REFINING OF CHLORIDE SALTS

PC-I125 l0 The present invention relates to processes for purifying chlorides of alkali or alkaline earth metals, and is particularly applicable to the cleaning of chloride salts used in processes for purifying nickel mattes by ch!orination. The selective chlorination of impurities present in a nickel matte has been the subject of much recent study. In Canadian Patent No. 955,756, assigned in common with the present invention, there is described the process wherein nickel chloride dissolved in a fused chloride solvent is used to chlorinate impurities such as iron, copper and cobalt for removal thereof from a nickel matte. In this process the molten matte to be chlorinated is contacted with a molten salt mixture consisting of a solvent salt, such as common salt or a mixture of sodium and potassium chlorides, and nickel chloride. Thus at the end of the purification process, the supernatant salt mixture consists of the solvent salt loaded with the chlorides of the impurities removed from the nickel matte as well as unreacted nickel chloride. This loaded salt must be treated to remove, and if desired recover, the impurity chlorides so that the salt can be recycled. In such a salt-cleaning treatment it is highly desirable not to remove any nickel chloride present in the loaded salt since this is required upon subsequent recycling of the salt. In the process described in the aforementioned Canadian Patent, the salt is cleaned by electrolyzing it in the molten state. Fused salt electrolysis is, of course, a complex technology and is predicated on the local availability of electrical power. Moreover such a cleaning process i0 also removes nickel chloride from the sali. Alternative salt cleaning methods suggested by other workers in the field have been far less attractive in that they involve the energy intensive cycle of dissolving the salt in water, purifying the solution and then evaporating to dryness to regenerate to solvent chlorides. It is an object of the present invention to provide an improved, convenient process for the regeneration of solvent salts used in matte purification processes. It is a further and important object of the invention to provide a process of low energy consumption which does not involve the solution of the salt and subsequent evaporation. According to the invention a process for refining a salt comprising at least one of the chlorides of alkali and alkaline earth metals, to remove therefrom at least one impurity selected from the group consisting of the chlorides of iron, nickel, cobalt, copper, lead, arsenic, zinc, manganese, cadmium, silver, bismuth, gold, tin, tungsten and titanium, comprises producing fragments of the salt, leaching the fragments with an organic liquid comprising a reagent which is effective to form with said at least one impurity an addition complex soluble in the organic liquid, and separating the impurity loaded organic liquid from the refined salt. The invention is particularly applicable to the refining of a loaded salt which has been used as impurity solvent in a nickel matte refining process, and which contains,in the form of chloride impurities, at least about 0.5% by weight of nickel and at least about 0.1% by weight of one or more of: iron, cobalt and copper. The present invention further provides a process of refining a nickel matte to remove therefrom at least i/i• one impurity metal, selected from the group consisting of iron, cobalt, copper, lead, arsenic, zinc, manganese, cadmium, bismuth, tin, tungsten and titanium, by selectively chlorinating the impurity metal(s), dissolving the impurity metal chloride(s) in a molten salt comprising at least one chloride of an alkali or alkaline earth metal, and separating the impurity-loaded salt from the refined matte, wherein the improvement comprises producing fragments of the loaded salt, leaching the fragments with an organic liquid comprising a reagent effective to form with at least one impurity metal chloride in the loaded salt an addition complex soluble in the organic liquid, and separating the impurity loaded organic liquid from the purified salt. Where, as is common, the salt contains significant amounts of nickel chloride, which may have been added as an anhydrous reagent or formed in situ as a result of bubbling chlorine through the matte to be refined, it is a particular advantage of the process of the present invention that the complexing reagent chosen for the salt cleaning reaction may be one which reacts selectively or preferentially with the impurity metal chlorides rather than with the nickel chloride present in the salt. It is of course essential that the complexing reagent used be ìnert with respect to the solvent salt which is to be cleaned, and that it be effective for forming an addition complex with the impurity metal chloride in the absence of an aqueous phase. Thus the many chelating agents which are effective only in liquid-liquid ion exchange reactions, would not be effective for leaching the impurities from the solid salt in the present process. Reagents which i0 1040 66 are known to be capable of forming addition complexes with, for example, ch!orides of iron, cobalt or copper and which can therefore be used in the present process include primary, secondary and tertiary amine hydrochlorides as well as quaternary ammonium chlorides. In practice the complexing reagent is used in the form of a solution, the solvent being an aliphatic or aromatic hydrocarbon or an alcohol or a mixture thereof. Numerous commercially available solvents may be used, the only essential requirement being the insolubility of the salt to be refined in the solvent used to dissolve the complexing reagent. Preferred solvents include kerosene, xylene, isodecanol or mixtures thereof. If is important that the loaded salt to be purified be in the form of particles sufficiently small to enable the extraction of impurities to proceed rapidly to a high degree of completion. Such particles could be obtained by granulation of the molten salt, or by cooling to solidify the salt and subsequently grinding it. It is preferred that the loaded salt be ground to particles smaller than about 200 microns, and preferably smaller than about 50 microns. Such a particle size enables satisfactory extraction results to be obtained when the residence time of the salt in the extractant is of the order of one hour for each stage of extraction. In general more than one stage of extraction will be needed according to the initial composition of the sali. The purified salt is finally recovered by filtration, and after rinsing thereof with organic solvent and drying, it can be reused in the metal purification process. The organic extractant used x ' 104O866 for purìfication of the salt can be recycled after appropriate purification, for example by contact with an aqueous phase which dissolves the impurities. The invention will be more readily understood from the following specific description of examples of salt purification in accordance with the invention. EXAMPLE I An organic extraction solution was prepared in the following manner. A mixture was made up which comprised, by volume, 68 parts of kerosene, 12 parts of isodecanol and parts of a reagent made by General Mills, Inc. and known by the trade name Alamine 336, which is a tri-alkyl amine with the alkyl chains containing 8-10 carbon atoms. The mixture was reacted with 4.5 N hydrochloric acid, after which the aqueous phase was separated from the organic phase which was then used for leaching impurities from a loaded salt in the following manner. An impure sodium chloride was synthesized in order to simulate a loaded salt which might be obtained when one type of nickel sulfide is refined in the presence of molten sodium chloride. The synthetic mixture was prepared by melting sodium chloride together with chlorides of nickel, copper, cobalt and iron and cooling to obtain a solid containing the following metal values: Copper: 4.15 weight percent Nickel: 4.55 weight percent Cobalt: 0.50 weight percent Iron: 0.22 weight percent This synthetic loaded salt was ground to -i00 mesh, Tyler Screen Size (TSS) and was leached by the 1040S66 organic liquid described above using a two stage leaching procedure. The first stage leach consisted of contacting grams of the salt with 250 mls of the organic liquid at 25°C for one hour. At the end of this time the partially purified salt was separated by filtration, washed with 130 mls of kerosene and then filtered and dried. This dried salt was then subjected to a second stage of leachìng by contacting it with 200 mls of the organic liquid at 25°C for one hour, at the end of which it was again separated, washed, filtered and dried. The metal values present in the salt before and after each of the leaching stages are given in Table 1 below: TABLE 1 Stage 1 Initial Final Stage 2 Initial Final Weight i00 SALT Comp0sitìon ( t, %) Cu Ni Co 4.15 1.15 1.15 0.80 4.55 0.50 4.85 0.10 4.85 0.i0 4.55 0.06 Fe 0.22 0.07 0,07 0.05 • i• • l0 Whereas the extraction of copper from the salt was less efficient in this test than the extraction of either cobalt or iron, it will be seen that the organic reagent used achieved the desired effect of extracting a large part of the copper, cobalt and iron but very little of the nickel. This is most readily apparent from the comparison of the percentage extraction of each of the metal values in each stage of the process, which are sho in Table 2 below: TABLE 2 Stage 1 Stage 2 Overall METAL EXTRACTION (%) Cu Ni Co 0 81 6 89 Fe ò EXAMPLE II The organic solution for this test was prepared by reacting 4.5 N hydrochloric acid with a mixture comprising, by volume, 20 parts of the tertiary amine: Alamine 336, with 80 parts of xylene, and separating the aqueous phase from the mixture. A sample of the synthetic salt described in Example I was ground to -325 mesh (TSS) and leached consecutively with 250 mls and 225 mls of the organic solution, following the same two stage leach procedure as described in Example I. Tables 3 and 4 below show the satisfactory results obtained in this refining test. _7_ TABLE 3 i0 Stage 1 Initial Final Stage 2 Initial Final H Se ight I00 SALT Composition (wt. %) CU 4.15 1.44 1.44 0.98 Ni Co 4.55 0.50 4.55 0.07 4.55 0.07 4.30 0.03 Fa 0.22 O.O3 0.03 0.03 TABLE 4 Stage 1 Stage 2 Overall METAL EXTRACTION (%) CU Ni Co 7 57 12 94 Fe f ï. i0 EXAMPLE III For this test, the organic solution used was identical to that described in Example Il above. In this case however the impure salt was synthesized so as to simulate the type of composition obtained when nickel sulfide is refined by chloridization in the presence of a sodium chloride-potassium chloride mixture. Thus the impure salt was prepared by melting 7 parts by weight of sodium chloride with 3 parts by weight of potassium chloride and small amounts of the chlorides of copper, nickel, cobalt and iron so as to give a metal content of: Copper: 1.50 weight percent Nickel: 1.52 weight percent Cobalt: 1.80 weight percent Iron: 2.80 weight percent. A i00 gram sample of this synthetic salt was leached in turn with 300 mls and 250 mls of the organic solution following the same procedure described in connection with Example I. Table 5 below shows the composition of the salt during the extraction, while Table 6 shows that after the second stage of leaching only 17% of th nickel chloride had been extracted from the salt while between 93 and 98% of the chlorides of iron, copper and cobalt had been eliminated. Stage 1 Initial Final Stave 2 Initial Final Stage 1 Stage 2 Overall 100.0 93.6 86.2 81.1 SALT Composition (wt. % Cu Ni Co 1.50 0.36 1.52 1.80 1.52 0.37 Fe 2.80 0.94 0.36 0.06 1.52 1.42 0.37 0.03 0.94 0.21 TABLE 6 Cu METAL EXTRACTION (%) Ni co Fe i•• i• It will be readily understood by those skilled in the art that the benefits of the present invention, i.e. the convenient removal of chloride impurities from a salt mixture without the need to dissolve the salt and thereafter reevaporate the solution, can be realized with the aid of many organic reagents other than those specified in the preceding examples. Thus use can be made of any of the various primary, secondary and tertiary amines known to be effective for complexing cobalt, copper and iron. Although in general such extractants have been advocated for use in liquid-liquid extraction processes, they are in fact effective in the non-aqueous extraction involved in the process of the present invention because, unlike chelating agents, they do not rely on an ion-exchange mechanism. It will be further understood that while the salt refining process of the invention is particularly applicable to the regeneration of the solvent salt mixtures described, it is also useful in other metallurgical processes. For example, in the process of electrorefining with the aid of a fused chloride electrolyte, it is necessary from time to time to remove impurities which have accumulated in the electrolyte. The process of the present invention can be used effectively for refining such electrolytes. Thus although the present invention has been described in conjunction with preferred embodiments, various modifications of the reagents and conditions described may be resorted to without departing from the scope of the invention which is defined by the appended claims. -llPC-1125/CAN. 1O4O866 The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: i. A process for refining a salt comprising at least one of the chlorides of alkali and alkaline earth metals, to remove therefrom at least one impurity selected fçom the group consisting of the chlorides of iron, nickel, cobalt, copper, lead, arsenic, zinc, manganese, cadmium, silver, bismuth, gold, tin, tungsten and titanium, comprises producing fragments of the salt, leaching the fragments with an organic liquid comprising a reagent selected from the group consisting of primary, secondary and tertiary amine hydrochlorides and quaternary ammonium chlorides, to form with said at least one impurity an addition complex soluble in the organic liquid, and separating the impurity loaded organic liquid from the refined salt. 2. A process in accordance with claim 1 wherein said at least one impurity in the salt to be refined consists of the chlorides of at least about 0.5% by weight of nickel, and at least about 0.1% by weight of a metal selected from the group consisting of iron, cobalt and copper. 3. A process for refining a nickel matte to remove therefrom at least one impurity metal, selected from the group consisting of iron, cobalt, copper, lead, arsenic, zinc, manganese, cadmium, bismuth, tin, tungsten and titanium, by selectively chlorinating the impurity metal(s) ,dissolving the impurity metal chloride(s) in a molten salt comprising at least one of the chlorides of alkali and alkaline earth metals, and separating the impurity-loaded salt from the