Preparation of Blast Furnace Feed

Originally, lump sulfide ores were fed to the blast furnace, but this tended to produce large quantities of matte, requiring appropriate levels of iron flux to form the matte. Silica fluxing was also important to displace lead from sulfates and to form a slag. Limits on the input of sulfur due to excessive matte formation were generally around 15 per cent in the feed material. Speiss (an iron-arsenic-antimony intermetallic) was often also present as a separate phase. 

At the Pontgibaud smelter in France, a reverberatory hearth was used for batch calcining, followed by elevation in furnace temperature to cause surface melting and sintering of the calcine into an agglomerated mass, rather than complete melting of the charge. This was withdrawn from the furnace, cooled and broken into lump for blast furnace feed. 

These converters could be considered the forerunners of today s updraft sintering machines. However, they had serious deficiencies they were batch operations, they generated much fume, and the work of manually handling and breaking the sintered material from the pots was laborious and unhealthy. 

This approach significantly improved the prodnctivity of both the roasting operation and the blast furnace, and lead smelters in the early 1900s had large numbers of converters producing blast furnace feed. 

Alternative processes at the time were the Bradford-Carmichael process, in which lead ore was mixed with dehydrated gypsum (plaster) as a binder, was formed into lumps and then processed in the converter, the Savelsberg Process, which fired ore and limestone over a fuel bed in a converter to produce a sintered material as blast furnace feed. 

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