As easily treatable gold resources continue to deplete globally, refractory gold ores—once regarded as “waste”—have become a major resource for the gold industry. Data shows that at least one-third of the world’s gold production comes from refractory gold deposits. In China, proven reserves of refractory gold ores exceed 700 tons.
However, extracting gold from such ores using traditional cyanidation processes often results in low recovery rates, high cyanide consumption, and significant environmental pressure. These challenges have become a core technical bottleneck restricting the development of China’s gold industry. Today, we will break down this “critical” problem in the gold industry and explore how scientists and engineers are “unlocking” the trapped gold.
I. First, Understand: What Is Refractory Gold Ore?
Refractory gold ore, in simple terms, is ore from which most of the gold cannot be effectively extracted using conventional cyanidation processes. The industry typically uses the gold cyanidation leaching rate as the sole criterion to classify gold ores into four categories:
- Cyanidation leaching rate below 50%: Extremely refractory gold ore
- Cyanidation leaching rate 50%–80%: Refractory gold ore
- Cyanidation leaching rate 80%–90%: Moderately refractory gold ore
- Cyanidation leaching rate 90%–100%: Free-milling gold ore
Currently, most new ores encountered in China’s gold mines fall into the moderately refractory category or above.
II. Why Is Gold Ore “Refractory”? Five Key Reasons
The essence of gold “not leaching out” is that the gold cannot fully contact and react with the cyanide solution. Specifically, there are five main obstacles:
1. Physical Encapsulation: Gold “Locked” in Mineral Lattices
This is the most common and most difficult cause. Gold in the ore exists as fine or even submicroscopic particles, tightly encapsulated by sulfide minerals such as pyrite, arsenopyrite, and pyrrhotite, or by silicate minerals like quartz. In some cases, gold is even embedded in the crystal lattice of sulfide minerals.
Even if the ore is ground to conventional fineness, these encapsulations cannot be liberated. The gold particles never come into contact with the cyanide solution and thus cannot be leached.
2. Oxygen- and Cyanide-Consuming Minerals: “Competitors” for Resources
Ores often contain associated sulfides and oxides of metals such as arsenic, copper, iron, antimony, and manganese. These substances are highly soluble in alkaline cyanide solutions and consume large amounts of cyanide and dissolved oxygen, forming various cyano-complexes and thiocyanates.
As a result, little cyanide and oxygen remain for dissolving gold, significantly slowing down gold oxidation and leaching.
3. Surface Passivation of Gold Particles: A “Non-Reactive Coating”
During ore oxidation and cyanidation, a dense film can form on the surface of gold particles. This film may consist of sulfides, peroxides, oxides, or insoluble cyanide compounds.
This layer acts like a “bulletproof vest,” isolating the gold from the cyanide solution and greatly reducing the leaching rate and final gold recovery.
4. Carbonaceous “Preg-Robbing”: Hijacking the Gold
This is a unique challenge in carbonaceous gold ores. Naturally occurring substances such as activated carbon, humic acid, graphite, and clay minerals have strong adsorption capabilities.
They preferentially adsorb gold ions that have already been leached by cyanide, causing gold loss in the cyanide tailings. This is the well-known “preg-robbing” effect in the industry.
5. Refractory Gold Compounds: Naturally Tough Chemical Nuts
In some ores, gold does not exist as native gold but as antimonides (e.g., aurostibite, antimonial silver-gold, antimonial copper-gold), solid-solution electrum, or other alloys.
These compounds react very slowly in conventional cyanide solutions and are nearly impossible to leach.
III. Optimal Pretreatment Methods for Different Ore Types
There is no universal pretreatment technology—only the most suitable one. Choosing the pretreatment method based on the refractory cause of the ore yields the best technical and economic results:
- Pyrite / Arsenopyrite / Orpiment / Realgar / Arsenosulfite type: Prefer pressure oxidation, roasting, nitric acid oxidation, or bio-oxidation
- Pyrrhotite type: Prefer alkali-assisted pre-aeration or bio-oxidation
- Sulfosalt type: Prefer chlorination or oxidation
- Telluride type: Prefer chlorination or oxidation
- Carbonaceous gold ore type: Prefer physical or chemical passivation to remove carbon
- Refractory siliceous ore type: No economically viable industrial treatment method currently available
Post time: May-20-2026
