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U ovom radu ispitivano je kako brzina hlađenja matične otopine utječe na rast kristala dinatrijevog tetraborat dekahidrata (boraksa) tijekom sonokristalizacije. Ispitivanja su se provodila u šaržnom kristalizatoru laboratorijskog mjerila s pregradama i radijalnim turbinskim miješalom čija je brzina vrtnje bila jednaka potrebnoj za postizanje stanja potpune suspenzije kristala (N JS = 324 o min -1 ). Ultrazvučno djelovanje na otopinu provodilo se pomoću homogenizatora, frekvencije 24 kHz i snage 400 W, kontinuirano pri 20 % amplitudi. Kristalizacija se provodila iz matične otopine zasićene pri 30 °C hlađenjem do temperature od 10 °C pri brzinama od 4, 6, 8, 10 °C h -1 . Kako bi se dobio uvid u utjecaj ultrazvuka na navedeni proces također se provodila i kristalizacija bez njegovog djelovanja pri istovjetnim procesnim uvjetima (N JS = 324 o min -1 , T z = 30 °C) i brzini hlađenja od 6 °C h -1 . Tijekom eksperimenta, nakon nuleacije, provodila se analiza kristala u matičnoj otopini metodom laserske difrakcije te se istodobno određivala i koncentracija matične otopine refraktometrijskom metodom. Iz rezultata provedenih analiza sagledane su promjene raspodjele veličina kristala, srednjeg volumnog promjera kristala i njegove standardne devijacije te specifične površine kristala tijekom procesnog vremena pri svim ispitivanim uvjetima. Produkti kristalizacije pri navedenim procesnim uvjetima su također podvrgnuti granulometrijskoj analizi prosijavanjem te je analiziran i njihov oblik. Za sve ispitivane uvjete određen je i utrošak snage privedene sustavu tijekom miješanja i ultrazvučnog djelovanja. Iz rezultata je uočeno da se u procesu sonokristalizacije bez obzira na brzinu hlađenja matične otopine svojstva kristala ne mijenjaju bitno s obzirom na raspodjelu veličina i njihovu srednju veličinu. Najveći utjecaj brzine hlađenja odrazio se na promjenu specifične površine kristala koja je pak posljedica sekundarne nukleacije u sustavu. S druge strane, kad se usporede rezultati provedenih analiza u sustavima sa ultrazvukom sa sustavom bez ultrazvuka može se zaključiti da utjecaj ultrazvučnog djelovanja na svojstva kristala značajno nadmašuje utjecaj brzine hlađenja. In this work, the influence of the cooling rate of the mother liquor on the growth of crystals of disodium tetraborate decahydrate (borax) during sonocrystallization was studied. The test was carried out in a batch laboratory crystallizer equipped with a radial turbine with four blades whose rotation speed was equal to that required to achieve a state of complete crystal suspension (N JS = 324 rpm). Ultrasonic irradiation of the solution was carried out with a homogenizer with a frequency of 24 kHz and a power of 400 W, continuously at 20% of the amplitude. Crystallization was carried out from a mother liquor saturated at 30 °C by cooling to a temperature of 10 °C at rates of 4, 6, 8, 10 °C h -1 . In order to gain insight into the influence of ultrasound on the process, crystallization was performed without ultrasound, under the same process conditions (N JS = 324 rpm, Tz = 30 °C) at a cooling rate of 6 °C h -1 . During the experiment, after nucleation, crystals in the mother liquor were analyzed by laser diffraction method and at the same time, concentration of the mother liquor was determined using the refractometric method. Changes were observed in crystal size distribution, mean volume diameter of the crystals and its standard deviation, as well as the specific surface area of the crystals during process time. The obtained products were subjected to sieve analysis, and the shape of the crystals was also analyzed. For all investigated process conditions, the power supplied to the systems by mixing and ultrasonic radiation was determined. From the results, it was observed that during the sonocrystallization process, regardless of the cooling rate of the mother liquor, the properties of the crystals do not change significantly with regard to the size distribution and their average size. The greatest influence of the cooling rate was reflected on the change in the crystal specific surface area, which is a consequence of secondary nucleation in the systems. On the other hand, comparing the results obtained in systems with and without ultrasound, it can be concluded that the influence of ultrasound on crystal properties significantly exceeds the influence of the cooling rate.

Cilj ovog rada bio je ispitati utjecaj veličine miješala u kristalizatoru sa i bez ultrazvučnog djelovanja na rast kristala boraksa tijekom šaržne kristalizacije pri kritičnoj brzini vrtnje miješala (N = N JS ). Kristalizacija se provodila u kristalizatoru laboratorijskog mjerila, hlađenjem matične otopine zasićene pri 30 °C do temperature od 15 °C, brzinom od 6 °C h -1 . U radu je korišteno radijalno turbinsko miješalo s četiri ravne lopatice (tzv. SBT miješalo), a kako bi se sagledao utjecaj njegove veličine na granulometrijske karakteristike kristala ispitivanja su se provodila pri tri različita promjera miješala, pri čemu su omjeri promjera miješala i promjera kristalizatora, D/d T , iznosili 0,43, 0,53 te 0,63. Istovjetna ispitivanja su provedena u kristalizatoru s djelovanjem ultrazvuka amplitude snage od 20 % kao i u kristalizatoru bez ultrazvučnog djelovanja. Tijekom provedbe eksperimenata provodila se granulometrijska analiza rastućih kristala metodom laserske difrakcije te je sagledan utjecaj promjera SBT miješala na vremensku promjenu funkcije gustoće raspodjele kristala u sustavu sa i bez djelovanja ultrazvuka kao i na promjenu srednjeg volumnog promjera kristala te koeficijenta varijacije. Kako bi se dobio uvid o utjecaju hidrodinamičkih uvjeta u kristalizatoru na karakteristike rastućih kristala te detektirala pojava aglomeracije kristala i sekundarne nukleacije sagledavane su fotografije kristala analiziranih optičkim mikroskopom kao i njihova specifična površina. Granulometrijskom analizom konačnog produkta utvrđeno je da se s povećanjem miješala srednja veličina kristala u oba sustava povećava. U sustavima bez ultrazvuka također se povećava udio finijih i grubljih kristala u produktu uslijed povećane sekundarne nukleacije i aglomeracije. U sustavma s ultrazvukom aglomeracija je izbjegnuta, a kristali su bili gotovo dvostruko manji, ali pravilniji. Također je određena i snaga privedena uslijed miješanja i ultrazvučnog djelovanja. Utvrđeno je da se ona u oba sustava neznatno povećavala s veličinom miješala, a u sustavu s ultrazvukom je bila gotovo petnaest puta veća. The aim of this study was to examine the influence of impeller size in the crystallizer with and without the ultrasound irradiation on crystal growth of borax during batch crystallization at the critical impeller speed (N = N JS ). Crystallization is carried out in a laboratory scale crystallizer by cooling the mother liquor saturated at 30 °C to a temperature of 15 °C, at the rate of 6 °C h -1 . A radial straight four blade turbine (abbrev. SBT) was used in the work, and the influence of impeller size on the formed crystals properties was examined at impeller to crystallizer diameter ratios, D/d T , of 0.43, 0.53 and 0.63, respectively. The same examinations were conducted in a crystallizer with an ultrasound irradiation at amplitude of 20 %, as in a silent crystallizer as well. During the experiments, a granulometric analysis of the growing crystals was performed by the laser diffraction method, and influence of the SBT impeller diameter on the changes of volume density crystal size distribution over process time was analysed in the system with and without ultrasound. The changes of the volume mean crystal diameter and its coefficient of variation over process time were also determined. In order to gain insight into the influence of hydrodynamic conditions in the crystallizer on the growing crystals habit and to detect the appearance of crystal agglomeration and secondary nucleation, photographs of crystals analysed with an optical microscope as well as their specific surface area were analysed respectively. The granulometric analysis of the final product revealed that the average crystal size in both systems increased with an increase in impeller size. In the silent systems, the proportion of finer and coarser crystals in the product also increased due to increased secondary nucleation and agglomeration. In the irradiated systems agglomeration was avoided, while the crystals were more than twice as smaller, but of a more regular shape. The power consumption due to stirring and ultrasound irradiation was also determined. In in both systems it slightly increased with impeller size, but in the system with ultrasound it was almost fifteen times higher.

Glavni cilj ovoga rada bio je ispitati istovremeno djelovanje mehaničkog miješanja i ultrazvuka na dinamiku rasta kristala boraksa. Sonokristalizacija hlađenjem izvršena je u staklenom kristalizatoru, pri čemu je volumen kapljevine iznosio 2,65 dm 3 , a brzina hlađenja 6 °C h -1 . Brzine miješanja SBT miješala odgovarale su onima potrebnima za postizanje stanja potpune suspenzije (N JS ) po Zwieteringovom kriteriju, a amplitude ultrazvučnog djelovanja (A) iznosile su redom 0, 20, 25 i 30 %. Određena je promjena koncentracije matične otopine potenciometrijski, kao i promjena apsolutne prezasićenosti pri navedenim ultrazvučnim amplitudama pri čemu dobiveni rezultati pokazuju da ultrazvuk utječe na promjenu apsolutne prezasićenosti, a samim time i na promjenu veličine kristala. Prikazana je i promjena veličine kristala s vremenom koja pokazuje prosječno sitnije kristalne produkte s povećanjem amplitude ultrazvuka. Također, određeno je i vrijeme dostizanja konačne veličine kristala te utjecaji ultrazvuka i miješanja na brzinu rasta kristala i njihovu veličinsku raspodjelu metodom laserske difrakcije gdje je uočljivo da se vrijeme potrebno za nastajanje kristala konačne veličine povećava s povećanjem amplitude ultrazvuka, ali i da se raspodjela veličina kristala sužava. Određena je i snaga potrebna za izvođenje eksperimenta. Dobivene vrijednosti ukazuju na to da je utrošak snage izražen po jediničnoj masi otopine boraksa čak do 10 puta veći kod ultrazvučnog djelovanja nego kod mehaničkog miješanja. S obzirom na rezultate eksperimenta, više amplitude ultrazvuka ne čine proces sonokristalizacije učinkovitijim te se amplituda ultrazvuka od 20% čini optimalnom zbog toga što ima najkraće vrijeme dostizanja konačne veličine kristala i energetski je manje zahtjevna od onih pri 25 i 30 %. The primary goal of this thesis was to examine the effect of simultaneous application of mechanical stirring and ultrasound irradiation on borax crystals growth rate dynamics. The cooling sonocrystallization has been conducted in a glass crystallizer with the liquid volume being 2.65 dm 3 and the cooling rate of 6 °C h -1 . Stirring speeds of the SBT stirrer matched the ones required for achieving the state of a complete suspension (N JS ) by Zwietering's criterion, while amplitudes of the ultrasound were as follows: 0, 20, 25 and 30 %.The change of the mother liquor's concentration was determined potentiometrically as well as the change of the absolute supersaturation during above-mentioned amplitudes. According to results, ultrasound irradiation affects absolute supersaturation as well as the change of crystal size during the process. Given the measured sizes of crystals, change in crystal size over time was shown and it is noticeable that continuous sonocrystallization yields averagely smaller crystals. Also, the time required for crystals to attain their final size, effects of both stirring and ultrasound irradiation on the growth rate and the crystal distribution determined by laser diffraction were presented for each amplitude. In general, the time required for attaining the crystalline product of final size extends with an increase of ultrasound amplitude. At the same time, crystal size distribution narrows. Power needed to perform the experiment was also determined. Results suggest that power consumed per unit mass of borax solution by stirring is up to 10 times lower than that of ultrasound irradiation. Considering all obtained results, it can be said that higher ultrasound amplitudes do not imply a more effective sonocrystallization process and therefore, the amplitude of 20 % seems like the optimal one with reasons being that it ensures the shortest time needed for attaining the final size of the crystal as well as not being as costly in terms of energetics as the amplitudes of 25 i 30 %.

U ovom radu izvršena je usporedba koncentracija boraksa izmjerenih potenciometrijskom i refraktometrijskom metodom tijekom provedbe šaržne kristalizacije ove soli postupkom hlaĊenja. Potenciometrijska i refraktometrijska metoda ne prikazuju izravno koncentraciju otopine nego je za njihovu upotrebu potrebno prethodno izraditi baždarne krivulje. Kod potenciometrijskog mjerenja baždarna krivulja predstavlja odnos potencijala ion-selektivne elektrode i logaritma koncentracije analizirane tvari, dok kod refraktomerijskog mjerenja ona predstavlja odnos refraktivnog indeksa i koncentracije tvari. U oba sluĉaja baždarne krivulje se konstruiraju pri konstantnoj temperaturi. S obzirom da će se obje metode primjenjivati tijekom kristalizacije uz kontrolirano hlaĊenje tako se i baždarenje prilagodilo uvjetima provedbe kristalizacijskog procesa. U šest otopina boraksa poznatih koncentracija (c= 0,05-0,187 mol dm -3 ) istodobno se provodilo mjerenje potencijala i refraktivnog indeksa pri brzini hlaĊenja otopine od 6 °C h -1 . Da bi se osigurala ujednaĉena brzina prijenosa topline u ispitivanom sustavu, prilikom baždarenja, brzina vrtnje miješala (N = 300 o. min -1 ) kao i volumen matiĉne otopine (V = 2,66 dm 3 ) održavani su konstantnim. Iz izmjerenog potencijala natrijeve ion-selektivne elektrode te refraktivnog indeksa izraĊene su baždarne krivulje i to za svaku cjelobrojnu vrijednost temperature u ispitivanom temperaturnom podruĉju od 30 do 10°C. Potom je izvršena šaržna kristalizacija boraksa tjedan dana i ĉetiri tjedana nakon baždarenja, odreĊene su koncentracije otopine objema metodama i usporeĊene s rezultatima volumetrijske metode. In this work, a comparison of borax concentrations measured by potentiometric and refractometric methods during the batch cooling crystallization of this salt was made. The potentiometric and refractometric methods do not directly show the concentration of the solution, but the calibration curves need to be constructed for their use. In potentiometric measurements, the calibration curve represents the relationship between ion-selective electrode potential and the logarithm of the concentration of the analyte, while in the refractomeric measurement it represents the relationship of the refractive index and the concentration of the substance. In both cases the calibration curves need to be constructed at a constant temperature. Since both methods will be applied during batch cooling crystallization, calibration has also been performed under the conditions of the crystallization. In six borax solutions of known concentrations (c = 0.05-0.187 mol dm -3 ), cooled by rate of 6 °C h -1 , the potential and the refractive index were simultaneously measured. In order to ensure a uniform heat transfer rate in the system, during calibration, the impeller speed (N = 300 rpm) as the volume of the solutions (V = 2.66 dm 3 ) were kept constant. From the measured potential of the sodium ion-selective electrode and the refractive index, calibration curves were constructed for each integer value of the temperature in the tested temperature range from 30 to 10 ° C. Batch crystallization of borax was then carried out one week and four weeks after calibration, the mother liquor concentrations were determined by both methods and compared with the results of the volumetric method. It was found that the refractometric method, immediately after calibration, shows a much larger deviation of the results than the potentiometric method compared to the volumetric one. However, within a few weeks after calibration, the deviations of the results obtained by refractometry remained unchanged, whereas due to the large deviation of results, the sodium ion-selective electrode had to be calibrated again.

U ovom radu je sagledan utjecaj promjera aksijalnog PBT miješala (engl. Pitched blade turbine) te amplitude ultrazvuka, A, na kritiĉnu brzinu vrtnje miješala, N JS, pri suspendiranju kristala natrijevog tetraborat dekahidrata (boraksa) u šaržnom kristalizatoru standardnih dimenzija koji je sadržavao razbijala virova. Ova ispitivanja provedena su u svrhu utvrĊivanja brzine vrtnje korištenih miješala za naknadnu provedbu sonokristalizacije boraksa u miješajućem šaržnom kristalizatoru s hlaĊenjem. U prvom dijelu rada izvršena je šaržna kristalizacija boraksa iz otopine zasićene pri temperaturi od 30 °C, te su odreĊene granulometrijske karakteristike kristala. Potom je izvršeno suspendiranje kristala u zasićenoj matiĉnoj otopini s tri promjera PBT miješala (d m /T = 0,43, 0,53 i 0,63). Pri svakom promjeru je prvo odreĊena minimalna brzina vrtnje miješala potrebna za postizanje stanja potpune suspenzije kristala, N JS , primjenom Zwietringova kriterija 1s. Potom je pri djelovanju ĉetiriju razliĉitih amplituda ultrazvuka takoĊer za svaki promjer miješala odreĊena kritiĉna brzina vrtnje miješala spomenutim kriterijem. Kako bi se sagledali energetski zahtjevi sustava izmjeren je zakretni moment pri provedbi miješanja kao i koliĉina osjetne topline koja se tijekom sonofikacije u sustavu povećavala. Iz ovih veliĉina konaĉno je izraĉunat ukupan utrošak snage privedene sustavu. Rezultati su ukazali da se kritiĉna brzina vrtnje miješala za postizanje stanje potpune suspenzije kristala mijenja s promjenom promjera miješala. Ova pojava posljedica je promjene strukture toka kapljevine koja prati promjenu veliĉine miješala. UtvrĊeno je takoĊer da se pri ultrazvuĉnom djelovanju stanje potpune suspenzije kristala postiže pri manjoj vrijednosti N JS , meĊutim utjecaj ultrazvuka ovdje je znaĉajno manje izražen od utjecaja promjera miješala. U radu je takoĊer utvrĊeno koji od ispitivanih uvjeta istodobnog djelovanja miješanja i ultrazvuka zahtijevanju najniži utrošak snage pri suspendiranju korištenih kristala. In this work the influence of pitched blade turbine (abbrev. PBT) diameter and ultrasonic amplitude, A, on just suspended impeller speed, N JS , of sodium tetraborate decahydrate (borax) crystals in a batch baffled crystallizer was investigated. These tests were carried out in order to determine the PBT impeller speed for the subsequent sonocrystallization of borax in an agitated batch cooling crystallizer. In the first part of the work, crystallization of borax from a solution saturated at 30 ° C was performed, and the properties of the product obtained were determined. Then, the crystals were suspended in saturated mother liquor at three diameters of PBT impeller (d m /T = 0,43, 0,53 i 0,63). At each of the impeller diameter, the minimum impeller speed required to achieve the state of complete crystal suspension, N JS , was determined applying Zwietring's criterion 1s. Then at four different amplitudes of ultrasound, just suspended impeller speed at each of PBT impeller used were determined by the same criterion. In order to estimate the energy requirements of the systems, during the mixing the torque was measured, as well as the amount of sensitive heat that increased during sonication of the system. From these quantities, the power consumption brought to the system was finally calculated. The results indicated that the critical impeller speed to achieve the state of complete suspension of the crystal changes with the change of PBT impeller diameter. This phenomenon is a consequence of the changes in fluid flow pattern caused by the size of impeller. It has also been found that under ultrasonic action, the state of complete suspension of crystals is achieved at a lower N JS value, however, the influence of ultrasound here is significantly less pronounced than this of impeller diameter. In this work is also determined which of the tested conditions of simultaneous mixing and ultrasonic actions required the lowest power consumption when suspending the crystals used.

Osnovni zadatak ovog rada bio je ispitati te usporediti utjecaj miješanja i ultrazvučnog djelovanja na kinetiku nukleacije boraksa u šaržnom kristalizatoru s hlađenjem. U kristalizatoru s miješanjem ispitivanja su se provodila pri trima različitim brzinama vrtnje miješala, dok se ispitivanje utjecaja ultrazvuka na kinetiku nukleacije izvršilo pri trima različitim amplitudama ultrazvuka. Eksperimenti su se provodili u kristalizatoru laboratorijskog mjerila, volumena 2,14 dm 3 , u kojem se matična otopina hladila linearnom brzinom od 6 °C h -1 . U prvom dijelu rada, za primijenjene brzine vrtnje miješala (N =100 -350 o. min -1 ) te amplitude ultrazvuka (A = 20 - 40 %), vizualno je određivana širina metastabilnih zona matičnih otopina zasićenih u temperaturnom području od 20 do 35 °C. Na temelju rezultata o širinama metastabilnih zona pri ispitivanim procesnim uvjetima, primjenom Mersmannovog nukleacijskog kriterija određen je dominantni nukleacijski mehanizam, a potom su izračunate i uspoređene brzine nukleacije. Na temelju vrijednosti brzina nukleacije pretpostavljene su karakteristike konačnog produkta kristalizacije s obzirom na veličinu kristala. Odstupanja od predviđenih pretpostavki prisutna su u onim sustavima u kojima nije bilo postignuto stanje potpune suspenzije. S obzirom da niti u jednom sustavu s ultrazvučni djelovanjem nije postignuto ovo stanje, preporuča se kristalizaciju boraksa uz ultrazvučno djelovanje provoditi u kombinaciji s mehaničkim miješanjem. The basic assignment of this study was to investigate and compare the effect of mechanical mixing and ultrasonic irradiation on kinetics of borax nucleation in the batch cooling crystallizer. In the crystallizer with mechanical mixing, the experiments were performed at three different rotational speeds, while the experiments with ultrasound irradiation were performed at three different ultrasound amplitudes. The experiments were carried out in a laboratory scale crystallizer, with a volume of 2.14 dm 3 , in which the mother liquor was cooled down by linear cooling of 6 °C h -1 . In the first part of the work, for the applied impeller rotational speeds (N = 100 - 350 rpm) and ultrasound amplitudes (A = 20 – 40 %), the metastable zones widths of the mother liquors saturated in the temperature range of 20 to 35 ° C were determined. Based on the results of metastable zones widths at the examined process conditions, using the Mersmann's nucleation criterion the dominant nucleation mechanism was determined and the values of nucleation rates were calculated. Also, the values of power consumption per unit mass of suspension saturated at 30 °C, at examined conditions were determined and compared. On the basis of values of nucleation rates, the characteristics of the final crystallization products were assumed regarding crystals size. Deviations from the predicted assumptions are present in those systems where the state of complete suspension has not been achieved. Since that this is the case inside the all of the systems with ultrasound irradiation, it is suggested to conduct crystallization of borax at applied mixing conditions but also to examine the nucleation kinetics of borax in the systems in which mixing and ultrasound are combined.

Cilj ovoga rada je bio ispitati utjecaja miješanja i ultrazvuka u šaržnom kristalizatoru s hlađenjem na kinetiku rasta kristala dinatrijevog tetraborat dekahidrata (boraks). Proces kristalizacije izvodio se u kristalizatoru laboratorijskog mijerila u kojem je volumen matične otopine boraksa iznosio 2,14 dm 3 . Detaljno je analiziran utjecaj brzine vrtnje miješala (100, 200, 300 i 350 o. min -1 ) te amplitude ultrazvuka (20, 30, 40 i 50 %), na promjenu koncentracije odnosno prezasićenosti matične otopine, promjenu linearne dužine kristala tijekom procesa, raspodjelu veličina kristala te privedenu snagu po jediničnoj masi otopine. Pri svim ispitivanjima korištena je otopina zasićena pri temperaturi od 30 °C hlađena je linearnom brzinom od 6°C h -1 . Eksperimentalni rezultati ukazali su da brzina vrtnje miješala kao i amplituda ultrazvuka utječu na kinetiku rasta kristala boraksa. U sustavima s miješanjem red rasta kristala iznosi oko 1,3 dok je u sustavima s ultrazvukom njegova vrijednost oko 2,0. U sustavu s miješanjem konstanta brzine rasta kristala raste s porastom brzine vrtnje miješala dok se u sustavu s amplitudom ultrazvuka nije uočen pravilan trend promjene ove veličine s amplitudom. Djelovanje ultrazvuka uzrokuje dobivanje produkta malog masenog promjera čija se veličina značajnije ne mijenja s promjenom amplitude, dok je u sustavu s miješanjem srednji maseni promjer kristalnog produkta raste s porastom brzine vrtnje. Privedena snaga po masi otpine je značajno veća u sustavu s miješanjem, ali u ovom slučaju je postignuto i stanje potpune suspenzije pri brzinama vrtnje većim od 100 o. min -1 , dok je u sustavu s ultrazvučnim djelovanjem ovo stanje nije postignuto ni pri najvećoj amplitudi. Zbog toga primjena ultrazvučnog djelovanja u sustavu bez miješanja nije preporučljiva, unatoč velikoj brzini rasta kristala. The aim of this research was to investigate the effects of mechanical stirring and ultrasound irradiation on crystal growth kinetics of disodium tetraborate decahydrate (borax) during the batch crystallization by controlled cooling. The crystallization was carried out in a laboratory scale crystallizer in which volume of the mother liquor was 2,14 dm 3 . The influence of the impeller speed (100, 200, 300 and 350 rpm) and the ultrasound amplitude (20, 30, 40 and 50%), on the concentration changes of the mother liquor, the changes of linear crystal size over process time, the crystal size distribution of the product and the power consumed per unit mass of the solution was analyzed in details. Experimental results indicated that the impeller speed as well as ultrasound amplitude influence the crystal growth kinetics of borax. In the system with mechanical stirring the value of the crystal growth order is 1.3, while in the systems with ultrasound it is about 2.0. In the agitated systems, the crystal growth rate constant increases with an increase of the impeller speed while in the system with the ultrasound it is not found a regular trend of this parameter with the amplitude. The ultrasound irradiation in the crystallizer causes the production of fines which size does not change significantly with amplitude, while in the agitated crystallizer crystal size increases with increasing impeller speed. The power consumed per unit mass of solution is significantly higher in the stirred crystallizers, but in those systems the state of complete suspension was achieved at the rotation speeds higher than 100 rpm, which in the systems with ultrasound this state was not attained even at maximum amplitude. Therefore, the sonocrystalization alone, without mixing is not recommended, despite of high crystal growth rates.

Cilj ovog rada bio je sagledati princip rada ultrazvuka te ispitati utjecaj amplitude ultrazvuka na veliĉinu kristala boraksa dobivenih postupkom kontroliranog hlaĊenja u kristalizatoru s miješanjem. U prvom dijelu istraživanja provedena je šaržna kristalizacija u reaktoru s miješanjem iz otopine zasićene pri temperaturi od 30 °C i hlaĊene brzinom od 6 ° C h -1 . Pri tome je praćena promjena koncentracije otopine kako bi se utvrdio poĉetak nukleacije i promjena koncentracije uslijed rasta kristala, a po završetku procesa izvršeno je prosijavanje i granulometrijska analiza produkta. U drugom dijelu radu sagledavan je utjecaj amplitude ultrazvuka na tri izdvojene klase prethodno dobivenog produkta šaržne kristalizacije uz miješanje. Pri ovim ispitivanjima su klase kristala srednje veliĉine od 45, 170 i 375 m, ultrazvuĉno su suspendirane u otopini acetona zasićenoj i termostatiranoj pri 25 °C. Amplitude ultrazvuka iznosile su 20, 30 i 40 %. Nakon djelovanja ultrazvuka u trajanju od 10, 20 i 30 min granulometrijska svojstva kristala analizirana su metodom laserske difrakcije. Istodobno, uz mjerenje veliĉine kristala odreĊivana je elektriĉna vodljivost otopine, , kako bi se sagledale koncentracijske promjene unutar otopine. Rezultati rada ukazali su da niti jedna od izdvojenih klasa kristala nije znaĉajno promijenila svoju veliĉinu tijekom procesnog vremena pri ispitivanim amplitudama ultrazvuka. TakoĊer ni vodljivost otopine nije se promijenila, zbog ĉega se može zakljuĉiti da navedene amplitude neće uzrokovati lom niti otapanje kristala boraksa te ih se može koristiti pri ispitivanju utjecaja ultrazvuka na kinetiku kristalizacije boraksa. The purpose of this study was to observe the ultrasound working principle and to examine the influence of ultrasonic amplitude on the size of borax crystal obtained by the controlled cooling in the batch stirred crystallizer. In the first part of the study, batch crystallization was carried out in a stirred reactor from a solution saturated at 30 ° C and cooled at 6 ° C h -1 . Concentration change of the mother liquor over process time was measured in order to determine the onset of nucleation and the change in the concentration due to crystal growth. Upon the completion of the process, sieving and granulometric analysis of the product was done. In the second part of the work, the effect of ultrasound amplitude on three classes of crystals obtained in a batch stirred reactor was examined. The classes of crystals of average size 45, 170 and 375 m were ultrasonically suspended in a solution of acetone saturated and thermostated at 25 ° C. Ultrasound amplitude was 20, 30 and 40%. After 10, 20 and 30 min of ultrasonic treatment, the granulometric properties of the crystal were analysed by laser diffraction method. At the same time, with the measurement of the crystal size, the electrical conductivity of the solution, , was measured in order to monitor concentration change within the solution. The results of the study showed negligible change in size of examined crystal classes over process time at the applied ultrasound amplitudes. Also, the conductivity of the solution has not changed, which indicated that applied amplitude will not cause breakage or dissolution of the borax crystals and can be used in the further study of influence of ultrasound on the crystallization kinetics of borax.

U ovom radu ispitan je utjecaj brzine vrtnje dvaju aksijalnih turbinskih miješala koja su se nalazila na zajedničkoj osovini na kinetiku rasta kristala dinatrijevog tetraborata dekahidrata (boraksa) tijekom njegove šaržne prekristalizacije postupkom kontroliranog hlađenja. Eksperimenti u radu izvodili su se u kristalizatoru ravnog dna volumena 15 dm 3 s omjerom visine stupca matične otopine i promjera kristalizatora, H/d T , od 1.3. Ovako visoka vrijednost navedenog omjera zahtijevala je da se na osovinu u reaktor u postave dva miješala. Oba korištena miješala bila su istog tipa, radilo se o miješalu s četiri ravne lopatice nagnute pod kutom od 45 ° (tzv. PBT miješalo), čiji je promjer u odnosu na promjer posude, D/d T , iznosio 0.33. U radu je detaljno ispitan utjecaj brzine vrtnje dvaju PBT miješala na promjenu prezasićenosti matične otopine, linearnu veličinu rastućih kristala te brzinu rasta kristala. Konačno, za sve primijenjene brzine vrtnje miješala procijenjeni su kinetički parametri rasta kristala. Rezultati ispitivanja ukazali su da se s povećanjem brzine vrtnje miješala prezasićenost u sustavu se smanjuje dok se linearna veličina kristala povećava. Brzine rasta kristala povećavaju se s povećanjem brzine vrtnje miješalo što s odrazilo i na povećanje konstante brzine rasta kristal. Dobiveni rezultati posljedica su pozitivnog međudjelovanja tokova dvaju miješala koja se stapaju čineći jednocirkulacijski tok. Opseg ovog toka se povećava s povećanjem brzine vrtnje što se odrazilo na poboljšanje uvjeta za rast kristala boraksa u ispitivanom sustavu. In this work the influence of speed of two axial impellers mounted on the same shaft on crystal growth of borax decahydrate during process of batch cooling crystallization were analysed. Experiments have been performed in a flat bottom, 15 dm 3 crystallizer whose tank diameter to liquid height ratio equalled 1.3. This aspect ratio required the use of a second impeller which was mounted on the same shaft. Stirring was conducted by using two impeller of same types, axial pitched blade turbine (PBT) with impeller to tank diameter ratio, D/d T, of 0.33.The aim was analysed the influence on impeller speeds on the changes of absolute supersaturation, linear crystal size and crystal growth rates as well. Eventually, the values of the kinetics parameters of crystal growth of for all impeller speed applied were estimated. The experimental results showed that during the process time absolute supersaturation of the mother liquor decreases while the linear crystal size increases with impeller speed increment. Crystal growth rates increases with impeller speed what reflected on the values of constant of crystal growth rate. Obtained results are the consequence of interaction of flows generated by each of impellers which merged in single loop flow. The size of this loop increases as impeller speed increases what improved conditions for crystal growth in system analysed.