Treatment of Lead Smelter Mattes

Normally copper in lead smelter feed is sufficiently low to fully dissolve in bullion and be recovered by copper drossing as part of the refining stage. However, in the case of high copper feeds (above five per cent of the lead content), a matte can be formed during smelting. This will require retention of sufficient sulfur to form the matte, which tends to be a mixture of lead, iron and zinc sulfides as well as copper sulfide. 

With direct smelting processes such as Kivcet, matte can be tapped directly from the furnace at the appropriate level, separate from bullion and slag. Where matte is separately produced from the blast furnace it is usual to separate slag first and then separate matte from bulUon in a separate forehearih or settling pot where it can rise to the surface and fieeze. Speiss can also form as a separate phase at this stage, as a frozen layer from cooled buUion. Speiss is usually a waste product, but depending on the smelter feed composition can be a point of concentration of nickel. 

The main method of processing matte is by oxidation with oxygen in a converter. Initially zinc and iron sulfides are oxidised first to ZnO and FeO respectively, followed by PbS oxidation and then CU2S to copper metal and SO2. 

Any lead bullion recovered from matte treatment will be rich in copper and can form a significant circulating load through the lead bullion refining stage (see Chapter 12 - Copper Removal or Copper Drossing). 

Converting of copper matte will produce blister copper , which can be cast into anodes for subsequent electrolytic refining. Converter dusts are predominantly lead oxides and basic sulfates containing zinc and can be recycled to the lead smelting operation. 

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