1 Basic Principles of Copper-Nickel Beneficiation
For flotation of copper-nickel sulfide ores, collectors and frothers normally used for copper sulfide minerals are commonly adopted. One fundamental principle is established: it is preferable for copper to enter the nickel concentrate, while nickel should be prevented from entering the copper concentrate as much as possible. This is because nickel suffers heavy losses during the smelting of copper concentrate, whereas copper can be recovered to a large extent in nickel concentrate smelting.
2 Beneficiation Processes (Direct Beneficiation)
Copper-nickel sulfide ores can be upgraded by beneficiation methods. At present, oxidized nickel ores can only be treated directly via smelting processes, which are divided into pyrometallurgy and hydrometallurgy.
Flotation is the primary beneficiation method for copper-nickel sulfide ores, while magnetic separation and gravity separation are frequently used as auxiliary processes.
There are two main flotation schemes for copper-nickel ores: selective flotation and bulk flotation. Selective flotation may be considered when the copper content is higher than nickel and the mineral paragenetic relationship is relatively simple.
Advantages: Copper concentrate and nickel concentrate can be obtained directly.
Disadvantages: Nickel minerals depressed during copper flotation are difficult to reactivate, resulting in low nickel recovery. Therefore, this method is seldom applied.
Copper-nickel bulk flotation is the widely adopted scheme at present. Its advantages include high nickel recovery and fewer flotation units required. Copper-nickel bulk flotation is similar to copper-sulfur bulk flotation.
(1) Bulk Flotation Flowchart
Applicable conditions: For ores with copper content lower than nickel. The obtained copper-nickel bulk concentrate is directly smelted into nickel matte, which is further treated by regrinding and flotation to produce copper and nickel products.
(2) Bulk Flotation + Separation Flotation
Applicable conditions: After bulk flotation, the bulk concentrate is separated into low-nickel copper concentrate and copper-bearing nickel concentrate. The nickel concentrate is smelted into nickel matte, and the nickel matte is then separated by flotation.
(3) Partial Bulk Flotation + Recovery of Partial Nickel from Bulk Flotation Tailing
3 Nickel Recovery Methods
(1) Gravity Separation + Flotation
(2) Magnetic Separation + Flotation
(3) Flotation
4 Characteristics of Copper-Nickel Flotation Process
(1) The optimum pH environment for nickel mineral flotation is weakly acidic, neutral or weakly alkaline medium.
(2) Higher xanthates such as butyl xanthate and amyl xanthate are used as collectors.
(3) Pyrrhotite containing nickel requires a relatively long flotation time.
(4) Nickel-bearing minerals such as pyrrhotite and pyrite are prone to oxidation and slime formation. Especially when nickel has uneven dissemination grain size, stage grinding is critical. Classified grinding must be strengthened. Generally, rough tailings are discarded after primary rough grinding; the bulk concentrate is classified and re-ground before cleaning or copper-nickel separation.
(5) Activation reagent schemes for pyrrhotite:
① Na₂S + CuSO₄
② Na₂SiF₆ + CuSO₄
③ (COOH)₂ + CuSO₄
5 Nickel Matte Flotation Process
5.1 Main Components of Nickel Matte
Ni₃S₂, Cu₂S, Ni-Fe-Cu alloy
5.2 Applicable Conditions for Nickel Matte Separation Technology
It mainly depends on ore properties, copper-nickel ratio, smelting process requirements and the distribution of platinum group metals. Direct copper-nickel separation from ore can simplify the smelting flow, reduce energy consumption and improve labor productivity.
5.3 Process Method
Magnetic-flotation separation is the main effective separation method for modern nickel matte. In the combined magnetic-flotation separation process, nickel matte is slowly cooled, crushed, ground and classified. Permanent low-intensity magnetic separators are used to separate the alloy from nickel matte. Xanthate or ester collectors are applied under high pH conditions to depress nickel and float copper.
Reagent regime: Butyl xanthate; sodium hydroxide as pH regulator. Nickel depression and copper flotation are realized under strong alkaline conditions. Roughing pH=13, scavenging pH=12, cleaning pH=14. (Reference: Jinchuan Copper-Nickel Mine)