Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
1999-03-12
2001-03-27
King, Roy V. (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C423S141000, C423S150400, C423S150600, C423S658300
Reexamination Certificate
active
06206951
ABSTRACT:
The present invention relates to a method for leaching sulfidic nickel matte, and particularly copper rich nickel matte as well as for leaching said matte together with metallic copper matte and/or copper-nickel matte. The leach of nickel matte is carried out as pressure leach by means of copper sulfate in one or several stages.
In the prior art there is known, among others, a method according to the U.S. Pat. No. 5,628,817, where the leach of nickel-copper matte produced in a pyrometallurgic process is first carried out in at least two atmospheric oxidation stages, with acid and copper as leaching agents. The precipitate from the second atmospheric leach is further leached at subsequent pressure leach stages, and consequently free oxygen does not essentially participate in the first pressure leach.
From the Finnish patent 98,073, there is known a method, according to which from the two mattes produced in the pyrometallurgic treatment of nickel concentrate, i.e. from flash smelting furnace matte and electric furnace matte, nickel is recovered in the same leach process. The smelting furnace matte (FSF matte) containing less iron is first leached in one or two atmospheric leach stages by means of oxygen and the anolyte of nickel electrolysis, and the formed precipitate is conducted to pressure leach. The solution obtained from the pressure leach is conducted to the leach of the matte (SF matte) that contains more iron, and the solution obtained from this leach stage in turn is conducted to the atmospheric leach stages of the smelting furnace matte. The precipitate created in the leach of the matte containing more iron is precipitated as jarosite.
A common feature for both of the above described methods is that nickel matte is first leached in one or two generally atmospheric oxidation stages, where the nickel and copper components Ni
3
S
2
ja Cu
2
S contained in the matte are leached by means of an acidic, copper and iron bearing recircle solution, so that along with the leach process, copper is first leached and then reprecipitated. Among the reactions that take place during the leach, the following are the most essential:
Ni
3
S
2
+H
2
SO
4
+0.5 O
2
NiSO
4
+2NiS+H
2
O (1)
Ni
3
S
2
+CuSO
4
+H
2
O+0.5O
2
NiSO
4
+2NiS+Cu(OH)
2
(2)
Cu
2
S +H
2
O+0.5O
2
CuS+Cu(OH)
2
(3)
The most important result from said reactions is that the primary nickel sulfide Ni
3
S
2
is transformed into secondary nickel sulfide NiS, and the primary copper sulfide, chalcocite Cu
2
S is transformed into secondary copper sulfide CuS. It is also important that a remarkable part of the sulfur contained in the matte is oxidized into sulfates, because it is considered that long delay times must be applied at these stages, in order to give this reaction, which is relatively slow at low temperatures, time to proceed. The oxidation of sulfur into sulfate takes place according to the following formula:
NiS+2O
2
NiSO
4
(4)
The precipitate recovered at the atmospheric leach stages is conducted to pressure leach, where nickel is selectively leached by means of a CuSO
4
solution, and copper is precipitated as digenite Cu
9
S
5
, which can also be represented in the form Cu
1.8
S:
6NiS+9CuSO
4
+4H
2
O
Cu
9
S
5
+6NiSO
4
+4H
2
SO
4
(5)
Simultaneously the secondary copper sulfide CuS reacts with the copper sulfate, forming digenite according to the following reaction:
6CuS+3CuSO
4
+4H
2
O
Cu
9
S
5
+4H
2
SO
4
(6)
From the above reactions (5) and (6) it is observed that in pressure leach, ⅙ of the sulfidic sulfur is oxidized into sulfates, and this sulfate, along with what is formed elsewhere in the process, must be removed from the solution, if the process has closed solution circulation, as is the case if the nickel recovery takes place by means of electrowinning. True enough, the expenses caused by sulfate removal are very high, because in general it is necessary to use expensive neutralizing agents, such as sodium hydroxide NaOH or sodium carbonate Na
2
CO
3
. This drawback of the process has, however, been accepted, because there has not been other available methods for carrying out a selective industrial-scale leach of copper with reasonable costs.
A surprising discovery of the present invention is that from a sulfidic nickel matte created when processing pyrometallurgic nickel-bearing material, and particularly from a copper rich nickel matte, nickel can be selectively leached by means of copper sulfate solution, by applying pressure leach at a high temperature without the above mentioned atmospheric oxidation stages, so that the oxidation of the sulfide contained in the matte into sulfate takes place in a smaller scale than in the prior art methods. After the pressure leach stage, there are the oxidation stages where the iron contained in the matte is precipitated, and the copper sulfide precipitates with a high copper content, formed in the pressure leach, are leached by means of oxygen and acid in order to generate copper sulfate. The pressure leach is carried out in one, two or several stages. If the process deals with essentially metallized matte coming from a further processing furnace located in succession to the smelting furnace, the leach thereof it is carried out as one stage in the leach process, and the copper and nickel bearing solution obtained from this stage is conducted to the last oxidation stage. The essential novel features of the invention are apparent from the appended claims.
Experiments that were carried out proved that in certain conditions, the reaction speeds in the following reactions can be sufficiently high, so that they also fulfill the requirements of industrial processes:
Ni
3
S
2
+3Cu
2
S+3CuSO
4
3NiSO
4
+Cu
9
S
5
(7)
8Ni
3
S
2
+27CuSO
4
+4H
2
O
24NiSO
4
+3 Cu
9
S
5
+4H
2
SO
4
(8)
From reaction (7) it is seen that sulfur is not oxidized at all, and in reaction (8) only {fraction (1/16)} is sulfurized. This means that if the matte contains an amount of copper which is 2× the equivalent amount as compared to nickel, the nickel can be leached selectively without any dissolution of sulfidic sulfur. If there is no copper, only {fraction (1/16)} of the sulfur is dissolved, i.e. 6.25% as compared to the ⅙, or 16.7%, of the prior art process. In practice this difference is significant, and it can be used for preventing the so-called sulfate swelling that occurs in the processes.
Although the description above refers to sulfidic matte, said matte generally also contains some metal phase, i.e. the amount of sulfur is insufficient in comparison with the given nickel and copper sulfide quantities. It has turned out that also the metal contained in the matte participates in the reactions as follows (Me═Ni, Co, Fe, Cu):
Ni
3
S
2
+3Me+18CuSO
4
15NiSO
4
+2Cu
9
S
5
+3MeSO
4
(9)
This again means that if {fraction (3/18)} (16.7 mole-%) of the metals contained in the matte are present as a metal phase, copper-free matte can be leached without oxidizing the sulfur. Among the important reactions of the present invention, let us also point out the reactions given below, where the digenite produced earlier is used as a neutralizing agent, said reactions taking place at the oxidation stage of the process:
CuSO
4
+Cu
9
S5+O
2
+H
2
O
Cu
3
(OH)
4
SO
4
+CU
7
S
5
(10)
FeSO
4
+Cu
9
S
5
+O
2
+H
2
O
Cu
3
(OH)
4
SO
4
+Fe(OH)
3
+Cu
6
S
5
(11)
Cu
9
S
5
+x
H
2
SO
4
+x
/2 O
2
Cu
9-x
S
5
+x
CuSO
4
+x
H
2
O (12)
In an autoclave, these reactions are very rapid already at temperatures below 100° C., and their proceeding is mainly dependent on the feeding of oxygen. Thus the degree of the reaction can be adjusted by adjusting the amount of oxygen. These reactions do not oxidize sulfur into sulfates. By means of the acid, the basic sulfate, antleri
King Roy V.
McGuthry-Banks Tima
Morgan & Finnegan , LLP
Oyj Outokumpu
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