CA1066062A - Recovery of nitric acid soluble transition metals from sulfur and iron containing ores of the same - Google Patents

Abstract

Abstract of the Disclosure This invention relates to a method of recovering one or more metal values of the group consisting of copper, silver, nickel, cobalt ant zinc from a sulfur an iron containing ore of the metal or metals. The method consists of intermixing the ore and at least a stoichiometric amount of nitric acid of about 30-50% by volume concentration to form an aqueous acid leach solution of the same. The solution is heated to a temperature at or above the melting point of sulfur while the solution is contained under pressure in a relatively inert atmosphere. The temperature of the solution is controlled to substantially solubilize the sulfur and the metal value or values in the acid soluble phase of the solution while substantially insolu-bilizing the iron values with respect thereto. The iron values are separated from the acid soluble phase of the solution, and the metal value or values recovered from the acid soluble phase. This process allows the metals to be solvent extracted from the liquor without the problem of lasting precipitates forming in the liquor and fouling the extraction process.

Description

The invclltion concerns thc hydrometallurgical recovery of nitric acid soluble transition metals such as copper, silver, nickel, cobalt, and zinc, from a sulfur and iron containing ore of the same. In particular, thc invention concerns the recovery of the metals by a process of leaching them into a nitric acid leach solution from which they are then recovered by any one of several conventional leach liquor metal recovery techniques.
One object of the invention is to provide a process of this nature wherein the leaching operation requires as little as one-half hour, and pro-duces a liquor containing upward of 99~ or better of the metal values.
Another object is to provide a process of this nature wherein the leaching operation selectively insolubilizes one of the additional iron and sulfur values with respect to the leach solution so that it can be removed as a com-mercially valuable byproduct, and at the same time produces a liquor from which the other additional value can be readily separated thereafter as another commercially valuable byproduct. A further object is to provide a process of tltis nature wherein the leaching operation produccs a liquor that lends itself to the known preferential precipitation metal recovery tech-niqucs, incluting electrowinning and hydrogen precipitation. A still further object is to provide a process of this nature wherein the metals to be re-covered, can be solvent extracted from the liquor without the problem oflasting precipitates forming in the liquor and fouling the extraction process.
Still another object is to provide a process of this nature wherein notwith-standing that the liquor is high in sulfate concentration, dissolved iron can be economically removed from the liquor without the addition of large amoun~s of acid neutralizer. A further object is to provide a process of this nature wherein the acid can be recovered or regenerated in substantially a one-to-one ratio by conventional techniques. A still further object is to provide a pro-cess of this nature wherein the hydrometallurgically insoluble values can also be recovered in relatively pure form. Other objects include the provision of a process of this nature wherein the leaching operation can be conducted in '~ .

.. . . . . ~ , .. . . . .. . . .

the presence of a relatively inert gas, including one as cheap as air, and including the vapor from the reaction itself. Further objects include the provision of a process of this nature wherein the whole spectrum of metal values in the ore can be recovered without penalty, and the purity of the same will be approximately 99.95%; wherein the process can be carried out in an essentially closed system and is essentially pollution free; wherein the process is largely exothermic so that there is little necessity for adding heat to it; and wherein the process can be conducted either continuously or on a batch basis. Still further objects include the provision of a process of this nature wherein the mechanical system for the process is subject to modularization and is adaptable to the ganging of several units of the system within a small area or space; wherein all of the process reagents are readily available and/or regenerable; wherein the ore need not be concentrated be-forehand; and wherein there is no necessity for employing pyrometallurgical processes in recovering the metal values from the leach liquor, nor for expensive structural materials in the system components, nor for excessively high operating parameters, such as temperatures and pressures.
This invention relates to a method of recovering one or more metal values of the group consisting of copper, silver, nickel, cobalt and zinc from a sulfur and iron containing ore of the metal or metals, comprising intermixing the ore and at least a stoichiometric amount of nitric acid of about 30-50% by volume concentration to form an aqueous acid leach solution of the same, heating the solution to a temperature at or above the melting point of sulfur while the solution is contained under pressure in a relative-- ly inert atmosphere, controlling the temperature of the solution to substan-tially precipitate the iron values from the solution, relatively separating the iron precipitate from the acid soluble phase of the solution, and recov-ering the metal value or values from the acid soluble phase.
Normally all of the acid insolubles are separated from the acid 1066(~6Z

solublc phaso before the metal valucs are removed therefrom. ~-e iron pre-cipitate may be scparated with the other acid insolubles, or it may be separa-ted in a different operation. Also, in the usual procedure, the sulfur is crystallized as a salt thereof and relatively separated from the acid soluble phase. The separation may be accomplished before or after ~he ~etal value or values are removed from the acid soluble phase.
For example, in a prescntly preferred embotiment of the invention, the temperature of the solution is controlled to precipitate the iron as a salt thereof and then the salt is relatively separated from the acid soluble phase. Afterward, the metal value or values are removed from the acid soluble phase, and the phase is evaporated to crystallize and relatively separate the sulfur therefrom in the form of a sulfate salt. Normally, the iron precipi-tation step is carried out during the leaching stage, whereas the sulfate salt crystallization step is carried out after the metal value or values are re-moved from the acid soluble phase.
In the above mentioned embodiment, the solution is heated to a tem-perature above about 125C and preferably 125-160C (257-320F). The iron precipitates directly from the solution in this latter range as a hydrous oxite of the same. The acid concentration is preferably about 40%. The leach requires about 30-60 minutes for a 9%t~ recovery of copper and the other metal values in a recycle system.
The prescr.bed temperatures normally require an over-pressure of at least 50 psig. However, for reasons of economy, the pressure seldom exceeds above 120 psig.
Because of the total leaching capacity of the acid, the leach re-action need not be cont.sined under an atmosphere which provides a supplemental oxidizing effect, and in fact the atmosphere may be inert with respect to the leach reaction. Therefore, the term "relatively inert" is used in describing the atmosphere, since the atmosphere may be an oxidizing gas, such as oxygen, or an oxygen-containing gas such as air; yet an oxidizing gas is not necessary to the process, and in fact, as indicated, a gas which is inert with rcspect to the leach reaction may be used in lieu of an oxidizing gas with equally good results. In short, the atmosphere need only be compatible with the re-action, and because of its cheapness, air is commonly employed as the pres-surizing gas. Other examples of suitable gases are nitrogen, argon and helium.
In addition, the vapor from the reaction itself may serve as the pressurizing medium.
For the best results, the leach solution is subjected to agitation while the heat is applied to it. The agitative effect is preferably mechani-cally generated and the gas is preferably intorduced into the leach container through the body of the agitator.
A still further advantage may be gainet by forming an aqueous sus-pension of tho ore and then adting the suspension to the acid, preferably by in~ecting the suspension into the acid in the leach container while the acid is under a~itation ant prcssurization therein.
The leach solution is preferably formed and heated in repeated batches, each of which is formet at a temperature of less than 100C before it is heated to a temperature at or above the melting point of sulfur, the heat transition being as rapid as possible, however, to minimize the forma~ion of "gummy" sulfur in the transition. Typical reaction formulae are given be-low FeS ~ H20 ~ 3HNO3 ~ Fe(OH3~ ~ H2SO4 ~ 3NO
3CuFeS2 ~ 17HN03 ~ 3CuSO4 ~ 3Fe(OH)3~ ~ 3H2SO4 ~ 17NO ~ H20 A continuous process is possible when the various parameters are controlled to effect the foregoing results.
Some sulfur may assume a molten condition and will float to the sur-face of the leach solution as a supernatant liquid. If the solution is flashed to the temperature of crystallization of the sulfur, ~uch as about 100C or less, the molten sulfur will agglomerate or solidify, and will form _ 4 --~066062 spherical boads o~ elemental sulfur which readily precipitate in the flash tank, and are removed as esscntially 97~ pure or greater elemental sulfur.
On the other hand, if the temperature of the solution falls below the melting point of sulfur, i.e. about 115~C, the sulfur will assume a gummy state, and the gummy material will agglomerate about the metal values, and will tend to insulate them from the reaction, so that as a result, clinkers are formed which include a large amount of the values that are sought.
In the flash tank, the temperature is critical only in that the m~lten sulfur should not be allowed to reassume the gummy state, in which it might then take up acid insolubles, such as silicates, which in turn would adulterate the sulfur by-product. Of course, it is also ~esirable to lose as little heat energy as possible in the flash step, and therefore, the tempera-ture in the flash tank is normally maintained at about 80-100C.
Since after about 60 minutes time, the additional quantity of values which are removed by the acid, is so insignificant AS to not warrant operating at longer times, the optimu~ leaching time is about 30~60 minutes.
When the leach liquor is high in nitrate, i.e. 5 grams per liter or greater, the nitrate acid metal values are preferably transferred into a sul-fate acid solution by solvent extraction, so as to render the solution more susceptible to the preferential precipitation techniques. It has been fount in this connection that when nitrate acid liquors of this concentration are preneutralized, they will not cause decomposition of the extractants commonly used in conventional solvent extraction processes.
- Moreover, it has been found that when the temperature of the leaçh solution is controllod to establish an iron content of no greater than 15 grams per liter in the leach liquor, and an acid neut~alizer is atded to the liquor to establish a pH of about 1-2 therein and to produce salts of the acid which are soluble in the liquor, the liquor can be contacted with a copper specific aqueous insoluble organic extractant liquid, while the foregoing pH
is ~aintained in the liquor, and the extractant will extract the copper into , .

the extractant liquid without the problem of insoluble metal hydroxides and/or other insoluble metal and acid neutralizer salts forming in the liquor. The organic extractant liquid and the liquor are then relatively separated from one another and the copper is recovered from the liquid.
Preferably, the acid neutralizer is selected from the group consis-ting of hydroxides, carbonates, bicarbonates and phosphates of ammonia and the alkali metals. A~monium, sodium and potassium hydroxide are the presently preferred neutralizers.
The extractant in the organic solvent liquid is preferably selected f~om the group consisting of the alpha substituted hydroxy oximes and the hydrocarbyl-substituted 8-hydroxyquinolines. ~
The invention provides a direct, one-step means of controlling the temperature of the leach solution to reduce the content of the iron values to 15 grams per liter or less.
Where the iron content is excessive, the liquor may be subjected to autoclaving at above about 300F to precipitate the dissolved iron as the oxide thereof. This effect is possible even where the liquor has a high sul-fate concentration.
In the final recov~ry stage, the metal value or values may be crys-~0 tallized, precipitated, and separated from one another in a gravity separator;
and/or preferentially precipitated as indicated. The precipitation step may be effected by reacting the previously neutralized (i.e. pH of about 4.2-7) sulfur-and^iron-free acid soluble phase, with a pressurized reducing agent in a heated ant pressurized autoclave to precipitate the metal value or values therefrom; or alternatively, electrowinning and other conventional tPchniques may be used for the recovery process. As indicated earlier, however, electro-winning is preferably preceded by solvent extraction, in order to transfer the metal values into a sulfate acid solution before they are recovered from the same.
If the leach liquor contains ~ore than a negligible amount of silver, ~066062 the silver may be recovered from the same by hydrogen precipitation or elec-trowinning, and either operation may be conducted before the liquor is subjec-ted to solvent extraction for removal of copper, because of the higher vxi-dizing potential of the silver.
To regenerate the acid, the gaseous phase in the leach container is collected externally of the container and the nitrogen gases are oxidized to the higher oxides of nitrogen, and intermixed with water in an absorption tower, The regenerated acid is then returned to the container for reuse. The weak nitric acid geDerated in the autoclave may also be returned to the con-tainer; or it ~ay be neutralized with ammonium hydroxide and remo~ed as anotherhighly salable by-product, ammonium nitrate, the difference in acid le~el be-ing made up from time to time by the addition of a small amount of new acid to the leach container.
The acid insoluble and acid soluble phases may be separated by cent-riuging or filtering the sulur and iron unloatet solution to remove the in-soluble phase from th~ soluble.
The ore may be in raw form or it may be enriched to a typical con-centration of the order of about 25-30~ by weight or higher.
The spent liquor contains soluble salts of the neutrali~ing agent.
These are recovered, for example, by evaporating the water in the liquor to crystallize the salts. Preferably, ammonia is used as the neutralizing agent so that the salts are principally nitrates and/or sulfates of ammonia.
Water, therefore, is the only component of the leach liquox returned to the environment, assuming that no carbonate was used as the neutralizing agent, in which case carbon dioxide would also be returned to the environment.
These features will be better understood by reference to the accom-panying drawing wherein the single FIGURE which is a flow sheet of the abo~e mentioned embodiment.
Referring now to the Figure, it will be seen that a portion of the ore or concentrate is fed from the storage site 2 to a mixing tank 4 where . . . , .: , .. -~06~i062 water is add~d to the same and the mixtur~ is agitated to form a slurry of the ore. Meanwhile, water and a stoichiometric amount of nitric acid are added to the autoclave ~, the acid being taken ~rom the holding tank ~. In tho autoclnve, the aqueous acid solution is agitated, and is brought UR to an operating temperaturc of about 257-320~F and preferably 280-300F. Also, a gas overpressure of about 80-100 psig is established, using compressed air or some other relatively inert gas as explained hereinabove. Ultimately, when the solution is at operating temperature, the ore slurry is injected into the solution through a metering pump and an acid concentration of about 30-50% by volume is established in the solution.
Where the ore contains sulfides, the sulfides are con~erted to elc-mental sulfur and/or sulfates, the a unt of one over the other being depen-dent upon the overall acid concentration, the temperature, the timc of slurry injection, ant the t~tal time of leaching. Generally, the longer the leach time, and the higher the tempcsature and overall acid concentration, then th~
greater is the formatioll of sulfate, Also, the longcr the leach timo and the higher the temperature and overall acid concentration, then the lower is the concentration of iron in the leach liquor as the liquor leaves the autoclave, and thè greater is the recovery of nitrogen oxides and thus the recovery of nitric acid. Typically, after about an hour of leach time in the foregoing temperature range, the sulfides of nickel, copper, silver, zinc and cobalt are substantially solubilized in the leach solution as nitrates and sul~ates thoreof, and the iron is substantially precipitated as a hydrous oxide of the same. The precipitate collects in the bottom of the autoclave with the other insolubles, and these are principally refractory materials such as silica, and noble metals such ~; gold and platinum.
As indicated, the sulfur does not always fully convert to the sul-fate form. Thereore, when the extraction is regarded as economically comp_ lete, the solution is pumped into a flash tank 10 where the pressure on the solution is released to abou~ zero psig and its temperature is redl~ced to ~ 066062 approxi~ately the boiling ~oint of the solution, i.e. about 200-220F. In the flash tank, any molten sulfur which was prcsent in the solution, solidi-fies and collects with th~ other precipitates in the bottom of the tank. The accu~ulated precipitates are then separated from the liquor in a filter 46, and are sent on to a separation and recoveTy stage 48 where the iron values are converted to iron oxide and the oxide is separated from the other precipi-tates. Any unreacted ore is returned to the autoclave 6 in line 50. The sili-cate fraction is sent on to a further recovery stage 52 where gold and plati-num, if present, are sepsrated and recovered from the fraction by conventional means.
Meanwhile, the filtered liquor is transferred from the filter ~6 to an agitated holding tank 54 where an acid neutralizing agent such as ammoni-um hydroxide is added to the liquor. The degree to which the acid is neutTa-lized is tependent upon the amount o unprecipitatet iron which remains in the liquor, the nature and content of the other metal values in the liquor, in-cluding the nature and content of the nickel, cobalt, silver, zinc and co M er values, and finally, the method to be used for separating tho unprecipitated iron, If the liquor contains only unprecipitated iron and copper as economi-cally recoverable values, then either of two options may be used for the re-covery of the iron values. See Iron Options 1 and 2 in the Figure. However,if the liquor contains a sizable amount of unprecipitated iron, as well as one or more of the nickel, cobalt, zinc, copper and sil~er values, then it is more economical to recover the iron values with what is indicated as Iron Option 1.
Where there is no unprecipitated iron present in the liquor, or the concentra-tion is relatively small, as for example, where the ore is essentially iron free, then neither o~ the two iron options need be use~.
Referring now to Iron Option 1, it will be seen that the solution in the holding tank 54 is transferred to an agitated autoclave 56, where the solu-tion is heated to a temperature of about 300-500F, and maintained under a pressure equal to the vapor pressure of the solution at that temperature.

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Also, additional acid neutralizing agent is added to the solution ;f the amount which was added in the tank 54 was insufficient. Ul~imatcly, the iron in the solution precipitates out as a ferric-oxid~/hydroxide mixture which is substantially free of non-ferrous metal values and in a form that is readily filterable from the solution. The solution is then transferred to a filter S8 with the iron precipitate, and the precipitate is recovered as another salable product, while the iron-free liquor is sent on to the next recovery stage in the process, using a feed line 60.
Alternatively, in Iron option 2, the iron containittg solution in the tank 54 is sent directly into the feed line 60 which introduces the solu-tion in turn into a solvent extractor 62. The extractor uses a copper-speci-fic extractant, and after the solution has been subjected to an extraction process for the copper, as shall be explained, it is then transferred to an iron neutralization and precipitation tank 64, where the solution is agitatet and a stoichiometric amount of a~monium hydroxide or some other acid neutra-Iizing agent is added to it. In this case, however, ferric hydroxide is pre-cipitated, and pH being in the range 4-7. The ferric hydroxide is filtered ant recoveret at 66, and the iron-tepletet aqueous salt solution is transfer-red in feed line 68 to an evaporation and crystallization vessel 70 where the salts in the solution are also recovered.
There is also an intermediate option for the circumstance wherein the solution in feed line 60 con~ains more than a negligible amour.t of silver.
In such a case, the solution is transferred to a silver recovery stage 72, 74 and 78 where the solution is subjected to either electrowinning or hydrogen autoclaving. In the latter instance, the solution is heated to 250-350F in an agitated autocla~e 72 and is exposed to hydrogen gas while bcing maintained at a total pressure of between 500 psig and 700 psig. Under these conditions, the silver is precipitated and thus separated from a solution containing other values such as nickel, cobalt, zinc and copper. The contents of the autoclave 72 are then passed through a filter 74 to recover the silver. ~le ,:
' ' ~ ' ' ' , ' silver-dcpleted solution is then returned to the feed line 60 where it may pass into the solvcnt e~tractor 62, or if the solution contains no copper, then it may go directly to a nickel-cobalt recovery stage 76, etc., where the latter values are removed, if they are present in the solution.
Alternatively, the silver contsining solution may be subjected to electrowinning at 78, and then sent on to the solvent extractor 62; or if the solution contains no copper at all, then it may be sent on to the nickel-cobalt recovery stage, as was done in the case of the autoclaving option.
Assuming now that the liquor in line 60 contains copper in desirable quantities, the liquor is subjected to extraction by an organic copper-speci-fic extractant such as a kerosene solution of LIX-64N, an extrac~ant made by ~eneral Mills Corporation of Minneapolis, Minnesota, The extraction process is accomplished in a multi-staged, counter-current extraction cell 62 wherein the aqueous phase is mixed thoroughly with the organic phase and then the phases are allowed to separate. Both phases are then transfcrred in counter-current fashion to other stages, and the opcration is repeated. Meanwhile, an acit neutralizing agent such as ammoniuln hydroxide is added to the aqueous phase to control its pH in the range of about 1-2, This aids in the transfer o~ the copper, snd assuming that there is proper mixing of the phases, three stages of contact, and a suitable aqueous to organic flow rate, copper is re-moved from the aqueous phase in amounts greater than 99%.
If no desirable metal values are present in the copper depleted aqueous phase, then it is sent directly to the evaporization and crystalli-zation vessel 70, However, if nickel and/or cobalt are present it is sent to the nickel/cobalt recovery stage 76, et. Meanwhile, the copper bearing organic phase is stripped of the copper~in a stripping tank 80, using a di-lute sulfuric acid stripping solution, The operation of this tank is much the same as that of the extraction cell 62, in that thc respective phases ~ -flow counter-current to one another and mix and separate in each stage. At the close of the operation, the copper depleted organic phase in the tank is ..... . - . ....... . .................... . . .
.. ' . ., - .. . ~ ' . ' - . :
. . .

~066C~62 recycled to the cell 62, and the acid-sulfate copper stripping solution is transferred through feed line 82 to either a hydrogen autoclav~ 84 or an clectrowinning tank 86.
ln the autoclave 84, the stripping solution is agitated and heated to an elevated temperature, i.e. 350-450F. In addition, the solution is exposed to hydrogen gas and is maintained at a total pressure of about 500 psig to 700 psig. Under these conditions, the copper precipitates as a finely divided powder which is substantially free of impurities. The powder is removed in a filter 88. The dilute sulfuric acid which is generated in the reaction is recycled to the organic stripping stage of tank 80.
In the electrowinning tank 86~ the copper i5 recovered by conven-tional methods of electrowinning and the dilute sulfuric acid which is gene-rated in the tank is recycled to the organic stripper 80.
Where nickel and cobalt are present in the liquor, they can be ex-tracted from the same by an organic extractant such as LIX-64N in kerosene, in a manner similar to the process for extracting the copper. See Nickel-Cobalt Option 2. Howe~er, for the extraction to take place, the ptl of the liquor must be maintained at about 6 or above, and this is accomplished by adding a sufficient amount of acid-neutralizing agent such as am~onium hydrox-ite, Once again, dilute sulfuric acid is used to strip the metals from theorganic phase, and the metals are removed in turn from the sulfate solution by electrowinning in tank 86. Meanwhile, the gene~ates sulfuric acid is re-cycled to the organic stripping stage. Alternatively, the metals may be re-covered by hydrogenation as indicated.
Where nickel and cobalt are present, the copper-depleted aqueous phase may also be subjected to the option of transferring it directly to either the hydrogenation autoclave 84 or the electrowinning tank 86. See Nickel-Cobalt Option 3.
Moreover, where the leach liquor does not contain an economically desirable quantity of copper, but does contain nickel and/or cobalt, then it .

.
. ...

10~i6062 m~y be transferred dircctly to the hydrogenation tank 84, or to the electro-winning tank 86. Soe Nickel-Cobalt Opt.ion 1. That is, the organic extraction stage may be by-passed.
In the hydrogenation proce~s, the nickel and/or cobalt-containing soluticn is agitated and heated to an elevated temperature of about 3~0-500F.
Also, a hytrogen overpressure is maintained to a total pressure of about 500 psig to about 900 psig, A metal seed or other suitable catalyst may also be used. Again, the metal or metals are recovered as a powder, and if both are recovered, they may be separated by any one of several conventional methods, including precipitating the co~alt as a carbonate in an ammonium carbonate solution, where the nickel is soluble.
If there is an appreciable amount of zinc present in the ore, the iron-tepleted aqueous salt solution leaving the filter 66 is su~jected to an ion exchange extraction tor other extraction process) in extractor 90, The organic phase is stripped and then the stripping solution is transferred to an electrowir,ning tank 92. ~eanwhile, the zinc-depleted aqueous phase in ex-tractor 90 is sent on to the evaporation and crystallization vessel 70.
Regardless of which path the process follows, the spent liquor in the vessel 70 is treated with a stoichiome~ric amount of an acid neutralizing agent. The liquor is then evaporated to crystallize the nitrate and/or sul-fate salts which are present. If ammonia was uséd as the acid neutralizing agent throughout the process, the salts are principally nitrates or sulfates of ammonia. These are quite salsble in the agricultural industry as fertili-zers.
To regenerate the nitric acid which is used in the autoclave 6, the gaseous phase is bled of~ from the autoclave and transferred to a condenser 32, where the water vapor in the phase is removed. The gases are then oxi-dized with either oxygen or air in an oxidizer 34, and the resulting higher oxides o~ nitrogen are passed counter-current with water in an absorption tow-er 36 to generate the acid, :-:
, . .

1~)6606Z

The gaseous phase in the autoclave 6 is part-cularly high in ni.t-rous oxides The regeneratcd acid is supplemented from an acid production plant 94 which is supplied in tur~ by an am~onia geDerator 96 that also supplies an ammonium hydroxide plant 98.
The following examples illustrate the process. In each of ~he first three examples, a 200 gram sample of the ore was processed in a stain-- less steel autoclave at a pulp density of 287 grams/liter. Using a theoreti-cal extraction of 100~ of the copper, silver or nickel, a leach liquor of about 60-lOD grams/liter was produced for optimum recovery of the metals.
EXAMPLE I
The first sample to be treated was a copper sulfide conccntrate with the following composition:
Copper,,, ,......... ,,......... 25.8 Iron..... , ,.... ,.............. 25.0~
Sulphur......... , ............. 38.7%
Silicon Dioxide................ .S.O~
Essentially this i5 a chalcopyrite concentrate containing chiefly the sulfides of Iron and Copper.
The concentrate had the following report on par~icle SiZ9:
Mesh (Standard Tyler) Weight (%) -48 1.3 -65 3.5 _100 5.2 -150 8.2 -200 7.0 -270 6.1 -325 8.7 Variances in temperature, overpressure, concentration ratio of acid 3U to mineral, time of leach, and degree of agitation were made to determine - ' :: -' ' ' .
.,... . ~:

~06606;Z
thelr effect on putting copper into solution.
After each samplo was leached, the rcsidue was washed, filtered, dried, and analyzed.
For a 200 gram sample, 654 milliliters of 40% acid is necessary to achieve stoichiometry.
The results are listed in the following tables, 1 through , ~, :. . , , ,:

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eXAMPLE II
Tho next sa~ple to be treatod was a copper^silrer concentrato with the following co~position:
Cu.................... ......24.6~
Ag....... ,,......................... ,,. ,,.138 OZ. P~R TONPe.......... ,.. .........,..... 27.0 S.,.,.......... ............ 38.0 Insolubles..... .............. . 7.4%
Only the time of leach required confirmation, in view of the para-meters establishet through Example 1.
The ~olume of acid was again in stoichiometric balance with theore, and the particle size tistribution of the ore was comparable to that of Example I.
(See Table 6, Page 22) EXAMPLE III
The last sample was a silver-nickel-copper concentrate with the ~ollowing composition:
Cu.,.. ...,.......... 22.8%
Ni,... ,..... ,......... ,. 6.7~
Ag.......... .......... ..122 OZ PER TON
Fe.......... .......... .23.0%
S........... .......... ..39.0 Insolubles..................... ..6.8~
- Again, only a time confirmation was neeted, and the results werebased on stoichiometry and a comparable distribution of particle size.
(See table 7, Page 23) 1.,.,.. , .~ . ..... ~ . .

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10660~Z

EXA~PLE IV
Filtered, raw acid, sulfate containing leach liquor from Exan~le I
at a pH of about 0.3, was boiled snd evaporated to dryness; whereafter the solids which remained were redissolved in water. It was observed that the iron solids did not go into solution, but remained for the most part as an insoluble oxide.
Separately, 300 milliliters of the leach liquor from ~xample I at pH 0.3 were evaporated to 150 milliliters, and ammonium hydroxide was added to bring the pH of the solution up to 1.7. Subsequently, the solution was heated in a stainless steel pressure bomb to a constant 150C (302F) while the bomb was purged of gases with oxygen for 20 minutes. When the bomb w~as opened, it was observed that ferric oxide had prccipitated.
Further tests were made in the bomb at higher temperatures. The oxide formed in each case, and temperatures of 200C (about 392F3 and above, actually formed a better ferr~c oxide product. However, at 150~C ~about 302F) a well bchaved, readily filterablc crystalline precipita~e of the oxide was formed in each case.
Other tests were also made, involving seeding the leach solution with various chemicals which it was thought might cataly~e precipitation when the solution was heated in an open vessel. However, none of the chemicals produced a well behaved precipitate of iron. Also, increasing the pH from 0.1 to 5.0 did not increase the filterability of the p~ecipitate in an open vessel.
EXAMPLE V
A stoichiometrically balanced, filtered, nitric acid leach liquor containing 50 grams per liter of copper and 35 grams per liter of iron as mixed sul~ate/nitrate, was heated in a stainless steel autoclave to 500F.
The stated temperature was held only for about 5 minutes, and the solution was allowed to cool rapidly. The pH was maintained at 1Ø Recovery of thc iron, as black ferric oxide, was 99~ of the total in solution. The solid was granu-lar and easily filterable, and contained no detectable copper.

'L066~6Z

EXAMPLE VI
It was observed that at tcmperatures above about 125C (2S7F), there was a sharp increase in sulfation of the sulfur in the unfil~ered leach liquor resulting from Exa~ple I. Moreover, it was observed that pH adjustments in the filtered leach liquors subjected to autoclaving in Example IV, did not appreciably affect the performance of the iron oxide precipitate. Therefore, tests were conducted in which the leach solution of Example I was subjected to temperatures above about 125C (2S7F) during the leach operation, and it was observed that a readily filterable hydrous oxide of iron precipitated di-rectly from the solution during the leach. In the region immediately aboveabout 160C t320F), the precipitate appears to be less susceptible to filt~a-tion.
A similar oxide precipitation effect is achieved with copper-silver and silver-nickel-copper samples such as those used in Examples II ant ~II.
Likewise, the effect can also be achievet with cobalt containing samples.
EXAMPLE VII
. . ~
A concentrate containing 15% copper, 10~ zinc and 17% iron was leachet with nitric acid at 40% concentration. The tomperature of the solu-tion was maintained at 138C (280P) and the pressure of the autoclave was hold at 80 psig for 45 minutes. The solution was agitated by an o~erhead stirrer at 1000 rpm.
The leached slurry was filtered to separate the solid fraction from tho filtrate. The solit fraction contained primarily precipitated hydroxides of iron. The filtered leach liquor contained 56.2 grams per liter of copper, 8,7 grams per liter of iron, and 30.1 grams per liter of zinc, EXAMPLE VIII
Zinc has a similar chemistry in nitric acid solution and can be oxpectet to react the sa~e as copper, silver, nickel and cobalt, under ~he foregoing parameters, when a zinc sulfide ors subjected to the process of Examples l-VII.

.~ .. .. - . . ~ .

~06606Z
ln the follewing Examples, leach liquors of the type developed in the foregoing Examples I-VIII are subjected to solvent extraction for the me-tal recovery stage, using either the aforementioned "LIX-64N," an alpha sub-stituted hydroxy-oxime manufactured by General Mills Corporation o. Minneapo-lis, Minnesota, or "Kelex 100", a hydrocarbyl-substituted 8-hydroxyquinoline manufacturcd by Ashland Oil and Kefining Company of Houston, Texas.
EXAMPLE IX
A leach liquor containing 53 grams per liter of copper and 5.9 grams per iiter of iron was contacted with an o~gar.ic solution of 30~ by volume of General Mills "LIX-64N" and 70~ by volume kerosene, in a three stage cotmter-current mi~er-settler apparatus. ~he pll of the li~uor was adjusted to about-1.5 before it was introduced to the first extraction stage, and behind each mixer-settler stage there was a pH adjustment tank from which the aqueous feed and aqueous recycle streams wcre drawn for the stago. In each of the tanks, the pH was continuously maintained zt about 1.5 by adding a~moniu~ hydroxide.
In sddition, ths tanks wcrs sizod so that tho hydroxide procipi~ates which formed, were redissolved, and screens and/or filter clo~hs were provided 50 that the precipitatcs could not be carried in to the next stage until they had redissolved, An organic to leach liquor feed ratio of 12.7 to I was used. With~
an aqueous recycle for each stage, this ratio was reduced to 1.12 to 1 to in-sure that the phases mixed at a good rate and that there was a good mass trans-fer rate. During the contact oporation, 5.9 milliliters per minuto of aqueous leach liquor were fed to the first stage, and 75.1 milliliters per minute of the organic phase were fed to the third stage. The aqueous phase exited from the settler into the pH adjustment tank, and of the soiution in the latter 61 milliliters per minute were recycled back to the mixing tank and about 6 milli-liters per minute wero advanced to the second extraction stage. This basic scheme was also followed for the remainder of the ex~raction stages. It was found that 85.3~ of the copper in the liqucr was extracted in ~he first stage, - . . . . -.
~, ; -: ' , ,, ' , 11.5% in the second stage, and 2.6~ in tho third stage. The raffinate flow-ing from the third stage pH adjustment tank contained 0.34 gram per liter of cspper, representing about 99.4~ extraction of the CoppeT None of the other metals in the liquor precipitatet during the entire operation.
EXAMPLE X
ln similar fashion, a filtered leach liquor containing 65 grams per liter of copper was contscted counter-currently in a continuous three-stage mixer-settler apparatus, ant the pH of the liquor was maintained at 1.5 bet ween stages through the addition of ammonium hydroxide to the same. Also, an organic to a~ueous flow ratio of 1.12 to 1 was maintained throughout by using an aqueous recycle stream. Again the organic phase contained 30~
"LIX-64N" in kerosene. 99.6% of the copper in the liquor was e%tractet with-out any other metal precipitating.
EXAMPLE XI
Pregnant organic phase was transferred continuously from an ex-traction section such as the above to a two-stage lcounter-current~ ~ixer-settler stripping apparatus, and an organic to aqueous flow ratio of 1.87 to I was maintain~d in the apparatus, Stripping was accomplished with a sul-furic acid solution containing 180 gra~s per liter of sulfuri~ acid. The initial electrolyte contained 20 grams per liter of copper and the final electrolyte concentration was 30 grams per liter of copper, thus representing a copper transfer to the electrolyte of 10 grams per liter. 93,4% of the copper in the pregnant organic phase was strippet and the balance was re-- cycled through the extraction section.
EXAMPLE XII
An elect~owinning apparatus was uset in conjunction with a continu-ous liquid ion exchange system of the type employed in fixamples IX - XI, The apparatus operated with a current density of 25 amps per square foot, ant with air agitation ant electrolyte recycle. The cathodes produced were ana-sO lyzed at 99.8 ~ or - 0.2% pure copper and with no detectable iron or lead .:~

~1066062 present. Tho electrical current efficiency was greater thall 87,7%.
EXAMPI,E XIII
The pH of a chalcopyrite leacn liquor was adjusted to 1.8 with a~monium hydroxide and the liquor was contacted twice with an organic solution containing 10~ of Ashland's "Kelex 100", 10% decanol, and 80% kerosene. The liquor contained 59.1 grams per liter of copper and 7.1 grams per liter of iron. Between contacts the pH was adjusted again to 1.8. An organic to aque-ous ratio of 8.4 to 1 was used. No detectable copp~r was left in the aqueous phase and the extraction was essentially 100~ complete. Sulfuric acid at 180 grams per liter was used to strip the copper fro~ the organic phase. Two con-tacts at the orgaDic to squeous ratio of 8.4 to 1 were made, 77~ of the cop-per was transferred to the aqueous sulfuric phase.

- 28 _

Claims (16)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of recovering one or more metal values of the group consisting of copper, silver, nickel, cobalt and zinc from a sulfur and iron containing ore of the metal or metals, comprising intermixing the ore and at least a stoichiometric amount of nitric acid of about 30-50% by volume concentration to form an aqueous acid leach solution of the same, heating the solution to a temperature at or above the melting point of sulfur while the solution is contained under pressure in a relatively inert atmosphere, controlling the temperature of the solution to substantially precipitate the iron values from the solution, relatively separating the iron precipitate from the acid soluble phase of the solution, and recovering the metal value or values from the acid soluble phase.

2. The process according to claim 1 wherein after the iron values are precipitated, the solution is flashed to precipitate any insolubilized sulfur therefrom and the sulfur precipitate is separated with the iron precipitate.

3. The process according to claim 1 wherein the acid insolubles are separated from the acid soluble phase before the metal values are removed therefrom, and the iron precipitate is separated concurrently with the other acid insolubles.

4. The process according to claim 3 wherein after the iron values are precipitated, the solution is flashed to precipitate any insolubilized sulfur therefrom and the sulfur precipitate is separated concurrently with the other acid insolubles.

5. The process according to claim 1 wherein the sulfur is crystallized as a salt thereof and relatively separated from the acid soluble phase after the metal value or values are removed therefrom.

6. The process according to claim 1 wherein the temperature of the leach solution is controlled to precipitate the iron as a salt thereof and then the salt is relatively separated from the acid soluble phase.

7. The process according to claim 6 wherein the relatively iron-free acid soluble phase is evaporated to crystallize and relatively separate the sulfur therefrom in the form of a sulfate salt.

8. The process according to claim 7 wherein the iron-precipitation step is carried out during the leaching stage and the sulfate-salt-crystal-lization step is carried out after the metal value or values are removed from the acid soluble phase.

9. The process according to claim 1 wherein the metal value or values are solvent extracted from the acid soluble phase and then recovered from the extractant liquid.

10. The process according to claim 1 wherein the leach solution is heated to a temperature of above about 125°C during the leaching stage to precipitate the iron as a salt thereof.

11. The process according to claim 1 wherein the leach solution is subjected to agitation during the leaching stage.

12. The process according to claim l wherein an aqueous suspension of the ore is formed and then added to the acid while the acid is under agitation and pressurization in the leach container.

13. The process according to claim 1 wherein the reaction gases generated in the container are collected externally of the container, oxidized to the higher oxides of nitrogen, and intermixed with water to regenerate nitric acid.

14. The process according to claim 13 wherein the regenerated nitric acid is returned to the container.

15. The process according to claim 1 wherein the acid soluble phase is subjected to autoclaving at a temperature of above about 300°F to pre-cipitate dissolved iron as the oxide thereof, and the oxide is relatively separated from the acid soluble phase before the metal value or values are recovered therefrom.

16. The process according to claim 15 wherein the acid soluble phase is subjected to autoclaving after the acid insolubes are relatively separated therefrom.