US1679337A - Heat treatment and concentration of copper ores - Google Patents

Description

July 3l, 1928.

J. c. NIQLJLIIJEN ET AL HEAT TREATMENT AND CONCENTRATION OF COPPER ORES Filed Sept. 14, 1925 www@ Patented July 31,I

UNITED STATESy PATENT oFFlcE.

JOHN COLLETT MOULDEN AND BRUCE TAPLIN, OF LONDON, ENGLAND, ASSIGN ORS TO METALS PRODUCTION COMPANY OF NORTH AMERICA Yoax, N. Y., a oon'rona'rroN.

INCORPORATED, F NEW 'HEAT TREATMENT AND CONCENTRATION 0F COPPER ORES.

Application 1filed September 14, 1 925, Serial No.

This invention relates to the heat treatment and concentrationof oxidized ores` of copper, that is to say chrysocolla (copper. silicate), malachite and azurite (copper 5 carbonate) cuprite and melaconite (copper oxide) and the like, and has for an ob]ect to render the copper therein readily recoverable. Y In.. previous United States specification No.' 1,440,186, a process is disclosed of attaining this end by heating in a-reducing gas at a temperature of about 400 C. In attempting to effect a similar reduction of a particular chrysocolla ore by admlxture of the ore with a solid fuel, in a. Proportion of about .Q1/2% with exclusion o oxygen, but without introduction of a separately generated reducing gas, We have found that upon heating to a temperature of 400 C. the chrysocolla showed no marked change 1n.

appearance: it retained its characteristic appearance, sometimes with a slight. reddish superficial coating. This material was found to be sparingly soluble in a solutlon of ammonium carbonate and ammonia; when leaching `was carried out by agitation, the maximum amount that could dissolved 'amounted to {i6-39%. When however the mixture of ore and carbonaceous material 'hadbeen heated for one hour at a temperature of 700 C. in a vessel from which oxygen was excluded, a very remarkable chan e was observed. The particles of clirysocol a had now acquired a greyish tint and copper with its character; istic pink colour was found in a very finely divided condition outside the particles. It was very noticeable that the copper had apparently migrated from the ore partlcles and was found in finely divided condition outside them. When the ore was heated in a rotary tube furnace the copper showed a marked tendency to segregate into reddish friable balls, sometimes as large as a quarter of an inch m diameter. 1

None of the material showed the characteristic appearance of silicate reduced under the conditions specified in the specii- 5o cation of U. S. Patent No. 1,440,186.

The friable copper was found to be readily 'soluble in a solution of ammonia and ammonium carbonate, an extraction of 97.6%

being obtained.

56,228, and in Great Britain October 29, 1924.

the chloride by washing it out with water previous to the heat treatment was found to prevent the effect above referred to, namely the formation of friable copper.

In the course of our experiments it has been found that when ores which contain oxidized copper uncombined with sulphur (hereinafter referred to as oxidized copper ores) are heated at a proper temperature in admixture with solid carbonaceous matter and in the presence of a haloid, the copper migrates out of the ore particles which originally contained it and is found outside them admixed with the charge. lVhen the ore contains oxidized compounds of copper other than chlorides or oxychlorides and the haloid is present as a salt of a metal other than copper, the reaction can be carried to a point at which practically all the copper in the said oxidized compounds is found in the product in the metallic state. The copper in the product can be extracted by leaching with an ammoniacal solvent.

Accordingly the invention comprises a process for the separation o`f copper from gangue in ores and like materials of the kind defined characterized by heating the ore in admixture with solid carbonaceous matter and in the presence of a haloid at a tempera ture (for example-a red heat) lower than the melting point of copper and yet adequate to produce 'areaction so that the cop per is caused to come out of the ore particles which originally contained it and is found outside -them in the metallic condition amongst the charge;

According to a feature of the invention the process may comprise the combination of steps which consists in heating the ore in admixture with solid carbonaceous matter andin the presence of a haloid to a temperature (for example a redheat) lowerthan the melting point of copper and yet adeuate to produce the reaction described so t at the copper is caused to come out of the ore particles which originally contained it and is found outside them amongstv the charge, thereafter cooling the ore and finally leaching it with an ammoniacal solvent to extract the copper.

In carrying the process into effect the atmosphere in WhichV the ore is heated should be neutral so as not to interfere with the reaction, although small amounts of reducingfgases may be liberated from the fuel without detriment to the process.

A parently the ore should not contain mar ed amounts of either alkali or acid which are free at the temperature of the reaction, andI according to the present invention the material may be subjected to the ste of removin or neutralizing free alka lnity or acidity prior to the heatin steps. Free alkalinity is, however, muc more harmful than free Iacidity because it may entirely prevent the reaction.

Alkaline matter can be Washed out of the ore with water, or, alternatively may be neutralized with acid, for exam le sulphuric acid. It has also been foun that commercial ammonium sulphate may be used in place of sulphuric acid, but sulphuric acid gives the best results.

Preferably after the heat treatment the.

ore is cooled in a non-oxidizing medium to a temperature at which the copper is not readily re-oxidized on exposure .to air.

A preliminar heating of lthe ore -(for example to 700 in a neutral or an oxidizing` atmosphere may be effected with advantage before admixture with the fuel. One practical advantage of such a preliminaiy heating step lies in the fact that the ore may thus be heated rapidly and economically by direct contact with combustion gases to a temperature suliicient to effect the reaction when the haloid salt and the solid fuel are subsequently admixed with it, Conse queiitly the supply of heat to the ore after admixture with the reagents can be reduced or obviated.

The process is found to be effectively carried out at temperatures lying between 500 and 700 C.

The time required for the heat treatmen may be reduced byy suitable procedure. Thus the ore may be disposed in layers of such thickness, or so agitated, that the charge readily becomes uniformly heated throughout, when the reaction is completed in from one to two hours from the time of introduction of the haloid salt and the fuel. A shorter time, say three-quarters of an hour or less may be effective.

Preferably thehaloid salt is a chloride of an alkali or of an alkaline earth metal, for

example sodium chloride or calcium Chloride. Haloids other than chlorides, however, are effective. For example, luorspar may be used. Even hydrochloric acid and also gaseous chlorine havebeen employed with success and the use of organic halogen compounds is not outside the scope of the invention. With any particular ore a simple preliminary trial will suflice to determine Sagasca ore mentioned above, may already contain the necessary amount of sodium chloride or its equivalent, while in other cases it is necessary to incorporate such a reagent with the ore. The o re may be either soaked with salt solution or the salt may be added dry.

Sulphide ores of copperA can be treated according to the process but these ores must be subjected to an oxidizing roast before submitting them to the process.

The carbonaceous matter employed may be bituminous coal, graphite, coke, orV wood charcoal. In fact it appears that any solid fuel will suiice.

According to the invention there may be combined with the steps above set forth leaching the ore with ammoniacal carbonate solution for extraction of the reduced copper. p

As alternatives, various means of hysical concentration have been found to e effective. The reduced copper appears to co1- lect upon the solid carbonaceous fuel so that in the inal product the copper-bearing particles consist of a co per skin or outer sheet on a core of coke-lile material.' When the process is conducted in a rotating tubular furnace under suitable conditions, the copper-bearing particles can be caused to aggregate into large granular masses which may e separated by sifting. They may also be separated by gravity concentration and this may be effective even when large aggregates are not formed.

In the preferred form of the process the ore, with or without preliminary heating is admixed with solid carbonaceous fuel and common salt and fed continuously into a zone which is maintained at a low red heat (for example 500 to 700 C.) in a neutral atmosphere and caused to pass therethrough at such a rate that on emergence the copper contents will have been segregated as described and thereafter the product is fed through a cooling zone in which the atmosphere is non-oxidizing and from which the product emerges sufficiently cooled to avoid re-oxidation of the reduced copper by atmospheric air. The apparatus employed may A suitable apparatus `is indicated diagrammatically in the accompanying drawing.

' 4In the drawing, A represents a rotatable tubular preheating furnace lined with refractory material.` The ore is introduced at one end from a hopper B and heating is effected by an internal gas flame from a burner C. The ore is thereby raised to a good red heat of say about 700 C. and it fallsin this condition into a closed charging hopper D provided with regulating valves D1, D2, which are preferably made of chrome steel. A mixture of solid carbonaceous fuel and common salt, is introduced into a hopper E provided with aregulating flap E1 at the bottom for admission. of fuel to the space below the valve D2. The ore from the valve D2 and fiiel and salt from theiiap E1 mix with one another in the chute F and are delivered thereby into a second rotating tubular furnace G lined with refractory material and provided, if necessary, with a. spiral conveyor and lifting bars (not shown). Means (not shown) may be provided to heat the furnace G externally if it is found that the temperature in this furnace tends to become too low for the reaction. The furnace G is prolonged at G1 to provide a cooling zone and means indicated at G2, G3 are provided for cooling its exterior surface. The cooled ore may thereby be reduced in temperature to C. or less and in this condition it is discharged through a hopper H and valves H1, H2 on to a conveyor K which carries it away for further treatment, e. g. leaching.

The following are examples of results obtained according to the process.

E @ample 1.

In this case the ore was obtained from the Sagasca mine in Chile and contained 4.7% copper almost exclusively in the form of chrysocolla. This ore contains naturally a small proportion (about 0.5%) of sodium chloride. About 300 grams of the ore was crushed to 10 mesh and was preheated for half an hour to a temperature of about 400 C. Bituminous coal or charcoal was then mixed with it in a proportion of about 21/2% of the Weight of ore and the mixture was introduced into a rotary tubular furnace. Oxidizing gases were swept out by means of a current of carbon dioxide which was then stopped.

The tubular furnace had a diameter of 5 inches and was rotated at the rate of 7 to 8 revolutions vper minute. The furnace was heated externally for one hour, at the end of which time heating was discontinued and the furnace together with its charge was allowed to cool. The ore was then found to contain nely disseminated copper, much lof whichr wasiin the formof ff'riable'balls with carbon nuclei distributed throughout kthe chargeand producedby thefrotarymoytion of the furnace.- The material. `was leached by agitation-:with a'coldfsolution containing 5%V ammoniaand I4%' Icarbon dioxide and a small amount of copper, for 116 hours. When the .leaching solution was removed the residues ywere washed ywith/an aqueous solution `of ammonia yand the tail` ings were foundto assay 0.12% copper.A The Fl'ue dust from the furnace ofl Lubumbashi, Katanga, Belgian Congo, was found yto contain about 13% copper in an oxidized form together with a considerable amount of coarse grain carbon.

lVhen this material was heated in a rotating cylindrical furnace in the presence of additional carbon and a suitable quantity of common salt, it was found that friable copper balls were produced, but these were of too fragile a constitution to be screened from the residues. The cause of this was tracedfto the coarse carbon in the crude material, and in-order to remove this coarse carbon the material was roasted in air to a temperature of about 700 C. After it had cooled it was found that it contained a perceptible amount of free alkali. rlhe cooled product was wetted with salt solution and then dried, mixed with fresh finely divided carbon and heated in a rotary furnace. Balls of copper were not produced and it wasl suspected that the free alkali was a source of trouble. The free alkali was therefore removedby washing it out with water, and salt solution was added and the material dried. Excellent copper balls were now produced by heating the material in a rotating furnace tovloetween 600 and 700 C. inthe presence of 2% of carbon crushed to pass a screen of 40 mesh (Institution ofMining andMctallurgy Standard). The quantity of salt added amounted to one-half of one percent of the `weight of the ore. The copper balls [contained 541% of' Cu and on separationfromthe ore by screening showed a recoveryof 91.6%. Similar results were obtained by, moistening the ore with a dilute solution of sulphuric acid containing 1% of H150;1 reckoned on the weight of the material, extraction of the alkali by washing being omitted. v

In this spcification the term ores and the like 1s intended to include not only naturally occurring ores but also copper-bearing materials which h avevbeen subjected to 1. A process for the separation of copper from gangue in ores and like materials of the ,kind defined characterized by heating the ore in admixture with solid carbonaceous matter and in the presence of a haloid at a temperature lower than the melting point of copper and yet adequate to produce a reaction so that the copper is caused to comeout of the ore particles which originally contained it and 1s found outside them in the metallic condition amongst the charge.

2. A process for the separation of copper from gangue in ores and like materials of the kind defined characterized by heating the ore in admixture with solid carbonaceous matter and in the presence of a haloid at a red heat so that the copper is caused to come out of the ore particles which originally contained it and is found outside them in the metallic condition amongst the charge. A

3. In the heat treat-ment of oxidized copper ores of the kind defined, the combination of steps which consists in heating the ore in admixture with solid carbonaceous matter and in the presence of a haloid to a temperature lower than the melting point of copper and yet adequate to produce the reaction described so that the copper is caused to come out `of the ore particles which originally contained it and is found outside them amongst the charge, thereafter cooling the ore and finally leaching it with an ammoniacal solvent to extract the coper. p 4. In the heat treatment of oxidized copper ores of the kind defined, the combination of steps 4which consists in heating thev f a temperature lower than the melting point of copper and yet adequate to produce a reaction so that the copper is caused to come out of the ore particles which originally contained it and is found outside them in the metallic condition amongst the charge and subsequently cooling the ore in a nonoxidizing medium to a temperature at which the reduced copper is not readily reoxidized on exposure to air.

6. In a process for the separation of copper from gangue 1n ores and like materlals of the kind defined, the combination of first heating the ore in a non-reducing atmosphere to a temperature suflicient to facilitate the subsequent reaction, and thereafter treating the ore in admixture with solid carbonaceous matter and in the presence of a haloid at a temperature lower than the melting point of copper and yet adequate to produce a reactionesthat the copper is caused to come out' of the ore particles which originally contained it and is found outside them in the metallic condition amongst the charge.

7. In a process for the separation of copper from gangue in ores and like materials of the kind defined, the combination of first heating the ore in a non-reducing atmosphere to a temperature sufficient to facilitate the subsequent reaction, and thereafter treating the ore in admixture with solid carbonaceous mattei' and in the presence of a haloid Vat a red heat so that the copper is caused to come out of the ore particles which originally contained it and is found outside them in the metallic condition amongst the charge.

8. In a process for the separation of co per from gangue in ores and like materia s of the kind defined, the combination of first heating the ore in a non-reducing atmosphere to a temperature sufficient to facili tate the subsequent reaction, and thereafter treating the ore in admixture with solid carbonaceous matter and in the presence of a haloid at a temperature lower than the melting point of copper and yet adequatcto produce a reaction so that the copper is caused to come out of the ore particles which originally contained it and is found outside them in the metallic condition amongst the charge, thereafter ,cooling the ore and finally leaching it with an ammoniacal solvent to extract the co per.

9. A process for tiie separation of copper from gangue in ores and like materials of the kind defined characterized by heating the ore in admixture with solid carbonaceous matter and in the presence of a haloid at a temperature lower than the melting point of copper but exceeding 500 C. so that the copper is caused to come out of the ore particles which ori inally contained it and is found outside t em in the metallic condition amongst the charge.

10. A process for the separation of copper from gangue in ores and like materials of the kind defined characterized by heating the ore in admixture with solid carbonaceous matter and in the presence of a haloid at a temperature lower than the melting point of copper and yet adequate to produce a reaction so that the copper is caused to come out of the ore particles which originally contained it and is found outside them in the metallic condition amongst the charfe the treatment being so carried out that the reaction is complete. in from one to two hours. l

11. In the process for the separation of ycopper fro'mgangue in ores and like materials of the kind defined, the combination of first heating"the ore in a non-reducing atmosphere to a temperature sufficient to facilitate the subsequent reaction, and thereafter treating the ore inadmixture with solid carbonaceous matter and in the presenceof a haloid at a red heat so that the.

c oppcn is caused to come out of the ore particles which originally contained it and is found outside them in th metallic condition amongst the charge the treatment being so .carried out that the reaction is complete in from one to tw o hours.

' 12. A process for the separation of copper from gangue in ores and like materials of the kind described characterized by heating the ore in admixture with solid carbonaceous matter and in the presence of a chloride of an alkali metal at a temperature lower than the melting point of copper and yet adequate to produce a reaction so that the copper is caused to come out of the ore particles which originally contained it and is found outside them in themetallic condition amongst the charge.

13. A process for the separation of copperl from gangue in ores and like .materials of the kind defined characterized by heating the ore in admixture with solid carbonaceous matter and in the presence of a chloride of an alkali metal at a. red heat so 'that the copper is caused to come out of the ore particles which originally contained it and is found outside them in the metallic condi tion amongst the charge.`

i 14z In the heat treatment of oxidized copper ores of the kind defined, the combination of steps which consists in heating the ore' in admixture with solid carbonaceous matter and inthe presence of a chloride of an alkali metal to a temperature lower than the melting point of copper and yet adequate to produce the reaction described so that thel copper is caused toy come out of theore 'articles which originally contained it an is found outside them amongst the charge, thereafter cooling the ore and finally leaching it with'an ammoniacal solvent to extract the co per. A

15. n the heat treatment of oxidized copper ores of the ln'nd defined,v the combination ofv steps which consists in heating the ore in admixture with solid carbonaceous matter and in the presence of a chloride of an alkali metal ata red heat so that the copper is .caused to come out of the ore particles which originally contained it and is found outside them amongst. the char thereafter cooling the ore and finally leac ing it with an ammoniacal solvent to extract the copper.

16. A process for the separation of copper from gangue in ores and like materials of the kind dened characterized by heating the ore in admixture with solid carbonaceous matter and in the presence of a chloride of an alkali-metal at a temperature lower than the melting pointr of copper and yet adequate to vproduce a reaction-so1that the copper is caused to come out of the ore particles which originally contained it and isgfand outside them in the metallic condition amongst the charge and subsequently'cooling the ore in a vnon-oxidizing medium to a temperature at which the reduced copper is not readily reoxidized on exposure to air.

17. In a process for the separation of cop- I Y per from gauge in ores and like materials phere to a temperature sufficient to facilitate the subsequent reaction, and thereafter treating the ore in admixturelwith solid carbonaceous matter and in the presence of a chloride of an alkali metal at a red heat so that the copper is caused to come out of the ore particles which originally contained it and is found outside them lin the metallic condition amongst the charge.

18. A process for the separation of copper from gangue'in ores and like materialsv of the kind defined characterized by heating the ore after de-zilkalination in admixture with solid carbonaceous matter and in the presence of a haloid at a temperature lower than the melting point of copper and yet adequate to produce a reaction so that the copper 1s caused to come out of the ore particles which originally contained it and is found outside them in the metallic condition amongst the charge.

19. In the heat treatment of oxidized copper ores of the kind defined, the combination of steps which consists in 'heating the ore after de-alkalination in admixture with solid carbonaceous matter and inthe presence of a haloid to a temperature lower than the meltin point of copper and yet adequate to pro uce the reaction described sothat the copper is caused to come out vof the ore particles which originally contained it and. is

.of the kind defined, the combination of first 115 'found outside them amongst the Ccharge, a

heating theore -in a non-'reducing atmosphere to a temperature sufficient to facilitate the subsequent reaction, neutralizing the ore, and'theeafter treatingthe' orein admixture with solid' carbonaceous matter and y.in the presence of a haloid at a temperature lower than the melting point of copper and yet adequate to produce a re action so that the copper is caused to come out of the ore partlcles which originally l contained it and is found outside them in the metallic condition amongst the charge.

21. A process for the. recovery of copper from-oxidized vcopper ores Whereipgthe ore is admixed with solid carbonaceousf'uel and common salt and fed continuousl into` a zone which is maintained at aired eat in a neutral atmosphere and caused to pass therethrough at such a rate that on emergence zone in which

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