US2971836A

US2971836A - Separation of nickel and cobalt

Info

Publication number: US2971836A
Application number: US655479A
Authority: US
Inventors: James D Hall
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-04-29
Filing date: 1957-04-29
Publication date: 1961-02-14
Anticipated expiration: 1978-02-14

Description

United States Patent 2,971,836 SEPARATION OF NICKEL AND COBALT James D. Hall, 21811 Westehester Road, Shaker Heights, Ohio N Drawing. Filed Apr. 29, 1957, Ser. N 655,479 12 Claims. (Cl. 75-419) The present invention relates to the chemistry of cobalt and nickel and is more particularly concerned with a novel process of making from cobalt-nickel aqueous solutions cobalt compound precipitates containing over 99 percent of the cobalt contents of said solution and containing not in excess of 1.0 percent of nickel.

The separation of cobalt from nickel where these ele ments exist in solutions as mixed salts is a classical problem in inorganic chemistry. However, this problem, unlike some other famous ones, is of substantial commercial significance and in fact, its practical importance is increasing constantly. Accordingly, the literature contains a number of disclosures of possible solutions to this problem, but to the best of my knowledge, prior to the present invention, there has never been known or used a method whereby separation of these two closely related elements in aqueous salt solution could be accomplished satisfactorily in a commercial operation. Processes which would apparently or allegedly enable quantitative separation in laboratory scale equipment have never proven similarly efiective in commercial scale operations. On the other hand, processes involving prohibitively high costs have been made to work in large scale use in the sense that they yielded cobalt and nickel products of good quality with respect to contamination by nickel or cobalt.

The method of my'present invention, which as indicated above, is free from the shortcomings and derelictions of the prior art and is adaptable to use upon any scale with uniformly satisfactory results. Thus, the present method is easyand inexpensive to carry out, involving relatively few steps and no complicated operations requiring expensive equipment or high labor costs because of special controls or skills required. Furthermore, product purity of both cobalt and nickel in terms not only of contamination by the other element of this pair, but of contamination by other materials including reagents employed in the process, is uniformly high and depending upon the requirements of the manufacturer or user of these products, may be adjusted easily to meet shifting standards or requirements Without complicating the process or adding materially to its expense. Surprisingly, the separations of this invention can be carried out effectively without regard to relative amounts of cobalt and nickel in the original solution and without limitation as to solution concentration. Thus large quantities of cobalt can be removed from relatively small amounts of nickel in solution with the same uniformly high purity product resulting as where the original cobalt and nickel contents are approximately the same or where the nickel is present in far greater amount than the cobalt.

In addition to the foregoing advantages, the present method ofiers the operator the choice of all the various soluble salts of nickel and cobalt as raw materials for the production of premium grade nickel and cobalt products. Similarly, this invention gives the operator a wide choice of reagents, and a certain amount of latitude in the choice of products which he might obtain directly through the use of this method. The present method is also applicable advantageously to a broad range of concentrations of both cobalt and nickel. As a result, it is not necessary to establish within reasonable limits any particular balance between cobalt and nickel salts in terms of relative or total quantities in a solution preliminary to beginning the processing of the solution in accordance with this invention. These advantages sum up to an overall economic advantage of substantial importance be cause of the possibility of the method being shifted in respect to raw materials, reagents, and products with market fluctuations.

The method of my present invention is predicated primarily upon my surprising discovery of the critical effect which the pH of a nickel-cobalt salt solution has upon the sharpness of the separation of these two elements from each other. I have found, in fact, that the optimum pH condition for separating and removing cobalt from a cobalt-nickel solution is about 2.4. In even large scale commercial operations, practically quantitative removal of cobalt from such a solution can be expected where the pH is closely maintained throughout at about 2.4. However, for most commercial purposes, a cobalt product of acceptable grade for most purposes will be obtained where the pH of the solution stands between about 1.8 and about 3.0 during the period of precipitation, separation and removal of the cobalt from the solution. In accordance with my present invention, as discussed more fully below, in my present regular commercial operations, solution pH is held within the range of about 2.0 to about 2.8 throughout the period of operation of this process.

Furthermore, I have-found that alkali hypochlorites, the heretofore conventional reagents for this general purpose, cannot be used to secure the new results and ad vantages of this invention. In other words, it is essential to add chlorine and alkali independently and separately and to maintain pH control as stated above throughout the period of the process that cobalt is being precipitated.

I have also found that if the temperature of the solution at the time that the cobalt product is precipitated and from that time on until after separation of the solid and liquid phases has been eflfected is between about 60 C. and 70 C., the removal of the cobalt product from the solution will be relatively quickly and easily accomplished. Best results in terms of ease and rapidity of separation of the two phases are obtained toward the upper end of this range and accordingly, I prefer to control the temperature during the operating period at about 70 C.

In general, the method of this invention has as its basic object the making of cobalt compounds of high purity, particularly with regard to nickel contamination, from solutions containing both cobalt and nickel in material amounts The making or preparing of these cobalt compounds in accordance with this method is carried out in What amounts to a unit process, only a single reaction vessel and only a single reaction medium being required for consistently satisfactory results. Thus this method comprises in its broadest aspects the steps of bringing chlorine into a solution containing cobalt and nickel so as to saturate the solution with chlorine and thereby reduce its pH from not more than about 3.0 to less than about 2.0 while the solution temperature is maintained between about 30 C. and about C., introducing an alkali into the solution, discontinuing the introduction of chlorine and alkali into the solution when the cobalt content of the solution has been substantially exhausted, and then separating and removing from the resulting liquid phase the solid phase containing cobalt compounds substantially free from nickel contamination.

Aqueous cobalt-nickel solutions suitable for use in the method of this invention are those containing more than about 1.0 percent of cobalt in which the cobalt and nickel are in the ratio of from one part of cobalt per ten parts of nickel to ten parts of cobalt per one part of nickel. Maximum cobalt and nickel concentrations of these solutions may at least in theory be the upper limits of solubility of the particular cobalt and nickel compounds contained in the solutions. In other words, the results of this invention can be secured over essentially the full range of solution concentration of cobalt and nickel compounds although, as those skilled in the art will recognize, for practical and commercial operations the cobalt compound concentration in the solutions should lie intermedlately in this theoretical range and I prefer that the cobalt concentration be relatively high for maximum yields of high-purity cobalt products. If a high-purity nickel product is an object, I prefer that the solution initially contain relatively large quantities of nickel compounds for the same reason] However, an important advantage of this invention is that whether it is premium cobalt or nickel products that are desired, the method can be appliedto virtually any aqueous cohalt-nickel solution simply by following the same basic procedure as is used in treating ideal or specially preferred types of solutions.

The step of bringing elemental chlorine into the solution is carried out preferably by bubbling chlorine ga into the solution in a suitable reaction vessel and this is done after the pH of the solution has been checked and adjusted if necessary to bring it down to not more than about 3.0. In theory, chlorine might be used to make this initial pH adjustment where the solution is more alkaline than pH 3.0, but this would be an expensive way to operate when sulphuric acid, for example, is available for the purpose at costs far below the least expensive form of chlorine. Furthermore, the purpose of adding chlorine in accordance with this invention is to saturate the solution with chlorine and this is accomplished by dropping the pH solution from not more than about 3.0 to less than about 2.0, suitably 1.5 to 1.8. .The solubility of chlorine in the solution will depend to a large extent upon the temperature of the solution.

In theory again, the solution temperature may range between 30 C. and 95 C., but I prefer that it lie between 60 C. and 70 C. The disadvantage of temperatures approaching the boiling point temperature of the solution is that chlorine solubility is very limited and chlorine losses may thereforebe excessive without any offsetting advantage such as substantial increase in reaction rate or the production of a more easily filtered cobalt product precipitate. The temperatures in the lower portion of this range on the other hand lead to the production of cobalt precipitates which are gelatinous or slimy and difiicult to separate and wash free from the reaction liquor and again there is no offsetting advantage such as an increased reaction rate or reduced chemical costs.

There is a certain flexibility in respect to the sequence of the preliminary steps of pH adjustment prior to chlorine saturation of the solution and adjustment of the solution temperature by either a heating or a cooling operation. Either or both of these adjustments may be made, in other words, at the same time or in sequence in accordance with the operators preference. Furthermore, as suggested above these adjustments may both or either be made after the chlorine is first contacted with the solution. The important consideration in this respect is the maintenance of the critical pH in the re action mixture over as much of the cobalt precipitation separation and removal periods as possible. This im plies the establishment of the critical initial pH as the first step or at least as an early step in the present 4 method and before chlorination has been'carried very far.

The temperature factor, while not nearly so critical as pH from the standpoint of product purity, is important commercially because its proper in accordance with this invention assures the production of a precipitate which lends itself to rapid and clean, separation from the liquid phase. For best results, the adjudstment of reaction solution temperature should be made at the outset and before chlorination has pro grossed to the point that substantial amounts of cobaltic hydroxide are being formed and precipitated,

Also, in accordance with my preference, the introduction of the chlorine is accomplished by bubbling chlorine gas into the solution at a plurality of locations in the vessel containing this solution in order to assure relatively uniform distributcn of chlorine and its oxidizing effects. Likewise, the alkali is continuously introduced into the solution at a plurality of locations and to aid in keeping the solution pH uniform throughout the base is used in the form of a relatively dilute aqueous solution. The chlorine and alkali solution are normally added to the cobalt and nickel salt solution simultaneously and at predetermined related rates to assure maintenance of the solution pH within the aforesaid range, but additions of one or the other may be temporarily increased or decreased in rate or discontinued in order to adjust the pH as necessary in accordance with my discovery set forth above.

While in general, any alkali may theoretically be employed to establish and maintain the critical pH range in the solution of mixed salts while the process of this invention is carried out, I prefer to use an aqueous solution of an alkali metal hydroxide and because of economic reasons, I now employ, in commercial operations, either an aqueou 50 percent solution of caustic soda or an aqueous 20 percent solution of soda ash. Any hydroxide or carbonate (including bicarbonates) of an alkali metal or an alkaline earth metal may be used for this purpose. However, calcium hydroxide and calcium carbonate and the corresponding compounds of barium, magnesium, and strontium and related compounds of alkaline character are generally of relatively little pratical interest in this invention process. Thus, where the salt solution is composed of sulfates, I do not use a calcium compound for pH adjustment or control because of the difliculty of preventing calcium sulfate contaminatlon of the final desired product. The problems which magnesium compounds present in terms of both cobalt product and nickel product purity are so substantial as to preclude the possibility of their use in most commercial operations at the present time. Compounds of lithium, barium, and strontium of this class, in addition to presenting problems in common with calcium or magnesium compounds, are normally too expensive to be employed in commercial operations of this type.

Potassium hydroxide and potassium carbonate, aside from the presently unfavorable economic picture, are quite satisfactory for use in accordance with this invention, particularly where the cobalt and nickel salts are sulfates.

Sodium and potassium silicates qualify in theory as alkalis for the present purpose but are not desirable here because of their cost and the fact that they could lead to contamination of the cobalt and/ or nickel products. The same may also be true of other salts of strong bases and weak acids. In any event, these alkaline substances do not represent either my preferred practice or a presently commercially feasible alternative to that practice.

Normally, the precipitation of cobalt in a plant operation will be complete within about 1% to 3 hours. I have found, in fact, in my ordinary commercial production, that for all practical purposes, it is not necessary to chlorinate the solution more than 2 /2 hours. However, those skilled in' the art will understand that this use and control p period will vary depending upon the efficiency with which the chlorine is used and distributed through the reaction mixture. They will also understand that it is possible quickly to determine the condition of the solution with respect to cobalt content at any time so that the chlorinaion step may be discontinued just as soon as cobalt oxidation is complete. It may be found desirable in the larger installations to follow closely the course of the cobalt oxidation reaction and precipitation in order to conserve time and reagents.

Since as stated previously and emphasized in the appended claims, it is important in accordance with this invention to selectively precipitate cobalt compounds from nickel-cobalt solutions and to do this progressively, it is essential to regulate the rates of addition of chlorine and alkali to the reaction solution throughout the cobalt precipitation period. It is also important to regulate the proportion of chlorine to alkali during the various stages of the cobalt precipitation period. When there is a substantial quantity of cobalt in solution, as at the outset of the chlorination of a relatively strong cobalt solution, the alkali-chlorine ratio may be relatively high. As the amount of cobalt in solution is diminished and the solution pH accordingly begins to climb toward 3.0, the alkali-chlorine ratio is substantially reduced, typically to about half the initial alkali-chlorine ratio. Then later, as the end-point of cobalt precipitation is closely approached, the proportion of alkali to chlorine will again be diminished finally to the point where no alkali or virtually no alkali is being introduced into the reaction mixture as chlorination continues. This, however, does not mean or imply that the alkali and the chlorine must be added simultaneously throughout the cobalt precipitation period, or that they must be added at adjacent points in the solution, or that they might in any way be premixed and added together to the solution. 0n the contrary, the alkali and chlorine may be added intermittently or alternately throughout the cobalt precipitation period or during any part thereof, and they may be introduced into the reaction vessel at widely spaced points. In no case, however, should they be premixed with each other for addition together or as alkali hypochlorite or other reaction product.

The course of the cobalt precipitation operation and reactions involved therein can be followed closely by means of a standard pH machine which electrically and practically instantaneously determines the pH of the solution, as those skilled in the art know and understand. Through the use of this machine or meter, the operator can adjust the rates of alkali and chlorine additions and can establish the required alkali-chlorine ratios and adjust these ratios or proportions from time to time in order to maintain close control over the cobalt precipitation and thereby progressively and selectively precipitate greater than 99 percent of the original cobalt content of the starting cobalt-nickel solution. Those slc'lled in the artwill further understand that because of the flexibility of this process and the opportunity for choice of the operator as to not only the rate of the cobalt precipitation operation but also the timing of the alkali and chlorine additions and the particular pH control points along the course of the cobalt precipitation period, it is not necessary or possible in fact to establish a particular inflexible set of conditions for the entire operation or for any given increment of the whole period within the general ranges, ratios, and rates set out above. Thus, for example, in a sequential or alternate alkali-chlorine addition operation in accordance with this invention process, one operator may add only alkali and another may add only chlorine, and still another may add chlorine and alkali in rigidly controlled ratio over one relatively long portion of the cobalt precipitation period.

When the predetermined end point of cobalt concentration in the salt solution has been reached, chlorination is discontinued, the supply of base is cut oil, and the re suiting solid and liquid mixture is then stirred for a period of from 5 minutes to 1 hour, according to the'degree of control exercised over solution pH during chlorina tion and the quality of the products required. This agitation of the mixture has the efliect of increasing the purity of the products by the physical means of bringing about better contact between the precipitate and the mother liquor and assuring uniformity of pH and other conditions throughout the mixture. A certain small amount of nickel hydroxide which may have been precipitated with the cobalt because of a local variation in pH outside the permissible range will thus be redissolved, and similarly any unprecipitated cobalt will be oxidized and dropped from the solution where previously a local condition permitted it to remain in soluble form.

If desired, the mixture may be blown with air to exhaust substantially all residual dissolved chlorine.

The final step of separating the precipitated cobaltic hydroxide from the resulting solution rich in high-grade nickel salt may be carried out in any suitable manner, depending upon the operators desires and the equipment available. Providing the precipitate is of loose, granular character, filtration will usually be preferred in effecting this separation. Where the temperature control has not been such during the precipitation period that the cobalt product may be easily filtered, a continuous centrifuge operation may be carried out. Alternatively, the cobalt product may be separated by decantation with the usual sequence of rinsing steps to assure clean separation. However, in any event, it is important that the pH of the mother liquor as well as the pH of all rinsing or washing solutions be within the range specified above and preferably near 2.4.

Cobalt-nickel solutions useful in the process of this invention are, generally speaking, those which contain primarily only cobalt and nickel compounds or salts in substantial quantities, i.e. in excess of about 1.0 percent of each said metal. Solutions that have proven particularly well suited for treatment by this process were those obtained through the digestion of high-temperature cobalt alloys by the methods disclosed and claimed in my United States Patent No. 2,716,588, granted August In typical commercial operations under that patent, the ultimate cobalt-nickel solution after removal of iron, chromium and manganese is a cobalt sulfatenicke-l sulfate solution of pH normally somewhat above 3.0, as between 4.0 and 5.0. However, this solution may suitably consist of the acetates, formates, fluorides, chlorides, phosphates, or nitrates of cobalt and nickel. There is no variation required in the method of this invention to accommodate any of these various composition possibilities of the initial cobalt solution and this is a further substantial advantage of this invention.

Those skilled in the art will gain further and better understanding of this invention on consideration of the following illustrative, but not limiting, examples of the present method:

Example I Two thousand gallons of a solution obtained through the practice of my inventions disclosed and claimed in my said United States patent were filtered in standard filter press, separating compounds of iron, chromium, and related elements in solid phase from dissolved cobalt and nickel values. The pH of this solution being relatively high, sulfuric acid was added in sufficient amount to bring the pH to about 2.4. This solution was then heated to bring its temperature to 70 C. and the introduction of chlorine in the form of bubbles of gas was begun. Substantially simultaneously aqueous caustic soda of 50 percent strength was dribbled into the solution at a predetermined rate necessary to maintain the pH within the standard separating range of 2.0 to 2.9. After 2 hours of'continuous chlorination under these conditions, with continuous agitation for better mixing, substantially all the cobalt had been precipitated in the form of cobaltic hydroxide. Chlorination was then stopped, as also was the introduction ofcaustic soda, and the mixture was agitated for a period of ten minutes and at the same time blown. with air to eliminate residual dissolved chlorine to a large degree. Separation of the solid phase from the liquid was accomplished by conventional filter press means with the result that the filtrate analyzed 0.75 percent cobalt (expressed as metal) and the cobalt product contained 0.75 percent nickel (also expressed as metal).

Example 11 Another solution obtained through the practice of my inventions disclosed and claimed in my aforesaid patent was treated in a total volume of 2000 gallons containing 280 pounds of cobalt (calculated as metal) and 140 pounds of nickel (also calculated as metal). After removal of compounds of chromium, iron and manganese, sulphuric acid was added to bring the solution pH to 3.0. The solution temperature was adjusted to 60 C. and chlorine was then bubbled into the solution contained in a corrosion resistant reactor vessel. An aqueous 20 percent solution of soda ash was dribbled into the vessel after the chlorine gas had been turned on and adjusted and for a period of several minutes a strong odor of chlorine is noted over the reaction mixture. The chlorine odor then faded and the pH ultimately dropped to 1.5, and

.then while the ratio of chlorine and soda ash was maintained constant the pH began to climb slowly. The solution at the minimum pH reading was saturated with chlorine. The course of the reactions involved in this process was followed by means of a pH machine and the ratio of chlorine and soda ash solution and the rates of introduction of chlorine and soda ash were adjusted to maintain the pH between about 2.0 and about 2.4. After about one hour during which the ratios of chlorine and soda ash and the rates of addition of these materials to the solution were maintained constant, the pH started upward abruptly and at the same time lightening of the color of the solution from black to dark brownish was noted. The addition of soda ash solution was then cut back gradually and the original black color returned as the pH fell back and steadied at between 2.2 and 2.4. A new reduced ratio of soda ash to chlorine was thus established to maintain this pH condition and in a short time the color of the solution began to change through reddish brown to red and then to a lighter and clearer appearance. The pH meanwhile remaining between 2.2 and 2.4. Containing the additions of soda ash and chlorine in the immediately previously established ratio, the pH of the solution gradually rose to 2.6 to 2.8 as the solution turned greenish in color, whereupon the rate of alkali addition was again cut back substantially while the rate of chlorine addition was maintained at the original level. The purpose of this alteration in the alkali-chlorine ratio was to maintain the solution pH below about 3.0 and thereby prevent precipitation of nickel compounds. The last traces of cobalt were extracted from the solution at this stage and again a strong odor of chlorine was noted. The pH of the solution thus shows a tendency to climb as the cobalt is precipitated from the solution and this tendency becomes more noticeable as the amount of cobalt content of the solution approaches exhaustion. Accordingly, during the final cobalt precipitation stage the soda ash was added only very sparingly and slowly to the solution and when the pH of the solution exceeded 3.0 the alkali addition was stopped entirely. At this point with chlorine still bubbling into the solution a marked frothing effect was observed on the surface of the reaction mixture. The chlorine was then shut off and the mixture filtered to separate the precipitated cobaltic hydroxide from the nickel solution which was thereafter treated for the precipitation and recovery of nickel. The

procedure used in precipitating nickel from the solution. comprised adding'more soda ash solution to bring the pH' to 7.8 to 8.0 while the solution temperature is maintained at between 60 C. and 70 C. I e

The cobaltic hydroxide upon analysis contained 0.9 percent nickel (calculated on the metal basis) and the nickel product contained 0.9 percent cobalt (also on the metal basis). This was well within the specifications for both these materials and represented a premium cobalt and nickel and a highly satisfactory commercial operation in terms of yields as well as purity.

Example III In still another operation involving the use of solutions obtained through the practice of my aforesaid patent processes, the initial solution of 2000 gallons of liquor containing 375 pounds of nickel to 42 pounds of cobalt as the sulphates was treated in accordance with the present method with recovery of high purity products of cobalt and nickel. In this case the solution temperature approximated 50 C. throughout the reaction period and the alkali employed was sodium carbonate which was added as a 20 percent aqueous solution beginning after the solution was saturated with chlorine, which was bubbled in the reaction vessel containing the solution through a manifold having a number of separate spaced openings. The chlorine and alkali were added at sep' arate ends of the reaction vessel but, as in Examples 1 and II, the reactions mixture was constantly agitated throughout the reaction period to assure uniform conditions and results. Also as in the foregoing operations, the ratio of alkali and chlorine was established at the outset by using the solution pH as a guide and following changes in the solution acidity as the reactions continued. The changes in the ratio of alkali to chlorine were made as before as the end point of cobalt removal was approached in stages. Following the removal of the cobalt from the solution, a phase separation was carried out to remove the cobaltic hydroxide from the reaction liquor which in turn was subsequently treated for the removal of nickel. Again, the yields ofcobalt and nickel were excellent as was the purity of each product in terms of the other. Cobalt recovery was over 99 percent of theoretical and the cobalt product contained 0.9 percent nickel (calculated as metal) and the nickel product contained 0.9 percent cobalt (on the same basis).

Example IV In another operation in accordance with this invention using a cobalt-nickel solution of the composition of the solution of Example 111 and generally the same procedure, the additions of chlorine and alkali may be made intermittently throughout the cobalt precipitation period. In this case the solution is saturated with chlorine and the chlorine-alkali ratio is established by following the course of the cobalt precipitation reactions with a pH machine and additions of chlorine and alkali are discontinued at intervals. Adjustments in the rates of the chlorine and alkali additions and the proportions of alkali and chlorine added are made as the cobalt precipitation proceeds as required at check points along the course of the cobalt precipitation period. Thus as in the case of the continuous addition of chlorine and alkali as set out in Examples 11 and Ill above, for instance, an initial ratio of chlorine and alkali is established and this is altered when the pH reaches 2.0 to 2.4 and the amount of cobalt remaining in solution is diminished to the point that the solution color and clarity is noticeably changed. Again, the chlorine-alkali ratio is altered just before the last of the cobalt is precipitated from the solution in order to prevent the pH of the solution from rising above about 3.0 and to prevent precipitation of nickel to contaminate the cobalt precipitate.

Example V Following the procedure of Example IV and using the same initial solution, the temperature of the solution may be ad usted to about 35 C. before chlorine is introduced therein. This temperature then may be maintained throughout the cobalt precipitation period. In this operation an aqueous 7 percent solution of sodium bicarbonate is the alkali and chlorine is again introduced as a gas into the solution by means of a manifold having a number of outlets in the reaction vessel below the solution surface. The cobalt precipitate in this case is gelatinous, slimy, and difiicult to separate from the solution and diflicult to wash free from all traces of nickel. Decantation may be employed as the first step and the precipitate may be washed by decantation technique and then finally filtered and washed again.

Example VI In another opera ion quite like that of Example III, a solution temperature may be initially adjusted to about 95 C. and maintained at substantially that level through out the cobalt precipitation period. Chlorine gas will again be introduced through a manifold into the solution and a 50 percent aqueous solution of potassium hydroxide will be employed as the alkali. The cobalt precipitation product will be separated suitably for filtration from the reaction liquor and washed and a high yield of premium grade cobalt hydroxide obtained.

I do not prefer to employ superatmospheric pressures or to apply vacuums to the reaction vessels during the cobalt precipitation period of the present process. Those skilled in the art will understand, however, that where the operator desires he may apply pressure or vacuum in carrying out this invention and thereby alter the outer limits of temperature set forth above. Such variations of thepresent process are contemplated by the ap ended claims although, as stated above, the optimum condition for operation of this process so far as temperature is concerned is in the range of 60 C. to 70 C., this being the temperature interval in which best results are obtained in terms of a granular, easily-filterable cobalt precipitate.

This application is a continuation-in-part of my prior application, Serial No. 441,669, filed July 6, 1954, now abandoned.

Having thus described this invention in such full, clear,

concise and exact terms as to enable any person skilled in the art to which it pertains to make and use the same, and having set forth the best mode contemplated of carrying out this invention, I state that the subject matter which I regard as being my invention is particularly pointed out and distinctly claimed in what is claimed, it being understood that equivalents or modifications of, or substitutions for, parts of the above specifically described embodiments of the invention may be made without departing from the scope of the invention as set forth in what is claimed.

What is claimed is:

l. The method of making from an aqueous cobalt-nickel solution containing more than about 1.0 percent of cobalt in which the cobalt and nickel are in the ratios of from one part of cobalt per ten parts of nickel to ten parts of cobalt per one part of nickel, a cobalt compound precipitate representing over 99 percent of the initial cobalt content of the solution and containing not in excess of 1.0 percent of nickel, which comprises the steps of bringing chlorine gas into the solution and saturating said solution with chlorine and thereby reducing its pH from not more than about 3.0 to less than about 2.0 while the temperature of the solution is maintained between about 30 C. and about 95 C.,introducing into the solution an alkali, finally discontinuing the introduction of chlorine and said alkali when the cobalt content of the solution has been substantially exhausted and separating and removing from the resulting liquid phase the solid phase containing cobalt compounds free from nickel contamination in excess of 1.0 percent.

2. The method of making from an aqueous cobalt-nickel solution containing more than about 1.0 percent of cobalt in which the cobalt and nickel are in the ratios of from one part of cobalt per ten parts of nickel to ten parts of cobalt per one part of nickel, a cobalt compound precipitate, representing over 99 percent of they initial cobalt content of the solution and containing not in excess of 1.0 percent of nickel, which comprises the steps of bringing chlorine gas into the solution and saturating said solution with chlorine and thereby reducing its pH from not more than about 3.0 to less than about 2.0 while the temperature of the solution is maintained between about 60 C. and about C., introducing an alkali into the solution as soon as the solution has been saturated with chlorine, simultaneously adding chlorine and said alkali to the solution, finally discontinuing the introduction of chlorine and said alkali when the cobalt content of the solution has been substantially exhausted and before substantially any nickel has been precipitated, and separating and removing from the resulting liquid phase the solid phase containing cobalt compounds free from nickel contamination in excess of 1.0 percent.

- 3. The method of making from an aqueous cobalt-nickel solution containing more than about 1.0 percent of cobalt in which the cobalt and nickel are in the ratios of from one part of cobalt per ten parts of nickel to ten parts of cobalt per one part of nickel, a cobalt compound precipitate representing over 99 percent of the initial cobalt content of the solution and containing not in excess of 1.0 percent of nickel, which comprises the steps of bringing chlorine gas into the solution and saturating said solution with chlorine and thereby reducing its pH from not more than about 3.0 to less than about 2.0 while the temperature of the solution is maintained between about 60 C. and about 70 C., introducing an alkali into the solution after the solution has been saturated with chlorine, intermittently adding chlorine and said alkali to the solution, finally discontinuing the introduction of chlorine and said alkali when the cobalt content of the solution has been substantially exhausted and before substantially any nickel has been precipitated, and separating and removing from the resulting liquid phase the solid phase containing cobalt compounds free from nickel contamination in excess of 1.0 percent.

4. The method of making from an aqueous cobaltnickel solution containing more than about 1.0 percent of cobalt in which the cobalt and nickel are in the ratios of from one part of cobalt per ten parts of nickel to ten parts of cobalt per one part of nickel, a cobalt compound precipitate representing over 99 percent of the initial cobalt content of the solution and containing not in excess of 1.0 percent of nickel, which comprises the steps of bringing chlorine gas into the solution and saturating said solution with chlorine and thereby reducing its pH from not more than about 3.0 to less than about 2.0 while the temperature of the solution is maintained between about 60 C. and about 70 C., starting introduction of soda ash into the solution while the solution is saturated with chlorine, finally discontinuing additions of chlorine and soda ash to the solution when the cobalt content of said solution has been substantially exhausted and before substantially any nickel has been precipitated, and separating and removing from the resulting solution the solid phase containing cobalt compounds free from nickel contamination in excess of 1.0 percent.

5. The method of making from an aqueous cobaltnickel solution containing more than about 1.0 percent of cobalt in which the cobalt and nickel are in the ratios of from one part of cobalt per ten parts of nickel to ten parts of cobalt per one part of nickel, a cobalt compound precipitate representing over 99 percent of the initial cobalt content of the solution and containing not in excess of 1.0 percent of nickel, which comprises the steps of bringing chlorine gas into the solutionand saturating said solution with chlorine and reducing its pH from not more than about 3.0 to less than about 2.0 while the temperature of the solution is maintained at about 63 C., bringing caustic soda into the resulting chlorine-saturated solution, adding chlorine and caustic soda separately to the said solution at rates and in proportions to each other such that cobalt is substantially continuously precipitated from the solution while nickel is retained in solution, finally discontinuing additions of chlorine and caustic soda when the cobalt content of the solution has been substantially exhausted and before substantially any nickel has been precipitated, and separating and removing from the resulting solution the solid phase containing cobalt compounds free from nickel contamination in excess of 1.0 percent.

6. The method of making from an aqueous cobaltnickel solution containing more than about 1.0 percent of cobalt in which the cobalt and nickel are in the ratios of from one part of cobalt per ten parts of nickel to ten parts of cobalt per one part cf nickel, a cobalt compound precipitate representing over 99 percent of the initial cobalt content of the solution and containing not in excess of 1.0 percent of nickel, which comprises the steps of bringing chlorine gas into the solution and saturating said solution with chlorine and reducing its pH from not more than about 3.0 to less than about 2.0 while the temperature of the solution is maintained between about 30 C. and about 95 selected from the group consisting of hydroxides and carbonates of alkali metals and alkaline earth metals into the resulting chlorine-saturated solution, separately adding chlorine and said alkali to said solution at rates and proportions to each other etfective to progressively and selectively precipitate cobalt from the solution while the nickel is retained in solution, finally discontinuing additions of chlorine and said alkali when the cobalt content of the solution has been substantially exhausted, and separating and removing from the resulting solution cobalt compound precipitate free from nickel contamina tion in excess of 1.0 percent.

7. The method of making from an aqueous cobaltnickel solution containing more than about 1.0 percent of cobalt in which the cobalt and nickel are in the'ratios of from one part of cobalt per ten parts of nickel to ten parts of cobalt per one part of nickel, a cobalt compound precipitate representing over 99 percent of the initial cobalt content of the solution and containing riot in excess of 1.0 percent of nickel, which comprises the steps of bringing chlorine gas into the solution and saturating said solution with chlorine and thereby reducing its pH from not more than about 3.0 to less than about 2.0 while the temperature of the solution is maintained between about 30 C. and about 95 C., introducing soda ash into the solution, bringing additional amounts of chlorine and soda ash into said solution and thereby progressively selectively precipitating cobalt from the solution while the nickel is retained in solution, finally discontinuing the introduction of chlorine and said alkali when the cobalt content of the solution has been substantially exhausted, blowing air into the solution until substantially all the chlorine thereby releasable from the solution has been eliminated from said solution, and separating and removing from the resulting liquid phase the solid phase containing cobalt compounds free from nickel contamination in excess of 1.0 percent.

8. The method of separating cobalt from an aqueous solution containing nickel and cobalt salts which comprises the steps of introducing chlorine into the solution, adding an alkali metal hydroxide to the solution to maintain the pH between about 1.8 and about 3.0, discontinuing the addition of chlorine and said hydroxide to the solution when precipitation of cobaltic hydroxide has substantially ceased, and separating and removing the resulting solid phase containing cobaltic hydroxide from C., bringing an alkali 12 the liquid phase containing nickel substantially free from cobalt contamination.

9. The method of separating cobalt from an'aqueous sulfuric acid solutioncontaining nickel and cobalt salts which comprises the steps of adding an alkali metal hydroxide to the solution pH to a value of about 2.4, heating the solution and bringing its temperature to about C., then continuously bubbling chlorine into said solution, continuously running aqueous caustic soda into the solution to maintain the pH between about 2.0 and about 2.8, discontinuing the additions of chlorine and caustic soda to the solution when precipitation of cobaltic hydroxide has substantially ceased, stirring the resulting solid and liquid mixture, and separating and removing the solid phase containing cobaltic hydroxide from the liquid phase containing nickel substantially free from cobalt contamination.

10. A one-stage process of separating cobalt and nickel values from a solution of their salts, which consists substantially of simultaneously adding chlorine and a material from a group consisting of alkali metal and alkalineearth metal carbonates to the solution in a ratio suflicient to maintain the pH initially between about 2 and 3 thereby precipitating more than 98% of the cobalt contained in the solution as a hydroxide while the nickel remains in solution, and rapidly separating the substantially pure precipitated cobalt hydroxide from the solution to prevent absorption of nickel.

11. The method of separating cobalt from an aqueous solution containing nickel and cobalt salts which comprises the steps of heating the solution to a temperature of between about 60 C. and about 70 C., introducing chlorine into the thus heated solution, adding to the solution a material selected from the group consisting of alkali-metal and alkaline-earth metal carbonates to the solution in a ratio sufficient to maintain the pH be tween about 1.8 and about 3.0, discontinuing the addition of chlorine and said material when precipitation of cobaltic hydroxide has ceased and separating and removing the resulting solid phase containing cobaltic hydroxide from the liquid phase containing nickel substantially free from cobalt contamination.

12. The method of separating cobalt from an aqueous solution containing nickel and cobalt salts which comprises the steps of heating the solution to a temperature between about 60 C. and about 70 C., continuously bubbling chlorine into the solution, continuously running into the solution a material selected from the group consisting of alkali metal and alkaline-earth metal carbonates in a ratio sufiicient to maintain the pH between about 1.8 and about 3.0, discontinuing the addition of chlorine and said material when precipitation of cobaltic hydroxide has substantially ceased and separating and removing the resulting solids phase containing cobaltic hydroxide from the liquid phasecontaining nickel substantially free from cobalt contamination.

References Cited in the file ofthis patent UNITED STATES PATENTS 2,367,239 Renzoni Jan. 16, 1945 2,377,832 Wallis et al. June 5, 1945 2,694,005 Schaufelberger Nov. 9, 1954 2,728,636 Van Hare et al. Dec. 27, 1955 2,778,728 Roy et a1 Jan. 22, 1957 FOREIGN PATENTS 755,044 Great Britain Aug. 15, 1956 775,788 Great Britain May 29, 1957

Claims

8. THE METHOD OF SEPARATING COBALT FROM AN AQUEOUS SOLUTION CONTAINING NICKEL AND COBALT SALTS WHICH COMPRISES THE STEPS OF INTRODUCING CHLORINE INTO THE SOLUTION, ADDING AN ALKALI METAL HYDROXIDE TO THE SOLUTION TO MAINTAIN THE PH BETWEEN ABOUT 1.8 AND ABOUT 3.0, DISCONTINUING THE ADDITION OF CHLORINE AND SAID HYDROXIDE TO THE SOLUTION WHEN PRECIPITATION OF COBALTIC HYDROXIDE HAS SUBSTANTIALLY CEASED, AND SEPARATING AND REMOVING THE RESULTING SOLID PHASE CONTAINING COBALTIC HYDROXIDE FROM THE LIQUID PHASE CONTAINING NICKEL SUBSTANTIALLY FREE FROM COBALT CONTAMINATION.