PURIFICATION OF ZINC MATERIALS

PURIFICATION DE MATIERES ZINCIQUES

English Abstract

Disclosed herein is a process for removing at least a portion of a manganese
constituent
from a zinc-bearing material, comprising the step of subjecting the material
to a first oxidation
mixture of SO2 and oxygen, at conditions sufficient to oxidize the manganese
constituent.

Claims

CLAIMS
1. A process for removing al least a portion of a manganese constituent from a
zinc-bearing
material, comprising the step of subjecting said material to a first oxidation
mixture of
SO2 and oxygen, at conditions sufficient to oxidize said manganese
constituent.
2. A process as defined in claim 1 wherein the material is maintained al a pH
sufficient to
precipitate manganese while minimizing precipitation of said zinc constituent.
3. A process as defined in claim 2 wherein said pH is between about 3 and
about 5.
4. A process as defined in claim 3 wherein said pH is between 3 and 4.
5. A process as defined in claim 4 wherein said pH is 3.
6. A process as defined in claim 1 wherein said oxygen is in the form of O2.
7. A process as defined in claim 6 wherein said oxidation mixture includes
Air,
8. A process as defined in claim 7 wherein steps (a) and (c) occur at a
temperature ranging
from about 40 to about 80°C.
9. A process as defined in claim 8 wherein steps (a) and (c) occur at a
temperature ranging
from 50 to 80°C.
10. A process as defined in claim 9 wherein steps (a) and (c) occur at a
temperature ranging
from 58 to 78°C.
11. A process as defined in claim 10 wherein steps (a) and (c) occur at about
70°C.
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12. A process as defined in claim 10 wherein steps (a) and (c) occur at about
60°C.
13. A process as defined in claim 6 wherein said SO2 is at a concentration
from 0.5% to 10%,
with the balance O2 gas.
14. A process as defined in claim 13 wherein said SO2 is at a concentration
from 1 to 8%.
15. A process as defined in claim 14 wherein SO2 is at a concentration from 2
to 3%
16. A process as defined in claim 7 wherein SO2 is at a concentration from
0.1% to 2%, with
the balance being Air.
17. A process as defined in claim 16 wherein said SO2 is at a concentration
from 0.2 to 1.4%.
18. A process as defined in claim 17 wherein SO2 is at a concentration from
0.4 to 0.6%.
19. A process as defined in claim 1 wherein said zinc bearing material is a
leach solution.
20. A process as defined in claim 1 wherein said zinc material is an
electrolyte solution.
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Description

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BACKCrROUND OF THE ThTVENT10N
1, FIELD OF THE ~TTVENT1;ON
The present invention relates to the pwification of zino-bearing materials,
more
particularly but not necessarily exclusively to zinc-bearing aqueous
solutions.
2. DESCRIPTION OF THE RELATED ART
Some zinc (Zn) ores, for example sphalerite, contain high levels of manganese
(Mn) that
cannot be separated using conventional mineral processing techniques, since
the Mn is present in
the crystal lattice. When Zn sulphides containing Mn impurities are roasted
and then leached,
they can, in some cases, produce leach solutions or electrolyte solutions
containing unreasonably
high levels of Mn.
Although some relatively small amounts of Mn are generally acceptable iz~ a Zn
electrolyte, for example, excessive quantities can create problems, since the
Mn is oxidized at the
anode in the form of Mn0 2, some of which falls at the bottom of the cell and
must be periodically
removed. Crreater concentrations of MnOZ can lead to significant reductions in
electrolytic
eff ciency,
It is generally known in the prior art that precipitating zinc and manganese
together, using
sodium carbonate or lime as naturalizing agent, can be carried out at
70°C and at pH values
between 5 and 7, However, in this case, zinc begins to precipitate before
manganese and
therefore most of the zinc would be precipitated with manganese which is
obviously not
acceptable, as shown in figure 1.
Another solution proposed by the prior art is to oxidize MnZ' to Mn~' so that
lvlnOz can
be removed by precipitation at a pH whcz'e ZnZ'" is soluble. Air and oxygen
gas are typically used
as oxidants in this case but they are generally uneconomically slow. Peroxide
or stronger
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oxidants, such as Caro's acid or ozone, are in many cases too expensive.
US Patent 2,816,819 to Wallis et al. discloses a system which uses S02/A.ir to
precipitate
iron from a cobalt- or a nickel-bearing solution. Canadian Patent 935,650
discloses a technique by
which a mixture of SOZIAir is used to precipitate a number of impurities from
a cobalt or a. nickel
solution. However, neither reference is concerned with techniques for reducing
impurities from
Zn-bearing materials.
Xt is an object of the present invention to provide an improved method to
remove at least a
portion of Mn from Zn-bearing materials.
SCY OF THE INVENTION
Briefly stated, the invention involves a process for removing at least a
portion of a
manganese constituent from a zino-bearing material, comprising the step of
subjecting the
material to mixture of SO,, and oxygen, at conditions sufficient to oxidize
the manganese
constituent.
Preferably, the material is maintained at a pH sufficient to precipitate
manganese while
minimizing precipitation of the zinc constituent.
BRIEF DESCR7rTION OF THE DItA'1~VINGS
Several preferred embodiments of the present invention will now be described,
by way of
example only, with reference to the appended drawing in which:
Fibure 1 is a plot of precipitation for Mn and Zn according to pH;
Figure 1 is a plot of precipitation using SOz/OZ mixture as an oxidant;
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DESC~tIPTION OF THE P~tEFERRED EME30D1MENTS
Briefly stated, the invention involves a process for removing at least a
portion of a
manganese constituent from a zinc-bearing material, comprising the step of
subjecting the
material to mixture of SOZ and oxygen, at conditions sufficient to oxidize the
manganese
comtituent.
Preferably, the material is maintained at a pI~ sufficient to precipitate
manganese while
minimizing precipitation of the zinc constituent.
Preferably, the process is carried out at a pH between about 3 and about 5,
more
preferably between 3 and 4. Still more preferably, the pH is 3.
If the p~ is higher than 5, for example up to 7, at least some residual Zn may
be
precipitated with the Mn. The hi;her the pH in this range, the greater the
quantity of Zn being
precipitated with Mn. In this case, it may be feasible either to process the
Mn subsequently with
the residual Zn in place or alternatively to subject the co-precipitate to a
mildly acidic solution
(such as at a pH of 3 to 4) to re-dissolve the residual zinc.
The pH limit of 4 is significant because, as the following examples
illustrate, residual Zn
has been found to appear in the precipitate at a pH value above 4 while there
appears to be no Zn
co-precipitate at pI-i values below 4. Therefore, it may be desirable, in some
circumstances, to
maintain the reaction at the lower end of the pH range, that is in the
vicinity of pH 3 in order to
minimize the likelihood of a Zn co-precipitate. This route may also be
enhanced by maintaining a
distribution of nucleation sites in the reaction, such as MnOz crystals.
The oxygen may be in the form of Oz or air or a mixture of both.
Preferably, the process occurs at a temperature ranging from about 40 to about
80°C,
.,
_,_
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more preferably at a temperature ranging from 50 to 80°C, still more
preferably at a temperature
ranging from SS to 78°C. For example, the process may be carried out at
about 70°C or,
alternatively, at abom 60°C.
It may also be desirable, in some cases, to raise the temperature above
80°C, for example
to an upper limit of about 130°C or higher in order to increase the
reaction kinetics of the process,
though this would need to be done under pressure, depending on the chosen
temperature. For
example, a temperature of 130°C would require a pressure of about 50
psi.
Preferably, in the case where the oxygen is present in the form of O~ gas, the
S02 is at a
concentration from about 0.5% to 10%, with the balance Oz gas, more preferably
from 1 to 8%,
still more preferably at a concentration from 2 to 3%.
In the case where the oxygen is present in air, the SO, is preferably ac a
concentration
ranging from about 0.1% to 2%, with the balance being Air, mere preferably
from about 0.2 to
1.4%, still more preferably from about 0.4 to 0.6%. For example, the
concentration may be about
0.5%.
The zinc material may be in a number of forms including an aqueous solution,
such as a
leach solution or an electrolyte solution.
The present process is beneficial in that it makes use of a relatively
inexpensive and
plentiful oxidant, a gas mixtwe of OZ/S02, or alternatively Air/SOz, or still
alternatively 100%
pure Air can be used together with equivalent amounts of 502, preferably added
as S02 in a
gaseous or liquid form, or added as a constituent in a solution containing,
for example, sodium
metabisulphite, ammonium metabisulphite, potassium metabisulphite or other
suitable forms of
metabisulphite.
Embodiments of the present invention will be described with reference to the
following
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Examples which are presented for illustrative purposes only and are not
intended to limit the
scope of the invention.
EXAMPLE 1
A, solution containing 5 g/~. Mn as MnSOa was sparged with a mixture of S02
and OZ at
different pH levels. The amount of Mn removed at each pH is shown in figure 2.
A comparison can be made between the precipitation of pH's of manganese
oxidized with
S0~10z as shown in figure 2 with the precipitation of zinc as shown in figure
1. The Mn is
removed from solution at pH levels ranging from about 3 to 5, However, in the
region from
about 3 to 4, the Mn is removed from solution while the Zn is soluble and
therefore remains in
solution.
LXAMpLE 2
A solution containing 18 g~. Mn as MnSOd was sparged at 60°C and at a
pH of 6.5 with
SOz/OZ mixtures containing 2% (v/v) SO2. After one hour, 25% of the manganese
had
precipitated. After 2 hours, 57% of the Mn had precipitated and after 4 hours,
99.5% of the Mn
had precipitated.
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Representative Drawing