US2835557A - Method of producing nickel by the carbonyl process - Google Patents

Description

May zo, 195s 'Filed Maron 5o, 1955 DE wn'T H. WEST ET AL 2,835,557 METHOD oF PRoDucING NICKELBY THE: cARBoNYL PROCESS 2 Sheets-Shree?l 1 IKZ-6:8

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May 20, 1958 DE wl'rT H. wEsT E-rAl. 2,835,557

METHOD OF PRODUCING NICKEL. BY THE CARBONYL PROCESSv Filed March 50, 1955 2 Sheets-Sheei 2 METHOD OF PRDUClNG NICKEL BY THE CARBONYL PROCESS De Witt Henry West, Port Eynon, and Alexander Bowen Simpson, rynmill, Swansea, Wales, assignors to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware Application March 30, 1955, Serial No.. 493,034

3 Claims. (Cl. 23-203) The present invention relates to an improved process for the extraction of nickel from oxidic material containing nickel and, more particularly, to an improved process for reducing roasted nickel matte or other nickel oxide material and then subsequently extracting the nickel by the Icarbonyl process.

It is well known to those skilled in the art that in the production of nickel by the carbonyl process two important operations are reduction of nickel oxide material to convert the nickel to the metallic state and volatilization of the metallic nickel as nickel carbonyl. When the raw material contained the nickel combined with sulfur or other elements of the `same nature, for example, a nickel matte or a sulde ore, this raw material was ground and then roasted to nickel oxide before the reduction operation. In the p reduction operation the roasted matte or other nickel oxide material was caused to travel downwards through a tower divided into a number of boxes, with the matte or other nickel oxide material being moved by rabbles in each box until it fell into the next box, and with the reducing gas llowing concurrently with the matte. The reducing gas was usually water gas. Substantially all the reduction was effected by the hydrogen in the water gas in that case. Sometimes pure hydrogen has been used as the reducing gas. When a sulphur-containing catalyst was used in the volatilisation step, it was commonly formed in situ by adding `elemental sulfur to the roasted matte. A temperature of 370 C. to 380 C. was considered the optimum temperature of reduction to obtain this sulfur in its most active form, and if higher temperatures were used there was loss of activity.

ln the aforementioned conventional carbonyl process, it has been found that, unless the matte or other raw material is finely ground, the rate of reaction in the reduc- L tion operation is low. However, very line particles have a considerable tendency to stick together during the reduction and form a cake that cannot be shifted bythe rabbles. Moreover, the rabbles tend to swage the particles together, thus increasing the amount of cake. In this process, the matte is so finely crushed that between 40% and 50% will pass through a 350 mesh B. S. S. (British standard screen) sieve, and then a period of 8 hours is required to effect the reduction at temperatures between 370 C. and 390 C.

It also has been proposed in the treatment of roasted nickel matte or other nickel oxide-containing material,

e. g., a roasted sulfide ore or a finely divided fraction obtained from ore containing'nickel oxide, to carry out the reduction operation in a lluidized bed. However, surprisingly, it has been found that before the reduction is4 complete the fluid bed loses its vcharacteristic turbulence and iirst becomes viscous or sticky, finally be- Y coming lightly sintered together with all the reducing gases passing through a few holes. It appears that when the reduction has proceeded so far as to produce metallic surfaces on the particles, these particles tend to stick together. This causes loss of iluidity ot the bed; 'and (itl ice

thereupon the transfer of heat to the particles from the gas is poor, the temperature of the particles falls and reduction ceases. The degree of reduction obtainable before the iiuidty of the bed is lost depends on the par'- ticle size of the charge, beds of finer particles becoming viscous at an earlier stage in the reduction than beds of coarser particles.

As an illustration of the diiculties encountered, an ordinary roasted matte used in the carbonyl process for nickel extraction and consisting largely of nickel and copper oxides with traces of precious metals was charged into a fluidized bed reactor of standard pattern, and reducing gas was blown in through a diffuser plate at the bottom of the reactor. Hydrogen was used as the reducing gas and introduced at a pressure such as to liuidize the iinely-divided roasted matte. When the particle size of the roasted matte was such that it would pass through a mesh B. S. S. sieve but be retained by a 240 mesh B. S. S. sieve, the bed collapsed when only of the nickel was reduced. With a liner charge, such that all the particles would pass through a mesh sieve and many of the particles were very fine, the bed collapsed when only 30% of the nickel was reduced.

Although attempts were made to overcome the foregoing difficulties and other disadvantages, none, as far as we are aware, was entirely successful when carried into practice commercially on an industrial scale.

We have now discovered-a novel carbonyl process which provides an unexpectedly rapid and eiiicient reduction of roasted nickel matte and other nickel oxide-con taining materials, for example, ores containing nickel oxide and roasted sulfide ores, resulting in high nickel extractions.

It is an object of the present invention to provide an improved and practical process for the treatment of nickel oxide-containing materials that will avoid the aforementioned disadvantages.

Another object of the invention is to provide an improved process for the treatment of roasted nickel matte and other nickel oxide-containing materials, for example ores containing nickel oxide and roasted sulfide ores,

'which involves a more expeditious reduction of the nickel oxide to metallic nickel than heretofore practical. It is a further object of the invention to provide an improved process which is capable to treating practically any nickel oxide-containing material and which can be carried into industrial practice on a large scale.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing in which:

Figure l is a flow sheet of an embodiment of the novel combination of operations for continuous operation; and

Fig. 2 depicts a flow sheet of the novel process showing a plant for continuous operation in more detail than in Fig. l.

Generally speaking, the present invention contemplates reduction of particles of nickel oxide under fluidizing conditions with special reducing gas which is diluted with a gas that takes no part in the reaction and does not reactchemically with any of the reagents or products. The diluent gas is preferably nitrogen. The reducing gas preferably is hydrogen. Gases other than nitrogen which may be employed as the diluent gas are carbon ,dioxide, steam, methane and the rare gases. The reducing gas mixture used must be free from hydrogen sultide and carbon monoxide, as both of these gases promote sticking of the particles together. Accordingly, water gas, either as such or after use for some other purpose, cannot be used as the reducing gas because of the carbon monoxide and small amounts of hydrogen sulfide it commonly contains.

It is found that the use of a gas mixture including a diluent gas according to the invention enables the proportion of nickel reduced before the collapse of the fluid bed to be increased, and under appropriate conditions the reduction may be made complete.

The minimum proportion of the diluent gas varies with both the gas itself and the particle size of the charge. The finer the particle size of the charge, the greater is the proportion of diluent gas which must be used if the reduction is to be complete before the bed collapses. Thus, with a roasted matte of particle size of about -l20, +240 mesh, B. S. S. sieve, and a bed temperature of about 380 C., a gas mixture composed by volume of about 84% hydrogen and about 16% nitrogen will reduce the oxide in the matte substantially completely. However, if the charge is coarser, say about 60, +120 mesh, B. S. S. sieve, less nitrogen is required.

More carbon dioxide than nitrogen is needed as the diluent gas to produce the same effect. For instance, if

a roasted matte of particle size of about -l20, +240 mesh, B. S. S. sieve, is treated at about 380 C., the maximum hydrogen content of the reducing gas mixture is about 66%. 5% steam and about 95% hydrogen will effect a substantially complete reduction.

If carbon dioxide is used as the 'diluent gas, the bed temperature should not exceed about 400 C., as at higher temperatures carbon monoxide may be formed.

For any given starting material and diluent gas, the minimum proportion of diluent gas may readily be determined by a simple trial experiment. Generally speaking, however, the proportion of hydrogen will not exceed about 95%. As the proportion of hydrogen is reduced the rate of the reduction reaction decreases, and becomes impracticably slow for commercial operation with less than about 35% or even 40% hydrogen.

The particle size distribution of the charge is also of importance. It is found that with two batches of starting material of the same mean particle size, the ore with the higher proportion of very line particles has a greater tendency to stick during the reduction and thus requires a lower concentration of hydrogen in the reducing gas mixture for complete reduction to be achieved.

When the nickel oxide is very finely divided, e. g. a matte that has been flash roasted and of particle size such that at least 40% of'it will pas sthrough a 350 mesh B. S. S. sieve, it has been found that complete reduction ofthe nickel oxide material may be facilitated by mixing sand or other nely-divided inert particles with the particles of oxide to prevent the particles from sticking t together as they become reduced. Unless finely-divided inert material is added, complete reduction of very inelydivided nickel oxide material may be dillicult or even impossible to attain. if a large enough proportion of such particles is used, it becomes possible to use an undiluted reducing gas, provided that this gas is free from hydrogen sulfide and carbon monoxide. The invention therefore comprises the use of such inert particles as an alternative to the use of a diluent gas. However, when a diluent gas is not used, it is necessary to use a mixture of a large proportion of inert particles and a small proportion of oxide which is expensive to handle, so preferably a diluent gas is always used. By adding inert particles to the oxide, the amount of diluent gas may be reduced, and by increasing the amount of diluent gas,

' the amount of inert particles required may be reduced.

As an example, llash roasted particles, when mixed with an equal weight of sand of 60, +100, B. S. S. sieve size, can be completely reduced at 380 C. with a mixture of 60% hydrogen and 40% nitrogen. When the proportion of sand was reduced to 45% by weight, the bed stuck at only 71% reduction.

The sand or other inert particles may be recovered for re-use either before or after the carbonyl extraction of the reduced oxide. The recovery can conveniently be Under similar conditions a mixture of about f 4 effected by gas elutriation, the reduced particles or what remains of them after partial or complete extraction of the metal being carried away while leaving the sand or other inert particles behind.

As indicated in the foregoing remarks, one of the factors contributing to the sticking together of the particles is the presence of hydrogen sulfide. Instead, therefore, of introducing a sulfur-containing catalyst for the subsequent nickel carbonyl volatilization operation by adding elemental sulfur to the ground matte or other nickel oxide-containing material, sulfur may be added in any convenient form, for example, as hydrogen sulfide, at a low temperature after the reduction has been completed. Furthermore, the temperature of reduction can new be raised to 450 C. to 500 C. in the absence of the catalyst without subsequent loss of activity or in any way impairing the reaction of the reduced material with carbon monoxide to form carbonyl after the low temperature treatment with hydrogen sullide. This increase in reduction temperature results in a greatly increased rate of reduction. In general, the reduction may be carried out between about 350 C. and about 500 C.

The process of the invention may be carried on as batch operation, but continuous operations using multiple bed reducers, or a number of reducers in series, or a combination of the two, is desirable.

In the continuous operation of the present process as depicted in the ow sheet of Fig. 1, a mixture of very finely-divided roasted matte and finely-divided sand or other inert particles is fed into the lluid bed of reducer 10. In accordance with the foregoing description, a gas mixture of hydrogen and a diluent gas is introduced at the bottom of the reducer under sucient pressure to uidize the charge therein. The reduced material s removed from the top of the fluid bed reducer and after cooling is passed at a controlled temperature, usually between 15 C. and 100 C., through a conveyor or vessel where hydrogen sulfide is introduced so that the reducedmaterial is uniformly sulded to a sulfur content of about 1% of the metallic nickel present. The cold sulfided material is then introduced into the rst uid bed volatiliser where it is treated with carbon monoxide to volatize the nickel as nickel carbonyl. It has been found that the product of the fluid bed reduction of roasted matte mixed with sand is particularly suited for carrying out the volatilization of the nickel as nickel carbonyl also under uidized bed conditions. Accordingly, it is preferred to maintain conditions in the volatiliser 11 also in the form of a fluid bed. Part of the nickel, for example, about 30% is extracted as carbonyl in this volatilizer. The mixture of partially extracted solids and sand from volatilizer 11 is introduced into a separator 12. The separator 12 preferably is a gas elutriator in which there is a current of carbon monoxide flowing at a velocity such that it carries the partially extracted metal particles upwards but allows the heavier sand and vdiilicultly-extractable material to fall downwardly. The recovered sand, which may contain ditlicultly-extractable material, is then returned to the start of the operation and mixed with make-up sand for admixture with fresh roasted matte or other nickel oxide material for introduction into reducer 10. The partially extracted metal particles how from the separator 12 in the stream of carbon monoxide to at least one additional volatilizer 13 in which the extraction of nickel as carbonyl is completed. This extraction also preferably is carried on under fluidizing conditions but in the last volatilizer the gas velocity must be relatively low since at this stage the particles are much lighter. The solid residues from the last volatilizer 13 may then be subjected to any suitable process for extraction of the precious metal values contained therein. The carbon monoxide circulation is a completely closed system except for make-up gas. Carbon monoxide is separated from the volatilizer exit gases and returned to the volatilizers and after decomposition of the carbonyl the recovered which there is a series of reducing vessels, such as 28, 29

and 30. The rst reducing vessel 28 may be fed with a mixture of roa-sted matte and sand from a mixed feed hopper 26 through a suitable valve, e. g., a rotary valve 27. The three reducing vessels are so connected that the solid material from the top of the liuid bed in the iirst reducing vessel 28 overflows to the next reducing vessel 29 in the manner usual in fluid bed operations. The reduced material leaving the top of the bed in the last reducing vessel 30 may be a mixture of metal particles and sand. This mixture flows in a stream to a first volatilizer 32. Hydrogen sulfide is preferably introduced into this stream by passing the gas in counter-current yto the solid material as the stream ows through a mixing vessel 31. Part of the nickel is extracted as nickel carbonyl in this first volatilizer 32 in which the particles preferably are also maintained in the form of a fluid bed. Particles from the top of the bed in volatilizer 32 overflow to vessel 33 in which there is an upward current of carbon monoxide flowing at a velocity such that it carried the partially extracted metal particles upwards but allows the heavier sand to fall downwardly into a sand hopper 34 and then to"a conveyor 37, e. g., a screw conveyor or other conveying means by which this sand is returned to the original feed hopper for re-use. The partially extracted particles are carried by the carbon monoxide to a separator, such as a cyclone and bag filter, where the particles are separated from the gas, the particles iiowing from the cyclone to one or more further volatilizers in which the extraction of nickel as carbonyl is completed. The carbon monoxide circulation is a completely closed system except for make-up gas -similar to the arrangement in the flow sheet of Fig. l.

The use of a sand-reduced oxide mixture, separating the sand for recirculation after partial volatilization of the nickel as nickel carbonyl, and then completing the nickel extraction has two important advantages. First, the density of the metallic particles decreases as nickel is removed, making separation from the sand easier. Second, the roasted matte, and particularly the flash roasted suliide material, contains a proportion of particles which are very diflicult to reduce and extract. These have a relatively high density even after partial removal of nickel from the bulk of the reduced material, and are recirculated with the sand through the reduction and volatilization stages. The particles will continue to circulate With the sand until suiiicient nickel is extracted for their density to -fall to that of normal partially extracted material.

The diffusion of the gases into the fluid bed during ryeduction is of considerable importance. The gas must be uniformly distributed over the whole area of the'bed so that no stagnant patches can be formed. Unless the cornplete bed is kept in a state of agitation, sticking together of the particles will occur in such a stagnant area which` 4 Will grow until eventually the bed becomes static.

The materials of construction of the uid bed reducer are important. The original experimental work was carried out in a glass uidizer having a sintered glass diffuser at the base. A larger model constructed of mild steel With a bronze diifuser plate gave trouble since sticking of theY reduced oxide to these metals occurred. It was found that the walls must be made of some metal or alloy having an oxide iilm which cannot be reduced by hydrogen at the temperatures at which We are operating. Aluminum or appropriate nickel-chromium alloys such as those sold under the trademark Nimonic have proved satisfactory. While ceramics would be suitable for eur- 4ing the sticking, they would, howevenseriously affect the heat transfer which is one of the great advantages of the iluidizing process. The diffuser plate is preferably made from ceramics. p

The height of the uid bed does not appear to aiect the sticking propensities. Thus, with an unsuitable gas mixture, no alteration in the bed height will stop the sticking from occurring. v

Rates of reduction using 1,500 grams of 150, `+250 calcined sinter matte have been determined in a 3 inch diameter udizer. With a kow of 1,800 litres per hour of mixtures of hydrogen and nitrogen the following figures were obtained.

Percent Time for Temperature oi' Bed Hydrogen Complete in Iugoing Reduction, Gases hours These reduction times are about half those required for normal types of reducers.

Rates of volatilization have also been determined under uidizing conditions and it has been found that 95% of the nickel can be extracted in 18 hours. Normally, the extraction takes about 80 to 90 hours to obtain a similar recovery.

One advantage of separating the sand at a stage when the metal particles have been partially extracted is that there is then a greater difference in density between these particles and the sand than would be the case if the separation were effected before the mixture entered any volatilizer at all. On the other hand, if the separation were left to the last stage the gas Velocity there would have to be sohigh as to give rise to a considerable dust problem.

Another advantage of separating the sand at a stage when the metal particles have been partially extracted is that particles which are difficult to extract will then have a higher density than those which, being easier to extract, have been extracted to a greater extent and so will be removed with the sand and ultimately returned to the first reducer.

In comparison with the conventional process in which the matte is agitated by rotating rabbles, the reduction is efected more quickly with a more compact plant. The particle size of the matte can be greater in the new process, giving considerable savings in grinding cost. Progressive sintering of the charge occurs in the conventional apparatus, so that the reducers have to be taken out of service at frequent intervals to allow the sintered cake to be mechanically removed and reground; but there is not such sintering in the present invention. Finally the volatilizers used in the preferred plant of the new process are smaller than the standard volatilizers.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview nad scope of the invention and appended claims.

We claim:

l. The improved process for the extraction of nickel as nickel carbonyl from nickel oxide-containing materials comprising mixing finely-divided inert particles with linely-divided particles of nickel oxide-containing material., treating the resulting mixture in at least one fluid bed with a reducing gas at nickel oxide-reducing temperatures, subsequently partially volatilizing the nickel inthe reduced material as nickel carbonyl by treatment of the mixed particles with carbon monoxide, separating and recirculat- 7 ing thefinelyidivided inert particles and any non-extracted particles, and then completing the volatilization of the nickel as nickel carbonyl by treating the partially-extracted, Finely-divided solids with carbon monoxide.

2. The improved carbonyl process for treatment of inelyedivided', roasted, nickel matte comprising mixing finely-divided sand with nely-divided particles of the roastednickel matte, treating the resulting mixture in a uid bed at nickel oxide-reducing temperatureswith a reduciugv gas mixture composed of pure hydrogen and an inert gas which takes no part in the reaction and docs not react chemically with any of the reagents or products thereof, and which is substantially free from hydrogen sulde and carbon monoxide, proportioning the inert gas in the gas mixture so that the nickel is substantially completely reduced; subsequently partially volatilizing the nickel in the reduced material as nickel carbonyl by treatment of the reduced material with carbon monoxide, separating and recirculating the finely-divided sand and any non-extracted particles, and then completing the volatilization of the nickel as nickel carbonyl by treating the partially extracted reduced material with carbon monoxide.

3. A process for the extraction of nickel as nickel carbonyl from nickel oxide-containing materials comprising reducing particles of nickel oxide-containing material in admixture Withparticles incapable of reacting with or adhering-to Anickel Vor nickel oxide-containing particles in at least one uid bed with a reducing gas containing hydrogen and substantially free from hydrogen sulfide and carbon monoxide, subsequently volatilizing the nickel in the mixture of particles by treatment of the reduced material with carbon monoxide in a plurality of volatilizers, the reduced mixture of particles entering the first volatilizer and the particles incapable of reacting with or adhering to nickel or nickel oxide-containing particles being separated from the mixture of particles before the last volatilizer.

References Cited .in the file of this patent UNITED STATES PATENTS 1,909,762 Grieb May 16, 1933 2,478,912 Garbo Aug. 16, 1949 2,538,201 Kalbach et al Jan. 1'6, 1951 2,560,175 Kalbach July 10, 1951 2,699,387 Osborn Jan. 11, 1955 2,758,021 Drapeau Aug. 7, 1956

Claims (1)

1. THE IMPROVED PROCESS FOR THE EXTRACTION OF NICKEL AS NICKEL CARBONYL FROM NICKEL OXIDE-CONTAINING MATERIALS COMPRISING MIXING FINELY-DIVIDED INERT PARTICLES WITH FINELY-DIVIDED PARTICLES OF NICKEL OXIDE-CONTAINING MATERIAL, TREATING THE RESULTING MIXTURE IN AT LEAST ONE FLUID BED WITH A REDUCING GAS AT NICKEL OXIDE-REDUCING TEMPERATURES, SUBSEQUENTLY PARTIALLY VOLATILIZING THE NICKEL IN THE REDUCED MATERIAL AS NICKEL CARBONYL BY TREATMENT OF THE MIXED PARTICLES WITH CARBON MONOXIDE, SEPARATING AND RECIRCULATING THE FINELY-DIVIDED INERT PARTICLES AND ANY NON-EXTRACTED PARTICLES, AND THEN COMPLETING THE VOLATILIZATION OF THE NICKEL AS NICKEL CARBONYL BY TREATING THE PARTIALLY-EXTRACTED, FINELY-DIVIDED SOLIDS WITH CARBON MONOXIDE.

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