AU2005282475B2 - Method of continuous fire refining of copper - Google Patents

Description

METHOD OF CONTINUOUS FIRE REFINING OF COPPER BACKGROUND OF INVENTION 1. Field of Invention: This invention relates to a method of intensive, continuous fire refining of 5 blister copper or secondary copper. 2. Description of the Prior Art: The fusion of copper concentrates produces matte and slag. The copper matte is converted into blister copper in Peirce-Smithconverters or continuous converting processes such as Kennecott-Outokumpu or Mitsubishi. The blister 10 copper is directed to fire refining process prior to electrolytic refining. The fire-refining is carried out in stationary air furnaces or rocking furnaces, known as anode furnaces because the commonest manner of molding refined copper is in the shape of anodes, which are transferred to the electrolytic refining. The fire-refining process is a classic discontinuous (batching) process that consists 15 of four stages: loading, oxidation and scorifying of impurities, reduction and molding of anodes. The total time of the refining cycle without the fusion stages varies from 10 to 24 hours. The oxidation stage depends strongly on the composition of the blister copper, especially on the contents of sulfur and oxygen, and can take from 1 to 3 20 hours with a typical intensity of air blowing of 1200 Nm 3 /h. The oxidation of the copper is followed by the scorifying of the slag, and depending on the content of impurities, particularly lead, arsenic and antimony, fusion agents can be applied for their extraction -silicon flux for the scorifying of lead, sodium flux (mixture Na 2

CO

3 CaCO 3 ) for the scorifying of the arsenic and antimony. The oxidized copper, after 25 oxidation stage contains from 5000 to 10000 ppm of oxygen. The copper is reduced by application of carboneous reducer or ammonia. The most common reducers in industrial use are petroleum or natural gas. One or the 1 other reducer ise injected with air into the melt through one or two nozzles. Copper reduction faces significant limitations in the process rate and efficiency of utilisation of the reducer. Copper reduction faces significant limitations in the speed of the process and efficient utilization of the reducer. The reduction stage of the liquid 5 copper charge, which fluctuates from 150 to 400 tons, varies in the range from 1.2 to 3.0 hours. The reported reductant efficiency is below 50%. The injection of liquid or gaseous reducers into the copper produces black carbon fumes in the outlet due to thermal decomposition of hydrocarbons. The partial use of carbon in the reduction of the copper's oxygen induces the presence of carbon particles in the reduction 10 gases, which are partly combusted if the burner flame is oxidising. Thus, the carbon particles are transferred to the oven's outlet gases, creating the black carbon fumes emitted from the chimney into the atmosphere. The oxidation and reduction of liquid copper has been practised for centuries and it was first described by Georgious Agricola (G:Agricola: "De Re Metallica", 15 translated from Latin, first edition 1556 by Hebert C. Hoover y Lou H. Hoover, Dover Publications, 1950, 535-536). After the oxidation of the copper with air in open hearth furnace and the removal of impurities, the copper was reduced with a wood. This reduction with sticks of wood (beating) is still practised in some smelters. L.Klein presented a new idea of the use of a reducing gas as a substitute of a 20 wood. ( "Gaseous reduction of oxygen-containing copper", J. of Metals, Vol 13, N8, August 1961, 545-547 ; U.S. Patent N' 2.989.397, June 1961). The study showed that the injection of natural gas with air provides a better solution than injecting only natural gas into the liquid copper. The copper deoxidization method with reformed natural gas and related apparatus was patented by Phelps Dodge Corporation in 25 USA and Canada. (C.Kuzell, M. Fowler, S. Davis y L. Klein: "Apparatus for reforming gases" U.S. Patent No 3.071.454, January 1963; "Gaseous reduction of oxygen containing copper", Canadian Patent NO 668.593, August 1963) R.Beck, C.Andersen and M. Messner patented the copper deoxidization process with a mixture of natural gas/air. ("Process for deoxidising copper with 30 natural gas-air mixture, U.S. Patent NO 3.619.177, November 1971). 2 The Anaconda Company patented a process of copper deoxidisation in a rocking furnace by injection via needles of a mixture of natural gas or Diesel oil and water vapour (W. Foard and R. Lear: "Refining copper" U.S.Patent N*3,529.956, September, 1970). 5 J. Henderson and W. Johnson patented for ASARCO, the method of reducing copper in a rocking furnace via nozzles ("Gas poling of copper", U.S.Patent NO 3.623.863, November 1971). In an article "Gaseous deoxidization of anode copper at the Noranda smelter", Canadian Metallurgical Quarterly, Volume 11, N* 4, 1972, 629-633 G. Mckerrow and 10 D. Panell revised the evolution of the copper deoxidization methods at the Noranda smelter by means of natural gas injected via nozzles into a rocking oven. J. Oudiz made a general review of copper reduction processes ("Poling processes for copper refining", J. of Metals, Vol 25, December 1973, 35-38), based on industrial data on reducer consumption, benefits and problems related with the use of various 15 reducers, reformation reactions and efficiency of the reducer. L.Lavrov ("Deoxidization of anode copper by natural gas and steam mixture", The Soviet Journal of Non-Ferrous Metals, Vol N*19, N*5, English translation, May 1978, 25 26) verified the use of a mixture of natural gas and steam injection through a needle. C. Toro and V. Paredes ("Partial substitution of Diesel petroleum by Enap-6 20 as a reducing agent in the process of obtaining anode copper at the Potrerillos smelter", 34th Annual IIMCh Convention, November 1983, Rancagua) developed in industrial scale and demonstrated the possibilities of the use of heavy oil (ENAP-6), with a high content of sulphur and a low price, for the reduction of copper. A continuous copper fire-refining process does not exist at global level. All the 25 smelters use either the classic open hearth furnace or the rocking anode furnace to produce fire-refined copper operating in batching mode.The only patented continuous fire-refining process is that of Wuth et al.: (W. Wuth, G. Melcher, H. Weigel, Klockner Humboldt Deutz AG: "Process for continuously refining contaminated copper in the molten phase", Patent N* ZA7603039, Germany, 1977 30 04-27), (Klockner Humboldt Deutz AG: "Method of continuous refining of impure 3 copper in the liquid phase", Patent N' GB1 525786, Great Britain, 1978-09-20), (H. Weigel, G. Melcher, W. Wuth (Klockner Humboldt Deutz AG): "Method for continuous refinement of contaminated copper in the molten phase", Patent N* US127408, USA, 1978-11-28), which was developed up to a small pilot plant s established in the sixties and never reached industrial implementation. The process is based on the continuous flow of copper to the two small open-hearth type ovens in cascade. In the first oven the copper is oxidized with air blown by means of vertical needles, while in the second oven the oxidized copper is reduced with petroleum or reducer gas injected through vertical needles.Each document, reference, patent 10 application or patent cited in this text is expressly incorporated herein in their entirely by reference, which means that it should be read and considered by the reader as part of this text. That the document, reference, patent application, or patent cited in this text is not repeated in this text is merely for reasons of conciseness. Reference to cited material or information contained in the text should not be 15 understood as a concession that the material or information was part of the common general knowledge or was known in Australia or any other country. Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of 20 any other integer or group of integers. SUMMARY OF INVENTION The industrial practice of fire-refining blister copper is its oxidation and subsequent reduction carried out in a stationary or tilting anode oven in a 25 discontinuous manner. This invention resolves this difficulty establishing operational continuity to the industrial process. The method consists of the use of a continuous gravitational flow of copper to two reactors in series connected by a canal, in which the degasification and extraction of impurities by scorifying is carried out in the first reactor followed by reduction of the copper in the second reactor. This intensive 4 operation of fire-refining blister copper or secondary copper is continuous, using packed beds to increase oxidation and reduction rates in each reactor, respectively, with shorter times of operation. In one aspect of the present invention, there is provided an intensive 5 continuous pyrometallurgical method for fire- refining copper in two reactors, said method comprising the steps of: (a) feeding impure copper in a continuous manner into the first oxidation reactor or oxidation chamber of a common reactor in which said reactor has a fire-resistant chamber to contain said copper; in which said fire 10 resistant chamber contains a bed packed with ceramic grains or other chemically neutral grains; (b) simultaneously supply combustion gases containing oxygen or air through said bed packed with ceramic grains; for the oxidation of the copper; for the formation of sulfurous gases; and to form a slag that collects 15 impurities; (c) bleed oxidized copper and refining slag continuously from the first reactor; (d) continuously feed oxidized copper to a second oxidation reactor or reduction chamber in a common reactor; in which this latter reactor has a fire-resistant chamber to contain said copper, in which said fire-resistant 20 chamber contains a bed packed with coal; (e) continuously reduce the oxidized copper with coal and reducing gases formed by partial combustion of the fuel and coal; and (f) continuously bleed reduced copper from the second reactor. BRIEF DESCRIPTION OF THE DRAWINGS 25 Figure 1: is an exploded sectional back and side view of the principle of the intensive copper fire-refining pyrometallurgical method in two packed bed type reactors in cascade. 5 DETAILED DESCRIPTION OF INVENTION This invention refers to a pyrometallurgical method of continuous refining of blister copper or copper scrap that makes use of a gravitational flow of liquid copper through two reactors in series. 5 Thus, the invention leads to a continuous copper refining method consists of following stages: a) Liquid copper (4) is transferred from a continuous converting furnace or from a holding furnace through a canal to the first oxidation reactor (7). b) Oxidation of the copper, removal of the sulfur to a gas phase and 10 removal of the impurities from the refining slag: - Dispersion of liquid copper and gravitational flow dropping through a packed bed of ceramic grains (3); - Injection of air optionally oxygen enriched or the mixture of air with natural gas or petroleum (2) through nozzles: 15 [CnHmlfuei + (n+m/2+k/2) [02air -- n[CO2]gas + m/2 (H20]gas + k/2 [O2]gas - Countercurrent flow of the air or combustion gases containing oxygen (2) rising within the packed bed (3); - Oxidation of the copper and the impurities: {Culcopper + 1/2 [O2]air - [Cu(O)]copper 20 [Cu(S)]copper + 2 [Cu(O)]copper - [SO2]gas [Me]copper + [Cu(O)lcpper -> [MeO]siag 2 [Cu(O)]copper -> [Cu20]siag 2 [As]copper + [Na2CO3]flux + 2.5 [O2]air -- 2 [NaAsO3]sag + [CO2]gas [Pb]copper + [SiO2]flux + 1/2 [02]air -> [PbSiO 3 ]siag 6 - Liberation of the sulfur dioxide from the copper (degasification of copper); - Formation of refining slag from cuprous oxide and oxide of the impurities such as iron, zinc, lead, arsenic and antimony; 5 - Optional loading of fluxes (6) determined by the content of impurities in the blister copper (silicon flux and/or sodium flux); - Separation of oxidized copper in the slag and slag in the hearth of the furnace; - Continuous bleeding of oxidized copper (8) through a siphon or 10 inclined orifice in the bleeding plate; - Continuous bleeding of slag (1) through the bleeding plate; - Evacuation of the hot gases (5) via a chimney. c) Continuous transference of oxidized copper (8) to the reduction oven through a canal;;d)Reduction of oxidized copper, containing from 5000 to 15 9000 ppm of oxygen, in the second reactor, reduction oven (12): - Dispersion of the liquid copper and gravitational flow through a packed bed of grains of coal or grains of coke having a low content of sulfur (13); - Injection of air optionally oxygen enriched or the mixture of air 20 with natural gas (15) through nozzles; . Partial combustion of the fuel: [CnHm]fuei + (n+m/4)/2) [O2]air - n[CO]gas + m/4 [H2]gas + m/4 [H2 0 ]gas [C]carbon + 1/2 [O 2 ]air - [CO]gas [H20]gas + [Cicarbon -> [H2]gas + [CO]gas 25 - Countercurrent flow of combustion gases containing carbon monoxide and hydrogen upwards from the packed bed (13); - Reduction of the copper: [Cu(0)]copper + [Cicarbon -> [Culcopper + [CO]gas 7 [CU(O)]copper + [CO]gas -> [CUlcopper + [CO2]gas [CU(O)]copper + (H2]copper -> [CU]copper + [H20]gas [CO2]gas + [C]cabon -- 2 [CO]gas [H2 0 ]gas + [Cicarbon -> [H2]gas 5 - Continuous bleeding of reduced copper (14) containing from 800 to 1800 ppm oxygen, through a siphon or inclined bleeding orifice; - Injection of air (11) through nozzles on the packed bed of coal for the post combustion of the reducing gases that leave the 10 bed; [CO]gas + %/ [O 2 ]air - [CO2]gas - Evacuation of the reduction gases (9) to a chimney; e) Transference of the refined copper (14) directly in the molding wheel or in a transport channel to a retaining oven. 15 The principle of the process is illustrated schematically in Figure 1. The blister copper (4) dispersed on the surface of the ceramic bed (3) flows descending in the shape of small veins and drops that come into contact with a flow of hot gases in countercurrent that contain from 5 to 20% of oxygen. An extremely high ratio of the area of the liquid copper surface (4) with regard to its volume gives, as a result, a 20 high rate of oxidation. The liquid copper (4) in movement increases the coalescence of bubbles of sulfur dioxide and their removal. The large contact area of the interface Cu 2 O/Cu induces the transference of the oxides of the impurities to the Cu20 and the formation of slag. The oxidation parameters, temperature and oxygen content of the 25 copper can be controlled precisely by the flow of air and the flow of fuel (natural gas, petroleum) through the nozzles (2). Similarly, the dispersion of oxidized copper (8) in the packed bed of charcoal (13) increases the surface area of reaction resulting in a 8 very high rate of reduction. There are two possible modes of operation in this latter case. First, the coal (13) can play the double role as a fuel and as a reducer. The combustion of coal (13) by injecting air through the nozzles (15) produces heat and carbon monoxide. The hot gases and the coal directly reduce the oxidized copper 5 (8). Second, the injection of natural gas with air or petroleum (15) generates hot reducing gases, which reduces the copper together with the charcoal. The temperature of the copper can be controlled in a precise manner by the flow of air and fuel (15), and the content of oxygen in the refined copper by the height of the packed bed of charcoal (13), which is loaded semi o continuously depending on its 10 consumption (10). a) This invention has following advantages compared with traditional methods for fire-refining copper: Investment costs are significantly lower due to the small size of the reactors for the same capacity of production; b) Labor requirements are lower due to the totally continuous operation mode; 15 c) Safety conditions of the fire-refining area are improved as a result of the operation using a smaller number of operators exposed to high temperatures; d) Control of the process is more precise due to the small inertia of the system. The copper's oxygen content and temperature can be maintained within a close range in a precise manner; 20 e) Fuel consumption is significantly low, particularly in the case of cooperation with the continuous conversion operation of copper matte and continuous molding of anodes - two molding rings. There are no periods of waiting time for loading and inter-operational standstill; f) Sulfur removal is even more efficient, in comparison with the anode ovens 25 equipped with porous plugs. The intensive movement of the liquid copper induces the coalescence of the bubbles of sulfur dioxide and their removal from the copper; g) Impurity removal level is high due to the development of the surface area of the cuprous oxide/copper and flux/copper interfaces; 30 h) The efficiency of the reducer is high from 30 to 50%, due to the countercurrent flow and high area of reaction; 9 i) The emission of gases with carbon black (soot) is diminished drastically reducing the negative impact of the process on the environment. EXAMPLE 1 The continuous refining of copper in a small smelter with a production 5 capacity of 40,000 t/year, which is equivalent to a flow of copper of 5 t/h. Blister (4) containing 3000 ppm 0 and 400 ppm S flows from a retaining oven to the first oxidation reactor (7) from an 11 m long canal. The oxidation oven (7) is a vertical cylinder with a diameter of 1.2 m and a height of 1.8 m. The internal space is a cylinder with a diameter of 0.6 m and a height of 1.4 m, filled with grains of the waste 10 of chrome magnesite bricks (3) having a diameter of 50 mm. The oven is equipped with three 25 mm diameter nozzles at the level of the oven of 700 mm, it has a siphoning block for bleeding the copper (8) and a bleeding block for the refining slag (1). The flow of natural gas (2) is maintained within the range of 3 - 8 Nm 3 /h and the flow of air (2) within the range of 250 - 400 Nm 3 /h. The temperature of the oxidized 15 copper (8) is controlled between 1190 - 1210 *C and the content of oxygen in the copper (8) between 7500 - 8500 ppm. The generation of slag (1) is close to 50 - 70 kg/h. The slag (1) is bled into a small, one-ton pot and recycled to the Pierce-Smith converters. The oxidized copper (8) flows through an 8 m long canal directly to the reduction oven (12). This oven (12) has the same dimensions as the oxidation oven 2O (diameter 1.2 m and height 1.8 m) and is filled with grains of charcoal (13) (10 - 40 mm in diameter). The air (15) is blown through three nozzles and is injected into the charcoal bed (13) with a flow rate of 300 - 500 Nm 3 /h; the charcoal (13) plays the role of fuel and reducer. No additional fuel is used. The consumption of charcoal (10) is within the range of 7 - 9 kg/t of copper. The temperature of the refined copper is 25 maintained within the range of 1190 - 1200 C and the content of oxygen in the copper (14) between 800 and 1200 ppm. The copper (14) is bled continuously into a pot and transported to a retaining oven. EXAMPLE 2 Continuous refining of copper in a smelter with a production capacity of 30 160,000 t/year using the Mitsubishi process. The production of copper corresponds 10 to a continuous flow of copper of 20 t/h. Blister (4) containing 3000 ppm 0 and 400 ppm S flows from the continuous conversion oven to the first oxidation oven (7) through an 18 m long canal. The oxidation oven (7) is a vertical cylinder with a diameter of 2.2 m and a height of 2.5 m. The internal space is a cylinder with a 5 diameter of 1.4 m and a height of 2.0 m filled with remains of chrome magnesite bricks (3), 50 mm in diameter. The oven (7) is equipped with three 50 mm diameter nozzles at the level of 800 mm; its bleeding block is a siphon for the copper (8) and a bleeding orifice for the refining slag (1). The flow of natural gas (2) is maintained within the range of 10 - 25 Nm 3 /h and the flow of air (2) within the range of 100 10 1500 Nm 3 /h. The temperature of the oxidized copper is controlled within the range of 1190 - 1210 0 C and the content of oxygen in the copper between 7500 - 8500 ppm. The generating of refining slag (1) is close to 200 - 300 kg/h. Said slag (1) is bled into buckets having a capacity of five tons and recycled to the Mitsubishi converter. The oxidized copper (8) flows through a 12 m long canal directly to the reduction 15 oven (12) that has the same dimensions as the oxidation oven (diameter 2.2 m and height 2.5 m) and is filled with grains of charcoal (13) (10 - 40 mm in diameter). The air (15) is blown through three nozzles and is injected into the charcoal bed (13) with a flow rate of 1000 - 2000 Nm 3 /h. The flow of natural gas (15) is maintained between 30 - 100 Nm 3 /h. The consumption of coal (10) is within the range of 4 - 6 kg/t of 20 copper. The temperature of the refined copper is maintained within the range of 1190 - 1200 *C and the content of oxygen in the copper (14) at about 800 - 1200 ppm. The copper (14) is continuously bled into the molding ring. Two rings ensure a continuous operation. 11

Claims (11)

1. An intensive continuous pyrometallurgical method for fire- refining copper in two reactors, said method comprising the steps of: 5 (a) feeding impure copper in a continuous manner into the first oxidation reactor or oxidation chamber of a common reactor in which said reactor has a fire-resistant chamber to contain said copper; in which said fire resistant chamber contains a bed packed with ceramic grains or other chemically neutral grains; 10 (b) simultaneously supply combustion gases containing oxygen or air through said bed packed with ceramic grains; for the oxidation of the copper; for the formation of sulfurous gases; and to form a slag that collects impurities; (c) bleed oxidized copper and refining slag continuously from the first reactor; 15 (d) continuously feed oxidized copper to a second oxidation reactor or reduction chamber in a common reactor; in which this latter reactor has a fire-resistant chamber to contain said copper, in which said fire-resistant chamber contains a bed packed with coal; (e) continuously reduce the oxidized copper with coal and reducing gases 20 formed by partial combustion of the fuel and coal; and (f) continuously bleed reduced copper from the second reactor.

2. A method according to claim 1, wherein stage a) said impure liquid is a liquid blister copper, copper melted from solid copper scrap metal or scrap copper.

3. A method according to claim 1, wherein stage a) the copper loaded as liquid metal 25 may contain from 0 to 20% of added solid copper loaded on the surface of the packed bed and melted with the hot gases that leave the oven.

4. A method according to claim 1, wherein stage a) said copper is dispersed by gravitational flow through the bed packed with ceramic grains. 12

5. A method according to claim 1, wherein stage b), the oxidization gases originate from the combustion of natural gas, petroleum or another fossil fuel with an with excess oxygen, corresponding to an oxygen content in said gases in the range of 5 to 21%. 5

6. A method according to claim 1, wherein stage b) the flow of fuel injected by the nozzles to produce the combustion gases depends on the size of the reactor and their heat loss varies from 0 to 2 kg/t of copper. Correspondingly, the flow of air varies from 50 - 100 Nm3/t of copper and the enriching in oxygen between 21 to 35%. 10

7. A method according to claim 1, wherein stage c), the impurities with higher affinity for oxygen than copper, such as iron, zinc, arsenic, antimony, are oxidized together with cuprous oxide to form a refining slag.

8. A method according to claim 1, wherein stage c) the addition of silicon or sodium fluxes is determined by the content of impurities; the addition of silicon varies 15 between 0 to 0.1% of the copper mass and the sodium flux, as a mixture of sodium carbonate and calcium carbonate, between 0 and 0.2% of the copper mass.

9. A method according to claim 1, wherein stage d) the oxidized liquid copper is dispersed by gravitational flow through the packed bed of charcoal or coke with low sulfur. 20

10. A method according to claim 1, wherein stage e) the flow of fuel injected into the reduction reactor through the nozzles varies between 0 to 5 k/t of copper depending on the size of the reactor and its heat losses; the flow of air through said nozzles between 70 - 299 Nm3/t of copper; the consumption of charcoal or coke varies between 3 to 8 kg/t of copper. 25

11. A method according to claim 1, wherein air is injected into the gases left by the second reactor via a nozzle on the charcoal bed for their complete post combustion. 13