8.3 Gravity Concentration & Magnetic/Electrostatic Separation

PRC Mining Engineer Licensure Examination Philippines

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1 Chapter 1: Surface Mining Methods & Pit Optimization

1.1 Surface Mining Unit Operations & Method Selection 1.2 Bench Geometry, Slope Stability & Geotechnical Pit Design 1.3 Cut-Off Grade Optimization & Lerchs-Grossmann Pit Limits

2 Chapter 2: Underground Mining Methods & Strata Control

2.1 Underground Mining Method Classification & Selection 2.2 Rock Mechanics, Stress Analysis & Strata Control 2.3 Underground Ground Support Systems & Excavation Design

3 Chapter 3: Materials Handling, Equipment & Mine Economics

3.1 Drilling, Blasting & Explosives Engineering 3.2 Mine Loading, Haulage & Materials Handling Systems 3.3 Mine Capital (CAPEX), Operating Costs (OPEX) & Financial Evaluation

4 Chapter 4: Mine Safety, Ventilation & Philippine Mining Laws

4.1 Mine Ventilation Network Analysis & Environmental Quality 4.2 Philippine Mine Safety Rules, Health & Disaster Prevention 4.3 Philippine Mining Act of 1995 (RA 7942), DAO 2010-21 & Mining Ethics

5 Chapter 5: Physical Geology, Mineralogy & Philippine Deposit Types

5.1 Structural Geology, Tectonics & Ore Controls 5.2 Igneous, Metamorphic & Sedimentary Ore Mineralogy 5.3 Major Philippine Ore Deposit Models

6 Chapter 6: Mineral Exploration, Geophysics & Core Logging

6.1 Geochemical & Remote Sensing Exploration Techniques 6.2 Geophysical Exploration Methods in Mining Geology 6.3 Diamond Drilling, Core Logging & QA/QC Protocols

7 Chapter 7: Geostatistics, Resource Estimation & PMRC Code

7.1 Ore Body Block Modeling & Spatial Variography 7.2 Inverse Distance & Ordinary Kriging Grade Estimation 7.3 Philippine Mineral Reporting Code (PMRC 2020) & Resource Classification

8 Chapter 8: Comminution, Sizing & Physical Mineral Separation

8.1 Crushing, Grinding & Bond Work Index Calculations 8.2 Particle Screening, Hydrocyclone Classification & Sizing 8.3 Gravity Concentration & Magnetic/Electrostatic Separation

9 Chapter 9: Froth Flotation & Extractive Hydrometallurgy

9.1 Froth Flotation Chemistry, Reagents & Cell Kinetics 9.2 Leaching Technologies (Heap, Agitation & Tank) 9.3 Precious Metal Recovery: CIP, CIL, Merrill-Crowe & Electrowinning

10 Chapter 10: Process Plant Flowsheets & Environmental Tailings Management

10.1 Metallurgical Plant Flowsheets & Pulp Mass Balances 10.2 Tailings Storage Facility (TSF) Design & Dam Safety 10.3 Acid Mine Drainage (AMD) Mitigation & Environmental Protection (EPEP/FMR/DP)

11 Chapter 11: 2025 PRC Blueprint, Prospecting Tools & Exploration Decisions

11.1 Official 2025 TOS, Three-Paper Structure & Exam Strategy 11.2 Prospecting Instruments, Base Maps & Surface Geological Mapping 11.3 Integrating Direct and Indirect Evidence for Exploration Decisions

12 Chapter 12: Mine Infrastructure, Sustainable Development & Climate

12.1 Power, Water, Drainage & Support-Facility Selection 12.2 Sustainable Development, Progressive Rehabilitation & Community Impact 12.3 Mining, Climate, Reforestation, Coal & Energy-Transition Minerals

13 Chapter 13: Mine Valuation, Financial Analysis & Due Diligence

13.1 Time Value of Money, Future Value & Present Value 13.2 Financial Statements, Mine Economics & External Price Drivers 13.3 Exploration Provenance, Technical Review & Legal Due Diligence

14 Chapter 14: Mine Organization, Communication & Accountable Leadership

14.1 Line and Staff Functions in a Mining Organization 14.2 Communication With Superiors, Peers & Subordinates 14.3 Authority, Responsibility, Delegation & Safety Accountability

15 Chapter 15: Philippine Mining Law, Indigenous Rights & Professional Ethics

15.1 Legal Hierarchy, Mineral Tenure & Compliance Analysis 15.2 Constitutional Participation, IPRA, FPIC & Ancestral Domains 15.3 RA 4274, Professional Scope, Ethics & Document Integrity

16 Chapter 16: Applied Mathematics & Mine Surveying

16.1 Engineering Mathematics for Safe, Efficient Mine Decisions 16.2 Survey Control, Instruments, Traverses & Error Adjustment 16.3 Topographic Maps, Underground Set-Out & Survey Timeliness

17 Chapter 17: Feasibility Studies, Data Quality & Project Decisions

17.1 Scoping, Pre-Feasibility & Final Feasibility Study Maturity 17.2 Data Accuracy, Assumption Control & Go/No-Go Decisions 17.3 Multidisciplinary Integration, Interfaces & Independent Review

18 Chapter 18: Mining Computer Applications, Digital Control & Global Developments

18.1 Computer Functions, Office Applications & Data Governance 18.2 Geological Modeling, Mine Planning, Scheduling & Valuation Software 18.3 Real-Time Control, Critical Minerals & Regional Mining Developments

19 Chapter 19: Earth Systems, Geologic Time & Philippine Hazards

19.1 Solar-System Origin, Earth Interior & Atmospheric Layers 19.2 Rock Cycle, Landforms & the Geologic Time Scale 19.3 Philippine Tectonics, Geologic Hazards & Mitigation

20 Chapter 20: Metallurgy, Foundry Practice & Assaying

20.1 Extractive, Physical & Adaptive Metallurgy Principles 20.2 Foundry Materials, Casting, Solidification & Defects 20.3 Sampling, Fire Assay, Cupellation, Parting & Assay Calculations

21 Chapter 21: Solid–Liquid Separation, Environmental Law & Mine Ecology

21.1 Thickening, Filtration & Solid–Liquid Separation 21.2 Philippine Air, Water, Waste & Hazardous-Substance Controls 21.3 Mine Ecology, Closure, Tailings, Waste & Community Livelihood

8.3 Gravity Concentration & Magnetic/Electrostatic Separation

Key Takeaways Explain This Topic AI

Concentration Criterion (CC = [rho_h - rho_f] / [rho_l - rho_f]) is a density-contrast screening tool, not a guaranteed size or recovery limit; liberation, size, shape, viscosity, throughput, and equipment determine actual separability.

Gravity concentration devices utilize fluid motion and differential density: jigs apply vertical pulsating currents, shaking tables use differential reciprocating motion and liquid film flow, and spirals leverage centrifugal and drag forces.

High-G centrifugal concentrators such as Knelson and Falcon units enhance recovery of fine, dense liberated particles, but achievable size and recovery depend on liberation, operating settings, feed preparation, and mineral properties.

Magnetic separation exploits susceptibility and field-gradient response; LIMS commonly recovers strongly magnetic magnetite, while higher-intensity or high-gradient systems may recover weaker minerals, with field ranges and performance equipment- and feed-specific.

Electrostatic separation differentiates particles by electrical conductivity via corona discharge (high-tension roll separators) or contact electrification (triboelectric separators), widely applied in titaniferous beach sand and chromite processing.

Last updated: August 2026

Gravity Concentration & Magnetic/Electrostatic Separation

Physical mineral separation techniques exploit intrinsic physical property differences between valuable minerals and barren gangue without altering chemical structures. The primary physical property differentials exploited in mineral dressing are specific gravity (density), magnetic susceptibility, and electrical conductivity. These methods can provide low-reagent preconcentration or recovery alternatives to flotation, but water, energy, dust, medium loss, tailings, and equipment impacts still require management.

Concentration Criterion & Gravity Concentration Theory

Gravity concentration separates mineral particles based on differential movement in response to gravity and fluid drag forces. The feasibility of wet gravity separation is predicted by the empirical Concentration Criterion ( C C CC CC ) : C C = ρ h − ρ f ρ l − ρ f CC = \frac{\rho_h - \rho_f}{\rho_l - \rho_f} CC = ρ l ​ − ρ f ​ ρ h ​ − ρ f ​ ​

Where:

• ρ h \rho_h ρ h ​ = Specific gravity of the heavy mineral ( g/cm 3 \text{g/cm}^3 g/cm 3 )
• ρ l \rho_l ρ l ​ = Specific gravity of the light gangue mineral ( g/cm 3 \text{g/cm}^3 g/cm 3 )
• ρ f \rho_f ρ f ​ = Density of the fluid medium (Water = 1.0 g/cm 3 1.0\ \text{g/cm}^3 1.0 g/cm 3 )
• Operational Rules for Gravity Separation Feasibility

Concentration Criterion ( C C CC CC ) Screening interpretation

High CC Density contrast is favorable and justifies gravity testwork.

Intermediate CC Separation becomes progressively more sensitive to feed sizing, liberation, shape, and device selection.

CC near 1 Density contrast alone offers little selectivity; another property or preconditioning may be needed.

Published CC-to-size tables are empirical heuristics, not physical guarantees. Use representative partition or recovery tests at the actual size distribution and solids conditions before declaring technical or commercial feasibility.

Gravity Separation Equipment & Mechanisms

Jigs (Harz, Denver, Pan-American Jigs) : Utilize vertical pulsation of water through a fixed screen basket, stratifying particles by differential acceleration, hindered settling, and consolidation trickling. Used for coarse lead, zinc, and alluvial tin ores ( 1 – 25 mm 1\text{--}25\ \text{mm} 1 – 25 mm ).

Wilfley Shaking Tables : Consist of a gently sloped wooden deck covered with linoleum or rubber and fitted with longitudinal riffles. An asymmetrical reciprocating motion (slow forward stroke, rapid return stroke) pushes heavy mineral particles along the riffle troughs, while a cross-flowing water film washes light gangue down over the riffles. Achieves sharp separation for fine feeds ( 0.05 – 2.0 mm 0.05\text{--}2.0\ \text{mm} 0.05 – 2.0 mm ).

Spiral Concentrators (Humphreys Spirals) : Open helical vertical sluices with a modified semicircular cross-section. As pulp flows downward, high-velocity fluid carries light gangue toward the outer rim under centrifugal force, while low-velocity fluid allows heavy minerals to concentrate along the inner radius, where splitter gates collect concentrate.

Centrifugal High-G Concentrators (Knelson & Falcon Concentrators) : Use a rapidly rotating bowl to multiply the settling force on dense particles. Depending on the model, fluidization and bowl geometry retain a dense bed and can recover fine liberated free gold. No universal lower size or recovery follows from nominal g-force; test liberation, feed rate, fluidization, cycle time, and concentrate mass pull.

Heavy Media Separation (HMS / DMS) : A Float-Sink process utilizing an artificial dense liquid suspension (milled ferrosilicon, SG = 6.8 \text{SG} = 6.8 SG = 6.8 , or magnetite, SG = 5.0 \text{SG} = 5.0 SG = 5.0 ) diluted in water to establish an intermediate medium density ρ m \rho_m ρ m ​ . Heavy ore sinks while light waste floats. Used extensively for pre-concentrating coal, iron ore, and diamonds.

Magnetic Separation Principles & Machinery

Magnetic separation isolates minerals based on differences in magnetic susceptibility ( χ \chi χ ), which determines the magnetic force ( F m F_m F m ​ ) exerted in an inhomogeneous magnetic field gradient: F m = V ⋅ χ ⋅ H ⋅ d H d x F_m = V \cdot \chi \cdot H \cdot \frac{dH}{dx} F m ​ = V ⋅ χ ⋅ H ⋅ d x d H ​

Where V V V is particle volume, H H H is magnetic field intensity, and d H d x \frac{dH}{dx} d x d H ​ is field gradient.

Mineral Magnetic Classification

Ferromagnetic : Strongly attracted by weak magnetic fields (e.g., Magnetite Fe 3 O 4 \text{Fe}_3\text{O}_4 Fe 3 ​ O 4 ​ , Pyrrhotite Fe 1 − x S \text{Fe}_{1-x}\text{S} Fe 1 − x ​ S ). Recovered using Low-Intensity Magnetic Separators (LIMS) operating below 0.3 Tesla 0.3\ \text{Tesla} 0.3 Tesla ( 3 , 000 Gauss 3,000\ \text{Gauss} 3 , 000 Gauss ).

Paramagnetic : Weakly attracted in strong magnetic fields (e.g., Hematite Fe 2 O 3 \text{Fe}_2\text{O}_3 Fe 2 ​ O 3 ​ , Ilmenite FeTiO 3 \text{FeTiO}_3 FeTiO 3 ​ , Chromite FeCr 2 O 4 \text{FeCr}_2\text{O}_4 FeCr 2 ​ O 4 ​ , Wolframite). Recovered using High-Intensity Magnetic Separators (HIMS) operating between 1.0 1.0 1.0 and 2.5 Tesla 2.5\ \text{Tesla} 2.5 Tesla ( 10 , 000 – 25 , 000 Gauss 10,000\text{--}25,000\ \text{Gauss} 10 , 000 – 25 , 000 Gauss ).

Diamagnetic : Repelled by magnetic fields (e.g., Quartz SiO 2 \text{SiO}_2 SiO 2 ​ , Calcite CaCO 3 \text{CaCO}_3 CaCO 3 ​ , Feldspar, Zircon). Report to non-magnetic tailings.

Magnetic Separator Configurations

Wet Drum LIMS : Revolving non-magnetic stainless steel drum containing internal permanent magnet arcs. Used in Concurrent (coarse feed), Counter-Rotation (heavy magnetite recovery), and Counter-Current (fine slurry) configurations.

High-Gradient Magnetic Separators (HGMS) : Utilize magnetized stainless steel wool matrix filters inside high-field solenoids to trap fine weakly paramagnetic slimes.

Electrostatic & High-Tension Separation

Electrostatic separation differentiates minerals based on electrical conductivity and surface charge retention.

High-Tension Corona Discharge Separator

Ore particles are fed as a thin dry layer onto a grounded rotating metal drum exposed to an ionizing corona wire charged at 20 – 50 kV 20\text{--}50\ \text{kV} 20 – 50 kV .

Conductive Particles (e.g., Rutile, Ilmenite, Magnetite): Rapidly transfer their acquired charge to the grounded metal drum upon contact. Uncharged, they are thrown off the drum by centrifugal force into the conductor collector hopper.

Non-Conductive Particles (e.g., Zircon, Monazite, Quartz): Retain their surface charge and become electrostatically pinned to the drum by image charges. Pinned particles travel to the underside of the drum, where a rotating brush sweeps them into the non-conductor hopper. Dry Feed Hopper

• |
• v
• +---------------------+ <-- Corona Electrode
• | High-Voltage | (20-50 kV Ionizing)
• | Corona Discharge |
• +----------+----------+
• |
• v
• +-----------------------------------------------+ <-- Grounded
• | Rotating Grounded Metal Drum | Drum
• +-------+-------------------------------+-------+
• | |
• v v
• (Centrifugal Throw) (Pinned / Brushed)
• +---------------------------+ +----------------------------+
• | Conductors (Rutile, FeTiO3)| | Non-Conductors (Zircon,SiO2)|
• +---------------------------+ +----------------------------+
• Philippine Mining Industrial Context

Physical mineral separation plays a vital role in Philippine mining operations:

Northern Luzon Magnetite Sands (Cagayan, Ilocos) : Exploits heavy beach sand placer deposits using wet dredge pumps, spirals for pre-concentration, and drum LIMS to produce high-grade magnetite concentrates ( > 62 % Fe >62\%\ \text{Fe} > 62% Fe ).

Zambales & Dinagat Chromite Dressing : Utilizes shaking tables and spiral concentrators to separate high-density chromite ( SG = 4.5 – 4.8 \text{SG} = 4.5\text{--}4.8 SG = 4.5 – 4.8 ) from serpentine gangue ( SG = 2.5 – 2.7 \text{SG} = 2.5\text{--}2.7 SG = 2.5 – 2.7 ), followed by dry high-tension separators to upgrade metallurgical-grade lump chromite.

Comparative Summary of Physical Separation Methods

Separation Technology Primary Physical Property Equipment Examples Particle Size Limits Typical Application

Gravity Concentration Specific gravity differential Jigs, Wilfley Tables, Spirals 0.05 mm to 25 mm Gold, chromite, alluvial tin

Centrifugal Concentration SG differential in high-G field Knelson, Falcon Concentrators 0.005 mm to 1.5 mm Free gold, PGM recovery

Heavy Media (DMS) Bulk media density ( ρ m \rho_m ρ m ​ ) Drum separators, DSM Cyclones 2 mm to 100 mm Coal washing, diamond DMS

Low-Intensity Magnetic High magnetic susceptibility Drum LIMS (<0.3 T) 0.01 mm to 10 mm Magnetite sand, iron ore

High-Intensity Magnetic Weak magnetic susceptibility Induced Roll, HGMS (>1.0 T) 0.002 mm to 3 mm Ilmenite, hematite, silica sand

High-Tension Separation Electrical conductivity Corona roll separators 0.075 mm to 1 mm Titanium minerals, zircon sands