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Low-Grade Gold Heap Leaching: rocess, Costs, and Design

Low-Grade Gold Heap Leaching:

Process, Costs, and Design

Low-Grade Gold Heap Leaching

As elevated gold prices in 2026 make low-grade resources more viable, producers face pressure to boost recovery while controlling costs. Heap leaching has become a preferred method for ores and tailings grading ~0.3–1.0 g/t. Compared with conventional milling and agitation leaching, it offers a simpler flowsheet, lower energy use, fewer equipment needs, and reduced capital and operating costs. It is widely applied to oxidized gold ore, by-product ore, low-grade off-balance material, and tailings.

This article walks through the complete heap-leaching circuit — ore preparation, pad construction, ore stacking, solution preparation and distribution, gold recovery, and heap rinsing — and explains how each step affects recovery and cost.

Contents

01

Ore Preparation: The Foundation of Efficient Heap Leaching

Ore preparation is a critical step in heap leaching. It typically includes crushing, agglomeration, and pretreatment, with the goal of improving ore leachability and heap permeability. Proper preparation helps prevent uneven liquid flow, ponding, channeling, and plugging, while also reducing reagent consumption and improving gold recovery.

Crushing

  • If the particle size is too coarse, gold liberation may be insufficient.
  • If the particle size is too fine, the heap may become compacted, causing poor permeability and channeling.

Therefore, selecting the right crushing size is essential for stable heap performance.

Agglomeration

For fine ore or ore with a high clay content, agglomeration is often necessary. When the mud content exceeds 8%, a binder such as cement or lime is commonly added at 3–6 kg/t, together with an appropriate amount of sodium cyanide solution. The moisture content is usually controlled at 8–12%, and the agglomerated ore is cured for 8–12 hours to form stable pellets.

Agglomeration offers several advantages:

  • Improves heap permeability
  • Prevents channeling and compaction
  • Enhances heap stability
  • Allows pre-cyanidation and early gold dissolution
  • Improves overall leaching efficiency

Common agglomeration equipment includes:

  • Rotary drum agglomerators
  • Disc pelletizers
  • Multi-stage belt agglomeration systems

Pretreatment

Pretreatment

Pretreatment may include the removal of oversize waste rock, clay, and other impurities to reduce unnecessary processing load. In some cases, leaching solution can also be added during agglomeration to pretreat the ore, further improving heap permeability and metal dissolution performance.

02

Heap Leach Pad Construction: The Environmental Protection Baseline

A properly designed heap leach pad is essential not only for production efficiency but also for environmental compliance. The pad base must have a reliable impermeable liner system to prevent cyanide solution leakage and protect surrounding soil and groundwater.

Heap Leach Pad Construction: The Environmental Protection Baseline
Heap Leach Pad Construction: The Environmental Protection Baseline

In most cases, the pad is lined with HDPE geomembrane with a thickness of not less than 1.5 mm. The base should also be equipped with:

  • Drainage channels
  • Pregnant solution collection pipes
  • Subsurface (blind) drains
  • Collection trenches
  • Pregnant solution ponds

These systems ensure that the leaching solution can be safely and efficiently collected without leakage, creating the necessary conditions for downstream solution treatment and gold recovery.

03

Ore Stacking: Building a Stable and Permeable Heap

The stacking stage generally uses a multi-lift, thin-layer stacking method. Each lift is usually controlled at 3–5 m, while the total heap height may reach 10–30 m, depending on ore characteristics, pad design, and operating requirements.

Stacking is commonly carried out using:

  • Mobile belt conveyors
  • Radial stackers
  • Construction equipment such as loaders and trucks

To ensure uniform solution distribution, ore should be spread in thin layers and the heap top should be kept relatively even. Alongside this, zoned heap management is often adopted to allow sequential leaching.

Ore Stacking: Building a Stable and Permeable Heap
Ore Stacking: Building a Stable and Permeable Heap

Several operating principles are important during stacking:

  • Avoid excessive compaction to maintain permeability
  • Ensure proper layered compaction for slope stability
  • Keep the heap surface uniform for even irrigation
  • Minimize segregation of fine and coarse particles

Well-executed stacking allows the leach solution to flow evenly through the ore bed and contact gold-bearing particles more effectively.

04

Leaching Solution Preparation: Balancing Recovery and Safety

The leaching solution is typically prepared using sodium cyanide (NaCN) or, in some cases, lower-toxicity, more environmentally friendly reagents. The reagent concentration is generally controlled within 0.01%–0.1%, approximately 100–1000 ppm.

Leaching Solution Preparation: Balancing Recovery and Safety

In parallel, lime (CaO) is added to maintain the solution pH at 10–11. This is a key control point because proper alkalinity can:

  • Suppress the volatilization of HCN gas
  • Improve operational safety
  • Prevent cyanide hydrolysis
  • Reduce the dissolution of harmful impurities

Stable reagent concentration and pH control are crucial for achieving good gold dissolution and safe heap leach operation.

05

Solution Distribution and Collection: Ensuring Uniform Leaching

Solution Distribution and Collection: Ensuring Uniform Leaching

The solution distribution system usually consists of:

  • Mixing or distribution tank
  • Pumps
  • Solution pipelines
  • Sprinkler pipes laid on top of the heap
  • Sprinklers or drip emitters

The irrigation rate is typically controlled at 0.1–0.2 L/(m²·min). In many operations, intermittent irrigation is used, with spraying time accounting for about 1/3 to 1/2 of the full cycle. This operating mode helps ensure sufficient leaching while avoiding heap saturation.

After percolating through the heap, the pregnant solution typically contains about 0.5–5 g/m³ gold, depending on ore grade, leach conditions, and leach cycle. The solution is then collected through the drainage system at the bottom of the heap and directed to the pregnant solution pond for further treatment.

Solution Distribution and Collection: Ensuring Uniform Leaching Solution Distribution and Collection: Ensuring Uniform Leaching
06

Pregnant Solution Treatment and Gold Recovery

After collection, the pregnant solution must be processed to recover dissolved gold. The most common method is activated carbon adsorption followed by desorption and electrowinning.

Activated Carbon Adsorption

The pregnant solution first enters adsorption columns or carbon adsorption systems, where granular activated carbon with a particle size of 2–4 mm is used to adsorb dissolved gold. The typical adsorption flow rate is around 10–15 m/h.

As the carbon loads with gold, it becomes loaded carbon, which is then transferred to the desorption stage once it reaches the target loading.

Desorption

Desorption is generally carried out under high temperature and high pressure, typically:

  • 120–150°C
  • 0.3–0.5 MPa
  • Desorption time: 8–12 hours

A hot sodium cyanide solution is used to strip Au(CN)

Electrowinning and Smelting

The desorption solution is then sent to an electrowinning cell, where gold is deposited on the cathode as gold sludge. The sludge is further dried, refined, and smelted to produce gold bullion.

Zinc Powder Precipitation

In some special cases, especially for ores with relatively high silver content, the zinc powder replacement method can also be used to precipitate gold and silver from solution.

Pregnant Solution Treatment and Gold Recovery
Pregnant Solution Treatment and Gold Recovery

Barren Solution Recycling

After adsorption, the barren solution can be returned to the leaching circuit for reuse. This helps reduce:

  • Fresh water consumption
  • Cyanide consumption
  • Overall operating costs

Solution recycling is one of the important reasons heap leaching can offer attractive economics for low-grade gold deposits.

07

Heap Rinsing and Reclamation

After the main leaching cycle is completed, the heap should be rinsed to recover residual dissolved gold and remove remaining cyanide. Rinsing is usually performed using industrial water with a pH of 8–10 for approximately 2–3 hours of continuous spraying.

Heap Rinsing and Reclamation

Rinsing can be stopped when testing confirms that:

  • Cyanide ion concentration is below the specified standard
  • Gold concentration in the rinse solution has dropped to a low level, such as below 0.1 g/m³

After the rinse liquor is drained, the heap can be unloaded. During unloading, a 2 m thick residue layer is often left at the bottom to protect the containment liner.

Proper rinsing and unloading are important for both environmental protection and site reuse.

08

Xinhai Gold Heap Leaching and Gold Processing Solutions

Start with testwork, not with equipment.

Heap leaching succeeds or fails on ore characteristics that cannot be judged by eye — clay content, permeability, gold occurrence, and preg-robbing potential. Xinhai’s in-house Mining Research Institute operates a CNAS-accredited laboratory and an industrial-scale pilot test base, completing 200+ metallurgical test programs annually across 70+ mineral types.

Before we recommend a flowsheet, we test your ore — and if heap leaching is not the right answer, we will tell you that too.

Xinhai Gold Heap Leaching and Gold Processing Solutions

From there, Xinhai provides full-process solutions for gold projects, including:

  • Ore dressing testwork
  • Process design
  • Heap leach pad design
  • Equipment supply
  • Installation and commissioning
  • EPC and EPCM services
  • Tailings and low-grade ore utilization solutions

With rich experience in gold beneficiation and mine development, Xinhai can help clients design economical and efficient solutions for low-grade gold resources under changing market conditions.

09

Selected Xinhai Gold Project Experience

Xinhai’s gold track record spans heap leaching, CIL/CIP, flotation, and tailings reprocessing routes — because the right process depends entirely on the ore, not on a preferred flowsheet. Representative projects include:

Project Scale Region
Zimbabwe Gold Tailings Reprocessing EPC Project 500 t/d Zimbabwe
Xinjiang Gold Project 2 Million t/a China
Mongolia Gold Projec 3 Million t/a Mongolia
Russia Gold Project 500 t/d Eastern Europe region
Malaysia Gold Project 500 t/d Malaysia

Process routes for each project were selected on the basis of ore testwork and metallurgical characteristics. If you would like the detailed process configuration for a specific project, our technical team can walk you through it.

Selected Xinhai Gold Project Experience Selected Xinhai Gold Project Experience

If you are evaluating a low-grade gold ore, oxidized gold deposit, or gold tailings project, Xinhai can help you determine whether heap leaching is the right solution through professional mineral processing testwork and engineering design.

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