Process for the Recovery of Cuprous Chloride in the Presence of Metal Impurities

1. Field of the Invention

The process of this invention deals generally with selective crystallization, as classified in Class 23, Sub-Class 296; and more particularly with the selective crystallization of cuprous chloride from particular solutions containing particular amounts of cupric chloride.

2. Prior Art

The separation of cuprous chloride from solutions possessing one or more of a number of metal impurities presents a problem, particularly in the rapidly developing hydrometallurgical copper recovery processes. As is well known, the main sources of copper today are copper sulfide ores, primarily chalcopyrite. Conventional pyrometallurgical techniques for recovering copper from its sulfide ores are objectionable due to the production of sulfur dioxide, a major air pollutant. Accordingly, hydrometallurgical developments are now being considered in the copper industry to produce pollution free processes for the recovery of copper from its sulfide ores.

Many of these hydrometallurgical processes are concerned with leaching the copper sulfide ore with ferric chloride and/or cupric chloride to form elemental sulfur prior to the recovery of the copper. The sulfur dioxide pollution problem is eliminated in these processes by converting of the sulfide sulfur directly to elemental sulfur.

One of the principal difficulties in these processes is the complete conversion of the copper in the copper sulfides to cuprous chloride, the preferred intermediate for the production of elemental copper. Generally the leaching reactions produce a mixture of cuprous chloride, cupric chloride and ferrous chloride. The prior art then reduces the cupric chloride to cuprous chloride, generally by means of elemental copper, in order to produce a solution containing only cuprous chloride and ferrous chloride, which may then be conventionally treated for the production of copper. This is necessary in that cupric chloride is not easily reduced to elemental copper in the presence of the various impurities which exist in the solutions, and also due to the fact that substantially more energy is required in order to perform this reduction. U.S. Pat. No. 3,798,026 to Milner illustrates such a process. Milner leaches his copper concentrate to produce a solution containing cuprous, cupric and ferrous chlorides, reduces the cupric chloride to cuprous chloride by means of cement copper, crystallizes a portion of the cuprous chloride from the resulting leach solution and reduces this cuprous chloride by means of hydrogen reduction to elemental copper, and treats the mother liquor from the crystallization step in order to produce cement copper, regenerate the leach reagents and remove the various impurities.

Another similar process is described in U.S. Pat. No. 3,785,944 to Atwood. This process discloses the recovery of metallic copper from chalcopyrite by leaching the chalcopyrite with ferric chloride to produce cupric chloride, reducing a portion of the cupric chloride to cuprous chloride by reacting it with fresh chalcopyrite feed, reducing the remaining cupric chlorice with metallic copper, reducing the cuprous chloride to metallic copper by electrolysis and conventionally regenerating the ferric chloride leach reagent and removing the impurities.

These and other similar processes represent notable advances in the art, but possess several important drawbacks. The electrolytic recovery of copper directly from the reduced leach solution, as disclosed in Atwood, produces a relatively impure grade of copper due to the amount of impurities plated with the copper during electrolysis. Also, in order to reduce the cupric chloride to cuprous chloride it is necessary to utilize elemental copper which has already been processed. This elemental copper is oxidized to cuprous chloride by the reaction with cupric chloride. Hence, this copper must remain in the process for a relatively lengthy period of time and additional energy must be consumed in order to again convert the cuprous chloride to elemental copper.

The Milner process represents an advance in the purity of the copper produced since in this process the cuprous chloride is first crystallized from the leach solution prior to its reduction to elemental copper. However, since a substantial amount of process impurities crystallize with the cupric chloride, Milner must either remove these impurities prior to crystallization or further treat the cuprous chloride crystals in order to remove the impurities. Furthermore, Milner's method of crystallization requires that all of the cupric chloride be reduced by means of elemental copper to cuprous chloride prior to the crystallization step, and as mentioned earlier this requires a substantial energy expense from the standpoint of oxidizing elemental copper which had previously been reduced, and also requires a substantially prolonged residence time before all of the copper is ultimately produced.

The process of this invention overcomes these drawbacks and presents several significant advantages. A particularly important advantage which results from the application of this process is that a substantially increased amount of cuprous chloride may be maintained in and therefore crystallized from the solution. The addition of cupric chloride increases the capacity of the solution for cuprous chloride while simultaneously minimizing the amount of iron in solution. As iron in solution presents a considerable problem during the separation of the cuprous chloride crystals from solution and the subsequent washing of the crystals, minimizing the amount of iron is highly desirable.

Another particularly important advantage is realized as a result of conducting the crystallization in the presence of one or more metal impurities commonly encountered in copper bearing ores. It has been surprisingly discovered that when the cuprous chloride is crystallized from a solution containing a substantial amount of cupric chloride that the amounts of certain impurities crystallized is vastly reduced. The cupric chloride apparently inhibits the inclusion of these impurities with the cuprous chloride crystals. The resulting cuprous chloride crystals are observed to be so pure in some instances that they may be directly reduced to elemental copper without the necessity of any additional purification processing. The crystallization step of this process may therefore be carried out without the necessity of first removing these impurities, as is required in the Milner process.

Furthermore, another primary advantage is recognized from the standpoint of the amount of energy required to conduct the process. As earlier mentioned when elemental copper is employed to reduce cupric chloride to cuprous chloride prior to crystallization the elemental copper is oxidized to cuprous chloride. The initial energy required to produce this elemental copper is wasted since additional energy must be consumed to again reduce the cuprous chloride to elemental copper. The process of the present invention obviates the reduction of this cupric chloride, thereby saving the considerable additional energy.

In its broadest aspects the process of the present invention isolates cuprous chloride from a solution as herein described. As is well known in the chemical literature, cuprous chloride is useful in a number of applications, including serving as an intermediate in various chemical reactions. Its primary commercial value is as an intermediate for the recovery of copper from various copper bearing ores.

This invention deals with a process for crystallizing cuprous chloride from a solution comprising cuprous chloride and one or more metal impurities selected from the group consisting of antimony, arsenic and bismuth, the critical requirement being that the crystallization take place in the presence of a cupric ion concentration of at least about 20 grams per liter.

This crystallization process is of primary value in processes for recovering copper from copper bearing ores, particularly copper sulfide ores, generally comprising concentrating the copper bearing ores, leaching the concentrate with ferric chloride in order to produce a solution comprising cuprous chloride, cupric chloride, ferrous chloride and the various metal impurities existing in the concentrate; crystallizing a substantial portion of the cuprous chloride from the leach solution resulting in cuprous chloride crystals and a mother liquor, which crystallization is performed in the presence of a cupric ion concentration of at least about 20 grams per liter; separating the crystallized cuprous chloride from the mother liquor; reducing the crystallized cuprous chloride to elemental copper; treating a substantial portion of the mother liquor with oxygen and hydrochloric acid in order to produce iron oxide and to regenerate cupric chloride and ferric chloride; and treating the remainder of the mother liquor in order to remove the various impurities.

The FIGURE sets forth a process flow diagram incorporating the process of the invention in a particular process for recovering copper from chalcopyrite feed materials.

The invention primarily deals with an improved crystallization process for removing cuprous chloride from various solutions. Solutions suitable for the application of this process are those which comprise cuprous chloride and one or more metal impurities selected from the group consisting of arsenic, antimony and bismuth. The solution must also comprise at least one suitable cuprous chloride solvent. A "suitable solvent" as the term is used throughout the specification and claims includes metal chlorides possessing sufficient solubility for cuprous chloride, preferably within the temperature range of about 40.degree. C to about 100.degree. C, including, for example, hydrochloric acid, the alkali metal chlorides, the alkaline earth metal chlorides, ferrous chloride and cupric chloride. Similarly the term suitable solution is intended to mean a solution possessing the above set forth characteristics.

The physical separation process employed with the process of the invention is crystallization. The term crystallization as used herein is intended to mean the physical process of cooling the solution in order to decrease the solution's capacity for cuprous chloride, thereby depositing the cuprous chloride as a solid. It is observed that this is within the ordinary context of the term when the term is employed in relation to solutions.

The amount of cuprous chloride in solution is not critical to the process, but when maximizing the yield of cuprous chloride crystals is desired it is preferred to operate the process with a solution at or near the saturation of cuprous chloride. Similarly the upper temperature limitation of the solution is not particularly important, as long as the temperature is below the boiling point of the solution. Of course generally speaking the higher the temperature of the solution the greater capacity it will have for maintaining additional cuprous chloride in solution. The solution is therefore preferably maintained from about 80.degree. to about 107.degree. C prior to the crystallization.

The solution may be cooled by most conventional means known in the art, such as heat exchange with other process streams, the use of cooling water, refrigeration, and other well known techniques.

The solution should be cooled to preferably at least about 30.degree. C, more preferably at least about 20.degree. C, and most preferably at least about 10.degree. C. The yield of cuprous chloride crystals generally increases as the temperature range which the solution is cooled increases.

Necessarily when cuprous chloride is crystallized from a solution in the presence of one or more of the enumerated impurities some of the impurities will be separated from the solution with the cuprous chloride. Further removal of these separated impurities is necessary if relatively pure copper is to be recovered from the crystallized cuprous chloride. This of course requires additional processing, as is disclosed, for example, in U.S. Pat. No. 3,798,026.

However, when cuprous chloride is crystallized from a suitable solution in the presence of sufficient cupric ions, the amounts of impurities concurrently separating are substantially reduced. This facilitates any additional purification processing, and in many cases actually eliminates the necessity for additional purification. The presence of cupric ion, preferably in the form of cupric chloride, during the cuprous chloride crystallization is therefore critical to the process. The minimum concentration of cupric ion necessary to achieve the advantageous results of the process is at least about 20 grams per liter, more preferably at least about 50 grams per liter and most preferably at least about 100 grams per liter.

The suitable solution from which the cuprous chloride is crystallized may result from a number of processes. Essentially the only requirement of such a process is the production of a suitable cuprous chloride solution. Preferable processes include those which comprise leaching copper sulfide ores to produce a solution comprising cuprous chloride, cupric chloride and a suitable metal chloride solvent.

The process flow diagram of the figure illustrates a relatively general process for recovering copper utilizing the particular crystallization process of this invention. The copper sulfide feed material containing one or more metal impurities selected from the group consisting of arsenic, antimony and bismuth is introduced into the leaching phase and reacted with ferric chloride and cupric chloride to dissolve the copper and iron, if present, and remove the sulfur. The remaining gangue is removed as tailings and discarded. The resulting leach solution primarily comprises cuprous chloride, cupric chloride and ferrous chloride, along with various metal impurities. The concentration of copper as cupric chloride present is monitored to insure that it is at least about 20 grams per liter. The leach reaction is generally carried on within a temperature range of about 80.degree. to about 105.degree. C.

This hot solution is then cooled to remove a substantial portion of the cuprous chloride in crystal form. The amount of cuprous chloride crystallized is dependent upon the various factors affecting the solubility of this compound, as earlier discussed. Depending on the composition of the solution, this crystallized cuprous chloride may be relatively free of impurities, and need not undergo additional purification processing. However, if in particular cases additional processing for purification is desirable, means known in the art, as for example set forth in U.S. Pat. No. 3,798,026, may be employed. The cuprous chloride crystals may then be reduced to produce substantially pure copper. This copper may undergo melting and casting in order to form pure ingots.

The mother liquor from the crystallization stage possesses the same composition as the leach solution which was introduced into the crystallization stage, with of course the exception of a substantially reduced cuprous chloride concentration. A substantial portion of this mother liquor may be introduced into a regeneration stage in order to recover a portion of the iron as iron oxide, oxidize ferrous chloride to ferric chloride and oxidize the remaining cuprous chloride to cupric chloride. The iron oxide is removed from the process, and the ferric and cupric chlorides are recirculated to the leach stage in order to treat fresh feed material. The remainder of the mother liquor is bled to the purification stage of the process, wherein the cupric and cuprous chlorides are reduced to elemental copper and removed from the process and the remaining impurities are conventionally recovered. The resulting iron solution may be treated by iron electrolysis in order to produce substantially pure iron at the cathode. The anode reaction in the iron electrolysis oxidizes ferrous chloride to ferric chloride, which is recirculated to the leach stage in order to treat additional feed material.

The feed materials for which this process may be employed include all copper bearing compounds which are capable of being converted to cuprous chloride. Suitable ores and concentrates include, for example, chalcopyrite, bornite, chalcocite, digenite, covellite, malachite, enargite, scrap copper and others. Chalcopyrite is a particularly suitable ore for the process.

Due to the grade of ores now being mined, concentration processes are commonplace. As a result of these various concentration processes the feed material is generally sufficiently fine in order to be directly introduced into the process. However, if necessary the feed may be further subjected to grinding in order to enhance the leach reactions.

The leach stage of the process is designed to dissolve the feed material and convert the sulfide sulfur to elemental sulfur while converting the copper sulfide copper to cuprous and cupric chlorides. A number of such processes are known in the art and would be suitable for this process, including for example the processes disclosed in U.S. Pat. No. 3,785,944, 3,789,026 and the Minerals Science Engineering article, Vol. 6, No. 2, April 1974 by Dutrizac, et al. entitled Ferric Ion as a Leaching Medium.

A preferable leaching technique, described herein with respect to its applicability to chalcopyrite, involves a three state countercurrent reaction utilizing ferric chloride and cupric chloride as the leaching agents. This leach process is perhaps best understood by first considering the third stage. This third stage receives heavily depleted chalcopyrite from the second stage and ferric chloride. The ferric chloride is obtained by the regeneration of ferrous chloride in a later stage of the process. The primary chemical reaction in this third stage is:

in order to insure the consummation of all of the chalcopyrite a substantial excess of ferric chloride is preferably employed at this stage. This excess ferric chloride will react with any cuprous chloride present to produce ferrous chloride and cupric chloride as follows:

The tails are then separated from the solution and discarded. This third stage leach solution, containing ferric chloride, ferrous chloride and cupric chloride is then introduced into the second stage.

The second stage receives partially depleted chalcopyrite from the first stage and the third stage leach solution. Additionally, regenerated ferric chloride and/or cupric chloride may be added at this stage. Again the primary reaction in this second stage is:

this reaction is preferably conducted such that essentially all of the ferric chloride is converted to ferrous chloride. The cupric chloride present in the system in turn reacts with chalcopyrite in order to produce cuprous chloride and ferrous chloride as follows:

any remaining chalcopyrite will be removed and sent to third stage. The second stage leach solution therefore contains ferrous chloride, cupric chloride and cuprous chloride. The ratio of cuprous to cupric chloride depends upon the reaction conditions employed in the second stage leach.

The second stage leach solution, after having been separated from the remaining chalcopyrite, is then recirculated to the first stage wherein it is contacted with the fresh chalcopyrite feed. If grinding is employed a portion of this solution may be mixed with the feed prior to the grinding. The leach solution containing ferrous chloride, cuprous chloride, and cupric chloride react with the fresh chalcopyrite feed according to the following reaction.

all of the cupric chloride is not converted to cuprous chloride, as chalcopyrite is not a sufficiently active reducing agent. Hence, the resulting leach solution from the first stage contains cuprous chloride, ferrous chloride, and cupric chloride. This solution is separated from the remaining chalcopyrite, and the chalcopyrite is sent to the second stage. The first stage leach solution is monitored to insure that cupric ion is present in sufficient concentration, as hereinabove discussed. This solution is then sent to the crystallization stage. No reduction of cupric chloride is necessary, nor in most instances is it desirable.

Generally the process is conducted such that at least a substantial amount of cuprous chloride is crystallized from solution, and under most circumstances it is preferable to crystalize as much cuprous chloride as practical. Preferably at least 25 percent of the cuprous chloride is removed in the crystallization step, more preferably at least about 35 percent, and most preferably at least about 50 percent is removed at this stage.

Impurities other than arsenic, antimony and bismuth may also be present in the solution from which cuprous chloride is crystallized. Many of these impurities, such as lead and zinc, have essentially no tendency to separate with the cuprous chloride and therefore do not present a problem. Other impurities which may tend to partially separate with the cuprous chloride may possibly be beneficially inhibited by the process of the inventor. One impurity, silver, if initially present is preferably removed from the solution prior to the crystallization, as a substantial amount of silver crystallizes with cuprous chloride. This silver removal may be accomplished by means known in the art. If, however, some impurities are crystallized with the cuprous chloride they may be removed by additional purification techniques, such as leaching or recrystallization, prior to the production of copper.

The cuprous chloride crystals are then separated from the mother liquor. Conventional solid-liquid separation techniques may be employed, including for example centrifuging. These crystals may then be washed as necessary prior to the reduction to elemental copper. This washing is preferably conducted with dilute hydrochloric acid. Under certain conditions, such as when the suitable solvent consists of a relatively high concentration of cupric chloride and a relatively low concentration of ferrous chloride, the washing step is facilitated since it is easier to remove iron from the cuprous chloride crystals.

Once the crystallized cuprous chloride has been isolated from the mother liquor, a numbr of techniques may be employed in order to reduce the cuprous chloride to elemental copper. The cuprous chloride may be dissolved and the copper cemented from the solution. Alternatively, it may be dissolved and recovered electrolytically by means known in the art. A preferable technique to be used in conjunction with this process is to reduce the cuprous chloride by means of hydrogen reduction. The hydrogen reduction process may be carried out by various means known in the art, as for example, those set forth in U.S. Pat. Nos. 1,671,003, 3,552,498; 2,538,201; 3,321,303 and others.

Upon completion of the reduction of the cuprous chloride to elemental copper the elemental copper may be further treated by melting and casting in order to facilitate further handling. When hydrogen reduction is employed the by-product hydrogen chloride formed may be used in the regeneration stage.

The mother liquor from the crystallization stage comprises ferrous chloride, cupric chloride and some cuprous chloride, along with the various process impurities. A substantial portion of this mother liquor stream is sent to the regeneration stage. In this stage the ferrous chloride is converted to ferric chloride and iron oxide and the cuprous chloride is oxidized to cupric chloride. The applicable reactions are as follows:

The hydrogen chloride may be obtained from the hydrogen reduction stage. The regenerated ferric chloride and cupric chloride may be recirculated to the leach stage in order to treat fresh feed material.

That portion of the mother liquor which is not processed in the regeneration stage is treated in the purification stage. Preferably, from about 3 to about 10 percent of the mother liquor is treated in the purification stage, and this range may vary depending upon the particular process employed and the impurity buildup in the process. This portion of the mother liquor is initially treated for the removal of copper. This copper removal may be accomplished, for example, by iron cementation or electrolysis. A preferable electrolytic process is that described by Hazen in U.S. Pat. No. 3,767,543. When electrolysis is employed a portion of the ferrous chloride from the leach stage may be circulated through the anode in order to oxidize this ferrous chloride to ferric chloride. The ferric chloride may then be reintroduced into the leach stage.

The solution from the copper removal stage is then further purified, removing any copper residue and other impurities such as zinc, lead, arsenic, antimony, bismuth, etc. The remaining ferrous chloride solution is then sent to iron electrolysis wherein iron and ferric chloride are produced. Alternatively all or a portion is sent to hydrolysis wherein ferric chloride and iron oxide are produced, as was mentioned earlier. In either case the ferric chloride produced may be utilized in the leach reaction.

The following examples demonstrate the crystallization of cuprous chloride from solutions comprising cuprous chloride, the designated metal impurities, and cupric chloride in various different concentrations. Each solution was saturated with cuprous chloride at 80.degree. C and then cooled to 15.degree. C in order to crystallize cuprous chloride. The amounts of each of the impurities crystallized with the cuprous chloride were then determined for each of the different cupric chloride concentrations. The results of Examples 1-6 are set forth in Table I, with the amounts of impurities which were crystallized with the cuprous chloride being tabulated for the various different concentration of copper as cupric chlorides in solution.

The initial solution of about 175 ml. comprised 214 g./l. iron as ferrous chloride, no cupric chloride, 1.02 g./l. Sb and 0.20 g./l. As. The total equivalent chloride concentration was about 271 g./l. and the solution was saturated with cuprous chloride at 80.degree. C.

The initial solution for this example having a volume of about 175 ml. contained 192 g./l. iron as ferrous chloride, 20.5 g./l. copper as cupric chloride, 0.72 g./l. Sb and 0.20 g./l. As. The total equivalent chloride concentration was about 267 g./l. and the solution was saturated with cuprous chloride.

The solution of Example 2 was duplicated with the exception of providing initially 159 g./l. iron as ferrous chloride and about 54 g./l. copper as cupric chloride. The total equivalent chloride concentration was about 265 g./l.

Again the solution of Example 2 was duplicated except the initial solution contained 105 g./l. iron as ferrous chloride and 112 g./l. copper as cupric chloride. The total equivalent chloride concentration was about 264 g./l.

The solution of Example 2 was again repeated except present were 93 g./l. iron as ferrous chloride and 170 g./l. copper as cupric chloride. The total equivalent chloride ion concentration was about 260 g./l.

The solution comprised no ferrous chloride and 117 g./l. copper as cupric chloride, with the rest of the components equivalent to the solution of Example 2, providing a total equivalent chloride concentration of 131 g./l.

The initial solution of this example comprised 214 g./l. iron as ferrous chloride, no cupric chloride and 0.52 g./l. Bi. The total volume of the solution was 175 ml. and the solution was saturated with cuprous chloride at 80.degree. C. The total equivalent chloride ion concentration was 271 g./l.

The solution of Example 7 was duplicated except 192 g./l. iron as ferrous chloride and 20 g./l. copper as cupric chloride were provided. The total equivalent chloride ion concentration was 267 g./l.

The solution of Example 7 was again duplicated with the exception of providing 93 g./l. iron as ferrous chloride and 170 g./l. copper as cupric chloride. The total equivalent chloride ion concentration was 260 grams per liter.

The solution of Example 7 was once again duplicated, except no ferrous chloride was provided and 117 g./l. copper as cupric chloride was present, representing a total equivalent chloride ion concentration of about 131 g./l.

The following table presents for examples 7-10 the amounts of iron and bismuth crystallized from the solutions with the cuprous chloride, along with the concentration of copper in solution as cupric chloride, as a result of cooling the solutions to 15.degree. C.