Note: Descriptions are shown in the official language in which they were submitted.
~U8938Z
,
~ .
. .
THIS INVENTION relates to a process for the oxidation
of ferrous salt solutions and to the use of the oxidised ,
~; solutions in the leaching of minerals.
~1 We have recently discovered that ferrous sulphate
solution can be oxidixed continuously to ferric sulphate
, - solution, in a vessel containing smooth spaced-apart plates or
tubes therein with the bacteria coated on the plates or tubes,
- if the solution is passed continuously between the surfaces of
¦ the plates or tubes.
`!
` 10 We have now found that the process is improved in a
surprising manner (which makes it suitable for commercial
. -i ,
--2--
. -. . .-
.: .. - . : ~ . . - ..
.. .. : . . ..
.
- . - . . :
, ....... . , : . :
1~)8938Z
exploitation) i. ferrous sulphate solution is oxidised
bacterially in the vessel containing acidified sulphuric acid
and also containing a structure which is honeycomed witn
passa~es capable of supporting a film of bacteria thereon.
The present invention provides a process for the
oxidation of a ferrous salt solution, which comprises passing
the ferrous salt solution in the presence of oxygen and at an
acid pH through a vessel containing a bacterial supporting
structure which is honeycombed with passages, the surfaces of
the passages having a bacterial oxidising agent present as a
film thereon, and the passages being of a size to permit the
movement of the solution therethrough, said bacterial oxidising
agent be~n~ capable of oxidising ferrous ions to ferric ions.
'
The term 'bacterial supporting structure which is
honeycombed with passages' means any structure containing a
large plurality ~ie more than 10) passages therethrough and on
.,
'r the walls of which a film of bacteria can be supported.
. Conveniently, there may be considerably more, eg 50 or more
` preferably a hundred or more, passages. The structure may be a
.1, . . . .
~' 20 preformed artificial structure and may contain tortuous
,. passages.
The structure may be a unitary structure comprising
a plurality of plates haviny relief formations projecting
outwardly from one or both sides thereof. The relief
t 25 formations may be permanently attached to a further adjacent
'~ plate. The relief formations may be corrugations projecting
.
-
. -, - : . - . ~ - :., ~ : . . ~ :
. . -
3~3Z
out~lardly from one or both sides of the plates. The corru-
gations may be substantially waveform in plan view so that the
passages are tortuous. The corrugations may be of substanti-
ally triangular or hemispherical cross-section. In one
embodiment, the str~cture may resemble a honeycomb in appear-
ance. The ferrous salt solution may be ferrous sulphate, eg a
solution which is used in the mining industry or in steel plant
pickling liquors. The oxidation process can be carried out
continuously by passing a moving stream of the solution over a
submerged structure which is honeycombed with passages. In
this way a fast rate of oxidation can be obtained. The product -
~obtained, when ferrous sulphate is oxidised may be used for
leaching minerals eg for extractive metallurgy or for removing
sulphur from coal.
The invention al50 provides a process for treating
mineral materials which comprises leaching the mineral with a
ferric salt solution obtained by the oxidation process of the '
invention.
~ ' ' ' ' .
Any suitable bacteria that will oxidise ferrous ions
-~ 20 to ferric ions may be used. For example, bacteria of the genus
thiobacillus ferrooxidans, thiobacillus thiooxidans, ferro-
-, bacillus ferrooxidans or ferrobacillus sulphooxidans may be
5 ~ . used to oxidise ferrous sulphate. The reaction proceeds
'~ according to the following equation:-
.~ . , . ' ' .
,~ 25 4FeSO4 + 2H2S04 + 2 Bacteria-~ 2Fe2~504)3 + 2H20.
f
.. ; . .
: -4-
` :. '. . , ' . .':
., , -, ~ '. . . : ' . : .
: . - - ~: , .: -
1~893~32
The equation shows that sulphuric acid is
required for c~nversion of ferrous sulphate to ferric sulphate,
and that the amount of ferrous sulphate governs the acid
re~uirement. The acid may be sulphuric acid on its own or may,
for eY~ample, be sulphuric acid mixed with another suitable
acid, eg hydrochloric acid in amounts up to about 10~ by
weight. To achieve oxidation of high concentrations of fer~ous
sulphate, equivalent high concentrations of sulphuric acid
optionally containing other acids, should be used. The
bacteria is sensitive to acidity and the pH conveniently is in
the range 0,8 to 2,5 more preferably 1,3 to 2. A pH of about
1,5 is particularly preferred for oxidising ferrous sulphate to
ferric sulphate.
.
We have found it convenient continuously to pass a
small volume of ~cldified ferrous sulphate solution into a
large volume of an iron sulphate solution, mainly comprising
acidified ferric sulphate but which may also contain other
! substances (for example ferrous and ferric chloride and
hydrochloric acid) and the bacteria, and in which the structure
. .
which is honeycombed with passages is submerged. The walls of
'~ the structure are coated with the film of bacteria. By having
a large volume comprising mainly acidified ferric sulphate,
dilution of the bacteria, and the pH of the solution, are not
unduly affected. The bacteria film is a surface film and is
continuously being destroyed and reformed over the large
surface area of the honeycomb or passages of the structure.
Thus the process can be carried out continuously.
~ --5
.
. . . . . .. . - ..
. - . . . . .
' . '; . ' - :
1~938;2
The structure may be of any suitable material having
passages therethrough and along which the solution may pass.
The distance apart of opposite sides of the walls of the
passages in the structure is sufficiently wide to enable the
.
solution containing entrained o~ygen contin~ously to pass
therethrough without being blocked by bacterial oxidising
agent. Experimentation has shownlthat the bacterial layer
generally is about 1 mm thick, so that a the passage walls
should be greater than 2 mm apart and conveniently between
- 10 about 3,5 and 10 mm apart. It is convenient to have the
maximum possible surface area available for the bacteria to
grow on. The surfaces of the structure may be of a plastics
material which is inert to the iron salts and to the acid. A
very suitable substantially rigid structure is the material
known by the Trade Mark 'Flocor' and sold by Imperial Chemical
Industries Ltd. 'Flocor' is a high void space and llght weight
` structure of polyvinyl chloride. It appears to be resistant to
; degredation by bacteria and acids under the reaction conditions
used. 'Floror' comprises a plurality of parallel planar plates
separated by and joined to a plurality of corrugated plates,
the corrugations being of waveform appearance in plan view and
` having transverse ribs. With this invention, there are not
base structures such as sand or rocks which could cement
-~ together, and hence the passages are not blocked. The process
~- 25 can therefore be carried out continuously. The plastics
structure may be totally submerged in the reaction vessel.
, '
~' :
,~ .
.,
. . .
.
- . ~ : . - . ~ . : . .
`, ' :
38;~:
The solution of the ferric salt can contain trace
elements or other materials to assist bacterial growth. Trace
elements or other materials to assist bacterial growth may be
traces of one or more of ammonium, nitrate, potassium, calcium,
magnesium, phosphae and chloride ions. ~ mixture of iron
sulphates, sulphuric acid, trace elements and bacteria can be
saturated with oxygen and passed over the film of bacteria
grown on the passage walls of the structure. The bacterial
film may also be present on the surfaces of the vessel con-
taining the structure. Once grown, the film can be self re-
generating to provide the oxidising surfaces for an apparently
indefinite period. The vessel in which the bacterial oxidation
takes place may be enclosed or jacketed to maintain it at an
optimum temperature in the range - 10 to 45C, preferably 30 to
35C. Oxygen saturation of the solution can be achieved by
lS introducinq air or oxygen into the solution using any suitable
type of submerged sparging, eg through a pipe, using a
mechanical aerator, or through a fritted disc. It appears that
; the rate of oxidation is directly proportional to the available
i surface area of the honeycomb. The air in contact with the
, ... ..
solution may be enriched with either or both pure oxygen and
carbon dioxide.
¦ The vessel containing the structure may be an
i elongated vessel, which conveniently is vertical. The ferrous
. t
salt to be oxidised may be introduced at the top, while air is
introduced from the bottom.
:l
` '
.
.
,
'', ''' ~' ' '~ '.
, , ~
;
8~38Z
. .
Ferric sulphate solution obtained by the process is
suitable as a leach liquor for use as a lixivant of minerals.
Thus, it can be used to treat coal to remove sulphur therefrom,
or can be used to obtain metals from their ores or from dumps
or the like. For extractive metaliurgy, where bacterial action
is used and the leach solution containing bacteria is recircu-
lated for re-use, high leach temperatures destroyed the
bacteria. With the present invention, it does not matter
unduly if the bacteria are destroyed in a high temperature
leach as, after the metal has been removed from the solution
and cooled, the present invention ls carried out under
conditions which favour reinoculation of the returned iron
sulphate solution with bacteria.
. .
-: I The ferric sulphate-containing solution can be used
lS to extract a number of metals from their ores. Examples are
` - uranium, copper, gold, lead, zinc, nickel, cobalt, molybdenum,
. j.
arsenic, antimony, cadmium, mercury, and other base metals.
~,, - ,
The ore can be leached with the ferric salt solution,
^ under the action of heating and/or stirring and/or agitation
. 20 and/or applying superatmospheric pressure, if necessary. The
~ ,. - .
desired metal can be separated from the leach liquor, and
i residual liquor may be recycled to the oxidation process of the
1-
invention for re-oxidation. Ores which may be treated can be
~! oxides, silicates, and particularly sulphides of the metal.
`- 25 Low grade, as wel~ as high grade ores can be treated. The ores
..... .
to be treated may be mine dump waste, copper-containing
.
. ,.;
~ ~ -8-
,,; .
.
~- . ; . -
,
938Z
.
silicate gangue, copper sulphides such as copper pyrites,
covellite, chalcocite, chalcopyrite, bornite (Cu5FeS5),
cubanite (CuFe2S3), enargite (Cu3AsS~), tetrahedrite (Cul2Sb4S13)
and tennantite (Cul2As4S13~; nickel sulphides and nickel
sllicate minerals SUC}l as garnierite (Ni6Si4Olo(OH)g), nickel
mattes (Ni3S2) pentlandite (Fe,Ni)gS8), millerite (NiS); cobalt
~ sulphides, arsenides or sulphur-arsenides, such as cobaltite
; (CoAsS), tetrahydrite, pyrrhotite mixtures with tetrahedrite
and/or chalcopyrite, sphalerite; copper seleniaes and tellurides,
carrollite (Co2CuS4); zinc and lead minerals such as sphalerite
~ZnS), galena (PbS), galena-sphalerite concentrates, Pb-Cu-Fe
mattes, boulangerite, (Pb5Sb4Sll), zinkenite ~Pb5Sb4S27),
jamesonite, (Pb5Fesb6Sll) and geocronite ~Pb55b2S8), iron
minerals such as pyrrhotite and pyrite (FeS2), molybdenum
minerals such as molybdenite (MoS2); arsenic and antimony
mlnerals such as orpiment (AS2S3), arsenopyrite ~FeAsS),
I ~tibnite, (Sb2S3); cadmium and mercury minerals; and uranium
,- minerals, such as uraninite or pitchblende (UO2 + x)' -
brannerite (UTi2O6), carnotite (K2(~O2)2 (UO4)23H2O), autunite
. 20 (Ca(UO2)2 (PO4) ; lOH2O) and gold slimes-
~. I , . .
-~ The ore may be milled in a first step, graded, and
~ the fine ore passed to a tank where it is mixed with water. ~he
:: ~
l aqueous mixture can be milled further and then passed to a
¦ -plurality of leach vessels. The leach vessels may be heated,
eg with steam and agitated, eg by stirring. Concentrated acid
and the ferric solution is added continuously to one or more of
the leach vessels. After passing through the leach vessels,
~ I .
_ g _
- , . :
~ . . ,. . . :
: . . . . .
.
, - . : . . . -~: . :
.
-
-
1~)8938Z
the leach liquor containing metal values is filtered and the
filtrate split into two parts. One part passes to an ion-
exchange column (from which the metal can subsequently be
s, eluted), and the barren solution is discarded. The other part
passes to a tank containing the honeycomb or other structure
. coated with a film of bacterial oxidising aqent. Oxygen or air
can be passed upwardly through the tank, and the ferric
solution obtained is recycled to the leach vessels.
~he accompanying drawings illustrate.a method of
carrying out the invention, and apparatus for use therein, in
. which drawings:
Figure 1 is a flow sheet showing a process for
~ 8eparating metals from their ores according to the lnvention;
;' ' Flgure 2 is a schematic section through a tank for
oxidising a ferrous salt; and
Figure 3 is a three-dimensional view of part of a
honeycomb for use in the tank.
, ',
Referring to Figure l,.milled ore from mill lO passes
to vessel 12 where it is mixed with water from pipe 13 and then
. 20 passed through a second mill 14. From here the slurry of ore
and water passes into a leaching vessel 16 which is in series
with further leachlng vessels 16.1 and 16.2. Each leaching
--, vessel is heated by steam from pipe 18 and contains a stirrer
~ . . 18, 18.1, 18.2.
~ . , .
: ,' ,,
,: i .
--10--
.
, ~
: :
1~)8938Z
Concentrated acid and ferric salt solution are passed
to thè first leaching vessel through piplines 20 and 22
respectively. The leached material is filtered at 24 and the
filtrate passed through pipeline 26 to point 28 where it is
split into approximately equal parts. The residue from the
filtér is sent for disposal along line 30.
,
One part of the leach solution is passed along
pipeline 32 to an ion exchanger 34 from which barren solution
s discarded along pipeline 36. The other part of the leach
solution is passed along pipeline 38 to a tank 40 containing a
submerged supporting structure 42 which is hone~combed with
passages. This tank and supporting structure are illustrated
ln greater detail in Figures 2 and 3. ~he walls 44 are of
waveform appearance and are triangular in cross-section.
' 15 The leach li~uor passing along pipellne 38 is an
- acidic solution comprising a ferrous salt possibly containing
: ~ .
, ` some ferric salt. The solution passes through passages 43 in
'~I the support, the walls 44 of which are coated on their surfaces
. ~ .
45 with a bacterial oxidising agent. Air is passed upwardly
zO through aerator 46, by means of pump 48. The solution is
oxidised by the bacteria in the presence of the air, and the
: ferric salt solution formed is recycled along the pipeline 22.
~, The metal is eluted from time to time from the exchanger 34 by
. ..
i passing eluant from pipe 50 through the exchanger and recover-
ing the metal-containing solution from plpeline 52.
~ The invention is illustrated by reference to the
l following non-limiting Examples.
.. . : . : : .:: .. , ~ - .... , : . . ... . :: , .: ::;: . ~ . . . :
. . .. , :, .... . .... . , . .,. .. ...... : : .. . ..
3~3Z
.,
. EXAM~LE l:
A cylindrical tank 3 metre high and 1,2 metre in diameter was
filled with ferrous sulphate solution. The volume of solution
was 3400 litre. A block of plastics honeycomb-like 'Flocor'
packing, 1000 mm by 1800 mm by 600 mm, of the shape illustrated
. in Figure 3, was submerged in the tank liquor. The specific
surface area was 93 M2/M3. Aeration was provided at the base
of the tank by a commercially available aerator giving 50
M /hour nominal air induction. After some weeks during which
the bacterial activity (using ferrobacillus ferrooxidans)
increased and reached a maximum the following data was
recorded:-
Temperature 32C
Feed flow rate 72 lltre/hour
Peed Ferrous 9,8 g/l
ferric 1,3 g/l
Sulphuric acid 9,0 g/l
. . Product Ferrous 0,25 g/l
Ferric l0,5 g/l
~:? 20 Sulphuric acid 0,88 g/l
H 1,5
. . Oxidation Rate 688 gram/hour
;' Surface area 100 M?
:~ . 2
;~ . Specific Rate . 6,88 gram/M /hour
: ' .
..
i'j
'
., . ' , ' , ' ' ,' . . .' ~ . -, , . -::
-: ... , .. . . .. : . . , - -
.. :. . . : .. . . ~ : :
- . . .. . . .
., . :.
, : .. . . - -
:.... .. : .. .-: . , :
- . . .:
: . , .:, - ,, . - :
)8~33~Z
The distance apart of the pas~age walls in the
honeycomb was about 4 mm.
l'he ferric iron/bacteria solution obtained was
added to an ore containing a useful mineral and pyxites
using the flow scheme shown in Figure 1. The ore ~tas
acidified with sulphuric acid ~o destroy any residual alka-
linity. ~-
;:
EXAMPLE 2: (Comparison Example)
Various other ways of oxidising ferrous sulphate were carried
out for comparison purposes, as explained below. The apparatus
used were:
1. A plate and spraY unit
! , . In this apparatus, ferrous sulphate solution was
I sprayed over the top of a plurality of plates coated with
~t lS bacteria, and the ferric sulphate was collected at the
;l bottom.
i 2. A bio-disc unit
:
; In this apparatus, a spindle, having a plurality
of bacteria-coated discs attached thereto, was rotated with
the discs ln the iron sulphate solution, fresh ferrous
~; sulphate solution being fed in from one end.
.~ , .
~ .
l~ 3. A filter-pack unit
In this apparatus, ferrous sulphate solution was
~i; passed downwardly through a tower packed with rings and
`'¦ 25 which were coated with bacteria. --
-13-
. . . . .
.. ...... . . . .
.. . . -, - - . . , ~ .
, . . , - -
. .
, . .:
1~)l3931~Z
.
4. A submerged honevcombed unit
In this apparatus (see the accompanying drawing)
ferrous sulphate was passed into an iron sulphate solution
containing an insert as illustrated in Figure 3 of the drawings
and coated with bacteria. Air was passed upwardly. This
treatment is referred to as 'Bacfox' treatment.
In each case, thiobacil]us ferrooxidans was used.
~he ferric sulphate was used to leach milled ore. In each
case, the following were used.
Solution treated 66560 tons/month
Ferrous iron concentration 5,0 g/litre
-~ Total ferric iron produced 460 kg/hr.
The following ~s a summary of the rate of oxidatlon
I and the capital and operating costs.
~ Fe Oxidation rateCapital Operating Cost
.
Un~t Gram/M2/hr. Gram/M3/hr. R R/ton -Cent/kg
` Solution Ferric
. Treated Produced.
-- .
, - Plate and
Z Spray 5,5 344 ND ND ND
.-:; 3 . .
Biodisc 3,78 -204 558 000 0,145 2,91
Filter
~`l pack 1,125 212 548 000 0,145 2,91
.s~ Bacfox
25treatment 7,46 693 - 113 800 0,031 0,63
, , . . . . . _ . .
, The economic advantages of the invention are
- ~ clear.
,
:
-14-
., . . ,. ~
, . , . . . .: . ..
. ~ : . .. . : - : - , . - ......... :
, . ,,. -. : , . . , .. ,--
. - . .. .- : .. : , - -.
0~93~Z
EX~PLE 3.
Using the leacning part of the scheme shcwn-in Figure 1 of the
dxa~ings, 500 g. of milled ore containing the equivalent of
O,36 kg. U3O8/ton were slurried with water. Thereafter the
slurry was milled and then passed to the leaching vessel 16
~here 350 g. of ferric sulphate solution from the tank 40
(prepared according to Example 1) were added. This solution
contained 8 g. of ferric iron. Concentrated sulphuric acid
equivalent to 15 kg./ton of ore were added, and the slurry was
leached for 2 hours at 55C. Thereafter MnO2 equivalent to l,O
~g./ton was added to oxidise any ferrous ions present. The
leaching was continued for a further 16 hours.
The slurry was filtered, washed, dr~ed, and assayed.
~he uranium content of the leached residue showed that 9O~ of
the uranium had been dissolved from the ore.
.
I~
A control test using the same ore but not using
ferric sulphate produced according to the invention, required
25 kg./ton of sulphuric acid and.3 to 4 kg./ton of MnO2 for
oxidation.
:i . ' ' " : '
EXAMPLE 4.
(a) The procedure illustrated in the flow sheet can be
carried out using covellite as the ore and acidic
t .- . ferric sulphate at abcut 35C, or an acidic ferric
' chloride and ferric sulphate mixture at about 98c for
.
.l 25 the leaching.
.. .
, :
-15-
''.. ' ' '. ,.' ..'' .'.. '., ' '' ,"", '' '' ", -~: ~' ~ .- '.-'.: . '.
- - . .. ,,- . ...
.. . ..
- . ~ . , , -: ~ :
, : - - . ,,: .
: ~ :. . , .
.. . .
.. .. .
15)13938Z
: `
(b~ When repeating the procedure for chalcocite, temperatures
in the range of about 23 to 95~C may be used.
.. . .
(c) When repeating the procedure for chalcopyrite, tempera-
tures in the range of about 27 to 100C may be used.
~d) ~en repeating the pxocedure for bornite, temperatures in
the range of about 23 to 98C may be used.
.
~e) When repeating the procedure for cubanite, and using
ferric sulphate, the temperature advisably should be in
the range of about 45 to 90C.
~f) When repeating the procedure for enargite, and using
' erric sulphate, the temperature advisably should be in
the ran~e of about 60 to 95C.
;
~g) When repeating the procedure for tetrahedrite, and using
ferric sulphate, the temperature advisably should be about
35C.
; .,
'''i ,
~h) When repeating the procedure for pentlandite, and using
ferrlc sulphate, temperatures may be in the range of about
, 25 to 60C.
.. ~ , .
.~. ~ ~
) When repeating the procedure for pyrrhotite, and using
`r 20 ferric sulphate, temperatures may be in the range of about
32 to 50C.
. ~ .
-16-
. . .
.
,, . . . ~ ... . . ..
,: , . - - . . - : -
... . ..
. : , . . ... ... , . . , .. , . : . - -.
.
938Z
. .
(j) When repeating the procedl~re for pyrite, and using ferric
sulphate, the temperature may be about 33 C.
EXAMPLE 5.
The procedure of Example 1 ~as repeated but using Thiobacillus
ferrooxidans to oxidise a ferrous sulphate and ferrous chloride
mixture containing 6,8 g/l of ferrous chloride and 13,6 g/l of
ferrous sulphate. A mixture comprising ferric chloride and
ferric sulphate was obtained. This is a stronger oxidising
agent than ferric sulphate alone and so can be used advan-
~o tageously for leachlng minerals.
;, , ' '.
.,','' i , ' . .
.,, ' .
. . .
.'' -.
--. .
.. : . , .
. . .
.
' .`~ ' .
. .~
~'. . ' '
, ~ ~
~ `'' ' . .
' ~ ,. , ~ , .
'`r~ :
