# Oxygen-enhanced heap leaching

The US EPA technical resource document on gold (1994) describes heap leaching as applying cyanide solution to low-grade ore placed on lined pads, and states that the reaction with free gold is oxygen-dependent, so the solution is oxygenated before application or during spraying.

## How a gold heap leach works

The US Environmental Protection Agency technical resource document on gold, published in August 1994, describes cyanide heap leaching as a relatively inexpensive method of beneficiating low-grade gold ores, while tank leaching is used for higher grade ore. It says heap leaching may involve some or all of these steps:

- preparing a pad with an impervious liner;
- crushing or agglomerating the ore, if necessary and cost effective;
- placing the ore on the pads with trucks, bulldozers, conveyor belts or other equipment;
- applying cyanide solution by drip, spray or pond irrigation;
- collecting the solution in ditches, pipes, ponds or tanks.

As the liquid percolates through the ore, cyanide complexes with the gold and other metals. The document notes that percolation efficiency may be a limiting factor, and gives an average leach cycle of approximately 3 months, citing a 1988 source.

## Why the leach solution is oxygenated

The same EPA document states that the reaction of the solution with the free gold is oxygen-dependent, and that the solution is therefore oxygenated before application or during spraying. For tank leaching, it describes one mine where air is injected to supply the oxygen needed for the cyanide to dissolve the gold; see [oxygen for gold leaching](https://library.ultracontrolo.com/industry/oxygen-for-gold-leaching/).

## Biooxidation heaps and forced aeration

A 1996 paper published by the Society for Mining, Metallurgy & Exploration (SME) states that heap biooxidation of sulphidic refractory gold ore requires large amounts of oxygen. The leach solution percolating through the heap brings in an insignificant amount, because the solubility of oxygen in water is 7 to 8 ppm at atmospheric saturation, and there are only three ways to provide oxygen to the heap: air flow by natural convection, diffusion of oxygen from the surface, or forced air ventilation.

The same paper puts the requirement, at maximum oxygen utilisation, at nearly 100 m³ of air per tonne for an ore containing 2% pyrite, and notes that the bacteria are dormant at oxygen concentrations below about 3% in air (1 ppm in solution).

## Oxygen-enhanced heap leaching tests

A 1990 SME paper reports preliminary column tests at Hazen Research in which oxygen-purged columns showed an increase in both the leaching rate and the maximum recovery of gold, and a reduction in cyanide consumption, compared with columns run with air. Its authors listed faster leaching kinetics, shorter cycle time, higher recoveries and more efficient use of permanent or reusable pad space as potential benefits, and stated that the concept required confirmation of technical and economic feasibility on a commercial scale.

## ULTRAOX VSA

Ultra Controlo lists gold leaching in mines among the applications of ULTRAOX VSA, its industrial oxygen plant. ULTRAOX VSA delivers 75% to 95% oxygen at 50 kPa, with an additional oxygen booster on demand for higher pressures; it is supplied on a skid or in a container, and can replace cryogenic systems with liquid oxygen tanks or work as the main source of supply. See [oxygen generators for mining](https://library.ultracontrolo.com/industry/oxygen-generators-for-mining/).

### Why does a heap leach need oxygen?

The 1994 US EPA gold document states that the reaction of the cyanide solution with free gold is oxygen-dependent, so the solution is oxygenated before application or during spraying.

### What did the 1990 oxygen-enhanced heap leaching column tests show?

A 1990 SME paper reported faster leaching and higher gold recovery in oxygen-purged test columns than in air columns, and stated that the concept required confirmation of technical and economic feasibility on a commercial scale.

## Sources

- [US EPA, Technical Resource Document: Extraction and Beneficiation of Ores and Minerals, Volume 2, Gold, EPA 530-R-94-013 (August 1994)](https://archive.epa.gov/epawaste/nonhaz/industrial/special/web/pdf/gold.pdf)
- [J. McMaster and C. W. Kenney, Oxygen-Enhanced Heap Leaching, Society for Mining, Metallurgy & Exploration (1990), abstract on OneMine](https://www.onemine.org/documents/oxygen-enhanced-heap-leaching)
- [R. W. Bartlett, Aeration Requirements for Heap Biooxidation of Refractory Gold Ores, Society for Mining, Metallurgy & Exploration (1996), abstract on OneMine](https://onemine.org/documents/aeration-requirements-for-heap-biooxidation-of-refractory-gold-ores-)
- [ULTRAOX VSA datasheet, p. 2 and p. 3](https://www.ultracontrolo.com/products/ultraox-vsa)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/industry/oxygen-heap-leaching/