9.2 Leaching Technologies (Heap, Agitation & Tank)

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

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

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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

9.2 Leaching Technologies (Heap, Agitation & Tank)

Key Takeaways Explain This Topic AI

Shrinking-core equations can test whether film transfer, product-layer diffusion, or surface reaction is rate-controlling, but apparent activation-energy ranges are diagnostic evidence rather than hard universal boundaries.

Heap-leach containment, drainage, lift height, agglomeration, irrigation, water balance, and leak detection are designed from ore tests, climate, foundation, chemistry, consequence, and current permit requirements; liner and application-rate details are site-specific.

High-Pressure Acid Leach (HPAL) extracts nickel and cobalt from tropical limonite laterites at 240 ∘ C − 270 ∘ C 240^\circ\text{C} - 270^\circ\text{C} 24 0 ∘ C − 27 0 ∘ C and 4.0 − 5.5 MPa 4.0 - 5.5 \text{ MPa} 4.0 − 5.5 MPa operating pressure using sulfuric acid in titanium-lined autoclaves.

Coral Bay Nickel Corporation (CBNC) in Palawan and Taganito HPAL Corporation (THPAL) in Surigao del Norte are landmark Philippine HPAL plants producing Mixed Sulfide Precipitate (MSP).

Bio-oxidation and bioleaching commonly use acidophilic microbial consortia, which may include Acidithiobacillus ferrooxidans, to regenerate ferric iron and oxidize reduced sulfur; performance depends on mineralogy, temperature, acidity, oxygen, nutrients, and inhibition.

Last updated: August 2026

Extractive hydrometallurgy involves the selective dissolution of valuable metals from crushed or ground ores using aqueous lixiviant solutions, followed by purification and metal recovery. Hydrometallurgical processing is increasingly applied to low-grade, complex, or oxide ores that are unsuited for conventional pyrometallurgical smelting or mineral flotation.

Thermodynamics, Mass Transfer & Kinetic Rate Models

The dissolution of a solid mineral particle in an aqueous lixiviant is a heterogeneous solid-liquid reaction. The process is commonly described by the Shrinking Core Model , which involves five sequential steps:

Diffusion of lixiviant reactants through the liquid boundary layer surrounding the particle.

Diffusion of reactants through any porous solid product layer (leached ash shell).

Chemical reaction at the unreacted mineral core interface.

Diffusion of soluble reaction products outward through the product layer.

Diffusion of reaction products back into the bulk solution.

The overall leaching rate is governed by either diffusion control (where mass transfer across the fluid film or porous shell limits the rate) or chemical reaction control (where the interface reaction rate is limiting). The temperature dependence of the reaction rate constant ( k k k ) follows the Arrhenius equation: k = A e − E a R T k = A e^{-\frac{E_a}{R T}} k = A e − RT E a ​ ​

Where E a E_a E a ​ is the activation energy ( kJ/mol \text{kJ/mol} kJ/mol ), T T T is absolute temperature ( K \text{K} K ), R R R is the universal gas constant ( 8.314 J/mol ⋅ K 8.314 \text{ J/mol}\cdot\text{K} 8.314 J/mol ⋅ K ), and A A A is the frequency factor. Low apparent activation energy can support a diffusion-control hypothesis and higher values can support a surface-reaction hypothesis, but mixed control, evolving surfaces, transport, and experimental range prevent hard universal cutoffs. Other key kinetic drivers include lixiviant concentration, solution pH, oxidation-reduction potential (Eh), mineral surface area, and dissolved gas mass transfer (such as oxygen dissolution).

Heap Leaching Design & Engineering Fundamentals

Heap leaching is a low-cost hydrometallurgical method for extracting gold, silver, and copper oxide ores from low-grade ROM (run-of-mine) or coarsely crushed deposits ( 10 − 25 mm 10 - 25 \text{ mm} 10 − 25 mm top size).

1. Pad Liner Infrastructure & Construction

To prevent environmental contamination and pregnant solution loss, heap leach pads are constructed over engineered containment liners. A composite clay or geosynthetic layer with an HDPE geomembrane is one common containment concept. Material, thickness, hydraulic performance, redundancy, leak detection, and drainage must follow site design and permit criteria. Perforated polyethylene drain pipes embedded in a protective gravel layer collect the draining solution above the liner.

2. Solution Distribution & Irrigation

Lixiviant (e.g., dilute sodium cyanide solution at pH 10 − 10.5 \text{pH } 10 - 10.5 pH 10 − 10.5 for gold, or sulfuric acid H 2 SO 4 \text{H}_2\text{SO}_4 H 2 ​ SO 4 ​ for copper oxide) is applied across the top of the heap using low-pressure drip emitters. Drip irrigation minimizes evaporation losses, aerosol drift, and heap surface crusting compared to impact sprinklers. Application rate is established by column tests, permeability, climate, solution inventory, oxygen demand, stability, and recovery response; any quoted range is project-specific.

3. Heap Height & Cycle Times

Ore is stacked in horizontal lifts ranging from 6 to 10 meters 6 \text{ to } 10 \text{ meters} 6 to 10 meters in height using conveyor stacking systems or low-ground-pressure dozers to avoid over-compaction. Total heap heights on permanent multi-lift pads can exceed 50 − 100 meters 50 - 100 \text{ meters} 50 − 100 meters . Leach cycle times vary from 60 days 60 \text{ days} 60 days for fast-leaching gold oxides to over 180 − 360 days 180 - 360 \text{ days} 180 − 360 days for copper sulfide heaps. Draining solution enriched with dissolved metal (Pregnant Leach Solution, PLS) flows to collection ponds, while barren solution from downstream recovery is reconstituted and recycled.

Vat Leaching, Agitation Tank Leaching & Autoclave HPAL Technology

When ores are high grade, fine-grained, or slow-leaching, reactor containment and intense agitation are necessary to accelerate recovery rates.

1. Agitation Tank Leaching

Finely ground ore pulp ( P 80 < 75 μ m P_{80} < 75 \text{ }\mu\text{m} P 80 ​ < 75 μ m , 40 − 50 % 40 - 50\% 40 − 50% solids by weight) is leached in a series of Continuously Stirred Tank Reactors (CSTR). Mechanical impellers maintain solids in uniform suspension, while spargers inject air or pure oxygen. Agitation-leach residence time and extraction depend on mineralogy, grind, chemistry, oxygen or oxidant transfer, mixing, temperature, and testwork; generic values do not define design performance.

2. High-Pressure Acid Leach (HPAL) for Nickel Laterites

High-Pressure Acid Leach (HPAL) is an advanced autoclave technology developed to extract nickel and cobalt from low-grade tropical nickel laterite ores—specifically the iron-rich limonite upper zone (goethite, FeO(OH) \text{FeO(OH)} FeO(OH) ).

In the HPAL process, ore slurry is fed into multi-compartment horizontal autoclaves constructed with titanium cladding or lead/acid-resistant brick linings. Concentrated sulfuric acid ( H 2 SO 4 \text{H}_2\text{SO}_4 H 2 ​ SO 4 ​ ) is injected at elevated temperatures ( 240 ∘ C − 270 ∘ C 240^\circ\text{C} - 270^\circ\text{C} 24 0 ∘ C − 27 0 ∘ C ) and high operating pressures ( 4.0 − 5.5 MPa 4.0 - 5.5 \text{ MPa} 4.0 − 5.5 MPa , or 40 − 55 bar 40 - 55 \text{ bar} 40 − 55 bar ). Under these hydrothermal conditions, sulfuric acid rapidly dissolves nickel and cobalt, while iron selectively hydrolyzes and precipitates out of solution as insoluble hematite ( Fe 2 O 3 \text{Fe}_2\text{O}_3 Fe 2 ​ O 3 ​ ): 2 FeO(OH) + 3 H 2 SO 4 → Fe 2 ( SO 4 ) 3 + 4 H 2 O 2\text{FeO(OH)} + 3\text{H}_2\text{SO}_4 \rightarrow \text{Fe}_2(\text{SO}_4)_3 + 4\text{H}_2\text{O} 2 FeO(OH) + 3 H 2 ​ SO 4 ​ → Fe 2 ​ ( SO 4 ​ ) 3 ​ + 4 H 2 ​ O Fe 2 ( SO 4 ) 3 + 3 H 2 O → Fe 2 O 3 ↓ + 3 H 2 SO 4 \text{Fe}_2(\text{SO}_4)_3 + 3\text{H}_2\text{O} \rightarrow \text{Fe}_2\text{O}_3 \downarrow + 3\text{H}_2\text{SO}_4 Fe 2 ​ ( SO 4 ​ ) 3 ​ + 3 H 2 ​ O → Fe 2 ​ O 3 ​ ↓ + 3 H 2 ​ SO 4 ​

This selective precipitation regenerates acid in situ and leaves a low-iron, nickel-cobalt-rich pregnant solution. Prominent industrial examples in the Philippines include the Coral Bay Nickel Corporation (CBNC) plant at Rio Tuba, Palawan, and the Taganito HPAL Corporation (THPAL) plant in Surigao del Norte. Both facilities process limonite laterite ores to produce Mixed Sulfide Precipitate (MSP) containing ~55% Ni and ~5% Co for global refining.

Bioleaching & Biomining Kinetics

Bioleaching (microbial hydrometallurgy) utilizes specialized acidophilic chemolithoautotrophic microorganisms to catalyze the oxidation of insoluble sulfide minerals.

Microbial consortia : Acidophilic iron- and sulfur-oxidizers may include Acidithiobacillus ferrooxidans , Acidithiobacillus thiooxidans , and Leptospirillum species. The named organisms are principally mesophilic or moderately thermotolerant under process-dependent conditions; separate thermophilic archaea or bacteria are selected for high-temperature circuits. Species, pH, temperature, aeration, nutrients, and tolerance must be established by testwork rather than assigned one 30–80°C range.

Mechanism : The bacteria oxidize ferrous iron ( Fe 2 + \text{Fe}^{2+} Fe 2 + ) to ferric iron ( Fe 3 + \text{Fe}^{3+} Fe 3 + ) and elemental sulfur ( S 0 \text{S}^0 S 0 ) to sulfuric acid ( H 2 SO 4 \text{H}_2\text{SO}_4 H 2 ​ SO 4 ​ ). Ferric ions act as a powerful chemical oxidant that attacks sulfide minerals such as pyrite ( FeS 2 \text{FeS}_2 FeS 2 ​ ), arsenopyrite ( FeAsS \text{FeAsS} FeAsS ), and chalcocite ( Cu 2 S \text{Cu}_2\text{S} Cu 2 ​ S ), breaking down the sulfide matrix and releasing trapped gold or soluble copper into solution. Bioleaching is widely applied to pre-treat refractory gold concentrates prior to cyanidation.