Qwestrum Engineering360 · Mining & Metallurgy · Mineral Processing
Screening and Classification
Screening separates by size aperture; efficiency E measures mass reporting to correct fraction. Hydrocyclones classify fines by centrifugal field — cut size d50 set by spigot, vortex finder, and feed pressure in closed grinding circuits.
Exam tip: keep SI units consistent end-to-end, write the governing relation symbolically before substituting, and sanity-check magnitude and sign.
Key formulas & points
Skim these first — then read the full notes below.
- Vibrating screens by aperture size
- Hydrocyclone size by spigot/vortex finder
- Closed circuit grinding control
Topic details
Introduction
Indian concentrators use vibrating screens ahead of secondary crushers and after mills. Circulating load 200–400% common in ball mill circuits — higher CL increases mill throughput but also overgrinding fines.
Scope in B.Tech and GATE syllabus
Hydrocyclone d50 controlled by spigot diameter (coarser if larger) and feed density. Singh & Singh mineral processing labs demonstrate sieve analysis and efficiency calculation.
Key relations & formulas
Formulas (Indian textbook notation)
Formulas (Indian textbook notation)
Formulas (Indian textbook notation)
Notation and sign conventions
Relation 1 —
Formulas (Indian textbook notation)
Write this relation with symbols exactly as in Wills Mineral Processing — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 2 —
Formulas (Indian textbook notation)
Write this relation with symbols exactly as in Wills Mineral Processing — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 3 —
Formulas (Indian textbook notation)
Write this relation with symbols exactly as in Wills Mineral Processing — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Fundamentals and definitions
Screen efficiency E = (mass correctly placed) / (total feed mass) × 100% — imperfect separation due to blinding, pegging, and near-size particles. Efficiency never 100% — aim 85–95% on industrial screens.
Governing relations in practice
d50 cut size: 50% of feed particles of size d50 report to underflow (cyclone) or pass screen aperture. Sharpness depends on hydrodynamics or screen mesh tolerance.
Design and analysis considerations
Circulating load CL = recycle to mill / new feed × 100%. High CL keeps mill full of grinding media contact — increases capacity until classification limit. Monitor pulp density and cyclone pressure.
Advanced theory and extensions
Vibrating screen: stroke, frequency, deck angle affect capacity and efficiency. Hydrocyclone: vortex finder pulls coarse to overflow in some configurations — verify convention in problem statement.
Assumptions and validity limits
State assumptions explicitly before using any relation for screening and classification — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.
Wrong assumptions invalidate the entire solution even when the formula is correct. In Mineral Processing viva and GATE descriptive questions, listing valid assumptions often earns separate marks.
Step-by-step problem approach
1. Read the question and list given data with SI units (common in Mineral Processing papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to screening and classification.
4. Use equation 1:
5. Use equation 2:
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to screening and classification.
4. Use equation 1:
.
5. Use equation 2:
.
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.
Applications & exam relevance
Screening and Classification appears in beneficiation plants. In Indian mining curricula this topic is tested because it connects theory to comminution and separation.
GATE and semester exams often combine screening and classification with earlier units — revise prerequisites before attempting mixed problems.
Industry interview panels sometimes ask: "Where did you use screening and classification?" — answer with a lab, mini-project, or plant visit example if possible.
Common mistakes in exams
• Efficiency > 100% from wrong mass balance
• Confusing cyclone overflow vs underflow coarse fraction
• CL calculated on volume not mass basis
• d50 as aperture size without 50% passing definition
• Confusing cyclone overflow vs underflow coarse fraction
• CL calculated on volume not mass basis
• d50 as aperture size without 50% passing definition
Quick revision checklist
Before attempting screening and classification problems, confirm you can:
1. Vibrating screens by aperture size
2. Hydrocyclone size by spigot/vortex finder
3. Closed circuit grinding control
2. Hydrocyclone size by spigot/vortex finder
3. Closed circuit grinding control
Revise the solved examples in Wills Mineral Processing — Standard reference and one previous-year GATE or university paper for this unit.
Worked examples
Try the problem first — open the solution when you are ready to check.
Guided practice — Screening and Classification
Problem
A standard Mineral Processing numerical on screening and classification supplies given data in SI units. Using efficiency E = and cut size d50 at 50% passing, find the unknown quantity and state whether the result is physically reasonable.
Solution
1. List all given quantities with units (convert to SI if needed).
2. Draw a neat labelled diagram — diagram marks are common in Indian B.Tech papers.
3. Select
4. Substitute values, compute, and attach correct units.
5. Sanity-check: magnitude, sign, and direction must match comminution and separation.
2. Draw a neat labelled diagram — diagram marks are common in Indian B.Tech papers.
3. Select
and write it symbolically before substitution.
4. Substitute values, compute, and attach correct units.
5. Sanity-check: magnitude, sign, and direction must match comminution and separation.
Cross-check with solved examples in your Mineral Processing textbook.
Conceptual check — Screening and Classification
Problem
In a Mineral Processing semester or GATE paper you are asked: "State the main assumption, the governing relation, and one practical consequence of screening and classification." What should a complete answer include?
📖 Standard books (India)
Wills Mineral Processing — Standard reference
Read: Syllabus unit
Referenced in Indian B.Tech syllabus
Explore related topics
See real mining & metallurgy careers
After exams and interviews, see how engineers actually built careers — milestones and decisions from people in the field.