Flocculation chemistry: which substance listed is not used as a surface-active agent or coagulant aid in flocculation operations?

Introduction / Context:
Flocculation and coagulation aggregate fine suspended particles so they can be separated more easily. Common agents include inorganic coagulants (alum, lime), coagulant aids (sodium silicate), and polymers. The question asks you to spot the item that is not a flocculation reagent at all.

Given Data / Assumptions:

• Aim: identify non-reagent among listed items.
• Surface-active or coagulant aids help aggregation by charge neutralization or bridging.

Concept / Approach:
Sodium silicate can act as a coagulant aid or dispersant depending on context. Lime adjusts pH and supports coagulation/precipitation. Alumina (or alum) forms hydroxide flocs aiding sweep coagulation. Quartz is simply silica mineral (sand), not a chemical flocculant or surface-active agent used to induce flocculation.

Step-by-Step Solution:
Identify chemicals with roles in coagulation/flocculation: sodium silicate, lime, alumina.Recognize quartz as inert mineral filler, not a reagent in flocculation chemistry.Select “Quartz.”

Verification / Alternative check:
Standard water treatment references list alum, ferric salts, lime, polymers, and aids like sodium silicate—never quartz—as flocculants.

Why Other Options Are Wrong:
Sodium silicate, lime, alumina: all function in coagulation/flocculation processes.

Common Pitfalls:
Confusing “silica” (as a fine colloid to be removed) with reagents that promote its removal.

Final Answer:
Quartz