Note: Descriptions are shown in the official language in which they were submitted.
9567
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The invention relates to a method and a de~ice for re-
moving from a liquid undesirable components dissolved therein.
An example thereof is the treatment of waste watsr ob-
tained when processing metal ores. The ores which are valuable for
obtaining metals compri~e these and other metals often in the form
of sulphides, or are being converted into 6ulphides for further pro-
cessing. From the ground ore the various metal compounds are sepa-
rated from one another by flotation in water. ~he residues com-
pri~ing i.a. sulphides which are no longer useful for further pro-
cessing, are drained together with the water. ~his i6 generally
done into natural or artificial ponds, which are large and rela-
tively 6hallow (generally called, in ~nglish, ~'tailings ponds~').
~herein these substance~ can ~ettle, and the dimensions of these
ponds are so that the water introduced therein at one end, before
being drained at the oppo~ite end into a lake~ water-course or the~
like viRan o~erflow, will have a suffi¢iently long residence time
in the pond for allowing all the entrained ore residues to 6ettle. -~
~his type of operation has been in use for a long time
already without any objections being met with. However it has ap-
`~ 20 peared that, on the bottom of such settlin~ lakes, bacteria will
;~ de~elop whlch convert the sulphides into soluble sulphates~ and,
at the same time, suIphuric acid is produced so that the p~ w
be lowered considerably. ~hereby heavy =etals such~as lead and cop-
per can arrive, together with the drained water, into the natural
surface water, which may gi~e rise to a substantial mortality among
fishes and to other undesirable effects. Since the lakes are rela-
tively 6hallow, sufficient Gxygen is present which is needed by the `~
bacteria for this conversion, and this activity increases at higher
temperatures, so that only during a short period at the end of the
winter the production of noxious dissol~ed substances decrea6es
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b~low the allowable level.
This has resulted in government regulations ordering to
re~ove such noxious substances from the drained ~later, or to start
this witnin a short term. This not only holds for settling ponds
to ~hich ore residues are still being supplied, but also for ponds
which are no longer in use but which can still collect rain water,
so that such undesirable substances will be permanently discharged
o~er the weir.
In order to remove such su~6tances from the water to be
- 10 drained, the addition of a bafie such as, for example, oalcium h~-
droxide, will already cause precipitation of heavy metals as a hy-
dro~ide. In order to obtain a possibly effective dosage, this should
be done in reaction vessels, after which the available substances
; can be separated in a separation stage, but this appear~ not to
pro~ide an e~fective solution either.
This is, in the first place, a consequence of the fact
that the hydroxides precipitate in an aqueous gel-like state which
is dif~iculty to be separated, and the remaining liquid remains
turbid because of more or les~ stably euspended hydroxide particles
which cannot be remo~ed effectively by means of the currently used
separators. Furthermore, when using calcium hydroxide as a base, it
will form with the ~ulphate present insoluble calcium sulphate
which will deposit as hard crusts on the walls of the reaction spac~
and the separator, and can only very di~ficultly be removed there-
from Even if another more expensive hydroxide will be used, the
`~ ~irst problem will remain existent.
~ he invention provides a solution for these problems,allowing to remove effectively the noxious components from the
; supplied liquid, whereas, when using iime as a precipitation agen~,
0 no calcium deposition on the walls will take place.
According to the invention, besides the auxiliary sub-
stances ser~ing to bring about precipitation of the undesired sub-
stances, a large number of substantially inert particles is added
to the liquid in the reaction space, which are adapted to serve as
nuclei on which the badl~ or not soluble compounds produced will
deposit, which nuclei and deposi~ adhered thereto can be easily
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separated from the li~quid.
In particular these nuclei can be completely or at least
partially constituted by the sludge consisting of components precipitated
by said auxiliary substances, which is returned towards the reac-tion space
either continuously or step-wise.
The effect of these nuclei appears to be the better as their
number is larger, the only condition being that the separator used in the
device is able to remove these nuclei from the water eompletely.
When returning the separated matter, only the increase thereof
which is a consequence of the reactions taking place in the reaction space
should be removed. This surplus matter is produced then in such a con-
eentrated condition that often valuable metals and the like may be separated
therefrom in an economically feasible manner, or other useful utilization
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thereof is possible.
In particular when the reactions may lead to the formation
of hard deposits such as of calcium salts, it is advisable to construct the
reaction space in such a manner that the reactions have ended before the
liquid will reach the separator, in partieular if a separa-tor such as a
plate separator is used, in whieh sueh deposits would lead to obstruetion.
If necessary, separation promoting agents can be added and/or
eoalescence apparatuses can!be used for improving the separation in the
separator, and still other auxiliary substances may be added into the
reaction space enhancing the precipitation of the separable substances,
e.g. by influencing the solubility product of the compounds produced.
As a reaction space use can be made of a plurality of vessels
eonnected in series and provided with stirring means, in which vessels the
reagents and the supplied liquid will have a sufficiently long residence
time for obtaining an effective development of the desired reactions, and
it is also possible to use tubes as the reaction space, in which a so-called
30 plug flow can be maintained, viz. a flow of which all portions have ;
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substantially the same residence time, and in which, nevertheless, an inter-
mixing will be produced by turbulences. Stirred vessels have the advantage
that the reactions therein can be easily adapted to varying conditions,
and tubeswith a plug flow therein have the advantage that the dosage of
the substances to be added can be very accurately adjusted so that over-
; dosing which is inevitable in stirred vessels can be avoided.
' The separator preferably comprises two stages, viz. a first
stage in which the greater part of the sludge can be separated, and a
second stage in which the liquid arriving from the first one can be sub-
mitted to a post-separation treatment, in order to remove therefrom the last
remnants of separable components, and the sludge removal from both stages
can be adjusted or controlled corresponding to the relative yield. Also the
pumps included in the sludge circulating and discharge ducts are preferably
adjustable, in order to allow the most favourable ratio between the
circulated and discharged amounts of sludge to be adjusted. Both above-
mentioned stages of the separator can, in particular, be constituted by a
supply chamber and the plate assembly respectively of a plate separator
of current design, communicating with mutually separated sludge collecting
~ spaces.
" 20 Between the sludge discharge of the separator and the return
duct a buffer vessel can be included so as to ensure a uniform sludge return
flow, which buffer vessel can be provided with a stirrer for keeping the
sludge sufficiently in suspension.
When using this method and device for treating waste water
resulting from processing sulphidic ores, the sulphur will be drained as
soluble and harmless sulphate in the treated water, and often valuable sub-
stances can be recovered from the thickened sludge, or another profitable
use of the sludge is possible.
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11~9~67
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The invention will be elucidated below by reference to a drawing,
~ showing in:
; Fig. 1 a highly simplified schematical representation of a device according
to the invention;
. 5 Fig. 2 a corresponding schematical representation of another embodiment of
this device;
Fig. 3 a schematical representation of a modified embodiment of the separation
part of the device of Fig. 2; and
Figs. 4 and 5 schematical representations of two embodiments of the
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reactor part of such a de~ice.
In ~ig. 1 the structure of a device for executing the
method according to the invention is shown in principle and in a
highly simplified manner.
The liquid to be treated, e.g. water containing heavy
metal and sulphate ions, and ori~inal;ing from a settling pond of
an ore processing plant, is supplied at 1 to a reaction vessel 2.
At 3 a substance is added thereto,causing precipitation of the un-
desirable substances. In the case uncler consideration, calcium hy-
droxide, e.g. as milk of lime, is used, causing, together with the
metal ions present in the water, the production of poorly soluble
hydroxide thereof. If only lime is added, more or less gel- or 801- :
like hydroxides will be produced, leading to difficul~y separabl~
sediment with a very hi~h water content, and the remaining liquid
will remain turbid because of the rather stably suspended hydroxide
particles. An effective separation will become ~irtually impossible
then. Moreover calcium sulphate will be formed, which will deposit
as hard crusts on the walls of the variou6 spaces and ducts.
According to the invention, as indicated at ~, a sub-
stance is supplied to the reaction ve6sel 2, the particles of which
are suitable for serving as precipitation nuclei for the difficultly ;~
soluble substances produced by the reaction, the number of these
nuclei being so large that all the precipitation will take place on
these nuclei. Duri~ deposition on such nuclei the influences which,
otherwise, lead to the ~el-like sediment or to more or less stable
suspensions, and probably the water coats surrounding the hydroxide
p~rticles, appear to have no or a smaller effect. ~he nuclei thus
loaded by deposited substances beoome, then, su~ficiently heavy for~
being easily separated by sedimentation ~rom the liquid. Also in-
soluble sulphatas etc. can~precipitate on such nuclei, so that
- crustaceous depositions on walls and the like will be a~oided.
If necessary additional substances can be supplied to the
reaction space, as indicated at 5, which may enhance the separation
of the difficultly solubla h~droxides, ~uch as, for instance, Fe3
ions, which can shift the solubility product of th~se hydroxides
(so-called co-precipitation).
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The liquid with t~e loaded nuclei suspended therein is
discharged through a duct 6, into which, if required, auxiliary substances
can be supplied at 7 which enhance the separation of flocculation. This
duct leads towards a separator 8 in which the nuclei can settle as a sludge
layer 9, and the cleaned liquid can flow off at 10. This liquid is stripped
of the undesired substances, but can still contain dissolved substances.
In the case of ore waste under consideration, sulphur leaves the device as
; a soluble sulphate in the water drained at 10, and the metals as, for instance,
lead and copper, and also iron and zinc, land as hydroxides in the sludge 9.
In the lower part of the precipitator 8 the sludge will gradually be thick-
ened, and can be removed at 11 continuously or discontinuously.
If necessary a stage 12 can be included in the duct 6, in which
stage coalescence of suspended particles can take place if this is conducive
to the separation thereof in the separator 8.
For the nuclei materials can be used which can be divided into
- particles having dimensions which are suitable for the deposition of the
compounds in question, and having surface characteristics which are suitable
; for their separation, such as, for instance, sand, chalk, coal waste, ore
residues, mine stone, lava and the like. The choice will be determined, in
the first place, by the availability of such materials.
All the material introduced at 4, augmented by the compounds
deposited thereon, is to be removed at 11. This can lead to difficulties,
` in particular because of the amount of sludge, and because of the fact that
; the greater part thereof consists of the added material which can lead to
difficulties when further processing the sludge. The character of the
substances separated from the liquid can, furthermore, hamper the draining
of this material.
It has now appeared, however, that the discharged sludge can
be used again as material for the nuclei. In particular it appears not to
be necessary to use therefor foreign matter since it is possible to use as
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- nuclei the difficultly or not soluble substances themselves formed by the
reaction. The structure of a device suitable for this purpose is shown
in Fig. 2, in which the same reference numerals have been used as in Fig. 1.
The sludge discharge 11 of the separator 9 now connects, on the one hand,
to a sludge discharge duct 13 with a discharge pump 14, and, on the other
hand, to a sludge return duct 15 with a return pump 16, which duct 15 is
connected again to the inlet of the vessel 2. The pumps 14 and 16 are
adjusted in such a manner that a considerable portion of the sludge removed
through the duct 11 is returned to the vessel 2, which portion is mixed
with the supplied liquid, the sludge particles then forming the aforesaid
nuclei.
If, initially, as indicated at 4, foreign matter is supplied,
this supply can be interrupted as soon as a sufficient number of nuclei is
present in the cycle. If at 13 so much sludge is discharged as corresponds
to the increase of matter caused by the reactions in the vessel 2, the
number of circulated nuclei will remain the same. The matter initially
su~plied at 4 will then gradually disappear from the cycle, and in the long
run only reaction products will remain as nuclei in the cycle. It is
also possible to omit the supply of foreign matter completely, and to
allow a gradual growth of the sludge amount to take place during a starting
period.
The amount of sludge discharged at 13 comprises, for instance,
only 1% of the amount circulated through the vessel 2 and the separator 8.
This is only an example, but is indicative for the order of magnitude which
may be used in practice. As the circulated quantity becomes larger, the
number of nuclei will be larger accordingly, and, as has appeared in practice,
the operation of the device will become better too. The separator 8, however,
should be adapted to cope with the large amounts of circulated sludge or
other matter used for the nuclei, which is the main limitatian imposed on
increasing this amount.
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As mentioned above, a thickening of the separated sludge will
take place in the lower part of the separator 8. This part can be made
conical to that end. For this thickening, however, a certain residence
; time is required. If a large amount of sludge is circulated, and has a
suitable residence time determined by the discharge flow through the duct
13, the sludge level will possibly rise, but this rise should not be so
large that -the discharge outlet 10 is reached thereby. If, on -the other
hand, the return flow by means of the pump 16 is increased, the residence
time will be shortened, which may lead to a dilution of the sludge bed 9,
causing this bed to expand, so that, then, the sludge may reach the dis-
charge outlet 10 too. Care should, therefore, be taken that the sludge
level will not rise too much. This can be easily determined in practice,
or can be continuously established by measurements.
The pumps 14 and 16 are preferably adjustable so as to allow
to adjust the most favourable discharge and return flows respectively. In
any case the sludge should be thickened as much as possible so as to
circulate a possibly large amount of sludge at a high through-put, and,
thus, to obtain a large number of nuclei, and, on the other hand, the
discharge and/or further processing of the sludge is facilitated if it
contains less water. The thickened sludge can, for instance, be returned
to the ore processing plant, in which useful metals may be recovered
therefrom. Furthermore the sludge can often be utili~ed in another manner.
In the case of settling ponds which are no longer in use, when locally
processing of the sludge is generally no longer possible, the sludge can
be returned to the settling pond, which is not harmful since the separated
metals are now present in the hydroxide form and not in the sulphide form,
and these hydroxides will favourably influence the acidity, thus counter-
acting the bacterial activity.
Fig. 3 shows a modified embodiment of the separation part of
Fig. 2. The liquid outlet 10 of the separator 8 is, now, connected to a
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postseparator 17 in which sti~ll separable remnants can be removed from the
liquid, and the purified liquid leaves the device at 18. The separated sludge
is discharged through a sludge discharge duct 19 connecting to the discharge
duct 11 of the separator 8. The ducts 11 and 9 are provided with a valve
or stop-cock 20 and 21 resp., which are adjusted in such a manner that the
~; flow rates therethrough correspond to the amount of sludge separated in the
separator 8 or postseparator 17 respectively. It is also possible to use
periodically opened and closed valves of which the open-period lengths
correspond to the amounts of sludge produced in the separators in question.
- 10 Controlling these valves can, if necessary, be done by means of sensors
establishing the sludge level in the separator 8 or 17 in question.
Although, in Fig. 3, the separators 8 and 17 are shown as
sepaFate elements, they can be united if required, and then the separator
. 8 can be the supply chamber ofaplateseparator having a plate assembly which
, 1
~i 15 acts as the postseparator 17, which supply chamber and plate assembly are
~s
'~ each communicating with a separate sludge collector. Also in the case
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of separate elements the postseparator can be constructed as a plate separator
which, then, can be completely adapted to removing relatively small sludge
amounts still present in the preclarified liquid.
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~; 20 Fig. 3 shows, moreover, a buffer vessel 22 connected to the
sludge discharge ducts andprovided with a stirrer 23, in which vessel the
sludge originating from the separators 8 and 17 is collected before being
drained or recirculated. Such a buffer vessel can also be used in the case
of a simple separator 8 of Fig. 2. Thereby it is ensured that a sufficient
~; 25 amount of sludge is available for being recirculated, so that fluctuations
in the supply can be smoothed. Furthermore a quantity of sludge can be
;'l stored therein, which, after interruption of the operation of the device,
can be used for starting the process again. The stirrer 23 serves to keep
the sludge sufficiently in suspension.
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'`30 The reaction part 2 of the device can be realised in various ways.
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Fig. 4 shows a number of vessels 24 each provided with a s-tirrer 25, and
forming together the reaction space 2. It is known that, although in a
vessel provided with a stirrer a good mixing is obtained, the residence
times of the components mixed with one another are rather widely spread,
since a small part, because of the complete mixing, appears already
immediately at the outlet. By connecting a plurality of stirred mixing
vessels in series, it can be insured that all parts have a given minimum
residence time which is sufficient for the progression oE the reaction.
The auxiliary substances required for precipitation is, for instance, added
to the first vessel 24, as indicated at 3; and~the auxiliary substances
serving for coprecipitation are added to the subsequent vessels 14, as
indicated at 5. The number of these vessels is, of course, not restricted
to the number shown.
Fig. 5 shows another embodiment of the reaction part constituted
by one or more tubes 26, which tube or tubes can be straight as shown, but
can also be curved, this, of course, depending on the available space
and/or the distance to be bridged. Such a tube should be chosen in such
a manner that therein such a turbulent flow will occur that a given supplied
quantity will move through said tube substantially as a plug, i.e. that
all parts thereof will have substantially the same residence time, although
therein a certain mixing will be brought about by turbulences. Such a tubular
reaction vessel has the advantage that the dosage of the substances to be
added can be done very accurately, this in contrast to the embodiment of
Fig. 4. As indicated again at 3 and 5, this supply can take place in
various points ofthe tube 26. Such a tube, however, is adapted to a definite
flow quantity, so that larger variations therein may be harmful for the
operation. Stirred vessels according to Fig. 4, on the other hand, allow
an adaptation to divergent amounts but the dosage is less accurate therein.
It will be clear that the device of the invention can be
modified in many wàys. Moreover the method and the device of the invention
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1129567
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are not restricted to processing ore waste, but can be used in all cases
where comparable conditions are met with. Also non-aqueous liquids can
be treated in this manner, if the components present therein can be made
precipitating by adding substances reacting therewith, and if the precipi-
tation can be promoted by the introduction of nuclei.
The sludge needs not to be recirculated continuously towards
the inlet of the reaction space. In the embodiment of Fig. 1, for instance,
the sludge collected at 11 can be recirculated batch-wise, or can be
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lead towàrds a.vessel arranged near the reaction space, from which the
sludge can be drawn off as required.r ~ ~- ~ ~ ~ = -~~-~ -~
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