US2396792A - Refining nickel - Google Patents

Description

Patented all".v l9, i946 a STATES REFINING NI William J. Kroll, NiaFails, N. Y.

No Drawing. Application 22, 1944,

. Serial No. 527,865

12 Claims. (or. 15-82) This invention relates to metallurgical proc= esses and more particularly to a process for refining nickel contaminated with metallic impurities to remove the metallic impurities therefrom.

Heretofore in the art, the preparation of substantially pure nickel or nickel containing relatively small amounts of metallic impurities has been exceedingly difiicult and has required the practice of complicated and costly processes.

The object of the present invention is to provide a process for the elimination of associated metal impurities from metallic nickel. I

Another object is to provide a process for discovered that, contrary to expectations based molten metal chloride fusions.

As a resultof this discovery I have devised an improved method of treating impure nickel to eliminate therefrom substantially an associated metal impurities which consists essentially in reducing or comminutlng the impure nickel to fine particle size and suspending or dispersing the same in a fused metal chloride bath containing nickel chloride for and extended time interval adapted to efiect or obtain a removal of the said associated metallic impuritiesby a displacement reaction between the said impurities and the nickel chloride, then separating the metal from the i'used bath.

There are many diflerent ways in which the present invention may be adapted in the art of purifying nickel of its associated metallic impuri-.

ties and of introducing the invention as an essential step in a process of recovering nickel from its ores. I will describe, first, the basic principles involved in the displacement reaction and, secondly, wherein this basic reaction may be adapted in the treatment of impure nickel metal powder in the elimination of certain heavy metal impurities and in the treatment 01 nickel scrap materials to eliminate therefrom associated metal impurities.

The basic displacement reaction of the present 7 invention is complicated, to a certain extent by alloy and intermetallic compound formation between the nickel and the displacing metal and by the relative rates of difilusion of the two metals into and through each other. To overcome this complication and to reduce the same to a low order, it is essential to reduce the nickel to a a small particle size or thin section thereby toreduce the diflusion path to the smallest distance that'is economically practical to obtain.

The reaction involved is essentially one of displacement according to one or more of the reactions below indicated;

(eta) This reaction will occur at all temperatures at which the Nifilz and the resultant chloride compound or the displacing metal may be main tained in a liquid anhydrous phase but the rate of the reaction increases markedly with increase in temperature and is most rapid at temperatures above about 700 C. and below the boiling point of the chloride compound of the displacing metal when boiling point lies below that of nickel chloride (975 CJ.

I have found, however, that by melting nickel chloride in a metal chloride fusion consisting principally of one or more of the chloride compounds of the most stable metal chlorides, such as the alkali and alline earth metal chlorides, a wide range of liquid anhydrous metal chloride fusion mixtures may be obtained that are highly stable and ant to omdation decomposition when heated in the open air to temperatures as high as 975 C. to 1000 C. and which are operative in accordance with the present invention at temperatures as low as 500 C. a

In general, though, I prefer to employ a metal chloride, fusion mixture consisting of potassium and sodium chlorides mixed in the ratio of 60% KC! and 40% NaCl and having a melting point of 650 C. To any given volume or this fusion mix I add N101: in the total amount desired relative to the associated metal impurities of the comminuted nickel dispersed therein, usually adding the said nickel chloride in such increments as may be necessary to maintain a large excess of NiClzv over that theoretically required and preferably between 25 to 50% NiClz (by weight) in the fusion mix. The addition of NiClz to this preferred fusion mixture or base chloride fusion normally lowers the melting point to below 500 C. and temperatures as high as 1000 C. may be safely employed without excessive loss by volatilization of the nickel chloride.

The amount of comminuted nickel immersed and suspended in the molten metal chloride bath may be varied widel without essential departure from the present invention as one skilled in the art will recognize, and is primarily dependent upon the total amount of impurities it is desired to eliminate in one treatment. As the displacement reaction involved results not only in a solutioning of the associated metal impurities but also in an enrichment of the metallic residue with precipitated nickel, in many instances it may be only necessary to lower the percentage of contained associated impurities materiall to obtain an intermediate purified nickel product containing the remaining impurities within tolerance percentages suitable, in some instances, for use in the trade. Again, it may be desired only to selectively remove one or more of the associated impurities, it being apparent that where two or more associated metal impurities are present in the nickel, the one higher in the displacement series will be dissolved out in major proportion before solutioning of the second impurity appreciably initiates.

In this connection, m investigations indicate the following approximate descending order for the various metals, commonly found associated with nickel, in the displacement series of metals in molten metal chloride baths containing nickel chloride: V, Mn, Zn, Cr, Fe, Co, Cu, Ni.

The alkali and alkaline earth metals and magnesium lie to the left of the list or above V and only a few metals lie to the right or below Ni. The metals A Pb, Sn, Cd, Al, Be, U, 'I'h, all he above Ni in this displacement series and if present in Ni also would be removed along with any of the metals in the series above noted.

With respect to the above series, some of the metals form intermetallic compounds which resist decomposition in accordance with this series. As an example, the intermetallic compound nickel silicide is more noble than Ni and very difflcult to break down, and in most cases the silicon content of nickel alloys is largely retained.

In the practice of the present invention, Iprefor to malntain'a temperature substantially below the boiling point of the chloride compound 7 of the displacing metal, but not over the boiling point of nickel chloride (975 to 1000 C.), and a temperature approximating 700 C. whenever practicable. However, temperatures as low as 500 C have been employed in the practice of the present invention with good results.

The melting and boiling points of the chloride compounds of the more common metal impurities are as follows:

As one specific example of the present invention, but not as a limitation thereof, nickel ture of the bath was maintained for about one hour at 650 C. at the endof which time the metal powder was separated from the fusion mixture and the cobalt content remaining therein determined by chemical analysis. The chemical analysis showed that 70% of the cobalt content of the nickel metal powder had been removed in this relatively short time of treatment.

By extending the time interval of treatment to two hours;-or by increasing the amount of mm: in the fusion mixture to increase the rate of the displacement reaction; or by reducing the particle size of the nickel powder to below 200 mesh; or by repeating the above treatment, the amount ofcobalt removed from the nickel powder may be varied widely. It is not always desired to effect a substantially complete removal of the cobalt in one extraction treatment, except where, in addition to cobalt, the metal powder contains undesired amounts of other impurities lower than Co in the displacement series. In that event substantially all of the Co must be removed before any of these other metals may be removed.

In general, I- prefer to employ higher concentrations of MC]: in the fusion mixture of alkali metal chlorides than given in the above example and concentrations within the range 25-50% are preferred so as to obtain as rapid a rate of displacement as possible at an operating temperature of 650-750 (3., thereby to materiall shorten the required time interval of treatment. With this high concentration of N101: in the fusion mixture I find that the amount of nickel powder incorporated therein for treatment may be greatly increased, the'precise amount of increase depending upon the total amount of associated impurities present.

Ni in the displacement series. With Cu, for example, a large excess of N10]: must be present in the fusion, whereas with Zn and Mn relatively a small excess is required. By maintaining such an excess, however, from '70 to of any given metal may be removed in each treatment and by repeating the treatment several times a sub-.

stantially complete removal may be eflected.

Where substantiall complete removal of these associated impurities only is desired, a second treatment using a molten flux substantially free of the displacing metal chloride is generally effective where the original amount of the contaminating metal is not excessive.

As a second specific example, a metal powder passing about mesh and consisting principally of nickel but containing copper in about the per- .centage usually present in Monel metal which powder was obtained by the hydrogen reduction of mixed Ni and Cu oxides, was suspended in a molten bath consisting oi'a 60/40 mixture a KC! and NaCl containing about 25% nickel chloride, the mixture being about two part fusionmixture' to one part metal powder. The bath temperature was maintained at 700 C. and the time interval of treatment approximated one-half hour. After separating the metal powder from the fusion mixture. chemical analysis of the metal powder showed that 72% of the copper had been removed in this short time interval of treatment. Longer time intervals of treatment have resulted in substantially complete removal (90-95%) of the copper content of this metal powder, and a second treatment in a similar fusion mixture usu ally resulted in an even greater purity nickel powder product.

As another example, nickel metal powder-containing Fe as an impurity when added to the fusion mixture used in the above second example in about the same relative proportions and under substantially the same time and temperature conditions resul ed in the removal of 80% of the ironwithin one-half hour and 90 to 95% of the iron at the end of an hour.

From the above examples. it is believed apparent that the removal of Co. Cu and Fe from nickel may be easily effected by the practice of the present invention. The metals .Al. Zn and Mn, are even more'easily removed in the same manner and under the same conditions. as these metals are higher than Cu. Co and Fe in the displacement series as here nbefore noted. In eneral. Mn. Zn and Al will be removed in higher percentages in one treatment than is usually obtainable with Cu. Fe or C0.

The ada ta ion of the inven ion to the tr atment of nickel scrap is of particular im ortance in the art. i asmuch as it is known that it is extremel .diiiicult in remelting scrap nickel to eliminat therefrom many of the metals as ociated therewi h in alloy or occluded form. S me of these metals may be removed in major part from the molten alloy by oxidation but some con taminating metals. such as iron and cop er, may not be separated from nickelin thi manner.

In accordance with the present inventi n, t e scrap nickel following reduction in particle size to pass 60 to 100 mesh in any convenient manner,

3 to a second treatment in afresh batch of the fusion mixture under substantially the same conditions for another hour, thereby effecting a removal of 90 to 95% of the associated metal impurities.

Whether ornot a third treatment is to be given forming Cu-containing nickel alloys, as an exis subjected to extended heat-treatment in a C. (the B. P. of NiClz) and as low as 500 C. without essential departure from the present invention, the specific temperature being selected with respect to the impurities present to obtain t e most economically practical rate of displacement with consequent shortest time interval of treatment to obtain the desired percentage of removal of impurities in the first treatment.

In general, from to 70% of the associated metal impurities may be removed from the nickel by means of the above fusion mixture, within a time interval of treatment approximating one hour. In general, I prefer to end the treatment after one hour and after separating the metal cake from the fusion mixture, subject the metal ample, the refining operation, of course, may be terminated when copper content of the nickel is within the tolerance limits of the alloy to be formed therefrom.

As an alternative practice a sequence of treat ments may be practiced on the scrapnickel whereby each of the contaminating metals are selectively removed.

Alternatively, also, the scrap nickel ma be melted, subjected to an oxidizing blast to remove some of the contaminating metals, cast into ingots, fragmented and comminuted to the desired particle size, and then treated in accordance with ispreferableto break the thin sectioned chips.

and turnings into relatively small fragments before treating in accordance with the present in- I vention regardless of section.

Various other modifications and adaptations of the present invention will be apparent to one skilled in the art from the above disclosure of the present invention but all such are contemplated asmay fall within the scope of the following claims.

What I claim is:

l. The method of treating a molten metal chloride bath containing nickel chloride to remove the nickel content of said bath as metallic nickel which comprises incorporating in said bath a finely divided metallic material having a melting point above the temperature of the bath and consisting at least in part of a metal higher than nickel in the solid metal-molten metal chloride displacement series at the temperature of heatins.

2. The method of treating a molten metal chloride bath containing nickel chloride heated to temperatures within the range 500-1000" C. to remove the nickel content of said bath as metallic nickel which comprises incorporating in said bath a finely divided metallic material having a melting point above thetemperature of the bath and consisting at least in part of a metal selected from the group of metals Al, Mn, Zn, Cr, Fe, Co, and Cu, r

3. The method of treating a molten metal chloride bath containing nickel chloride to remove a good part of the nickel content of said bath as metallic nickel which comprises heating the bath to a temperature within the range 500-1000 C. and incorporating a finely divided alloy of nickel and copper in said bath the amount of the copper in said alloy being substantially less than that theoretically required to displace substantially all of the nickel from the chloride combination.

4. The method of removing metallic impurities from nickel which comprises reducing the impure nickel to small particle size and dispersing the small particle sized material in a molten metal chloride bath consisting of a mixture of nickel chloride and metal chloride compounds of metals relatively high in the displacement series inthe system solid metal-molten metal chloride, and heating the said bath to a temperature within the range 500-1000 C. for a time interval pronickel chloride, said highly stable metal chlorides being selected to provide a fusion temperature within the range 500 to 1000" C.

6. The method of removing metal impurities from metallic nickel which comprises reducing the impure nickel to relatively small particle size and suspending the small particle sized material in ,a metal chloride fusion consisting of a mixture of alkali metal chlorides and nickel chloride having a temperature within the range sou-100m '7. The method of claim 6, wherein the amount of said nickel chloride is maintained in large excess of that theoretically required to remove substantially all of the said metal impurities b a displacement reaction.

8. The method of claim 6, wherein the amount of said nickel chloride is maintained in large excess of that theoretically required to remove substantially all of said metal impurities by a displacement reaction and wherein the time interval of treatment is limited to that effecting a removal of the major portion of said impurities within an economically practical short time and wherein the said treated metal is subjected to at least one other treatment in at least one more bath of said fusion mixture to obtain a removal of the greater portion of the remaining metal impurities.

9. The method of treating metallic nickel to eliminate therefrom associated metallic impurities oi? the group consisting of Cu, C0, Fe, Cr, Zn and Mn, which comprises reducing the impure nickel to fine particle size and suspending the said fine particle sized material in a molten metal chloride, bath containing nickel chloride and metal chlorides higher than Mn in the displacement series of solid metals in fused metal chlorides at temperatures within the range 500-l000 C.

10. The method of claim 9, wherein said molten metal chloride bath consists of a mixture of KCl 4 and NaCl.

11. The method of claim 9, wherein the amount of said nickel chloride is in large excess of the theoretical amount required to obtain substantially complete removal of said metal impurities by a displacement reaction.

12. The method of claim 9, wherein the time interval of immersion in said bath is limited to a time interval providing for the removal of the major proportion of said metal impurities within a relatively short time interval and wherein the metal is given further treatments in new batches of said fusion mixture to remove the major portion of the remaining impurities.

WILLIAM J. KROLL.