US3850620A - Pyrometallurgical process for producing metallic copper from copper sulfide concentrates - Google Patents

Abstract

The invention utilizes a modified Peirce-Smith converter to smelt copper sulfide concentrates and to produce flue gases sufficiently high in SO2 content to be useful for the production of sulfuric acid, thereby avoiding the usual air pollution associated with reverberatory smelting. Copper concentrates and flux are continuously fed above and onto the surface of a high grade copper matte produced and maintained in a conventional Peirce-Smith type of converter modified for the purpose. The molten material is blown with oxygen-enriched air, and smelting heat is attained by the exothermic heat of the reaction and by supplying and burning fluid fuel above the molten bath. Periodically, feed and blowing are halted and excess matte and/or slag separately skimmed off, the matte being charged into a separate converter for blowing with air in the usual manner. The slag is treated to recover most of its copper content by milling or by pyrometallurgical cleaning in a separate furnace.

Description

United States Patent [191 Themelis et a1.

[ Nov. 26, 1974 Conn; Russell R. Beck; John V. Wagner, both of Salt Lake City,

Utah

[73] Assignee: Kennecott Copper Corporation,

New York, NY.

22 Filed: Apr. l8, 1973 [21] Appl. No.: 352,723

[52] US. Cl 75/74, 75/72, 75/76 [51] Int. Cl C22b 15/00 [58] Field of Search 75/72, 74,- 76, 73, 75; 266/35, 41

[56] References Cited UNITED STATES PATENTS 3,139,336 6/1964 Dean 75/76 3,281,236 10/1966 Meissner 75/73 3,437,475 4/1969 Themelis et a1. 75/76 3,473,918 10/1969 Foard 75/74 3,627,510 12/1971 Vogt et a1. 75/76 Primary ExaminerWalter R. Satterfield Attorney, Agent, 0r Firm-Mallinckrodt & Mallinckrodt 57 ABSTRACT The invention utilizes a modified Peirce-Smith con verter to smelt copper sulfide concentrates and to produce flue gases sufficiently high in SO content to be useful for the production of sulfuric acid, thereby avoiding the usual air pollution associated with reverberatory smelting. Copper concentrates and flux are continuously fed above and onto the surface of a high grade copper matte produced and maintained in a conventional Peirce-Smith type of converter modified for the purpose. The molten material is blown with most of its copper content by milling or by pyrometallurgical cleaning in a separate furnace.

7 Claims, 3 Drawing Figures P T T IIIIvzs I974 50,520

F/G CONCENTRATES AND FLUX BURNER BURNER HIGH GRADE MATTE RADE (l P (70%10 80"/ b 2 8? Y ll weight GUS BLow BLOW (0xYGEN- (OXYGEN- ENRICHED AIR) ENRICHED AIR) TO SULFURIC ACID PRoDUCTIoN F/G FLUE GASES (Y /O-Q /o s0 BURNER SLAG 4 /5 HIGH GRADE MATTE (70% f0 80% by weigh) Cu.)

SLAG (SKIMMED TwICE PER CYCLE) MATTE /4 CooLING PIT MILLING CONCENTRATES HIGH GRADE MATTE RECIRCUL TED (70% 1o 80% by BLOW weIght Cu.) BLOW (AIR) (AIR) I AILINGS DI sCARDED METALLIC COPPER SMALL AMOU SLAG RECIRC PYROMETALLURGICAL PROCESS FOR PRODUCING METALLIC COPPER FROM COPPER SULFIDE CONCENTRATES BACKGROUND OF THE INVENTION 1 Field The invention is in the field of processes for the smelting of copper sulfide concentrates to produce a copper matte (Cu S, FeS) and for the converting of such matte to metallic copper by blowing with air, yielding flue gases which are sufficiently concentrated in sulfur dioxide to be useful in the production of sulfuric acid.

2. State of the Art It has been customary in the production of the metallic copper from copper sulfide ores to subject flotation concentrates derived from such ores to smelting in reverberatory furnaces for obtaining low grade (e.g., 20-40 percent Cu) copper matte, and, thereafter, to convert such copper matte to impure metallic copper in Peirce-Smith Converters, which are cylindrical vessels each equipped with a hood and mouth through which the molten matte is periodically charged from a ladle transferred by crane from a reverberatory furnace. The converter is equipped with tuyeres through which air is normally blown into the matte. The resulting gases, high in S0,, content, are discharged through the mouth of the converter into a flue for passage to a sulfuric acid plant.

Even though air pollution from the converters has been largely avoided by utilizing the offtake gases therefrom for the production of sulfuric acid, the offtake gases from the reverberatory smelting furnaces are too dilute in sulfur dioxide to be so utilized. Thus, they are customarily discharged into the atmosphere, with consequent undesirable air pollution.

Some of the disadvantages of reverberatory smelting have been overcome by a continuous process carried out in a single reactor vessel, see US. Pat. No. 3,437,475 granted to Nickolas J. Themelis and Paul Spira on Apr. 8, 1969. However, such a process requires a large capital investment in new equipment and is, therefore, economically not practical for existing smelters equipped with reverberatory furnaces and Peirce-Smith converters. The same is true of other continuous processes, such as disclosed in US. Pat. No. 3,281,236 granted to Herman P. Meissner on Oct. 25, 1966.

Attempts have been made in the past to smelt copper concentrates in a converter by means of oxygen injection. However, these have been largely unsuccessful because the converter has been used as a batch convetting vessel, without providing auxiliary heat. Thus, oxygen utilization efficiency has been low and control of the system haphazard, since the operators have had no way of compensating for the large heat losses encountered during emptying and refilling the converter with matte. I

In addition, such schemes have been based on the availability of seed" matte to start the cycle, which has meant that the use of reverberatory furnaces has been essential.

' SUMMARY OF THE INVENTION ,In accordance with the present invention, smelting of a copper concentrate together with a silica flux IS carried out on a semi-continuous basis in a conventional converter vessel by the provision of a burner above the molten bath for the injection and burning of a fluid fuel, such as fuel oil, a gaseous fuel, or a stream of dispersed coal dust. A high grade matte (approximately within the range of from to percent by weight Cu) is maintained in the converter by properly balancing rates of material feed, fuel feed to the bumer, and blowing of the matte with oxygen-enriched air, as well as the degree of oxygen-enrichment of such air.

The feed of concentrate and flux, the burning of fuel above the bath, and the blowing with oxygen-enriched air are continuous, except at such times as matte and/or slag are being skimmed off. The level of matte need never drop below a given minimum level, which is based on optimum utilization of the oxygen supplied with the air. This means higher smelting capacity per pound of oxygen than has heretofore been the case in conventional oxygen smelting procedures.

Slag skimmed off from the smelting converter will contain an amount of copper to make subsequent treatment, e.g., by casting into pits, cooling, and milling, economically possible for copper recovery. Copper loss in the tailings from the milling procedure is normally no more than takes place in the ordinary reverberatory slag.

Matte near the white metal stage is drawn off from the smelting converter and transferred to a standard converter to be finished by the usual blowing with air to metallic copper. It is possible at this stage to add precipitate (cement) copper or other cold dope for melting and merging with the converter copper produced from the matte.

In contrast with the prior art, the present invention is based on the utilization of existing Peirce-Smith converters, which, with minimum modification and expenditure, can be made adequate to carry out the smelting duty of the usual reverberatory furnaces and to also perform a preliminary converting function. This invention, therefore, eliminates the need for reverberatory. furnaces, thus resulting in great reduction .in fuel and operating costs. Existing reverberatory furnaces may be dismantled to provide plant area for other purposes or may be merely left idle, thereby eliminating undesirable air pollution. The additional S0 of high concentration provided by the smelting converters will provide additional feed for existing sulfuric acid plants normally operated in conjunction with copper converting facilities. In the present process, matte from the reverberatory is not necessary since the auxiliary fuel burner can be used to smelt an initial matte batch and from thereon the process is self-sustaining.

THE DRAWING The best mode presently contemplated for carrying out the invention is illustrated in the accompanying converting operation of FIG. 2 are handled for each operating cycle of the process.

' DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENT The invention can be carried out in existing converter facilities of copper producing plants by making minor modifications in the conventional converters making up part of the production facilities of such plants. Most modern facilities utilize the Peirce-Smith type of converter. Such a converter can be readily modified for practice of the combined smelting and converting stage of the present process. In fact, such a converter may not even require modification if equipped with a so-called Garr gun, as is often provided forthe introduction of flux, and with an end port in which a burner can be installed. Under such circumstances, it is only necessry to provide an appropriate supply of a mixture of copper concentrate and flux for the gun, a burner and a fuel supply therefor, and oxygen injection facilities for blower air supplied to the converter tuyeres. This is all well within the skill of the art. If desired, feed of copper concentrate and flux can be accomplished through the usual converter hood and mouth, the minor modification required to permit this being also well within the skill of the art. The normal function of the mouth and hood in discharging offtake gases from the converter into the flue provided for same is maintained; and such gases are preferably treated in customary manner for the production of sulfuric acid in the usual sulfuric acid plant, since the combined smelting and converting produces S of sufficient concentration for the purpose.

A diagramatic representation of such a modified Peirce-Smith converter is designated 10 in the figures of the drawing. A molten bath of copper matte 11 is maintained within such converter 10 at all times in minimum depth sufficient to adequately cover .the tuyeres for efficient blowing. FIG. 1 illustrates the converter at the end of one cycle of operation and about to start another cycle, it being preferred to continue the injection of fuel above the matte 11 between cycles to maintain proper temperature of the molten bath.

The matte 11 is of high grade,,.having a copper con tent approximately within the range of white metal, rather than the usual low grade matte (from 20 to percent by weight) normally fed to a converter from the reverberatory furnace. The term white metal as used herein denotes Cu S.FeS, having a copper content within the range of about 70 to 80 percent by weight. For the combined smelting and converting stage of the process as shown in FIG. 2, a copper ore concentrate derived in the usual manner by flotation and preferably formed into green pellets to minimize dust after haaving been mixed with the usual silica flux, is fed into the converter 10 either through the usual hood modified for the purpose as indicated above or through a Garr gun, heat additional to the normal exothermic provided by the reaction being supplied in the space 12 above the white metal by means of a suitable burner, as previously mentioned and as indicated. Fuel supplied to the burner in any suitable manner is burned above the bath to supply the additional smelting heat required over and above that provided by the exothermic heat of the converting reaction that goes on simultaneously with the smelting reaction-in the converter 10.

For converting purposes, the molten bath of high grade matte 11 is blown in conventional manner, but with oxygen-enriched air rather than with the usual atmospheric air alone. Oxygen enrichment is typically within the range of 25 to 35 percent oxygen concentration.

As indicated in FIG. 3, slag 13 is periodically skimmed from the top of the molten bath 11 during the smelting and converting stage, twice per cycle being normal practice. The slag contains about 5 to 8 percent Cu by weight as compared to about 0.35 percent for reverberatory furnace slag and about 10 to 12 percent for continuous smelting and converting processes carried out in a single reaction vessel. Thus, such slag is well suited for treatment by milling or pyrometallurgical treatment for recovery of its copper content. For the purpose of milling, the molten slag 11 is advantageously run into a cooling pit for solidification and cooling and is then treated by the usual crushing, grinding, and flotation to produce copper concentrate for recirculation into the feed of the present overall process and tailings for discard as waste.

For each cycle of the process, excess matte is drawn off from the molten bath of white metal, as indicated in FIG. 3, and is transferred to a standard copper converter 14 for additional blowing with air in customary manner to produce metallic. copper with a minimum of slag, if any. Such slag as may be formed is recirculated to the smelting converter 10. An adequate amount of the white metal matte 11 is left in the smelting converter 10 to cover the tuyeres for effective utilization of the oxygen in the oxygen-enriched air blown through such tuyeres.

The white metal matte drawn off from the combined smelting and converting vessel 10 is preferably transferred to converter 14 by a conventional ladle, and is blown in such converter 14 in customary manner with air alone.

Metallic copper is drawn off periodically from the finishing converter 14 and represents the final product of the process. If desired, cement copper or other copper dope may be added to the molten bath in finishing converter 14 for melting and for thereby increasing output of metallic copper.

Although this cyclic process is semi-continuous, experience has shown that the non-blowing periods, during which excess matte and/or slag are drawn off from the smelting converter 10 are relatively short in comparison to the total blowing time, which can be over percent of operating time. Accordingly, the heat loss per ton of metallic copper produced has been shown to be less than in conventional oxygen smelting practice.

EXAMPLE the enriched air injected into the converter could be controlled at a constant level of from 21 to 35 percent oxygen.

In a typical test run, an initial charge of molten white metal matte containing 71% Cu was run into the con-' verter to a depth adequately submerging the tuyere openings, and fuel input to the burner was controlled manually on the basis of readings from a radiamatic pyrometer focused on the molten bath surface.

A mixture of moist copper sulfide flotation concentrate and a silica flux was charged continuously into the converter through the special hood opening at the rate of 40 tons/hour while simultaneously blowing the molten matte with oxygen-enriched air averaging 29 percent oxygen and while operating the burner on a normal basis. The feed of concentrates, flux, and oxygenenriched air was continued along with operation of the burner until the molten bath, containing matte and slag, filled the converter to its maximum operating level. The feed of ore concentrates, flux, and oxygenenriched air was then discontinued and the molten bath allowed to settle into a supernatent layer of slag and a molten pool of copper matte while still operating the burner. The supernatant layer of slag was then skimmed from the converter while continuing to operate the bumer at a reduced firing rate and copper matte was withdrawn, leaving a pool of copper matte in the converter of sufficient depth to adequately submerge the tuyere openings.

The processing cycle was repeated until 406 tons of dry concentrate had been smelted and converted to copper matte containing approximately 75 percent copper by weight.

The average composition of slag removed from the converter was 5% Cu and 26% SiO The average fuel consumption (natural gas) during the test period was 0.56 million B.T.U. per ton of dry concentrate, and the consumption of oxygen was 0.14 tons per ton of dry concentrate smelted.

The gases removed from the converter dumg the process varied from 7 to 9% S0 after hood dilution and were processed in a conventional sulfuric acid plant. A slag sample from the converter was cooled and milled into a concentrate containing 26.4% Cu. The tailings from the milling of the slag contained less than 0.25 percent copper by weight.

The tests showed that it is practical to adapt existing copper converting facilities to the present process and that copper smelting and converting can be carried out to meet new anti-pollution regulations, with very small capital outlay.

Operation of similar Peirce-Smith converter facilities on a commercial test basis handling concentrate and flux feed at a rate of approximately 500 tons per day has further substantiated the capabilities of the process of this invention.

Whereas this invention is here specifically illustrated and described with respect to a certain preferred form thereof, it is to be understood that variations are possible without departing from the inventive concepts particularly pointed out in the claims that follow.

We claim:

1. A pyrometallurgical process for producing metallic copper from copper sulfide concentrates, comprising substantially continuously feeding a copper fulfide concentrate and a flux therefor into a conventional, airblow, copper converter vessel, said vessel containing a high quality, molten bath that, except for accumulating slag and still unmelted feed, consists substantially only of high grade copper matte having a copper content approximately within the range of about percent to about percent copper and a depth at least covering the tuyere openings so as to be adequate for blowing; blowing said bath with oxygen-enriched air having an oxygen content within the range of about 25 percent to about 35 percent by weight, while introducing and maintaining above said bath sufficient heat additional to the exothermic heat of reaction of the bath to effect smelting of said concentrate and flux, the said feeding, blowing with air, and introducing of additional heat, and the degree of oxygen enrichment of said air, being controlled to substantially maintain the said high quality of the molten bath of copper matte; periodically halting the continuous feeding and the blowing end, during the halting periods, skimming off from said bath either slag alone or both slag and matte, the quantity of matte skimmed off being substantially no more than will leave said bath of matte sufficiently deep to cover the tuyere openings for blowing purposes, whereby the smelting reaction condition is maintained within said converter vessel from skimming period to skimming period; continuing the continuous feeding of copper sulfide concentrates, the blowing of said bath with said oxygen-enriched air, the introduction of additional heat, and the control thereof between the skimming periods; and treating the matte skimmed off from said converter vessel in a separate converter vessel for the production of metallic copper.

2. A process in accordance with claim 1, wherein the copper ore concentrate fed into the converter. vessel has a moisture content approximately with the range of from 7 to 12 percent by weight.

3. A process in accordance with claim 1, wherein cement copper is added to the charge of white metal matte in the separate converter.

4. A process in accordance with claim 1, wherein the feed is introduced into the converter above, and is deposited onto, the superficial surface of the bath.

5. A process in accordance with claim 1, wherein the slag has a copper content of about 5 percent to about 8 percent and including the additional step of treating the slag for the recovery of its copper content.

6. A process in accordance with claim 5, wherein the slag is reduced to finely divided condition as a flotation feed and is treated by flotation for recovery of a copper concentrate.

7. A process in accordance with claim 6, wherein the copper concentrate from the slag is recirculated to the smelting converter.

P0405) UNITED STATES PATENT OFFICE t QQERTIFICATE 0F CORRECTION Patent No; 3, 850; 620 Dated November 26, 1974 Inventor(s) Nickolas John Themelis et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 6, at the end of line 4, the word "fulfide" should be sulfide and at the end of line 23,

the Word 'fend" should be and Signed and sealed this 21st day of January 1975.

LSEAL) Attest:

MCCOY M. GIBSON JR. '6. MARSHALL DANN Attesting Officer Commlssloner of Patents

Claims (7)

1. A PYROMETALLURGICAL PROCESS FOR PRODUCING METALLIC COPPER FROM COPPER SULFIDE CONCENTRATES, COMPRISING SUBSTANTIALLY CONTINUOUSLY FEEDING A COPPER FULFIDED CONCEBTRATE AND A FLUX THEREOF INTO A CONVENTIONAL, AIR-BLOW COPPER CONVERTER VESSEL, SAID VESSEL CONTAINING A HIGH QUALITY, MOLTEN BATH THAT, EXCEPT FOR ACCUMULATING SLAG AND STILL UNMELTED FEED, CONSISTS SUBSTANTIALLY ONLY OF HIGH GRADE COPPER MATTE HAVING A COPPER CONTENT APPROXIMATELY WITIN THE RANGE OF ABOUT 70 PERCENT TO ABOUT 80 PERCENT COPPER AND A DEPTH AT LEAST CONVERTING THE TUYERS OPENINGS SO AS TO BE ADEQUATE FOR BLOWING; BLOWING SAID BATH WITH OXYGEN-ENRICHED AIR HAVING AN OXYGEN CONTENT WITHIN THE RANGE OF ABOUT 25 PERENT TO ABOUT 35 PERCENT BY WEIGHT, WHILE INTRODUCING AND MAINTAINING ABOVE SAID BATH SUFFICIENT HEAT ADDITIONAL TO THE EXOTHERMIC HEAT OF REACTON OF THE BATH TO EFFECT SMELTING OF SAID CONCENTRATE AND FLUX, THE SAID FEEDING BLOWING WITH AIR AND INTRODUCING OF ADDITIONAL HEAT, AND THE DEGREE OF OXYGEN ENRICHMENT OF SAID AIR BEING CONTROLLED TO SUBSTANTIALLY MAINTAIN THE SAID HIGH QUALITY OF THE MOLTEN BATH OF COPPER MATTE; PERODICALLY HALTING THE CONTINUOUS FEEDING AND BLOWING END, DURING THE HALTING PERIODS, SKIMMING OFF FROM SAID BATH EITHER S2LAG ALONE OR BLOTH SLAG AND MATTE, THE QUANTITY OF MATTE SKIMMED OFF BEING SUBSTANTIALLY NO MORE THAN WILL LEAVE SAID BATH OF MATTER SUFFUCUENTLY DEEP TO COVER THE TUYERE OPENINGS FOR BLOWING PURPOSES, WHEREBY THE SMELTING REACTION CNDITION IS MAINTAINED WITHIN SAID CONVERTER VESSEL FROM SKIMMING PERIOD TO SKIMMING PERIOD; CONTINUING THE CONTINUOUS FEEDING OF COPPER SULFIDE CONCENTRATES, THE BLOWING OF SAID BATH WITH SAID OXYGEN-ENRICHED AIR, THE INTRODUCTION OF ADDITIONAL HEAT, AND THE CONTROLLED THEREOF BETWEEN THE SKIMMING PERIODS; AND TREATING THE MATTE SKIMMED OFF FROM SAID CONVERTER VESSEL IN A SEPARATE CONVERTER VESSEL FOR THE PRODUCTION OF METALLIC COPPER.

2. A process in accordance with claim 1, wherEin the copper ore concentrate fed into the converter vessel has a moisture content approximately with the range of from 7 to 12 percent by weight.

3. A process in accordance with claim 1, wherein cement copper is added to the charge of white metal matte in the separate converter.

4. A process in accordance with claim 1, wherein the feed is introduced into the converter above, and is deposited onto, the superficial surface of the bath.

5. A process in accordance with claim 1, wherein the slag has a copper content of about 5 percent to about 8 percent and including the additional step of treating the slag for the recovery of its copper content.

6. A process in accordance with claim 5, wherein the slag is reduced to finely divided condition as a flotation feed and is treated by flotation for recovery of a copper concentrate.

7. A process in accordance with claim 6, wherein the copper concentrate from the slag is recirculated to the smelting converter.

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