JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year NON-FERROUS EXTRACTIVE METALLURGY Previous Question Paper (March - 2021 - R18)

Copper is primarily extracted from sulphide ores. The most important ores include Chalcopyrite (CuFeS₂), which is the most abundant, Chalcocite (Cu₂S), Bornite (Cu₅FeS₄), and Covellite (CuS).

The pyro-metallurgical extraction of copper from sulphide ores involves the following sequential stages:

1. Concentration: The crushed ore is subjected to froth flotation to separate the copper-bearing sulphides from gangue minerals, producing a copper concentrate.
2. Roasting: The concentrate is heated in a limited supply of air to partially remove sulphur as sulphur dioxide and convert some iron sulphides to oxides.
3. Smelting: The roasted ore is smelted in a reverberatory furnace or flash furnace with silica flux. This produces a molten matte (a mixture of Cu₂S and FeS) and a slag (iron silicate) which is tapped off.
4. Converting: The molten matte is transferred to a converter. Air is blown through the melt, oxidizing FeS to FeO (removed as slag) and converting Cu₂S to metallic copper, known as blister copper due to the evolution of SO₂ gas.
5. Refining: Blister copper is further purified through fire refining followed by electrolytic refining to achieve high-purity copper cathodes.

Flow sheet summary: Ore → Crushing/Grinding → Froth Flotation → Roasting → Smelting (Matte formation) → Converting (Blister copper) → Electrolytic Refining → Pure Copper.

A reverberatory furnace is a metallurgical furnace used for smelting copper concentrates. Its primary principle is the reverberation of heat, where fuel is burned in a separate firebox and the heat is reflected or radiated from the low-arched roof down onto the charge (ore/concentrate) placed on the hearth.

The furnace consists of a long, rectangular hearth lined with refractory bricks, a firebox at one end, and a flue at the other. The charge is fed through openings in the roof. As the hot gases pass over the charge, they provide the thermal energy required for melting and chemical reactions.

The working process involves the following steps:

• Charging: Copper concentrates, fluxes (silica), and recycled materials are introduced onto the hearth.
• Melting and Smelting: The burning of fuel (pulverized coal, oil, or gas) generates high temperatures (1200°C–1300°C). The heat reflected from the roof melts the charge.
• Chemical Reactions: Within the molten bath, iron sulfide reacts with oxygen and silica to form a liquid iron silicate slag, while the copper sulfide remains as a molten matte.
• Tapping: Due to density differences, the molten matte (heavier) settles at the bottom and is tapped periodically, while the slag (lighter) floats on top and is skimmed off through a separate tap hole.

The furnace is characterized by its ability to process fine concentrates without the need for sintering, as the charge remains relatively stationary on the hearth, preventing dust losses that would occur in blast furnaces.