CA1129567A

CA1129567A - Method and a device for removing from a liquid undesired components dissolved therein

Info

Publication number: CA1129567A
Application number: CA333,591A
Authority: CA
Inventors: Jacob Pielkenrood
Original assignee: Pielkenrood Vinitex BV
Current assignee: Pielkenrood Vinitex BV
Priority date: 1978-08-11
Filing date: 1979-08-10
Publication date: 1982-08-10
Also published as: NL7808387A; SG20184G; AU532602B2; PH16192A; BR7905125A; AU4943779A; GB2027685A; ZA798528B; ES483258A1; MY8500478A; GB2027685B

Abstract

ABSTRACT OF THE DISCLOSURE

A method and a device for removing from a liquid undesired components dissolved therein, in particular waste water obtained in the processing of metal ores, by converting such components into substantially insoluble compounds which are separated from the liquid before draining the latter.
According to the present invention substantially inert particles are used which, when mixed with the liquid in the reaction space, will act as nuclei on which the substantially insoluble compounds formed by said conversion reaction will preferably deposit so as to avoid deposition thereof on parts of the device, which nuclei and adhered deposits can be easily separated from the liquid.
To that end the device of the invention comprises a reaction space with means for supplying the liquid to be treated and substances for bringing about the conversion reaction, as well as additional means for supplying to said space precipitation nuclei, said reaction space being connected to a separator for separating said nuclei from the treated liquid, which nuclei can be returned towards said additional means if required.

Description

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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 ,~ i', . , .

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 , 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 ;

~1~295~;7 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 - 4a -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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5 ~ 1 ~ a ~ 7 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).

S ~ S ~ - 6 -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 -X
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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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. 12~,v7 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 ..... . .

:: ~ 1295~ ' 9 _ 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 :, :
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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5 6 7 lo -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 , .~

- lOa -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 .. . .
lead towàrds a.vessel arranged near the reaction space, from which the sludge can be drawn off as required.r ~ ~- ~ ~ ~ = -~~-~ -~

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for removing from a liquid undesired components present, and dissolved, therein, in which, in a reaction space, additional substances are added, converting these components into badly or not soluble compounds, which compounds are then separated from the liquid before the liquid is drained, characterised in that a large number of substantially inert particles is added to the liquid in the reaction space, which particles are adapted to serve as nuclei on which the badly or not soluble compounds produced will deposit, which nuclei and deposits adhered thereto can be easily separated from the liquid.

2. The method of claim 1, characterised in that the quantity of the material for the nuclei is at least several times larger than the amount of undesired substances present in the supplied liquid.

3. The method of claim 2, characterised in that the ratio between the amount of the material for the nuclei and the amount of supplied undesired substances is chosen as large as possible as is compatible with the operation of a settling stage in which this material is separated from the liquid.

4. The method of claim l, characterised in that at least a part of the material for the nuclei is formed by the material separated from the liquid and recirculated towards the re-action space.

5. The method of claim 4, characterised in that a part of the separated material is discharged, said part corresponding to the increase caused by the reactions with the additional substances.

6. The method of claim 5, characterised in that the ratio between the amount of recirculated and discharged material is adjustable.

7. The method of claim 1, characterised in that a part of the additional substances is adapted to influence the solubility product of the badly or not soluble compounds produced in the sense of a reduction of the solubility.

8. The method of claim 1, characterised in that, before supplying the liquid to the separation stage, substances promoting the separation are added.

9. The method of claim 1, characterised in that, before supplying the liquid to the separation stage, a coalescence treatment is performed thereon.

10. The method of claim 1, characterised in that the separation takes place in two stages, and in that the material discharge from these stages takes place substantially pro-portional to the material separation in the stage in question.

11. The method of claim 1, characterised in that the reactions take place in a plug flow, into which the dosed reagents are added in consecutive points.

12. The method of claim 1, characterised in that the reactions take place in a plurality of consecutive, and particularly stirred, vessels into which the dosed reagents are added.

13. The method of claim 1, used for treating a liquid containing metal ions with not or badly soluble hydroxides, in particular heavy metals characterised in that the additional substances contain soluble hydroxides.

14. The method of claim 13, characterised in that the additional substances for influencing the solubility product contain Fe3+ ions.

15. The method of claim 13 or 14, characterised in that the liquid is waste water originating from processing sulphidic ores, and containing heavy metal and sulphate ions.

16. The method of claim 13 or 14, characterised in that the liquid is waste water originating from processing sulphidic ores, and containing heavy metal and sulphate ions, further characterised in that calcium hydroxide is added as an additional substance, the formed calcium sulphate also being deposited on the nuclei.

17. A device for executing the method of claim 1, comprising a reaction space for treating the supplied liquid, provided with means for adding thereto additional substances adapted to convert the undesired components into not or badly soluble compounds, characterised by means connected to the reaction space for supplying thereto material that is adapted to serve as precipitation nuclei, and by a separator connected to this reaction space designed to-remove said nuclei with the compounds deposited thereon from the liquid.

18. The device of claim 17, characterised in that the reaction space and the separator are adapted for processing amounts of material for the nuclei which are substantially larger than the amount of substances in the supplied liquid which are to be removed therefrom.

19. The device of claim 17, characterised in that it is designed for recirculating the sludge separated in the separator towards the reaction space.

20. The device of claim 19, characterised by a return duct connected to the sludge discharge space of the separator, leading towards the inlet of the reaction space.

21. The device of claim 20, characterised in that the return duct is provided with a branch duct through which a part of the sludge discharged from the separator can be removed from the device.

22. The device of claim 21, characterised in that the return and branch duct are each provided with a pump.

23. The device of claim 22, characterised in that the ratio between the pump yields is adjustable.

24. The device of claim 17, characterised in that the reaction space is provided with means for supplying thereto still other additional substances for influencing the solubility of the formed compounds.

25. The device of claim 17, characterised in that the connection between the reaction space and the separator is provided with means for supplying separation promoting agents.

26. The device of claim 17, characterised in that the connection between the reaction space and the separator is provided with means for executing a coalescence treatment.

27. The device of claim 17, characterised in that the separator consists of two stages with interconnected sludge discharge outlets.

28. The device of claim 27, characterised in that the sludge discharges are each provided with an adjustable valve.

29. The device of claim 28, characterised in that the adjustment of the valves can be controlled in conformity with the sludge level to be expected or actually attained in the separator in question.

30. The device of claim 17, characterised in that both stages are a part of a single separator with separate sludge discharge spaces for both stages.

31. The device of claim 17, characterised by a buffer vessel between the sludge discharge outlet of the separator and the return duct.

32. The device of claim 17, characterised in that the reaction space consists of one or more tubes provided with means for introducing reagents in suitable points.

33. The device of claim 17, characterised in that the reaction space consists of a plurality of stirred vessels connected in series, provided with means for supplying reagents therein.

34. The device of claim 17, characterised in that the inlet is connected to a settling pond for waste products of ore processing.