AP617A

AP617A - Recovery of metal values from slags in an open arc D.C. furnace.

Info

Publication number: AP617A
Application number: APAP/P/1995/000748A
Authority: AP
Inventors: Derek Alan Hayman; Glen Michael Denton
Original assignee: Mintek
Priority date: 1994-06-10
Filing date: 1995-06-07
Publication date: 1997-10-10
Also published as: AU2055395A; ZA954458B; AU697503B2; AP9500748A0

Abstract

A process is provided for the recovery of metal values from slag emanating from a matte production

Description

THE RECOVERY OP METAL VALUES PROM SLAGS

FIELD OP THE INVENTION

This invention relates to the recovery of metal values from slags, and, more particularly, from slags which are produced in matte production processes, such as those produced in the treatment of a concentrate for the recovery of nickel and copper therefrom. Still more particularly, but not exclusively, the invention is concerned with the recovery of cobalt from slags produced in matte production processes. This includes both the slag product in the production of a green

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! matte, and the converter slags produced in the ΐ subsequent treatment of a green matte to produce a white matte.

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BACKGROUND TO THE INVENTION

Sulphide mattes are produced in many different metal 5 recovery processes and, most particularly, in the production of nickel and copper from flotation or other concentrates containing same.

Generally, a green matte is firstly produced. The slag from the production of such green matte is often discarded. There are thus vast quantities of such slags in dumps at certain plants.

The green a white converter matte matte slag.

is then blown in a converter to produce and another slag, herein termed the

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Both slags, but in particular the converter slag, often contain a significant quantity of cobalt, in addition to certain amounts of copper, nickel and, usually, significant proportions of iron.

The converter slag is usually recycled to the furnace in which the green matte is produced and some of the metal values contained therein are recovered, whilst a substantial proportion is lost. This process also has the disadvantage that the oxides are recycled to the sulphide treatment step thereby re-mixing the sulphide and oxide cycles.

OBJECT OF THE INVENTION

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It is the object of this invention to provide for the improved recovery of metal values contained in slags emanating from matte production processes and, in particular, but not exclusively, from a converter slag.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a process for the recovery of metal values from a slag emanating from a matte production process comprising sub-dividing the slag, or using it in an already molten state, and treating it in a furnace with carbonaceous reductant to form a metal phase and a slag phase,

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- > recovering the metal phase, and treating it for the recovery of any desired metal values therein.

Further features of the invention provide for the slag to be a converter slag produced in a nickel and copper recovery process during blowing of a green matte to produce a white matte; for the amount of carbonaceous reductant employed to be less than the stoichiometric amount required to reduce all metal oxides in the slag to metal and, more particularly, for the amount of carbonaceous reductant to be chosen so as to limit the reduction of iron oxides present in the slag to thereby enhance the proportion of other metal values, in particular cobalt and, most particularly, for the amount of carbonaceous reductant employed to be from 30% to 60% of said stoichiometric amount; for the reduction to take place at a temperature of at least 1400°C and preferably 1500 - 1600°C; for the carbonaceous reductant and slag to be either fed simultaneously to the furnace or, more preferably, for the slag to be pre-melted prior to feeding of the carbonaceous reductant to the furnace; and for the reduction to take place in an open arc furnace of the type in which the molten metal bath in the furnace forms

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ΚΓ .

part of the electrical circuit of the furnace and the other electrode is positioned above such bath.

The invention still further provides for the metal produced in the reduction process to be leached, conveniently with spent electrolyte from a copper or nickel electrowinning process; and for iron to be precipitated out of the resultant leach solution by decreasing the pH appropriately. The cobalt, copper and nickel can then be separated from each other and recovered using any suitable hydro-metallurgical process.

The invention also provides a matte production process in which a green or a white matte is produced in a smelter and the resultant slag is treated by a process defined above.

In order to test the invention, various experiments were carried out and, in order that the invention may be more fully understood, certain of such experiments will be described below.

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DETAILED DISCUSSION OP THE INVENTION AND EXPERIMENTAL TEST RESULTS

In experimental tests conducted in order to initially demonstrate operation of the invention, a converter slag sample, which had certain inclusions of matte therein, was treated according to the invention. The slag and matte had the following compositions:

ANALYSIS OF THE RAW MATERIALS

Analyses (mass %)
	Co	Cu	Ni	Fe#	Si02	MaO	A1203	CaO	s
Slaa	0.8- 1.1	0.35- 0.45	1.ΟΙ.2	48.5	30.4	0.5	0.3	<0.1
Matte	1.75	13.2	47.4	8.5	-	-	-	-	24.4

#Total iron

The carbonaceous reductant was a sub-divided coal which had the following analysis:

COAL ANALYSIS

	Proximate analysis
15	Moisture, %	0.8
	Volatiles, %	25.0
	Ash, %	11.9
	Fixed carbon, % tbv diff.)	62.3
	Ash analysis
20	Total silica, as Si02 %	42.6
	Aluminium, as A1203 %	26.7
	Total iron, as Fe203 %	15.3
	Calcium, as CaO %	6.27
	Magnesium, as MgO %	0.25
25	Sulphur	2.3
	Total	102.3

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The tests were conduct τά in a 200kVA open arc furnace which employed the molten bath as the anode, and a single, elevated electrode with feeding being effected from the top of the furnace. In order to commence operation of the furnace an 8 hour warm up period was employed during 10kg of converter matte and 80kg of converter slag were melted down. At the end of the warm up period the heel material was tapped, after which a number of batches of converter slag and reductants were treated with different parameters and the following results were achieved. For this purpose as much of the matte as was reasonably possible was removed from the slag by hand.

Operating at a total power of lOOkW (made up of a heat loss estimate of 55kW and a specific energy requirement of 0.15kWh/kg of feed) and an operating temperature of 1509°C an alloy was produced having an

analysis	of
4,62%	cobalt
6,74%	copper
28,55%	nickel,
44,27%	iron.

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The slag, on the other hand, contained 0,28% cobalt

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0,^3% copper, and

0,40% nickel

Feeding of the slag	and reductant were carried out
simultaneously	and	the	amount	of	carbonaceous
reductant used	was	6% by	weight	of	the converter

slag, i.e. 34,3% of the stoichiometric amount which would have been required to reduce all the metal oxides present in the slag.

In a second series of tests in which the coal addition was increased to 8% (45,7% of stoichiometric) and the specific energy requirement raised to approximately 0,55kWh/kg of feed, the average tapping temperature was 1489°C.

The alloy produced had a composition of

cobalt	4,23%,
copper	5,74%,
nickel	24,52%, and,
iron	50,86%.
The slag	contained
cobalt	0,23%
copper	0,36%, and,
nickel	0,31% respectively

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It is to be noted that the increase in reductant resulted in an increased dilution by the iron.

In a subsequent series of tests 6% coal (34,3% of stoichiometric) was added only after the slag addition had been melted down over a period of a half an hour. The tapping temperature was 1465°C and the alloy produced had a composition of

5, 18%	cobalt,
7,91%	copper,
34,17%	nickel, and,
35,61%	iron.
The slag	contained
0,29%	cobalt
0,35%	copper, and
0,33%	nickel.
A still	further series
of the	coal and,
temperature was even
produced	contained
5,52%	cobalt,
8,34%	copper,
34,9%	nickel, and,
36,01%	iron

of tests employed 8% by weight
in	this	case,	the tapping
lower at	1412°C.	The alloy

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The sl-'g contained

cobalt	0,25%
copper	0,30%, and,
nickel	0,17%.

Larger scale tests were then carried out in a 500kW

open arc DC	furnace	. In all	cases	these runs	were
carried by	melting	the slag	first	and adding	the
carbonaceous	reductant to	the	molten	slag
subsequently	. The	reason for	this	is that it is

envisaged that in practice, molten slag from a matte production process will immediately be treated according to the invention while still in its molten, or at least hot, state.

In each case, accordingly, the sub-divided solid slag was firstly fed to a molten bath in the preheated furnace at a rate automatically controlled to ensure that the feed and energy inputs were balanced and to provide a constant temperature of operation. After the batch of slag had been added to the furnace the sub-divided coal was then added over a period of time under similar conditions.

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In this case the slag ha an average composition of

	0,93 mass percent Co; 0,49 mass percent	Cu;	1,47
	mass percent Ni; 50,8 mass percent Fe;	29,2	mass
	percent SiO₂; 0,18 mass percent CaO;	0,22	mass
5	percent MgO; 0,4 mass percent Al₂O₃; and	1,07	mass

percent S.

The coal analysis, on average, had a moisture content of 0,2 mass percent; 26,2 mass percent volatiles; 11,35 mass percent ash; and 62,45 mass percent fixed carbon.

Runs were carried out under five different conditions and the results, on the basis of cobalt recovery, are set out below in Tables 1(a) and 1(b).

MAIN FACTORS AFFECTING COBALT RECOVERY - TABLE 1(a)

CONDITION	BATCH MASS (kg)	MASS COAL BY WEIGHT	%0f STOICHIOMETRIC	COBALT RECOVERY
1	500	8	43.5	75.0
2	500	9	49.0	71.3
3	500	11	59.9	69.5
4	1000	11	59.9	81.8
5	1000	9	49.0	86.1

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MAIN FACTORS AFFECTING COBALT RECOVERY - TABLE 1(b)

CONDITION	MELT DURATION (min)	REDUCTION DURATION (min)	TOTAL TIME (min)	MELT TEMP •c	TAP TEMP •c
1	124.0	91.1	215.1	1520	1495
2	652	86.2	151.9	1528	1514
3	60.6	852	145.8	1498	1454
4	141.0	144.0	298.3	1543	1314
5	1152	150.5	266.0	1407	1375

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It will be noted that coal additions of at least 9% (49,0% of 10 stoichiometric) gave cobalt recoveries of greater than 80% under suitable conditions.

It will be understood that numerous different parameters and operating conditions may be used without departing from the scope of the invention. Also, the invention is not limited to 15 the recovery of metals identified above. Also, the slag may be a slag produced in the green matte production furnace.

Claims

1. A process for the recovery of metal values from a slag emanating from a matte production process comprising sub-dividing the slag, or using it in an already molten state, and treating it in a

5 furnace with carbonaceous reductant to form a metal phase and a slag phase, recovering the metal phase, and treating it for the recovery of any desired metal values therein.

2. A process as claimed in claim 1 in which the

10 slag is a converter slag produced in a nickel and copper recovery process during blowing of a green matte to produce a white matte.

A process as claimed in either of claims 1 or 2 in which the amount of carbonaceous reductant employed is less than the stoichiometric amount required to reduce all metal oxides in the slag to metal.

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4. A process as claimed in claim 3 in which the ί amount of carbonaceous reductant is from 30% to i

ί 60% of said stoichiometric amount.

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5. A process as claimed in any one of the preceding

5 claims in which the reduction takes place at a

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I temperature of at least 1400°C.

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6. A process as claimed in claim 5 in which the said temperature is from 1500°C to 1600°C.

7. A process as claimed in any one of the preceding 10 claims in which the carbonaceous reductant and slag are fed simultaneously to the furnace.

8. A process as claimed in any one of claims 1 to 6 in which the carbonaceous reductant is fed to the furnace subsequent to the slag being premelted

15 therein.

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9. A process as claimed in any one of claims 1 to 8 in which the reduction is carried out in an arc furnace of the type in which a molten metal bath forms part of the electrical circuit of the

10.

11.

10 12.

15 13.

AP.00617 furnace and the other electrode is positioned above such bath.

A process as claimed in any one of the preceding claims in which the metal produced in the reduction process is leached followed by decreasing of the pH to precipitate iron.

A process as claimed in claim 10 in which leaching is effected using spent electrolyte from a copper or metal electrowinning process.

A composite process comprising a matte production process in which either white or green matte is produced in a smelter and the resultant slag is treated by a process as claimed in any one of claims 1 to 11.

A process for the recovery of metal values from a slag substantially as herein described and exemplified.