Industrial_Screening_Mineral_Processing.pptx

Industrial_Screening_Mineral_Processing.pptx

1. Industrial Screening in Mineral Processing Understanding Screening Efficiency and Performance Factors

2. Introduction to Industrial Screening • Screening is used for size separation from 300 mm to 40 μm. • Dry screening is used for material above 5 mm, while wet screening is common down to 250 μm. • Below 250 μm, classification is often preferred due to cost and efficiency.

3. Objectives of Screening • Sizing or Classifying: Separating particles by size. • Scalping: Removing the coarsest fractions. • Grading: Preparing products within specific size ranges. • Media Recovery: Recovering magnetic media from ore. • Dewatering: Removing free moisture from slurry. • De-sliming/De-dusting: Removing fines from feed. • Trash Removal: Eliminating coarse fibers or tramp material.

4. Screen Performance and Efficiency • Screen efficiency is determined by the degree of separation based on particle size. • Efficiency formulas are derived from mass balances and relate to the performance of coarse and fine product streams. • Circulating load impacts efficiency, particularly in closed circuit operations.

5. Efficiency Calculations • Efficiency (EU) of fine product stream: EU = (f - o) / (f * (1 - o)) • Efficiency (EO) of coarse product stream: EO = (f - u) * (1 - o) / ((o - u) * (1 - f)) • Circulating Load (C) related to screen efficiency: C = 1 / (EU * f) - 1

6. Factors Affecting Screen Performance • Particle Size: Near-mesh particles reduce efficiency by clogging apertures. • Feed Rate: High feed rates reduce efficiency by forming particle beds. • Screen Angle: Affects particle velocity and dwell time, influencing passage through apertures. • Particle Shape: Irregular shapes like mica may screen poorly.

7. Vibration and Moisture Effects • Vibration: Enhances screening by throwing particles and promoting stratification. • Moisture: Damp feeds can blind screens; wet screening is preferred for finer sizes. • Screen design improvements focus on reducing moisture-related issues.