floculants the electrostatic repulsion between the protein molecules can be reduced and this will lead to attraction of protein molecules and formation of floc.

Answer 2

Flocculation is the process of particles coming together to form larger clumps, which can then settle out of a solution. Precipitation is the formation of a solid within a solution that becomes insoluble and settles out. In flocculation, the particles remain suspended in the solution, while in precipitation, the particles solidify and settle to the bottom.