What exactly is flocculation? Simply put it is an aggregation process in which many small particles coalesce into a small number large flocs – hence flocculation. It is a process that occurs naturally in nature (for example, snowflake formation) but it can also be deliberately engineered for various purposes, typically as part as a biotechnology, petroleum, paper or mining industry process.
In the first step, coagulation chemicals are added to the sample to adsorb to the small particles and nullify their surface charges. This is necessary because the negative surface charges of such small particles prevent aggregation and settling. When opposing charges are added to the mixture, the particles can stick together to form the large, stable and well suspended submicron flocs which are the aim of this exercise. In order to ensure the coagulant chemicals are properly dispersed in the solution, as well as the particle collision which results in submicron floc formation, rapid mixing is required
The second step, the actual flocculation into the large aggregates, requires more prolonged gentle mixing – as well as the addition of a high molecular weight flocculant. This flocculant adsorbs to the submicron flocs and bridges the gaps between them. As the particles are drawn closer together Van Der Walls forces come into play, attracting them closer together and overcoming the energy barrier to flocculation. Loosely packed flocs consequently form. Aggregation, increased bonding, and strengthening the flocs proceeds until the visibly suspended macroflocs form. Once the flocs reach the proper weight and size sedimentation of the macroflocs occurs. Beware, however, that macroflocs are super-sensitive to mixing. Once they are torn apart by shear forces it's next to impossible for them to reform.
As you can see, Floc formation, though based on a natural process requires careful and substance specific intervention. Merkel will be happy to assist you in selecting the proper coagulants and flocculants for your particles as well as to advise you on the best mixing protocol for efficient flocculation and sedimentation.