Liquid–solid separation terminology: the operation that splits a suspension into a clear supernatant liquid and a denser underflow slurry is called

Introduction / Context:
Process engineers frequently handle suspensions that must be separated into a clear liquid and a concentrated slurry. Correct terminology avoids confusion when specifying thickeners, clarifiers, and conditioning steps. Two distinct ideas are particle aggregation (coagulation/flocculation) and separation by gravity (sedimentation/clarification).

Given Data / Assumptions:

• Feed: a dilute suspension of solids in a liquid.
• Objective: obtain a clear supernatant and a concentrated underflow (slurry).
• No chemical addition implied unless stated.

Concept / Approach:
Sedimentation is the gravitational settling of particles, yielding a clear supernatant above and a denser slurry below. Clarification refers to the overall process of producing a clear liquid (often the supernatant product), sometimes used as a broader term. Coagulation and flocculation are pretreatments that alter particle interactions to enhance settling but are not the separation itself.

Step-by-Step Solution:
Identify the physical phenomenon: gravitational settling of suspended particles.Name the operation: sedimentation (in thickeners/clarifiers).Recognize that coagulation/flocculation are chemical conditioning steps, not the separation outcome.

Verification / Alternative check:
Thickener design equations (e.g., batch settling tests) use sedimentation velocities to size equipment for achieving the required split between supernatant and underflow—reinforcing that the separation is sedimentation.

Why Other Options Are Wrong:
Coagulation: neutralizes charges using coagulants; not the final separation step.Flocculation: builds larger flocs via polymers; a conditioning step.Clarification: often the name of the process goal (clear liquid), but the physical operation producing the split is sedimentation.

Common Pitfalls:
Using “clarification” and “sedimentation” interchangeably; while common in industry, exam questions typically reserve “sedimentation” for the gravity-driven split into supernatant and slurry.

Final Answer:
sedimentation