Separation of Copper Sulphide and Nickel Sulphide Matte in Nickel Sulphide Ores
The separation of copper sulphide and nickel sulphide matte is a critical step in the processing of nickel sulphide ores, particularly in complex polymetallic deposits where copper and nickel occur together in sulphide minerals such as pentlandite ((Fe,Ni)₉S₈), chalcopyrite (CuFeS₂), and pyrrhotite (Fe₁₋ₓS). Efficient separation is essential to produce high-purity nickel and copper concentrates, optimize metal recovery, and reduce downstream refining costs.
In conventional processing flowsheets for nickel sulphide ores, the ore is first subjected to crushing, grinding, and flotation to produce a bulk sulphide concentrate containing both nickel and copper sulphides. However, because copper minerals are typically more amenable to flotation than nickel minerals, selective flotation techniques are employed to separate copper from nickel at an early stage. Differential flotation is commonly used, where pH control, selective collectors (e.g., xanthates), and depressants play a key role..jpg)
One widely adopted method involves depressing nickel sulphides while floating copper sulphides. Sodium hydrosulfide (NaHS) or sodium sulfide (Na₂S) is often used as a depressant for nickel minerals in alkaline conditions (pH 10–12), allowing chalcopyrite to be selectively floated with collectors such as potassium amyl xanthate (PAX). This approach has been successfully implemented at operations such as the Sudbury Basin mines in Canada and the Kambalda operations in Western Australia.
Alternatively, in cases where copper content is low or where bulk concentrate treatment is preferred, the bulk sulphide concentrate may be smelted to produce a mixed copper-nickel matte. In such cases, the separation must occur during hydrometallurgical or pyrometallurgical refining. The most common industrial process for separating copper and nickel from matte is the Mond process or variations thereof, but more frequently, electrowinning or solvent extraction-electrowinning (SX-EW) routes are applied after leaching.
A key method used historically and still relevant today is the chloride leaching process. In this approach, the mixed matte is leached with hydrochloric acid or chlorine-containing solutions under controlled redox potential. Copper dissolves preferentially as Cu²⁺ due to its higher solubility and oxidation potential compared to nickel. Nickel remains largely undissolved or can be selectively precipitated later. This technique was employed at the Falconbridge Nickel Refinery (now Glencore’s operations) using a combination of atmospheric and pressure leaching.
Another established method is the use of pressure acid leaching (PAL), particularly for low-grade or complex mattes. In PAL systems operating at elevated temperatures (200–250°C) and pressures, both copper and nickel dissolve into solution. Subsequent selective precipitation or solvent extraction allows separation: for example, LIX reagents such as LIX 84-I are effective in extracting copper from acidic sulphate solutions while leaving nickel in the raffinate..jpg)
Recent advancements have focused on improving selectivity and reducing environmental impact. For instance, bioleaching using acidophilic bacteria like Acidithiobacillus ferrooxidans has been studied for selective dissolution of copper from mixed sulphides due to differences in microbial oxidation rates between chalcopyrite and pentlandite. However, industrial application remains limited due to slow kinetics and process control challenges.
Thermodynamic studies support these separation strategies. The standard electrode potentials indicate that Cu²⁺/Cu⁺ (+0.15 V) and Cu²⁺/Cu (+0.34 V) are more favorable for reduction than Ni²⁺/Ni (−0.25 V), enabling selective electrochemical recovery. Additionally, phase equilibria data from systems like Cu-Fe-S-Ni show that during smelting, copper tends to concentrate in the matte phase while minor adjustments in oxygen potential can influence metal distribution.
Industrial practice demonstrates that integrated flowsheets combining flotation, smelting, and hydrometallurgical purification yield optimal results. For example, Norilsk Nickel employs a combination of selective flotation followed by electrorefining of blister copper-nickel alloy to achieve high-purity products.
In conclusion, the separation of copper sulphide and nickel sulphide matte relies on differences in mineral floatability, solubility under oxidative conditions, and electrochemical behavior. The choice of method depends on ore mineralogy, economic factors, environmental regulations, and desired product specifications. Established technologies—such as differential flotation with depressants, pressure leaching with solvent extraction—are supported by decades of operational data and thermodynamic principles, forming the backbone of modern nickel-copper separation processes.
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