CA1039065A

CA1039065A - Copper cementation

Info

Publication number: CA1039065A
Application number: CA232,831A
Authority: CA
Inventors: David L. Jones; Kohur N. Subramanian
Original assignee: Vale Canada Ltd
Current assignee: Vale Canada Ltd
Priority date: 1975-08-05
Filing date: 1975-08-05
Publication date: 1978-09-26
Also published as: AU497685B2; GB1524417A; ZA763702B; NO762663L; FI61205C; FI762159A; JPS5220325A; FR2320356A1; FI61205B; NO143912B; JPS5938290B2; FR2320356B1; AU1549676A; NO143912C

Abstract

ABSTRACT OF THE DISCLOSURE:
A nickel matte which has been subjected to a partial leach with chlorine and/or oxygen in the presence of a cuprous ion bearing aqueous solution is subsequently used as an agent for cementing copper out of solution.

Description

PC-1126 ~039~6~ `
The present invention relates to the cementation of copper from aqueous solutions, and is particularly though not ~xclusively applicable to the process of recovering nickel from nickel mattes by means of chlorine leaching.
The leaching of nickel from a matte by contacti~g an aqueous slurry of the matte with chlorine is a convenient first step for obtaining a nickeliferous solution from which, after purification, a refined nickel product can be recovered for example by electrowinning. A particularly efficient procedure for dissolving virtually all of the nickel present in a matte without dissolving an unde~irably high amount of the sulfur present consists of subjecting the matte to the action of chlorine in the presence of an aqueous solution containing copper and sufficient chloride ions, typically 100 grams per liter (g/l) or more, to ensure solubility of cuprous ions. In such a process reaction is believed to take place between the matte and cupric ions in solution, the chlorine serving to regenerate the cupric ions. Such a procedure has been known for some time, and a more recent variation thereof wherein the redox potential is controlled during the leach so as to achieve preferential dissolution of some of the metals in the matte i~ described in Canadian Patent 967,009.
At the conclusion of the leach, it is generally necessary to reduce the level of dissolved copper in the nickeliferous leach solutions so as to be able to carry out efficiently the subsequent purification and electrowinning operations. A well known technique for lowering the copper content of solutions comprises cementation with a less noble element than copper. The use of an element such as iron for ~_"7 jk'~

103~6S
this purpose has the undesirable effect of introducing into the solution an impurity which must subsequently be removed, whereas the use of elemental nickel for this purpose is necessarily costly. A commercially attractive proposal involves the use of matte for the cementation purpos~s.
In U.S. Patent 2,180,520, a copper-nickel solution i9 treated with copper-nickel matte to effect copper cementa-tion. The matte advocated for such purposes is one which is comparatively low in sulfur, i.e. preferably the sulfur content of the matte amounts at the most to 1/3 of the copper content. In an alternative cementation process, described in Canadian Patent 967,007, the nickel-copper solution is treated with elemental sulfur in combination with a matte having an atomic ratio of nickel to sulfur greater than 1.
It is an object of the present invention to provide an improved copper cementation process wherein nickel mattes can be used effectively regardless of whether the atomic ratio of nickel to sulfur therein is lower or higher than 1.
Another object of the invention is to provide an improved process for the recovery of nickel from nickel mattes.
The present invention provides a process for cementing copper out of an aqueous chloride-containing solution comprising forming a ~lurry of a nickel matte in a cuprous ion bearing aqueous solution containing at least 10 g/l of copper, introducing an oxidizing agent selected from the group consisting of chlorine and oxygen into the slurry in an amount sufficient to cause only part of the nickel in the matte to dissolve, and contacting ~he :;

~a3s(~s chloride~containing solution from which copper is to be cemented with the partially leached nickel matte.
The invention further provides a process for recoverinq nickel from a matte by chlorine leaching com-prising contacting a cuprous ion bearing aqueous slurry of the matte with chlorine in the presence of at least 10 g/l of dissolved copper to provide a solution containing nickel and copper, and subsequently lowering the level of copper in the solution by causing the solution to react with nickel matte which has been subjected to partial chlorine leaching in the presence of copper ions.
In accordance with another, and most preferred aspect of the invention, an improved process involving relatively few material handling steps is provided for recovering nickel from a matte by chlorine leaching. In this most preferred process, the matte is slurried with a cuprous ion bearing aqueous solution containing at least 10 g/l of copper, chlorine is introduced into the slurry to cause nickel in the matte to pass into solution, the chlorine introduc~ion is discontinued before all the nickel has been leached from the matte f the partially leached matte is maintained in contact with the nickel-and copper-containing leach solution so as to cement copper out of the solution, and the cemented copper and leach rssidue are separated from the solution.
The oxidizing agent used in the cour~e of partially leaching the nickel matte to activate it for cementation purposes needs to be effective to regenerate cupric ions from cuprous ions. The use of gaseous oxygen, chlorine or mixtures thereof enables such cupric ion regeneration to be ~039()~iS
achieved inexpensively without the introduction into the solution of undesirable foreig~ ions. When oxygen is used appropriate acid addition is required during the leaching operation.
The matte which is partially leached and then used for cementation will conveniently be the same material from which nickel is to be recovered. However, this is in no way essential and any alternative nickel matte available may be used for the cementation.
The reason for the improved cementation properties of activated nickel mattes is not clearly understood.
Whatever the mechanism may be, it has been surprisingly found that:
a) the efficiency of cementation obtained with a given matte, as judged for example by the reaction kinetics, is greatly improved ~y the partial leaching;
b) addition of sulfur to the matte is unnecessary to achieve efficient cementation; and c) partially leached nickel mattes can be used effectively as means for cementing copper, re-gardless of whether the atomic ratio of nickel to qulfur therein is greater or smaller than 1.
The degree of leaching of the nickel matte necessary to achieve the desired activation is not critical and pre-ferably between 15 and 60% of the nickel in the matte is -caused to dissolve during he partial leach. In the most preferred nickel recovery process involving consecutive leaching and cementation reactions resulting from a single matte aadition to a copper-containing solution, the extent - -. ; . . - . . . . .

1039~65 of leaching, i.e. the period of ch~orination, will be selected so as to ensure that the amount of matte remainin~
when the chlorine flow is discontinued is at least sufficient to reduce the amount of copper in solution down to the desired level.
The chlorine leach of the matte, whether carried out for complete dissolutionof nickel to be recovered or for the purpose of producing partially leached matte for use in copper cementation, needs to be performed in the presence of copper ions. ~his is to ensure efficient leaching of nickel while minimizing sulfate formation. In practice at least 10 g/l, and preferably 30 g/l or more, of copper should be present in the solution in which the nickel matte i8 slurried. It should be under~tood that while it is convenient to describe the processes of leaching and cemen-tation separately, the processes may in practice occur simul-taneously when chlorine is being bubbled through the matte slurry. Thus the cementation can be considered as a com-peting reaction which can take place during the chlorine leach. ~ecause any cementation accompanying the leaching process results in lowering the level of dissolved copper, it is necessary to select the initial level of copper in solution in accordance with the composition of the matte to be leached. For example, a copper level of 30-40 g/l is de irable when the sulfur content of the nickel matte to be leached is of the order of 20%.
The leaching reaction can be conducted at tempera-tures as low as about 60C, but preferably the matte slurry should be maintained at ~0-110C. The temperature can generally be maintained by the exothermicity of the leaching reaction.

The nov1el cementation of copper with the aid of partially leached nickel matte finds a most useful application in an improved overall process for recovering nickel from impure nickel mattes. The most preferred nickel recovery process in accordance with the present invention comprises the following steps:
i) the impure matte is slurried with a copper-containing aqueous solution and partially leached with chlorine;
ii) the chlorine flow is discontinued and the partially leached matte is allowed to cement copper out of the leach solution;
iii) the leach solution from step (ii) is separated from the solids which comprise cemented copper and matte residue;
iv) the leach solution from step (iii) is purified by means of solvent extraction and/or ion-exchange to remove therefrom impurities such as iron, copper, cobalt,arsenic, lead, bismuth, etc.;
v) the pur~fied solution from step (iv) is subjected to electrowinning to recover pure nickel and generate chlorine for recycling to leach further matte in step (i) above and step (vi) below:
vi) the solids from step (iii) are slurried with spent electrolyte from step ~v) and treated with chlorine to effect complete leaching of the solids, thereby resulting in a copper-and nickel-containing solution for recycling to perform step (i) on fresh matte, and a residue consisting essentially of sulfur.

~3~0f~5 To ensure efficiency of the complete leach of step (vi), ~ portion of the copper-and nickel-containing solution obtained in that step is internally recycled thereby ensuring the desired level of dissolved copper at the onset of this complete leach.
To aid in the understanding of the present invention some specific examples will now be described.
EXAMPLE
A partially leached matte was prepared as follows:
200 g of granulated matte analyzing, by weight, nickel : 70.8 %
copper : 0.54 %
cobalt : 1.48 %
iron : 0.38 %
sulfur : 26.4 was slurried with 750 mls of a slightly acidic chloride solu-tion containing 100 g/l of nickel and 30 g/l of copper at 90CO Chlorine gas was introduced into the slurry at the rate of 2.5 grams per minute. After 14 minutes the chlorine flow was discontinued and analysis of the leach solution showed a nickel content of lSS g/l and a copper content of 10.9 g/l indicating that cementation had been taking place during the leach. The residue comprised 167.4 g of partially leached matte containing no elemental sulfur (as determined by washing with hot toluene) and analyzing, by weight:
nickel : 58.3 %
copper : 8.5 %
sulfur : 30.9 %.
The above partially leached matte was used for . .: , .. . . .

~.039(~65 copper cementation as follows: 150 g of the partially leached matte was added to 750 mls of an acidified copper sulfate solution containing 10 g/l of copper at 90C.
The slurry was stirred and sampled for copper determination at 30 minute intervals. The results are shown in Table 1 below. For the purpose of comparison a cementation was carried out in an identical manner to that described above except that, instead of the partially leached matte, 150 g of the original, unleached, granulated matte were used.

Matte Used~~ Cementation Period Copper in Solution (minutes) (a/l) . .......... _ . ~ ...... .
Partially leached 0 10.0 1.03 0.05 0.002 ;
o I 10 ':
~ Thus it can be seen that cementation carried out in accordance with the process of the invention reduced the copper level in solution in 30 minutes to a lower level than that resulting from ~0 minutes of cementation with non-activated matte.

A nickel extraction te~t was carried out using the same matte which constituted the starting material in Example 1. A fir~t sample ~55 grams) of this matte was chlorine ~3~Yd to completion in 750 mls of an acidified solu-tion containing 97.5 g/l of nickel and 9.0 g/1 of copper by bubbling chlorine at 1~6 grams per minute for 30 minutes through the slurry, the temperature of which rose from ..... .. . .

~lJ39(~65 9~ to 103~. A second portion (95 grams) of the same matte was now added to the slurry and the chlorine flow continuecl for a further 40 minutes. This period was sufficient to leach the matte only partially. The chlorine flow was then discontinued and a sample of the residue was removed for analysis. The slurry was kept stirred and the copper level in solution was determined at intervals. The results of the cementation can be seen in Table 2 below.

TimeMatte Addition Copper in Solution tmins) (g) (2~
0 55 9.0 N.D.
70* _ 7.2 150 0.85 240 _ 0.10 380 0.06 *Chlorine flow was di~continued at this point.
N.D. = not determined.
The residue sample of a duplicate test taken after 70 minutes of leaching was washed with hot toluene to remove any elemental ~ulfur present therein, and thereafter analyzed for nickel and sulfur. ~he atomic ratio of nickel to sulfur was found to be 0.55, and X-ray diffraction examination ~howed the absence of any Ni3S2 phase. Thus it will be seen that the nickel sulfide acting as cementation agent from the point at which chlorine leaching wa~ di~continued was a matte wherein the Ni~S at~mis ratio was well below 1.

The following test illu~trates an application of the cementation proceR~ of the invention to a practical ~ 3gl~
flowsheet for nickel recovery from a nickel matte.
1st Stage Leach:
2000 grams of a granulated matte analyzing,by weight:
nickel : 77.2 copper : 0.49 %
cobalt : l.l9 iron : 0.80 %
sulfur : 19.4 %
was added to 8.6 liters of a 60C chloride solution contain-ing 160 g/l of nickel and 40 g/l of copper. 20 grams per minute of chlorine were bubbled through the slurry for 30 minutes during which time the slurry temperature increased to boiling point (110C). The chlorine flow was discontinued and the slurry ~tirred for a further 105 minutes to effect cementation of copper. The solution was then filtered and found to contain 250 g/l of nickel and 0.37 g/l of copper.
After purification by conventional means this solution was used for electrowinning nickel.
2nd Stage Leach~
~he spent electrolyte from the electrowinning operation, B.2 liters containing 75.5 g/l of nickel and no copper, was mixed with l.9 liters of the chloride solution containing 160 g/l of nickel and 40 g/l of copper. The residue from the 1st stage leach (1574 g) was added to this solution which was at 74C and had a pH of 1.5. The slurry was then stirred and chlorine was introduced at 20 g/min.
The chlorine was absorbed quantitatively for 68 minutes.
At this point the chlorine flow rate was reduced by 50%
and discontinued after a further minute, since chlorine in the off-gases was evidence of completion of the reaction.

1~)3~6S
Durin~ the leach the slur~y temperature had increased to boiling point, but on completion of the reaction, the slurry had begun to cool down.
The slurry was filtered and the residue (382.7 g) was found ~o be essentially sulfur and analyzed, by weight:
copper : O.lS %
nickel : 1.16 cobalt : O.Og %
iron : O . 5 5 96 sulfur : 97 . 4 % .
The filtrate obtained could then be recycled to perform a 1st stage leach on a fresh sample of matte.
It will be evident from the above specific examples that where reference i5 made herein to the treatment of a copper-containing solution with an activated (i.e. partially chlorine-leached) nickel matte, such a matte need not necessarily be activated prior to its addition to the copper-containing solution. Indeed the matte may be activated in situ, as was the case in Examples 2 and 3 above.
While the present invention has been specifically described with reference to preferred embodiments, various modifications may be made to the procedures and conditions described, without departing from the scope of the inventlon, which is defined by the appended claims.

,

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for recovering nickel from a matte by chlorine leaching wherein the matte is slurried with a cuprous ion bearing aqueous solution containing at least 10 g/l copper, chlorine is introduced into the slurry to cause nickel in the matte to pass into solution, the chlorine introduction is discontinued after 15 to 60% of the nickel has been leached from the matte, the partially leached matte is maintained in contact with the nickel-and copper-containing leach solution so as to cement copper out of the solution, and the cemented copper and leach residue are separated from the solution.

2. A process as claimed in claim 1 wherein the aqueous slurry is maintained at about 60 to 110°C during introduction of the chlorine.

3. A process as claimed in claim 1 wherein the cuprous ion bearing aqueous solution contains at least 30 grams per liter of copper.

4. A process as claimed in claim 1 wherein at least part of the matte to be leached is introduced into the slurry during the chlorine introduction.

5. A process as claimed in claim 1 including the further steps of subjecting the solution separated from the cemented copper and leach residue to purification and recovering pure nickel therefrom by electrowinning.

6. A process as claimed in claim 5, including the further steps of mixing spent electrolyte from the electrowinning step with the cemented copper and leach residue, and treating the mixture with chlorine, in an amount sufficient to ensure dissolution of the cemented copper and substantially complete leaching of the leach residue, thereby obtaining a slurry wherein the solids consist essentially of sulfur.