The Copper Flash CC Smelting Process

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Process Overview and Historical Development

Flash smelting is a pyrometallurgical process primarily used for smelting copper sulphide concentrates, though it has significant applications in nickel sulphide concentrate processing. The technology, developed by Finnish mining company Outokumpu Oy from 1948 onwards, saw widespread adoption by mid-1971 as numerous mining companies acquired licenses and established processing plants.

Advantages Over Traditional Methods

Unlike reverberatory furnace smelting, where sulphide oxidation primarily occurs in converters and matte grade depends on concentrate analysis, flash smelting enables predetermined sulphide oxidation degrees. The process utilizes oxidation reaction heat to maintain furnace heat balance, potentially achieving autogenous operation when iron and sulphur contents are sufficiently high.

Process Fundamentals

Copper flash smelting involves injecting fine, dried copper sulphide concentrate and silica flux with air, oxygen-enriched air, or oxygen blast into a hot furnace (≈1500K). This process triggers rapid reactions between sulphide minerals and oxygen, resulting in:

• Controlled oxidation of Fe and S from the concentrate
• Substantial heat generation
• Efficient solids melting

Process Outputs

The process yields three primary products:

1. Molten copper-rich Cu-Fe-S matte (45-65% Cu), containing most copper from the concentrate plus unoxidized Fe and S
2. Molten slag containing iron oxide, gangue, and flux oxides
3. Off-gas comprising SO₂, N₂, and potentially CO₂ and H₂O if supplementary fossil fuel is used

Raw Materials

The main inputs include:

• Copper concentrate
• Silica flux
• Air
• Industrial oxygen

Chemical Reactions and Thermodynamics

The fundamental reactions occurring in the flash furnace can be represented by the following equations:

These reactions are characterized by their strongly exothermic nature, providing the majority or entirety of energy required for:

• Heating the furnace contents
• Melting the charge materials
• Superheating the furnace products

When industrial oxygen or highly oxygen-enriched air is employed as the oxidant source for these reactions, the process can operate with minimal or no additional fossil fuel combustion in the furnace. This characteristic makes the process particularly energy-efficient compared to traditional smelting methods.

The heat generated from these oxidation reactions is crucial for maintaining the furnace heat balance. In cases where the concentrate contains sufficiently high levels of iron and sulphur, the smelting process can become autogenous, meaning it can sustain itself thermally without external fuel input.

Concentrate Characteristics

The feed materials typically undergo flotation concentration before reaching the smelter. The optimal particle size range of 50-100 μm is ideal for flash smelting, requiring only drying before furnace entry. Common minerals include:

• Chalcopyrite (CuFeS₂)
• Pyrite (FeS₂)
• Bornite (Cu₅FeS₄)
• Chalcocite (Cu₂S)
• Covellite (CuS)
• Quartz (SiO₂)

Typical concentrate compositions contain 20-30 mass % Cu, 25-35% Fe, and 25-35% S.

Furnace Operation

Figure 1: Flash smelting furnace

The flash smelting furnace features hydrocarbon fuel burners positioned concentrically in the reaction shaft. These burners maintain optimal temperature conditions for proper reaction rates and concentrate melting. Process efficiency largely depends on dry concentrate composition, particularly the mixture of Cu₂S and CuFeS₂.