Separation of minerals

Details Separation of minerals Separation of minerals

1998-06-30

2001-01-09

Lithgow, Thomas M. (Department: 1724)

Classifying, separating, and assorting solids

Fluid suspension

Liquid

C209S167000

Reexamination Certificate

active

06170669

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to beneficiation of ores and, more particularly, to a process for enhancing the floatability of iron-bearing sulphides while leaving other sulphides and non-sulphides unfloatable.
BACKGROUND OF THE INVENTION
In many parts of the world, valuable metals such as gold, nickel and platinum group metals (PGM's) occur in iron-bearing sulphides such as pentlandite, pyrrhotite and arsenopyrite. These minerals are recovered selectively from the ores by flotation. While flotation is a remarkably efficient process, one of its most significant limitations for iron-bearing sulphides is that fine particles are not recovered efficiently and a great deal of fine valuable sulphides are lost to the tailings. For example, for pentlandite which is a nickel-iron sulphide it is not unusual for as much as half the nickel which fails to float in a nickel concentrator to be less than 10 &mgr;m in size. The improvement of fine particle recovery has been the subject of a great deal of research, much of which has focussed on the use of different types of flotation cells such as column cells.
OBJECT AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for improving the recovery of metal values preferably contained in ores having a fine particle size.
It has now been found that a major reason iron-bearing sulphides float poorly at fine sizes is that their surfaces are oxidised and to a large extent covered by an iron hydroxide film which renders them poorly floatable with conventional sulphide flotation reagents. It is the applicants opinion that these iron hydroxide films present in iron-bearing sulphide systems consist of ferric hydroxide. A process has been devised by the applicants that strips this surface film for a time sufficient to allow collectors to adsorb. Surprisingly the method is efficient at the pH values typically used in sulphide flotation (pH 7 to 10), a result which would not be predicted by current knowledge. The process involves a complex series of reactions each with different kinetics and it is an understanding of these kinetics that permits the improved separations.
Accordingly, the invention provides a flotation process for the separation of iron-bearing sulphide containing ores including the steps of
(a) conditioning an aqueous pulp of iron-bearing sulphide containing ores with an oxy-sulphur compound said pulp having a pH of between about 7 and about 10, to a level to modify an iron hydroxide film on the surface of said iron-bearing sulphides in said ores
(b) adding a collector to said conditioned aqueous pulp,
(c) raising the pulp potential to a level sufficient for the collector to adsorb onto the surface of the sulphide ore,
(d) bubbling gas through said aqueous pulp and thereby subjecting the aqueous pulp to froth flotation to produce a froth containing said sulphide containing ores, and
(e) recovering said froth to obtain a concentrate relatively rich in the sulphide containing ores.
The process of the invention is particularly useful in recovering metal values contained in metal bearing iron sulphide mineral ores in a size fraction which is below a critical particle size where conventional floatability decreases. Ores having a particle size below such a critical size usually constitute the tailings of conventional primary flotation processes.
As would be appreciated by those skilled in the art, the critical size is system dependant and will generally vary greatly depending on the assay of the mineral ores being processed and the type and quantity of collectors used.
The process of the invention is particularly useful for recovering metal values from sulphide ores in which the ore particles have metal bearing iron sulphide mineral inclusions preferably less than 20 &mgr;m in size and most preferably less than 10 &mgr;m, these being the typical size found in the tailings of a primary separation. The process of the invention may be used for floating particles having such inclusions, the size of the ore particles being as much as 130 &mgr;m.
To modify the iron hydroxide film on the surface of the metal sulphides to enable a collector to adsorb onto the surface thereof, it is preferable that the reducing agent condition the pulp to a pulp potential, E
h
in accordance with the following formulae within a practical period of time:
E
h
=0.271−0.059pH*
where pH* is the pH of the conditioned pulp,
and E
h
is the pulp potential (Standard Hydrogen Electrode) (SHE) in Volts.
It is preferable for the E
h
to reach this level within a practical limit of 10 minutes.
There are very few reducing agents which are able to reduce the pulp potential below the required level to modify the ferric hydroxide film on the surface of the metal sulphide minerals within a practical time limit.
The preferred reducing agents capable of reducing the pulp potential below the required level are oxy-sulphur compounds which dissociate in the aqueous media to form oxy-sulphur ions having the general formulae:
S
n
O
y
z−
where n is greater than 1; y is greater than 2; and z is the valance of the ion.
The oxy-sulphur compound is preferably dithionite which both brings about the necessary reducing conditions and reacts with the iron hydroxide films. Other combinations of reducing reagents which may include oxy-sulphur compounds that reduce the ferric hydroxide film may be used.
Once the pulp has been conditioned with sufficient collector to float the sulphides, the pulp potential is then raised to cause the collector to adsorb onto the iron-bearing sulphides thereby rendering these sulphides strongly floatable. However the effect may not be sustained for any extended period of time because the ferric hydroxide films reform under the oxidising conditions needed for sulphide flotation. Nevertheless, by arranging the flotation equipment appropriately, and repeating the process if necessary, a great deal of additional fine valuable sulphide mineral can be recovered.


REFERENCES:
patent: 5372726 (1994-12-01), Straten
patent: 5411148 (1995-05-01), Kelebek et al.
patent: 5439115 (1995-08-01), Beyzavi
patent: 38199/85 (1985-08-01), None
patent: 69283/87 (1990-02-01), None
patent: 24911-92 (1995-08-01), None
patent: 2151316 (1996-12-01), None
patent: 96/01150 (1996-01-01), None

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