US3744992A - Method for converting copper - Google Patents

Abstract

A METHOD FOR REMOVING ANTIMONY FROM A MATERIAL WHICH COMPRISES AT LEAST ONE OF THE SUBSTANCES COPPER AND COPPER SULPHIDE. OXIDIZABLE IRON OR OXIDIZABLE IRON COMPOUNDS ARE ADDED TO THE MATERIAL WHILE THIS IS IN A MOLTEN CONDITION, THE SAID OXIDIZABLE IRON OR COMPOUND BEING OF A TYPE WHICH ARE SOLUBLE IN MOLTEN COPPER OR COPPER SULPHIDE AND WHICH HAVE A LOW ANTIMONY CONTENT. THE DISSOLVED IRON IS THEN ISOLATED FROM THE MELT BY A PARTIAL OXIDATION PROCESS, SIMULTANEOUSLY OXIDIZING ANTIMONY AND BINDING THE SAME TO THE IRON OXIDE.

Description

United States Patent 3,744,992 METHGD FGR CONVERTING QOPPER Sven Anders Lundquist, Skelleftehamn, Sweden, assignor to Boliden Ahtiebolag, Stockholm, Sweden No Drawing. Filed Nov. 39, 1970, Ser. No. 93,914 Claims priority, application Sweden, Dec. 23, 1969, 17,828/69 Int. (ll. CZZb 15/14 US. Cl. 75-46 5 lClaims ABSTRACT OF THE DISCLOSURE A method for removing antimony from a material which comprises at least one of the substances copper and copper sulphide. Oxidizable iron or oxidizable iron compounds are added to the material while this is in a molten condition, the said oxidizable iron or compound being of a type which are soluble in molten copper or copper sulphide and which have a low antimony content. The dissolved iron is then isolated from the melt by a partial oxidation process, simultaneously oxidizing antimony and binding the same to the iron oxide.

The present invention relates to a method for removing antimony from a material comprising at least one of the substances copper and copper sulphide.

In the manufacture of high grade copper, e.g. for use with electrical appliances, it is necessary to employ an electrolytic refining stage, in order to obtain the requisite degree of purity of the copper. The anodes used in the electrolysis have a copper content of from 98.099.5% Cu and 2.00.5% impurities, these impurities being substantially isolated during the actual process of electrolysis. The type and quantity of impurities present in the copper to be electrolytically refined play an important part in the endeavour to obtain a trouble-free electrolysis. Strict limits are placed on certain impurities, while greater tolerance is permitted with regard to other impurities. It may therefore be necessary to pre-refine the copper anode so that the permitted limits are not exceeded.

Antimony is a metal which has a particularly deleterious effect on the quality of copper refined by electrolysis and endeavours have been made to reduce the quantity of antimony in such copper to a content of at most 1 gram/ton. If the percentage of antimony in the copper anode is too high, for example more than 350 gram/ ton, there is formed during the electrolysis a floating slime of antimony, arsenic and, in certain instances, bismuth, which is liable to infect the copper cathode in a manner whereby the tolerance limits placed on the presence of antimony in the electrolytically refined copper is exceeded, thereby jeopardizing the quality of the copper. Moreover, this floating slime is also liable to result in growths on the cathode, which may cause short circuiting between the anode and the cathode, resulting in a reduced current yield.

Antimony can not generally be removed from antimony-containing copper minerals by enrichment processes, since in the majority of antimony-containing copper finds the antimony is chemically bound to the copper. Extensive separation of antimony by enrichment processe results in copper losses which are too high to make such processes economically feasible. In order to reduce the content of antimony in copper products, it has hitherto been necessary to select crude materials of restricted antimony content or to use various metallurgical processes which only afford limited antimony purification. A large number of ore finds, which can not be processed economically under present day conditions, would be ac- Patented July 10, 1973 cessible for the production of high grade copper if more effective antimony purification methods were to be devised.

With currently used techniques, the copper is subjected to a pre-refining process before being electrolytically refined, the pre-refining process including a number of metallurgical treatment stages, such as roasting, matte smelting and conversion. Each stage of the refining process can be used to remove a certain percentage of antimony. In the roasting stage, antimony is removed by volatilization, although expulsion of antimony seldom exceeds roughly 20% of the total antimony content.

A slag builder, normally silicon dioxide, is charged to the process while smelting the roasted products, wherewith a slag and matte are formed which contain practically all the copper present in the charged material.

When smelting the roasted copper goods, generally called matte smelting, the antimony content is distributed between the slag and matte phases. It is not economically possible to influence this distribution to any great extent, for example by varying the composition or quantity of the slag.

Subsequent to separating the slag phase, the matte is transferred in a molten state to a converter, where it is oxidized with air or air enriched with oxygen-gas to form substantially copper metal, sulphur dioxide and iron oxides. The iron oxides are simultaneously converted to slag by adding silica sand.

The relatively long oxidation treatment in the converter is, in itself, an effective copper refining method, although it is far from suflicient with respect to purifying the copper of antimony.

Several proposals have been made for reducing the antimony content in the product obtained in the converter (the blister copper), including treatment methods using a solid or liquid slag. For example, it has been proposed to use alkali (soda) as the main constituent in a refining slag, whereby antimony oxides are more easily dissolved in the slag, thereby providing a slightly improved refining effect. Treatment with alkali is well known and generally employed. Treatment of blistered copper with CaO has also been proposed, as will be seen, for example, from the German Pat. No. 1,137,223. These refining methods have the disadvantage that the effect afforded thereby is primarily dependent on direct contact between the phase surfaces metal bath-slag bath and/ or solid slag. Even though the metallurgical equilibrium according to the aforesaid German Patent indicates a good refining eifect, serious difliculties exist in practice in obtaining the requisite reaction velocity.

These disadvantages are eliminated by means of the present invention, wherein the molten copper sulphide or the copper is added with oxidizable iron or oxidizable iron compounds which are soluble in molten copper or copper sulphide and which have a low content of antimony, whereafter the dissolved iron is isolated in a conventional manner from the melt by partial oxidation with air or air enriched with oxygen-gas. Examples of suitable oxidizabie iron compounds are pyrites and pyrrhotite. These compounds are suitably charged to the process in pelletized form.

It has been established experimentally with respect to copper conversion that the conversion of antimony from copper matte, copper sulphide or copper metal to slag is directly correlated with the oxidation of iron in the matte and metal melt. When converting copper matte which contains antimony, the major portion of the antimony content passes from the copper and is re-found in the converter slag. By studying the phases of the solidifying converter slag, inter alia in microprobes, it has been established that antimony is present in an oxidized form and (Fe(I-I) Zn, Cu)0. (Fe(III), Al, Sb) O in which both copper and antimony are present in small concentrations.

The content of antimony of converter slags having different contents of magnetite was established experimentally and the results are shown in the table given below:

Magnetite content: Antimony content This confirms the assumption that there is a strong chemical bond between iron and antimony in oxidized form. By carefully following the copper conversion process, it was clearly established that the antimony transfer rate from copper matte and copper metal to slag is functionally directly correlated with the oxidation of iron in the matte or copper.

Upon oxidation of the melt, the iron content is practically completely oxidized before any appreciable quantity of copper is oxidized. In sulphurous environments, i.e. when the refinement process is to be carried out with matte melts, the sulphur from the sulphides is oxidized in parallel with the iron and reduces the slag forming rate with a constant supply of oxidant to the system. Subsequent to being oxidized, the iron oxide floats to the surface, bearing the isolated antimony. The iron oxide is then either mechanically scraped from the surface of the copper melt or, subsequent to forming slag with silicic acid, is decanted 01f in liquid form.

The described refining method, in which iron or iron compounds having a low antimony content are charged to the refining system, is suitably carried out in connection with copper conversion processes andin a copper converter, although, of course, it may be carried out in other types of furnaces, such as, for example, flame furnaces or rotary furnaces. Iron scrap, iron-copper-scrap, iron sulphides or chalcopyrite are examples of suitable iron additives free or essentially free from antimony which can be charged to the system. The most efiective of these with respect to removing antimony is naturally iron scrap, while the least effective is chalcopyrite, although when using iron scrap and iron sulphide the conversion period is lengthened without increasing the production of copper. Suitable oxidants are air-oxygen or air enriched with oxygen. The oxygen is preferably introduced beneath the surface of the bath, either by means of tuyeres or a lance.

The invention will now be illustrated with reference to the following single example.

4 EXAMPLE In a copper converter which was charged with matte containing 35% copper and 0.14% antimony, the copper sulphide, subsequent to blowing the matte, contained 0.04% antimony. For the purpose of further reducing the antimony content, granulated FeS was added in a quantity of 6% of the quantity of copper and, subsequent to oxidation of the quantity of charged FeS to FeO and Fe O the antimony content in the ready-blown copper had dropped to 0.02%. Other charges having the same starting material and treated in the same manner, although lacking additions of FeS, contained, subsequent to readyblowing, 0.035-0.040% Sb. With a later test, copper sulphide was treated in the same converter with a matte of low copper content and low antimony content. The copper sulphide charge, approximately 130 tons, was treated with 10 tons of matte. The antimony content was reduced thereby from 0.06% to 0.03% in the ready-blown copper. The antimony content, without the addition of matte of low copper content, was 0.045% after ready-blowing.

It is evident from the example that the method of the present invention enables the antimony content in the produced copper to be considerably reduced and that this reduction enables a material rich in antimony to be processed without risk that the antimony content will impair the quality of the product.

What is claimed is:

1. A method for removing antimony from copper sulphide, characterized in that to the copper sulphide in molten state is added oxidizable metallic iron which is soluble in molten copper sulphide and has a low content of antimony, whereafter the dissolved iron is isolated from the melt by a partial oxidation, antimony being at the same time oxidized and bound to the iron oxide, which forms a separate insoluble phase in the melt.

2. A method according to claim 1, characterized in that iron is added in the form of scrap iron.

3. A method according to claim 1, characterized in that iron is added in the form of iron-copper scrap.

4. A method according to claim 1, characterized in that the method is effected in a copper converter.

5. A method according to claim 1, characterized in that oxidation is carried out with oxygen-air or an air enriched with oxygen.

References Cited UNITED STATES PATENTS 103,434 5/ 1870 Du Motay --76 970,686 9/ 1910 Clamer 7576 1,886,903 11/1932 Ralston et al. 75-74 3,258,330 6/1966 'Ito 7576 X 3,262,773 7/ 1966 Fritze 75.76 3,432,289 3/ 1969 Spitz 75-76 X 3,561,951 2/ 1971 Themelis 75-76 X L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner