A METHOD OF PURIFYING NON-FERROUS METAL MELTS FROM FOREIGN ELEMENTS

Abstract: In a method of purifying melts, substantially comprising non-ferrous metals, preferably copper and lead, from impurities in the form of not-readily separable elements, such as cobalt, nickel, lead, bismuth, antimony and arsenic, there is injected into the melt at least one solid reactant with the aid of a carrier gas. During the process of injection the melt is maintained under strong turbulence. The carrier gas and the solid reactant are selected so that there is formed with the impurifying element or elements a product whose melting point is higher than the temperature prevailing in the melt, which has a density different from that of said melt. The resultant product is then separated from the melt. The melt may, for example, comprise copper, and the impurifying elements may be nickel and/or cobalt, and the reactant silica, which forms a solid product with nickel and/or cobalt. Suitably, the melt can also contain an oxidant, such as iron (III) oxide or copper oxide. The melt may also comprise crude lead and the impurifying elements antimony and/or arsenic. In this case the oxidant may be lead oxide, which may also function as the solid reactant for forming a solid product. Other combinations are also conceivable.

Description: A METHOD OF PURIFYING NON-FERROUS METAL MELTS FROM FOREIGN ELEMENTS The present invention relates to a novel method of purifying melts of non-ferrous metal from foreign elements, such as cobalt, nickel, lead, bismuth, antimony and arsenic. It is known to remove foreign elements from metal melts by forming slags, drosses and like sep¬ arable products. It need only be ensured that the coefficient of distribution between metal and the formed product is such that the foreign substances to be removed are enriched in the product, which substances can then be separated from said product. One is dependent, however, on the fact that the distribution coefficient is often non- advantageous, and that for process technical reasons, a theoretic¬ ally favourable distribution cannot always be achieved, and that consequently a relatively high content of the molten metal is often dissolved in the resultant product phase and/or an undesirably high residual content of the foreign substance is obtained in the non- ferrous metal melt. It is therefore desirable to improve the possibilities of removing foreign substances from metal melts with a high degree of selec¬ tivity and without appreciable losses, particularly when the sub¬ stances have a low activity in the melt or have reaction character¬ istics similar to those of the melt, e.g. in accordance with the oxygen potential diagram, which losses would require the resultant product to be worked-up separately and to contain large quantities of the metal constituting the main ingredient of the melt. Thus, it is possible to remove nickel from a crude copper melt with the aid of so-called thin slag, whereat there is obtained a slag containing copper and nickel in a ratio of about 3.5:1. In the case of high nickel contents, this means that a relatively large quantity of copper must be treated in a separate nickel-recovery process, and that the total process becomes very expensive. It has now been found that an improved relationship between the amount of impurities in the slag, drosses or other separable products can be improved by injecting into the melt with the aid of a carrier, o:-.;?ι gas a solid reactant, such as an oxidant, reductant and slag former, while creating a turbulence in the melt, which reactant at prevailing temperatures reacts with the substance to be removed but which does not react to any appreciable degree with the non-ferrous metal con- stituting the main ingredients of the melt, thereby to form a product having a melting point which is higher than the prevailing temperature of the melt. Further, the turbulence created in the melt must be so strong and the reactant introduced in such a manner that reactions taking place during the process can proceed over a suf- ficient reaction time and have a sufficient contact surface. The solid reactant can be injected with a carrier gas which is oxidizing, reducing or neutral, whereat an oxidizing carrier gas is preferably used when the substance to be removed from the melt is first to be oxidized and then bound to the slag with the aid of the solid re- actant. It will be understood that the solid reactant may comprise an oxidant, which can be chosen selectively with respect to the substance to be removed, whereat the main constituent of the melt is not oxidized to any appreciable extent. This also applies to other kinds of solid reactants which can be used in accordance with the invention, such as solid reductants and slag formers. The characterized features of the invention are disclosed in the following claims. A satisfactory turbulence can be created in the melt by carrying out the reaction in a reactor vessel in which the melt is agitated by electrical, mechanical or pneumatic means. Mechanical turbulence can be achieved by carrying out the reaction in a rapidly rotating reactor vessel, e.g. a reactor vessel of the Kaldo type or of the kind normally known as a top-blown rotary reactor. Pneumatic turbu¬ lence can be achieved, for example, in a non-rotating converter of, for example, the LD type, side-blown converters, such as converters of the PS-type, and bottom-blown converters of, for -example, the Thomas type. Preferably, however, there are used injection metal- lurgical methods which will also create the necessary turbulence. Thus, it is preferred in carrying out the method of the invention to use such injection metallurgical methods in which a solid powder- ous reagent and gaseous carrier are introduced into the melt at a location beneath the surface of the bath, with such impulse that a heavy turbulence is created in the whole of the melt, said reagent and carrier being introduced into the melt through lances extending into said melt or through tuyeres arranged in the wall of the reactor vessel. In this respect, there can be used, for example, a reactor vessel of the kind described in SE,B, 7303382. Thus, it is an essential feature of present application that both the supply of solid reactant into the melt and the removal of formed product from the melt is carried out by using a carrier gas and that simultaneously the reactions in the melt are sped up by means of the violent turbulence of the melt. Prior art processes in this technical field have utilized either a turbulent melt bath, such as TBRC and Kaldo converters, by which the reaction may be sped up, but a .fast removal of the solid reaction product is made difficult thereby, which leads to considerable drawbacks, or solely the injection of reactants by means of carrier gas. By this latter method the reactant m y be to a certain extent distributed into the melt and thereby the reaction is sped up, but the carrier gas will entrain unreacted reactant to an extent which is too high to be desirable, thereby considerably reducing total efficiency of the process. By the com¬ bination of injection and turbulence provided by the present inven- tion is the reaction speed so rapid that removal of unreacted re¬ actants is to a great extent avoided. The forced transportation of solid reactant through the turbulent melt according to present inven¬ tion gives, however, a surprisingly good synergetic effect, which contributes to the process economy. The method is suitable for application in the purification of melts of non-ferrous metals in those cases where it is possible to obtain between the added substances and the substances to be removed a solid compound having a melting point which is higher than the prevailing temperature in the bath of non-ferrous metal. Such solid compounds may comprise oxides, sulphides, arsenides, antimonides and suicides, and corresponding oxygen-containing compounds, such as sulphates, arsenates, antimonates and silicates. As an example of a suitable system comprising oxidation and slag-forming can be men¬ tioned a blister copper melt containing nickel and cobalt in quan- tities greater than 0.1%, said quantities rendering it difficult to subsequently refine crude copper electrolytically. In this case con¬ veniently finely powdered iron(III)oxide, silica and an inert car¬ rier gas are injected through a lance or tuyeres into a reactor vessel which is suitable for carrying out injection metallurgic treatment processes. When found together with quartz, nickel oxide and cobalt oxide form not-readily dissolved silicates, which are collected in a slag phase. As a result of the formation of silicates, the resultant oxides obtain a very low activity in the slag, thereby enabling the slag to be effectively refined. The slag, whose density differs from that of copper, has very low solubility in crude copper, thereby enabling the resultant slag phase to be effectively sepa¬ rated. A further example of a suitable system for purifying non-ferrous metal melts in accordance with the invention, including oxidation and slag-forming processes, is a crude-lead melt containing anti¬ mony. Iron(III) oxide can also be used in this case as the oxidant, and silica as the additive, for forming a suitable solid product. In general, the oxidant used shall be of a kind which will not oxidize the non-ferrous metal to any appreciable extent. It lies within the scope of one of normal skill in this art, in each par¬ ticular case to select from available oxidants a suitable agent having the ability of oxidizing the foreign elements but not the non-ferrous metal, and one in which the oxide of a respective for- eign element is able to form a solid compound at prevailing tem¬ peratures. It will be obvious that it is not possible when applying the method of the invention to remove any foreign substance whatso¬ ever, but that the removal of these substances depends on the existence of a selective oxidant for the foreign element in question, The oxidant for forming a solid substance with the resultant oxide suitably comprises a so-called slag former and is conveniently a basic oxide when the oxide of the foreign element is an acid oxide, and vice versa. A metallurgist of average skill should, in this case, be capable of selecting a suitable additive. Examples of oxidants suitable for use in accordance with the inven¬ tion include iron(III)oxide and oxides of non-ferrous metals, such as copper oxide, lead oxide, manganese oxide and the like. Examples of additives include quartz, lime and other slag formers. Partic¬ ularly suitable non-ferrous metals which can be purified advan- tageously when practising the method of the invention include copper, nickel, lead and other metals contaminated with selectively react- able, foreign substances. As beforementioned nickel, bismuth and antimony constitute in copper impurities which render further working of the copper difficult, and which unless removed from the final product result in poor-quality products which can only be sold at reduced prices. The presence of bismuth, arsenic and antimony in lead is particularly undesirable. As before inferred, it also lies within the scope of the invention to separate the foreign substance in the form of other solid com¬ pounds than oxides and silicates. Thus, the invention can also be applied for refining lead with respect to, for example, antimony and arsenic, by injecting into a lead melt components which form a speiss with arsenic and antimony, preferably iron powder, which is suitably injected into the melt with the aid of a neutral or slightly reducing carrier gas. Further, copper can be e iminated from lead in a single stage to a much higher degree than was hitherto possible with conventional methods, by injecting into the melt finely divided sulphur or a suitable finely-divided metal sulphide, e.g. an iron sulphide, with the aid of a neutral or reducing carrier gas. A further advantage is that the refining stages for non-ferrous metal melts can be carried out in one and the same reactor vessel, which hitherto has only been possible to a very limited extent. The invention also affords the possibility of obtaining a transitory phase contact between a non-ferrous metal phase containing contami¬ nating elements and a solid phase containing the element or the compound which is to be reacted with the impurifying element or a compound thereof, at the same time as the re-reaction at the subse¬ quent permanent phase contact is greatly limited, whereby a signif¬ icant increase in the efficiency of the desired reaction and the reaction rate thereof is obtained compared with the single occurring permanent phase contact in conventional purifying methods. EXAMPLE 1 A mixture of 3330 kg of e 2 0 3 and 660 kg of Si0 2 in powder form was charged to a converter containing 30 tons of blister copper holding 4.3% nickel by injection through a tuyere in the bottom of the con- verter, with nitrogen as a carrier gas. The whole of the mixture took 30 minutes to be injected and a solid product, comprising mainly nickel silicate 2Ni0 • Si0 2 J in powder form was separated out. The residual content of nickel in the blister copper was measured to <0.01%. The resultant nickel silicate was then treated in a further reactor for recovering the nickel content. EXAMPLE 2 Iron filings carried in a nitrogen carrier gas were introduced into an LD-converter containing 10 tons of crude lead in molten form with an arsenic content of 7.4% As and a temperature of 650°C through a lance immersed in the molten lead, at a speed of 55 kg/min for about 20 minutes, whereafter the arsenic content of the melt was measured to less than 0.01% As. The resultant iron speiss, obtained in powder form, and the lead melt could then be separated from one another by tapping off the melt through an opening in the bottom of the con¬ verter.

Claims: CLAIMS: 1. A method of purifying melts consisting mainly of non-ferrous metal, preferably copper and lead, from impurities in the form of difficultly separable elements, such as cobalt, nickel, lead, bis¬ muth, antimony and arsenic, characterized in that at least one solid reactant is injected into the melt with a carrier gas while simulta¬ neously creating a turbulence in said melt, whereat the reactant and carrier gas are selected so that there is formed with the compound a product whose melting point is greater than the prevailing tempera¬ ture of the melt and whose density is different from the density of said melt; that the formed solid product is continuously trans¬ ferred to the melt surface by means of the carrier gas and there¬ from separated from the melt. 2. A method according to Claim 1, wherein the reactants and carrier gas are injected into a converter through lances or tuyeres. 3. A method according to Claim 1 and Claim 2, wherein the solid reactants contain an oxidant for the impurity in question, which oxidant will not oxidize non-ferrous metals at the prevailing tem¬ perature of the melt, and a substance which together with the re¬ sultant oxide of said impurifying alement is able to form the solid product at said prevailing temperature. 4. A method according to Claim 3, wherein the non-iron metal melt comprises copper and impurifying elements of nickel and/or cobalt, and wherein the oxidant comprises iron(III)oxide or copper oxide and the substance which forms a solid product with the impurifying element is silica. 5. A method according to Claim 3, wherein the non-ferrous metal melt comprises crude lead and impurifying elements of antimony and/or arsenic, and wherein the oxidant is lead oxide, and the substance which forms a solid product with the impurifying element is also lead oxide. c>;?ι 6. A method according to Claim 1, wherein the non-ferrous metal melt comprises crude lead and the impurifying elements are antimony and/or arsenic, and wherein a solid reactant in the form of finely- divided iron is injected into the melt with the aid of a neutral or reducing carrier gas to form solid speiss. 7. A method according to Claim 1, wherein the non-ferrous metal melt comprises crude lead and the impurifying element is copper, and wherein a solid reactant in the form of sulphur or metal sulphide is injected into the melt with the aid of a neutral or reducing carrier gas, to form a solid copper sulphide.

Inventors: JENSFELT T
Applicants: BOLIDEN AB
Application year: 1980
Main classification: C22B9
IPC codes: C22B9, C22B13, C22B15