Difference Between Flocculation and Precipitation

Main Difference – Flocculation vs Precipitation

Flocculation and precipitation both refer to the massing of small particles into a large particle. But there are differences between the two terms. Flocculation is used in water treatment plants along with coagulation techniques in order to remove suspended particles in water. Precipitation has many applications in both laboratory scale and industrial scale. The main difference between flocculation and precipitation is that flocculation forms floccules whereas precipitation forms precipitates.

Key Areas Covered

1. What is Flocculation
     – Definition, Sedimentation, Uses
2. What is Precipitation
     – Definition, Properties
3. What is the Difference Between Flocculation and Precipitation
     – Comparison of Key Differences

Key Terms: Flocculating Agent, Flocculation, Floccules, Flocculated Suspension, Precipitant, Precipitate, Precipitation, Sedimentation, Suspension

What is Flocculation

Flocculation is the process in which colloids in a suspension can be obtained in an aggregated form. These aggregates then act as large individual particles. The aggregates formed in flocculation are known as floccules. Flocculation can occur either spontaneously or due to the presence of a flocculating agent.

Figure 1: Flocculation

A flocculated suspension is a suspension where flocculation has occurred. These suspensions show a high rate of sedimentation. This means, the floccules sediment faster than in a deflocculated suspension. The sediment formed has a higher volume than expected because the floccules are porous and can entrap liquid while settling to the bottom of the suspension.

Flocculation causes the increase of particle size in a suspension. This change is observable as it changes the particle size from microscopic to macroscopic scale.  Floccules are often visible to naked eye.

A common use of flocculation is the coagulation-flocculation treatment for drinking water and wastewater. Water from natural sources and industrial waste are composed of dissolved chemicals and suspended particles. Coagulation is used to remove charged particles present in the water. Coagulants with opposite charges are used for this. Flocculation is the next step in the water treatment. There, a gentle mixing is done to allow the formation of floccules. Then these floccules are allowed to settle down. Then the sediment can be removed.

What is Precipitation

Precipitation is the formation of an insoluble solid mass in a liquid solution; this insoluble solid mass is called the precipitate. A precipitate is formed when two soluble ionic compounds are mixed. Soluble ionic compounds can break into their ions in the solution. Then these ions can react with each other to form a precipitate or stay as a solubilized ion in that solution. The chemical species that cause this precipitation is called precipitants.

In addition, precipitates can form when the temperature of the solution is lowered. The low temperature reduces the solubility of salts, causing them to precipitate in the solution. The formed precipitate may stay as a suspension in the solution if there isn’t sufficient gravity. But later on, the precipitate particles will sediment to the bottom of the container unless disturbed.

Figure 2: AgCl Precipitate Formation

Precipitation is a very important phenomenon since the formed precipitate is visible. The formation of a precipitate can indicate the presence of a chemical reaction. For example, the reaction between silver nitrate (AgNO₃) and sodium chloride (NaCl) will form a white precipitate of silver chloride (AgCl).

Difference Between Flocculation and Precipitation

Definition

Flocculation: Flocculation is the process in which colloids in a suspension can be obtained in an aggregated form.

Precipitation: Precipitation is the formation of an insoluble solid mass in a liquid solution.

End Product

Flocculation: Flocculation forms floccules.

Precipitation: Precipitation forms precipitates.

Applications

Flocculation: Flocculation is used in water treatment plants.

Precipitation: Precipitation is used in both industrial scale and laboratory scale applications.

Liquid Phase

Flocculation: Liquid phase in which flocculation takes place is a suspension.

Precipitation: Liquid phase in which precipitation takes place is a clear solution.

Causes

Flocculation: Flocculation can occur spontaneously or due to flocculating agents.

Precipitation: Precipitation occur due to reaction between precipitants.

Method

Flocculation: Flocculation can be done by gentle mixing.

Precipitation: Precipitation can be done by adding a precipitant.

Conclusion

Flocculation and precipitation form large solid mass out of small masses. Flocculation is the process of formation of solid aggregates from small particles. Precipitation is the process of formation of an insoluble solid mass. The main difference between flocculation and precipitation is that flocculation forms floccules whereas precipitation forms precipitates.

References:

1. “Coagulation-Flocculation.” Coagulation-Flocculation | SSWM, Available here.
2. “Precipitation Reactions.” Chemistry LibreTexts, Libretexts, 11 Nov. 2017, Available here.
3. Helmenstine, Anne Marie, Ph.D. “Precipitate Definition and Example in Chemistry.” ThoughtCo, Feb. 11, 2017, Available here.

Image Courtesy:

1. “Flocculation” By Brittany2442 – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Silver chloride (AgCl)” By Luisbrudna – Own work (CC BY-SA 4.0) via Commons Wikimedia