7-Generation of Hydrogen Peroxide and Removal of Cyanide From Solutions Using Ultrasonic Waves

8/8/2019 7-Generation of Hydrogen Peroxide and Removal of Cyanide From Solutions Using Ultrasonic Waves

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Desalination 216 (2007) 209221

Generation of hydrogen peroxide and removal of cyanidefrom solutions using ultrasonic waves

E.Y. Yazc, H. Deveci*, I. Alp, T. UsluDepartment of Mining Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey

Tel. +90 (462) 377-3681; Fax: +90 (462) 325-7405; email: [email protected]

Received 20 February 2006; Accepted 28 December 2006

Abstract

The generation of hydrogen peroxide and the decomposition of free cyanide by ultrasonic waves were studiedand the statistical analysis of the results for significance was performed using Erguns test (essentially One-wayAnalysis of Variance (ANOVA) for gradients). Effects of the ultrasonic intensity, the external addition of hydrogen

peroxide, aeration, temperature and pH on the rate and extent of formation/accumulation of hydrogen peroxide weredemonstrated. The generation of H2O2 was found to increase with increasing the ultrasonic intensity (9114 W/cm

2),

which also controls the accumulation of H2O2 in solution (400 ml). External addition of H2O2 or high temperatures(>3050C) appeared to suppress the production of H2O2 in water. Formation of H2O2 tends to be adversely affectedby the increase in alkalinity (pH 410.5) whilst effects of air-saturation prior to the ultrasonic irradiation and aerationduring the ultrasonic irradiation were shown to be statistically insignificant. The results have also shown that a highultrasonic power input is required for the degradation of cyanide ([CN]0: 20 mg/l, 200 ml) to become significant (i.e.25% reduction in cyanide level at 114 W/cm2). The removal of cyanide by ultrasonic irradiation appeared to besubstantially enhanced with the aid of additives (NaCl and CCl4) with the complete removal of cyanide in the

presence of 24 g/l CCl4. These findings suggest that ultrasonic treatment could be used more suitably for thetreatment of the effluents containing low concentrations of cyanide and the addition of NaCl and CCl 4 is essentialto improve its effectiveness.

Keywords: Ultrasonic; Hydrogen peroxide; Cyanide; Environment

1. Introduction

Over the years the technology of ultrasoundhas found industrial applications mainly in the

*Corresponding author.

fields of biotechnology, material processing andmedicine with its great potential for use in thetreatment of industrial wastes [19]. The exploi-tation of ultrasound in these processes is based onthe phenomenon known as cavitation, which

0011-9164/07/$ See front matter 2007 Published by Elsevier B.V.doi:10.1016/j.desal.2006.12.018


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E.Y. Yazc / Desalination 216 (2007) 209221210

induces physical, mechanical and chemicaleffects on solids and aqueous solution. Cavitationis characterised by the formation, growth andviolent collapse of cavities in a liquid mediumaccompanied by the generation of hot spots

with severe localised conditions of temperature(>103 C) and pressure (>103 atm) [6,10,11].Cavitation also leads to the formation of inter-mediate radical species such as H, HO and HO2

[Eqs. (1) and (2)] with high oxidising power,which subsequently undergo a range of reactionswith the eventual generation of hydrogen per-oxide [Eqs. (3) and (4)] in solution [4,7,12,13].The production of radical species and hencehydrogen peroxide appears to be dependent on

the frequency and intensity of ultrasonic irradi-ation, the properties of aqueous phase and exter-nal factors such as bubbled gas [7,8,1316]. Theaddition of chloride and carbon tetrachloride mayimprove the effectiveness of ultrasonic treatmentof wastewaters [2,17].

H2O 6 H + HO (1)

H + O26 HO2 (2)

HO2 + HO26 H2O2 + O2 (3)

HO + HO6 H2O2 (4)

Wastewaters produced in gold-leaching andmetal-plating operations may contain appreciablequantities of hazardous cyanide-containing com-

pounds [1821]. The remediation of cyanidecontaining solutions and slurries involves naturalattenuation, chemical and biological oxidation,complexing/precipitation and recovery/recycling

processes [2227]. Due to the inherent limitationsof these processes, the evaluation and/or develop-ment of potential alternatives are requisite tofulfil ever stricter environmental discharge regu-lations. In this regard, the capability of ultrasoundto generate highly oxidising reagents in-situcoupled with the occurrence of extreme con-

ditions of pressure and temperature probablymakes it a potentially powerful and suitabletechnique for the remediation of waste solutionscontaining inorganic and organic contaminants[2,8,9,14,15,17,28].

In this study, the generation of hydrogen peroxide by ultrasonic irradiation was inves-tigated. Various factors including ultrasonicintensity, temperature, pH, air and hydrogen

peroxide addition on the rate and extent ofproduction of hydrogen peroxide were studied.Furthermore, the effectiveness of ultrasound forthe removal of cyanide from solutions wasevaluated at different ultrasonic intensities in the

presence or absence of carbon tetrachloride and

chloride. Statistical assessment of the experi-mental results was also undertaken to examine thedifferences between the varying experimentalconditions for significance.

2. Materials and methods

Reagent grade sodium cyanide (NaCN),sodium chloride (NaCl) and sodium hydroxide(NaOH) were used to prepare solutions in dis-

tilled or deionised water. Hydrogen peroxide(H2O2, 35% w/w) and carbon tetrachloride($99.8% CCl4) solutions as received were used asthe stock solutions.

A laboratory type, high intensity ultrasonicgenerator system (750 W, 20 kHz) equipped witha horn transducer system and a titanium alloyhorn tip (13 mm in diameter) was used as asource of ultrasonic irradiation. The actual inten-sity of the power output of the system at differentamplitudes was determined calorimetrically [7].The experiments were performed in a jacketedPyrex reactor (1000 ml) connected to a water bathmaintained at the desired temperature (Fig. 1).The agitation of reactor contents was conductedusing a magnetic stirrer. The effects of ultrasonic

power intensity (9114 W/cm 2), temperature (2580C), pH (4.010.5), the addition of hydrogen


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E.Y. Yazc / Desalination 216 (2007) 209221 211

Fig. 1. Schematic representation of the experimental set-up.

peroxide (0.51 mg/l) and aeration (0.27 l/min)on the generation of hydrogen peroxide in 400 mldeionised water were studied. The degradation ofcyanide (20 mg/l CN!) from a synthetic solution(200 ml) by ultrasonic irradiation was carried outat different power intensities (46114 W/cm2)and, concentrations of carbon tetrachloride (824 g/l CCl4) and sodium chloride (0.51 M).

During the experiments, a number of sampleswere removed at predetermined intervals to moni-tor the concentration of hydrogen peroxide andcyanide. The concentration of hydrogen peroxidewas determined colorimetrically using a filter

photometer at 520 nm. Free cyanide was analysed by titration using a standardised silver nitratesolution (0.001 M) andp-dimethylaminobenzal-rhodanine (0.02% w/w in acetone) as the indi-cator [29]. pH and temperature were alsomonitored during the experiments. pH was

adjusted to the desired level by the addition of1 M NaOH or 1 M HCl. In the cyanide degra-dation experiments, pH was maintained con-sistently at 10.511.0 to minimise the loss ofcyanide in the form of HCN. The replicate testsshowed that the relative standard deviation ofexperimental data was in the order of 5%.

2.1. Statistical methodology for the analysis of

data

Despite the general availability of a variety ofstatistical techniques, the time-dependent natureof data (i.e. concentration varying with time)restricts the use of many conventional statisticalmethods for the analysis of experimental data[30]. Powell and Jordan [31] demonstrated acorrective technique based on Erguns test [32]for the eradication of time-dependency of data. Inthis study, Erguns test (essentially One-wayAnalysis of Variance (ANOVA) for gradients)[31] was adopted as the statistical methodology toeradicate the time-dependency and to examine thedifferences between the varying experimental

conditions (i.e. US power intensity, pH, tempera-ture etc. on the production of H2O2) forsignificance.

Zero-order (for H2O2 generation) and first-order (for CN!degradation) reaction models wereused in conjunction with Erguns test for thestatistical analysis of the results. The model

parameters (the rate constants, k0 ork1) were ini-tially determined using regression analysis. Thegoodness of fit of the models for each set of

data was also evaluated and the rate constants, k0ork1 (i.e. gradients of the plots of [H2O2] vs torln ([CN!]/[CN!]0)vs t) produced with statisticallyacceptable correlation coefficients (at$95% con-fidence interval) were assigned as an estimate ofthe rate characterising the data. It is pertinent tonote that only the data at 0.5 M NaCl wereacceptable at a 90% confidence interval andhence not included in the statistical analysis.Erguns test was then applied to test for thesignificance of differences, i.e., the equality of the

gradients (reaction rates) as a Null Hypothesis.The details of statistical analysis procedure usedherein and the outlines of the mathematicalmethodology for Erguns test can be found else-where [31]. The outcomes of the statisticalanalysis of the various tests are summarised inTable 1 where the significance of the differences


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Table 1Summary of the statistical analysis of the experimental results using Erguns test ( represents the level of significance andthe test results are presented as significant at 5%, highly significant at 1% and extremely significant at 0.1% levels)

Statistical Test Fvalue Fcritic () Significance

Generation of hydrogen peroxideEffect of ultrasonic intensity9114 W/cm2 32.64 7.10 (0.1%) Extremely significant28114 W/cm2 10.98 9.01 (0.1%) Extremely significant46114 W/cm2 4.47 3.89 (5%) Significant73 vs 114 W/cm2 3.09 5.32 (5%) Not significant

Effect of initial H2O2 (01 mg/l) 11.13 9.55 (1%) Highly significantAeration vs pre-aeration vs no aeration 3.46 4.46 (5%) Not significantEffect of temperature (2580EC)

at 46 W/cm2 8.44 7.32 (0.1%) Extremely significantat 114 W/cm2 4.93 4.34 (1%) Highly significant

Effect of pH (410.5)

at 46 W/cm2 8.78 8.02 (1%) Highly significantat 114 W/cm2 5.75 4.26 (5%) Significant

Decomposition of cyanide

Ultrasonic intensity (46 vs 114 W/cm2) 28.75 25.42 (0.1%) Extremely significantEffect of initial H2O2 (0 vs 0.5 mg/l) 14.23 12.25 (1%) Highly significantEffect of addition of CCl4 (024 g/l) 48.49 21.69 (0.1%) Extremely significantEffect of addition of NaCl (01 M) 33.45 12.32 (0.1%) Extremely significant

is indicated either at 5% (significant) or 1%

(highly significant) or 0.1% (extremely signi-ficant) levels.

3. Results and discussion

3.1. Generation of hydrogen peroxide by ultra-

sonic irradiation

Fig. 2 illustrates the generation of hydrogenperoxide in water irradiated at different ultrasonicintensities in the range of 9114 W/cm2. Theconcentration of hydrogen peroxide in solutiontended to increase in a linear manner (R2$0.99)with time at all the intensities tested. The generaltendency of this trend to deviate from linearity

particularly towards the end of the irradiation period could be attributed to the concomitantdecomposition of hydrogen peroxide formed. As

shown in Figs. 2 and 3, the rate and extent of the

production of hydrogen peroxide were observedto increase with increasing the intensity of ultra-sonic irradiation. Over the experimental period of60 min the concentration of hydrogen peroxide insolution at a power intensity of 114 W/cm2 wasrecorded to be 0.34 mg/l (Fig. 2) with a zero-order rate constant of 610!3 mg/l/min (Fig. 3)corresponding to a three-fold increase in the rateof accumulation of hydrogen peroxide in solutioncompared with that at 9 W/cm2. Statistical analy-sis of the data suggests that the power intensity isan important parameter enhancing the productionof hydrogen peroxide (Table 1). Notwithstandingthis, the difference recorded in the production rateof hydrogen peroxide was found to be statisticallyinsignificant in the power intensity range of 73114 W/cm2 (Table 1).


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Fig. 2. Effect of intensity of ultra-sonic irradiation (9114 W/cm2)on the accumulation of H2O2 indeionised water (400 ml) at252C.

Fig. 3. Effect of intensity of ultra-sonic irradiation (9-114 W/cm2) onthe rate of the accumulation ofH2O2 in deionised water (400 ml)at 252C.

It appeared that the rate of the formation ofhydrogen peroxide in solution increased in alogarithmic manner with the increase in theintensity of power. This, in turn, suggests that thedecomposition of hydrogen peroxide formedcould occur and probably increase with increas-ing the ultrasonic intensity i.e. the level of theaccumulation of hydrogen peroxide in the system

is controlled by the ultrasonic intensity. This wasconsistent with the data presented in Fig. 4showing the decrease in the rate and extent of theaccumulation of H2O2 in solution upon theexternal addition of H2O2 into the medium. Thissuppressing effect of the addition of H2O2 wasalso confirmed to be statistically significant(Table 1). Nam et al. [33] also observed a similar


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Fig. 4. Effect of the addition ofH2O2 (0.51.0 mg/l) on the accu-mulation of H2O2 in deionisedwater (400 ml) at 114 W/cm2 and252C.

suppression effect of initial peroxide dosing onthe accumulation of hydrogen peroxide in solu-tion. They suggested that HO radicals formedcould be scavenged by excess hydrogen peroxide

present in the system [Eq. (5)].

HO + H2O26 H2O + HO2 (5)

Hong et al. [14] reported a significantly higherrate of formation of hydrogen peroxide(1.43 mg/l/min in a 50-ml volume under the ultra-sonic irradiation of 60 W/cm2 at 20 kHz) than thatobserved in the current study. This could beattributed largely to the lower volume of water(50 ml, c.f. 400 ml) and the shorter irradiation

period (6 min, c.f. 60 min) these authors tested tocollect data. They also noted the occurrence ofthe partial decomposition of H2O2 formed con-currently with the ultrasonic irradiation in

progress. Nam et al. [33] indicated that theformation/accumulation of H2O2 in solutionincreased in a linear manner during the initial

period of 6 min; thereafter, it severely sloweddown towards a limiting value. The production ofH2O2 was also reported to be dependent on thefrequency of ultrasonic irradiation and occur

optimally at the frequencies of >200 kHz [7,13,34,35].

The presence of dissolved gas or small gasbubbles in the irradiated liquid media has beenreported to promote cavitation [7]. Although theformation of H2O2 appeared to be enhanced oradversely affected when the aqueous phase wasair-saturated (i.e. pre-aerated to increase the

dissolved gas content) or aerated at an air-flowrate of 0.27 l/min. over the irradiation period,respectively (Fig. 5), statistical tests did not detectany significant difference between the formationrates of H2O2 under these conditions (Table 1).Hua and Hoffmann [34] investigated the effect ofsaturating gas on the production of H2O2 in therange of frequencies of 20.2513 kHz and foundthat the production rate of H2O2 was significantlyhigher in Kr- and Ar-saturated solutions thanin O2-saturated solution, particularly at lowfrequencies.

Although temperature is known to influencecavitation process [7], its effect on the produc-tion/accumulation of H2O2 is often disregarded.Fig. 6 illustrates the effect of temperature of theirradiated medium in the range of 2580C on theaccumulation rate of H2O2 at the ultrasonic


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Fig. 5. Effect of air-saturation priorto and aeration during ultrasonicirradiation (114 W/cm2) on theaccumulation of H2O2 in deionisedwater (400 ml) at 252C.

Fig. 6. Effect of temperature (2580C) on the accumulation rate ofH2O2 in deionised water (400 ml)at 46114 W/cm2 and 252C.

intensities of 46 and 114 W/cm2. The rate andextent of H2O2 production were recorded to peakat a certain temperature, which appearedcontingent upon the ultrasonic intensity (i.e. 30Cat 46 W/cm2 and 50C at 114 W/cm2) (Fig. 6).The reduction in the accumulation of H2O2 atelevated temperatures could be ascribed to thedecrease in the sonochemical effect [7] and the

thermal decomposition of H2

O2

formed [27].Yazc [27] demonstrated that temperatureadversely affects the stability of H2O2 with rapidand extensive (81% over 3 h) decomposition ofH2O2 at 50C. In addition, as depicted in Fig. 7,

pH appeared to be a significant factor affectingthe formation of H2O2 (Table 1), which wasfavoured at low pHs irrespective of ultrasonic


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Fig. 7. Effect of pH (4.010.5) onthe accumulation rate of H2O2 insolution (400 ml) at 46114 W/cm2

and 252C.

intensity (e.g. zero-order rate of 8.010!3 mg/l/min at pH 4 compared with 5.910!3 mg/l/minat pH 10.5 under the ultrasonic intensity of114 W/cm2).

3.2. Removal of cyanide from solutions by ultra-

sonic irradiation with or without additives

Ultrasonic irradiation of aqueous solutionsleads to the formation of powerful oxidants suchas HO radicals and H2O2 as demonstrated in the

previous section. This phenomenon can then beexploited for the oxidative treatment of waste-waters containing various organic and inorganic

pollutants such as cyanide species. Hydrogenperoxide is an effective oxidant industrially usedfor the destruction of cyanide species [Eq. (6)]

present in the effluents of gold/silver leachingand metal finishing operations [24,36].

CN- + H2O26 CNO! + H2O (6)

Fig. 8 illustrates the effect of the intensity ofultrasonic irradiation on the removal of cyanide(20 mg/l) at 30C. At 46 W/cm2, the removal ofcyanide was found to be negligible. Increasing

the power output from 46 to 114 W/cm2 wasnoted to lead to a 4.6-fold increase in thedestruction rate of cyanide with ~25% reductionin cyanide level over 2 h (Fig. 8). This enhance-ment was also affirmed by the statistical analysisof the data (Table 1). These findings appeared to

be consistent with the data for the effect ofultrasonic intensity on H2O2 generation (Figs. 2

and 3). Hardcastle et al. [37] also demonstratedthat the rate and extent of degradation of cyanideincreased with increasing the ultrasonic intensityin the range of 40400 W/cm2. In contrast, Shir-gaonkar and Pandit [17] found that the removal ofcyanide was independent of the ultrasonicintensity in the range that they tested. In thecurrent study, the first-order rate constant for thedestruction of cyanide was determined to be8.510!6 and 3.910!5 s!1 at 46 and 114 W/cm2

respectively, which are of the same order ofmagnitude as the literature data [14,17,37]. Thediscrepancies in the rate of cyanide destructioncan be attributed to the differences in the experi-mental conditions such as reaction volume,ultrasonic intensity and frequency, in particular.In this regard, Hong et al. [14] and Hardcastle etal. [37] have shown that reaction volume is a


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Fig. 8. Effect of intensity of ultra-sonic irradiation (46114 W/cm2)on the degradation of cyanide insolution (20 mg/l CN!, 200 ml) at

pH 10.5 and 302C.

Fig. 9. Effect of the addition ofH2O2 (0.510 mg/l) on the rate ofthe degradation of cyanide(20 mg/l CN!, 200 ml) by ultra-sonic irradiation (114 W/cm2) at

pH 10.5 and 302C.

significant factor controlling the degradation rateof cyanide.

It was interesting to note that the externaladdition of H2O2 adversely affected the decom-

position of cyanide (Fig. 9). This could be linkedwith the earlier observation for the suppressingeffect of initial H2O2 addition on the accumu-

lation of H2O2 (Fig. 4) presumably due to the partial decomposition of H2O2 formed/addedunder ultrasonic irradiation.

Degradation of aqueous carbon tetrachloride(CCl4) by ultrasonic irradiation is known to occurleading to the formation of various productsincluding free chlorine, which is a powerful


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Fig. 10. Effect of the addition ofCCl4 (824 g/l) on the degradationof cyanide (20 mg/l CN!, 200 ml)

by ultrasonic irradiation (114 W/cm2) at pH 10.5 and 302C.

oxidant for many organic or inorganic pollutants[2,4,13,17,24,38,39]. Fig. 10 illustrates the posi-tive effect of CCl4 addition on the degradation ofcyanide at a power intensity of 114 W/cm2. Alsoconsistent with the results of the statisticalanalysis of the data, a significant increase (~5.49fold) in the rate of the destruction of cyanide wasrecorded in the presence of CCl4 (824 g/l). The

removal of cyanide at 8 g/l CCl4 appeared toalmost level-off following an initial period of30 min (Fig. 10). This could be attributed pre-sumably to the depletion of CCl4 in solution sincethe complete removal of cyanide was observed ata higher initial concentration of CCl4 (24 g/l). The

positive effect of additives including CCl 4 on theultrasonic treatment of various organic and inor-ganic contaminants has been reported [2,17,33,39]. In agreement with the current findings,Shirgaonkar and Pandit [17] also observed anincrease in the degradation rate and extent ofcyanide (from a 1% w/v NaCN solution, 50 ml)with the addition/increasing the concentration ofCCl4 (1.5931.8 g/l) at the power amplitudes ofonly 1020% (the actual intensity of the poweroutput of their system at these amplitudes notgiven). They reported a reduction of up to 40% in

cyanide level in the presence of CCl4 comparedwith only 13% in the absence of CCl4. Theenhanced removal of cyanide in the presence ofCCl4 can result from the formation of oxidantssuch as free chlorine and Cl radicals as thedegradation intermediates or products of CCl4 aswell as H2O2 or OH

radicals under ultrasonicirradiation [17,38].

Previous studies [2,39] also demonstrated thebeneficial effect of the addition and increasing theconcentration of NaCl (up to 1.38 M) on the rateand extent of ultrasonic degradation of organic

pollutants such as phenol. In the current study,the removal of cyanide in the presence of NaCl(0.51 M) was also examined under an ultrasonicintensity of 73 W/cm2 (Fig. 11). No significantchange in the initial cyanide level at 0.5 M NaClwas observed to occur over the irradiation periodof 90 min. However, as also confirmed by thestatistical analysis of the data, increasing concen-tration of NaCl to 1 M substantially improved therate and extent of the removal of cyanide. It may

be of practical significance to note that thedegradation of cyanide appeared to progress at afirst-order rate of 4.310!5 s!1 during the initial

periods of 45 min. It deviated from this trend with


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Fig. 11. Effect of the addition of NaCl (0.51.0 M) on the degra-dation of cyanide (20 mg/l CN!,200 ml) by ultrasonic irradiation(73 W/cm2) at pH 10.5 and 30

2C.

a sharp reduction in the rate of the removal ofcyanide in the following periods. Although therationale behind this behaviour was unclear, itcould be related with the reduction in theavailability of residual NaCl for the formation offree chlorine and Cl radicals in sufficientquantity.

It may be inferred from these findings thatultrasonic treatment can be used suitably for thetreatment of the effluents containing low levels ofcyanide. However, considering the fact that theeffectiveness of the ultrasonic treatment may besignificantly enhanced with the aid of additivessuch as NaCl and/or CCl4, a new process basedon the use of such additives can be developed forthe treatment of wastewaters with high cyanidecontent. It is also highly likely that the effec-tiveness of ultrasonic treatment and hence theremoval of cyanide can be improved further athigh frequencies in view of the reports [13,34,35]that the rate and extent of the generation of H2O2and the degradation of CCl4 (i.e. the formation offree chlorine and/or Cl radicals) increase withincreasing the frequency of ultrasonic irradiation.Ultrasonic processes can be considered as a

green process with no hazardous by products inthat, when added, CCl4 is readily degraded toform eventually Cl! in solution. Nevertheless, theassessment of energy costs for the developmentof an ultrasonic process is required since the

power consumption of the large scale ultrasonicsystems was reported to be relatively high e.g.

206 kW per h for a unit capacity of ~28 m3

/h[40].

4. Conclusions

This study has shown that the ultrasonicirradiation of aqueous solutions leads to thegeneration of hydrogen peroxide, the rate andextent of which are controlled by the ultrasonicintensity, the hydrogen peroxide concentration insolution, temperature and pH. Significance oftheir effect was demonstrated by the statisticalanalysis of the data using Erguns test based onOne-way Analysis of Variance (ANOVA) forgradients. Increasing the power intensity in therange of 9114 W/cm2 increases the formation ofH2O2 in solution. External addition of H2O2,increase in pH (410.5) and in temperature


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beyond 3050C appeared to adversely affect theaccumulation of H2O2 in solution probably due tothe concomitant decomposition of H2O2 formedengendered by ultrasonic irradiation itself, highalkalinity and temperature. However, increase in

temperature up to 3050C depending on theintensity of ultrasonic irradiation was shown tofacilitate the formation/accumulation of H2O2.The findings on the ultrasonic degradation ofcyanide with the statistical analysis of data haverevealed that the application of high powerintensities in the presence of additives such as

NaCl and CCl4 in sufficient quantity is essentialfor the effective removal of cyanide from solu-tions. The removal of cyanide was found to belimited (25%) even at the highest level ofultrasonic intensity of 114 W/cm2 while it wasalmost complete in the presence of 24 g/l CCl4under the same conditions.

The current study highlights the importance ofvarious parameters and additives for the potentialdevelopment of an effective ultrasonic treatmentmethod for the remediation of wastewaters. Fur-thermore, the statistical methodology adoptedherein has proved a useful tool for the accurateinterpretation of the experimental results.

Acknowledgement

The authors would like to express their sincereappreciation to the Research Foundation ofKaradeniz Technical University for the financialsupport via the research projects (Project Nos:2002.112.8.3 and 20.111.002.7).

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7-Generation of Hydrogen Peroxide and Removal of Cyanide From Solutions Using Ultrasonic Waves

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