US2814564A - Method of purifying metals and consolidating the same - Google Patents

Description

Nov. 26, 1957 w. M. HAYDEN 4 METHOD OF PURIFYING METALS AND CONSOL'IDATING THE SAME Filed July 17, 1957 FEED OF METAL BEARING SOLIDS TREATING LIQUORS LEACH ING OPERATION WASTE TO DISCARD METAL IN SOLUTION REDUCTION AUTOCLAVE A REDUCING GAS.

METAL POWDER INVENTORI WILLIAM M. HAYDEN W km ATTORNE s BYM ,a lag 2,814,564

METHOD OF PURIFYING METALS AND CONSOLIDATHIG THE SAIVIE William M. Hayden, New York, N. Y., assignor to Chemetals Corporation, New York, N. Y., a corporation of Delaware Application July 17, 1957, Serial No. 672,479

3 Claims. (Cl. 75-211) This invention relates to the production of wrought metal articles; and more particularly it relates to recovering copper, nickel or cobalt in wrought form from an impure, raw material containing such metal, by dissolving such metal from the raw material in an aqueous leach solution, then introducing a hydrogen reducing gas into such a solution at an elevated temperature and pressure to precipitate the metal in substantially pure pulverulent form, rolling the precipitate into consolidated bar form While in its freshly reduced state, and then working the consolidated bar into a wrought shape.

It is well known that copper, nickel and cobalt can be recovered from scrap or from ores or concentrations containing them by dissolving the metal from the raw material in an aqueous solution and then heating the solution at an elevated temperature and pressure with a reducing gas. The metal is precipitated in substantially pure form, more or less pulverulent in character. In its precipitated form the metal has at best only rather limited fields of use. Generally it must be converted to a wrought shape in order to be useful. Such conversion, however, is not a simple matter. Melting the pulverulent precipitate and casting into shapes for rolling is not economically desirable because such procedure entails large losses of the metal due to oxidation. Melting in vacuum or in a non-oxidizing or reducing atmosphere greatly increases the cost of the operation. Hot extrusion of the pulverulent metal in a reducing atmosphere has been proposed but this procedure also is costly. Fabrication of the metal into wrought or other shapes by conventional techniques of powder metallurgy has not proved satisfactory, partly because such techniques are suitable only for making rather small articles, and partly because the pulverulent metal precipitate has not proved itself to be uniformly suitable for fabrication by the methods of powder metallurgy.

I have discovered that despite the non-uniform behavior of the pulverulent precipitate in conventional powder metallurgy fabrication procedure, it is possible to secure good and consistent results in the consolidation of such precipitate into a bar which can be worked further into a wrought shape when the precipitate is consolidated by a rollin operation. In this operation the precipitate is passed between rolls which preferably are arranged with their axis in a common horizontal plane. The rotating rolls work the compacted pulverulent metal mass by a sort of tumbling action just prior to passage of the metal particles into the bite of the rolls. Then, as the metal becomes caught in the bite of the rolls, it is efiectively consolidated into bar form, in which form it can be handled and worked, as by sintering and further rolling, to produce a wrought shape.

The invention includes the discovery that when a hydrogen metal precipitate is subjected to a rolling operation to consolidate the same promptly after it has been precipitated or while the metal particles of the precipitate are still in their freshly precipitated state, or have been Patented Nov. 26, 195.7

maintained in such a state, a substantially superior wrought metal structure can be produced in a rapid and continuous manner when compared to a similar hydrogen metal precipitate which has been allowed to age to any substantial extent.

In preparing wrought metal structures it is first necessary to partially consolidate the metal powder into a green compact which can be subsequently worked into the final, full density wrought metal. The green compact must have sufficient green strength to withstand further handling and working without breaking.

The non-aged precipitates, according to this invention, present a clean, fresh, uncontaminated metal particle surface into the bite of the compression rolls resulting in a high green strength partially consolidated compact which can be readily and easily handled and subsequently worked in a continuous process without breaking. The high green strength can be obtained by a single pass through the compression rolls.

Powders which have been aged to any substantial extent are very difficult to bond due to the lack of fresh and clean surfaces. Partially consolidated compacts formed therefrom are fragile and lack adequate green strength for further handling or processing in a continuous process. Partially consolidated compacts formed from aged powders obtained by a single pass through the compression rolls possess green strengths as low as one-half and below that obtainable by rolling fresh or non-aged hydrogen metal precipitates under the same conditions.

Partially consolidated hydrogen metal precipitate compacts formed from fresh or non-aged precipitates can be easily and very adequately sintered and further worked into wrought metal shapes of a quality suitable for commercial use. Such partially consolidated metal compacts exhibit no blistering during the sintering operation and result in uniform, strong, full density, wrought metal structures.

The partially consolidated hydrogen metal precipitates formed from aged precipitates blister considerably during the sintering operation and, as a result, they cannot be further Worked into wrought metal shapes of a quality suitable for commercial use. They are generally nonuniform and do not possess adequate strength and otherwise lack good physical and electrical properties.

The reason for the blistering of the partially consolidated compacts formed from aged powders is not known. However, it is believed to be due to the presence of hydrogen on the surface of the precipitatedparticles in combination with metal oxides, such as copper oxide, which forms as a film on the precipitated particles due to aging. It is theorized that the hydrogen present on the metal particles reacts with the metal oxides, such as copper oxide, during the sintering operation forming water. The water is vaporized internally of the metal compact and its escape therefrom results in the blistering.

In addition, the partially consolidated metal compacts are generally sintered in an inert gas atmosphere such as hydrogen. The hydrogen of the inert gas atmosphere may also react with the copper oxide to form water which would result in blistering. If the inert gas used contains carbon, carbon dioxide gas would probably be formed which would also cause blistering.

If an aged precipitate is rolled any contamination on the surface of the particles such as metal oxides is compacted internally of the partially consolidated compact. The failure to remove all of these contaminants during the sintering operation, which causes blisters as referred to above, would further result in a weak and non-uniform wrought metal strip. No such problems are encountered if the hydrogen metal powder is rolled while it is still 3 fresh or maintained in the fresh state according to this invention.

The problems above referred to do not exist if the metal powders are to be melted and cast. The contaminants present are not ground into the consolidated strip, but instead rise to the top of the melt and can be easily removed therefrom.

Aging of the precipitate, insofar as it affects the ability of the metal particles to be roll-bonded into a consolidated bar of good quality, is not simply a matter of time and cannot be defined in terms of any fixed period of time. Much depends on how the precipitate is handled following its formation. If it is carefully freed from leach solution and other contaminants, and is protected from oxidation and contamination in other ways, a relatively long period of time, say a matter of weeks, may elapse without deleterious aging of the metal particles. On the other hand, if the precipitate is inadequately freed of leach solution or residual salts, or if it is exposed to contaminating atmosphere, or is stored in contaminated vessels, it may age (in the sense that it loses its freshly precipitated character for purposes of roll-bonding) in a matter of hours or even minutes. The hydrogen metal precipitates can be maintained in their freshly precipitated state by freeing them of contaminants such as the leach solutions, and storing them in an inert non-oxidizing or non-contaminating atmosphere.

Prior to rolling of the metal powder, it may be, if desired, washed and/ or dried. However, this is not always necessary, and the metal powder may even be rolled directly while still wet with the liquor from which it was precipitated, provided the powder is in the freshly precipitated state and is promptly subjected to the rolling operation.

The character of the metal precipitate varies considerable depending on the particular reducing gas used to form it, and with the nature of the solution from which it is precipitated. Precipitates from acid or substantially neutral solution, and precipitates formed with sulfur dioxide or carbon monoxide as the reducing gas, are coarse and grainy, whereas precipitates from alkaline (ammoniacal) solution are relatively fine. Of all these various precipitates, I have found that those formed by the action of hydrogen on ammoniacal carbonate solutions of the metal (copper, nickel or cobalt) are most advantageous for roll-bonding. The flow characteristics of such precipitation, the particle size and shape, and the character of the surface of the metal particles, all are superior to precipitates prepared from other solutions and with other reducing gases for the purposes of working into Wrought shapes by the method of this invention.

The process of the present invention may best be set forth in general terms by referring to the drawing which depicts the metal powder producing features of the present invention in the form of a flow sheet, while the metal rolling portion is depicted as an apparatus.

The impure raw material, bearing at least one of the metals selected from the group consisting of copper, nickel and cobalt, is first fed into a suitable leaching tank. A leach solution is then introduced into the leaching tanks to effect a leaching of the raw material to solubilize the metal values contained in the raw material. After the leaching, any waste or insoluble matter remaining is discarded. The clear leach solution is then transferred to a reduction autoclave into which a reducing gas is introduced to reduce the metal contained in the leach liquor and precipitate the same in the form of a powder. The resultant metal powder is then directly fed, after washing and/ or drying if desired, into a hopper 2 which guides the metal powder into a roll gap formed by the pressure rolls 3 and 4. The pressure rolls 3 and 4 compress the metal powder into a wrought metal form as shown at 6. The strip or sheet 6 is then fed into a suitable sintering furnace 7 and may also be subjected to further rolling operation by the rolls 8 and 9 to enhance the mechanical strength and ductility of the strip or sheet 6.

Leaching procedures to place the metal values of an ore or scrap and the like in solution for subsequent reduction is a highly developed and well-known art. So far as the copper, nickel and cobalt of the present invention are concerned, the exact leaching procedure may be widely varied. The most advantageous procedure involves either acid or ammoniacal leaching. Either the acid or ammoniacal leach may be used with or without oxidation, depending upon the content of the raw material being treated. Generally, sulfuric acid is used in acid leaching and some ferric sulfate is often added therewith. Ammoniacal leach liquors also often contain ammonia salts such as carbonate and complex metal ammonium ions. The present invention is applicable to a raw material containing copper, nickel or cobalt when treated by any such procedures and the invention is not limited to any particular type of leaching, the important aspect being that one or more of the metal values is dissolved in an aqueous solution and thus capable of being reduced to a powdered metallic form by means of a reducing agent. For purposes of the following description of a specific and preferred embodiment of the invention, it will be assumed that the desired metal (copper, for example) is dissolved in an ammoniacal carbonate solution. The leach solution containing the copper or other metal values is separated from the waste material or insoluble matter by any suitable means such as decanting or filtering. At this point, if desired or if necessary, the resultant clear solution may be purified so that it contains but a single gas reducible metal salt. The resulting solution is then transferred to an autoclave in which the dissolved metal is reduced to form a pure metallic powder.

The concentration of the leach liquor after or just before transfer to the high pressure autoclave should first be adjusted so that its metal content is such so as to assure a good yield of the metal powder. The leach liquor should be adjusted to a concentration of dissolved metal up to about 200 grams per liter, but below that at which in the absence of a reducing gas a substantial amount of a compound of the metal will precipitate when the solution is heated to above its boiling temperature, and preferably to above 250 F. After adjustment, the leach liquor may be heated to 250 F. or higher prior to introducing it into the autoclave, or, if desired, after it is in the autoclave. After the adjusted solution is in the autoclave, a suitable reducing gas such as carbon monoxide or hydrogen is introduced to effect reduction of the metal salt to produce the metallic precipitate powder. The temperature of the reduction reaction should be maintained at above about 250 F. and preferably 300 F. to 350 F. The minimum partial pressure of the reducing gas should be about 50 p. s. i. and the total pressure should be sufficient to prevent boiling. A pressure of about 900 to 1,000 p. s. i. is preferred and is suflicient to prevent boiling of the usual solution. During this reduction period the reducing gas reacts with copper (or nickel or cobalt) in the leach liquor and precipitates the metal in powder form.

Although the maximum copper (or other metal) content is as noted above, it preferably should not exceed about l35-150 grams per liter, because at higher concentrations precipitation of other copper compounds is likely to occur. Generally, with ammoniacal carbonate liquors, the metal concentration will preferably be below 130 grams per liter and sometimes advantageously below 100 grams per liter.

Copper and other metal precipitates that have been reduced with hydrogen gas produce consolidated bars that are decidedly superior to precipitates or powders produced in other manners. The hydrogen-precipitated copper powder, for example, yields a rolled consolidated bar of more uniform density and greater strength in the fully rolled condition than copper powder reduced by other gases; and it yields, upon sintering and working, a final wrought shape of better physical properties than corresponding articles similarly prepared from precipitates produced by other reducing gases.

Following is a specific example, taking the production of copper powder as illustrative, of the method of the present invention:

Copper-bearing scrap was first introduced into a suit-- able leaching tank and leached by a leach liquor analyzing approximately 60-65 grams per liter of copper (approximately 90% cupric), 150-170 grams per liter of ammonia, and 100-110 grams per liter of carbon dioxide at a temperature of about 135 F. for about 6 to 8 hours. After this leaching step the insolubles were removed from the pregnant leach solution by filtration. The clear leach liquor was then fed into a high pressure autoclave equipped with an agitator. Hydrogen gas was introduced into the autoclave until the pressure reached 900-1000 p. s. i. and this pressure was maintained by regulated admission of hydrogen for approximately 35 minutes. The temperature throughout the reduction step was kept constant at 350 F. During the reduction step with the hydrogen, finely divided metallic copper precipitated. After the autoclave was relieved of its pressure, the copper powder precipitate was allowed to settle, and then was decanted and washed. Promptly thereafter (within 24 hours), while the metal particles were still in their freshly precipitated condition, the precipitate was fed between a pair of pressure rolls and was thereby consolidated into bar form. The consolidated bar was then sintered by introducing it into a sintering furnace and there heating it to a temperature just under the melting point of copper for a period of about two minutes. The sintered bar was then subjected to a further rolling operation by which its cross-sectional area was reduced about 50%. The resulting wrought copper article possessed excellent ductility and mechanical strength, approximating that of wrought copper.

This application is a continuation in part of my earlier application Serial No. 412,700, filed February 26, 1954, now abandoned.

I claim:

1. The method of recovering a metal selected from the group consisting of copper, nickel and cobalt in Wrought form from an impure raw material containing such metal which comprises dissolving such metal from the raw material in an aqueous leach solution, then introducing a hydrogen gas into said solution while the solution is under super atmospheric pressure and at a temperature exceeding its normal boiling temperature, whereby the metal is precipitated in substantially pure pulverulent metallic form, separating said precipitate from the residual solution, rolling said precipitate promptly while the metal particles thereof are still in their freshly precipitated state into a consolidated bar, and subjecting the consolidated bar to sintering and further rolling to form a wrought metal bar.

2. The method of recovering a metal selected from the group consisting of copper, nickel and cobalt in wrought form from an impure raw material containing such metal which comprises dissolving such metal from the raw material in an aqueous ammoniacal carbonate solution, heating the solution under super atmospheric pressure to an elevated temperature exceeding 250 F. and introducing hydrogen gas into said solution at said elevated temperature, whereby the metal is precipitated in substantially pure pulverulent metallic form, separating said precipitate from the residual solution, maintaining the hydrogen metal precipitate in its freshly reduced state, rolling said precipitate into consolidated bar form, and subjecting the consolidated bar to sintering and further rolling to form a wrought metal bar.

3. The method of recovering copper from an impure cuprous raw material and working it into wrought metal form which comprises dissolving the copper from said raw material in an aqueous ammoniacal carbonate solution, heating said solution under super atmospheric pressure to an elevated temperature exceeding 250 F. and introducing hydrogen gas into said solution at said elevated temperature, to precipitate the copper in substantially pure pulverulent metallic form, separating said precipitate from the residual solution, rolling said precipitate promptly While the copper particles are still in the freshly precipitated condition into a consolidated bar, and subjecting said bar to sintering and further rolling to form a wrought metal bar.

No references cited.

Claims (1)

1. THE METHOD OF RECOVERING A METAL SELECTED FROM THE GROUP CONSISTING OF COPPER, NICKEL AND COBALT INLT IN WROUGHT FORM FROM AN IMPURE RAW MATERIAL CONTAINING SUCH METAL WHICH COMPRISES DISSOLVING SUCH METAL FROM THE RAW MATERIAL IN AN AQUEOUS LEACH SOLUTION, THEN INTRODUCING A HYDROGEN GAS INTO SAID SOLUTION WHILE THE SOLUTION IS UNDER SUPER ATMOSPHERIC PRESSURE AND AT A TEMPERATURE EXCEEDING ITS NORMAL BOILING TEMPEATURE WHEREBY THE METAL IS PRECIPITATED IN SUBSTANTIALY PURE PULVERULENT METALLIC FORM, SEPARATING SAID PRECIPITATEED FROM THE RESIDUAL SOLUTION, ROLLING SAID PRECIPITATE PROMPT-LY WHILE THE METAL PARTICLES THEREOF ARE STILL IN THEIR FRESHLY PRECIPITATED STATE INTO A CONSOLIDATED BAR, AND SUBJECTING THE CONSOLIDATED BAR TO SINTERING AND FURTHER ROLLING TO FORM A WROUGHT METAL BAR..

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