CONTINUOUS FIRE REDUCTION OF LIQUID COPPER

Abstract

DESCRIPTIVE SUMMARY CONTINUOUS FIRE REDUCTION OF LIQUID COPPER PREVIOUS ART Smelting of copper concentrates produces matte and slag. Copper matte is converted into blister copper in Peirce-Smith, Hoboken discontinuous converters or by using continuous converting processes such as the Kennecott-Outokumpu or Mitsubishi processes. Blister copper is directed to fire refining process prior electro-refining. The fire refining process is a classical batch process consisting of four stages: charging, oxidation and impurities slagging, reduction and anode casting. After oxidation and slagging, copper contains from 5000 to 10000 ppm of oxygen. Oxygen must be reduced to 800 or 1,200 ppm prior to the anodes casting. Continuous conversion processes, as the Mitsubishi and Kennecott-Outokumpu processes, and the classical conversion processes in Peirce-Smith or Hoboken converters use to work in the blister over-oxidation mode due to their tendency to work with higher grade matte. Thus, blister copper may contain from 4,000 to 6,000 ppm of oxygen. If content of impurities, especially arsenic and antimony, is low enough for not requiring addition of fluxes, blister copper needs only to be degasified, and is ready for reduction. Copper is reduced with fossil reducers or ammonia. The most commonly used reducers are oil and natural gas. Oil or natural gas is injected with air into the bath of molten copper through tuyeres. Copper reduction faces significant limitations in the process rate and efficiency of reducer utilization. Reducer efficiency is below 50%. Injection of liquid or gaseous reducer into the copper produces black fumes in off-gas due to the thermal decomposition of hydrocarbons. Partial carbon utilization in reduction of oxygen from copper causes the presence of carbon particles in the reduction gases, which are partly burnt if the burner flame is oxidizing. Carbon particles are transferred to the furnace off-gas, creating black fumes, which are emitted through a chimney to the atmosphere. L. Klein suggested the use of a gaseous reducer instead of wood, "Gaseous Reduction of Oxygen-Containing Copper", J. of Metals, Col 13, No. 8, August 1961, 545-547, US 2,989,397 June 1961. The study showed that injection of natural gas with air is a better solution that the injection of natural gas only into the liquid copper. The method for deoxidizing copper with reformed natural gas and the related apparatus were patented by Phelps Dodge Corporation in USA and Canada. C. Kuzell, M. Fowler, S. Davis and L. Klein: "Apparatus for Reforming Gases"; US 3,071,454, January 1963; "Gaseous Reduction of Oxygen-Containing Copper", CA 668,598, August 1963.