Note: Descriptions are shown in the official language in which they were submitted.
1 33 1 ~95
SYSTEM ANC~ METHOD FOR THE EXTR~CTION OF
CYANIDE E'ROM ~AlLS LIQUOR
Thc present invention r~lates to a method and a
system for treating by ~eration a liquid contai~ing a
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component to separat~ th~e ~omponent from the liquid. In
particular, the present invention relates to a method and
10 a 3ystem ~or tre~ting by aeration a liquid Gontnining - -
cyanide to separate cyanid~ from the liq~id.
~t i9 known to flcrate ~ liquid to sep~rAte from
e~e liquid any dissolved gases in the l~quid. For
example, it is known to aerate liquid containing
15 dissolved cyanide to separate the cyanide from the
liquid.
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One problem associated with known aeration
techniques i9 that a considerable volume of air is required
in proportion to the volume of liquid.
An object of the present invention is to
alleviate the problem described in the preceding paragraph
and to provide a more efficient and cost effective method
and system for treating by aeration a liquid containing a
component to separate the component from the liquid.
In a broad aspect, the present invention relates
to a method of separating a component from a liquid
containing the component, comprising passing the liquid
downwardly through each aexation column in an array of
aeration columns arranged in stages so that the liquid
flowing from an outlet of one aeration column in a first
stage is divided into two or more streams which are
introduced into separate aeration columns in a successive
second stage and passing air serially through each of the
aeration columns in each stage counter-current to the
liquid to entrain at least a portion of the component in
- the air thereby to separate at least the portion of the
component from-the liquid.
In another broad aspect, the present invention
relates to a system for separating a component from a
liquid containing the component, comprising a plurality of
aeration columns to receive the liquid therethrough, the
aeration columns arranged in a series of stages so that in
use liquid which flows through one said aeration column in
a first stage is subsequently divided into at least two
separate streams and the streams are directed into separate
aeration columns in a second stage downstream from the
first stage, eàch aeration column having an inlet for
spraying liquid downwardly through the column and an inlet
for directing a stream of air upwardly through the column
so that the liquid and the air flow in counter-current
relationship and a means to direct air serially through
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each aeration column in each stage in counter-current
relationship to the liquid to entrain the component in the
air, thereby to separate the component from the liquid.
According to the present invention there iB
provided a method of separating by aeration a component
from a liquid containing the component comprising, in a
first stage, passing the liquid counter-current to a stream
of air to entrain a portion the component in the air
thereby to separate the portion from the liquid,
~ubsequently dividing the liquid into a plurality of
divided portion~3, and, in a second stage, passing each
divided portion counter-current to a stream of air so as to
entrain a further portion of the component in the air -
thereby to separate the further portion from the liquid. -
Preferably, the component comprises cyanide.
Preferably, according to the present invention
there is provided a method of separating by aeration
cyanide from liquid containing cyanide, comprising:
(a) adjusting the pH of the liquid to be in the acidic ~-~
range to cause the formation of free hydrogen cyanide -~
gas in the liquid;
(b) passing the liquid through an array of aeration
columns arranged in stages so that the liquid flowing
from one aeration column in a first stage is divided
into two or more streams which are introduced into
separate aeration columns in a successive second
stage; and - ~--
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(c) passin~ air t~rough the aeration columns
counter-current to the liquid to entrain the
free hydrogen cyanide gas, thereby to separate
cyanide from the liquid.
~ccording to the present invention therc is
also provided a system for separating a component from a
liquid containing the component, comprifiin~:
(a) a plurality of aeration columns to : t~,
receive thc liquid therethrough, the aeration
columns arranged in a series of stages so that,
in use, liquid which flows through one said
aerati.on column in a ~irst stage is
subsequently divided into at least two separate
streams and the streams are directed into
lS separate said aeration columns in a second
stage downstream from the first st~e: and
~) means to direct air t~rou~h the aeration
columns counter-current to the liquid to
entrain the component in the air, thereby to
separate the component from the liquld.
~` Preferably, when the system is u~ed to sep~rate
cyanide from a liquid, in accordance with the invention
the system oomprises a means to adjust the pH of the
liquid to be in tho acidic range to cause t~e formation
25 of free hydro~en cyanide ~as in the li~uid prior to the
introduction of th~ liquid into the aeration columns.
The term "column`' is understood ~erein to mean
any container or the like, suoh as an open ended tube
which is adapted to receive liquid therein.
The term "aeration" i~ understood herein to
mean a process in which a liq~id is exposed to th~ action
of air or any other ~ration gas.
The invention is now descr~bed in moro detail
with reference to a specific c~bodiment thereof. The
35 description is ~ade with reference to the acco~panying
drawings, in which;
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~igure 1 is a schematic block diagram of a
tailings treatment process in its entiret~; -
Pigure 2 is a detailed schematic drawing
showing the particular arrangement of the aeration
5 columns and c~ustic circulation tanXs used in the
proccss;
Fi~ure 3 is a block diagram showing the
principal of passing air through t~e aeration columns in
a serial manner without changing the volume of air
10 relative to each aeration eolumn; and -~
Fig~re 4 is a detailed schematic diagram
showing th~ manner in which air passes through a single
pair of separation and absorption aeration col~mns
counter-current ~ith the liquor And c~ustic solution.
The specific e~bodiment concerns a system and
proces~ for treating tailings from an extraction plAnt
for the reco~ory of gold or other minerals.
In. one known process for extracting gold fro~
its ore, cyanide is dissolved in water and ~he resultant
20 solution is used to leach gold from d~posits of ore. In
t~c leaching process, some of the cyanide remains in the
tailings or the residue f~om the. plant. The purpose of
the system and process dcscribed herein is to treat the
tailinqs so as to r~move suf~icient of the cyanide to
25 enabl~ the tailings to be disposed of in an
environmentally satis~actory condition.
The system and procefis initially comp~ises
~orming a tails liquor from the tailin~s dump which is
dccanted by known meAnS 1 and pumped to a mixing chamber
30 2~`
Acid Rtored in a bulk ac1d storage tank 3 is
pumpQd by ~n acidification doaing pump to the chamber for
AdmixtUrc with the tails liquor so as to adjust to thc pH
of the liquor into the acid rang~ thereby to eause th~
35 formation of free hydrogen cyanide gas which is retained
in the liquor.
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_ From th~ mixi~g chamber 2, the liquor is pumped
into a sand-floc cohtact tank 4. Coagulant, ~locc~l~nt
and make-up sand from respective s~orage tanks 5, 6 and 7
are added to the sand-floc contact tank 4. The mixtur~
S is agitated and flows h~ ~ravity to a constant density
tan~ 8
The underflow from the const~nt density tank 8
is pumped to a ~yclone 9. The cyclone underflow is
returned to the sand-floc contact tank 4 for re-use. The
10 cyclone overflow is directed to a settling pond 10 from
which liquor is drawn off and returned to t~c sand-floc
contact tank 4 and the liquid is transferred to pondage.
The liquor from the constant density tank B
flows by gravity through sand filters 12 and then is
15 pumped to a column 13a. The column 13a is a preliminar~
aeration column for the separation of cyanido from the
liquor. In this re~ard, th~ liquor is sprayed into the
column 13a a,nd flows downwardly therethrough
counter-current to a stream of air directed upwardly
20 through thc column 13a. The stream of air is drawn fr~m
the constant density tank 8 and has the effect of
entraining a portion of the free hydrogen cyanide gas in
the liquor. The air is drawn from the top of column 13a
and is directed through an absorption column 13b for
25 ab~orption of the hydrogen cyanide gas into a caustic
solution.
The liquo~, with a reduced cyanide
concentration, which collects at ~he bottom of the oolumn
13a is pumped to an array of aeration columns, generally
30 identified by the numerall 14, to remove a ~urther portion
of the c~anide in the liquor. The aeration column~ in
thu array 14 are Arranged in ~ta~e* so that the liquid
flowing from onc aeration column in a fir~t stage is
divided into t~o strea~s which are introduced into two
35 s~parat~ aeration columns in a successive second staqe.
~he aeration columns in the array 14 are also arranged to
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receive therethrough alr in counter-current flow to the
flow of liquor, thereby to entrain free hydrogen cyanide
gas in the air. The array 14 of aeration columns i9
described in more detail hexcinafter.
The liquor. with a substantially red~ced
cyanide concentration, which passes thro~gh the final
~tage of the array 14 of aeration columns, is conveyed to
a final aeration colu~n 15. Thc liquor i~ passad
downwardly through the aeration co~umn 15 counter-~urrent
10 to an upward flow of air drawn from the atmosphere.
The liquor from the final aeration column 15,
being clean and substantially free of cyanide, is passed
through columns 16 which Contain carbon to colloct any
residual gold in t~e liquor. The liguor from the columns
15 16 is suitable ~or disposal. Such disposal may ~e by
direct transfer to a tailings impoundment system or via A
pH correction stage 17 where a suitable reagent such as -~ -
lime or caustic soda is added to rai~e the p~ of the
l~quor t~ a level ~uitable for dischar~e into the
20 environment.
The array 14 of aeration columns is now
described in more detail with reference to Figures 2 and
4. The array comprises a plurality of pairs of aeration
columns 14a, 14b, ... 14c''' w~ich ar~ arranged in thre~
25 stages. The first stage comprises the pair oP aeratlon
col~mns 14a, the second stagc comprises the pairs of
aeration columns 14b, 14b' and the t~ird ~tage comprises
the pairs of aeration columns 14c, 14c', 14c'' and
14c'''-
Each pair af ae~ation columns 14a, 14b
14C''' compris~s, an aeration column 25 ~or use in
connection with tho sep~ration of free hydro~en cyanidc
gas from liquor by means of a counter-curren~ flow o~
air, and an aeration column 26 for use in connection with
35 the absorption of hydrogen cyanide ~as ~rom the air in~o
a stream o~ caustic solution.
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The separation column 25 and absorption column
2~ in each pair are separated ~y an intermediate air duct
29 which maintains liquor in separation column 25 and
caustic solution in ~bsorption column 26 whilst al.lowing
5 air flow 27 to pass serially through bot~ columns fro~ an
inlet air port 28 disposed in the separation column 2S to
an outlet air port 30 disposed in the absorption ~olumn
26. In this manner air is passed serially through the
columns 25, 26 in each pair.
The liquor i~ introduced in a spray through an
inlet liquor port 31 disposed nuar the top of ea~h
separntion ~olumn 25 and flows downwardly and is
discharged through an outlet ].iquor port 33 near the ~ase
of e~ch separation col~mn 25. Each separation column 2S
15 contains a bed of pao~ing material 32 s~spended theroin
to promote dispersion of the downward flo~ of liquor and
upward flow of air thereby to en~ance aeration of thc
liquor ~nd,.as a consequence, to enhance entrainmcnt of
the free hydrogen cyanide gas in the air.
: 20 Similarly, the caustic solution is introduced
in a spray thro~gh a Gaustic inlet port 34 disposed ncar
the top of each absorption column 26 and flows downwardly
and is discharged through a ca~stic outlet port 36
disposed near the bas~ of ~ach absorption colu~n 26. In
25 addition, each absorption column 26 contains a bed of
packing material 35 suspended ther~in to promote
., dispersion o the downward flow of caustic solution and
upward flow of air thereby to cnhance aeration of the
caustic solution and, as a consequ~nce, to enhance
30 absorption oF the hydrogen cyanide gas in the caust.io
solution~
Th~ pairs o~ aaration colu~ns 14A~ 14b, ...
14c''' are lntercon~ect~d to allow ~clectlvc cir~ulation
of tho li~uor and thc cau~tic solution. Figure 2 ~hows
35 the physicnl arrangement of the pairs of aeration columns
and the circulation system for liquor and caustic
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solution, and Figure 3 shows the conceptual diRposition
of the separation column~ 25 in each pair o aeration
eolumns at ~h~ variou~ stages.
The liquor is introd~ced into the first stage
5 of the array 14 which ~ompri.ses the pair of aeration
columns 14a. The liquor is introduce~ into the
separation column 2S thereof at the inlet liquor port 31
and flo~s do~nwardly to the ~ase of the separation column :
25. ~he liquor discharged from the outlet port 33 ifi
10 circulated by a liq~or p~mp ~7 to the second stage of the
array 14 which comprises the pairs of aeration columns
14b and 14b'. The stream of liquor is split equally so -~
that ~alf of the original volume is introduced through
inlet port 31 into the separation colu~n 25 of thc pair
15 o aeration columns 14b and the other half is introduced
throu~h the inlet port 31 i.nto the separation column 25
of the pair of aeration columns 14~'. After flowing
throu~h the second stag~ the liquor is discharged ~rom
the outlet ports 33 of respective separation columns 25
20 and i9 collectively circulate~ by a second stage pump 38
to the third stage of the array 14 whieh comprises the
pairs of aeration columns 14c, 14c', 14c'' and 14c'''.
The recollected liquor is split equally into four streams
such that a quarter of the original volume 1~ introduced
25 into the sepAraeion colu~n 25 of the pair o~ aeration
columns 14c and so on up to the pair of aeration columns
14c'''. After discharge from the third stagc the liquor
is combined in a single pipeline 38 and i~ transferred ~o
tho final aeration stage 15 and thcnce to the columns 16 .
30 prior to eventual discharge as shown in ~igure 1 of the
drawings.
Thc cau~tic ~olution i9 pumped f~om a-bulk
caustic storage tank 19 via a pip~ line 39 and initially
is dischar~ed into a causti~ circulation tank 20a
35 intended to supply the third stage o~ the array 14 of
aeration columns, i.e. Gonverse to the supply o liquor
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w~ich is fed initiall~ to the first stage of the array 14
as described in the pre~eding paragra~h. Water from a
water storage tank 23 is also pumped i~to the third stage
caustic circulation tank 20a via a pipe line 2~. In a
5 closed circuit arrangement, ~he diluted caustic solution
accumulated within the thi.rd stage circulation tank 2~a
is circula~ed by means of a third stage caustic
recirculation pump 40 from the circ~lat.ion tank 20a to
each of the absorption columns 26 in the th.ird stage of
10 the array 14, i.e. the absorpti~n col~mns 26 in the pairs
of aeration columns 14c, 14c', 14c'' and 14c'''. ~n each
of the absorption columns 26 of t~e third stage, the
caustic solution is sprayed from the top through the
inlet liquor ports 34 and flows through the absorption
15 columns 26 and subsequently is di~charged through the
outlet liquor ports 3~. Each of the outlet ports 36 of
the absorption columns 2fi of t~e third stage are
connected to a common return pipe line 41 w~ich
discharges back into the third stage recirculation tank
20 20a, wherein excess caustic solution subsequently is fed
via pipe line 42 to a second stage circulation tank 20b.
The accumulated caustic solution in the second stage
circulation tank 20b in turn is pumped via a second stage
caustic recirculation pump 43 to each of tho absorption
25 columns 26 of the second stage, i.e. the absorption
columns ~6 in the pairs of aeration columns 14b and 14b'.
As in the third ~tage, the caustic solution is sprayed
into the absorption columns 26, through inlet ports 34
and flows downw~rdly and i8 discharged throu~h the outlet ~r/.
30 ports 26 thereof. Subsequent~y, the discharged caustic
solution iS fed to a common rcturn pipe line 44 for
return to the second ~ta~e oircul4tion tank 20b, thus
providin~ a closed loop circulation. The exces~ caustic
~olution contained within the second ~ta~e caustic
35 circul~tion tank 20b in turn is suppl~cd to a first~stagc
caust~c circulation tank 20c via pipe line 45. Caustic
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solution ~upplied to the first stage cir~ulation tank
20c, in tur~ is pumped via the first stage recirculation
pump 46 to the absorption column ~6 of'the first stage;
i.e. the abgorption column ~6 of the pair of aeration ~-~
5 ~olumns 14a. The caustic solution, as in ~he previous
stages, flows downwardly and subsequently i9 discharged
through the o~tlet port 36 for return via pipe line 47 to
the first sta~e circulation tank ~Oc. ~o complete the
circuit, excess ~austic solution in the first stage
10 circulation tank 20c in turn is fed to a final caustic
circulation tank 20d to be subsequ~ntly returned for use
in the mineral recovery plant for leachin~.
It should be ~vident that the concentration of
absorbed cyanide within the causti~ solution in~reases as
15 the caustic solution is cir~ulated from the third staqe
~o the ~irst stage for collection in the final
circulation tank 20d. It should also be evident that
each stage of the array 14 of aeration columns receives
therethrou~h substantially the sa~c volume of liquor and
20 that cach pair of aeration columns 14a, 14b, ... 14c'''
in each sta~ receives thcrethrough substantially the
same volume of liquor and causti~ solution.
Air is drawn serially throug~ the pairs of
aerator ~olumn~ 14a, 14b, ... 14c''' by fan~ 48a and 48b
25 disposed respectively at the outlet air ports 3~ of the
pair ~f aeration columns 14c' and th~ pair of aeration
columns 14c'''. The inlet air ports 28 of the pairs of
aeration columns 14a, 14b are vented to the atmosphere so
that air may be drawn from the inlet ports 28 to the
30 outlet ports 30 in ~ serial ~ashion through t~e aer~tion
columns. As h~s been p~viously deqcribed, the
in~crm~diate ~ir ducts 29 b~twccn ad~acent se~aration and
absorption columns 25, 26 in ea~h pair o~ aeration
columns are arran~ed so as to crsate risin~ air streams
3~ counter-current to the downward flow o~ liquor and
causti~ solution in the aeration columns.
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An i~portant aspect of the ¢~bodiment of the
invention as described herein is the circulation of
liquor and air through the stages o the~array 14 of
aeration columns. This is best illustrated in Figure 3
S where it can be secn that an init~al volume of liquor is
passed wholly through the first sta~e comprising the pair
of aeration columns 14a and is s~bsequently divided into
two half vol~mes which respec~ively pass through the
second stagc comprising the pairs of aeration colunns
10 14b, 14b'. The hal volumes of cyanide liq~or are
subsequently divided again at the third stage ~omprisin~
the pairs of a~ration columns 14c, 140', 14c'', 14c' " so
that quarter volumes o~ the original liquor volume arc
passed throu~h each pair of aeration columns of the third
15 stage. These quarter volumes are then recombined into A
single supply pipe for eventual delivery to the final
aeration sta~es ~s previously described. Simultaneously
with the reduction in volume of the liquor, a single
volume of air is passed through the various colu~n~
20 serially so that each separation and absorp~ion column
25, 26 i~ treated with the same vol~me of air.
Therefore, the air to li~uor ratio increases as the
liquor passes through the pairs of aeration columns in
successiv~ stages without an increase in the amount of
25 air requir~d in ~he system. As a consequence, thore Is
an improvement in thc contact time for the liquor and air
and a conseq~ential improvement in the ~eparation of
c~anide from the liquor.
It should be appreciated that the scope of the
30 present invention is not limited to the particular
embodiment h~rein descr;ibed. In particular, the
invention is not limited to application to gold
extraction proccsse~ and can be ufied elsewhere ~or tho
separation of cyanide from a liq~id. Furthe~, the
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invention is not restricted to the separation o~ cyanide
from a liquid and relat~s to the separation o~ any
dissolved gas from a liquid.
There exists scope ~o vary both the application
5 of the present invention and the form of the invention
from the embodiment herei.n described.
In this regArd, other applications of the
invention include all cyanidc containin~ waste solutions
and liquors such as:
(a) mineral processing liquorsS
(b) el~ctroplating solutions;
tc) electro~inning solutions; and
(d) ~annery liquors.
In addition, variations to the e~bodiment
15 herein described include:
(a) the use of all and varied flocculating
and coagulating agents;
(b) the usc of any inert, particulate
matorial herein before referred to a~ "sand";
2Q (c) the use of a multiplicity of any or all
of steps 1-8 shown in Figure 1;
~d) the use of a multiplicity of any or all
of th~ separation columns 2S;
(e) the use of A multiplicity of any or all
25 of the absorption columns 26S
(f) the use of an~ and all combinations of
separation and absorption columns 25, 26 so as to effect
variation in the air:liquor ratios employed;
(q) the use of a multiplicity of final
30 aerntion stages 15 shown in Figure l;
(h) the use of any subsequent water
conditioning pro~cs.~ spe~ifically to regulatc dis~harge
pH and compo.sition including repeatin~ the application of - .
any or all o~ the stages herein before desc~ibed5 And
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~ i) the use of agents to materially change
and/or control the temperature at which the process takes
place.
In particular, whilst in the preferred
5 embodiment a strea~ of liquor flowin~ from a separation
~olumn in one stage is divided into two ~qual-volume
portions for introduction into separation colllmns in the
successiv~ stage, it can readily be appreciated that the
invention is not so limited and the stream of liquor
10 could be divided into more than two portions which may or
may not be of equal volu~e. Further, whilst in the
preferred embodiment the array 14 of aeration columns is
arranged in three stages, it can readily be appreciated
that any suitable number of sta~es could be used.
15 Further, whilst in the preferred embodiment the air is
piassed through t~e pairs of aeration col~mns serially, it
can rcadily bo appreciated that any suitable air flow
could be used.
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