Introduction:
Flocculation is a process used to separate suspended particles from water by causing them to come together and form larger particles called flocs. This is achieved by the addition of a flocculant, which promotes the aggregation of particles and improves their settling characteristics. In the case of iron removal from water, the addition of lime is commonly used as a flocculant.

Explanation:
The process of flocculation of iron from water by the addition of lime can be categorized as chemical precipitation. Here's why:

1. Chemical precipitation:
Chemical precipitation is a process in which a chemical reactant is added to water to form a solid precipitate that is insoluble and can be easily separated. In the case of iron removal, the addition of lime (calcium hydroxide) raises the pH of water, which promotes the precipitation of iron as iron hydroxide. The reaction can be represented as follows:

Fe2+ + 2OH- → Fe(OH)2↓

The formed iron hydroxide precipitates out of the solution and can be easily separated by sedimentation or filtration.

2. Lime as a flocculant:
Lime (calcium hydroxide) is commonly used as a flocculant in water treatment processes. When added to water, lime reacts with the dissolved carbon dioxide to form calcium carbonate, which acts as a coagulant aid. The reaction can be represented as follows:

Ca(OH)2 + CO2 → CaCO3 + H2O

The calcium carbonate formed acts as a seed for the aggregation of suspended particles, including iron. As lime is added, the pH of water increases, which promotes the formation of larger flocs and enhances the settling characteristics of iron particles.

3. Iron removal:
Iron is often present in water sources as dissolved ferrous ions (Fe2+). These ions can be oxidized to form insoluble ferric hydroxide (Fe(OH)3) by the addition of an oxidizing agent such as chlorine or oxygen. Once oxidized, the ferric hydroxide can be flocculated and removed from the water by the addition of lime.

Conclusion:
In summary, the flocculation of iron from water by the addition of lime is an example of chemical precipitation. Lime acts as both a flocculant and a coagulant aid, promoting the formation of larger flocs and enhancing the settling characteristics of iron particles. The formed iron hydroxide precipitates out of the solution, allowing for its easy separation from water.