CA1116762A - Process for treating cyanide and cyanate-containing wastewaters - Google Patents

Abstract

PROCESS FOR TREATING CYANIDE AND CYANATE
CONTAINING WASTEWATERS

ABSTRACT OF THE DISCLOSURE

A process for treating a cyanide and cyanate-containing aqueous influent such as a wastewater stream is provided. A two-stage method is included for destroying a cyanide-containing in-fluent which comprises;
(a) introducing said cyanide-containing influent into a first ozone-contacting zone;
(b) contacting said influent in said first zone with a second ozone-containing gas, at least a portion of said second ozone-containing gas comprising a first ozone-depleted gas with-drawn from a second contact zone to form a first cyanide-depleted effluent and a second ozone-depleted gas;
(c) introducing said first oyanide-depleted effluent into a second ozone-contacting zone;
(d) contacting said effluent in said second zone with a first ozone-containing gas to form a second cyanide-depleted effluent and a first ozone-depleted gas;
(e) withdrawing said first ozone-depleted gas from said second contact zone; and (f) withdrawing said second cyanide-depleted effluent from said second zone.
A single stage method is also provided in this invention.
Both single stage and double stage embodiments employ a turbine-gas injector in each ozone-contacting zone to accomplish a high mass transfer of the ozone-containing gas to the influent.
In both the single stage and double stage method, the cyanide-depleted effluents may be recycled to the aqueous influent stream prior to its introduction to either the first or second ozone-contacting zone or to the contacting zones themselves to destroy cyanides and cyanates in these effluents. This destruction is accomplished by allowing residual ozone or other oxidizing species in the recycled effluent to react with the cyanide/cyanate species and reducing influent concentrations by diluting the influent entering the contacting zones while at the same time obtaining lower ozone-containing gas to liquid (G/L) ratios.
In a further embodiment of this invention a method for treating a cyanate-containing influent formed by oxidizing cyanide by any of the above described methods is provided which comprises further multiple ozone-treatment stages.

Description

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1 BACKGROUND_OF THE INVENTION
3 This invention is primarily concerned with a method ~or 4 treating aqueous cyanide-containing liquors with an ozone-contain ing gas to substantially destroy the cyanide content therein.
6 The present invention is also concerne~ with destroying substan-7 tial amounts o~ cyanates in such liquors formed by the initial 8 oxidation of cyanides.
9 , Simple cyanides as well as complex cyanide compounds are present in the waste ef~luents ~rom certain chemical operations 11 such as metal plating processes, photographic processes, mining 12 operations, and metal refining processes. Because o~ the toxio 13 nature of these cyanides and the potential hazard o~ oontaminatin 14 water supplies, these ef~luents cannot be discharged into rivers or lakes without pretreatment to reduce cyanide levels. This con-16 tamination problem is not avoided by disoharging such e~luents 17 on land since the cyanides can eventually pass through the soil 18 and reach water supplies. In order to protect the environment and 19 the public at large, federal and state governments have prescri~e~d limits on the levels of cyanides in ef~luents discharged ~rom such 21 chemical operations.
22 Cyanates, which are formed by the initial oxidation of 23 cyanides, are less toxic than cyanide but nonethele~s present a 24 potential danger to the environment. Government regulations have not yet been promulgated f'or cyanate discharge but it is expected 26 that such regulations will be forthcoming. Therefore, there is a 27 substantial need ~or an e~ficient method of destroying cyanides in 28 wastewater effluents to acceptable levels and also ~or a method 29 which reduces the cyanate content in the e~luent finall~ discharg 3o ed to the environment~

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1 In the past, attempts at substantially destroying cyanides

2 contained in Wastewater ef~luent streamS hav0 either been too

3 inef~icient o~ too expensive for large scale commercial treatments .

4 For example, toxiC cyanides can be precipitated aS insoluble

5 heavy metal compounds by the addition o~ a heavy metal salt to a

6 cyanide-containing liquor. Unfortunately, complete elimination

7 0~ cyanides iS no-t accomplished by this method and it requirec

8 co~tly and bulky equipment.

9 Oxidation of cyanides to cyanates and then to carbon dioxide and nitrogen by alkaline chlorination has also been described in 11 the art. One of the initial products, cyanyl chloride, however 12 iS also toxic and destruction o~ it iS slow which o~ten result8 13 in incomplete treatment o~ the e~luent. Moreover, the addition 14 Of agents to control p~ adds to the total di9solved solid9 in the e~fluent.
16 The USe of peroxides to oxidize cyanide has al90 been sUg-I7 gested bUt iS considered commercially prohibi-tive due to the high 18 co~t of materials.
19 Another problem shared by the above methods i8 their inabil-ity to break down metal-complexed cyanides such as iron cyanide.
21 More recently, ozone-containing gase9 SUCh as ozone-air, 22 o~one-oxygen and ozone-air and oxygen, either alone or in combin~
23 ation with a U.V. light treatment, have been employed as cyanide-24 treatment agents for wastewater effluents because they are relat-ively inexpensive to produce and are ef~icient oxidants ~or 26 cyanides. Ozone rapidly oxidizes cyanide to cyanate if a high mas~
27 transfer of ozone to the e~fluent is accomplished. The oxidation 28 ol cyanate to gaseous nitrogen and carbon dioxide however, is 29 kinetically controlled and therefore requires significant addition 3o al contact time With ozone. Metal complexed oyanide9 SUCh as iron _4_ '~ ' ` ` ~ i7~

1 cyanides are not usually destroyed by ozonation.
2 Xn U. S. Patent No. 3,920,547 to R. L. Garrison et al, a 3 method for the destruction of cyanides, particularly cyanides 4 complexed with iron in an aqueous cyanide solution is pro~ided comprising contacting the solution with an ozone-containing gas 6 while simultaneously irradiating the aqueous cyanide solution with 7 ultra-violet light. The method is preferably carried ou-t while 8 maintaining the pH of the solution between 5 and 9 at temperatures 9 o~ between 30C. and 70C. It is also preferred to contact the a~ueous cyanide solution and ozone- containing gas in a plurality 11 o~ separate zones, one atop the other in a tower, counterourrently 12 or by parallel flow,with the simultaneous irradiation with UV ligh-13 being carried out in at least one o~ the separate contact zones, 14 preferably in the last zone where the cyanide ion concentration is 1~ a minimum and reac-tion rate must be enhanced.
~6 To provide for a more e~icient dispersion o~ ozone-contain-17 ing gas, each zone in the tower can be equipped with a means to 18 provide small bubbles in the solution such as a mixer, porous ston 19 diffuser, ozone ejector or other suitable means to obtain a sat-is~actory mass transfer of ozone from the gas to the liquid phase.21 In U. S. Patent No. 3,732,163 to W. Lapidot, a process and 22 apparatus for treating industrial waste ~treams is described 23 employing a plurality of ozone treatment zones wherein a major 24 portion (70~ to 95%) of the liquid to be treated is introduced into the upper portion of a ~irst ozonation zone and the remaining 26 portion of the li~uid is introduced into a second ozonation zone, 27 each zone comprising a packed tower. An ozone-containing gas mix-28 ture enters the bottom of the first zone, contacts the liquid 29 therein and is discharged to the lower portion of the second zone.
3o The treated effluent from the first and second zones can aach be ~ 67~2 ..`

l ret~rned or combined and returned to the natural source from where 2 the liquid was obtained or can be recycled for ~se as fre~h water~
3 The outlet ~tream from the second zone can be directed to the 4 fir~t zone to insure that this portion of the water receives the full ozone treatment at all -times. ~he ga~eous stream removed 6 from the upper portion of the second ozonation zone is then util-7 ized for the regeneration of the ozone-oontaining gas by ~ixin~
8 with oxygen, drying, bleeding to remove nitrogen and then intro-9 ducing it to an ozone-generation device.
The present invention, on the other hand, deal~ with an 11 efficient method of treating a cyanide-containing aqueous liquor 12 with an ozo~e-containing ga~ in at lea~t one ozone-contacting zone 13 to destroy cyanide~ contained therein by providing a high-ma9s ~ tran~fer of ozone to the aqueous liquor.
The high mass transfer of ozone to influent i~ accomplished 16 by employing a turbine gas injector in each zono. The injector 17 spins a portion of the wa~tewate:r influent in a turbine-bladed 18 impeller rotor at high speed and mixe~ the wastewater with an 19 ozone-containing ga~, which gas i~ broken down into small bubble~
by the mixing and di~tributed in the influent portion. ~hi3 strea 21 of ozo~e-containing gas and influent is then injected into the 22 zone containing a volume of wa~tewater influent.
2~ ~y recycling at least a portion of treated liquor from the 2~ contacting zone to either the influent liquor stream or to the zone itself, or by retaining said portion in a holdin~ zone and 26 then recycling, additional cyanide a~ well as cyanate, formed as 27 an intermediate in the cyanide oxidation, is also oxidized by the 28 direct ozone treatment in the zone and the residual oxidants in 29 the recycled liquor.
~0 ~hen carried out in two or more ozone-contacting ~ones where I ~.1676~

1 ¦ in at lea~t a portion o~ an ozone-containing ga3 ~rom an ozone 2 ¦ source contacts liquor in the lat-ter zones and the expended gas 3- ¦ therefrom is used as at least a portion of the ozone treating gas 41 for the earlier stages, with any remainder o~ treating gas being 5¦ supplied by the ozone source, substantially complete ozone util-I ization is achieved in destroying cyanide.
71 ~y recycling or retaining and recyclin~ at least a portion 8¦ o~ treated ef~luent from one or more latter zone~ to an earlier 9¦ zone or to incoming untreated liquor itself, incraa~ed cyanide

10¦ and cyanate oxidation is accomplished. In addition, certain free

11 ¦ and complexed metals in the wastewater such as copper, iron and

12 ¦ zin¢ are oxidized to an insoluble and ~ilterable or settleable

13 I state.

14 ¦ A process ~or substantially destroying cyanate which is

15 ¦ ~ormed by the oxidation o~ cyanide by any o~ the cyanide-treat-

16 menb prooes es ~ bhi~ lnvenbion i~ also provid~d.

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1 ¦ SUMMARY 0~ THE_INVENTI0 2 I ~
3 ¦ Basically the present invention comprises introducing a 4 ¦ cyanide containing liquid influent into at least one ozone treat-5 ¦ ment zone wherein the influent is mixed wi-th an ozone-containing 61 gas at high speed to impart a high vaIocity to the influent and 71 to break the gas into small bubbles. This treatment achle~ee a 81 high mass transfer of ozone to the influent thereby insuring 9¦ optimum reaction conditions for the oxidative destruction o~
10¦ cyanides contained therein.
11 1 The ozone treatment zone preferably comprises a tank or re-12¦ actor having an inlet and outlet for influent introduction and 13~ treated e:~fluent withdrawal, respectively. The tank or reactor 14¦ also has a ga~ outlet at the top thereof for withdrawal of ex-15 ¦ pended ozone-containing gas.
16¦ This high mass transfer of ozone to influent is accomplished

17¦ by employing a gas injector associated with the ozone treatment

18¦ zone which comprises a cylindrical casing extending into the zone

19¦ having an enlarged section at its lower end comprising a pair of

20¦ oppo~ed shroud members. 3etween the shroud member~ is an elong-

21 1 ated annular gap to allow the gas-liquid mixture to pass from the

22 ¦ casing into the zone, ~ shaft is rotatably mo~nted within the 231 casing coupled to a means for rotating the shaft sRch as an elect-24 ¦ ric motor. The shaft has a turbine blade impeller rotor mounted 251 on its lower end which impeller extends into the enlarged section, 26 ¦ ~y rotating the shaft, cyanide-containing wastewater influent is 27 ¦ drawn into -the water intake of the spinning impeller at the bottom 28 ¦ of the casing while ozone-containing gas is drawn into the casing 29 ¦ via a gas inlet tube communicating with the inside of the ca~ing ~0 ¦ just above the enlarged section. The gas is mi~ed with influent :

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1 expelled by the high speed lmpeller thus breaking the ga~ into 2 qmall bubbles which exit the injector through the elongated gap ~ in the ~orm of a mixture of bubbles and influent.
4 A wastewater influent line can also be directlg connected to the bottom of the injector in the contact zone for maximum 6 cyanide destruction with maximum ozone transfer. Thi~ i~ espeeial- .
7 ly preferred for use in the first ozone treatment ~one a~ will be 8 deseribed in more detail below.
Such turbine gas injectors as described above have been used heretofore in bio-oxidative treatment~ of non-eyanide containing 11 liquor9 but their use for treating cyanide-containing wastewaters 12 has not been deseribed heretofore.
13 The ozone-eontaining ga~ u9ed to treat the wastewater can be 14 an ozone-air, ozone-oxygen or oz;one-air and oxygen mixture as ~5 prepared by eonventional ozone ~renerators. Sueh ozone generators 16 are eapable of produeing gas mi~tures from an ~ir ~ouree eontain 17 ing ~rom about 1.0% to 3.5% ozone by weigh-t. From an oxygen 18 ~ouree sueh generators produce ozone-in-oxygen or ozone-in-air and oxygen gas mixtures containing from 2,5~ to 7.5~ ozone by weight.
~he proeess of this invention ean be used to destroy high 21 eyanide-containing effluents containing lO0 p.p.m. total eyanide 22 or more, medium cyanide concentrations of 50 to 100 p.p.m. total

23 cyanide as well as low eyanide-eontaining ef~luents, i.e, oontain-

24 ing 50 p.p.m. total eyanide or les~.
Although ~ubstantial amounts of total eyanide-eontaining 26 3peeies can be destroyed bg u3ing one eontact zone equipped with 27 a turbine ga~ injector, it is preferred to employ at least a two 28 stage method comprising;
29 (a) introducing a cyanide-containing liquid influent into 3o a ~ir~t ozone-eontacting zone;

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~, 1 (b~ contacting said,influent in said first zone with a 2 second ozone-containing gas, at least a portion of said second-3 ozone-containing gas comprising a first ozone-depleted gas with-4 drawn from a second contact zone, to form a first cyanide deplete effluent and a second ozone-depleted gas;
6 (c) introducing said cyanide-depleted effluent into a 7 second ozone-contacting zone~
8 (d) contacting said effluent in said second zone with a , 9 first ozone-containing gas to form a second cyanide-depleted effluent and a first ozone-depleted gas~
11 Substantially complete ozone utilization is accomplished by ~2 one of two methods, i.e., either all fresh ozone-con-taining gas 13 from an ozone source is introduc:ed in-to the second zone and the 14 exhaust gas therefrom is introduced into the first zone, or, a fraction o~ fresh ozone-containi.ng gas is introduced into the 16 second zone, the exhaust gases therefrom are combined with the 17 balance of fresh ozone-containing gas from the source and the so 18 combined ozone fractions are then introduced into the first zone.
19 '~astewater flow optimization 'can be obtained by withdrawing a portion of the treated effluent wastewa-ter from the first andjo 21 second zones and recycling it to the influent or to the first zone 22 directly. In the case of a single-stage treatment a portion of 23 treated effluent can be recy'cled from the single o~one contacting 2~ zone to incoming influent or to the zone directly. This flow 2~ scheme will reduce -the amount of total cyanide that must be treat-26 ed in the first stage and will also allow ozone to react with some 27 f the cyanate contained and/or formed in the first and second 28 stages. ~esidual oxidants in,,the treated effluent such as ozone, 29 peroxide or oxygen species and metallic oxides are also mixed with 3o the raw cyanide-containing in~luent by recycling, thereby renderin ~1.67~i2 ,.

1 them effective for the oxidation of total cyanides and cyanates.
2 Moreover, the total ozone gas-to-liquid ratio can be decreased 3 by recycling thereby increasing the system efficiency. It has 4 also been found that 90% of the total copper and complexed iron and 100% of the total zinc in the wastewater are oxidized in the 6 process to insoluble and settlable solids whi:ch can be removed 7 by filtering or settling after one or the other stage whioh sub-8 stantially reduces the total metals, total cyanide and cyanide 9 amenable to chlorine in the wastewater. This can be accomplished without a pH adjustment.
11 Cyanate destruction in the wastewater effluents from the 12 first or second stages can be achieved by retaining the effluents 13 in holding zones or tanks before further treatment with ozone 14 by recycling. This allows cyana.te to react with residual oxidantt to form gaseous carbon dioxide and nitrogen. As previously ment-~6 ioned, reaction of cyanate to gaseous carbon dioxide and nitrogen 17 is Isinetically controlled and requires extended con~act periods 18 to go to complation. In the case of a single stage treatment a 19 single holding zone is employed after treatment in the zone.
Three or more additional contacting zones are preferably 21 used for cyanate destruction, the number of contacting zones de-22 pends on the initial concentràtion of cyanate and the desired 23 level of cyanate in the effluents. More contacting zones o~fer 2~ higher utilization of ozone, particularly when low effluent con-centrations of cyanate are required.
26 Wastewater flow for cyanate destruction, like cyanide 27 destruction, is from the earlier zones to the latter zones with 28 counter current ozone-containing gas flow from the latt`er stages 29 to the earliar stages, at least a portion of -the ozone-depleted 3o gas from a latter stage being used as the ozone-oontaining gas ~6~i2 ~or the next earlier stage with the remaining portion of ozone-containing gas, if any, being supplied by the ozone source.
In accordance with one broad aspect, the invention relates to a process for treating an aqueous cyanide-containing influent comprising: (a) providing an ozone-contacting zone having an operating turbine gas injector associated therewith said injector comprising a hollow casing extending into said zone having an enlarged section at the lower end thereof, said enlarged section having an annular elongated gap which extends into said zone, a shaft rotatably mounted in said casing, a turbine-bladed impeller rotor mounted on said shaft and extending into said enlarged sectionr said rotor ~aving a liquid intake section, means for rotating said shaft, and a gas inlet communicating with said casing above said enlarged section; (b) introducing said influent to said zone, at least a portion of said influent being introduced to said liquid intake section; (c) introducing an ozone-containing gas to said gas inlet; (d) mixing by spinning said impeller at least a portion of said influent with said ozone-containing gas in said enlarged section to ~orm a stream of bubbles of said ozone-containing gas in said influent and injecting said stream into said zone; and (e) withdrawing a cyanide-depleted effluent from said zone.
BRIEF DESCRIPTION OF THE DRA~INGS
Fig. 1 is a front view of a reactor for treating cyanide-containing wastewater influents according to this invention having associated therewith a tur~ine gas injector which effects high mass transfer of ozone to influent.
Fig. 2 is a front view of a reactor having associated therewith a turb~ne gas injector wherein the influent line to said reactor is directly connected to said gas injector.

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Fig. 3 is a sectional view of a 'rfail-safe"
modification of Fig. 2.
Fig. 4 is a flow diagram of the process embodiments of this invention.
Fig. S is a process block diagram which includes the processes of Fig. 4 and also a cyanate destruction process.

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1 DETAII,ED DESCRIPTION_OF THE PREFERRED EMBODIMENTS
3 Fig. 1 shows a reactor containing a turbine gas injector 4 used to effect high mass transfer of ozone to cyanide-containing in~luent in the prccess of this invention. Such turbine gas 6 injectors are manufactured by the Kerag Co. o~ Richterswil, 7 Switzerland and are sold in the United States by the T.I.I. Corp.
8 o~ Lindenhurst, New York.
9 The reactor is shown generally by 11 and consists of a cylindrical tank 12 having a water inlet 13 and a water outlet 14 11 at opposing sides thereof. Mounted atop the tank 12 and extending 12 through the top wall 15 thereof is an electrio motor driven turbin 13 gas injector shown generally by 16.
1l~ The injector 16 comprises a hollow cylindrical casing 17 mounted under electric motor 18 and extends into the tank through 1~ the top. ~he casing 17 is seourlsd to -the upper wall 1~ of the 17 tanlc by collar 19 which si-ts in an annular recess 20 in the top 18 wall and is secured therein by means of bolts 21. Bolted to the 19 outside of the casing at its lower end i9 upper shroud member 22 which flares outwardly from the casing. Mounted below the upper 21 shroud member 22 by means of bolts 23 is lower shroud member 24 22 which is, for the most part, a mirror image of upper shroud member 23 22. The upper and lower shroud members together form an outwardly 24 flaring collar or enlarged section at ths bottom o~ the casing.
There is a small annular, elongated gap 25 between the flared ends 26 of the shroud members which can be varied by adjusting bolts 23.
27 The upper shroud member 22 and lower shroud member 24 form interna 28 chamber 32. The lower end of the lower shroud member 24 is 29 flanged and is bolted to the flanged end o~ water intake section 3o 26. An inwardly protruding section 27 at the lower inner section ~ i7~Z

1 of the lower shroud member 24 defines an annular space to accomo-2 date impeller intake section 33 which will be described in 3 more detail below.
4 Rotatably mounted inside the casing 17 is shaft 28 which is coupled to motor 18 and extends to the lower end of the casing.
6 The shaft i~ rotatably supported by bearing 29 in the casing at 7 top wall 15. A seal 30 located just below the top wall in the 8 casing prevents ozone and other gases from reaching the bearing 9 and motor. Mounted at the lower end of shaft 28 is turbine-bladed impeller rotor 31 which fits closely within chamber 32. The wa-ter 11 intake end 33 of the impeller is nested within the annular space 12 defined by section 27.
13 A gas inlet line 34 extends from the top of the tank 12, 14 through collar 20 and joins -the casing 17 above shroud collar 22.
A gas outlet ~0 is located in the top of the tank.
16 The tank 12 is also e~uipped with water guide baffle 3~ near 17 water~ inlet 13 which baffle directs water flow to the inlet sectio 18 26 of the injector. An overflow weir 36 is mounted inside the 19 tank near outlet 1~ to control liquid level in the tank. ~ounted on the water guide baffle 3~ and overflow weir 36 are baffle fin~
21 37 which prevent liquid in the tank from developing a vortex 22 during op~r~ion of the injec~or. Additional ~in~ are equally 23 spaced around the inside of the tank (not shown). In operation 2~ o~ the tank and injector o~ Fig. 1, cyanide-containing influent is introduced to the tank through inlet 13 and around guide 26 ba~fle 35 to a level indicated in the Figure. The motor 27 is 27 energized and rotates shaft 28 and impeller 31 at high speed while 28 ozone-containing gas from an external supply is connected with gas 29 inlet 3~. A portion o~ the influent in the tank i~ drawn into the 3a in~ak~ 33 ~ ~he spin~in~ pe~ler 3~ whil~ ~ th~ g~o ~im~ o~one , ~:~3L67~
.
., 1 containing gas is drawn into the casing 17 where it is mixed with 2 influent expelled from the high speed impeller inl~kespace between 3 the impeller and elongated gap to impart a high velocity to the 4 influent stream and to break the gas into small bubbles. ~he liquid stream and ga~ mixture are injected through the elongated 6 gap 25 into the mass of influent liquid in the tank as shown by 7 the arrow~. Momentarily, as the gas-water vortex action is slowed 8 by the maqs of liquid in the influent plenum volume, the gas 9 velocity pressure is converted into high sta-tic pre~sure in con~
10 1 tact with the extended surface interface of the water and acoom-11 ¦ plishe~q a high mass transfer of ozone to liquid in the tank~
12 ¦ Sinoe the impeller 31 draw~q in the gas stream, the ga~ line to 13 ¦ the tank is under negative pressure, thereby reducing the po~
14 ¦ bility of gas leakage into the ambient environment.
¦ The bubble size of the injected ga~ depend~ upon a number of 16 ¦ parameters including the speed or r.p.m. of the impeller, the widt~
17 ¦ of the elongated gap 25, the ozone-containing gas to liquid in~lu-18 ¦ ent ratio, the viscosity of the influent, the t~mperature of the 19 influent and the static pressure head o* liquid influent in the tank. By adjusting these parameter~ ~uch bubble eize~ can be 21 controlled to between about ~ mm. to about 60 mm. in diameter and 22 preferably from about ~ mm. to 5 mm. for optimum ma~ transfer 23 conditions.
24 After treatment in the injector, treated effluent is with-drawn from the tank through outlet 14. Expended ozone-containlng 26 ga~ is withdrawn from the tank through gas outlet 40.
27 ~ig. 2 shows an alternative construction of the tank 12 28 wherein wastewater in~luent is connected directly to the bottom 29 of the injector 16. In this con~truction, influen-t line 38 enter~
3o through the ~ide wall of tank 12 where it is bolted to shroud 1~7~ 1 1 member 24. Inlet 13 and guide baffle 35 as shown in Fig. 1 are 2 eliminated and fin 37 is mounted on the wall of tank 12. ~his 3 con~truction allows all wastewater influent to be fed directly to 4 the injector 16. It has been found that such a construction is desirable for the first stage of ozone treatment in the multi-6 stage embodiment of this invention whereas the construction u~ed 7 in Fig. 1 i9 preferred for the second or labter s~agee.
8 Figure 3 i~ a sectional view of a fail-safe embodiment of ~ig. 2 showing only the lower portion of injector 16. In this 12 .

1 a 21 .

23 .
24 .

28 .

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1 ¦ embodiment, the wastewater in~luent line 38 is not directly con-2 ¦ nected with the bottom o~ the injector but ~lares outwardly in 3 ¦ an inverted frustro-conical shape 39 a short dis-tance below 4 ¦ shroud member 24. Such construction prevents excessive pressure 51 on the impeller 31 at high flow rates of influent thus preventing 61 damage to the impeller and motor. Excessive pressure i9 relieved 7¦ by letting a portion of the influent escape into the tank between 81 the edge of ~he ~lared section 39 and the bottom of the injector.
91 During underflow conditions, wastewater from the tank is drawn 10¦ into the frustro-conical shape 39 for turbine optimization.
11¦ Fig. 4 is a flow diagram of process embodiments o~ this 12¦ invention which includes;
131 A. A single-stage ozon~ treatment~
1~¦ B. A single-stage ozon~ treatment with reoycling o~
1~¦ troated e~fluent to influent;
16 ¦ C. A double-stage ozone treatment; and 17 D. A double-stage ozone treatment with recycling o~
18 treated effluent to influent.
19 Ozone-containing gas flow in -the single-stage ozone ~reat-ments, is from an ozone-containing gas generating source direotly 21 to the stage or zone containing water to be treated, with the 22 exhaust or expended gas being discharged from the system. In 23 the case of the double-stage ozone treatments, either all ozone-2~ containing gas may be introduced into the second stage and the 2~ exhaust gas withdrawn therefrom introduced as the ozone-containing 26 gas to the first stage or a portion of the total flow of ozone-27 containing gas may be introduced into the second stage, the ex-28 haust therefrom combined with the remaining portion of ozone-con-29 taining gas and the combined gases introduced as the ozone-contain 3o ing gas to the first stage.

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, 1 A Sin~le-Stage 0,zone Treatment 3 Referring to Fig. 4, cyanide-containing wastewater influent 4 enters the system in line 61 where it is directl~ introduced to the bottom of an operating turbine gas injector 64 as shown in 6 Figure 2 which is housed in Reactor No. 1. Valve 62 in oonjunc~
7 tion with flowmeter 63 regulate wastewatsr influen~ flow ~o 8 Reactor No. 1.
9 Connected to the gas inlet 64a of the injector is line 78 which conducts ozone-containing gas generated in ozone generator I1 70. Flowmeter 79a and valve 80b are used to measure and oontrol 12 flow through line 78.
13 Such ozone~containing gas can be an ozone-air, ozone-oxygen 14 or ozone-air and ox~gen mixture wherein the ozone compri~es for example f~om about 1.0% to 3.5% by weight of the mixture when 16 using an air feed to the ozone generator,About a 2% by weight 17 ozone-in-air mixture is preferred. Through the high rotational 18 speed o~ the impeller in the injector 64, the in~luent is ~ed 19 into the impeller and mixed with ozone-containing ga~ drawn into the casing o~ the injector to ~orm a mixture of very fine bubbl~s 21 of ozone in the influent.
22 After t,he ozone-containing gas and wastewater influent 23 mixture are distributed into the plenum volume of influent in 24 Reactor No. 1 in the form of a mixture of fine bubbles of ozone in the influent and allowed to react, the expended ozone-contain 26 ing gas from Reactor No. 1 is withdrawn therefrom in line 66. Th 27 flow through line 66 is monitored by flowmeter 67.
28 Treated wastewater effluent from Reactor No. 1 is withdrawn 29 in line 65 and may be removed from -the system by directing flow 3o to Hold Tank No. 1 via line 92 and valve 91 and from the Hold`Tan ~ 7~2 '.' ,~ .

1 to line 90 via valve 93, pump 87 and valve 89. Valves 68 and 88 2 are closed.
3 The above-described Single-Stage Ozone Treatment is part-4 icularly useful for treating low cyanide-containing wastewaters ~ ie; 50 ppm or less cyanide.

7 B. Sin~le-Sta~e Ozone Treatment With Rec.vclin~
8 of Treated Effluents Alternatively, treated effluent from Reactor No. 1 in Hold 11 Tank No. 1 may be recycled to line 61 through line 86, valves 88 12 and 93 ancl pump 87. By recycling the trea-ted ef~luent in the 13 Hold Tank, residual oxidants in the effluent are allowed to des-14 troy additional cyanide and time is allowed for the kinetically-controlled conversion of some oyanate to carbon dioxide and nitro-16 gen to take place.
17 The treated e~fluent from Reactor No. 1 combined with the 18 in~luent feed in line 61 at about double the original flow rate 19 are contacted with ozone-containing gas in ~as injector 64 of Re-actor No. 1. IThe recycling of treated ef~luent containing a re-21 duced cy~nide content to incoming in~luent in line 61 reduces the 22 amount of total cyanide that ~ust be treated in Reactor No. 1 ther _ 23 by allowing a portion of the ozone-containing gas to react with 24 cyanate in the influent. Additional unreacted oxidants in the treated effluent are also mixed with -the raw cyanide-containing 26 wastewater thereby rendering them effective for the oxidation of 27 total cyanide and cyanate. The recycling also reduces the ozone-28 containing gas-to-liquid influent ratio since less cyanide must be 29 treated thereby rendering the process more e~ficient.
3o ` A~ter treatment in Reaotor No. 1, treated recyoled and raw 1~ 62 1 wastewater may be separated from the system in line 90 as mention- .
2 ed above in connection with the single-stage ozone treatment, 4 C. Double-Sta~e Ozone Treatment 6 The wastewater ~low in Reactor No. 1 of the double stage 7 ozone treatment is the same as in the single-stage treatment ex-8 cept that the ozone-containing gas introduced into the gas inlet 9 64a of Reactor No. 1 comprises at least a portion of the expended ozone-containing gas withdrawn from Reactor No. 2 whioh will be 11 described in more detail hereafter.
12 Treated wastewater effluent from Reactor No. I is withdrawn 13 in line 65 and enters Reactor No. 2 by opening valve 68. As 14 shown in Fig. 1, the effluent enters Reactor No. 2 at the water 1~ inlet in the ~ide of the Reactor. A por-tion o~ the e~fluent i9 16 then drawn up the water inle-t of turbine gas injector 6~ in, 17 Reaotor No. Z. Line 65 may also be directly connected to the 18 bot-tom o~ turbine gas injector ~4 as in Reactor No. 1. (see ~ig.2 19 Treated effluent from Reactor No. Z is withdrawn in line 83 where it can be separated from the s~stem by closing valvo 102 21 in line 98.
22 The ozone-containing gas generated in ozona generator 7~ l~
23 introduced into Reactor No. 1 and No 2 by either of the following Z4 schemes.
2~ In one scheme, all ozone-containing gas from generator 7Q
26 is introduced ~nto the gas inlet 64a of turbine gas injector 64 27 f Reactor No. 2 via line 99 and 71, through valves 73 and 101.
28 Flowmeter 100 in line 99 and flowmeter 72 in line 71 monitor gas 29 flow. After contac^ting and reacting with the influent in Reactor . 30 No. 2, the ozone-depleted gas is withdrawn in line 74 monitored 31 by flowmeter 77 and enters line 7~ when valve 76 is in the closed 1 position. The ozone-depleted gas in line 75 connects with:~line 2 78 via valve 79 and flowmeter 80 to the gas inlet 64a of turbine 3 .injector 64 of Reactor No. 1. This scheme is preferred for low 4 cyanide-containing influent~
In the seoond scheme, which is preferred for high cyanide-6 containing influents, a portion of ozone-containing gas from 7 ozone generator 70, e.g. from 1~ to 99%, preferably 50% ~ 10% o~
8 , the total,may be introduced into the turbine gas injector of 9 Reactor No. 2 through line 71 and the remaining portion introduce into line 78 where it is combined with ozone-depleted gas exhaust ll ed from Reactor No. 2 in line 75. ~he ozone conoen-tration of the 12 ozone-depleted gas determines whether or no-t it is reused in 13 Reactor No. 1. This offers maximum flexibility in operating the 14 system for variatio~sin cyanide concentrations in the influent.
A por-tion of the ozone-depleted Igas from Reac-tor No. Z' may also 16 be withdrawn from the system through line 81.
i7 18 D. Double-Sta~e Ozone Treatment ~ith Rec~clin~ of 19 Treated Effluent 21 ~reated effluent from Reactor No. 2 can also be withdrawn 22 through line,98 where it is i~troduced into Hold Tank No. 2. If 23 desired, the effluent may be retained in the Hold Tank for from 24 about 5 to 15 minutes to allow residual oxidants to destroy ¢yanid and some cyanate.
26 The effluent is withdrawn from Hold Tank No. 2 in line 84 27 through valve 85 where it enters line 86 and is introduced to 28 wastewater influent line 61 by pump 87 through v,alve 88. Raw 29 wastewater influent and recycled effluent are then introduced to 3o Reaotor No. 1. A portion of the recycled effluen-t in line 86 may ~ -20-1 be dumped via line 90 by opening valve 89.
2 Hold Tank No. 1 may also be employed -to accept treated 3 effluent from Reactor No. 1 by closing valve 68 and opening valve 4 91 in line 92. Treated effluent in Hold Tank No. 1 may then be withdrawn to line 86 where it is combined with treated effluent 6 from line 84. If desired, treated effluents in Reacto~ No. 1 7 or No. 2 need not be retained in any Hold ~anks but may be direot-8 ly recycled to influent line 61 as indicated by dotted lines 102 9 and 103.
A portion of treated effluent in line 86 may also be re-11 cycled to Reactor No. 2 in lines 94 and 65 by opening valve 9~
12 and olosing valves 88 and 89. The advantages o~ r~cycling ha~e 13 been discussed above in connection with the single-stage treatment 14 with recycyling of treated effluent.
~ It has been found that by emplo~ing a single-stage oæone 16 treatment with no recycling, abou-t 80% to 90% of the total cyanide 17 in the original wastewater influent can be destroyed rapidly i.e.
18 in less than 10 minutes. In the case of single-stage treatment 19 with recycling, even greater amounts of total cyanide in the treated recycle ef~luents are destroyed as well as significant 21 amounts of cyanide in the combined raw influent. Significant 22 amounts o~ additional cyanate are also destroyed in the case o~
23 the double-stage reaction wi-th no recycling.
24 In the double-stage treatment with recycling of treated effluent, even greater amounts of cyanide and cyanate are destroye~ 1.
26 It has also been found that the ozonation treatment accord-27 ing to this invention also oxidizes simple and complexed metals 28 in the cyanide-containing wastewater to form a precipitate. This 29 precipitate can be filtered or settled to remove the metals as wel:
~0 as reduce urther the total cyanide in the wastewater influent.

ll l ~ i;7~i~
.

1 For example, in the case of a cyanide-containing influent also 2 containing small amounts of copper, iron and zinc, free and com-3 plexed with cyanide species, about 90% of the copper and comp.Lexed 4 iron and about 100% of the zinc can be removed in the second stage of a double-stage ozone treatment, with or without recycling o~
6 effluent.
7 It has also been found that by regulating the ozone flow in 8 the double-stage process according to the schemes outlined above, 9 100% ozone utilization can be achieved by controlling gas ~o liqui l 11 ratios for specific cyanide influen-t concentration~.
2 . . .

17 , .

19 .

2a ., ~ 76~
.~

1 Figure 5 is a block diagram of a process for substantially 2 destroying cyanate contained in a cyanide-depleted effluent strea 3 such as that discharged ~rom line 83 of ~igure 4. Such e~fluent 4 contains substantial amounts of cyanate derived from cyanate orig ~ inally present in the wastewater in~luent stream in line 61 and 6 from cyanate formed by the initial oxidation of cyanides in 7 Reactors No. 1 and No. 2 by any of the methods hereinbe~ore dis-8 cussed.
9 The left portion of Figure 5 is essentia~ly a repe-tition of Figure 4 in block diagram form showing only essential wastewater 11 lines, ozone-containing gas lines, Hold Tanks and Reaotors.
12 The right portion of Figure ~ is a block diagram of a cyanate 13 destruction process.
14 Effluent from line 83 enters the first reaotor, Reactor No.
3' ~ a multi-reactor system comprising Reactors No. 3,4 and ~, 16 eaoh of whioh reactors may be similar ln construction -to Reactors 17 No. 1 and No. 2. However, since the oxidation of cyanate to 18 nitrogen and carbon dioxide is kinetically and not mass ~rans~er 19 controlled it is unneoessary to employ turbine gas injector~ as in Reactors No. 1 and No. 2, although such injectors may be employ 21 ed, if desired. Conventional ozone ejectors or diffusers are 22 also satisfactory. Effluent ih Reactor No. 3 is reaoted with ~n 23 ozone-containing gas and withdrawn in line 105 whers it may be 24 discharged in line 106 if desired, depending on the levels of cyanate destroyed in the effluent. Preferably, however, the 26 effluent in line 105 is introduced into Reactor No. 4 where it is 27 again treated with an ozone-containing gas and withdrawn in line 28 107. This effluent may be discharged in line 108 depending on 29 the desired degree of cyanate destruction or introduoed into 3o Reactor aO~ 5. After ozone -treatment in Reactor nO~ s~ the treat--Z~_ ~

~ i2 .` I ,, 1 ¦ ed effluent is withdrawn in line 109 where it is either removed 2 ¦ from the system in line 110 or sent to lurther ozone reactors 3 ¦ (not shown), if necessary, to further deplete cyanate.
4 The ozone distribution system in the cyanate destruction ~ process o~ Figure 5 is similar to the system for destroying 6 cyanide. An ozone-containing gas source such as an ozone-air, 7 ozone-oxygen or ozone-air and oxygen gas generator as indioated 8 by 111, introduces ozone-containing gas to each Reactor by one 9 or the other o~ the ~ollowing methods.
In the first method, a portion of ozone-containing gas is 11 introduced into one or more of the later reactors and the exhaust 12 gases therefrom combined with ~he remaining portions of ozone-13 containing gas being introduoed to one or more earlier zones.
14 For example, an ozone-containin~; gas in line 112 may be introduced into each o~ Reactors 3, ~ or 5 through lines 113,114 and 115, 16 respectively (eg 1/3 to each). Exhaust ozone-containing gas from 17 Reactor No. 5 in line 116 is addod to fresh ozone-oontaining gas 18 in lines 114 and/or 11~ through lines 117 and 118, respectively.
19 Exhaust ozone-containing gas from Reactor No. 4 i8 withdrawn in line 119 and combined with ozone-containing gas in line 115 to 21 Reactor No. 3. Exhaust ozona-containing gas from Reactor ~oO 3 22 is removed from the system in'line 120. A similar procedura is 23 used for two contacting zones as in the cyanide-destruction method .
24 In the second method all ozone-containing gas is introduced 2~ to a later zone and the exhaust there~rom used as the ozone-con-26 taining gas to be introduced to an earlier zone. For example, 27 ozone-containing gas in line 112 is introduced into Reactor No.
28 via line 113, the exhaust gas therefrom in line 116 introduced 29 into Reactor No. 4 through lines118 and 114, ancl the exhaust gas 3o ~ from Reacto o. 4 in line 119 introduced ~nto Reactor No. ~

. '.
.,, , ' ~ : ' ~ 676.~

1 through line 115. ~xhaust ozone-containing gas is removed from 2 the system in line 120. I~ two reactors are used, all ozone-oon-3 taining gas is introduced ~nto Reac~or No. 4 and the exhau~t ther _ 4 from used in Reactor No. 3.
Although the ozone source 70 for Reactors No. 1 and No. 2 6 is shown in Figure 5 as being separate from ozone source 111, it 7 i5 within the scope of this invention to provide a ~ingle ozone 8 source to serve all Reactors shown in ~igure 5.
9 Since the conversion of cyanate to nitrogen and carbon dioxide is kinetically controlled, it is necessary that a cyanate-11 oontaining influent be contacted with ozone for longer period~ of 12 time to destroy cyanates than for cyanide destruotion.
13 Experimentally it has been determined that 50% o~ all cyana e 14 can be destroyed using one reao-tor e.g. Reactor No. 3, after abou 3 minutes of oontact time with an ozone-containing gas and about 16 70% to 75% can be destroyed within 60 or 90 minutes. Ozone util-17 ization is from about 50~o to 60% o~ the dose when continuously 18 introduced to the reactor. If two cyanate-destruction reactors 19 are employed, e.g. Reactors No. 3 and No. 4, with all ozone-con-taining gas introduced to Reactor No. 4 and the exhaust gas there-21 from introduced to Reactor No. 3,from 50% to 65% of the cyanate 22 can be destr~yed within 20 to 30 minutee ~nd from 82% to ~6% O~n 23 be destroyed within 60 minutes. Ozone utilization is as high a~
24 75% during the first 30 minutes.
It has been estimated that about 90~ or greater of the 26 cyanate contained in the effluent in line 83 can be destroyed 27 within about 20 to 30 minutes using three stages as described 28 above and that even mors cyanats can be destroyed by using addi-29 tional ozone-contacting zones.

:~li67~.~

1 EXAMPLES 1 to 4 3 These Examples illustrate a Double-stage Ozone Treatment of 4 a low cyanide-con-taîning wastewater stream as illustrated in Figure 4 wherein the wastewater stream in line 61 is first intro-6 duced into Reactor No. 1, then to Reactor No, 2 and finall~ w~th-7 drawn in line 83. The reaction time in each Reactor was about 5 8 minutes for each Example.
9 In Examples 1 to 3 the total cyanide concentration (CNT) of each influent stream was 46.9 mg/l, the cyanide amenable to 11 chlorine oxidation (CN~m Cl) was 43.9 mg/l, the free cyanide oon-12 centration (CNF) was 19.3 mg!l and the cyanate conoentration (CNO) 13 was 9.6 mg/l. In Example 4 the CNT was 44.6 mg!l the CNAm Cl 14 was 40.1 m ~l, the CNF was 17.5 mg/l and the CNO was 6.6 mg/l.
The pH o~ each in~luent was between 9.5 and 9.7.
16 The total copper and iron contents were about 21.5 and 1.3 17 mg/l, respectively, for all ~xamples and the total ~inc content 18 was about 0.3 mg/l.
19 The ozone-containing gas ernployed was a 2.3 wt. % ozone in-air mixture for Examples 1 to 3 and a 1.6% wt. % ozone-ln air 21 mixture for Example 4.
22 In Example 1, 100% of the fresh ozone-containing gas gen-23 erated in generator 70 was introduced into Reaotor No. 2 With the 24 exhaust ga3 therefrom introduced as the ozone-containing gas to Reactor No. 1.
26 In Example 2, 40% o~ the fresh ozone-containing gas was 27 directed to Reactor No. 2 and the exhaust therefrom was mixed wit 28 60% of fresh ozone-containing gas introduced to Reactor No. 1.
29 Example 3 employed the same ozone gas flow as Example 2 ex-3o cept that ths wastewater flow through Reactors 1 and 2 were ~6~i2 . ..

1 doubled, i.e. from 3 G.P.M. to 6 G.P.M. (gallons per minute) or 2 11.34 1/min. to 22.68 l.p.m. (liters per minute).
3 Example 4 was also identical to Example 2 except that the 4 ozone concentration was reduced.
Table 1 below lists the relevant parameters of the process 6 in eaoh Reactor (R1 & R2).
7 Table 2 summarizes the over-all prooe3q pRrame~er~ o~ ~able 1 r the system.

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~ 762 1 Ozone utilization as indicated by the % 03 reacted in Table 2 2 was about 100% for Examples 1 and 3 while Examples 2 and 4 show 3 excellent but somewhat lower efficiencies. Example 4 had the 4 highest gas to liquid ratio (G/L ratio) while Example 3 had the lowest. ~lthough the ozone da-ta for Examples 2 and 3 show a low 6 amount of ozone being introduced to Reactor No. 2, the cyanide 7 reduction (22.7 mg/l for Ex. 3) indicates a greater amount of 8 ozone being injected than the data indicates. However, the over-9 all system efficiency of ozone utilization to total cyanide re-duction (03/CNT) was excellent for Example 3. Examples 1 and 4 11 resulted in maximum CNT removal leaving only iron complexed 12 cyanides in -the effluent from Reactor No. 2. The 03/CN~ ratio 13 was 3.5 (dose and used) for Example No. 1 and since the CNO/CNT
14 ratio was much lower in Reactor No. 2 of Example 1, some o~' the ozone was used ~or CNO degradati.on (Table 1). Reactor 1 was very 16 ef~icient with respect to 03/CNT ratios less than 3.0 for all 17 Examples(except No. ~)which is due to the high mass transfer o~
18 ozone to ~he wastewa~er stream. Example 4 had the lowest o~one 19 concentration in the gas stream. The higher ~low rate ~or Exampl 3 3 was the most efficient system requiring only 1.8 mg 03 dosed/mg 21 CNT reduced both for dose and used o~one rates (Table 2). All 22 Examples also showed substantially complete removal of free 23 cyanide and cyanide amenable to chlorine oxidation; pH values of 24 the stream did not change ~ignificantl~ for all Examples.
With regard to the metal contents in the influents of each 26 Example, it was found that a 90% reduction in soluble iron was 27 achieved in Example~ 1 and 2 with somewhat les~ reduction in the 28 other Examples, all of which reductions were evidenced by the 29 formation of an Fe-CN complex precipi-tate. In Example 3 all Fe-CN complexe~ remained in solution due to th9 increa~ed flow lll67~a 1 ¦ rate. A 90~ soluble copper reduction was obtained in Examples 1 2 ¦ and 2 with less rsductions in the other test runs. In most cases 3 ¦ soluble zinc was also completely precipitated. ~olor and turbid-¦ ity increased with the addition of ozone due to the precipitation ~ ¦ of the metals; higher turbidity always being obtained after the 6 ¦ second ozone injeotion (R2). The highes-t turbidity readings were 7 ¦ assooiated with Examples 1 and 2 which indicated that turbidit~

10 ~ value could be used to prediot the degree 0~ ~e6al preoipitation¦

2 I . ' ' .

18 ~ `

21 I , ' - 2~ . ' `
22s . '.

` 27 1 ~6 ~J~ ~
..

1 XAMPLES ~ to 8 3 These Examples illustrate a Double-Stage Ozone Treatment 4 of a high cyanide-containing wastewater stream following the procedure of Examples 1 to 4, respectively.
6 In Examples 5 to 7, the CNT was 95 . 5 mg/l, the CNAm Cl was 7 82.3 mg/l, the CNF was 56.0 mg/l and the CNO was ll.l mg/l.
8 In Example 8 the CNT was 106.5 mg/l, the CNAm Cl 79 5~ the CNF
9 26.0 and the CNO 17.0 mg/l. The pH of each influent was between 10.10 and 10.20.
ll Total copper and iron contents in each influent were about 12 64 mg/l and 4.7 mg/l respectively.
13 The ozone-containing gas employed was a 1.69 wt.% ozone-in-14 air mixture (Examples ~ to 7) and a 1.49 wt. % ozone-in -air mix-1~ ture (Example 8). The same ozone dose rate (3.0 gr/min) was 16 employed for Examples 5 to 7 while a dose rate of 3.2 gr/min was 17 employed for Example 8. To obtain sufficient ozone to react with 18 the high CNT, high G/L ratios were required for ~xamples 5 to 7 19 but Example 8 required a lower G/L ratio due to the doubled water-flow rate.
21 Tables 3and 4 below summarize the relevant p~oce~s paramete~ 9 22 ~or each sta~e of each Exampl~ and for the overall sy~tem, respec~
23 tively.

26 , ~ 1~ 762 I
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_ _ .. _. _ _ _ _ . 1~i7~i~

1 Ozone utilization for all Examples was 100% for the system 2 as shown in Table 1~, A 75~1 835fo~ 100% and 795~o ozone utilization 3 was obtained in Reactor No. 2 for Examples 5 to 8~ respectivaly.
4 The reduc-tion in CNT values ~or Examples 5, 6 and 8 were excellent (exceeded 90%). Example 7 removed the most CNT with the 6 highest efficiency, however the wastewater flow rates were tao 7 high ~or the amount o~' ozone available to trans~er (100% utiliz-8 ation). CNO values varied slightly in Reactor No. 2 for Example 9 Nos. ~ and 6 which indicates that some of the ozone reacted with the CNO after the oxidizable cyanides were reacted. Example 7 11 had the grea-test increase in CNO since there was insufficient ozon 12 to react with the oxidiæable oyanides. Examples 5, 6 and 8 also 13 showed complete removal o~ CNF and CNAm Cl and Example 7 showed 14 10 and 20 mg/l,respectively in the R2 effluent which was due to 1~ the increased ~low rate through ~he system.
16 Example 5 showed an 85% reduction in copper and iron with 17 Examples 6 and 8 resulting in 905~o copper reduction with 405~o and 18 705~ iron reductions. respectively. Example 5 and 8 had 905fo zinc 19 reductions while Example 6 had a 505fo zinc reduction. No signif-ioant =etal duotiona were o:tained in Exampl- 7.

2278 .

3o ~ lia7~i2 1 EXAMPLES 9 to 12 3 These Examples illustrate a Double-Stage Ozone Treatment 4 with Recycling of Treated Effluent of a low cyanide-containing wastewater stream as illustrated in Figure 4 wherein the waste-6 water stream in line 61 is first introduced in-to Reactor No. 1, 7 then to ~eactor No. 2 whereafter it is passed to Hold Tank No. 2 8 for a short period of time and combined with incoming influent in 9 line 61. The in~luent in line 61 was set at a flow rat-e of 3 G.P.M. and the recycled effluent was mixed with the influent at 11 approximately 3 G.P.M. This resulted in flow rates of 6 G.P.M.
12 in each Reactor after the first recycling. The initial wastewater 13 influent was reacted 5 minutes each in Reactor No~ 1 and No. 2, 14 before discharge into the Hold Tank. After recycling, e~fluent from Reactor No. 2 was discharged.
16 In all Examples the CNT of the influent was about ~l~.6 mg/l, 17 the ~NAm Cl was 40.1 mg/l for Ex. 9 and 10 and 40.~ mg/l for 18 Examples 11 and 12; the CNF was 17.5 mg/l for Ex. 9 and 10 and' 19 23.0 for Ex, 11 and 12; and the CNO was about 6.6 for all Examples The total copper and iron contents were about 21.5 and 1.3 21 mg/l respectively for all Examples and the total zinc content was 22 about 0.3 mg/l.
23 The ozone-containing gas employed was apout a 1.60 wt. %
24 ozone-in-air mixture for Examples 9 and 10 and a 2.10 wt. % ozone-in-air mixture for Examples 11 and 12.
26 In Example 9, the ozone-in-air gas flow was controlled to 27 allow 60% of the generated gas to be directed to Reactor No. 1 and 28 ~0% to ~eactor No~ 2, the exhaust gas from ~eactor No. 2 being 29 combined with the 60% fraction before entering Reactor No. 1. The 3o ozone ~low in Example 10 was similar to that of Example 9 except , . 1~

1 that 40% of the generated gas was directed to Reactor No. 1 and .
2 60~ to Reactor No. 2. The ozone flow in Example ll was similar 3 to that of Example 9,and Example 12 was similar to Example 10 4 except for the increase in ozone concentration as previously ment-ioned. In addition, exhaust gas from Reactor No. 2 in Examples 6 ll and 12 was not combined with the ~resh o~one-in-air mixture to 7 Reactor No. 1.
8 Tables 5 and 6 summarize the data obtained for eaoh stage I ~ f the system res eotively.

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. 11~67~.~

1 As the Tables show, ozone utilization was excellent ~or all 2 Examples but was grea-ter ~or Examples 11 and 12 (more than 98%) 3 than for 9 and 10 (more than 95~). The gas to liquid ratios for' ~ Examples 11 and 12 were less than 2 for both reactors while Exampl s 5 9 and 10 used gas to liquid ratios of about 4 and 2 for reactors 6 1 and 2,respectively. Metal analysis indica-ted that the amount 7 of iron-complex in the effluent discharged would result in approx-8 imately 4 mg CNT/l of effluent. Only Example 9 slightly exceeded 9 this value indicating substantially complete cyanide destruction.
Examples 9, 11 and 12 had essentially no CNO increase in Reactor 11 No. 2 substantiating complete cyanide destruction in addition to 12 some ozone reac-ting with the CNO. Example 10 had the highest CNT
13 entering Reactor No. 2 and also had an increase in CNO.
14 Soluble iron was reduced in the disoharged effluent by from 1~ 40% to 82% and soluble oopper was reduoed from about 38% to 84%~
16 the amount o~ reduotion being lowest in Example 9 and highest in 17 Example 12. Zino reduction was~about 67% in Example 11 and 87% in 2~ Z~ampl~
Z

. .

. _40_ .i .1~67~2 1 EXAMPIES 1~ to 16 3 These Examples illustrate a Double-Stage Ozone Treatment 4 with Recycling of Treated Effluent o~ a high cyanide-containing wastewater stream following the procedure of Examples 9 to 12, 6 respeotively.
7 The CNT o~ the in~luent was 106~5 mg/l ~or Ex. 13 and 14 8 and 107.8 mg/l for Ex. 1~ and 16. The CNAm_Cl for Example 13 was 9 79.5 mg/l. No CNAm Cl for Examples 14 to 16 were determined.
The CNF of Example 13 was 26.0 mg/l and the CNF for Examples 15 11 and 16 was 48.0 mg/l. The CNF for Example 14 was not measured.
12 The CNO for Example 13 and 14 wa~ 17.0 mg/l and for Examples 15 13 and 16 was 14~0.
14 Total copper and iron contents in each in~luent were about 1~ ~ 64 mg/l and 4.8 m ~l respeotively. Total zino oontent was about 16 0.4 mg/l.
17 The ozone-containing gas employed was a 1~49 wt. % ozone-in-18 air mixture (Examples 13 and 14) and a 1.74 wt. % ozone-in-air 19 mixture (Examples 15 and 16). The same ozone dose rates were applied in each Example (3.1 gr./min).
21 Tables 7 and 8 summarize the relevant process parameters 2~ ~or eaob st e c~ eaoh Example ~nd the overall ~y3bem, r-sp~obi~e~

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1~676%

l As the tables show, all Examples had 100% ozone utilization 2 for the system. Ozone dosed and ozone used for Reactor No. 1 in 3 each Example were identical indicating 100% ozone utilization.
4 The 03/CN~ ratios for Reactor No. 1 in each Example were low, ranging from 1.2 to 2.4 for Examples 14, 15 and 16 and 3.4 for 6 Example 13 with a ratio of approximately 3.0 for the ~ystem ~or 7 all Examples.
8 hll CNT was removed from the influent as indicated by the 1 ffluent sr rsoi culation dats~ (Effl. snd Ee .~, . ~ L67~

1 ¦ EXAMPIES 17 to 1 2 l 3 ¦ These Examples illustrate a Single-Stage Ozone Treatment 4 with Recycling o~ Effluent of a low cyanide-containing wastewater stream as illustrated in Figure 4 wherein the wastewater stream 6 in line 61 is introduced into Reactor No. 1, passed to Hold Tank 7 No. I and then recycled to line 61 via line 86. The reaction 8 time in each Reactor was about 5 minutes for each Example.
9 In Example 17, untreated effluent was passed through Reactor No. 1 once at~ G.P.M. and not recycled. All fresh generated 11 ozone-containing gas was introduced to Reactor No. 1 in one pass.
12 In Example 18 e~fluent ~rom Reactor No. I wa~ passed to Hol 13 Tank No. I (18~) and then recyclad through Reactor No. 1 again 14 (18~
Example 19 comprising retained (19A) and recycled e~fluent 16 (19B) were the same as 18A and llBB except that the ~low rate 17 bhrough the reactors was doubled. (6 G.P.M.) 18 The CN~ for all Examples was 39.3 mg/l; the CNAm Cl was 19 3~.6 mg/l; the CN~ was 12.0 mg/l; and the CNO was 3.9 m ~ l.
In all cases the ozone-containing gas was a 2.10 wt. % ozone 21 in-air mixture generated in ozone generator 70.
22 Table~ ~ andlO pelow summarize the individual and ~tJ~tem 23 parameters.

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I
1 ¦ As the table~ show, a 70~o ozone utilizationlwas accomplished ¦for Example 17, while 18 and 19 had a 76% and g6~ ozone ~tiliza~
3 ¦tion, respectively. Example ~9 had a high e~ficiency due bo the 4 Ihigh flow rate (6 G.P.M.) and low G/~ ratio~ (1.8 for 19A and ¦1.3 for 19B) No excess ozone was recycled in these Example~
6 1 ~ince only one Reaction Tank having a bottom feed configuration .
7 ¦ wa3 available, Thie configuration tank can be used ~or both 8 ¦ Reaction ~anks (No. 1 and No. 2) in a double stage system with ozone containing gas flow being the same as in previous Example~.
All Examples ~howed substantial destruction of GNT. In 11 addition, the CN~m al was eliminated in Example~ 17 and 18 while 12 Example 10~ had about 6.9 mg/l left in the effluent.
13 . ~ .

: . .
16 . .

:

22~ .' . .
.

26 .
. 27 . .

29 .
. 30 '.~
. -48~

1~6~
'..' 1 EXAMPL2S 20 and 21 3 In Example 20, a low cyanide-containing wastewatar influent 4 having the same composition as that o~ Examples 1 to 4 was treat-ed according to the procedure of Example 1 (Double-Stage Ozone 6 Treatment) to substantially destroy all cyanides contained there-7 in and then further treated to destroy c~anate in a third ozon-8 ation stage as shown in Figure 5, ie, using Reactor No. 3.
9 The procedure comprised introducing the cyanide-depleted effluent containing about ~7 mg CN0/l into an ozone-reactor cQn 11 taining a gas turbine ozone injector and recycling the e~fluent 12 through a holding tank and then through the reactor again contin-13 uously for about 3 hour~ (180 minutes) at 3 G.P.M. A 2.0 w~. %
14 030ne-in~air mixture at a flow rate o~ 2.~ m3/hr. (58.8 gr/hr o~
o~one) was continuously introduced into the reactor ~or the entir 16 period.
17 Re~erring to Figure 5, this procedure simulated introducing 18` a cyanide-depleted, cyanate-containing e~fluent in line 83 to 19 Reactor No~ 3 and allowing ozona-containing gas from generator 111 to be introduced to Reactor No. 3 through line 115 for a~out 3 21 hours after which treated e~fluent was withdrawn in line 106 ~ia 22 line 105.
23 Analysis ~or oyanatQ and ozone were conducted every 10 2~ minutes during the prooedure.

26 ~able 1 summarizes the results.

~ 76~.

¦ TABLE ~ ~Ex.20) I, Time CN0 ~ ~ ~ ~3 (mins.) mg/l EXHA~S~ US~Di US~D
./hr. gr./hr, %
0 47.2 _ - _ _ -0 30.8 28.2 30.6 52.0 28.8 27.0 31.8 54.1 21.4 27.3 31-5 53.6 12.5 3~3 28.5 48.5 10.8 34.2 24.6 41.8 1~.1 35~7 23.1 .39~3 9-3 37~5 21.3 36.2 6.4 42.3 16.5 28.1 4.9 43.8 15.0 25-5 100 3~9 45.6 13.2 22.~
110 3~4 47.4 11.l~ 19.4 120 3~9 46.8 12.0 20.1 140 3.0 49.2 9.6 16.3 160 1.7 51.0 7.8 13.3 180 1.0 47.4 11.4 19.4 As the table shows, the initial value of 47 mg CN0/1 was reduced by more than 50% (21.4 mg CN0/l) in 30 minutes and by more then 75% (11 mg CN0) in 60 minutes. A value of 1 mg CN0/l was obtained after 180minutes. More than 50% ozone utilization was obtained during the first 30 minutes and de¢reased therea~ter as the CN0 decreased.
In Example 21, the same procedure as outlined above was used for a high-cyanide -containing wastewater influent. After depletion of cyanides according to the procedure o~ Example ~, a c~anide-depleted effluent containing about 92 mg CN0/l was contacted with a 2.2~ ozone-in-air mixture for 4 hours acoording to the procedure of Example 20. The ozone gas ~low was 5.3 m3/hr .

-5o-`

1~3L676.~

(137.4 gr./hr. of ozone).
Analysis for cyanate and ozone were conducted every 1 minutes.
Table 12 summarizes the results.

TABLE 12 (Ex.21) CNg~l Lr ~r grU./~hDr. U%~D

0 92-3 79.2 5B.2 42 1~ 51.9 80.1 ~7-3 42 3o 5-7 8~.6 ~2.8 38 50.2 92.2 I~.2 33 _ 99.2 38.2 28 _ 108.7 28.7 21 27.6 113.7 23.7 17`
105 28,5 117.0 20.4 15 120 19.2 119.6 17.8 13 150 11.3 . 124.0 13.4 10 180 ~.2 124.7 12.7 9 210 4.7 1~9.7 7-7 6 240 2.5 132.3 5-1 4 _ As table 12 shows, the CN0 wa~ reduced by 46% (50 mg CN0/l) in 30 mînutes and by 70% (28 mg CN0/1) in 90 minutes. A value of 2.5 mg CN0/l was obtained after ~ hours.
Between 3~% to 4;2% ozone utilization was obtained during the ~irst 30 minutes and decreased as the CN0 decreased te les~
than 20% after 90 minutes.

~ 67~2 1 EXAMPLES 22 and 2 3 In these Examples, a low and high cyanide-con-taining waste-4 water influent was first depleted of cyanides according to the procedure of Examples 18A and 18B (Single-Stage Oæone Treatment 6 with Recycling of Effluent) and then introduced to further ozone 7 oontacting zones to destroy cyanate as shown in Figure 5.
8 In Example 22, a low cyanide-depleted in~luent containing 9 about 21 mg CNO/l was introduced into Reactor No. 1 containing a gas turbine ozone injector at a flow rate of 3 G.P.M. After 11 treatment with an ozone-containing gas, the effluent from Reactor 12 No. 1 was introduced into Reactor No. 2, treatod with an ozona-13 containing gas, withdrawn and introduced to Hold Tank No. 2.
14 From Hold Tank No.2 the effluen~i was re-introduced to Reactor No.
1 and the entire process repea-ted for 3 hours (180 minutes).
16 A 1.9 wt. % ozone-in-air mixture wa~ continuously introduced into 17 Reactor No. 2 at a flow rate of 2.5 m3/hr.(56.3 gr/hr of ozone) 18 as the ozone-containing gas and the exhaust therefrom used as 19 the ozone-containing gas ~or Reactor No. 1.
Re~erring to Figure 5, this procedure simulated introducing 21 a cyanide-depleted, cyanate-containing effluent from Reaotor No.
22 2 in line 83 to Reactor No. 3~for 90 minutes reaotion time with 23 ozone-containing gas, withdrawing effluent in line 105 and intro-24 ducing it to Reactor No. 4 for another 90 minutes. After which the effluent is withdrawn in lines 107 to 108. Ozone-containing 26 gas flow simulated introducing the gas generated in generator 111 27 to Reactor No. ~ through line 112 and withdraw-i.ng the exhaust gas 28 therefrom in line 119 for introduction to Reactor No. 3.
2~ Analysis of CNO and ozone were taken after e~ery 10 or 15 3o minutes. The results are summarized in Table 13 below.
.

7~2 ~A~LE 13 (Ex.22) Time CNO O O O
(mins.) mg/l EXHA~ST US~D US~D
gr./hr. gr./hr. %
_ ~ ._ ~l~ R2 R1 R2 _ _ O 21.~ 9.0 18.0 g.O38-3 ~4 15.0 8.4 16.2 7.840.1 8~
11.1 10.1 18.6 8.~37~7 82 9~3 13.8 24.010.232.3 7~
l~O 5 ~ 16.8 27.310.529.0 7o 4.4 19.2 27.6 2.428.7 55 3~4 23.1 27.0 3.9~9.3 ~9 2.7 27.6 3~3 2.726.0 51 2.0 33-6 38.6 5~o17.7 40 2.2 39.0 ~2.0 3~o14.3 31 ~0 1.5 40.8 48.0 7.28.3 28 ,~(~0 1.2 ~2.6 ~8.0 ~'48.3 24 '~0 0.7 44.~ 49.2~.1 ~ 7~1 22 l As table 13 shows, an initial value of 21 mg CNO/l was reduoed b~ abou-t 50% in 20 minutes and by 86~ (3.4mg.CNO/l) after 60 minutes. A value of 0.7 mg CNO/l was obtained af-ter 1~0 min-utes; however after about 40 minutes, CNO destruction decreased slowly with time. This procedure resulted in a more rapid CNO
destruction than in Example 2~. More than 75% ozone utilization was obtained during the first 30 minutes. Ozone utilization continued to decrease as the CNO decreased, but more than 50% ~
the dose rate was used up to 75 minutes reaction time. ~herefore this flow scheme greatly improved the ozone utilization for cyanate destruction compared to Example 20.
¦ Exampla 23 followed the procedure of Example 22 except that ¦ the cyanide-depleted, influent was derived from a high cyanide-¦ containing wastewater influent and contained 95.2 mg CNO/l.

¦ The ozone-containing gas used was a 2.0 wt. ~o ozona-in-air mix-¦ ture at a flow rate of ~.3 m3/hr. (128.5 gr/hr of ozone). Total I :
I -53~
I

', ', ~ ~6'~ 2 reaction time was 240 minutes (4 hours).
Analysis for CN0 and ozone was conducted every 15 minutes.
Table 14 summarizes the results.

TABLE 14 (Ex. 23) __. ...__ _ Time CN0 0 0 ~ 0 (mins.) mg/lEXHA~ST US~D US~D
_ ~ /hr. ~ ~/hr ~o 0 95.226.7 66.8 40.161.7 79 ~0.244.5 78~9 34.449.6 65 33.766.1 94.1 28.034.4 49 28.372.5 100.5 28,028.0 44 16.886.5 106.8 20.321.7 33 13.59.3 111.9 21.616.6 3o 13-391~.1 115.8 21.712.7 27 105 8.59l~.1 118.3 24.210.2 27 120 8.995.4 118.3 22.910.2 26 150 3 095 7 119.6 23.98.9 26 180 3.295.2 119.6 24.48.9 26 210 2.29~.2 119.6 20.48.9 23 240 1.0102.~ 119.6 17.28.9 20 As Table 14 shows, the initial value of 9~.2 mg CN0/l was reduced b~ 65% (3~ mg CN0/l) in 30 minutes and by 82% ~17 mg CN0 /l) in 60 minutes. Less than 10 mg CN0/l was obtained in 105 minutes with 1 mg CN0/l in the e~fluent after 240 minutes re-action time.
. ~bout 50% ozone utilization was obtained during the ~irst 30 minutes and 30~ was still obtained a~ter 75 minutes.
. ' ` .
.

~ -~4- `

Claims (43)

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

1. A process for treating an aqueous cyanide-containing influent comprising:
(a) providing an ozone-contacting zone having an operating turbine gas injector associated therewith said injector comprising a hollow casing extending into said zone having an enlarged section at the lower end thereof, said enlarged section having an annular elongated gap which extends into said zone, a shaft rotatably mounted in said casing, a turbine-bladed impeller rotor mounted on said shaft and ex-tending into said enlarged section, said rotor having a liquid intake section, means for rotating said shaft, and a gas inlet communicating with said casing above said enlarged section;
(b) introducing said influent to said zone, at least a portion of said influent being introduced to said liquid intake section;
(c) introducing an ozone-containing gas to said gas inlet;
(d) mixing by spinning said impeller at least a portion of said influent with said ozone-containing gas in said enlarged section to form a stream of bubbles of said ozone-containing gas in_said influent and injecting said stream into said zone; and (e) withdrawing a cyanide-depleted effluent from said zone.

2. The process of claim 1 wherein said ozone-containing gas is selected from the group consisting of ozone-in-air, ozone-in oxygen, and ozone-in-air and oxygen.

3. The process of claim 1 wherein at least a portion of said cyanide-depleted effluent is combined with said influent and introduced into said ozone contacting zone.

4. The process of claim 3 wherein said portion of cyanide-depleted effluent is retained in a holding zone before being combined with said influent.

S. The process of claim 1 wherein said bubbles have an aver-age size of between about 1/2 mm. and about 60 mm.

6. The process of claim 1 wherein said influent further comprises cyanate and a metal selected from the group consist-ing of iron, copper, zinc and mixtures thereof.

7. A process for treating an aqueous cyanide-containing influent comprising;
(a) providing an ozone-contacting zone having an operating turbine gas injector associated therewith said injector comprising a hollow casing extending into said zone having an enlarged section at the lower end thereof, said enlarged section having an annular elongated gap which extends into said zone, a shaft rotatably mounted in said casing, a turbine-bladed impeller rotor mounted on said shaft and ex-tend ing into said enlarged section, said rotor having a liquid intake section, means for rotating said shaft, and a gas inlet communicating with said casing above said enlarged section;
(b) introducing said influent to said zone, at least a portion of said influent being introduced to said liquid intake section;
(c) introducing an ozone-containing gas to said gas inlet;
(d) mixing by spinning said impeller at least a portion of said influent with said ozone-containing gas in said enlarged section to form a stream of bubbles of said ozone-containing gas in said influent and injecting said stream into said zone; and (e) withdrawing a cyanide-depleted effluent from said zone.
(f) combining at least a portion of said cyanide-depleted effluent with said cyanide-containing influent; and (g) repeating steps (b), (c), (d) and (e).

8. The process of claim 7 wherein said ozone-containing gas is selected from the group consisting of ozone-in-air, ozone-in-oxygen, and ozone-in-air and oxygen.

9. The process of claim 7 wherein said portion of said cyanide-depleted effluent is retained in a holding zone before being combined with said cyanide-containing influent.

10. The process. of claim 7 wherein said bubbles have an average size of from about 1/2 mm. to about 60 mm.

11. The process of claim 7 wherein said influent further cyanate and a metal selected from the group consist-ing of iron, copper, zinc and mixtures thereof.

12. A process for treating a cyanide-containing aqueous influent comprising;
(a) providing a first and second ozone contacting zone, each zone having an operating turbine gas injector associated therewith, said injector comprising a hollow casing extending into said zone having an enlarged section at the lower end thereof, said enlarged section having an annular elongated gap which extends into said zone, a shaft rotatably mounted in said casing, a turbine bladed impeller rotor mount-ed on said shaft and extending into said enlarged section, said rotor having a liquid intake section, means for rotating said shaft; and a gas inlet communicating with said casing above said enlarged section;
(b) introducing said cyanide-containing influent into said first ozone-contacting zone; at least a portion of said influent being introduced to said liquid intake section of said injector in said first zone;
(c) introducing a second ozone containing gas into said gas inlet of said injector in said first zone, at least a portion of said second ozone containing gas comprising a first ozone-depleted gas withdrawn from said second ozone-contact-ing zone;
(d) mixing by spinning said impeller of said inject-or, in said first zone at least a portion of said influent with said second ozone-containing gas in said enlarged section to form a stream of bubbles of said second ozone-containing gas in said influent and injecting said stream into said first zone to form a first cyanide-depleted effluent.
(e) withdrawing said first cyanide-depleted efflu-ent into said second ozone-contacting zone, at least a portion of said effluent being introduced to said liquid intake sec-tion of said injector in said second zone;
(f) introducing a first ozone-containing gas into said gas inlet of said injector in said second zone;
(g) mixing by spinning said impeller of said inject-or in said second zone at least a portion of said first cyanide-depleted effluent with said first ozone-containing gas in said enlarged section to form a stream of bubbles of said first ozone-containing gas in said effluent and injecting said stream into said second zone to form a second cyanide-depleted effluent and a first ozone depleted gas;
(h) withdrawing said first ozone-depleted gas from said second contact zone; and (i) withdrawing said second cyanide-depleted ef-fluent from said second zone.

13. The process of claim 12 wherein each of said first and said second ozone-containing gases is selected from the group consisting of ozone-in-air, ozone-in-oxygen, and ozone-in-air and oxygen.

14. The process of claim 12 wherein said first ozone-contain-ing gas is an ozone-in-air mixture comprising from about 1.0%
to 3.5% by weight of ozone.

15. The process of claim 12 wherein said first ozone-contain-ing gas is an ozone-in-oxygen or ozone-in-air and oxygen mix-ture comprising from about 2.5% to about 7.5% by weight of ozone.

16. The process of claim 12 wherein all of said second ozone-containing gas comprises said first ozone-depleted gas.

17. The process of claim 12 wherein from about 1% to about 99% of said second ozone-containing gas is comprised of said first ozone-depleted gas.

18. The process of claim 12 wherein at least a portion of said second cyanide-depleted effluent withdrawn from said second zone is combined with said cyanide-containing aqueous influent.

19. The process of claim 18 wherein said portion of said second cyanide-depleted effluent is retained in a holding zone before being combined with said cyanide-containing aqueous influent.

20. The process of claim 12 wherein all of said influent is introduced directly to said liquid intake section of said injector in said first zone.

21. The process of claim 12 wherein said bubbles have an average size of between about 1/2 mm. and 60 mm.

22. The process of claim 12 wherein said cyanide-containing aqueous influent further comprises cyanate and a metal select-ed from the group consisting of iron, copper, zinc and mix-tures thereof, a portion of said cyanate being oxidized and said metal being precipitated in said zones.

23. A process for treating a cyanide-containing aqueous influent comprising;
(a) providing a first and second ozone contacting zone, each zone having an operating turbine gas injector associated therewith, said injector comprising a hollow casing extending into said zone having an enlarged section at the lower end thereof, said enlarged section having an annular elongated gap which extends into said zone, a shaft rotatably mounted in said casing, a turbine bladed impeller rotor mount-ed on said shaft and extending into said enlarged section, said rotor having a liquid intake section, means for rotating said shaft; and a gas inlet communicating with said casing above said enlarged section;
(b) introducing said cyanide-containing influent into said first ozone-contacting zone; at least a portion of said influent being introduced to said liquid intake section.
of said injector in said first zone;
(c) introducing a second ozone-containing gas into said gas inlet of said injector in said first zone, at least a portion of said second ozone containing gas comprising a first ozone-depleted gas withdrawn from said second ozone-contact-inf zone;
(d) mixing by spinning said impeller of said injec-tor in said first zone at least a portion of said influent with said second ozone-containing gas in said enlarged section to form a stream of bubbles of said second ozone-containing gas in said influent and injecting said stream into said first zone to form a first cyanide-depleted effluent;
(e) withdrawing said first cyanide-depleted efflu-ent into said second ozone-contacting zone, at least a portion of said effluent being introduced to said liquid intake sec-tion of said injector in said second zone;
(f) introducing a first ozone-containing gas into said gas inlet of said injector in said second zone;
(g). mixing by spinning said impeller of said injec-tor in said second zone at least a portion of said first cyanide-depleted effluent with said first ozone-containing gas in said enlarged section to form a stream of bubbles of said first ozone-containing gas in said effluent and injecting said stream into said second zone to form a second cyanide-depleted effluent and a first ozone depleted gas;
(h) withdrawing said first ozone-depleted gas from said second contact zone; and (i) withdrawing said second cyanide-depleted ef-fluent from said second zone.
(j) combining at least a portion of said second cyanide-depleted effluent with said cyanide-containing aque-ous influent; and (k) repeating said steps (b) to (i).

24. The process of claim 23 wherein each of said first and said second ozone-containing gases is selected from the group consisting of ozone-in-air, ozone-in-oxygen, and ozone-in-air and oxygen.

25. The process of claim 23 wherein said first ozone-contain-ing gas is an ozone-in-air mixture comprising from about 1.0%
to 3.5% by weight of ozone.

26. The process of claim 23 wherein said first ozone-contain-ing gas is an ozone-in-oxygen or ozone-in-air and oxygen mix-ture comprising from about 2.5% to 7.5% by weight of ozone.

27. The process of claim 23 wherein all of said second ozone-containing gas comprises said first ozone-depleted gas.

28. The process of claim 23 wherein from about 1% to about 99% of said second ozone-containing gas is comprised of said first ozone-depleted gas.

29. The process of claim 23 wherein said portion of said second cyanide-depleted effluent withdrawn from said second zone is retained in a holding zone before being combined with said cyanide-containing aqueous influent.

30. The process of claim 23 which further comprises combining a portion of said first cyanide-depleted effluent withdrawn from said first zone with said cyanide-containing aqueous influent.

31. The process of claim 30 wherein said portion of said first cyanide-depleted effluent is retained in a holding zone before being combined with said cyanide-containing aqueous influent.

32. The process of claim 23 wherein said cyanide-containing aqueous influent further comprises cyanate and a metal select-ed from the group consisting of iron, copper, zinc and mix-tures thereof, a portion of said cyanate being oxidized and said metal being precipitated in said zones.

33. The process of claim 12 wherein said influent further contains cyanate and said first and second cyanide-depleted effluents contains cyanate formed by ozonation of said cyanide containing water in each of said zones.

34. The process of claim 33 wherein at least a portion of said second cyanide-depleted effluent is further treated by the steps of:
(j) introducing said effluent to a third ozone contacting zone;
(k) contacting said effluent with an ozone-containing gas until a cyanate-depleted effluent is obtained;
and (l) withdrawing said cyanate-depleted effluent from said zone.

35. The process of claim 34 wherein said ozone-containing gas is selected from the group consisting of ozone-in-air, ozone-in-oxygen, and ozone-in-air- and oxygen.

36. The process of claim 34 wherein said ozone-containing gas is an ozone-in-air mixture containing from about 1.0% to 3.5 ozone by weight.

37. The process of claim 34 wherein said ozone-containing gas is an ozone-in-oxygen or ozone-in-air and oxygen containing from about 2.5% to 7.5% ozone by weight.

38. The process of claim 33 wherein at least a portion of said second cyanide-depleted effluent is further treated by;
(j) introducing said effluent successively into a plurality of further ozone-contacting zones arranged in series;
(k) contacting said effluent with an ozone-con-taining gas in each zone to form a cyanate-depleted effluent, at least a portion of the ozone-containing gas in the earlier zones being comprised of an ozone-depleted gas withdrawn from a latter zones; and (l) withdrawing a cyanate-depleted effluent from any one of said zones.

39. The process of claim 38 which comprises two ozone-con-tacting zones.

40. The process of claim 38 which comprises three ozone-con-tacting zones.

41. The process of claim 38 wherein said ozone-containing gas is selected from the group consisting of ozone-in-air, ozone-in-oxygen, and ozone-in-air and oxygen.

42. The process of claim 38 wherein said ozone-containing gas is an ozone-in-air mixture containing from about 1.0% to 3.5%
ozone by weight.

43. The process of claim 38 wherein said ozone-containing gas is ozone-in-oxygen or ozone-in-air and oxygen containing from about 2.5% to 7.5% ozone by weight.