Solid–liquid separation from slurries:\nWhich equipment is primarily used to separate coarse particles from a slurry containing fine particles?

Difficulty: Easy

Correct Answer: Classifiers

Explanation:


Introduction / Context:
Slurry processing often requires splitting a mixed particle-size distribution into coarse and fine fractions prior to grinding, flotation, or thickening. Different devices target different size ranges and cut sharpness. Understanding which unit prioritises coarse removal assists in designing crushing–classification circuits in minerals and chemical processing.


Given Data / Assumptions:

  • Feed is a slurry containing a wide size distribution.
  • Goal is to remove or separate the coarse particles.


Concept / Approach:
Classifiers (e.g., rake, spiral) rely on gravity settling in a controlled flow to return coarse particles (sands) while allowing fines (slimes) to overflow. Hydrocyclones can make fine cuts but are often used for finer separations and can misplace coarse in some conditions. Thickeners concentrate fines by settling but are not designed as precise classifiers. Decanters remove liquid from slurry but provide limited size discrimination compared with dedicated classifiers.


Step-by-Step Solution:

Identify target: preferential removal of coarse solids.Match process: gravitational classification with rakes/spirals suits coarse splits.Choose “Classifiers.”


Verification / Alternative check:
Standard grinding circuits pair ball mills with spiral classifiers to close the loop on coarse recirculation, underscoring their role in coarse/fine separation.


Why Other Options Are Wrong:

  • Thickeners: concentrate fines but not designed for sharp coarse/fine classification.
  • Hydrocyclones: often used for finer cut sizes; may be acceptable but not “primarily” for coarse removal in classic teaching.
  • Decanters/clarifiers: focus on liquid–solid split, not selective coarse removal.


Common Pitfalls:
Assuming all settlers are equivalent; classifiers are tuned to size-based return/overflow duties.


Final Answer:
Classifiers

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