ZA200210364B

ZA200210364B - Treatment of effluent.

Info

Publication number: ZA200210364B
Application number: ZA200210364A
Authority: ZA
Inventors: Pieter Jansen; Bruno Sceresini
Original assignee: Atomaer Pty Ltd
Priority date: 2000-06-01
Filing date: 2002-12-20
Publication date: 2004-02-03
Also published as: WO2001092162A1; AUPQ790900A0

Description

LL.D MKISCH, ina us o #2Xi0120603270 10 Dec 2002 11:22 P.04 good

TREATMENT OF EFFLUENT

FIELD OF THE INVENTION

: 5 . The present invention relates to & process for the treatment of effuent and relates parficulatly, though not exclusively, to a process for the treatment of industrial effipent

BACKGROUND TO THE INVENTION

Gases emiticd during Various phases of the steel making process are scrubbed fo remove particulate material before discharge to etmosphers, Some steel mills suffer from a particolarly serious problem in maintaining the scrubber water cirouit which may be summarised es follows:

The hot gases are scrubbed to recover partioulans materials such as dust, coke/carban and metal ames, but carbon fn the flue gas forms carbonic acid in the scrubber water, : which dissolves particulates such as iron, calcium, sulphates, ets. oe Thi scrubber efluet temsperaturs is between S0-65°C and is too hot t adc eye from tho atmosphere. e Tho sorubbor cfflusatis cooled in ooling towers, which by design ere aerators. «The cooling water sdsorbs oxygen, which cxcidises ths frog, which Ja tims peecipliziss onto tho cooling tower packing causing a reduction in efficiency, and eventually the . weight of precipitate collapses the packing. : An alkali, currently caustic soda, is used to contro! pH, but contaminant salts such as sulphate ions accumulate and a bleed stream must be discarded fo avoid pipeline and equipment scaling ios acl MKISCH — va 2X :0124603270 GRIFFITH Back Dec 2002 11:22 P.05 2408 o A substantial volamo of cooling Water is discarded to evaporation ponds, This is bath " castly and wasteful of a scarce resource. eT o! Very significant chemical dosing costs are incurred in maintaining the water quality. a e : Water treatment consultants are at a loss to find @ solution to the problem. Their best ; solution is to build bigger evaporation ponds. . Scale and suspended solids in cooling water can lead to serious equipment damage.

There is another serious problem with cyanide generation fn certain aveas within steel making plants, Depending on tis process within the steel meking plant, the oyanide is produced as & mosult of high temperature reactions between carbon and nitrogen, This problem is probably common to most steel making processes. ‘Tho cyanide accumulates in the scrubber circuit water and a bleed stream must be discarded to evaporation ponds to keep te ayauide concentration from atsining dengerons levels, The presence of cyanide in the evaporation ponds presents an environments] hazard, particularly if some of the wastewater leaks into ground water. A typical serdbber water elroutt contains between 100 end 150ppm free cyanide. This is a dangerously high cancentration, as 50 pput eyanide in talllng water i ful to binds and 100-150 ppm cyanide solution would be fatal fo un ad if swallowed.

SUMMARY OF THE INVENTION

The presest invertlon was developed With 2 View to providing a process for the restent of effluent that is effective in substantially reducing the concentration of sohible meta] salts andlor cymide in the offivent. Tt will be epparent fiat the process may have application to the treatment of effiuent’s front sources other than steel mills.

Throughout this specification the term “comprising” is used inalusively, in tho ase that there may bo other features and/or stops included in the aveation not expresly defined or comprehended in the features or steps subsequently defined or described.

: 19 Dec 2002 11:23 P.06 aor 2D MKISCH | raa os os Ee ng 608270 GRIFFITH Aer °c @oos —-— : -3-

What such other features and/or steps may include will bo apparent from the : specification read 2s a Whole. ’ According % one aspest of the resent invention thers is provided 8 process for the treatment of effluent, the process comprising the steps of; : diverting a steam of effluent containing dissolved metals and/or sulphates through an in-line reactor; } 10 reacting tho effinent with an oXygen-containing gas in the In-line reactor Wherein said dissolved metals and/or sulphates are precipitated out of solntion; separating a clarified solation from the precipitated sludge; and. recycling the clarified solution.

Typically to effioent is m aqueons effluent foes an industriel processing. plant

Preferably lime or canstic soda is added to the effinent prior to said sep of reacting the effluent in order to control the pH. Prefecebly sald oxygen-containing gas is injected directly into the in-line reastor adjacent an intake poet.

Advantageously the nine tescior employed In the process of the vention is a

FILRLAST (registered trade mark) multipbass staged passive reactor such 6s hat described in US Pater No, 5,741,466. The contents of US 5,741,456 we incorpomted herein by reference.

According 0 amothes aspect of fe present ixvestion ier is provided a proves or fie , treatnent of effluent, the process comprising the steps of diverting a sidestream of effluent containing eyatids through a firt in-line mixer;

Fr WD MXISCH coA OL © »} 2X 1Q124603270 GRIFFITH ne Dec 2002 11:23 P.07 @on7 reacting the effluent with Caro’s acid in the first iu line reactor wherein said cyanide is oxidised to harmless cyanate; and, - . recycling the efffuent with oyanate. :

Prefbrably fhe Cam's acid is produced immediaféty prior fo reacting in said in-line reactor,

Advantageously the Caro’s acid is produced by reacting sulphuric acid and hydrogen

Ppeseaide in & second inling reactor which discharges directly into a Seedling immedistely

Peior to the first fn-line reator. :

Actording to a finther aspect of the present invention there is provided 8 process for the treatment of scrubber effluent, the process comprising the steps of: diverting a stream of scrubber efffusnt containing dissolved metals and/or sulphates and cyanids through a first in-line reactors reacting the scrubber effluent with an oxygen-contuining gas fn the first {o-fine reactor wherein said dissolved metals and sulphates arc precipitated out of solution: separating s clarified solution from the precipitated studge: reacting the clerificd solution with Caro's acid in a second in-line reactor wherely said cyanide is oxidised to harmless cyanate; and, recycling the clarified solution to the socobber clrouit

BRIER DESCRIPTION OF THE DRAWINGS

In order to facilitate a better understanding of the nature of the invention ane embodiment of the process for the treatment of industrial effinent will now be described in detail, by way of example, with reference to the accompanying drawings, in wich:

JD M_KISCH ‘nA vi © Fax: 0124603270 uKIrrFLLIR ae Dec 2002 11:23 P.08 aogs

Figure 1 is conceptual flow diagram fustretng one embodiment of a prefered process ‘ for the treatment of industrial effluent in accordance with the invention: eo . Figura 2 iltrates graphically ho redaction in iron conosatration askleved using fhe preferred process for the treatment of scrubber efffuent in sosordance with the fnveation:

Figwo 3 illustrates graphically the reduction in ‘TDS, calcium hardness and sulphate coricentration using the profirred process in fh treatment of scrubber efffucnt; 20 Figure 4 illustrates @ conceptual flow diagram Mlusrating a sccond embodiment of a prefered process for the treatment of industrial effiueat in accordance with the inveation:

Figure 5 illustrates graphically the reduction in C20 consumption achieved using the

Preferred process for the treatment of acid mins water cfffuent in sccordance With the invention; and,

Figure 6 illustrates graphically the reduction in iron conoenfretion, heavy mets], salt contaminants and sulphate concentration using the preferred process in the treatment of

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

EE mee tte reece eC evita \ &

As 0oled above, oysnide ges is formed ding fhe sieel-maldug process and is adsorbed in the gas scrabber circuit. As shown in Figure 1, 8 typical gas sarobbe circuit comprises a scrubber 10 fimough which the scrubber wash water falls and is collected in a scrubber bottoms surge tank 12, The scrubber wash water is recycled via pimp 14 to the top of the scrubber 10. It will be seen that as cyanide is adsorbed in the gas scrubber ciruit fo concentration of cyanide in the scrobber wash water can rise to dangerous levels, Cyanide } concentration is controlled by sending a bled stream 16 to an evaporation pond.

However, as noted above this presents the potential risk of cyanide leakage into the environment, The prefered process of treating this bleed stream, as illustrated in Figure 1,

207 ” M KISCH | rAA 0) oO »d 2X30124603270 GRIFKITH wa Dec 2002 11:24 P. 09 Qoos

A cyanide monltor 18 continuously analyses the concentration of cyanide fn the scrubber. bottoms surge tank 12. An upper limit of the eyenide concentration is set for fie moniter 18, md whenever the conoeatraion exceeds fis upper Limit » flow control valve 20 is operated to control the amen of bleed in ths bleed stream 16, The large volume of wash water In tho scrubber cirouit buffers the rate of change in oyanide conceatation and therefore. & low rate changs is expected. The flow control valve 20 also controls the bleed stttam from tho sorubber water pump 14 for the removal of dissolved metals andlor sulphates from the serubber wash water, In order to rednioe the concentration of dissolved. ructals and sulphates in the scrubber water, the bleed stream 16 is passed through sa foe

Biri reactor 22,

In the iltustrated exmbodimet, in-line reactor 22 is 8 satlo reactor in fhe Soma of a

FILBLAST reactor, howover it will be understood that any suitablé in-ins resctoc may be employed, Oxygen er an axygen-containing gas is injected into the FILBLAST

Foastor 22 to react with the scrubber effluent so that the dissolved metals and sulghates se precipitated ont of solution. Preferably lime or caustic soda 1s added to the sorubber efffoent in the bleod steam 16 prior to reacting in the in-line roactar 22 in oder fo reise the! iH and neutralise tho solution, Some precipitation Will ocour #5 a result of this neutralising, however te reaction is quite slow md fusfficicat. Reecting the scrubber efflpent wrth an oxygen-coataining gas in the in-line reactor 2 is believed 0 accelerate ) the process of oxidation/procipitation, Without wishing to be baund by theary, it is believed, for example, that the ferrous (Fel+) Sons are converted to fectlo (Fé) ions in the in-lino reactor, The ferric ions precipitate mach more quickly from solution, fur example, by reaction with the lime to produce Fe(OR), Precipitation of any sulphates andlor oftier dissolved metal salts in the scrubber efffusnt is also acoelerated by reacting }

A clarified sation iis then separated from fhe precipitated sludge fn clarifier or thickemgs 24and tho claified solution 26 i rooycled to the Scrubber circuit, Pup 28 discharges he precipitated sindge 0 a settling dam, The precipitate is of the jarosite spocies of iron ror idd MKS, FAA DL O pas 128603270 GRIFFITH HAGE Dec 2002 11:24 F-10 doo complexes and is readily settled and filtered, rendering possible the disposal of filer cake as a viable altemative to slodge disposal, ‘This represents » significant Ingrovement in view of the more environmentally moocptable materials handling characteristics of the filter cake compared to studge. The shndpe may contain cyanide in which case it will probally require treatment through a cymide destruction process, for example, using

Carsaid, -

The clarified solution 26 may also contain cyanide and is therefore pumpsd via pump 32 toa cyanide destruction facility 30. There are two processes commonly used for oyatide destroction. Either process may be employed in the cyanide destruction facility 30, The

Into sulpkor dioxide method uses air or oxygen, copper supbate and sulphur dioxide (elfber gaseous, or a sodium sulphide salt) to convert the cyanide to cyanate. The second method utilises Cero’s acid which also oxidiscs the cyanide to pantoric cyanate. A method of mixing ambient temperate Kydmgen peraxids and sutphurlc acid in 8 mixing ful is described fn US Patent Nos. 5,439,663 and 5,470,564, A process for the treatment of cyanide in effluents with Caro's acid is described in US Patent No, 5397482. :

In the process ilinstcated in Figure 1, hydrogen peroxide and sulphur: acid are employed but the mixing efficicnoy and Caro's acid ind arc cahanced by uiilisiog a suitably sized

FILBLAST reactor 34. ‘The inline reactor 34 is used to react the acid and hydhogen peroxide and discharge the Caro’s acid directly into the feedline of clarified solution fiom, pop 32 immediately prior to a cyanide destruction reactor 36. Because the Caro’s acid is discharged into the Soodstroam immediately prior 0 catering the cyanide destruction reactor 36, there is no time for the Caro's acid to decompose prior to reaction. A fxther advantags of the described cyanide destruction facility 30 is that it is totally enclosed, and ast operates wnder pressure there is no Loss of decomposition prodvets to atmosphere, if indeed any decomposition produots have time to fon diring the milliseconds time elapse from mixing w reacting, Cyanide-fres water is discharged fiom the cyanide destruction reactor 36 to the scrubber water surge tank 12.

co DUKISO LoL JFRCQIRA003070 | wad DC 00211524 PAL wo one RCT/AU01/00641 -&

Preliminary test rosuls indicats that the described process is ahle to reduce the iron i solution by 97.6%, total dissolved solids (TDS) by 47.8%, calcium hardness byS3.6%and sulphate by 62%. Figures 2 and 3 illustrate graphically the improvement in the treatmext of scrubber effluent fiom a steel mill using the described process. An interesting result is ) & the lowering of the calcium content even though lime was added to the scrubber water fo ralse the pH. The steel mill enmreatly uses cariitic soda becanss lime addition resals in scale fiymation. Test work has shown that fhe product from conventional caustic soda : dosing in an aghtated vessel saves w filo of scalo on fe walls of tho beaker, whereas the product froma the FILRLAST reactor leaves so evidence of soale on tho beaker. :

In the descafbed process the eatmeat of the scrubber effuent to remove dissolved metals anilior sulphates is combined with a cyanide destruction ficility to ddress both problems fn the steel mill scrubber effioent. However, tho removal of dissolved metals andlor sulphates is tmportant in #5 own right to maintain cooling tower efficiency. Tron precipitation from hot scrubber bottoms is important to prevent iron oxidation in the cogling towers, resulting In sludge bullbup and 2 lowering of cooling fywer officiency with eventual collapse of the packing, Hot scrubber bottoms may or may not contain cyanide, depending on the process within the steel making plant. However, when the process of precipitation of dissolved metals is combined with eyanide destraction, it is preferable to ramove the iron before cymmide destruction a8 the fron will increase the consimpticn of Caro’s acid, By maintaining the scrubber circuit water below say 30 ppm fie cyanide, it will be safh to discharge the precipitated studgs to a storage pond. The optimum fies cyanide concentration in the scrubber water will be maintained 85 low 23 possible, us it can be reliably controlled by the oy znide monitor 18, as

Figwwe 4 flinstrates a second embodiment of the process for tho treatment of industrial efftuent ia accordance with the invention, in this case for the treatment of sold mine water (AMW). Acid mine water can be generated witkin & mine site, for exemple, from underground operations, fiom open pits of in the anoff fiom mine waste duns,

Bacterial oxidation cfifuent converts sulphide minerals into sulphuric acid and the essociated metals into soluble sulphate such as iron, copper, rickel, cobalt, zinc, etc which wer nD WKH a or 0 WEXRIEAO05270 pr mace EC 2002 1135 P12 @o12 report to the wastewster streams (efflueat). The resultant acid mine water is therefyre also . contaminated with heavy metals, Other motallugical processes, apert from mining - _ Operations, als generals wastewater toatns fiat contain heavy metal and anon species ’ suth #3 sulphate, carbonsis and chlocdes. Mangaoese, casio, eseais, to ae typically fini fos process effueat sroams oe wifi contaminated gente wats

Canadien Environsuenial and Metallurgica] Inc. (CRMI) has developed & wate feat techaology kaw as the high density sludge (HDS) peocess for the treatment of acid mia drainage. The HDS process is essentially an improved lime precipitation system in which ~~ - lime is added to the wasts water to muse the pif of tho effluent This forms metal : hydroxides which in tor fim a precipitate and settle out. The setting may be done in a tallings pond or a clarifier. A flocenlating ageat may be added to improve the settling characteristics of the precipitate, In the HDS process sludge i removed from the clarifier and returned to 8 tk af the head of toe circuit where the ime is added price to the shudge :

Hime mixture being added fo the treatment plat ifent, Using this proccss, the density of the soled sindge can be fncressnd to over 20% solids o higher, The main adventage of the HDS process is the increase fom 2% solids 10 30% solids which rocaces (oe volume of shidge produced by over 95% The HDS sludge typically drains to a much higher percent solids, Near-complete precipitation of the metals in the effluent as hydroxides duning the oovtliztion ep, coc according to the Following soactios:

M480, 5+Ca"+2(OH+2H,0_,M(OH),+CsS0,.20,0 I)

NIEOF HICH SOHIHER0 MUR HICESCLHE oD) a5 : }

A typical HDS acid mine water treatmeot fhcllty requires a mumber of mixing tanks : flocculant dosing vessels, shudge recycln facilities, ofc, Figure 4 illustrates a modified

HDS process in which a stream of the effluent is diverted tiroagh an ja-line reactor fn accordance with the process of the invention, A stream of tho acid mine water (AMW) is diverted to a first stage in-line reactor 40, Lime story formed in & lime slurry nix tank 42 is added to. the eflinen prior 0 reaction in the inline reactor 40. As with Go fg cond MKIEH, al oo JFRXIQLM603270 i wad DEC 2002 11:25 P13 Rosa eabodimay, Ge in-line reactor 40 is pecfiably a FILBLAST reactor, Tho FILELAST reactor 1s pacticalarly advantageans, es it provides in ntease bigh-shear mixing 200s, nd : oe the cross-flow characteistio imparted 10 th gas crea within fhe reactor creates mts es particles in the high shear conditions, Ths FILBLAST reactor also has very high pases to volume mio compared with ofter statis of mechasically driven Hghe<hea devices. It is beloved that it is fhe combined eft of these reacion cntancing chérastexistics that results in the formation of tho jarosito species noted above, The effipeat fact reacts with mm cxygen-coutatuing gas in the FILBLAST reactor 40 aod aay dissotved metals end/or sulphates are procipitated out of sobation.

Without wishing to be bound by theory, it is thought that te high shear coadions ceeated within the FILBLAST reactor accelerate the process of oxidationfaeeiglation in accordance with the equations (1) and (2) above, However, other reactions may also be ~~ occanting witia the in-line reactor, Industis] effocat contining other metal and gab. mel fous may require removal with ofber suitable prodipitucts besides fim. Ay sulphates andor other pecipitatod metal sls can then bo removed from the eecigitated shudge. Flooculunt rusy be added to ths effucot from a Soccnlent mixing tack 44 pre to seeding with an axygea-contzining gas in a second stage FILELAST rescioe 46. The main purpase of the second stage FILRLAST rescior 46 i fo increase the amouat of : stiphate removal by the addition of specific chemical reagents. Injeifion of si at reactor 461 optional. Depending an the patie of ie shdge widiticns checrical reagents my be

Injected in fc second sage reactor 45 to fille precipitation of ho metal sudlor sulphate species in solution.

Tho pecoipitated shodge fiom the sooond stag FILBLAST reactor 46 flows to a elie o thickener 48 for separation of a clarified solution which is discharged o 1 clear wager tank 50, The clarified water may ber recycled for use In fhe lime slurry or focculens mixing tanks 42 and 44, or may vadergo further treatment 52 fo produce potable Wabes -

The precipitated slodge is discharged. from clarifier 48 to # alndgo dispose] faslity, or optionally to a heavy metals recover plant 54, In the modified HDS process descelbed, the :

Precipitated sludge may be suffictently dense that recyeling is not required. However, if

Fay: 19 Dec 2002 11:25 P.14

Sn MKISCH | ras o1L o SEGeen GRIFFITH HACK i @o14 wo oLm2162 PCY/AUDLA0G41 -11- rsyele is applic the recycle sveam is fected nt ha ed teas pipelne peo tte ; fist stage FILBLAST rector 40, and does not requis a seperate ming vessel, ) Figures 5 end 6 illustrate graphically the improvement in the treatment of acid ming water § cffluent using the described process.

Now that peered embodiments of the proces fr the treatment of industial afc have been described in detail, it Wl be apparent that the process provides & umber. of 0 ®: it substantially reduces the concentration of dissolved metals and/or sulphates in the effluent; an: it reduces the wastage of water as most of the water can be recycled after 15 . tregtment; : :

Gi) In the case of the treatment of scrubber effluent, it improves the efficiency of the : cooliog tower and extends the life of the cooling tower packing and it provides a

Gv) 1 reduces the capital costs by eliminating some plant, and provides 2 more . enargy efficient pmoess for fhe treatment of cfffnent.

Numerous vaiations end modifications wil suggest themselves to persons sidled fn gs 2s checalcal englnceciag and process art, in addition to those already described, withogt departing from the baslo inventive concepts, All such variations and modifications are ta bo cansidered within the soope of the present invention, the nature of which 35 to be ) determined from the foregoing description and the appended claims,

Claims

. 2002 11:26 P.15 ae .D MKISCH | ras wa © »§ 2X 0124605270 GRIFFITH mor Dec ois wo oe21 62 PCT/AT01/00641 12 THE CLAIMS DEFINING THE INVENTION lL A process for the treatment of effinent, the process comprising the steps of . diverting a stream of efilucet containing dissolved metals md/or sulphates through an in-fine reactor: reacting the effiuent with an oxygen-containing gas in the indine reactor whansin said dissolved metals and/or sulphates ate precipitated out of solution; 0 separating a clarified sofution froen fue prooipisated shudge; end, 2 A poocess fox the treatment of effiusat os defined fn Claim 1, wherain the edflugat is en cfflueat from an indnetrial processing plant, a A process for the treatment of effineat as defined in Claim 1, wherein Hime or emustic soda is added to the efffuent prior to said step of reacting fhe effincnt in axder 1p

4. A process for the treatment of cffiuent as defined in Claim {, wheeein said CXygen-coutsining gas is injected ditently imo the in-line reactor adjacent en intake port.

5. A process for the weatment of effive as defined in Claim 1, wherein another suitable precipitant is added to the efaeat prior 30 said step reacting the effiuzat.

6. A process for the trestment of effluent as defined in Claim 1, wherein a sultahyy. flocculent is added to the effluent prior to said step of reacting the effluent 7 - A Process for the treatment of effinet, the process comprising the steps of oo DMKISCH LoL Lf8X30124603270 GRIFFITH Bey Dec 2002 11:26 P16 @oLe diverting a sidestream of effluent containing cyanide through a firstindine mists reacting the effluent with Caro's acid fn the first in-line reactor wherein said - cysalde is oxidised to harmless cysnate; and, : : recycling the cfflwent with cyanats, . R A process for the treatment of effluent as defined in Claim 7, wherein the Caro’s acid bs produced immediately prior to reacting in said in-line reactor. 9, A process for the treatment of effluent as defined in Claim 7, wherein the Caro’s acl is produced by reacting sulphuric acid end hydrogen peroxide in 2 seound in fine reastor which discharges directly fnto a feed line fmmediately prior t the first jadi CI :

10. A process for the treatment of scrubber efftnen, the peocess comprising the steps : of : diverting a stream of sorubber effluent containing dissolved metals and/or sulphates and cyanide through a fist in-line reactor; reacting the scrubber effinent with an axygen-contalning gas in the first in dine reactor wherein sald dissolved metals and sniphates ere precipitated out of solation; 2s spiraling a ciarifzed 1 solution from the prosipitated Sludge; Yeacting the clarificd solution with Caro’s acid in a second in-line reactor wherein ] said cyanide Is oxidised to harmless oyunate; and, + reoycling the clarified solution to the scrubber circuit.