Oxidative Leaching Explained: The Albion Process™ Guide

Key takeaways

• Oxidative leaching breaks down sulphide minerals with oxygen, which makes the leached sulphide concentrate suitable for downstream, conventional extraction methods to recover locked metals such as gold, copper, nickel, cobalt and zinc.
• Most sulphide minerals will not leach at atmospheric pressure. Ultrafine grinding to 80% passing 10 to 12 microns strains the mineral lattice and prevents passivation, enabling atmospheric oxidative leaching.
• The Albion Process™ combines IsaMill™ ultrafine grinding with oxygen injected at supersonic velocity into atmospheric leach reactors that run close to the boiling point of the slurry, with no high pressure autoclaves required.
• Glencore Technology reports recoveries of up to 97% from refractory gold concentrates and over 99% from chalcopyrite copper concentrates.

Oxidative leaching is the step that releases metals locked inside sulphide minerals. Many gold, copper, cobalt, zinc and nickel deposits hold their value in sulphides such as pyrite, arsenopyrite, chalcopyrite and sphalerite. These minerals do not dissolve readily, and in refractory gold ores they can lock gold away from cyanide. Oxidising the sulphide concentrate breaks the mineral down so the contained metal can be recovered by conventional processes such as cyanide leaching, or solvent extraction and electrowinning.

Oxidation is traditionally carried out with heat, pressure or bacteria. The Albion Process™ takes a different route: it oxidises finely ground concentrate at atmospheric pressure. This article explains what oxidative leaching is, why grind size determines whether it can happen at atmospheric pressure, how the plant and chemistry work, which metals it suits, and how a project is developed. The figures come from Glencore Technology's published papers and operating sites.

What is oxidative leaching?

Oxidative leaching is a hydrometallurgical process that uses oxygen to break down sulphide minerals, releasing the contained metals they contain into solution or into a residue from which they can be recovered. The sulphide is oxidised to elemental sulphur or sulphate, and the economic metal is then recovered by an established downstream process.

In the Albion Process™, the feed is a base or precious metal concentrate. The process can boost recoveries for zinc, copper, molybdenum, cobalt, nickel, lead, platinum group metals and refractory silver and gold. For precious metals, the oxidised residue goes to a cyanide leach. For base metals, the metal is recovered from solution by direct electrowinning or by solvent extraction and electrowinning.

Why don't sulphide minerals leach at atmospheric pressure?

Most sulphide minerals cannot be leached under normal atmospheric conditions for two reasons: the intact mineral lattice resists oxidation, and the products of the leach reaction coat the mineral and stop it reacting. That coating is called passivation. Leach products such as iron oxides and elemental sulphur precipitate on the mineral surface and block chemicals from reaching it. Passivation is normally complete once this layer is 2 to 3 microns thick.

Ultrafine grinding solves both problems. Grinding introduces a high degree of strain into the sulphide mineral lattice, and the number of grain boundary fractures and lattice defects rises by several orders of magnitude compared with unground minerals. This lowers the activation energy for oxidation and enables leaching at atmospheric pressure. Grinding to 80% passing 10 to 12 microns also prevents passivation, because each particle disintegrates before the precipitate layer becomes thick enough to stop the reaction.

How does atmospheric oxidative leaching work?

Atmospheric oxidative leaching in the Albion Process™ works in two steps: mechanical liberation in an IsaMill™, then chemical liberation in a train of oxygen-fed leach reactors. The ultrafine grinding stage grinds the concentrate to a narrow size distribution. The IsaMill™ uses inert grinding media, produces clean mineral surfaces, and can run in open circuit at high slurry density, which limits the water entering the leach.

The ground slurry then flows through a series of interconnected Albion Leach Reactors. Oxygen is injected into the base of each reactor at supersonic velocity using Glencore Technology's HyperSparge™ lances, which maximises oxygen mass transfer. Each reactor is agitated with hydrofoil impellers and has a corrosion-resistant alloy steel shell.

The leach is autothermal. Heat released by the oxidation reaction sets the slurry temperature, typically in the range of 90 to 98°C, close to the boiling point of the slurry. No internal heating or cooling systems are needed, and excess heat leaves as water vapour in the off-gas. Each reactor can be bypassed, so one vessel can be taken out for maintenance without stopping the leach.

Sources: Glencore Technology, The Albion Process for Refractory Gold; Albion Process™ "How it works" and "Flowsheet options" pages.

What is the chemistry of oxidative leaching?

In the Albion Process™ leach, sulphide minerals are oxidised in two steps: first to a soluble sulphate and elemental sulphur, then the elemental sulphur is oxidised to sulphuric acid.

• Step 1: MS + H₂SO₄ + ½O₂ → MSO₄ + S⁰ + H₂O
• Step 2: S⁰ + H₂O + 3/2 O₂ → H₂SO₄

The leach pH is the main control. It sets how much of the elemental sulphur is oxidised in step 2, from a few per cent to full oxidation, with pH setpoints in the range of 1 to 6. The flowsheet options then depend on the metal being recovered.

Source: Glencore Technology, Albion Process™ "Flowsheet options" page.

For refractory gold, operating near neutral pH has practical benefits. Acid and iron released from the pyrite are neutralised inside the leach, so no separate solid-liquid separation or neutralisation circuit is needed before the cyanide leach. No elemental sulphur is formed, so the residue has very low cyanide consumption relative to bacterial or pressure leach circuits.

What factors affect oxidative leaching performance?

Five factors drive oxidative leaching performance: grind size, oxygen mass transfer, pH control, temperature and the mineralogy of the feed.

• Grind size. The concentrate must be fine enough to prevent passivation, which in the Albion Process™ means 80% passing 10 to 12 microns with a narrow size distribution.
• Oxygen mass transfer. Oxidation needs oxygen to reach the mineral surface. Supersonic HyperSparge™ injection, designed together with the agitator, delivers high mass transfer rates.
• pH control. The pH setpoint governs the extent of sulphur oxidation and the downstream chemistry.
• Temperature. The leach is autothermal: heat from the oxidation reaction holds the slurry close to its boiling point, with no external heating or cooling.
• Feed mineralogy. Each concentrate responds differently, which is why every project starts with testwork on representative samples.

Which metals can oxidative leaching recover?

Atmospheric oxidative leaching can recover a wide range of base and precious metals from sulphide concentrates. Albion Process™ plants have treated refractory gold concentrates, chalcopyrite copper concentrates, zinc concentrates and copper smelter dust.

Glencore Technology's published installation list includes refractory gold concentrate plants at Las Lagunas in the Dominican Republic and Ararat in Armenia, copper concentrate treatment at Sable in Zambia, copper smelter dust at the MIM smelter in Australia, and lead-zinc concentrate plants in Spain, Germany and at McArthur River in Australia.

At the GPM Gold Project in Armenia, the existing carbon-in-leach (CIL) circuit recovered only around 20 to 30% of the gold from the sulphide material. After an Albion Process™ plant was added to oxidise the sulphide concentrate, recovery from the sulphide concentrate rose from 20% to over 98%, and plant-wide recovery reached 88% against a design target of 86%.

How does atmospheric oxidative leaching compare with pressure oxidation?

Atmospheric oxidative leaching avoids the autoclave, which is the main difference from pressure oxidation (POX). Glencore Technology reports that the Albion Process™ has much lower capital cost than POX plants, and that because it operates at atmospheric pressure, it avoids the risks of POX operation. It also cites a recent study suggesting ongoing operating costs are a third lower.

The plant itself is simpler. Albion Leach Reactors are atmospheric vessels rather than pressure vessels; there is no complicated equipment operating at high pressure, and individual reactors can be bypassed if needed. The Albion Process™ has been commissioned and brought to design recovery and throughput in as little as six weeks.

In 2026, Rox Resources selected the Albion Process™ for Youanmi after extensive testwork and an assessment of multiple processing routes. The technology was chosen as a lower-capital, more practical alternative to pressure oxidation that delivered the metallurgical performance the project required.

How is an oxidative leaching plant developed?

An Albion Process™ plant is developed in stages from laboratory testwork to full scale, without a pilot plant stage, and a process guarantee is provided. Glencore Technology states that the three-stage development from lab to full scale delivers design throughput and plant recoveries.

The first phase of project development is a testwork program to confirm that the feed responds to the process and to gather design data. Glencore Technology can then provide a +35% Class 4 study of capital and operating costs. As an introduction, it offers a high-level desktop capital and operating cost estimate at no cost, once given a concentrate composition and a planned throughput. Glencore Technology supplies the plant as a lump sum equipment design and supply package, including the IsaMill™ grinding plant and the modular oxidative leach circuit.

Frequently Asked Questions

What is the difference between oxidative leaching and cyanide leaching?

Oxidative leaching and cyanide leaching do different jobs. Oxidative leaching breaks down sulphide minerals so locked gold is exposed. Cyanide leaching then dissolves the exposed gold. In the Albion Process™, the oxidised residue from a refractory gold concentrate goes directly to a cyanide leach, with no separate neutralisation stage in between.

Does oxidative leaching need a pressure vessel?

Not with the Albion Process™. Ultrafine grinding makes the sulphides reactive enough to oxidise at atmospheric pressure, so the leach runs in atmospheric Albion Leach Reactors instead of an autoclave. The reactors operate close to the boiling point of the slurry, heated only by the oxidation reaction itself.

What grind size is needed for atmospheric oxidative leaching?

The Albion Process™ grinds concentrate to 80% passing 10 to 12 microns. Leach products passivate a sulphide particle once they form a layer 2 to 3 microns thick. At this grind size, each particle disintegrates before that layer can form, so leaching continues at atmospheric pressure.

Can an oxidative leaching plant be designed without a pilot plant?

Yes. An Albion Process™ plant is developed in three stages from laboratory testwork to full scale, and Glencore Technology states that a pilot plant stage is not needed. A process guarantee is provided. Testwork on representative concentrate samples confirms amenability and supplies the design data for the full-scale plant.

How much does an oxidative leaching plant cost?

Cost depends on concentrate composition and throughput. Glencore Technology provides a free high-level desktop capital and operating cost estimate once it has both, and can follow testwork with a +35% Class 4 study. The Albion Process™ Calculator gives an order-of-magnitude CapEx and OpEx estimate with a high-level equipment list.

Getting started with oxidative leaching

Oxidative leaching unlocks metal from sulphide concentrates that conventional processing cannot recover economically. The traditional routes rely on heat, pressure or bacteria. Atmospheric oxidative leaching uses a different principle: grind the concentrate fine enough, and the sulphides will oxidise in simple atmospheric reactors.

The key points are consistent across the plants described here. Grind size decides whether leaching can happen at all, because 80% passing 10 to 12 microns prevents passivation. Oxygen mass transfer and pH control decide how fast and how completely the sulphides oxidise, and what the downstream chemistry looks like. And because the process runs without an autoclave, the plant is simpler and faster to install, with individual reactors that can be bypassed for maintenance.

The same approach applies across gold, copper, zinc and other base metals, with the leach conditions changed to suit each concentrate. At GPM in Armenia, it lifted recovery from the sulphide concentrate from 20% to over 98%.

Every concentrate is different, so the starting point is testwork. To scope oxidative leaching for your concentrate, start with the Albion Process™ Calculator, read how the Albion Process™ works, or contact the Albion Process™ team for a free desktop cost estimate based on your concentrate composition and throughput.

Technical references

• Glencore Technology. The Albion Process for Refractory Gold.
• Glencore Technology. Introduction to the Albion Process.
• Glencore Technology. Albion Process™ Installation List.
• TOMS Institute. Technology for Processing of Refractory Gold-Containing Concentrates (IMPC 2016).