Converting Furnace & Anode Furnace

A diagram of a Converting Furnace	A diagram of an Anode Furnace

In the Mitsubishi Process syphoned copper matte from the Slag Cleaning (CL) Furnace flows by launder into the converting C-Furnace. In this circular furnace, matte is continuously converted to blister copper. Inputs to this furnace include: oxygen enriched blowing air (30-35%), limestone flux, coolant, anode scrap, and molten copper matte. Like the S-Furnace, the top-blown lances are produced from a high-chrome steel alloy from Kubota Metal Corporation. The air enrichment here is lower than that of the S-Furnace. The C-Furnace reactions are highly exothermic so that the heat balance must be carefully controlled to hold the bath temperature as low as possible.

The converter reactions are:
Cu₂S (matte) + O₂ 2 Cu (blister) + SO₂
3 FeS (matte) + 5 O₂ Fe₃O₄ (slag) + 3 SO₂
CaCO3 (flux) CaO (slag) + CO2

In addition, some Cu2S is oxidized to Cu2O:
Cu₂S (matte) + 2 O₂ 2 Cu₂O (slag) + SO₂
2 Cu₂O + Cu₂S 6 Cu + 5 O₂

The blister copper (99% Cu and 0.5% S) is steadily syphoned from the C-Furnace then delivered by "tilting" launder to the anode furnace for further processing. The C-slag contains 12-18% copper, mostly as Cu₂O, overflows the furnace and is water-granulated then recycled to the S-Furnace. The SO₂ enriched off-gas passes through a waste heat boiler and precipitator before being combined the S-Furnace off-gas and delivered to the acid plant. The stack gases at the Kidd smelter typically have a concentration under 0.3 ppm SO₂.

The C furnace uses a multi-lance system (similar to that of the S-Furnace) to inject flux, oxygen-enriched air, and coolant down into the high intensity reaction zone in the melt. Limestone, however, is the chosen flux for the C-Furnace, since a more fluid ternary slag of the Cu₂O-CaO-Fe₃O₄ type is desired.

The C-Furnace has several advantageous environmental features since it is one stationary furnace instead of several rotary type furnaces. It is tightly sealed and can produce much smaller volume of gas with higher SO₂ concentration for the acid plant feed. This allows a more compact acid plant design. The continuous nature of the process allows off-gas which is stable both in volume and strength, resulting in easier operation and lower maintenance costs at the acid plant.

Click here to go back to the Mitsubishi process flow-sheet page