Coagulation Process Explained

This solution analyzes the statements regarding the coagulation process in water treatment to identify the correct ones.

Statement Analysis

• A. Coagulation makes smaller colloids to adhere to each other to form large floc particles. This statement is correct. Coagulation is the process where destabilized colloidal particles aggregate to form larger, settleable flocs.
• B. Colloids are continually involved in Brownian movement. This statement is correct. Brownian movement, the random motion of colloidal particles due to collisions with molecules of the medium, helps keep them dispersed but also facilitates particle collisions necessary for coagulation.
• C. Colloids are stable because of their surface charge. This statement is correct. The surface charge (typically negative) on colloidal particles creates electrostatic repulsion, preventing aggregation and maintaining stability. Coagulation overcomes this repulsive force.
• D. Coagulants are preferably trivalent cations. This statement is correct. Trivalent cations, such as Aluminum (e.g., $Al^{3+}$ in alum) and Iron (e.g., $Fe^{3+}$ in ferric chloride), are highly effective coagulants because they can neutralize charges and destabilize colloids efficiently, following theleftharpoons rule.
• E. Coagulants are soluble in neutral pH. This statement is incorrect. While solubility varies, many common coagulants like aluminum sulfate and ferric chloride become less soluble or precipitate significantly as the pH approaches neutral or becomes alkaline. Optimal coagulation often requires specific pH ranges, and precipitation can hinder their effectiveness.

Conclusion

Based on the analysis, statements A, B, C, and D are correct. Statement E is incorrect.

Therefore, the correct option includes statements A, B, C, and D only.