GB779872A - Process for roasting sulphide ores - Google Patents

Abstract

Sulphide ores of a grain size of about 1 mm. down to dust fineness are roasted by introducing the ore into the upper part of a furnace and introducing oxygen-containing gas into the lower part of the furnace through a horizontally disposed rotating distributing device, the roasted ore being withdrawn from the lower part of the furnace and the product gas being withdrawn from the upper part, the ore descending with a swirling motion to form a dense phase fluidized bed. The ore may be introduced in the upper periphery of a cylindrical furnace so that it swirls gradually downwards to the middle of the furnace or alternatively the ore may be introduced axially into the upper part of the furnace and led downwards towards the periphery. Suitable apparatus is described and claimed in Specification 779,871. Temperature control may be effected by mixing cool burnt ore or dust separated from the product gas with the fresh ore introduced or alternatively inert substances may be added to the ore. The air for roasting may be admixed with cooled recycled roaster gases. Reference is made to the roasting of pyrites and zinc blende. According to an example a cylindrical furnace 3 metres in diameter was charged with 50 tons of pyrites per day in a size of 1mm. down to dust fineness, the ore remaining in the furnace in a layer 2 metres deep for about eight hours. The roasted product consisting largely of ferric oxide together with a minor amount of iron sulphide and gangue was withdrawn at the bottom of the furnace whilst the product gas which left the furnace at a temperature of 950 DEG C., contained 7 volume per cent of sulphur dioxide and 11.8 volumes per cent of oxygen. The product gas was cooled in a steam boiled to a temperature of 350 DEG C. and sufficient of this cooled gas was admixed with the roasting air to reduce the product gas temperature to 900 DEG C.